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Can we tell that dinosaurs were cold blooded based of bones and fossils or is that just the popular theory? | One of the things scientists look at is rate of growth which they can see from patterns in the bone. Cold blooded animals have limited growth rates - essentially their metabolism isn't fast enough to sustain high growth rates. From patterns in dinosaur bones, it suggests many dinosaurs were warm blooded. However some exceptions to this rule in animals today are also cited. Tuna fish and sea turtles for example are technically "cold blooded" but have some capability of regulating and generating body heat. So, there is given some leeway to suggest dinosaurs might have also fallen in this inbetween category of being half and half between cold blooded and fully body temperature regulating warm blooded. | 18 | 24 |
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What is the difference between blood types and why do our bodies only accept the correct type? | Biologically, ABO blood types are just seen as different combinations of sugars attached to some of the proteins within red blood cell membranes. The reason mismatching is problematic is because your body will initiate an immune response against the donor blood because the blood type is still an antigen. You don't attack your own cells because there is a process during lymphocyte (white blood cells that handle specific immunity) maturation, that will cause any cell that reacts too early (i.e. activates while still in the thymus or bone marrow) to die.
ABO however are not the limit of blood types. Technically there are *hundreds* of different blood groups. | 16 | 24 |
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eli5 How does laser cooling work | Things to know/remember beforehand:
* Temperature is the random motion/bouncing around of molecules and atoms
* Light gets absorbed by atoms when the particles of light (photons) matches very specific kinetic energies that depend on the atom they're possibly getting absorbed by. This energy is directly related to the lights color (which is also it's frequency and wavelength). Otherwise the light just passed through without doing anything
* If you are traveling towards the source of the light, you will see the light shift more "blue" (higher energy and frequency, shorter wavelength), opposite is true if you're moving away. This is called Doppler shift
* When a photon gets absorbed by an atom, the momentum and energy of the photon gets transferred into the atom (conservation laws)
So, when scientists want to cool individual atoms with lasers, their goal is to slow down that random motion of the atom. What they do is set up a bunch of lasers that are tuned to emit light *just below* those absorption energies. This way, the light only gets absorbed when they're moving towards each other (like a head on collision) because the light gets shifted into those energies to absorb. The energy is conserved by making the electrons jump to higher orbits around the atom, while the atom itself slows down to conserve momentum. This causes the atom to cool to as low as a few millionths of a degree above absolute zero | 102 | 36 |
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[Harry Potter] ELI5: How does sacrificial protection(i.e. Harry gaining"blood protection" from Lily's sacrifice) work and is it consistent throughout the series? | Okay I've seen people try to explain this but it almost always seems convoluted and makes me think that it's not consistent and people are trying to make excuses for it.
How exactly does this protect Harry? How does this enable him to burn Quirrell? Does he use these powers any other time?
Can someone please give me a simple explanation and tell me if it is consistent? Thanks. | # How to Grant Love's Protection
1. Be a Wizard.
2. Someone (henceforth called killer) is threatening to kill one or more people you love (henceforth called lovees).
3. The killer gives you the choice to save yourself. Having the choice matters! If you were just going to die anyway, it doesn't count!
4. Choose to die, then get killed by the killer.
# What Exactly Does it Do
1. The killer—and only the killer—can no longer physically touch the lovees without being destroyed.
2. Spells cast by the killer on the lovees don't work properly. Magical enchantments put on the lovees will be spontaneously dismissed and other spells might bounce off or work at reduced potency.
# Bonus: The Lovees Are Your Blood Relative
1. A third party may cast a special protective charm on the lovees if they are a blood relative of the person who sacrificed him- or herself.
2. This amplifies the original love's protection because blood ties are really important in magic. Even a Killing Curse cast by the killer against the lovees will be fully deflected, with almost little harm to the lovees.
3. To maintain this extra protection, the lovees must live with a shared blood relative. It's ok if most of the time they are somewhere else, but they must spend some time there (e.g., summer break) at least once every year.
4. The killer or any of his or her associates cannot enter the shared blood relative's house.
5. This extra protection is immediately cancelled if either (a) the lovees no longer call the house of the shared blood relative their home OR (b) they reach the age of magical maturity, 17.
6. This special blood protection charm was created by Albus Dumbledore.
# For Dark Wizards: Love's Protection and You
1. There's no counterspell you can use to dispel the protection (whether the base one or the fortified blood relative one).
2. If you happen to lose your body and then recreate it using the blood of one of the lovees, you may affect that lovee as though he or she didn't have the protection.
3. However, even if you use a lovee's blood for resurrection, if that lovee's has the special blood protection, you won't be able to enter the shared blood relative's house.
3. If you use a lovee's blood for resurrection, you might act as a "positive energy Horcrux" for that person, meaning the lovee will not die as long as you live.\*
4. If you use a lovee's blood for resurrection and you have created any number of Horcruxes, your soul can be healed completely if you feel remorse.
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*^(Further conditions might apply. Please check your destiny is intertwined with the lovee's by word of prophecy and that you're using a legendary wand whose master is the lovee.) | 32 | 46 |
[Prometheus] How could the Engineers have created humanity while the fossil record of humans and their ancestors is well-documented and shows a clear line of human speciation from other primates? | Basically, when the Engineer sacrifices himself to create humanity, wtf is going on in that sequence? Was it an Earth prior to microbial life? Couldn't have been considering the abundance of liquid water, a thick atmosphere, and enough oxygen for the Engineers to breathe. Was it the Mesozoic? Mammals already existed by then. Was it the cenozoic? *Primates* already existed by then. By the way, would Engineers count as some sort of primate at any rate? Are all Earth primates actually descendants of Engineers? How tf does any of this make sense? | The engineers seen in the beginning are at a very early stage of Earth's development. Iirc it's hundreds of millions of years ago. They seeded their own genetics into the muck of earth and created a series of evolutionary events that would end in humanity. A near identical species to themselves but with several cultural and biological differences to make it an experiment rather than a cloning practice. | 373 | 427 |
ELI5: Do honey products help or harm bees? | I've heard about bees being endangered and it being dangerous to our ecosystem. Some honey products (ex: the young girl's honey lemonade business featured on Shark Tank recently) advocate for saving the bees. Does purchasing honey help this issue or are we draining these resources and therefore hurting this endangered species? | Bee farms depend on a healthy colony of bees to produce honey, so any business that is based on honey will intrinsically be good for bee populations. As for whether that will solve issues of endangered bees, no it will not. Bee farms encourage large populations of bees, but in very concentrated areas. To help with pollination and support the Earth's ecosystem, bees need to be widespread.
In short, buying honey will help a little, but it won't hurt. | 37 | 46 |
ELI5 how’s does my brain recognise “fake” computer graphics which are intentionally designed to not fall within the “uncanny valley?” I’m watching a movie action scene which I know is unreal yet it’s perfectly “real” at the same time? | Generally the difference is light. If the light is hitting objects at different angles, or if it’s not passing through partially transparent objects like skin, your mind will see that something is wrong. | 285 | 390 |
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[Star Trek] Instead of the various Alpha Quadrant powers always fighting over colony planets in far-off star systems, why don't they use their amazing technology to terraform new planets much closer to home for habitation? | Terraforming is a lengthy process. We actually do see it going on a few times.
The Genesis device was intended to be a system for rapid terraforming, but between the death of David Marcus, the Genesis planet proving to be unstable, and the Klingon Empire declaring Genesis a weapon of mass destruction, the major Alpha Quadrant powers signed a treaty banning further experimentation with it. | 42 | 36 |
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ELI5: What exactly happens to muscles when you massage them and why is it good for them? | Massaging reduces the production of compounds called cytokines, which play a major role in inflammation. Also, it stimulates mitochondria which helps convert glucose into energy used for cell repair and growth. Massage causes microtrauma also, which stimulates nutrient flow to the targeted area and speeds recovery. | 11 | 52 |
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eli5: Why do most racing vehicles (F1, IMSA etc) lose control immediately the second they touch grass where a 'passenger' car would retain some control? | A normal tyre is made to handle all kinds of surfaces.
Race tyres, especially slicks, are only made for race tracks. Also really stiff suspension means race cars loose traction even quicker than normal cars. | 49 | 22 |
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Does Justice Exist? | My friend and I are engaged in an argument on whether justice actually exists or not, and I naturally gravitated to the more skeptical view that justice doesn't exist.
So far, I've discussed deconstructionism and variance (across history and time), but does anyone have any other interesting rationales?
Perhaps equally as important, does anyone have any arguments on why justice exists? | In the first book of The Republic, Thrasymachus in dialogue with Plato, claims justice is "the advantage of the stronger". Plato spends the rest of the book trying to pin down what exactly justice is by formulating a polis in which he believes it resides, allowing him to trace it back to the individual. That book is a decently long read by one of the most important philosophers to ever live and yet didn't produce a definite answer to this question. | 62 | 47 |
CMV: There is no Reason to Care about my "Roots" or "Heritage" most who say they are, are lying. | Whenever people ask me about my heritage and family culture, my answer is usually something along the lines of "I'm not really sure." They usually respond with, "don't you care about your roots?" and I can't help but answer no.
Plenty of folks have a rather baffled expression, and I have no idea why. I mean, to me my culture is 21st century free market capitalism, lol. I like money, food, women, and friends. I like to dress well, make money, and play video games. There is not much to know outside of that, except what is needed in acquiring these things. I'm also well versed in not being a dick to people. That's not to say I'm this totally selfish guy with no vision outside of himself, I care about societal advancement particularly the impact technology will have for our health and enjoyment. But I'm not sure if I care about much outside of reducing suffering and making people happier.
But I cannot fathom the negative reactions I get from some people, and in many cases, I can't help but see them as shallow hypocrites. People who say they feel connected to their heritage are such bullshitters imho. Buying a cheap scarf with an alpaca on it manufactured in bulk in china, does not make you in touch with your hispanic roots. I sort of view people who call themselves spiritual in the same light as well. They go on and on about how people are becoming so self-centered and this instant gratification society and how the next generation are ridiculous, but they are literally sold bullshit products all the time and eat it up. It just doesn't make a lot of sense to me. Why shouldn't I hold this view? Why should I change it? Why should I care about my roots?
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> *This is a footnote from the CMV moderators. We'd like to remind you of a couple of things. Firstly, please* ***[read through our rules](http://www.reddit.com/r/changemyview/wiki/rules)***. *If you see a comment that has broken one, it is more effective to report it than downvote it. Speaking of which,* ***[downvotes don't change views](http://www.reddit.com/r/changemyview/wiki/guidelines#wiki_upvoting.2Fdownvoting)****! Any questions or concerns? Feel free to* ***[message us](http://www.reddit.com/message/compose?to=/r/changemyview)***. *Happy CMVing!* | Can you pinpoint which view you want changed? It seems there are two major points:
1) Most people who care about their roots or heritage are lying
2) you shouldn't care about your roots
Do you want both of them challenged? Just one? Are we to convince you that most people who care about their roots are not lying, or are we to convince you that you should care about your own roots? Or both/either? | 26 | 89 |
What is the philosophical basis for respect of human corpses? Or is it just cultural? | Is there anything philosophically/ethically wrong with desecrating a human body? It feels intuitive that there is, but I am having trouble identifying if the basis and have been unsuccessful in finding one. | Consequentialist argument: People will be upset by your treatment of the body in unaccepted ways. So, if your treatment doesn't outweigh that in good, it shouldn't be done. And yes, this is based on only certain cultures. If the cultures changed, the judgment would too.
Virtue argument: The way we treat inanimate objects might cultivate habits or traits in us that affect how we treat people or other things. If what we're doing to the corpse creates bad habits or sullies the trajectory of our life, we shouldn't do it. Relatedly, if it affects our social standing negatively, we shouldn't do it without good reasons to counter it.
It's gonna depend on what we're talking about. Cremation? Necrophilia? Plasticizing and creating an artwork from it? Mandatory organ donation? Eating it to survive? For recreation? | 43 | 68 |
ELI5: How come when you do nothing all day you're more tired than when you're productive? | Hormones, or signals for your body, require a stimulus to be activated. The stimulus could be stress, fear, arousal, pain, motion, etc.
When you sit around and do nothing, your body senses that it does not need to be alert, so nothing is stimulated and you stay tired.
When you are actively engaged in doing something, your body becomes aware that you may need to be alert or ready for action, and it prompts you accordingly. | 22 | 59 |
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I believe that college students should only be required to study courses relative to their major. CMV | College students in America are required to complete all courses in their major in addition to a number of general education requirements. For example, I am a biology major but I also have to take courses in history, english, foreign language, arts, etc.
This is a total waste of money and time for me. I could complete my degree earlier if these classes were eliminated, leaving me with less debt and providing me with an even stronger foundation in biology.
I understand that basic math and writing skills are important in all areas of study, so I would be alright with having math and writing courses still be a part of all majors, with the opportunity to be placed out of these courses if proficiency in them is exhibited.
The idea of a well-rounded student is a fantasy. Students often do whatever it takes to get a decent grade in gen eds and all of that information gets flushed right out once the class is over. Even if taking those classes does make a person slightly more knowledgeable, none of the students who enjoy those classes would rather have taken them than have less debt. | For many students going into college, they don't know what their major is at all. Kids change their majors *all the time*.
If anything, general requirements are a good way to introduce students to different topics or fields and produce a foundation to make sure they can adequately be informed about what a department is like.
And besides, for most serious colleges, their overwhelming mission is to educate students — not to be a diploma mill.
Part of educating means making a person as well-rounded as possible. You state how important basic math and writing skills are.
What about basic history? Basic biology? Basic understanding of the world and foreign countries? I'd argue that it's also extremely critical to becoming a well-rounded and highly functioning member of society. | 33 | 45 |
ELI5: why water doesn’t make a good lubricant | It’s just kind of counter intuitive to me. I would expect water to to make things slicker but instead it often seems to make them rougher to move/touch or seems to chafe your body | What makes a lubricant good is that the molecules in the lubricant interact weakly with each other. This means that they can slide freely on top of each other. If you have many of these sliding molecules then you get a good lubricant which also "slides" on a macroscopic (visible) level.
Water molecules, on the other hand, interact very strongly with each other. This means water has higher cohesion than oils, which is not a favorable feature for lubricants.
Edit: rewrote the last paragraph to remove an ambiguous statement that could be interpreted as water being more viscous than oil, which is completely untrue.
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Teaching a stats course this term. Student who rarely attends has asked for detailed walk-through of class activities, beyond the guidelines I already provided. How to proceed? | I'm running a statistics course for the first time. The lecture and tutorial slide include very basic information on the theory behind statistical tests, and on how to run them. I've left a lot of details out of the slides to encourage attendance to lectures. Students who attend class and take notes should be able to use these to practice in their own time and seem to be doing quite well in class activities so far.
However, a student who barely ever attends class has asked me to upload detailed questions and instructions online. I have uploaded some instructions and questions we explored in class, to be nice.
He has now emailed me again to ask for a walk-through of how to deal with data sets, and answers for each dataset. I am reluctant to do this, first because this is stuff I've been doing repeatedly in the last few lectures. Secondly I don't have a lot of time to compile a huge document with all the results we obtained from several data sets in class. Students who took notes should have these results already.
Is it unreasonable of me to suggest to him that he should attend class if he wants a more detailed walk-through? And should I even provide the answers he has asked for?
I would be more understanding if this person would have missed 1-2 sessions, but I have rarely seen this person in my course and as such I don't feel particularly motivated to provide further materials. On the other hand I am concerned about potentially getting a poor rating for this module from him. It is a very small class so a single low rating could bring the average down. More experienced people, what would you do?
Any suggestions would be much appreciated!
Edit: I should add I already offered to see him during office hours in a previous email, but he decided to just ask for more information instead. | You tell the student to do the following
1. Attend class
2. Attend office hours
3. You will not make special accommodations just for them as it is unfair to the rest of the students
4. Ignore the rating. If you do your best to teach all the students then it will work out, even for a small class. | 50 | 21 |
ELI5: How do trees get rings that can tell us their age? | How are the rings formed? Also, can you calculate a tree's age by measuring the outside of it? | Trees grow from the center outward and different factors change the look of what grows. Lighter wood correlates to spring and darker wood correlates to winter (given the dramatic differences in weather between the two seasons). Since each year has either a spring or a winter, all we have to do is count how many winters a tree has been through to give a good estimate of it's age. | 26 | 22 |
ELI5: How does AI (Bots) work in video games? | AI in games has to have a couple things first; you have to have a designed goal for the AI to do first, and allow it access to stuff to achieve that goal.
In a video game this might turn out to be something like a standard fighting game; where the AI is designed to win the match, and is given access to button combination inputs to achieve that. If they want to get a bit into it with difficulty settings, they could change which moves/combos the AI can execute, or how quickly it reacts.
In something else like a strategy game, they tend to give the AI certain goals to hit before launching an attack/defending an attack. IE: Have 10 builders/harvesters, 20 attackers, and 2 defensive structures; then issue commands to move attackers across the map toward a target destination.
How that all is built is basically programming the AI, although depending on what you want the AI to do, it might range from just mashing buttons to figuring out pathfinding for a giant army. And in plenty of cases, the person programming the AI might let the AI cheat a bit.
Now in cases where people argue they want difficulty to mean something more than enemies become bullet sponges, while the player hits like a wet noodle. They want the difficulty increase to mean enemies are smarter too - but that comes at a cost in programming & CPU cycles. Is it really worthit to add in more in-depth AI that checks whether one room is good to hang out in because it has a lot of cover (and having all the programmatic checks and balances to go with that), or use those precious spare moments on the CPU to push out a few more frames per second? | 23 | 42 |
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ELI5: The differences between acetaminophen, ibuprofen, & aspirin? | I know that aspirin helps blood clot, ibuprofen is a muscle relaxer, & acetaminophen is an NSAID. Yet all are recommended for (& provide relief for) headaches. This overlap I don't understand, what do these medicines have in common? | What's common is that they all affect the way your body creates and processes pain, but that's about it.
Why three separate ones exist is because they all have different chemical structures, and are handled when you take them by separate "metabolic pathways" (the process in which they are absorbed into, affect, and are eventually removed from the body) which make them better or worse for treating certain conditions. They all treat pain, but some are better for sprains than others (where swelling is an issue), some cause a little internal bleeding, some are better at reducing a fever, and they have different side effects.
For example, if you have liver issues, don't take acetaminophen because it's hard on that particular organ.
(But a correction: aspirin helps AVOID blood clots. That's why low dosage programs can help avoid heart attacks.) | 13 | 37 |
ELI5: How come flies and other bugs can so easily get into my house through a small crack in the window but then freak the fuck out and aimlessly fly at the glass trying to get out? | Flies and other insects are attracted to the carbon dioxide your body gives off, along with the smells of food and other household byproducts. This mixture of gasses flows out of the cracks in your house and gives the insects something to track down.
When they're trying to leave, there's nothing attracting them out, so they're just trying to follow the light and nothing else. Insects aren't intelligent enough to understand windows, so they stupidly bounce off over and over. | 65 | 50 |
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What makes a circular paper airplane fly so well? | Like this one: http://www.youtube.com/watch?v=k8Yehe2dbyQ | Stability.
1. Circles are very hard to deform compared to other shapes. This means the "wing" will not flutter or collapse, which is the main problem when working with paper.
2. Having all of that weight at the bottom means it won't flip over, and won't roll over. It also looks like it is placed so that the more it begins to nosedive, the further forward the center of lift moves, keeping it level.
3. Straight wings make lots of whirling, messy air from their tips (like when you push your hand through a bath of water). These both slow the plane down because it has to pull the big balls of air along with it, and shake it about (point no. 1). In some passenger planes you can see little vertical "winglets" on the wing tips, which help reduce this. "Circular" wings have no tips, so they don't have this problem at all! | 10 | 27 |
[Superman] why doesnt superman just go inside a giant star and overcharge himself to the point of godhood? wouldnt that be more beneficial to helping ppl? | >wouldnt that be more beneficial to helping ppl?
Not really- He doesn't need more power. He's good for that- if anything, he feels he has *too much* power.
The main issue with him helping as many people are limitations, either in the sense of he wants to have a life outside saving people or in that he has ethical objections to lasering tyrants from space. He doesn't want to give those up (he's not a utilitarian) and if he changed his mind, he wouldn't need to overcharge to do that. | 511 | 520 |
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Is it less difficult to become a professor at a smaller, less research oriented university? | I went to a small (2000 people) school for undergrad. We didn’t offer PhDs and while some professors did research, many seemed to solely teach. The environment was much different than the research-focused state school where I did my PhD.
I’m not that interested in continuing intensive research. I finished grad school in April and went into industry. I’d like to stay here for awhile, but I loved the environment of my undergrad school and would be interested in possibly becoming a professor that focuses on teaching rather than research down the line.
Are these jobs still extremely difficult to get? I’m aware how tough tenure track positions are, but I’m curious if these positions are similar.
If it is relevant, my field is engineering.
Thanks! | I’ve served on numerous hiring committees at a teaching intensive PUI about the same size as your undergrad over the past 15 years and here’s the deal: it’s not about being more or less difficult. It’s about what kind of difficult. If you are a top researcher in an R1 PhD program with 5 tier 1 pubs and 1 semester as the instructor of record when you were ABD, you would not get hired at our institution. That’s not what we want. You can certainly come from those R1 programs, but you need to have a full teaching portfolio. Maybe one or two low tier pubs that show you know the field, but that’s it.
It’s not that it’s easy or hard, it’s just a different kind of hard than research track positions. | 82 | 55 |
CMV: I think once you become a "grown-up" and have family, you become depressed. | My mom and dad don't really live what would be considered a "happy" life. My dad has anger issues, hates his job (got laid off 7+ times) and is constantly stressed out. My mom told me today, "I think people tend not to like me...". She seems to have self-esteem issues which is ridiculous because she is the sweetest, caring and most loving person I know.
Also, it seems like once you're used to your job, and family (grown-up), you lose all your friends. I haven't heard of my dad talking to a single friend ever since I was a toddler, and the only friends he talks to now are at church. And even then, they never hang out outside of church. Growing up into the church, I've been constantly surrounded by the same families with the same cookie-cutter parents. This reinforced the notion that parents just get used to life and go through that stagnant cycle of work, bills, church, etc. I also understand that with age, connections grow thin and the only the best friendships survive because of the dedication required to keeping in touch.
I know that my view isn't correct, and many families out there are happy, but I really need to hear it for confirmation.
Edit: I've found the answers- thank you all for the valuable insight. Reddit delivers. | The fundamental things that makes people happy and keeps people going are goals. Your life should always be building towards something- whether it's getting a new computer, tending a garden, beating that video game, having and raising kids- people necessarily hate stagnation. You hear it all the time- "Honey, we're in a rut."
Now, stagnation is certainly a pitfall of adulthood, but it isn't an inevitability. And it's a subtle difference, so the confusion is easy. | 16 | 17 |
Eli5 How come you can look up at a height and it not seem so high, but looking down from that same point the drop seems a lot further. | Like if you’re looking at a point that is just above your head it doesn’t seem that high up off the ground. But if you were to jump from that height to the ground, the distance seems further. | A lot comes down to having a point of reference. If you're on the ground and you look up to a skyscraper, you're also looking at a bunch of empty sky
When you're up on the skyscraper looking down, you see other buildings, streets, cars and people, and they look tiny, so you have a better measure of the distance
This is the same phenomena that causes the moon to appear bigger when it's lower on the horizon | 14 | 16 |
CMV: the feeling "I'm wasting my life" is more dependent on selection bias than any life decisions | Sometimes I watch movies or listen to music or even meet people and think 'I'm not alive like they are alive. I'm stuck in some grey humdrum cubical of existence while they are out there experiencing what life should feel like."
I am currently feeling that way now and so to cheer myself up I've decided that feeling is just because I have to live through every minute of my life, even the dull bits, but I am seeing the edited highlights of everyone else's. Sometimes its not even highlights its just fiction, like pictures that are edited to look better than any real person could or a carefully choreographed video of what looks like the worlds best party but is really just some bored, out of work actors on the 15th take.
I feel like i've definitely had moments where I felt truly alive but they seem very far away now...does anyone really live like this the whole time?
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> *Hello, users of CMV! This is a footnote from your moderators. We'd just like to remind you of a couple of things. Firstly, please remember to* ***[read through our rules](http://www.reddit.com/r/changemyview/wiki/rules)***. *If you see a comment that has broken one, it is more effective to report it than downvote it. Speaking of which,* ***[downvotes don't change views](http://www.reddit.com/r/changemyview/wiki/guidelines#wiki_upvoting.2Fdownvoting)****! If you are thinking about submitting a CMV yourself, please have a look through our* ***[popular topics wiki](http://www.reddit.com/r/changemyview/wiki/populartopics)*** *first. Any questions or concerns? Feel free to* ***[message us](http://www.reddit.com/message/compose?to=/r/changemyview)***. *Happy CMVing!* | Person A who has taken some risks to do the job they really want to do or try out the things they really want to do and person B who took the safe route through life and never quite figured out how to do the things they really want to do aren't on the same path.
Sure not everyone's life will be happy all the time, but there are some people who set things up to maximize any opportunities that come their way, while others are just the "plankton" of life. Some people are content to stay in one place and eat the food as it drift by, but can't turn a simple opportunity into a series of opportunities. Some people create a blog and turn that into a full time career.
If you're worried that you are living a "plankton" life then start moving. | 11 | 28 |
ELI5: If programs are lines of codes, how do we see images? Especially in gaming where there are so much interactive objects on screen. | Are you thinking that if you looked really closely at your screen, like with a microscope, you would see the code, and that somehow it makes up the image? Code is just what tells your screen how to make an image.
Think of it like this. Your screen has thousands of little empty dishes we call "pixels". We can put any kind of colored ball into one of these dishes. Code tells your computer which colored ball goes in which dish. After your computer reads the code and puts the correct colored balls in the correct places, then when you back out and look at everything at once, you see an image. | 32 | 19 |
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ELI5: What is Borderline Personality Disorder? | Friend I grew up with was just diagnosed with BPD. What is it? Is that why he never got along with his family? | It is a mental health diagnosis that does impact people's ability to maintain close and long term relationships including family, friends and lovers. While there are several criteria and characteristics a few significant ones reported by many suffers include:
1) The feeling that there is a "hole" inside of them that needs filling
2) The thought that a close intimate relationship will fill that hole
3) Hot and cold running emotions toward people close to them, the swings from "you are the greatest person ever" to "you are trying to destroy me" can be sudden, frequent and seeming unprovoked.
These things (and a few other) conspire to keep the person out of long term relationships and hopping from intense relationship to intense relationship in that constant search to fill the "hole". | 72 | 115 |
Does Einstein's theory of relativity connect electric and magnetic fields? | Yes; namely under changes of inertial frames in relativity (Lorentz transformations) E and B fields mix into eachother.
Super minimal example to show this: static charge, there's only an E field. You change reference frame, it gets moving and therefore part of the E has turned into a B.
Said in modern words, this implies E and B must be part (components) of a larger object that "transforms well" under Lorentz transformations, that is to say it doesn't mix into anything else, just into itself. This object is the Maxwell tensor F. | 80 | 272 |
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How do large scale shops/malls supply WiFi on such a big scale? | How do shopping malls and big supermarkets supply a (considering it’s size) stable WiFi connection across such a large area? Sent using a shopping centres WiFi with a solid 20mb download. | This could be a very long reply basically involving a course in wifi engineering, however, in simple terms it looks like this.
1. They use multiple commercial grade access points which are all controlled by a central controller device. This keeps track of connected devices and ensures the device connects to the ap with the best signal as it roams.
2. AP placement is carefully calculated to provide consistent coverage as well as load balance number of devices per AP.
3. Radio channel space is carefully planned to prevent interference (CCI)
4. AP are all connected to central controller by a fast (at least GB) wired netowrk.
5. The entire netowrk is connected via 1 or more fast broadband/ethernet internet circuits
There is a lot more to it, but that is the basics. | 23 | 21 |
ELI5: Why are rural and urban cultures so different? | One specific example: I recently asked my dad who lives in rural Australia if people in his community/town are homophobic, and he replied in a "D'uhh"-ish tone: "YES!!!" | Density and variety. You're squeezed into a much closer area, and a much more diverse one.
In terms of tolerance (sexually, racially, etc), one of the best ways to reduce intolerance is to expose people to different lifestyles.
In rural areas, it's not uncommon to have the same 100 or whatever neighbors for your entire life.You know them all by name, and they're all pretty much like you (immigration into rural areas is low). In the US, that usually means white and Christian.
This tends to lead to an "us vs them" mentality, especially when you add in things like news telling you about all the horrible things going on. Many rural people might never meet or meaningfully interact with someone who is gay/black/Muslim etc.
It's a lot harder to be afraid or hateful when your office mate who you BBQ with on the weekend is one of those things, and he's a decent guy.
In terms of other things, it often comes down to density. It's a lot easier to trust your neighbors when you know them all by name, and they've been babysitting your kids. In a city, you might buy a coffee, and never see that guy again. Even if say, 0.01% of the population are creepy, you probably pass by a few every day, just due to the sheer numbers. | 17 | 15 |
I believe that space travel should not be one of the priorities of mankind. CMV | I think that space travel is an interesting concept, and I don't argue against learning more about outer space, however when I hear people complain about NASA's budget I just don't see what all the fuss is about. I mean, why should governments, whose main priority is to benefit the people and their respective nation, be forking over money to travel to places that will do little to benefit Earth (Although I do agree that many governments should top spending as much on their militaries)
This probably comes down to personal preference, but I also think that the places we have the potential to go to in space aren't very interesting. If we really want to explore the unknown why not explore the deep ocean, that would be less expensive and we would actually see new species, while we probably won't find anything as interesting in our solar system.
Ultimately, I think that we should focus on our own planet before others, but I am open to arguments as to why we need to travel into space. | There's lot that the space program(s) can do and has done to benefit folks back here on Earth:
* Detecting near-earth asteroids from orbit. As our sensor technology has improved, there are now proposals for placing a satellite in orbit around the sun to look for potential Earth-bound asteroids. This may give us a chance to attempt a deflection or prepare for an impact.
* Space-based services for Earth. GPS, Satellite TV, Satellite Phones, Satellite Internet/data, Satellite photos. All of these things have been made possible by the launch capability developed for the space program (and the military) and all of them have major applications on earth. GPS has become the 'stealth utility', synchronizing the clocks at cellular telephone sites, providing a high-resolution timing signal for electronics labs and providing location data for innumerable applications. Many broadcasters turn to satellites for up-linking their programming to distant locations. Satellite phone and data allow men and women to connect to the outside world in the most distant of places on Earth.
* Development of new technologies. The space program has historically caused a number of talented engineers to solve difficult problems, some of which might have applications back on earth. This can run the gambit from advanced materials that can withstand the rigors of spaceflight and re-enter to the Apollo program's demands of compact computing equipment and the semiconductor industry. | 17 | 16 |
How likely are we really to contract a virus or disease by drinking from the same cup? | Given two scenarios:
Your average US resident, sharing a drink from the same a cup of alcohol and also a cup of water (since I assume there would be less contamination in alcohol).
Your third world country resident, from lets say the Democratic Republic of Congo, sharing a cup of water and also a cup of liquor.
Personally what I think the whole "don't share cups" is ridiculously overblown, but I am curious. | It depends on the disease or virus and how it's transmitted.
If we're talking flu virus...don't share that cup! Herpes is also very virulent, but only at the site of infection. If someone has a visible cold sore, don't share that cup!
Some viruses don't spread very effectively through saliva, though they may be present. A famous example is HIV. HIV is very sensitive to the environment outside the body and can't survive for more than a few seconds in open air. If someone has HIV and isn't bleeding from the mouth, go ahead and share that cup :) | 114 | 271 |
ELI5: The difference between mass and weight | Edit: Thanks for the answers, everyone! | Your mass is a given quantity regardless of where you are. Its how much "stuff" you are made of. Weight is how gravity acts on your mass so you weigh less on the moon because there is less gravity but your mass is the same anywhere you go in the universe. | 20 | 21 |
CMV: Religion as a whole does not need to be abolished. | **Disclaimer:** I'm an atheist.
With that out of the way, let me explain my view. [Many people on CMV](https://www.reddit.com/r/changemyview/wiki/general#wiki_against_religion) have expressed views that religion is harmful to society and has stopped the advancement of science in society. Common examples are used such as killings and wars that have took place on the premise of religion.
However, I do not believe that religion as a whole needs to be abolished. While I feel that certain fundamentalist views need to be abolished, in general most religious people do not engage in such activities, and instead seek to carry out the values of peace, love, etc. that keeps a society together. I think that as long as religion is kept a personal matter, it is alright for religion to exist.
By "personal matter" I mean that people should not engage actively to uphold their own form of morality, and instead follow the rules that keep a community together. For example, while Christians may be against homosexual rights, they should not engage in activity that discriminates against homosexuals or support anti-homosexual policies, but instead advocate against homosexuality on a moral basis. This is under the assumption that homosexuality does not cause any harm to society, which I will not discuss further.
Assuming that people do abide by these conditions, I see no reason why religion would cause harm to society. CMV.
---
**Clarifications (will update as time passes):**
1. By personal matter, I make an exception for the spreading of ideas (such as discussing religion with your children or converting others). The crux is that your actions must not harm others.
2. I'm proposing that by keeping religion as a "personal matter", most harm will be curbed.
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**List of common arguments (will update as time passes):**
**A** stands for argument, **CA** stands for counterargument.
**A:** Publicly endorsing beliefs that are not supported by strong scientific evidence can be seen as causing harm to society and slowing down progress.
**CA:** I do not think that publicly endorsing religion will cause a significant effect. People are already inclined to believe many things that are not supported by strong scientific evidence. For example, superstitions, pseudoscience, stuff on the internet on sites such as *cough* Reddit *cough*, and much more.
**A: ** Particular parts of religion clash with science. You are either forced to continually change and amend all religions to keep in line with the current scientific world view, or you are telling people to choose religion over science, harming scientific advance.
**CA: ** I'd opt for letting people decide, since it is impossible to amend all religions to keep in line with science. This will definitely harm scientific advance. *[to be completed when I sort out my thoughts]*
---
After spending an hour, I couldn't think of a counterargument to the above arguments. I've awarded the deltas. Thanks for changing my view, /r/changemyview!
I will try to come up with a modified solution and see if that works out. Hope I've at least inspired some discussion on this matter.
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> *Hello, users of CMV! This is a footnote from your moderators. We'd just like to remind you of a couple of things. Firstly, please remember to* ***[read through our rules](http://www.reddit.com/r/changemyview/wiki/rules)***. *If you see a comment that has broken one, it is more effective to report it than downvote it. Speaking of which,* ***[downvotes don't change views](http://www.reddit.com/r/changemyview/wiki/guidelines#wiki_upvoting.2Fdownvoting)****! If you are thinking about submitting a CMV yourself, please have a look through our* ***[popular topics wiki](http://www.reddit.com/r/changemyview/wiki/populartopics)*** *first. Any questions or concerns? Feel free to* ***[message us](http://www.reddit.com/message/compose?to=/r/changemyview)***. *Happy CMVing!* | Publicly endorsing and advocating beliefs that are not actually supported by strong enough evidence could be seen as causing harm to society and slowing down progress however, even if indirectly.
EDIT: And this might apply even when the belief leads to some beneficial behaviors, such as 'You should be nice to people because (insert religious motivation)'
| 20 | 107 |
ELI5: Why is gargling salt water known to help with sore throats, but eating chips doesn't? | If the salt in salt water can aide the sore throat, why wouldn't the salt in chips, french fries, or any other salty food also be a suggestion to help? | There's a phenomenon called 'osmosis' which plays its role here.
When two different liquids with different concentrations are separated by a semipermeable membrane (the one that allows one-way flow only), the liquids would flow in such a way that they attain a state of equilibrium, i.e. now the concentration of both the liquids is same.
The bacteria which cause the sore throat also have their skin similar to a semipermeable membrane. When you gargle with salty water, the inner 'fluid' of bacteria (which makes them live, in a literal sense) oozes out (in order to equalize the concentrations of these fluids-salt water and bacterial body fluid). This kills the bacteria and their 'active fluid' is washed away when you gulf-out the liquid. Thus they loose their dominance on the sore throat and you feel relaxed. | 47 | 24 |
ELI5: what is Keynsian economics? | In classical economics it’s all about supply and demand. If supply is higher then prices go down. If demand is higher then prices go up.
Keynes added the actions of a central government to the model, allowing management of overall demand, and preventing extremes of recession and inflation.
In other words, it recognises that governments aren’t exactly the same as other market participants, essentially because they also make the rules of the market. | 85 | 55 |
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Why do quarks have "charges," and how does this work? | I know that protons have a +1 charge because of their constituent quarks (+2/3, +2/3, -1/3), but I was curious as to what forces cause quarks to have these fractional charges and how it works. | Rather than forces creating charges, charges are what specify how forces interact with particles. Here we're talking about electric charge, which is usually defined in particle physics so that the electron has charge -1 (with no units). Then the fact that up-type quarks have charge 2/3 means that, in an electric field, they experience a force 2/3 as strong and in the opposite direction when compared with electrons. Down-type quarks experience a force in the same direction as electrons but 1/3 as strong.
Electric charges are not forced to be integers or fractions, but we observe that all the particles we know about have integer or fractional charge with a small denominator (relative to the electron charge). Even more surprisingly the fractional ones are never found alone in nature---they always are joined together (confined) into integer-charge particles. HOWEVER the reason they are confined has nothing to do with their electric charge, and everything to do with their *color* charge, which relates to the strong interaction. It's a pretty interesting arrangement that is potentially explained by grand unified theories that join all of the forces, including color and electromagnetic, together.
As a bonus fact, note that electric charge is special among the fundamental forces and charges in the Standard Model, because it's the only one that isn't *forced* to be quantized (come in integer multiples, in this case multiples of 1/3). (It *happens* to be, experimentally.) Mathematically this is because electromagnetism is defined by an abelian gauge theory, which allows any charge, while the weak and strong forces are non-abelian gauge theories which only allow fixed units of charge. Grand unification puts the abelian part of the Standard Model inside a larger non-abelian group, forcing the charge to come in fixed units. | 13 | 23 |
How did we create precision-engineered components without a precision-engineered machine to make them? | Patience and Polishing.
Basically how you create anything with precision. Rough cut. Smooth cut. Smoother cut. Coarse polish. Fine polish. Super fine polish.
You just have to do this to the machine. It's feedback. Measure and cut repeatedly. | 165 | 352 |
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Why do diabetes patients sometimes need their limbs amputated? | Pretty much self explanatory. What happens to their limbs that causes them to be totally unsalvageable? | Diabetes causes high levels of glucose in the blood, which can damage just about any organ in the body. It affects the nerves in the feet, a condition called peripheral neuropathy, so patients lose sensation. It also causes vascular changes, hardening and clogging the arteries so the feet don't get enough oxygenated blood. That means patients might not feel an irritation until it breaks the skin, allowing bacteria to enter the wound. Because the blood supply is poor, the body has a diminished capacity to fight the infection, so the wounds don't heal. | 22 | 20 |
How exactly does nothing (or almost nothing) react with glassware? | I've been watching CodysLab and HTME on YouTube and seeing them put all those incredible reactive and dangerous into glass started wondering why/how it works? Are there other things that are as resistive to chemicals as glass is? | It really depends on the chemical in question, but plastics can hold lots of things and even some things that glass cannot (think of how many household chemicals are sold in plastic containers). Some metals are also great at holding things, especially various grades of stainless steel.
The main reason this works is that there are relatively few ways that glass can interact with chemicals inside. The surface of glass is a bunch of Si-O bonds with usually H+ hanging onto the surface O, or some other positive ion like Na+. For anything that isn't basic enough to pull that proton off the surface the glass will be fairly inert. However, this means that glass is really bad at holding strong bases. If you ever mix up a solution of NaOH you best store it in a plastic bottle.
Plastic is good in different ways. Plastics are not usually susceptible to basic attack, and most are fine against acids as well. However, some organic solvents can worm their way into the polymer chains and essentially melt the container or just leak through, and that isn't a problem organic solvents have with glass. | 54 | 57 |
ELI5: What can a "good lawyer" do that a normal lawyer can't? | You hear of big businesses getting their way in court when they otherwise wouldn't because they have "good lawyers". Same with convicted criminals; a convicted man can receive a lesser sentence because he has a "good lawyer". I don't understand what being a "good lawyer" entails. All I can think of is that a good lawyer has a better way of words, can persuade people easier, pull up random obscure laws pertaining to something or whatever, but it's still confusing to me.
| All those things you touched on - knowledge of case law, experience, grasp of logic etc.
Many criminal cases rely on a combination of physical and circumstantial evidence in order to convince a judge/jury 'beyond reasonable doubt'. A good criminal defence lawyer understands (and predicts) the argument being put forth by the prosecution, and the key aspects that the argument relies on (eg. A witness seeing the defendant at particular time/place), and will dismantle these aspects and throw on as much doubt as possible (eg. Asking a witness How did you know it was Person A? How close were you? Do you wear glasses? Had you been drinking? Had you seen his face before on to reports?).
Going through all the details of a case is time consuming for a lawyer, which makes them expensive. Quite often (and particularly with public defenders) it's not that a particular lawyer is bad, they simply didn't have enough time to mount a good defence.
As for corporate law, big companies maintain a lot of documentation in their contract and legal negotiations. They hire big firms because they have the resources to trawl through the many thousands of documents relevant to a case. Against this, a sole practitioner or smaller firm would just get swamped, and would probably seek an alternative (deal, agreement etc.) to going to court. They might have been in the right, but just don't have the resources to win. Sometimes plaintiffs with similar grievances with a big company will pool their resources behind the one firm in order to make a 'class action'. | 14 | 31 |
ELI5: Since I live in a country, state, and city with modern waste water treatment facilities, how is running water while shaving, brushing teeth, showering, ect. wasting water? | Isn't water reclaimed, treated and reused? Since it is not destroyed (by changing states) can it truly be wasted? | More accurately it's about the resources (energy, chemicals, facilities, etc.) needed to obtain water from the environment, treat it to make it potable (IE safe for you to drink), and then distribute it to everyone in the area. Then, after the water has run from your tap down into your drain, more energy, chemicals, and facilities are needed to move all the wastewater to wherever it's being treated, remediate it (make it safe to release into the environment or back into the drinking water system), and then push it out to wherever it's going, either into waterway of some sort, or back into your drinking water.
All of those steps cost materials, time, and energy to happen, so that's what's really being "wasted." | 21 | 16 |
CMV: I believe that trigger warnings are unhealthy, and institutions shouldn't tailor their content around them | Edit: I evidently haven't thought this through very much, and my argument is criticising the wrong group of people. I think the bulk of my argument is a knee-jerk reaction to Tumblr-folk who misuse the term "trigger" to mean being offended or not happy about a trivial thing. I recognise that this is clearly not the same thing as a genuine trigger, for someone who has been through PTSD or suffered a genuine trauma.
If people are unclear on terms, a "trigger warning" is a quick notice given before a speech, video, body of text etc., warning the audience that its content may trigger certain traumatic memories. For example, if a video talks about rape, it might have a trigger warning so that victims of rape can avoid it if they want to avoid painful recollections.
I don't think this is healthy, and should not be encouraged as a practice. The victim of a trauma is always, eventually, going to come across stimuli that might be "triggering", it's not the responsibility of society to avoid giving those stimuli. They might end up studying rape in psychology, or law, or ethics, or a variety of classes. Should the professor start his class with "By the way, today we're going to be talking about rape, and if anyone's uncomfortable with that, you're welcome to stay out of the class"? No; there are potentially infinite possible things that could trigger a person, and a
professor shouldn't be expected to account for all of them.
Some considerations. Firstly, if the lecturer was showing something that would reasonably upset a lot of people (violence, abuse, suicide etc,) then yes, please put a notice at the start of a class. Secondly, I think the professor in this situation should be accommodating, and if a student specifically approaches or emails him about content they find uncomfortable, then the professor ought to make accommodations within reason.
But, it's not the professor's job to foresee any possible triggering content - picture the sort of people you find on /r/TumblrInAction who are triggered by trees. I'm being silly, of course, but some people can't tolerate things that most people are perfectly okay with, and when that's the case, the person shouldn't *expect* teachers, friends and family to accommodate for them.
And if a psychology student came up to the professor in the scenario and told him she found the Millgram experiment disturbing and didn't want to see any content relating to it, then the professor is entitled to raise eyebrows as to why the student is taking the class.
I've perhaps not worded the argument very coherently, so, **tl;dr**, people with triggers shouldn't expect people to accommodate their behaviour, and should learn to deal with those stimuli.
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> *Hello, users of CMV! This is a footnote from your moderators. We'd just like to remind you of a couple of things. Firstly, please remember to* ***[read through our rules](http://www.reddit.com/r/changemyview/wiki/rules)***. *If you see a comment that has broken one, it is more effective to report it than downvote it. Speaking of which,* ***[downvotes don't change views](http://www.reddit.com/r/changemyview/wiki/guidelines#wiki_upvoting.2Fdownvoting)****! If you are thinking about submitting a CMV yourself, please have a look through our* ***[popular topics wiki](http://www.reddit.com/r/changemyview/wiki/populartopics)*** *first. Any questions or concerns? Feel free to* ***[message us](http://www.reddit.com/message/compose?to=/r/changemyview)***. *Happy CMVing!* | > Firstly, if the lecturer was showing something that would reasonably upset a lot of people (violence, abuse, suicide etc,) then yes, please put a notice at the start of a class.
Do you not include rape in this consideration? Because this is pretty much all anyone wants. | 12 | 21 |
Eli5: How does a battery company produce say a double A battery that's better or worse than a competitor if it's the same thing? | Do generic products just like add less juice and more popular ones add more or something? | Firstly there are several different chemistries that are used in AA batteries. Some are more expensive and have higher capacity than others.
The consider that a battery is not just a pot of chemicals. There are various components including a carbon anode, separator, exterior can etc. The quality of these affects the capacity and internal resistance of the battery.
Edit to add: rechargeable batteries have even more variation because the robustness of different geometries to repeated cycling is not trivial to optimise. | 27 | 27 |
CMV:All drugs should be legalised | Drugs are supposedly illegal because they are harmful and can cause damage to the user and people around them.
How is this reasoning justified when alcohol, tobacco, obesity, motorbikes, skydiving, going into a tiger enclosure and many more are all legal. All of them and more can be harmful to the people doing it and people around them.
Either, we should never be allowed to do anything because it might hurt me or someone else, or there is some logic behind the reasoning. If someone wants to take drugs, is it not their body, and therefore their right?
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> *This is a footnote from the CMV moderators. We'd like to remind you of a couple of things. Firstly, please* ***[read through our rules](http://www.reddit.com/r/changemyview/wiki/rules)***. *If you see a comment that has broken one, it is more effective to report it than downvote it. Speaking of which,* ***[downvotes don't change views](http://www.reddit.com/r/changemyview/wiki/guidelines#wiki_upvoting.2Fdownvoting)****! Any questions or concerns? Feel free to* ***[message us](http://www.reddit.com/message/compose?to=/r/changemyview)***. *Happy CMVing!* | All negative effects of narcotic substances can indeed be mitigated by responsible use and quality control. It is not, however, currently possible to educate people to use drugs with care (e.g. to limit dosage) due to how destructive addiction can be mentally. It is also impossible to create and ensure standards for drug substances, which are highly toxic by nature.
Moreover, drugs are not entirely victimless. While they directly harm only their consumer, addiction itself and mental health degradation due to organic damage can be harmful to others by harming interpersonal relations and pushing people towards criminal behavior. | 41 | 121 |
Eli5: Why does meat from different animals taste so different? If it’s all muscle shouldn’t it be pretty similar? | I can reason through cow and fish tasting different but not cow and pig. | Diet, environment, DNA and activity level will have an enormous impact on the taste of individual meats.
There are times where two animals of the same species will taste different depending on how the individual animals grew up. | 47 | 39 |
How does a photon move? | A photon is an excitation of the electromagnetic field which is described by a wave propagating through space - **always** with speed c = speed of light. So a photon simply always moves - it can't be at rest. The reason for this is that the photon is massless and the solutions to its governing wave equation therefore has constant dispersion.
Did this answer your question? | 19 | 40 |
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ELI5: how can laptops fit over 1tb of storage and 16gb of ram in a tiny chill while PCs need massive ram sticks and often large SSDs? Why isn’t PC ram as small? | The main reasons why PCs are larger are ease of access and cooling. Cooling is very important to improve performance and durability. If you make everything small and cram it into a small space, you can’t have good cooling so the system will have to slow down as it heats up. The bigger your RAM stick is, the faster it can dissipate heat. The more space you have between your parts, the more airflow and cooling you get. | 62 | 27 |
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Why does choked flow happen and why it is related to the speed of sound ? | I'm diving into the venturi effect (example: rocket nozzles and chocked flow happening in the admission valve of a ICE) and it seems that when the gas approaches the speed of sound, the flow starts to choke. Why does this happen ? | To preface this answer: information about a medium travels at the speed of sound in the medium. So if you change the conditions of a flow at one point, the effect on the medium travels at the speed of sound upstream in the medium.
If you imagine a venturi nozzle and a flow condition where the speed of sound is achieved at the throat, and your downstream flow is travelling at greater than the speed of sound, any disturbances downstream of the throat won't propagate upstream. Picture yourself splashing around in a river where the flow travels faster than the wave speed; no one upstream of the river will be able to see your splashing around. Now there are two ways to achieve a choked flow scenario from here:
* ~~Increase the pressure upstream of the throat~~ **EDIT:** Forcibly increase flowrate upstream of the nozzle
* Decrease the pressure downstream of the throat.
If you try ~~increasing the pressure~~ forcing the flowrate to increase upstream of the nozzle (perhaps by increasing power on a compressor), you end up forcing air to get to Mach 1 before the throat. If you picture it does that instantaneously before the throat, because of how supersonic flow behaves it will actually decelerate to subsonic flow just downstream of the Mach transition. And speed up again and slow down again, etc. etc.. This just creates a bunch of shocks in your convergent nozzle where heat is generated but the flow doesn't speed up. And once it gets to the throat, it hits mach 1 anyways and accelerates in the divergent section.
If you decrease pressure downstream, on the other hand, you get a situation of underexpansion at the outlet of your pipe system. Unlike subsonic flow where the information about the new reduced downstream pressure propagates through the system quickly and stabilizes the flow pressures and velocities, the underexpansion remains at the outlet in the form of an expansion fan. Remember: information can't travel in a medium faster than the speed of sound, and if the flow travels faster than the speed of sound, the information downstream never propagates to the rest of the system.
EDIT: Changed "increase pressure upstream" to "increase flowrate upstream". Your behavior from the reservoir leading up to the throat will not depend on absolute pressure of the reservoir. | 423 | 2,528 |
As an applicant, what would be some good questions to ask during a PhD interview? | I have a PhD interview coming up and I can't seem to think of an impactful question that I may ask at the end of the interview. As an applicant, I think that I would need to ask something that may showcase my readiness and motivation for the PhD position. The questions I have in mind feel a little too basic. I would really appreciate some suggestions.
Thank you :) | I would ask how things were going for people who got their PhD's at their department. It's a potential huge investment by both parties, and if they are worth their salt they should be able to present actual employability numbers. | 74 | 95 |
Why do I sometimes lose weight on days when I eat much more than I should have? | I've been trying hard to lose weight - and succeeding. I've lost more than forty pounds over the past five months, since I started running and eating right. Yesterday I ate waaaay too many calories, and it wasn't a workout day. But when I woke up this morning, I had lost two pounds! This isn't a unique experience. It has happened in the past. I'm 30, 6'4", 285lbs. I've been trying to eat under 2,500 calories every day. Yesterday I probably ate closer to 3,500, maybe more.
TL;DR - in the context of a calorie cutting diet & exercise program, I ate a ton more calories than I should have and woke up two pounds lighter. Why? | There are a lot of short term factors that case your weight to fluxuate beyond your core weight loss, your water content in particular.
If you drank a lot and ate a small amount of high sodium foods, you would would have been overhydrated for your weigh in.
Then the next day, you eat a lot, include some diuretics, then maybe sweat a little more than usual that night, you'd be underhydrated, enough to compensate for the extra food you ate.
Also note that bathroom scales are sensitive to temperature and humidity, and aren't always that accurate to begin with. A 2 lbs. swing is not terrible significant. | 11 | 21 |
How did species survive in the days just after the K-Pg Extinction event? | The K-Pg Extinction event (aka the Chicxulub impact, widely known as being the impact that killed the dinosaurs) "devastated the global environment, mainly through a lingering impact winter which halted photosynthesis in plants and plankton" (Wikipedia). And yet numerous different species, the ancestors of all organisms today, somehow pulled through.
How, exactly, could anything survive this? How did plants survive without sunlight, or animals survive without anything to eat? I can understand scavenging for days and weeks on dead plant matter and decaying cadavers, but how was this sustainable for months and years? I just don't get what the means of survival were for long enough for the dust clouds to subside and photosynthesis to resume.
Thanks for any insight. | Here like with all things, that description is a vast oversimplification meant to make it easy to understand.
It wasn't that photosynthesis stopped altogether. The dust made sunlight very dim like a very cloudy day for years. Which made it hard for larger plants and things with high energy demands to survive, but smaller plants whom had evolved to live in the shadow of the larger plants could survive; especially after the larger plants died and stopped shading them and taking up the ground nutrients.
But because all the large plants died, so did the animals that needed the large plants for large quantities of food. As did the large carnivores that needed the large herbivores. However the small animals (some of the first mammals) were able to subsist even thrive on the smaller plants. | 23 | 33 |
If the minimum wage becomes $15 an hour, what about workers making more than that? | If the minimum wage becomes $15 an hour for someone working in fast food with no higher education, what about some one who is already making $15/hr with a college degrees taking on an entry level job in their field that does require a degree or those who are making just above them like $17 or even $20? Wouldn’t they want their wages to be increased too to make it fair, which in turn would increase all of the rest of the wages through like a domino effect? | Their wages could go up for a variety of reasons.
1.) The minimum wage increases demand for slightly above minimum wage skill workers. This increase in demand pushes wages up.
2.) Workers outside options are better now, so someone who was making $15 is going to need to be paid more or other compensation improvements to keep them around. | 43 | 39 |
eli5: What is rent seeking and most specifically defensive rent seeking? | Rent seeking is behavior that increases someone's income without increasing wealth. In economics, most transactions are done because both people are better off, when a baker sells a loaf of bread it's because the baker values the money more than the bread, while the buyer values the bread higher than the money.
An economic rent is something that doesn't do that. A simple example is a license to be a baker. If the government only wants 20 bakeries in the town, and makes that many licenses there will be 20 bakers who get the licenses and who make more money than bakers in the next town over, but whose bread doesn't make their buyers any better off. | 29 | 39 |
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CMV:The farming industry has only itself to blame for the lack of young people who aspire to become a farmer. | Please note I am not talking about hobby farms.
We read all the time about the average age of farmers getting older and older and very few young people aspire to be farmers. The farming industry has only itself to blame. The cost of entry to become a farmer is incredibly expensive and the going rate for decent farmland is so expensive no one except wealthy people or corporations can afford it. Where I live the average acre is $10,000, and at a minimum you'll need 100 acres to break even. So, a million dollars and we haven't even started the actual practice of farming yet. Add in another million for equipment and seeds and an aspiring farmer is in the hole millions of dollars for a relatively risky career choice.
If I want to become a lawyer I study and go to law school. If I want to become an engineer I study and get an engineering degree. If I want to open a restaurant I become a chef or hire a chef. If I want to become a farmer I must be born into farming.
If this was really a problem either the farming industry would come together to entice people to become farmers or the government would force land owners to not sell to anyone other than an owner-occupier farmer. Either of these is unlikely.
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> *This is a footnote from the CMV moderators. We'd like to remind you of a couple of things. Firstly, please* ***[read through our rules](http://www.reddit.com/r/changemyview/wiki/rules)***. *If you see a comment that has broken one, it is more effective to report it than downvote it. Speaking of which,* ***[downvotes don't change views](http://www.reddit.com/r/changemyview/wiki/guidelines#wiki_upvoting.2Fdownvoting)****! Any questions or concerns? Feel free to* ***[message us](http://www.reddit.com/message/compose?to=/r/changemyview)***. *Happy CMVing!* | Are young people willing to become employees on corporate owned farms? After all, if a corp buys farmland, they still need someone to actually run the place - that person would be still be a farmer.
If "yes" - then young people DO want to be farmers.
If "no" - then your explanation about price of land does not really explains this, as you don't need a million dollars to be hired by a corporation to farm. | 256 | 784 |
ELI5: why insects are attracted to lights | Insects navigate by using a reference point of light. Normally this would be the sun or the moon. They are far enough away that insects can put the sun/moon at a certain degree in their vision, and they know they will be traveling in the direction they need.
If they end up using a street light, things don't go as planned. Because the light is so much closer, as they try to keep the light at the same degree, they end up circling in towards it. | 36 | 33 |
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How does Captain America's shield always come back? | Most of the time Captain throws his shield into mid air, hits 3 guys and it somehow just ends up just coming back to his hand. Is there some kind of explanation for this or is it just something that just ''happens''? | A combination of training and experience have left Cap with a high level of awareness of angles and vectors. Its unknown whether he has the academic understanding of a mathematician, or the instinctual understanding of a pool shark, but he is able to almost instantly and instinctively calculate the appropriate angle to make such a throw. | 121 | 103 |
ELI5: interval workouts are often recommended. Why is a 20 minute interval run peaking at say 80% better than running at 70-80% intensity for the full 20 minutes, which will probably result in a greater distance covered? What is the benefit of the short breaks? | HIIT (High-Intensity Interval Training) takes advantage of how our bodies use energy. When we keep our heart rate high for too long, we begin to use glycogen as our main source of energy. Utilizing the rest period fluctuates your heart rate up and down, so we can continue to use stored fat as our main source of energy. This kind of exercise is super good for burning calories and creating a strong cardiovascular system, but not very good at building muscle mass.
HIT (High-Intensity Training) is better for overall strength training. However, it is a LOT harder on the body, and a LOT harder to accomplish for most people. It isn't so great for burning calories, and it puts a lot of stress on the cardiovascular system, so if you haven't done your due diligence in working up to that point, it's probably not that good for you. | 25 | 36 |
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Do all trees have a common 'tree' ancestor? Or did multiple plant species evolve separately toward what we know as trees? | Forestry student here. There are two main groups that of plants which have trees: the gymnosperms ("naked seeds" mostly conifers) and the angiosperms (flowering plants). The gymnosperms are the older group. There were already recognizable coniferous trees in the Mesozoic era. The angiosperms arose in the late Jurassic/ early Cretaceous period.
As far as we know, the tree form arose separately in both groups. Note that the angiosperm family also contains plants such as water lilies, orchids, carrots, etc. Since we know from the fossil record that the angiosperms are a recent evolution it makes more sense for a smaller plant to have evolved into the angiosperms than it does for a plant with tree form to found such a diverse group.
TL;DR All trees have a common plant ancestor but that ancestor was not a tree. | 195 | 503 |
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ELI5: Why do our noses run when it’s cold? | It's your body putting out fluids to keep the air you're breathing at a safe level of humidity and moisture for your lungs. If the air is too dry, your lungs can get damaged and prone to infection. When it's cold, the air gets drier, so your nose may start running to help keep the air moist.
Of course - colds are also more common in cold weather. Your nasal passages get dried out and damaged, which means viruses can get into your body more easily, causing colds. Additionally, you spend more time inside with the windows closed around other people who are more susceptible to colds. So, you may find you just get more colds - causing runny noses - in the winter as well. | 12 | 19 |
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ELI5: How does a seed "know" which way is down or up to grow? | Edit: I know it has to do with gravity. I'm asking the biological proccess that makes a seed know which way to go. | Plants can sense gravity due to special containers (organelles) that store starch in a plant cell. The starch is rather dense compared to the rest of the cell so that the container will be affected by gravity. The containers are entangled in a mesh (actin) which can sense the direction they are moving. Based on these signals a special hormone (auxin) is distributed in the shoot to indicate the growth direction.
This is only one of many possible mechanisms. | 36 | 31 |
ELI5: Why is a rape on a college campus handled as an administrative problem by the school, rather than as a criminal matter, handled by the police? | *edit
Thanks for all of the comments and discussion. It seems to be a pretty even split between
Title IX.
The universities have their own police and are their own jurisdiction.
The university's investigate along side police.
Trolls.
Special thanks to /u/HB2490 for [this comment.](http://www.reddit.com/r/explainlikeimfive/comments/2o1tfe/eli5_why_is_a_rape_on_a_college_campus_handled_as/cmj5bss)
| They typically are handled by both.
If someone reports a rape to the police, and the suspect is a student, there will usually be two separate investigations or trials. One will be done by the police, go through the criminal courts....etc.
During the same time, the university may also run an investigation into any "honor code" or student conduct violations. Most universities have some sort of a student code of conduct that you agree to. So maybe the court will find you not guilty, but the school will. Or vice-versa. Same with punishments, the school may be more or less harsh than the courts (expulsion from the school vs probation by the courts). | 2,250 | 4,008 |
ELI5: Why are so many old websites hosted at universities like MIT? | I Googled for the lyrics to "You're a Mean One, Mr. Grinch" and up came [this ancient HTML document from the days of Web 2.0](https://stuff.mit.edu/people/dpolicar/writing/poetry/poems/meanGrinch.html).
I've noticed that Google will often point me to these very old, rudimentary webpages that are 20 years old or so, and often hosted at American universities like MIT.
So my question is, why do these websites exist in the first place, and why do they still exist? | The web (not the internet itself) was first created at CERN (a physics lab) as a very useful tool for sharing information, so it made sense that academic institutions would be early adopters because 1. they like sharing clever things they've learned 2. are full of geeks 3. have enough money to buy big servers
They often gave students a little bit of space (like a megabyte) to host their own webpages, presumably thinking PhD students would write something to do with their dissertations but of course were really just X-Files episode guides and REM fansites.
Why do they still exist? Because nobody has taken them down! | 2,408 | 2,189 |
ELI5: What’s the difference between a therapist, psychologist, and psychiatrist? | A therapist is a generic term for someone who provides counseling services. Pretty much anyone can be a therapist (although laws vary).
A psychologist is a slightly more specific term referring to someone who holds a licensure that normally requires a Graduate-level education in psychology (normally clinical psychology).
A psychiatrist is a medical doctor with a specialization in mental illness. The most notable distinction is that psychiatrists can prescribe medication, while the other two categories cannot. | 103 | 72 |
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Is quantum mechanics truly random or merely unpredictable? | because theres a huge difference
Edit: What im asking is whether we actually KNOW if the universe is not deterministic or whether it might be but we just cant tell. What brought this idea to mind was thinking about the idea of parallel universes and whether randomness is necessary for that to be possible. | The idea you're looking for is that of *hidden variables*. Einstein disliked the idea that quantum mechanics was non-deterministic so much that he proposed there exists a theory deeper than quantum mechanic that is deterministic but reproduces the seemingly random results of quantum mechanics. These theories also fixed what Einstein saw as a problem with non-locality (faster than light communication) in quantum mechanics.
A decade or two after Einstein died a John Bell showed by contradiction that a hidden variable theory could never produce the results we see in quantum mechanics experiments. Using the following assumptions,
1. Experimenters have free will,
2. Logic is valid way to reason,
3. Hidden variables exist,
4. Hidden variables are local,
he derived a set of inequalities. He then found an experiment that violated these inequalities. This means at least one of the assumptions listed above is wrong.
The commonly accepted one is that 3. is faulty and that quantum mechanics is actually random. The idea that hidden variables, an idea specifically introduced to ensure quantum mechanics was local, were in fact non-local would probably upset Einstein much more than the idea of reality not being deterministic.
edit: added the assumption that free will exists, as ichthyic points out as being necessary. | 22 | 36 |
How does a broken bone connect again once the two healing pieces reach eachother? | It depends on various principles, including where the bone is and how they connect to each other. If anatomic reduction is achieved and the segments are compressed, then you get primary bone healing which is direct growth of the osteons on each other. If the segments are not compressed and there is micromotion at the site, you get callus formation and the bone remodels itself. Children are better at this than adults - hence why children get casted more than surgically fixed. | 13 | 24 |
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ELI5:What exactly happens in your body when you drink water? | I get solid food, but what specifically happens when water enters the stomach and then afterwards. | Your body balances the water in the blood, the cells, and the spaces in between. A small amount stays in the intestines to help digestion while most is absorbed into the body across tiny pores. When the water crosses the pores it also helps transport vital electrolytes into your body. Then the water enters the blood stream and quickly reaches a balance with the other spaces: the insides of cells and in between the cells. The kidneys use the water in your blood to filter the waste products into urine. Some water even goes back into the lower intestines to help make stool. | 100 | 152 |
Would electronics last longer if left on all the time, or switched on/off as needed? | I've heard it both ways:
Some claim that as long as all components are well below thermal limits, electronics left on 24/7 will last longer because they're not subject to the stresses caused by the components expanding and contracting due to warming up/cooling down.
But a lot of people think that electronics last longer the less they're on because they spend less time in the "stresses of being on"... but these people never elaborate on what, exactly those stresses are.
So, who's right? And why? What are the most significant forces at work here? | Product Development Engineer here - it varies by product. It's a very interesting question, because thermal cycling (on/off) is a very stressful condition for electronics that causes a lot of catastrophic failures. On the other hand most devices are rated in hours useful life, so leaving a device on is generally not the best choice if it will spend a lot of hours without anyone using it.
For lifetime rating, products are generally subjected to three main categories of abuse (others if it will be an outdoor or waterproof product): Elevated temp. operating tests, thermal cycling tests, and vibration testing. Generally the weak point of any given product is due to a particular design choice, and thus could be any one of those tests. If you're trying to decide about how best to use a particular device, you probably need to look up how it tests. I've been looking for test standards for you to read, but none are free. In LED lighting, we adhere to IES LM-80, which describes mostly elevated temperature testing. For UL compliance we'll need to pass some ASTM vibration testing (maybe D3580), and for customer certification we'll need to have data on storage life and cycling.
I know it seems like a cop out, but the best way to ensure long life of your device is to operate it in a cool environment where it won't get any extra thermal stress, and to use it as infrequently as possible. The maximum stress from cycling would be if you turned it on just long enough to get hot, then left it off just long enough to get cool before turning it back on, so if you're turning on a TV 20 times a day, you're probably doing it wrong. | 374 | 427 |
ELI5: Why does running cold water sound different from running hot water? | The differences in density and viscosity are the causes.
Cold water will have a higher pitch due to the stronger surface tension and hot water will have a lower pitch due to the weaker surface tension breaking up the water before it hits the glass or whatever you may be pouring it into.
That's why coffee or something warm will have a low sound and a cold glass of water will sound higher. | 24 | 20 |
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Why aren't there more eye colors? | Your eye color derives from the same biochemical pigment compound that gives you your skin color: melanin. Melanin is *vaguely* yellow-brown-ish when light scatters off it, which is why skin comes in colors in the yellow-brown range.
Eyes which have no pigment in them at all appear pale blue, because of how light scatters off the eye. Add melanin in various proportions, and you get the whole range of human eye colors, from various shades of blue and green to brown to hazel (which is a mixture of green, brown and yellow).
There aren't any other eye colors because those are the only combinations it's possible to make by combining the natural blue of pigment-less eyes with melanin in various distributions and concentrations. | 38 | 23 |
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ELI5: why does squinting help when trying to read something small or far away? | Squinting works because it decreases the effective size of the iris. The small opening, like a smaller f stop on a camera, although it decreases the amount of light entering the retina, increases the depth of field... That means the range over which things stay in focus increases. If there is enough light to see, more things are in focus and they are in better focus than they were before the squint. That's it | 45 | 37 |
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CMV: Stores should mark the full price of goods on the shelf. | This was something that really annoyed me when i visited America being charged a difference price to what was on the shelf for goods. I think that stores should include tax on the shelf price for items they sell, it's ridiculous that stores can advertise a product at a certain price and charge another for it. It means that customers have to do the calculations themselves rather than by themselves, and because stores usually like to advertise products at a nice round number, the product usually ends up actually costing a less convenient number.
For example a soda might be $2.99 on the shelf and really cost $3.14 giving you 76 cents in coin change rather than 1c. (Also fuck pennies but I think people won't disagree on that.)
Please change my view and explain what this systems benefits are. | This system allows businesses with multiple locations to have standardized prices. This is good fit the business, because it makes labeling inventory easier, and it means they don't have to spend time re-labeling their inventory if the tax rate changes.
It also means that there's less internal competition between nearby locations of the same business. People are more likely to go to the location with lower sales tax if the list price of the item is lower. This makes it harder for businesses to justify having multiple nearby locations, and will cut tax revenue from areas with higher sales tax. | 137 | 325 |
ELI5: What prevents our eyeballs from being able to look left and right at the same time? | Edit: not talking about cross eyed. Talking about left looking left, and right looking right | Eye movement is one of the most complicated aspects of the nervous system. There are 6 main muscles and 3 main nerves that control each eye around 3 axes. As others are saying it's very common for the left eye to look right and the right eye to look left at the same time (i.e. cross-eyed)—this happens when we look at something close to us and is called convergence.
However, we are generally not able to make the left eye look left and the right eye look right at the same time. This is due to a connection in the brainstem called the medial longitudinal fasiculus (MLF). This is a difficult ELI5.
If you want your left eye to look left, you need the left lateral rectus muscle, which is controlled by the left abducens nerve (cranial nerve VI).
If you want your right eye to look left, you need the right medial rectus muscle, which is controlled by the right oculomotor nerve (cranial nerve III).
The MLF runs from the abducens nucleus on one side to the oculomotor nucleus on the other side and is activated whenever the brain activates the abducens nerve, so when your brain sends a signal to look left with your left eye, your right eye also gets a signal to look left.
Thus in people who are neurologically intact, when one eye moves outwards, the other eye essentially always follows. The MLF specifically can be affected by a variety of neurologic disorders, classically multiple sclerosis. | 380 | 808 |
CMV: while white racism upholds power structures, saying only white people can be racist absolves other races from accountability | For context: I’m South Asian, and I have lived in Europe for more than three years.
I recently read Reni Eddo-Lodge’s book ‘why I no longer talk (to white people) about race’ and I mostly agree with her.
Except one point: that only white people can be racist, and all other groups are prejudiced.
I agree with the argument that white racism upholds power structures at the disadvantage of marginalised groups.
What I do not agree with is that other groups cannot be racist - only prejudiced. I don’t see a point of calking actions that are the result of bias against a skin colour ’prejudiced’ instead of ‘racist’.
I have seen members of my own diaspora community both complain about the racism they face as well as making incredibly racist remarks about Black/Chinese people. Do these uphold power structures? No. Are these racist? Yes. Are these racist interactions hurtful for those affected? Yes.
I had a black colleague who would be incredibly racist towards me and other Asians: behaviour she would never display towards white colleagues. We’re her actions upholding a power structure? I’d say yes.
I believe that to truly dismantle racism we need to talk not only about white power structures but also how other groups uphold these structures by being racist towards each other.
So, change my view... | So we should note here that all of sociology is an approximation. Humans and human societies are infinitely complex. We can't fit it all into words. What we can do is create models that reflect how we think societies work, while recognizing that these models are only ever a partial description of what's really going on. There is no model which is perfect, and which model we use is a choice.
So with that in mind, people like Reni Eddo-Lodge who focus on a structural reading of racism have intentionally moved away from the conception of racism at the psychological/interpersonal level and instead focus on racism as a product of larger social structures. The "Capital R" Racism that matters, as far as these people are concerned, doesn't have much to do with individuals making racist remarks against other individuals. It has almost everything to do with political and social structures that go beyond individuals.
This is a conscious choice to re-focus attention on a different kind of racism. The problem with the model of racism as an interaction between individuals is that people tend to focus on the *symbolic* rather than the material. So, you'll have people arguing that George Floyd for example didn't die because of racism because none of the cops who killed him seem like racists. They didn't target him because they personally hate black people, so that's not racism, right? Conceiving of racism as typified by prejudiced remarks leads people to excuse and ignore materially racist social structures because nobody said the n-word while they were enacting structural racism. Moreover, this conception of racism leads people to think that racism is just unavoidable and the natural product of people of different races interacting - see *Crash*, 2004 for one of the most egregious examples - which is not really helpful at all. If you think of racism primarily as when a person of a certain race says a naughty word at a person of a different race, then you will never be able to actually change any of the material effects of structural racism, because it will be invisible to you.
So the "Racism = prejudice + power" model of racism attempts to rectify this misunderstanding of racism by focusing on the institutional and the systematic rather than the individual. Structural racism can exist even when none of the individuals involved are overtly racist. That's the issue that needs more focus. Of course, this model is only a model. We can't account for all the infinitely reconfigurable scenarios of human existence with a model. The central story of the model is one of white people holding control of political and social structures that are systemically racist, so that's where the focus is. | 419 | 2,854 |
My colleague just destroyed the writing of my latest paper | I'm 34 and I've got 8 first author papers out (out of the others with my name of it there are at least another 5 where I contributed also to writing quite a bit). Therefore I hoped that I learned to write decently enough. However, I know I'm not particularly good and, until I was in high school, I always had super-low marks in writing (4 or 5 out of 10, with 6 the passing vote).
Now, I've been tasked to do a job (and to write a paper about it) that I don't believe much in. So I keep asking my colleague (same "level" but life scientist instead of physical scientist) what she and the PI would like to have written in the paper.
Today, I asked this colleague if I could have feedback on my work. And... she basically told me (in a positive way, she was trying to help me not to criticize me) to rewrite it from scratch. "Just copy the methods from the previous papers so that it finally follows a logical structure, and I'll take care about modifying the text to a publishable form".
I'm lost. After 10 years in doing this job I'm still not able to produce a "decent" paper. WTF am I supposed to do? | im only undergrad level so this is purely anecdotal, but when i was working with some chemistry friends of mine the way they wrote was very different to life scientists. maybe get an opinion from somebody in your faculty | 217 | 120 |
ELI5: Why are most images from space B&W when we have so many tiny, light, color, high resolution cameras on the market? | Many images you see of space are not captured with visible light (for various technical reasons, it not always easy or possible to capture certain objects or certain features of objects in space with visible light).
Some images are instead captured using radio, microwave, infrared, ultraviolet or even x-ray light. Only visible light has any association with color. All other types of light have no color (from a human perspective) and we translate these images into monochromatic visible light that we (humans) can see.
Sometimes professionals will take these monochromatic images and create colorful artistic renditions of what they think the object(s) would look like in visible light or they may add color to highlight or emphasize certain parts of the object.
~~Also, as /u/riconquer mentioned, bandwidth is also an issue. A raw image file with color is typically 3x larger than one that is black and white. When bandwidth is limited and/or speed is important and/or color is not important, black and white photography may be used on spacecraft even when such spacecraft may be equipped with color cameras.~~ [See /u/SchighSchagh's response] | 18 | 26 |
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ELI5: How do electromagnetic waves (like wifi, Bluetooth, etc) travel through solid objects, like walls? | So, when a ray of light hits something, it can basically do one of three things:
It can go right through, with a slight angle that reverses when it comes out the other side, like light passes through glass or water.
It can bounce off at an angle, like light does with a mirror or a bright piece of colored plastic.
Or it can get "eaten" and heat up the object, like when light hits something dark.
Objects are different colors because light is different wavelengths, and some wavelengths get eaten while others pass through or get bounced off.
A solid "red" object is red because green and blue light get eaten more than red light, while red light bounces off more than green or blue. A transparent "red" object is red because green and blue light get eaten more than red, while red passes through more than red or green.
Now, infrared and radio are also just different "colors" of light that we can't see; think of a radio antenna or a WiFi receiver as a kind of "eye" that can see those colors, while a transmitter is like a "lightbulb" that blinks in those colors.
Walls happen to be "transparent" to radio even though they're "solid" to visible colors, just like a stained glass window is "transparent" to some colors and "solid" to others. | 18,040 | 12,087 |
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ELI5: The Mandlebrot Set and fractals in general. | I can recognize the Mandlebrot Set by looking at it, and, thanks to Jonathan Coulton, I even know the formula, but I still just don't get it.
| The mathematical rule that creates the Mandelbrot set is relatively simple (at least, if you're comfortable with complex numbers from a decent algebra class). It works like this:
Pick a complex number *c*. Let's say we pick c=1. Once you've picked it, start with zero and repeat the following process: square the previous number, than add *c* to it. In this case, we'd generate the sequence 0, 1 (0^2 + 1), 2 (1^2 + 1), 5 (2^2 + 1), 26 (5^2 + 1), and so on, and this sequence runs off to infinity.
On the other hand, if we picked c=-1, the sequence would go 0, -1 (0^2 + -1), 0 ((-1)^2 + -1), -1, 0, -1..., and never runs off to infinity.
The Mandelbrot set is the set of all numbers that do *not* run off to infinity this way. | 19 | 33 |
ELI5: Why are our ears shaped the way they are with all their weird ridges? Why aren't they more simply shaped like a funnel? | Part of the shape is to allow the ear to efficiently collect sound waves. However, part of it is also to disrupt the collection - allowing the angle of sound to have a greater effect on what you hear, allowing you to use your ears to sense the direction sound is coming from.
Other shapes are there to keep water from pooling into your ears (from sweat) and to drain efficiently at the same time. Plus, the shape needs to be strong enough to not easily be damaged (heat, cold, fights etc) yet not be a massive resource drain to build them. Additionally, the shape has to be formed by evolution - so each bump and twist and turn has to come about by random mutations that happen to work better for one thing, but maybe worse for another. | 229 | 161 |
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ELI5 If HDMI has a really high Gb bandwidth and is readily available on most computers, how come its not used for data/file transfer? | Think of a computer network like the road network - You can make turns, merge, drive onto highways and bumble along country roads, all part of the same system. But there's a tradeoff - You have to follow a lot of rules to participate, so that you get from your starting to point to your destination without being rammed off the road. Also, the car you drive has to be up to code, and carries lots of safety features and standardized/tested parts to meet the requirements that make it 'road worthy'.
HDMI is more like a drag strip. There's one start and one finish, and you're completely isolated from the regular road network. Your car is adapted for this - You'll get from start to finish real fast, but you're not about to make any hairpin bends. You also lack turn indicators and all the other formal stuff that's part of participating in a proper road network. But the tradeoff is you can go really fast because you're isolated.
Computer Networks are like the road network and HDMI is like the drag strip.
How come HDMI isn't used for data transfer? Because there's not many cases where you purely want to go 1-to-1 between 2 points in a fixed fashion. In cases where you do, the speed isn't worth the cost of adding HDMI support over something much cheaper and well-supported like USB 3. | 46 | 92 |
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Explain to me the Strong and Weak Nuclear force. | I understand the way gravity interacts with the universe as well as the force of electromagnetism, but I'm confused as to how the strong and weak nuclear force is propagated and what effect it has on anything. | The weak interaction is mediated by W and Z bosons, which are unusually massive, and so decay very quickly. The short decay time of W and Z bosons contributes to the comparatively weak strength and short distance of the weak interaction. The primary "effect it has on anything" is the beta decay form of nuclear decay. Beta decay allows, for example, the decay of carbon-14 to nitrogen-14.
The strong interaction is mediated by massless particles called gluons. It binds quarks together to form hadrons, including protons and neutrons. The strong interaction is about 100 times stronger than electromagnetism at the atomic level, and most of the mass-energy of protons and neutrons comes from the field energy of the strong force. Similar to how electromagnetism is divided into + and - charges, the strong interaction has three "color" charges. The color charge is balanced within a proton or neutron, but there is a residual strong force, also called the nuclear force, that acts between protons and neutrons which holds them together in atomic nuclei. | 22 | 118 |
[DC] When does Batman ask for help? | Batman is known for his intellect, detective skills and technological prowess when it comes to fighting crime, but when does he throw in the towel and ask for help? | As early and often as possible. Batman would simply not be able to function if he wasn’t getting help, whether it’s from Alfred, Gordon, one of the Robins, or any other member of the Batfamily.
The idea that Batman refuses to ask for help mainly comes from the Arkham games, but even then he’s still constantly receiving information and advice from Alfred and/or Oracle. | 60 | 32 |
ELI5:Why do so many medicines (pain pills, muscle relaxers, antihistamines,etc.) have a side effect of sleepiness? | All of the types of medicines you described work by basically stopping your body from doing something it would normally be doing, often by interfering with the ability of your nervous system to communicate the messages necessary to do it. A side effect of that can be to generally slow down your nervous system overall, which manifests (among other ways) in you feeling sleepy. | 11 | 27 |
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ELI5 how does the same hormone exert different effects in different target cells? | Sorry if this is a repost. I couldn't any similar questions. | Think of a hormone as a key that turns that flips switches and turns on chemical pathways of cells. The switches they turn on are called cell receptors. Think of them as on and off switches that are turned on by the turning of the hormone key. Hormone (keys) flip very specific switches. Some cells have switches that can be turned on by the hormone key, others do not. Some cells have many switches and when they are all flipped on, they have bigger or different effects. If a cell has that specific hormone receptor (switch), then it will be activated by the hormone. | 11 | 122 |
CMV: There is no reason why religious beliefs and practices should get more respect than other beliefs and practices | What I mean is when people are given a free pass for something because it is 'part of their religion,' when somebody else with the same beliefs and practices would get more criticism. For example, many people are vegetarian and vegan for moral reasons. They believe that animals deserve more rights than they are given. I see people sometimes expressing the view that you shouldn't be expected to cater to vegetarians or vegans, unless it's a health restriction... or a part of their religion. Why is the religious person given more respect for their dietary choices? To be clear, I'm not talking about law at all, I'm talking about being polite and respectful.
Hello, users of CMV! This is a footnote from your moderators. We'd just like to remind you of a couple of things. Firstly, please remember to read through our rules. If you see a comment that has broken one, it is more effective to report it than downvote it. Speaking of which, downvotes don't change views! If you are thinking about submitting a CMV yourself, please have a look through our popular topics wiki first. Any questions or concerns? Feel free to message us. Happy CMVing! | In theory, religion is something that is a more fundamental part of who you are. Religious practices aren't necessarily something you choose to do, but something you feel compelled to do for the sake of your safety, life, or after-life.
The consequence for a vegan eating meat is emotional turmoil, but the consequence for a Muslim eating pork may be eternal damnation. Whether or not the consequence is real, it certainly affects the religious person more. | 21 | 40 |
ELI5: What do scientists mean when they say that light is an electro magnetic wave? | I've seen one multiple educational videos that draw light as two orthogonal waves traversing through space. What is that trying to represent?What exactly is going up and down?
Furthermore, why do people often make the analogy that light acts like a ripple in a pond? | There is an electromagnetic quantum field (EMQF) permeating all of space. Electric fields and magnetic fields are classical representations of interactions involving this EMQF.
Light is a fluctuation in this EMQF, and this representation explains the photoelectric effect (which isn't explained in classical electromagnetism).
If you think of a flash of lightning, it's a lot like a rock tossed into a still pond. This large electric current agitates the gas atoms in the atmosphere, and when they relax they release light in all directions, like how the rock sends waves in all directions on the pond. The surface of the pond is 2D, and the EMQF is 3D, but otherwise it's similar. | 11 | 17 |
Is spin a bulk property? Does it make sense to talk about the spin of a macro object by adding up spins of individual particles, the same way that we can talk about its charge by adding up the individual charges? | Yes. You can define a single spin of a collection of large number of quantum mechanical particles of certain spins in the same way you define the total spin of 2 or 3 particles.
The simplest example to consider would be a spin chain of noninteracting spins.
The wave function can be written as
|w>=|w1 w2 ... wN> with appropriate combination to make sure that it is an eigenstate of S(total)^2.
The total spin along a particular direction(say z) of the state would just be the summation of spin along that direction of all the states.
The total spin would be given by the eigenvalue of S(total)^2 which is s(s+1) hbar^2. For N spin 1/2 particles, s would be N/2. (Or a constant factor times N/2)
So, the total spin would be N(N+1) hbar^2 (multiplied by some constant factor).
In the classical limit, N is taken to be infinite(N>>1) and hbar is taken to be small such that the different components of the spin commute. The classical or macro spin will then have a magnitude proportional to (N hbar).
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A chicken egg is 40% calcium. How do chickens source enough calcium to make 1-2 eggs per day? | edit- There are differing answers down below, so be careful what info you walk away with. One user down there in tangle pointed out that, for whatever reason, there is massive amounts of misinformation floating around about chickens. Who knew? | Chickens are omnivores, but free-range chickens eat a great many insects, and insect exoskeletons are similarly rich in calcium. They'll also eat just about anything else, including small mice, voles, moles, lizards, etc., bones and all.
In a commercial setting, they are supplemented with oyster shells, or whatever source is cheap. Home chicken keepers sometimes feed old eggshells back to their chickens.
Chickens fed more calcium will lay eggs with thicker shells, and they can accept a fairly wide range, but a deficit will yield fragile eggs. | 6,404 | 10,136 |
CMV: Marriage doesn't make much sense in the modern world (modern western standards) and I don't see the need to get married. | People don't need legal paperwork to enforce a union anymore, now marriage is (or should ideally according to modern western standards) based on a mutual decision to stay together. There are benefits such as tax cuts, custody rights for children of course, but these are outweighed IMO by the disadvantages when things don't work out, such as divorce fees, wealth splitting enforced by courts. If the argument is about commitment, several other large gestures such as having a child together or buying a property are probably bigger commitments than signing a symbolic piece of paper. Again in the past when marriages were more about securing alliances or people controlling each other marriage was more important but now legal contracts should have little to do with love. Of course I am assuming modern western standards are the most enlightened in allowing freedom and that freedom is an important thing to have over social stability which could be enforced by forced marriage / social pressure and legal penalties for adultery that exist in other cultures. | Marriage provides legal protections if one partner plans to take time away from a career to raise children.
Marriage is legally recognized and can gain access to things like spousal visas for non citizens.
When you make an irreversible decision, your brain feels better about it than a reversible one because it will retroactively find reasons to justify your decision as correct. By going for an irreversible relationship, your brain will feel better about it and create more justifications. | 45 | 41 |
When an airlock is breached in outer space, what happens to the air that gets sucked into the vacuum? | Let's say that a spaceship has a compromised airlock. The air is sucked out through the breach, and everyone onboard dies. What happens to the air that gets sucked out of the spaceship and into the vacuum? Does it disperse like dust? Does it stay in one place? Does it drift in one direction forever? | Suction is a macroscopic effect. Particles in an area are constantly moving in all directions, and this motion averages out under static conditions. When containment in space is lost, there is an unbalancing of particle motion at the barrier between the pressurized area and the unpressurized space. More particles are moving outward into space, and no particles are moving into the ship from space.
On that level, it is easy to see what happens to the air particles - they continue on the trajectory they had when they left the ship. Remember Newton's law: a particle in motion stays in motion until acted on by a force. Once the particle leaves the ship, it continues on its trajectory until affected by another force. | 32 | 39 |
ELI5: Why was Cesium-133 atom chosen for defining "1 second" under Standard International? | I remember years ago in high school my physics teacher explained to us that Standard International defines 1 second as "the time needed for Cesium-133 to vibrate 9.192.631.770 times". Is there any particular reason why Cesium-133 was the element chosen for this purpose?
Edit: wow, my first silver award! Thank you! | Accuracy & consistency are the most important things for SI determination. Caesium has a very, very high resonant frequency.
A quartz clock is accurate to something like 1 second in a couple of years.
A caesium atomic clock is accurate to something like 1 second in a million years. | 227 | 221 |
ELI5: Photography terms - Aperture, Exposure, etc | I'm a photography beginner and I just can't process (terrible pun) the terminology. Whenever I think I have a grasp of the terms, I go and play with the various settings and end up taking terrible pictures.
So, photography related terms like Aperture, Exposure and so on, explain them like I'm five.
Thanks | Photography is essentially pretty simple - you have a black box with some film inside that reacts to light. When you push the button, something called a 'shutter', which is basically a door, opens up and lets light in. There are a few settings you can change, but it's all controlling how much light gets into that box.
Shutter speed is how long that door stays open for. The longer the door stays open, the more light gets into the box.
Aperture is how big the door is. When you have a bigger door, it will let more light in.
And different film reacts differently to light shining on it. Some film is very sensitive to light and some is not. This is called the ISO value.
All three of these exist in a relationship to make your picture. When you're letting light in, if the door stays the same size then and you open it for only half as long, half the amount of light will get in, right?
But if you make the door twice as big, but only open it for half as long, it's the same amount of light!
If you make the film twice as sensitive to light, to make the same picture you'd have to open the door for half as long or make the door half the size.
There are reasons to make each choice - smaller doors make more of the picture stay in focus, faster opening and closing mean you can take pictures of things that are moving fast, and less sensitive film makes less grainy pictures.
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Why can't your immune get rid of bacterial STDs like syphilis etc? | It varies depending on the pathogen. When it comes to syphilis in particular, the outer cell membrane has unusually few of its own antigens (proteins) in it, which makes it harder for the immune system to detect it. It can also vary its antigens by gene conversion.
That said, the immune system can combat syphilis. It's just usually not enough to clear the infection. When the bacteria lyse (split open), their internal components are easily recognized by the immune system - their camouflage is only skin-deep. This can actually be a problem when treating syphilis, as a bunch of bacteria dying at the same time can make the immune system overreact to the suddenly abundant foreign antigens etc.
STDs aren't necessarily anything special in terms of ability to evade the immune system. Lots of pathogens have found ways to do that. Mycobacterium tuberculosis, for example, has a coating that allows it to survive inside the phagolysosome of macrophages; the substances the macrophage pumps into the phagolysosome would kill almost any other bacterium. | 20 | 26 |
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Why didn't the Vikings unleash apocalyptic plagues in the new world centuries before Columbus? | So it's pretty generally accepted that the arrival of Columbus and subsequent European expeditions at the Caribbean fringes of North America in the late 15th and early 16th centuries brought smallpox and other diseases for which the natives of the new world were woefully unprepared. From that touchpoint, a shock wave of epidemics spread throughout the continent, devastating native populations, with the European settlers moving in behind it and taking over the land.
It's also becoming more widely accepted that the Norse made contact with the fringes of North America starting around the 10th century and continuing for quite some time, including at least short-term settlements if not permanent ones. They clearly had contact with the natives as well.
So why the Spaniards' germs and not the Norse ones? | To understand this you need to understand the nature of epidemic diseases and the Viking voyages of exploration (as opposed to the later ones of Columbus).
Epidemic diseases in general do not persist well in small isolated populations. They tend to spread rapidly, making everyone immune or dead.
The Vikings did not sail directly from Norway to North America. Their ships probably weren't up to the task of making the crossing all at once, at least not reliably. Instead, they colonized Iceland, and a small group colonized Greenland, and a subgroup of that group went to North America. The population living on Iceland was fairly small, and the number living on Greenland was very small. As a result, it would have been quite difficult for a disease to make it all the way across. Some ship would have had to carry the disease to Iceland, where it would have had to persist in the population long enough for someone infected to get around to sailing to Greenland (and not die on the way), where it would have had to persist in that population long enough for someone to sail over to North America, where some unlucky native would have had to catch it and spread it from his tribe off of Newfoundland and out into the rest of the continent. That's a lot of low probability events, especially since ships did not pass all that frequently to Greenland or even at times Iceland. Contrast this with Columbus et. al. leaving from populated, disease-ridden cities in Europe and sailing right over to the Americas. All you need in that case is a sick sailor to make the passing. | 290 | 353 |
Why does a higher level of overall education in a society correspond with a lesser incidence of social problems? | It has been shown to generally correspond, but why?
Is it that educated people make better decisions about whatever social problem we happen to be talking about (safe sex, domestic abuse, etc.)? Do they make better decisions because they have better information on that subject **in particular**?
Or is that higher education levels makes those sorts of behaviors less attractive because of the opportunities available to them?
In other words, is it the specific education about the social problem or is it a side effect of higher levels of education?
| There is also a discipline that is learned through course work that teaches people to analyze situations before taking action. The further education takes someone, the more important proper analytical thinking becomes. This does not mean that a person who is less educated is more prone to illegal or immoral action, or a person that is more educated is less prone to illegal or immoral action; rather a further educated person is more apt to think out the action, and the consequences of the action, before deciding to follow through with the action. This does not seem to equate with crimes of passion. | 13 | 24 |
ELI5: How can children learn two or more languages without mixing them while growing up? | Simply: I have a little sister, she's 3 years old. Since I'm always watching some american/british series and tv shows (like Steven Universe), she's growing up watching those with me (we are brazilians, so she's growing listening and speaking mostly portuguese ~~and nonsense~~)
I couldn't help but notice that recently, she's noticing the differences between portuguese and english, for example, I'm watching something, then she comes and says:
"Ela disse 'ball' haha" (she said 'ball' haha)
or then
"Blue, why are you watching english?"
Sometimes I even ask things like: "Do you wanna listen to 'Let it Go' in english, or portuguese?" and she freaking understands the difference between both, and reply either "english" or "portuguese".
**How so?** | Young children are still at an age where they are learning language and the constructs of it. This makes it easier for them to acquire new language, because they can learn the ins and outs of both languages at fairly quickly. They're not "cemented" into one language yet. Their brains have a plasticity to them that make it easier to form new connections in contrast with an adult brain that isn't as moldable.
I teach 3 year olds, have several bilingual students, and one trilingual student. She has been slower on the uptake of language at all, because she gets the languages confused, but even in the last 3 months of school she's become more fluent in both English and Spanish (both of which are spoken at school). It's really amazing to see what a three year old's brain is capable of. | 15 | 19 |
What are the long term consequences of forcing our rivers to stay on the same path? | The effects vary wildly depending on the location and river and it is a very complicated topic, but here are some basic impacts.
Ecological impacts are almost always involved. Often man-made barriers that prevent river convulsion or migration are much different than the natural river banks, and so it can easily completely disrupt the local riparian ecosystems (which can then impact other nearby ecosystems). There are low-impact ways to keep rivers on the same path, but they tend to require a lot more money, planning, and maintenance, so they are not always used.
Redistribution of sedimentation is another major impact. Rivers will usually be forced to stay on a single path in places where they are depositional, rather than erosional (since erosional portions of rivers are usually highly channelized naturally). In most cases, rivers naturally build up sediment in one location until the channel becomes unstable, at which point they will convulse to a different location on the flood plain and start building up sediment there, and so on. Forcing a river to one location will force the sedimentation to only occur in one place. This can be problematic for a whole slew of reasons, but one famous example is with New Orleans. Naturally, the sediment from the Mississippi would offset the subsidence of the area. But since the river has been constrained, the sediment is all transported offshore. Because the city was built on this subsiding land it is now below sea level and at a huge risk from flooding. Which is why it is the home of the most expensive natural disaster in the United State's history.
Also, forcing a river to follow a single path usually means you make the river "straighter". Such as taking a meandering river, straightening it out, then using the extra land that creates for development. But this effectively increases the gradient of the river, which can have major impacts on upstream and downstream sedimentation and erosion, which can be problematic and expensive. The process of channelizing a river can also change how it transports and processes pollutants.
Of course, forcing a river to a single permanent channel can also do a lot of good for nearby human communities, and in some cases can help with ecological conservation efforts. So it's complicated. | 12 | 33 |
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ELI5: Especially in the winter when there's snow on the ground, why does everything have a blue hue to it just before sunrise and sunset? | Light diffuses (understand deviated) when propagating in the air. How much it diffuses depends on the wavelength (its color).
The sun emits a wide array or wavelength, and its "blue rays" are among the most disrupted by air. That is why the sky by day is blue. They are so much deviated that they look like coming from where the sun is not, giving the sky its opaque blue look. (Imagine air particles acting like tiny mirrors in random directions, reflecting only blue light)
Now imagine the sun being slightly beyond horizon. Rays that makes the light look "white" are for the most part not reaching you. Except blue ones.
As they are redirected by diffraction, they reach places the other ones do not have a direct path yet/anymore. That is why before dawn/after dusk everything is blue-ish. (Snow only makes it more noticeable because it's white.) | 1,211 | 8,326 |
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