How far away is the light that would reveal the Big Bang?

Question: I guess theoretically if we could go faster than light, which we clearly cannot, at some point we'd be able to see the big bang itself. Just curious - how far away is that light?
Comment: Theoretically, if we instantaneously go far, far away in any direction, we'd see pretty much the same kind of things as we do around here. Because the theoretical models typically assume large-scale isotropy and homogeneity.
Comment: @StanLiou: Surely the closer you get to the edge of the universe the more _vastly and unimaginably different_ the sights? Isotropy and homogeneity don't have all that much to do with it — the Universe was a remarkably different place in its very initial moments.
Comment: @LightnessRacesinOrbit my statement was in regards to instantaneous FTL travel, so no going backward in cosmological time. If you more than ~47 Gly from Earth instantaneously, you won't see the Big Bang. And if homogeneity and isotropy are correct on above this scale (and they might not be!), you will see the large-scale structure pretty much same as from Earth.
Comment: @Stan I don't understand. Seems like the moment something happened, light was dispatched and unless particles traveled faster than the speed of light to obstruct that light, if I were to appear in front of that light, for a single tiny moment, I'd see that little white dot that would've appeared the moment the big bang began (and then see everything that happened afterward). Why not? Light point A -> same light at point B [observer]. Where's the complication?
Comment: @Stan: What? No...
Comment: Seeing the light from the big bang is a bit like seeing the light of the glowing earth's core.   It's hot enough to glow, so, why can't we see it?

We can't see it because the moments after the big bang weren't clear.  The entire universe was opaque like pea soup, only much hotter.    It was only after the free electrons bound the the available atomic Nuclei that the universe became clear enough for light to travel through.
Answer: The particle horizon is the point where light arriving at us now would've had to have been emitted at the big bang (though note this is hypothetical as the Universe did not become transparent to light until it was several 100,000 years old).. How far away it is depend on the model you use (not to mention there are several different distance measures in cosmology), but it's proper distance is reckoned to be about 46.9 billion light years.
A note of caution though, when calculating the particle horizon cosmic inflation is usually ignored. What is light arriving (again hypothetically) from usually called the particle horizon therefore would be actually light that was emitted from just the end of the inflationary epoch. If you were to take a model with a big bang singularity and inflation the "true particle horizon" would in fact be much further away.
Answer:
I guess theoretically if we could go faster than light, which we clearly cannot, at some point we'd be able to see the big bang itself.

If we travel instantaneously across the universe (as measured by cosmological time), then no, theoretically that's not the case. Our theoretical assumptions involve large-scale homogeneity and isotropy, meaning that the view different observers is basically the same regardless of where they are, at least at the same cosmological epoch. This is called the cosmological principle.
Mind, because of the way relativity works, an FTL drive might also be capable of taking you back in time, so perhaps you could theoretically see the Big Bang after all. But that's obviously more to do with time travel than going to distant places.

Seems like the moment something happened, light was dispatched and unless particles traveled faster than the speed of light to obstruct that light, if I were to appear in front of that light, for a single tiny moment, I'd see that little white dot that would've appeared the moment the big bang began (and then see everything that happened afterward). Why not? Light point A -> same light at point B [observer]. Where's the complication?

You seem to have an implicit assumption about where the Big Bang occurred. It actually occurred everywhere. Including here. See this question.
Imagine looking out to the most distant galaxy that you can barely see. Because of the finite speed of light, you are looking at it not as it is, but as it was in the distant past. You are just now catching light from that distant place.
If you were instantly transported to that place, and look back to where the Milky Way should be, you won't see it, but rather as this area of space was in the distant past.  You'll be just catching light from somewhere the Milky Way area.
In other words, you will see light from the distant past no matter where you go. Because the Big Bang happened everywhere, light from it (well, actually from recombination epoch later, because the universe wasn't transparent before then) is present everywhere. And hence it'll look about the same no matter where you go, again assuming isotropy and homogeneity.
Answer: Seeing (or not) the "light from the big bang" has little to do with how fast we can travel.
The cosmic microwave background is here and now; you can pick it up as short wave radio interference. This light was emitted when the universe had cooled to about 3000 degrees, some 400,000 years after the big bang.
The problem is that before that time the Universe was opaque to radiation. That is, light that was emitted was quickly reabsorbed or scattered before it could travel very far. If that were not the case then we would be able to see light from an even earlier epoch. It would be red shifted because of the expansion of the universe by factors of well over a thousand.
In fact there is (or is predicted to be) "radiation" all around us from the first second after the big bang, in the form of low energy neutrinos. Neutrinos interact extremely weakly, so the universe became transparent to them at much higher densities than it did for light. These particles have been travelling the universe since, in all directions, gradually losing energy to the expanding space. Efforts are underway to detect these neutrinos, which would be a superb vindication of the big bang model.
Answer: There is no "far enough away" to see the big bang.
The bang was the creation of space and time, so every view within the universe is a view from inside the bang. To see it from outside, you'd have to view the bang from whatever space the universe is embedded in; assuming it is embedded in a higher space, and that space has something like a time-axis.
The 3.7°K microwave background photons hitting us right here, right now is the best view of the consequences of the bang that we'll ever get; barring exotic SF scenarios of course.
Comment: Forgive me if my observations are due to the lack education in Astronomy, but I see two problems with this: 1) Space, true space, is literally "nothing", therefore the Big Bang could not possibly have created space. It simply filled it. 2) "time" is only a measurement of changes / events in space. So sure - the first time any "thing" in the universe moved, we had time. But unless light didn't exist in the moment the big bang began, I see no reason that light would not have been emitted into the empty space surrounding the big bang. I see no reason that same light wouldnt still exist now
Comment: @CuriousWebDeveloper your point (1) is very mistaken, but probably deserves its own question. I'm uncertain as to whether something like it was asked before on this site, but it's an interesting issue regardless.
Answer: the light from the big bang is in your living room... because that is where the big bang took place... did you know you were so special? Just kidding, but maybe I misunderstood your question. I think what you are asking is, well if you look into deep space you are looking back in time since it takes light X amount of years to travel to the observer. So look far enough back and you would see the big bang right? We already thought of it, and the problem is you can't see the moment of the big bang, because there were no such thing as photon's at that moment. It took about 400,000 years (an afternoon nap on the scale of the universe) for the intensity of the moment of creation to simmer down enough atoms could form removing the opacity of the universe freeing photons to begin their cosmic journeys.. If you were to look out that far you would just see a big opaque blob like trying to look into the center of the sun.  The light from that moment still exists and you do see it... you just don't SEE it. The spectrum of the sun's light that has the highest intensity is in the visible light wavelength.  One would imagine that all species of the universe see in the same wavelength and thus we would all agree on what visible light is. This is not true. We see in the visible wavelengths because of evolution.  Our eyes adapted to the highest intensity light available. Think about natural selection. Ancient primates who could see better would be better hunters. So those who were utilizing the highest intensity light the best would be ideal mating candidates giving birth to more off spring with eyes like there own (a little theory of mine). If you grew up on a planet with a sun that gave off a lot of infrared light you would see in infrared.  Anyway, what I am getting at is if we somehow managed to evolve to this point on a rock with no companion star (an impossibility for all intents and purposes) in some dark corner of the universe where there was no other really intense light around, theoretically eyes would have evolved to see in the cosmic microwave background because it would be the only light available.  CMB radiation (the afterglow of the big bang) is ubiquitous. It is everywhere at once. It gets cooler as time goes on as space time stretches, stretching the wave length of the light making it harder and harder to detect. I hope that answered your question.
Comment: Photons were created when the first hydrogen atoms converted into helium however the universe was thick opaque plasma mess and was too blurry to see back that far. Once things expanded and cooled off the first stable atoms formed and the photons were free to fly about hope that answers your question
Comment: Quick question: you weren't quite clear - did the photons not exist yet or could they just not escape the stuff of the big bang yet. And if they did exist, what about the ones on the very edge that would've escaped? Light would've traveled a bit faster than the other stuff right? Others have said space doesn't exist past the edge of the big bang, so I guess the photons on the edge would have nowhere to go?
Comment: Wrong. No photons from that time survive today. The oldest "light" we see now is the microwave background radiation, and that's quite a bit older.


Where to connect c wire at furnace for Honeywell Wi-FI thermostat

Question: We are installing a new honeywell wifi thermostat have an extra blue wire in our bundle.  We aren't sure where to connect the blue wire on the furnace board.

Click for larger view
Answer: First off, the green wire should connect to the G terminal on the thermostat. It's connected to the G terminal in the furnace, and so should also go to the G terminal on the thermostat.
At the thermostat, the extra blue wire should connect to the C terminal.  Depending on the furnace (read the documentation, and analyze the schematic to be sure), you should be able to connect the other end of the blue wire to either of the C terminals in the furnace.


Differential cross section in momentum space?

Question: Suppose I have a spherically symmetric potential and I can find its cross section in configuration space (i.e position-space), $d\sigma / d\theta$. Now I need to find its distribution $d^2\sigma / p_rdp_rdp_\theta$ in momentum space. How can I do this?
Answer: By definition, the cross-section of a potential $d \sigma$ is equal to $d N/n$, where $dN$ is the number of particles, which are deflected in some specified direction and $n$ is the particle (2d)density in the beam before deflection. By definition, particles in the beam all have some initial momentum $p_0$.
As in any potential field the energy is conserved, the momenta of all the particles remain the same as before scattering, so $\sigma \sim \delta(p_r-p_0)$. When it comes to $p_\theta$, the distribution is actually exactly described by $\sigma(\theta)$. That is, the particles with a given $\theta$ are exactly the particles, described by $p_\theta$, and hence $\dfrac{d \sigma}{d p_\theta}=\dfrac{d\sigma}{d\theta}$.
Accounting for both dependencies one may write $\dfrac{d \sigma}{d p_\theta}=\dfrac{d\sigma}{d\theta}\delta(p_r-p_0)$.


Can I naturally carbonate a sweet hard lemonade?

Question: I'm thinking of brewing some hard lemonade, and from what I've read, I'll need to neutralize the yeast with sulfites if I want to prevent it from getting too dry. Will I need to force carbonate after that? Is there a way to make a sweet, carbonated, hard lemonade using natural carbonation / bottle conditioning?
Answer: The answer is similar to the one in this post, but the short answer is that your safest bet is force-carbonating.
The problem with bottle conditioning is that you've already killed most of your yeast, and even if you were to successfully repitch, there's really no good way to "turn off" fermentation when you reach your target carbonation.
There are also some potential issues with trying to stop fermentation halfway through - it would be best to ferment it fully to the alcoholic strength you want, let the yeast settle, rack, then add a stabilizer, and add sugar for sweetness at that point.
This way, the yeast will be able to clean up off-flavors at the end of the fermentation cycle, and you mitigate risks of the campden/sulfites not fully neutralizing the entire yeast population.
Comment: Also, Chris has a great explanation of stabilizers here: http://homebrew.stackexchange.com/questions/2752/campden-tablets-to-control-final-sugar-content/2756#2756
Answer: Once you sulfite the lemonade to neutralize the yeast you cannot bottle condition.  The sulfite will prevent any further fermentation which is necessary for bottle conditioning.  The only option is to force carbonate.
Although you could bottle still and add charged water to add fizz or bottle condition the dry lemonade and then sweeten at the time of drinking.
Answer: If you want natural carbonation your best bet is to find a yeast will naturally low attenuation.
For example White Labs WLP720 is a wine/mead yeast to make sweet wines and mead as the attenuation is less than 75%.
I don't know how well it will go with your lemonade. You could also try looking for sweet cider yeasts I think Wyeast may do something like that.


Why do we find a large number of nude male characters in ancient Greek paintings and sculptures?

Question: Why do we find a large number of nude male characters in ancient Greek paintings and sculptures? What was the social status of nudity in ancient Greece?
Answer: I have dealt with this question in my article, "Nudity as a Costume in Classical Art," in American Journal of Archaeology 1989, which can be accessed either through JSTOR or through Academia.com, under my name. I am also editing a multi-author book, Nudity as a Costume in the Ancient Mediterranean, where I take up the subject of Greek nudity again.
The answer to your question is that the naked kouros, and the Greek athlete, were citizens. Nudity was confined to the exercise ground, where the young men prepared for war. Only citizens served in the army, so basically male nudity was a sign of citizenship. Slaves were also shown nude, but they were shown as ugly as misshapen, not the image of the kalos kagathos, "beautiful and noble" young citizens of Athens.
Comment: Great answer! Welcome to the site. I hope to see more from you in the future.
Comment: What's a *kouros*?  Not everyone here is familiar with Greek.
Comment: Interesting theory. I'm sure you're well-qualified to speak, and your argument is cogent. Perhaps there is also a factor of artistic natural body that Ancient Greek culture celebrated in the human body amongst other things, and which in modern Western society has been suppressed through contemporary attitudes (prudishness, even)?
Comment: @Joe http://en.wikipedia.org/wiki/Kouros
Answer: The Metropolitan Museum of Art in New York has a great page on this exact topic. The key ideas why there is so much male nudity are two-fold:

the Greek reverence for athletic competitions,
and the athletic male as the pinnacle of those athletic competitions.

Because the Greeks felt that sport was such an important part of what was good about humanity, and male competitors embodied that idea, they sought to capture it in their art work. Later on when the Renaissance masters came along they emulated those themes.
As far as the social status of nudity in Ancient Greece the reality is a little unclear. People were likely not nude in public all the time, but they may have been some of the time as this article pointed out.
So, in summary, male nudity in art was revered, and actual nudity in public was probably limited.
Comment: Its a subject matter that seems quite likely to get a web page blocked by over-agressive web filters too.
Comment: Nope! That is not a 404. You may have been the victim of regional copyright protection system.
Comment: Unfortunately the article linked from your second link, is a 404.
Answer: There is yet another reason why the male nude was common in Greece.
The Greeks were obsessed with perfect proportions in all of their art, for they saw these proportions as a sign of the divine cosmos.  Perhaps the most notable of these monuments is the Parthenon and its Golden Mean ratios, a temple dedicated to Athena which, very clearly links perfect proportions to the divine.  This ideology permeated everything in Greek culture and philosophy. Think, for example, of Pythagoras and his discovery of musical intervals and their perfect proportions, or the so called Platonic solids.
The human body inherently is a study in the Golden Mean.  All of the limbs of the body adhere to some form of Golden Mean ratio and the Greeks knew this.  Greek statues were there to celebrate the divine by exploring the perfection of the human body.  Note that almost no Greek Statue (and being careful here, since many Greek statues we know are actually Roman copies of Greek originals) shows a body that is not perfect.  Also note that any garment that covers the body will be human made and thus not part of the divine.  To see divine creation you must draw the nude.
Now combine this with the subject matter of Greek statues which, are typically mythical heroes or heroines and gods and goddesses.  Such perfect statues were the only way that the perfection of heroes, heroines, gods, and goddesses could be worshipped.  By the word worship here I mean a celebration that includes being awed and inspired.
So basically the nude literally shows "naked perfection," and no other creation was seen as more perfect as the body of the idealized male.


Dock disappearing when using the Show Recents menu item?

Question: I just discovered that if I Turn Hiding On and right click on the iTunes app in my dock and press Show Recents, then my dock will no longer appear when I move my mouse to the bottom of the screen until I log out and back in. I have the latest version of Lion and I was wondering if this was only me.
Comment: I don't have the "Show Recents" option... what does it do?
Comment: @jtbandes: IDK. If press it, I get a launchpad-type effect but the screen is a bit darker with nothing on it.
Comment: Show Recents is an option you can use to show recently opened documents in a closed application.
Comment: @jmlumpkin Ah, yes, it only works with closed applications. It's equivalent to "Show All Windows" for open applications.
Answer: This may be only you, which could be an issue with the preference files, etc.
Show recents (with a Dock that hides) for me shows the transparent dark screen, and whatever icons that should be there for that app, and shows the dock fully available.
Once clicking on the desktop though, to get out of this mode, my dock hides again as it should.
I would recommend removing the Dock preferences, which is located at ~/Library/Preferences/com.apple.dock.plist, and then restarting the dock.
You should open the Terminal (/Applications/Utilities/Terminal.app), and then run:
rm ~/Library/Preferences/com.apple.dock.plist

then run
killall Dock

to restart the dock. You may have to set up your dock icons again, but this may help the dock not showing back up after using 'Show Recents'
Answer: To explain show recents:
https://discussions.apple.com/thread/3258198?start=0&tstart=0
Basically, if the app is closed you can right click on it in the Dock and have it show recently opened documents.
As for it killing the Dock, no, my Dock is in hiding mode, and I can show recents on iTunes and it still reappears afterwards.


Will force-carbonated beer remain carbonated if poured into a bottle and capped?

Question: If I pour kegged beer into bottles and immediately cap them to take with me for the evening, will it remain well-carbonated?
Comment: If this is something you think you're going to do often you can look into investing in something like Blichmann's beer gun. http://www.blichmannengineering.com/beergun/beergun.html. It fills up the bottle with CO2 before filling with beer to minimize carbonation loss.
Comment: Yeah, cheers.  I asked this question before learning anything about counter-pressure filling.  The beer gun is a great device, or so I've read (and heard on BrewStrong).
Answer: I recommend over carbing a little in the keg to help make up for losses.
Chill your bottles down to help minimize the loss.
And don't pour!!! You can retrofit a bottle filler onto the end of some beer line and fill like that from a bev out connector.
You can also jam a peice of tubing like on a standard racking cane (3/8ths??) into a cobra tap.  Make it as long as the bottles you want to fill and fill from the bottom up. This really minimizes carb loss and oxidation. Burp the keg and use only enough pressure to get the beer flowing (5-6psi).
Answer: I often do this with swing-top bottles.  The carbonation suffers a little, but is fine for a day trip or evening out.
Put the bottles in the freezer an hour or so before filling.  Warmer liquid does not hold as much CO2 and this prevents your beer from warming up upon touching the bottle.  Fill all the way up and cap on foam.  Pour and immediately cap, don't fill a few in a row before capping.
Read the answers to this question, too.
Answer: Using a growler to take to parties is often the easiest option. Easy to fill, you probably already have a few around and will stay carbonated for a couple of days when filled from your regular tap. Bottling and capping is something I reserve exclusively for gift giving and competition entry and those recipes usually benefit from bottle conditioning anyway.
Answer: Yes!  With a father that wants to try each of my beers, I often fill growlers directly from the keg after the beer carbonates (its just easy).  As long as you "cap" it immediately and chill it, the carbonation will hold.  I actually got a picture message last night of a stout I gave him 6 months ago in a growler that still had good carbonation.  If you are planning on drinking the bottles that night....you'll be good to go.  Hope this helps


Using Multiple Keyfiles in Truecrypt

Question: Suppose if I have a truecrypt container who's main password is 20+ characters long and say, I use three random pictures as a keyfiles. It seems this way I could even use five keyfiles at random but what's the advantage of using them?
Isn't it just using one key file would be sufficient for improving security of password?
Answer: To know the strength of your password, don't look at its length, but at its potential. A password is as good as it is random, i.e. as good as the number of other values it could have assumed.
A simple case is when the password was generated as a sequence of random letters, each letter chosen uniformly and independently of the other letters. Since there are 26 letters, a 20-letter password implies 2620 = 19928148895209409152340197376 combinations. An attacker trying to guess the password will need, on average, to try half of them before hitting the right one. The accumulated cost would be tremendous, so the attacker would have very little chance of breaking through it. This number of possible, equiprobable combinations is often called entropy (not exactly the same notion as in physics, but close enough) and traditionally expressed in bits: you have an entropy of n bits if the number of equiprobable combinations is close to 2n. With 20 random letters, this means about 94 bits of entropy.
Moreover, TrueCrypt uses a good password hashing function, namely PBKDF2 with a random salt and 1000 (or 2000) iterations. Password hashing is a subtle matter, and TrueCrypt does it correctly.
To make the story short, if your password entropy is anywhere beyond 70 bits, your security is fine -- meaning that the cost of brute-forcing the password would far exceed the cost of simply obtaining the data through other means, such as abducting you and your family, or simply buying you out. We are talking about several (many) billions of dollars here... So, with random letters (all lowercase, let's make it simple to remember), 15 letters are enough. If you add uppercase letters and digits in the mix, 12 letters suffice, but the password may be harder to remember, and harder to type, especially on tablets/smartphones.
A crucial point of password generation is the need for good, impartial randomness. If you chose the password in your head, then it is not random. Witticism is not randomness; quite the opposite indeed. It is hard to estimate how much random can be a human-generated password, but it is often observed that such passwords are assumed by their owners to be a lot more random than is actually the case.
In the example above, I used letters but the calculation easily expands to any set of "symbols", even words. See this answer for details on a famous example.

The key files serve two purposes:

To provide some extra entropy to a weak password.
To provide some extra entropy which does not come in through the same path as the password.

Indeed, a poor password can be brute-forced if it does not have enough entropy, but even good passwords can be preyed upon through various methods: keyloggers, well-placed security cameras, sleep-talkers... Some of these methods will grab the password but not the key file, so the key file may save your skin in some situations.
The key file adds some security only insofar as the attacker does not know the file contents. However, it is a file. It is written on physical media. It is made available to the machine itself upon disk unlocking. We must assume that someone who steals the machine will also have a copy of all the files which could serve as key files (it depends on where you store them, but they are probably close to the machine since you need them to boot it). So the secrecy of the key file is not about the file contents, but about which file is used. For instance, if you have 100 possible files, then entropy is multiplied by 100 (in "bits" notation, this means about 6.6 extra bits). On the other hand, you have to remember which file was used, so that's some extra effort beyond the one needed for the password itself.
Personal opinions:
I note that key file processing in TrueCrypt is singularly homemade and weird; my cryptographer's senses are quite alarmed at this assembly of CRC-32 and haphazard scrambling. It would have been much simpler and better to simply hash each file, then hash the concatenation of the hashes and the password itself.
Also, the scenarios where key files have any value are rather restricted: these are scenarios where the attacker could grab the password, but not the key file, or not the information about which key file was used. For instance, a camera which has a view on the keyboard may also see your screen and easily obtain that information.
Therefore, I deem key files "not worth it" and I find that using the brain memory capacity to remember the key file to use is better employed at remembering a stronger (more random) password.
Comment: @SalvadorDali Entropy bits per character is log2(n) where n is the size of the character pool, so for 26 (a-z) that's 4.7 bits per character. 4.7 bits per character * 20 characters = 94 bits of entropy.
Comment: Thanks for explanation. But can you please tell how you derive that: "20 random letters, this means about 94 bits of enthropy"
Comment: I know this post is a bit old, but according to the recent audit (http://istruecryptauditedyet.com/), the fact that they use PBKDF2 instead of scrypt and the fact that the number of iterations is hard-coded means that this version of TrueCrypt won't be able to keep up with GPU speeds.
Answer: TrueCrypt uses up to one megabyte of the keyfile to increase the randomness of the given password. Thus even one file with properly random content would probably be enough to defeat brute force attacks. (Well, up to the 64 bytes of the final internal password length, which is still plenty enough these days.)
Though using true random data inside the keyfile would probably be better, since estimating the true randomness of an image file is sometimes hard to estimate. And TrueCrypt comes with a proper keyfile generator for that.
Of course, all this is assuming your password and keyfiles are never available for the supposed attacker. One use for multiple keyfiles would be to select random six among say, one thousand pictures. Possible combinations would be around 1015, and rough calculations say that even with test speeds up to millions of files per second, it still would take a couple of decades to find out the right combination. The biggest downside is probably decreased usability, since now you also have to take care (and backup!) the set of keyfiles as well as the encrypted file.

Using Multiple Keyfiles in Truecrypt


Why is the observable universe so big?

Question: The observable universe is approximately 13.7 billion years old. But yet it is 80 billion light years across. Isn't this a contradiction?
Comment: Do you have a reference for that 80 billion light year figure?  I've personally never heard that before.
Comment: http://en.wikipedia.org/wiki/Observable_universe has 93 glyr for the _diameter_. Easy to forget whether you're speaking opf radius or diameter in this context. I nearly did, in looking up the number.

Considering how fuzzy these kinds of measurements are, I think 80 glyr is credible for another, perhaps older, estimate. Professionals use redshift as a directly-measurable proxy for distance because it is so difficult to get a reliable translation of redshift to distance.
Comment: Well, yeah... Big Bang and all...
Comment: If I'm not mistaken, this question has been asked - and answered - before: http://physics.stackexchange.com/q/12049/ Someone had linked the OP to: http://physics.stackexchange.com/q/11803/
Comment: Note that your only referring to the observable universe, not the actual universe size. The actual universe size could be much much bigger than 80 billion light years across. The fraction that we can observe is smaller than the actual size.
Comment: You're assuming that it started with a size of zero.
Comment: duplicate of http://physics.stackexchange.com/questions/25076/how-large-is-the-universe
Comment: The universe can (and [does](http://physics.stackexchange.com/q/44386/10851)) expand faster than the speed of light, given the appropriate definitions.
Comment: related: https://physics.stackexchange.com/questions/400457/what-does-general-relativity-say-about-the-relative-velocities-of-objects-that-a/400458#400458
Answer: This question implicitly refers to the visible universe, but we should state that explicitly, as otherwise the question doesn't make any sense.
It may seem like we shouldn't be able to see more than 13.7 billion light-years (13.7 giga-light-years, or glyrs) away, but that reasoning omits the expansion of spacetime according to General Relativity. A photon emitted from somewhere near the beginning of the Universe would have traveled nearly 13.7 glyrs if you had measured each light-year just as the photon crossed it, but since those light-years that you measured have expanded since the photon passed through, that distance now adds up to about 80 glyrs.
Comment: Dear Andrew, which of the two passages below reflect what you mean to convey:   (1) The visible universe is now 80 bly's across, or (2) the visible universe is 80 bly's across.
Comment: The first statement is modified with the inclusion of 'Now', and is equivalent to stating "the visible universe is 13.7 bly's across, but were it possible to measure the distance right now instantaneously (C*[infinity]) the actual displacement is 80 bly's. The second statement is equivalent to "leaving aside the redshift, the information payload of the photon contains two numbers, one representing the displacement at source, and the other representing the payload on arrival.
Comment: But this is not true - the photon carries only one quanta of visual information. Either the physical packet of visual information is consistent with a displacement at emission of 13.7 bly's or it is consistent with a displacement at emission of 50 bly's or whatever it's supposed to be.
Comment: The last sentence is wrong. The radius of the [observable universe](https://en.wikipedia.org/wiki/Observable_universe) is about 45.7 billion light years. A photon emitted as cosmic microwave background radiation (the oldest light we can see) has therefore travelled 45.7b ly to reach us. No light has travelled more than this distance since the universe began.
Comment: So I may better understand, may you provide a citation/source where the latter number is derived? - the distance the primordial photon has traveled accounting for cosmological expansion. This number is oft quoted but I wanna see a derivation
Answer: The radius of the observable universe is about 46 billion light years, which is considerably greater than its age of about 14 billion years. Since the radius of the observable universe is defined by the greatest distance from which light would have had time to reach us since the Big Bang, you might think that it would lie at a distance of only 14 billion light years, since $x=ct$ for motion at a constant velocity $c$. However, a relation like $x=ct$ is only valid in special relativity. When we write down such a relation, we imagine a Cartesian coordinate system $(t,x,y,z)$, which in Newtonian mechanics would be associated with a particular observer's frame of reference. In general relativity, the counterpart of this would be a Minkowski coordinate frame, but such frames only exist locally. It is not possible to make a single frame of reference that encompasses both our galaxy and a cosmologically distant galaxy. General relativity is able to describe cosmology using cosmological models, and this description is successful in matching up with observations to a high level of precision. In particular, no objects are observed whose apparent ages are inconsistent with their distances from us.
One way of describing this difference between special relativity's $x=ct$ and the actual distance-time relationship is that we can think of the space between the galaxies as expanding. In this verbal description, we can imagine that as a ray of light travels from galaxy A to galaxy B, extra space is being created in between A and B, so that by the time the light arrives, the distance is greater than $ct$.
None of this has anything to do with inflation. Inflation makes certain testable predictions about cosmological observations (e.g., it predicts that the universe is spatially flat), but it's irrelevant for understanding why the radius of the observable universe has the size it does in comparison to the age of the universe. Inflation may not even be correct. If inflation turns out never to have happened, it will have no effect on this particular question.
It turns out that we can get a surprisingly good estimate of the size of the observable universe using a simplified FRW cosmological model consisting only of dust, i.e., nonrelativistic matter. The approximation is good because the universe has spent most of its history dominated by matter, with only a very short period early on that was radiation-dominated, and another fairly recent era that is dominated by the cosmological constant. In accord with the current observational data, we make a second approximation, which is that the universe is spatially flat. In a spatially flat FRW model, the $r-t$ part of the metric is of the form $ds^2=dt^2-a^2dr^2$, where the scale function $a$ depends on time. For a photon, $ds=0$, and we can then show that the proper distance traversed by a photon since shortly after the Big Bang is given by $L=a \int dt/a$. For a matter-dominated solution, $a$ is proportional to $t^{2/3}$, and we find $L=3t$. This is quite close to the $L/t$ ratio of about 3.3 given by the most realistic models. It also makes sense that the result is somewhat greater than 3, because the universe has now entered an era in which its expansion is accelerating. In the future, $L/t$ will become greater and greater.
Comment: Ben, the sticking point (just personally for me) is referring to an observable universe. Observable means the physical packet of visual information in a quanta of incoming light contains two displacement values, one being the displacement at emission and the other being the displacement at absorption inclusive of the expansion of space during transit. Leaving the cosmological redishift to one side, that is clearly not the case.
Comment: What that means is that the physically observable universe is 13.7 bly's but that a real size of 80 bly's is inferable from theory. That is not the same as a direct measurement. The observable universe is therefore 13.7 blys
Comment: Ben, can you expand on your math above?
How do we get from 13.7 to 80?
Diameter = 13.7 radius * 2 = 27.4
27.4 * 3.3 = 90.42
90.42 is quite a lot more than 80.
This is in line with the wikipedia estimate of 90.68 here https://en.wikipedia.org/wiki/Universe#Size.2C_age.2C_contents.2C_structure.2C_and_laws
Answer: The universe is commonly defined as the totality of everything that exists, including all physical matter and energy, the planets, stars, galaxies, and the contents of intergalactic space.
No one knows if the universe is infinitely large, or even if ours is the only universe there is.
Although our view of the universe is limited, our imaginations are not. Astronomers have indirect evidence that the universe of galaxies extends far beyond the region we can see. But no one knows if the whole universe is infinitely large - large beyond limit.
According to the leading theories, other parts of the universe may look very different from our own - and may even have different laws of nature. We may never be able to find out for sure. But it is possible that clues to the answer lie in plain view, just waiting to be discovered!
I should note also the "80 billion light years across" it doesn't count as a contradiction. I don't know what your reference is but I believe that this concerns the region that we can see yet of this Universe.
Answer: You can travel as close to the speed of light as you want, but (assuming you're made from matter) you can't travel at the speed of light or faster.
So there's no reason why galaxies can't be receding from each other at 99.9999% the speed of light.  However, this isn't the whole story, as the expansion of spacetime can do funny things.  The universe isn't actually expanding as you'd expect from everyday life, as a explosion would, and there wasn't a "single point" that you can point to and say "that's where the big bang happened", it happened where you're sitting, and on the dark side of the moon, and just around the corner from Alpha Centauri...everywhere in fact.
Picture a graph - the point on the graph aren't moving away from each other (ie point A goes from (1,1) to (2,2) and point B goes from (5,5 to 7,7)) - instead, the whole graph, piece of paper and all, is being stretched.
This stretching is allowed to happen faster than the speed of light, as no matter actually has to change coordinates for it to happen.
In relation to the title of your question, the best answer is to ask "compared to what?".
Answer: Briefly...
Consider a photon emitted 13.8 Gly ago (Gly = billion light years). As it travels through space, not only its getting farther away from its source due to traveling at the speed of light $c$, but photons distance also increases as the universe grows.

Technically...
To get technical, the expansion of the universe is captured by the scale factor $a(t)$ which is governed by the Friedmann's equation:
$$\frac{(a'(t)/a(t))^2}{H_ 0^2}=\frac{\Omega _{\text{R0}}}{a(t)^4}+\frac{\Omega _{\text{M0}}}{a(t)^3}+\frac{\Omega _{\text{$\kappa $0}}}{a(t)^2}+\Omega _{\text{$\Lambda
$0}}$$
where
the Hubble constant $H_0 = 67.8 \frac{\text{km}/\text{s}}{\text{Mpc}} = 0.0693 /\text{Gyr}$,
the present value of the radiation density $\Omega _{\text{R0}} = 0.0000905$,
the present value of the matter density
$\Omega _{\text{M0}} = 0.308$ (which mainly consist of dark matter) ,
the present value of the curvature density $\Omega _{\text{$\kappa $0}} = 1 - (\Omega _{\text{R0}} + \Omega _{\text{M0}} + \Omega _{\text{$\Lambda
$0}}) = 1$,
and the present value of the cosmological constant $\Omega _{\text{$\Lambda $0}} = 0.692$. These values are from the Plank Collaboration 2015. This equation can only be solve numerically. The following figure shows scale factor as a function of time:

In cosmology, the amount of distance a photon can travel in a given time is known as the comoving distance or the comoving horizon denoted by $\eta$:
$$\eta = \int_{0}^{t}\frac{c dt}{a(t)}$$
which again has to be evaluated numerically. By numerically integrating from 13.799 Gyr ago until the present time, a particle horizon of 43.5 Glyr is obtained which is the radios of the observable universe. One should take this value with a grain of salt since it is highly sensitive to $H_0$.

Biologically...
I would like to focus on "Why the observable universe is so big?" from different perspective. Alternatively we can ask why the observable universe is 13.8 Gyr old! This is not such an odd question to ask if we state it as the following: "Why are we, as observers, happen to look at the universe 13.8 Gyr after the big bang?" Given that intelligent life on earth took ~3.5 Gyr to rise and the conditions of the universe were too harsh to permit evolution of life during the first ~10 Gyrs, one could expect that most pockets of intelligent observers would form and study the universe ~15 Gyr after the big bang. However, it is very surprising to find ourselves at the dawn of formation of life given that life would flourish for many giga-years to come.
Answer: This is not a contraction.  Special Relativity does not say that nothing can travel faster than the speed of light.  Rather, it says that no regular matter can travel faster than the speed of light.  Therefore, instead of thinking galaxies move away from each other, think that the space between them is increasing.  That would mean that the space itself can beat the speed of light.
Comment: It seems information can't travel faster than the speed of light either.  I think the distinction between traveling through space versus traveling because of space expansion is important for this.
Answer: Yes this does sound like it might be a contradiction but in fact it isn't. It's because the universe has been expanding rapidly in every direction since the big bang and our observations are limited by the speed of light.
For example if we observe a distant quasar that appears to be 10 billion light years away, the light from the quasar is 10 billion years old (which is why quasars are known for being some of the most ancient phenomena in the universe). In the time it took for that light to reach us the universe has been expanding. In fact the expansion has been accelerating all that while so the distance between us and that quasar is at this present time considerably larger than 10 billion light years.
If we had a means to observe distant objects as they appear right at this instance, not only would we have a type of time machine but we might observe the universe to be 80 billion light years across, although I cannot vouch for the accuracy of the 80 billion light year figure given on the wikipedia page.
Astronomers and physicists also struggle with the question of "what is it that the universe expanding into". Is it expanding into empty space and if so is there anything that lies out there beyond our universe at some vast distance? If so, the universe may be infinite.
Or does the universe fold back in on itself on some higher dimensional plain i.e. if we had a hypothetical means to travel faster that the rate of the expansion of the universe and travelled in a straight line, would we eventually end up back in the same spot? In this scenario the universe would have a theoretical boundary at any one time.
Comment: The two final paragraphs are both completely wrong.
Comment: Also "the expansion has been accelerating all that while" is wrong. Acceleration only began about 5 billion years ago when dark energy began to dominate. Before that, gravity dominated and the rate of expansion had actually been slowing.
Answer: The question asks about opposite edges of the observable universe, but it's a special case of a more general question:

How can two objects that move away from a common point for a time $Δt$ end up more than $2cΔt$ apart?

You don't need to understand general relativity to understand the answer to this question, since it can happen even in special relativity. For the rest of my answer I'll assume a basic familiarity with special relativity.
Alice and Bob zero their stopwatches at a common place and time, then move away from each other for 1 second as measured by the stopwatches (or as measured by saying "one potato"). How far apart are they at the end? That is, what is the spacetime interval between the two events of the stopwatches reading 1 second?
It's easy to show* that if they both move inertially, then the interval at the end is $\sqrt{2(γ{-}1)}$ light seconds, where $γ$ is the gamma factor of their relative speed. Since $γ$ can be arbitrarily large, so can the distance. It exceeds 2 light seconds when $γ>3$ ($v \gtrsim 0.94c)$, and it exceeds any finite value for a large enough (sublight) relative speed.
In Minkowski spacetime, the triangle inequality only holds when all three sides of the triangle are spacelike. In other cases, the length of the third side isn't constrained at all by the lengths of the other two. Our thought-experiment is the case where two of the sides are timelike and the third is spacelike. The case where all three sides are timelike is the twin paradox: the stay-at-home twin can be arbitrarily old when the traveling twin returns from their two-second jaunt.
We can make this look a little more like a cosmology by introducing Carol, Ted, etc. who also move inertially away from the same point (which we'll dub the big bang) for 1 proper second. They move at different speeds, but we'll require that the relative speeds of nearest neighbors be similar to each other (this is the homogeneity assumption in cosmology). Also, instead of measuring the straight-line spacetime interval between the most distant movers, we'll measure the intervals between nearest neighbors and add them up.
If you plot the worldlines of all the movers, the points where their stopwatches read 1 second will lie on a hyperbola with the equation $t^2-x^2 = 1\,\text{s}^2$ in inertial coordinates.** The distances we measure are polygonal approximations to distances along this hyperbola. You might think that these distances would be longer than the straight-line distances; actually, they're shorter, because as usual everything is backwards in spacetime. But they aren't enough shorter to change the fundamental conclusion that arbitrarily long distances are possible. You can always make a larger distance by increasing the relative speed of adjacent movers, or by adding more of them at the extremes.
This toy model is more than just an analogy. If you start with the ΛCDM model that describes the real world (post-inflation) and take all of the densities continuously to zero in an appropriate way, it continuously morphs into this toy model. In every intermediate model, sufficiently distant objects are farther apart than $2c$ times the cosmological time since the big bang, and there's no point in the process of taking the limit at which the reason for that changes. The spacetime of the real world is curved, but the nonzero curvature isn't the reason that this counterintuitive behavior is possible. The real reason is the mixed metric signature of spacetime.

Aside from the failure of the triangle inequality, another reason people find this so confusing is probably the heavy emphasis on Cartesian (inertial) coordinate systems when teaching special relativity. Einstein had a good reason in 1905 to construct this type of coordinate system: he was trying to make a connection to the traditional Newtonian picture of space and time for the benefit of his audience which still believed in that picture. Today, 115 years later, no one believes in that picture, but we still teach it. There's so much drilling of Cartesian coordinates and related formulas (time dilation, length contraction, etc.) that people get the idea that this is how the universe really works. In truth, the universe doesn't care about our coordinate systems. The closest thing in the real world to a universal network of synchronized clocks is the expanding galaxies, and they don't follow a Cartesian grid, but a kind of polar grid (albeit on a curved manifold). If you define "distance" and "time" by reference to a Cartesian grid, then you can't get more than $Δx=2cΔt$ away; but if you define them by reference to the polar grid that actually (after a fashion) exists, then you can – even in the limit where spacetime is flat.

* Pick units where 1 second = 1 light second = 1, and inertial coordinates where the starting point is $x=t=0$, Alice doesn't move, and Bob moves on the x axis. Then Alice's final position is $(x,t)=(0,1)$ and Bob's is $(x,t)=(γβ,γ)$, and the distance between them is $\sqrt{(γβ-0)^2-(γ-1)^2}$ = $\sqrt{2γ-2}$.
** If you add more spatial dimensions, it's a hyperboloid, which in Minkowski space is a surface of constant negative curvature. This model is a zero-density limit of the FLRW cosmology, and this is why space is negatively curved in that limit, and not flat as you might expect: the FLRW coordinates are analogous to polar coordinates and "space" is a sphere of constant radius (cosmological time). In a Euclidean space it would have constant positive curvature; in Minkowski spacetime everything is backwards.

Why is the observable universe so big?


keep template's shape in different browser size on pc

Question: Is that possible to keep away website of browser size changes like decrease browser size or restore down on pc or laptop?
I wanna keep my website's shape in one shape in pc or laptop when user change the size of browser.
For instance, if user decrease the size of browser, show up some scroll or something like this.
I'm using default joomla template  Protostar.
My desire is attached by screenshots. :(
Comment: It is not easy to follow you on your question and screenshots - but likely, if I understand right, you need different templates/styles per devices, or what? There is a plugin https://extensions.joomla.org/extension/digi-template-switch-pro/ that you can use for this.
Answer: If you change the media queries from min-width to min-device-width, and max-width to max-device-width in /templates/protostar/css/template.css then this would probably do what you are after.  This should apply the responsive behaviours based on screen width and not browser window width.
You can do this under Extensions > Templates > Templates > Protostar Files > CSS > template.css
Note that this is only in the media query bit, ie @media (max-width: 767px) { and not where min-width or max-width is a style being applied  and not a media query.
It is important to point out that changing core files is not recommended, as future patching may over-write your changes.  However, since you can update that file in the admin, and it doesn't create an override, I'm unsure whether Joomla may actually think this is an okay thing to do.
I have to say, it sounds a bad idea to be doing this at all.  A fully responsive site is a good thing!
Comment: Richard I've found seven "@media min and max-width"
in template.css. I've changed the them, all of em. nothing happened.
I don't know, which one would be change! I've thought about your last sentence. Maybe it's better to give it up man.
Answer: Do you have a reason why you don't want the site to change depending on the screen size? Responsiveness of a website is very important in this day and age. If you do however want a complete static website it would be better to create your own template rather than try and override all the Protostar styling.
You could create a new template based off Protostar but remove all the media queries and go from there.


Approximate function from sample data

Question: Let $f\colon\mathbb{R}^n\to\mathbb{R}$ be a function. I don't have function definition. It's described as a fuzzy inference system. I have the inference system and can manipulate sample data for each output variable.
I need a polynomial approximation of $f$ (say $g$) having only inputs/outputs of $f$. Such a procedure should be computationally rational and precise enough. For functions defined as $h\colon\mathbb{R}\to\mathbb{R}$ I'm using Beziere curves of degree 4 to approximate polynomial segments and then use normalized B-Spline to calculate Taylor series.
Answer: You are looking for interpolation:
Newton polynomial

Approximate function from sample data


Where or what is the guitar table

Question: I have just done a classical guitar test and one of my comments was not to put my right hand on the guitar table. Can anyone tell me what it is, i am just using a standard classical guitar and no google results say what it is. I am guessing it is just near the bridge but if i am wrong plear correct me.
Comment: In what nation and in what language was this "guitar test"? I'm curious as to who would use the term "table" in this context.
Comment: I see he or she responded to the question's answer in Spanish. Table translates to Mesa... in reverse, Mesa can be Table but can also be Board... perhaps "board" (in Spanish) short for "soundboard" (whatever that is in Spanish) led to the confusion?
Comment: Its Australian.
Answer: The top of an acoustic guitar (steel-string or classical) is also referred to as the table. This is the flat piece of wood making up the front of the guitar's body when in playing position (which is a bit confusing!) It is the flat piece of wood which has the sound-hole in it, and which has the bridge stuck to it. This part of the guitar is also called the sound-board or face.
Here is my own quick sketch showing which bit of the guitar is the table (try not to laugh too much...):

When playing with a standard classical guitar technique, it is best not to rest the right-hand or any of the right-hand fingers on the table, as it restricts the hand's movement, making it difficult to play all of the strings easily with the thumb and fingers.
Comment: gracias mucho , su información es muy apreciado
Comment: Wow, I've never heard this before. I wonder if it's primarily used in classical guitar circles.
Comment: I've certainly heard other classical guitarists use this term, if not often. I've also read the term in books about classical guitar. But I hadn't heard it used for steel-string acoustic until I checked some online sources today.
Comment: Though some 19th century method books do allow, or even encourage resting the little finger on the sound board.  Ukuleles are still played that way.
Comment: That's true; I've certainly seen that in the diagrams in Sor's teaching materials, and others too. But I haven't seen any modern classical guitarists using this as an orthodox technique.
Answer: "Don't put your arms on the guitar table" is a tongue-in-cheek way of telling you to fix your posture, it references the age-old lament of parents everywhere trying to instill dinner-table etiquette into their teenagers:  "get yer darned elbows OFF THE TABLE..."   :)
Comment: This is an interesting explanation, but I doubt it's true. Have you got any reference for this claim, please?

Where or what is the guitar table


Why do exchanges have a buy/sell column in their trade history?

Question: Why is there a type column in the trade history on exchanges like btc-e.com and vircurex.com? If all the trades are between two users on the exchange why is a buy/sell type needed? And if there is one entry for buy shouldn't there be an equal entry for sell because the person buying is buying from someone who is selling.
Comment: See [Investopedia](http://www.investopedia.com/terms/m/marketmakerspread.asp) or [Wikipedia](http://en.wikipedia.org/wiki/Bid%E2%80%93offer_spread). Unless I'm mistaken, your transaction is with the market maker.
Comment: @RedGrittyBrick No, most exchanges don't buy/sell directly to/from you. They simply provide the platform for buyers and sellers to find each other, and they take a fee off each transaction.
Answer: Yes, if someone buys at a particular price, someone else must sell at that price. But they didn't place their orders at the same time. The buy/sell indicates the direction of the filled order. This is needed to make sense of the price.
Imagine an apple exchange where no trades are occurring. Then someone walks in and buys or sells an apple for $1. Do you care whether the person who walked in bought or sold? Well, yes. If the person bought an apple for $1, that means before they walked in, someone was willing to sell an apple for $1 but nobody would buy it. If that person sold an apple for $1, that means before they walked in, someone was willing to buy an apple for $1 but nobody would sell it. So without knowing the direction of the transaction, you can't tell what the price is telling you about the state of the market prior to that transaction.
This is very important in a market that isn't very liquid. For example, say the cheapest anyone is willing to sell a Bitcoin is $1,000, but the most anyone is willing to pay for a Bitcoin is $900. If it stays that way for a while, all the executing buys will be at $1,000 and all the executing sells will be at $900. If you just saw alternating $1,000 and $900 prices without knowing all the buys were at $1,000 and all the sells were at $900, you'd think the price was changing when it's actually constant. Orders that don't execute at all aren't listed because no money changes hands. So the people selling at $1,000 and buying at $900 won't be listed as transactions.
Answer: These are orders. You place an order to buy at, say $600, and it is listed on that list as a bit. It will stay there until someone places a ask to sell at $600 or lower.
The spread between them is an indication of liquidity, or how easy it is to make a transaction go through on the site. If they are very close, lots of BTC/USD is likely to be able to be bought/sold quickly.
Another indication you can gain from this is market depth. You can look at the list and figure out how much will the price change if I buy $1000. Say there is a sell order for .1 BTC that costs $100 ($1000 BTC/USD), another with .5 BTC for $505 ($1010 BTC/USD and another with .38 BTC for $395 ($1020 BTC/USD). By spending your $1000 at one time, you will not be able to spend all of it at the current price ($1000 BTC/USD), but will end up buying those .38 BTC for $1020. The more money is necessary to more the price significantly, the deeper the market is and the easier it is to make large transactions.
For more info, look up bid/ask spread and market depth.
Comment: I just realized you are asking about trade *history*. Oh well, I put to much effort into those explanations to delete them.
Answer: It's like any market for anything of value. Like stocks or bonds or coins.
The bid price is the price someone has asked to purchase that item for. The asked price is the price someone is asking to sell the item for.
So, if someone is saying they will sell 1 BTC for $600 USD and someone else says they will buy 1 BTC for $599 USD, these are orders waiting to be fulfilled. As long as nothing changes, these numbers stay the same.
Now, if someone else comes along and sees someone is willing to buy for $599. and they are willing to sell for $599. They put in an order to sell, and they sell the 1 BTC to the buyer for $599. If there is no one else willing to buy for $599 and the next willing buyer wants to buy at $598. Then the bid price lowers to $598. while the ask is still $600.


Why do we still don't know exact birth & date year of the Buddha?

Question: I just want to know:
1)Why do we still don't know exact birth & date year of the Buddha?
2)What are the factors that is limiting in knowing Buddha's birth & death year?
3)Why many people/countries/traditions contradict? Many countries following different traditions, follow different Buddhist calendar year i.e. years since Buddha left.
4)Even the recent Nat Geo Excavations reveal he might be born in 6th Century B.C. A 2013 news which still doesn't official claim nor does it leave a convincing conclusion till date, on whether their findings are indeed perfect or not. Nor their findings seems to be accepted if its true.
5)Does the pali text gives any reference to the same?
Comment: This seems to be a question about the difficulty of getting exact dates from the archaeological record when there's no historical record (or an imperfect historical record). You might get a better answer if you ask this on [the History.SE site](https://history.stackexchange.com/questions).
Comment: @ChrisW:Ok i will try that.....
Answer: Knowing the precise date of the Buddha's birth is not very useful knowledge within the Buddha's teaching, as it is presented in the Pali Suttas. How will knowing this precise birthday help any student transcend their own suffering? Only the most worldly and materialistic forces within any tradition would care about such superficial things.
The Pali Suttas(and arguably the Sanskrit Sutras) are the closest to what the Buddha actually taught. All traditions derive their truth from the Suttas/Sutras and other truths that might or might not be so compatible with the Buddha's actual original teaching. These additions were made for reasons of culture, politics and practicality IMHO.
If one wants to know what was likely the truth that the Buddha taught then one might stick to the core teachings that the Buddha repeated over and over again in the Suttas/Sutras.
It seems to me that these core teachings fit within themselves with great precision. Their potential is so awe inspiring to me that I wonder what, in 2500 years, has been stopping so much of humanity from embracing the Buddha's teaching or any teaching like the Buddha's teaching.-Metta :)
Comment: Yes, the personal history of the Buddha is very poorly documented I think. I'm not even sure he was a prince. It could be that he was just a well off individual. It is possible that many suttas that have not been repeated over and over again by the Buddha were not as true as we might want to believe. At least that's how it has been taught to me from various  teachers. This doesn't mean we can't be humble to the Buddha whatever  the truth is. If you see the Dhamma, you see the Buddha.
Comment: *"...seems to me that these core teachings fit within themselves with great precision..."* because it's the truth, truth is not learnt, it's naturally presented everywhere. Wisdom is not learnt, though learning is a process to arrive at *not-learning*. The highest is *Nothing-to-learnt* (無學), usually refer to Arhat.
Comment: @lowbrow: you are right when it comes to HIS teachings, I was just curious how on earth we still don't have any idea about it & reason behind it. Was it improper documentation or something like that.
Comment: @Mishu right but all audiences aren't ready for that...or maybe they are depending on the way the teacher teaches.
Answer: The story of the Buddha's life according to the Pali Canon can be found here. According to it, the Buddha lived for 80 years.
A chronology of the Buddha's life and Theravada Buddhism can be found here.
According to this Wikipedia page, Year 1 of the Buddhist Calendar started on 13 May 544 BCE according to the Burmese religious tradition and the 11 March 545 BCE according to the Thai religious tradition. Historical or archaeological dates for the Buddha's passing are around ±100 years from the traditional dates.
From here:

BE = Buddhist Era. Year 1 of the Buddhist Era calendar is the year of the Buddha's Parinibbana (death and final release), which occurred
  in the Buddha's eightieth year (480 BCE according to the "historical"
  timeline; 544 BCE by tradition).
The actual date of the Buddha's birth is unknown. According to Buddhist tradition, the Buddha's birth took place in 624 BCE, although
  some recent estimates place the Buddha's birth much later — perhaps as
  late as 448 BCE {1}. 560 BCE is one commonly accepted date for the
  Buddha's birth, and the "historical" date for that event that I adopt
  here.
Events in the timeline prior to -250 CE are shown with two CE dates: the date based on the "traditional" nativity of 624 BCE,
  followed by the date based on the "historical" date of 560 BCE. After
  -250 CE the "historical" date is dropped, since these dates are more appropriate only in discussions of earlier events.
To calculate the CE date corresponding to an event in the Buddhist traditional calendar, subtract 544 years from the BE date. The BE
  dates of well-documented historical events (particularly those in the
  twentieth century) may be off by one year, since the CE and BE
  calendars start their years on different months (January and May,
  respectively).
{1} The Buddhist Religion: A Historical Introduction (fourth edition)
   by R.H. Robinson & W.L. Johnson (Belmont, California: Wadsworth, 1996)


composing a piano piece using specific scale

Question: Hi I was wondering how I would go about composing a piano piece using the tonality of a Hungarian minor scale and what chords I could use that would fit with this. Thanks
Answer: The process for creating chords from scales is actually pretty simple. First, write out the notes in the scale and give each note a number, for the A Hungarian Minor Scale this would be:
A_B_C_D#_E_F_G#
1_2_3_4__5_6_7

To get a basic triad chord, you take the 1-3-5 notes. This is a process called "stacking thirds" because the notes are a third apart.
Taking the 1-3-5 notes gives:
A-C-E which is an Am chord. You can then add any extensions you want such as the 7th, which would be G#, or the 6th which would be an F, etc.
Then you repeat this process by moving to the next note in the scale and assigning it the number "1".
B_C_D#_E_F_G#_A
1_2_3__4_5_6__7

All the notes are still the same, but we just shuffled them around to give the next note in the scale (the B note) the number "1".
Taking the 1-3-5 notes gives: B-D#-F which is a Bb5 chord. Then as before you can add any extensions, 7th (A note), 6th (G# note), etc. that you want to this chord.
Repeat this process moving to each of the notes and you will have all of the chords which are built from this scale.
Comment: Just to riff off your excellent answer, you can use some simple 1-3-5 chords to establish a bass line and play a melody overtop it.  When you take the time to see all the keys on the piano that fit within the key of your choosing, have fun walking up and down the scale.
Answer: You could start out by experimenting with the diatonic triads built from the scale. In cm they would be cm D(b5) Eb(#5) F#dim G Ab bm. For more colour, try four tone chords: cm(maj7) D7(b5) Ebmaj7(#5) F#dim7 Gmaj7 Abmaj7 bm6.


Getting rid of ants and insect Islamic way?

Question: In summer days my house inhabits a lot of ants.I searched for a anti insect drug but they told me that there is no drug that gets rid of ants without killing.  I don't want to make a sin what do I have to do? Does Islam allow me kill insects in situations like this? what do you offer me as a Muslim?
Comment: Really great to hear that you love animals so much.. I never hurted an ant or a mosquito in my life.. they too have the same right to live on this earth as us.. we can't kill them nor prevent them from enjoying the food and land, as us. We should and never dominate over other creatures. Best way to get rid of them is to leave them like that ( thats what I do ) and after sometime they go their way. If we have kindness to such small creatures God will be kind with us. Do onto others what you need to be done by God. So treat the ants in the same way as you want the God to treat you.
Comment: http://www.greenlivingtips.com/articles/217/1/Ant-deterrent-tips.html ?
Comment: Imagine, our house getting crashed by some supernatural force, and not letting us to eat and do anything. Ants also have intelligence ( I being a computer and mathematics expert can tell you about bee intelligence and ant intelligence and relations they keep ) . So we can't hurt their relations. As far as I remember, I didn't even destroy the webs that spider created and my room is full of such webs. I don't even use honey, as to collect one drop of honey one bee visit one million flowers. Remember our property dragged by someone, how much bad we feel. Same should be reflected to animals too.
Comment: [this](http://eshaykh.com/halal_haram/get-rid-of-cockroach/) and [this](http://www.islamhelpline.com/node/9453) says it is ok. But I don't know how credible source those are.
Comment: @yasar11732 : No religion says to be cruel to some creatures. If cockroaches and ants are predators that are feeding and destroying our property, then aren't we predators stealing honey ? aren't we predators cutting down the homes of animals ( forest trees ) ? If they are tolerating us well, so should WE. Some religions say that for food one can consume them, but I too don't completely agree on it, and [this](http://islam.stackexchange.com/questions/2355/please-clarify-my-befuddlement-regarding-the-sacrifice) question of mine speaks about the same regard, that has not got any answers still .
Comment: here is a link how to catch ants http://www.wikihow.com/Catch-Ants-for-an-Ant-Farm
Comment: @denfromufa why the bounty if there's a good answer i think you won't find a better one than that of مجاهد as it is the most detailed and best referenced and goes ahead with my search results. Even if i might disagree in some words like prohibited to kill, as some scholars allow it as the very last possibility in case that ants etc. would cause harm to us.
Answer: It is prohibited to kill ants.  The Prophet {Peace Be Upon Him} has prohibited the killing of ants and three other creatures:

Narrated Abdullah ibn Abbas :
The Prophet (sallallahu 'alaihi wa sallam) prohibited to kill four
  creatures: ants, bees, hoopoes, and sparrow-hawks.
حَدَّثَنَا أَحْمَدُ بْنُ حَنْبَلٍ، حَدَّثَنَا عَبْدُ الرَّزَّاقِ،
  حَدَّثَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، عَنْ عُبَيْدِ اللَّهِ بْنِ
  عَبْدِ اللَّهِ بْنِ عُتْبَةَ، عَنِ ابْنِ عَبَّاسٍ، قَالَ إِنَّ
  النَّبِيَّ صلى الله عليه وسلم نَهَى عَنْ قَتْلِ أَرْبَعٍ مِنَ
  الدَّوَابِّ النَّمْلَةُ وَالنَّحْلَةُ وَالْهُدْهُدُ وَالصُّرَدُ .

So it is haram to kill ants, it would also be bad to have someone else like an exterminator kill the ants, for it would mean that he will also be doing haram.
Furthermore, if someone stops at a place, or goes to bed at night and says:

أَعُوذُ بِكَلِمَاتِ اللَّهِ التَّامَّاتِ مِنْ شَرِّ مَا خَلَقَ
I seek refuge in the Perfect Word of Allah from the evil of what He
  has created

Nothing would harm him, until he moves from that place.  Narrated by Muslim

The only things that could be given is tips on how to rid of them without killing them.
Marc Gravell gave a link a good link
Some of the tips:

Pouring lemon juice around areas ants frequent.
Pouring boiling water over their tracks (destroys the scent trail)
[Put a] sugar trail away from the house to [the] compost pile and put out the intent that they would find a greater feast there.
Comment: What is interesting about this hadith is that w/o bees humans would not exist on Earth.  Even Einstein said, "If the bee disappears from the surface of the earth, man would have no more than four years to live."  http://www.thedailygreen.com/environmental-news/latest/einstein-bees#ixzz25BEIPuaH Not that it need my approval, but this hadith is a really good one.
Comment: What if you paid someone else to do it for you?  (like an exterminator)
Comment: that doesn't make sense, if you know something is wrong why would you have someone else do it? I don't understand your question.
Comment: It's just a question.  "basically you just do not kill them" - so then if you had someone else kill them or you know that they will be killed, is that considered part of the hadith?
Answer: According to Shia jurisprudence any insect that harm or we suspect they may harm is allowed to be killed, even though its name appear in Quran, including ants. As a more general rule, if I've understood right, killing animals or insects or plants for a reasonable and religiously-admittable reason is allowed (exceptions always may arise though!); but for not admittable reasons, like for fun or as sport and etc. it would be a place for problem. Killing some animals like snakes and scorpions may even be encouraged. Specifically, there is a Hadeeth from Imam Sadiq peace be upon him that killing the ants is allowed whether they will harm any or not "ِلَا بَأْسَ بِقَتْلِ النَّمْلِ آذَيْنَكَ أَوْ لَمْ يُؤْذِينَك", however, there are Ahadeeth that suggest not to kill the honey bees, and there are Ahadeeth that allows killing some insects like mosquitoes only if they harm you.
Also note that sometimes apparently contradicting Ahadeeth may be found that are not really contradicting, they are either wrongly narrated or the translations are problematic, e.g. for ant we have at least two Arabic word: "النمل" and "الذر". Consult here and here, all in  Persian, for more explanations, from Fiqh perspective and from Ethic perspective. Also see the section "بَابُ جَوَازِ قَتْلِ الْحَيَّاتِ وَ النَّمْلِ وَ الذَّرِّ وَ سَائِرِ الْمُؤْذِيَاتِ وَ كَرَاهَةِ قَتْلِ حَيَّاتِ الْبُيُوتِ مَعَ عَدَمِ الْخَوْفِ مِنْ أَذَاهَا" of the great Hadeeth book "وسائل الشیعة". Finally note that this is never true while being in Hadj!
Meanwhile, it is reported from an authentic tradition from Imam Ali (A.S.) that whoever recites the following Duala at bed-time his poverty and problems will disappear, and will not be harmed by any dangerous insect:

اَلّلهُمَّ اَنْتَ اْلاَوَّلُ فَلا شَيْءَ قَبْلَكَ وَاَنْتَ الظّاهِرُ فَلا شَيْءَ فَوْقَكَ وَاَنْتَ الْباطِنُ فَلا شَيْءَ دُونَكَ وَاَنْتَ اْلآخِرُ فَلا شَيْءَ بَعْدَكَ اَلّلهُمَّ رَبُّ السَّمواتِ الْسَبْعِ وَرَبُّ اْلاَرَضينَ السَّبْعِ وَرَبُّ التَّوْراةِ وَاْلاِنْجيلِ وَالزَّبُورِ وَالْقُرآنِ الْحَكيمِ اَعُوذُبِكَ مِنْ شَرِّ كُلِّ دابَةٍ اَنْتَ آخِذٌ بِناصِيَتِها اِنَّكَ عَلى صِراطٍ مُسْتَقيمٍ
Allaahumma Antal Awwalu Falaa Shay'a Qablaka Wa Antadh-Dhwaahiru Falaa Shay'un Fawqaka Wa Antal Baatwinu Falaa Shay'a Doonaka Wa Antal Aakhiru Falaa Shay'a Ba'adaka. Allaahumma Rabbas-Samaawaatis-Sab'I Wa Rabbal Aradheenas-Sab'I Wa Rabbat-Tawraati Wal Injeeli Waz-Zaboor Wal Qur'aani-l Hakeem. Aoodhu Bika Min Sharri Kulli Daabbatin Anta Aakhizun Bi  Naaswiyatihaa, Innaka Alaa Swiraatum Mustaqeem.
source

This dua has worked fine for me at bedtime but I haven't tested this solution in other times.
Comment: This is strictly not an answer! Please [edit] it or it would most likely stand deletion.
Comment: added a paragraph to more directy answer the question, please check if you may admit the edit.
Answer: Generally the fitwa of Shia scholars is that if they are harmful they can be killed but if not harmful you are not allowed to kill.
There are chemicals for killing them if they are harming. But blocking their whole may cause them go other place.
Ants are free in my home. But they are not too much. They walk and eat some food they find on floor and live in peace and we have no problem with them. Sometimes one of them want to eat my skin when I am sleeping and I blaw it. It reminds me when I will be in grave and insects eating me.
The Prophet said:

فاکثروا ذکرالموت

Increase remembering death.
They are useful for this hadith.
Also about animals there is an interesting story.
One scholar at way saw a baby sparrow fallen from tree and children playing with it. He did not care and passed.
At night he felt has not the proper spiritual state like past. He made dua to know the cause. At dream he saw one said him a sparrow complained against you to God. He was sad until one day he saw another sparrow fallen and a snake wants to eat it. And he saved the complain with his wand. Again at dream he heard one said hm: appreciated you a sparrow to God.
It is said that some scholars at winter when sparrows cannot find seeds on snow go and provide wheat for them.
Comment: many insects also are allowed to easily live in our place ;) after all I read a Hadeeth that was saying Allah created the ears with a water that prevent the hurting insects from entering the ears, however, yet they can, not only from the ears but also nose and worst maybe from the mouth (bad for those who sleep with open mouth!). Anyway, an insect entering one's head was the torture for Namrud, pharaoh of Babilon in the time of Ibrahim peace be upon him. So better praying for Allah not to let them in!
Answer: I am not a Muslim to provide you authentic references from Quran and Hadith, but as far as my knowledge is concerned I will try to address your queries ad seriatim

During the Hajj Pilgrimage, my friend told me that, any Muslim should be in the state of IHRAM and should be completely away from killing ants, lice and any parasites. " Killing insects: It is forbidden to kill insects or even throwing them down or brush-off an insect originating from one's own body e.g. parasites, lice, bugs, fleece, etc. There is no harm to transfer them from one place to another and the expiation for this rule being violated is to give a handful of food to the poor. "  . I am adding the source here.
Its really a happy thing that Islam ( I started reading scriptures before short time, and hence don't know that they exist in the religion ) speaks about love towards such small creatures, on the other hand as I said previously ( refer to my comments above ) we have no right to dominate over other creatures. Every creature is a mere creation of God, and that is the humanitarian approach.  "The Holy Prophet Muhammad (S) was asked by his companions if kindness to animals was rewarded in the life hereafter. He replied: 'Yes, there is a meritorious reward for kindness to every living creature'." (Bukhari)
" , All creatures on earth are sentient beings. "There is not an animal on earth, nor a bird that flies on its wings - but they are communities like you." (The Quran, 6:38) clarifies these points.
There is not a single religion on the face of this world that teaches to be cruel. Islam also says the same thing, as I gave the references above. We can't call anything a predator. Many people kill rats for coming into their fields and eating away the paddy. I ask them, do they create the Paddy by their own? They take the help of the nature's sun-light, nature's water, and nature's earth. I heard one joke that my friend shared.

God laughs on two occasions. He laughs when the physician says to the patient's mother, "Don't be afraid, mother; I shall certainly cure your boy." God laughs, saying to Himself, "I am going to take his life, and this man says he will save it!" The physician thinks he is the master, forgetting that God is the Master. God laughs again when two brothers divide their land with a string, saying to each other, "This side is mine and that side is yours." He laughs and says to Himself, "The whole universe belongs to Me, but they say they own this portion or that portion."

So we are living on mutual exchange policy. No land belongs to us, even though we have registrations etc, but AN ANT HAS A SAME RIGHT TO LIVE AND ENJOY THE RESOURCES AS A HUMAN HAS. Not only ant, any creature for that instance.  If we call, other creatures as predators, we are the worst predators, for taking the milk from cows, stealing the honey from honey-bees , cutting the plants and building houses etc.,
God never created these things for us . Even though Bible and Quran speaks that God has made the creatures for consuming and other purposes, they should be respected as homo sapiens, only that they don't have rationality. If God created the creatures for Eating purpose, why could he give the element of pain for them? (He could have created them , in such a way that they couldn't experience pain and don't have relations ). The present day science ( bee intelligence and ant intelligence ) reveal that,  they too have feelings, and they too keep relation-ships in their language.
I am happy that Quran and other scriptures have revealed it thousands of years ago, when Science didn't advance. You can read more on this here . The reference provides beautiful words in Quran that condemn testing animals, blood sports and hunting.
Salute to Quran's kindness towards creatures. People due to their misconceptions change the rules to satisfy themselves. But no religion says to be cruel towards other animals.
-Thank you.
Comment: -1: Although I appreciate your kind-heartedness towards every living means, OP asked if it is allowable in Islam. Your answer, except for hajj point, doesn't adress the original question. Instead, it discusses ethical and philosophical aspects of such act. And hajj point is a special case, and doesn't apply to everyday life.
Comment: @yasar11732 : Brother, Yes thank you. You showed me where I stand. But that is an indirect clue, which you missed. If in Hajj pilgrimage, the killing or hurting is not allowed, it indirectly leads you to some point that, at-least people will be kind in those days during the Hajj pilgrimage . That's the inner meaning. There is an inner meaning behind any ritual. If some ritual teaches someone something, it don't mean that its temporary, it means that its permanent and good. Contd..
Comment: @yasar11732 : As we humans can't have tolerance and patience for following that all our life, at-least following that for some short span of time, is good and well. It don't necessarily mean that it should be only followed during that time. It was a slow initiation, and the intention of prophets is to implement them at a local scale ( for some short period ) so that that could get habituated and people may follow it for all their life leading to Global sense . BTW, I clearly specified that I am not worth of answering, as I am not an expert in Quran and Hadith. Thank you once again.God is great
Comment: It is important to note that the "God laughs..." quote is not Islamic in origin.  It comes from a Hindu source, I believe.
Comment: Regarding the Hajj point, it is not completely true. Killing in Haram is forbidden. However, there are five animals that are malicious and permissible to kill, whether in the Haram or not - www.subulassalaam.com/articles/article.cfm?article_id=159


Is a passport required for an Alaska cruise that has a stop in Canada?

Question: So I'm thinking of taking a cruise from Seattle to Alaska. One of the stops is in Victoria, British Columbia, Canada and I was wondering if passengers would require a passport to get off at that stop?
Comment: What does the cruise operator have to say about it?
Comment: How long is the stop ?
Comment: 11am arrival, 10:30pm departure.
Answer: You are actually asking two separate questions:

When my cruise ship stops in Victoria, will the Canadian border people let me come into the country for a day visit without a passport?
When my cruise ship, which was at least briefly in another country, returns to the USA and I want to get off it (probably in Alaska for some day activities, but very certainly in Seattle when you want to return to your home) will I be allowed into the United States without a passport?

There was a time when US citizens could come into Canada without a passport, with drivers licenses and such like. It's possible that at the cruise terminal you could get by with less than a passport. Here is the CBSA advice. Note the birth certificate to prove US citizenship along with the drivers license to prove you are the person named on the birth certificate. If your name has changed since you were born you'll need paperwork to establish the identity chain. I wouldn't risk it myself, but the worst case here is that you aren't allowed to go have your day trip. US citizens don't need visas to visit Canada, but without a passport, how do the border people know you're a US citizen? It's not a requirement for boarding cruise ships, getting drivers licenses, and so on.
The second case is much more serious. You want to be sure you will be let back in. Current rules say that if the cruise starts and ends at the exact same US port you don't need a passport, even if it stops in other countries. Essentially they are trusting the cruise ship not to take on random passengers in the foreign ports and help them enter the US. That said, they still recommend you have a passport just to make life smoother. (Here's Carnival's page on the topic - you can probably find a similar page on the site of the cruise provider you're considering.)
So if there is a reason why just getting a passport isn't an option, the cruise isn't impossible (US businesses have found ways to deal with the fact people just won't get passports) but life will be smoother if you have one. I'd recommend getting one.
Comment: A US passport card would also work for entry into Canada
Comment: Canada still accepts [photo ID plus birth certificate for US citizens](http://www.cbsa.gc.ca/travel-voyage/td-dv-eng.html#_s2a), so the Canada shore excursion is not ruled out.
Comment: For the record, [here's the page from US Customs' website on closed-loop cruises.](https://help.cbp.gov/app/answers/detail/a_id/1139/~/documents-needed-to-take-a-cruise)
Answer: The embarkation officer in Seattle will deny boarding of an Alaskan cruise if you do not provide either a passport or other accepted proof of citizenship, such as a US state or city-issued (not hospital-issued) birth certificate and driver's license. It is not at the discretion of the cruise line whether to let you onboard if you do not have the required documentation. People are denied boarding even if they say they will stay onboard the ship when it stops in Canada – they will simply not let you go if you do not have the right documents.
If you do travel with only a US birth certificate and driver's license, and some emergency arises while you are in Canada, note that you will not be able to fly back into the US (you would have to get back by land or sea). You will likely be required to sign a form when you check-in that states you understand these risks of travelling without a passport. This is why it is strongly recommended to travel with a passport.
Answer: You have not stated your country of origin. If you are a US citizen there is no objection for both as US citizens do not require any authorization to enter or exit Canada. Re: visiting Alaska, the state is in USA and so you can visit or remain there as long as you can.
Comment: I did say the cruise would be going from Seattle to Alaska, and Seattle is in the United States..
Comment: @neubert I think by 'country of origin' they meant citizenship, not source-destination.


Is the Vista sidebar slowing down my computer?

Question: I have Windows Vista and I've installed some fancy new gadgets to the Vista sidebar. Is this application a major RAM consumer or something?
I don't have a slow computer, but I'd like to know
Comment: What gadgets are installed?
Answer: It depends what Sidebar Gadgets you're using.
Poorly written ones can leak badly, as Ed Bott notes..
You should keep an eye on the memory usage of sidebar.exe to see what's happening.
Comment: ... and each added Gadget increases the memory used by the sidebar.exe application. A lot of gadgets = High memory usage.
Answer: Have you checked the memory utilization with Process Explorer?
If you name the gadgets, people here may be able to give you their first-hand experience too.
Answer: From what I have learnt, it's best not to run the sidebar in Vista as I beleive it slow's down the system. I depends on the type of machine you have, but I noticed a difference even on a 2.13 Dual core system with 4gb of Memory when I disabled the sidebar.
Comment: "you believe"? I find your beliefs fascinating! :) Can you provide links or other evidence?
Comment: Welcome to Super User!  Even if you don't always provide credible outside sources, your answers can still be helpful sometimes, but it is always better to provide sources when you can.
Answer: From a non-techie point of view, have you tried removing all the gadgets from the sidebar?
Then if there is a very noticeble slowing down of your PC as you slowly add the gadgets you like back onto the sidebar, you will have found a problem gadget that can be avoided in future. If there is never an appreciable change in PC speed, only a gradual one then it would appear to be the sidebar itself or simply then 23481274243 gadgets you have installed upon it, no?
Answer: As Jeff said it always depends on what gadgets you are using. Try the following:
First of all disable all gadgets and restart the windows sidebar.
When you've found a gadget of interest turn on process explorer (http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx) or the native Windows task manager and have a look at the "sidebar.exe" process (Hint: having 3rd party gadgets enabled there are probably two processes named "sidebar.exe"). Then enable one gadget and use it for some time and keep a look at the cpu and ram usage. When it's ok start over with the next gadget. This way you should be able to find out which of the chosen gadgets waste system ressources and you can sort them out. Sadly many of those useful gadgets are not well coded and those are the ones that slow down the system. Keep in mind, too, that having a lot of real time monitoring gadgets enabled always slows down the system. I never use more than two of those.
Answer: Most of these answers are about how to speed up a slow system.  You don't have a slow system, so I'd answer "Not really".  However, it may be a contributing factor to any future slowdown.
To check, I'd open Task Manager (Ctrl+Shift+Esc) and go to the Processes tab.  Then sort by name and find sidebar.exe; if it's consuming a lot of CPU or memory compared to your other programs, than it is slowing down your computer.  If not, then it PROBABLY isn't (though it might still be; see the Coding Horror article about various performance causes, which is currently down).  This approach can work for any program.


Rear end Differential - rebuild or replace with used?

Question: I have a 01 Ford F 150 with 320K miles. I love this truck and don't plan on ever selling it. I thought the bearings were going out in the back right side so I took it to mechanic. Two different mechanics say the rear end needs to be rebuilt or replaced. One says if I'm going to keep it I should rebuild it. Second says I should replace it with a used one (rebuilt never works). They can both do either and are about the same price. Rebuilt has a warranty but used one will have warranty for only 45 days. One can tell me the used one has 130k miles on it the other doesn't know because its already pulled. What is recommended rebuilt or replaced??
Comment: it depends how lucky you are, the "used" one could break after 46 days and you will have wasted a fair amount on it just to replace it again, where as the rebuilt one would probably last a lifetime. people always seem to have a downer on rebuilt parts but if it's done correctly there' just as good as a brand new part
Comment: Did they not give you more of an explanation as to why a rebuild would be a problem?  Why not replace the bearing yourself?
Comment: The first guy pushed me to have it rebuilt being that I was going to keep it. He doesn't do it himself he sends it out to some one who specializes in it and as mentioned it will be warranted. The other rI think will rebuild himself and I assume does't do it that often. It is about $1200 used and $2300 rebuilt. I am just not a handyman to do it myself and even if I were I just don't have the time to do it.
Comment: If you're going to keep an older vehicle, you'll want to learn some of the more basic repairs.  I have a `73 landy and can do bearings in 60 minutes after way-too much practice.
Answer: My suggestion would be to buy a differential bearing and seal kit for the rear end yourself and have a knowledgeable mechanic install it for you. This, as the name implies, consists of bearings and seals. A master kit will have the shims in it as well, but when you are just doing bearings in the diff, you can usually put the old shims back in to get everything back to right. You'll want bearings such as Timken or Standard Gear which have great reputations. The reason this is my suggestion is, if you buy these parts, you know exactly what has gone into the diff. If you rely on the mechanic to get you the parts, they could get the cheapest thing they can get away with. These parts will last long enough for their warranty period, but you wouldn't want to trust them much longer.
@JasonJanowitz is right in that getting a used one is a crap shoot. It could be 6-months or two days away from needing a rebuild ... you just don't know. Getting your rear end rebuilt gets you back to exactly where your truck needs to be. There's no guess work. Just because you have 320k miles on it doesn't mean any of the hard parts are shot. As long as it hasn't gone dry and it hasn't been over worked, they are probably fine. If they aren't, getting a new set to put in really isn't all that expensive and shouldn't cost you much more in labor than a rebuild alone would cost.
You really need a knowledgeable mechanic to do this. Don't get a mechanic "friend" to do it for you as this is probably one of the easiest things to screw up on a vehicle if you don't know what you're doing. It's not something a mechanic can just wing and get it right. Most mechanics would get instruction from another knowledgeable mechanic while they are watching to ensure things are right. There is preload in the front bearing which measures in the lb-in realm (meaning, you tighten the front bearing down, then while it's free, you check the preload to the lb-in range ... some mechanics can turn it free hand and tell when the preload is correct.) The steps involved are not something you'll just read in a book or watch in a video and figure out.
Answer: If the price is the same go with the rebuilt.  Better warranty and more knowledge.  With the used one you dont know its history to this point and it may be 6 months away from needing a rebuild.
Answer: Rebuilt is always the way to go and buying really good parts is a must,the most important and hardest thing to do is to find a mechanic that has a good amount of experience that is specific to this task
Answer: you simply don't have enough information here.  If it's really a problem with one side, you probably just need a bearing and an axle.  With that many miles, the pinion gears could be worn to the point that you get enough slop back and forth that the axle doesn't ride right on the bearing.  If that's NOT the case (and it's easy to test just by grabbing the wheel and pulling in and out on it while the truck is on a lift) then find out in DETAIL why they want to replace the whole rear end.  Your symptoms point to a bearing.
Answer: For sure, get the new differential.  I replaced mine for $1600 and it has lasted.
Comment: @Criggie - Be that as it may, this answer is still just an opinion, which really doesn't make it very usable.
Comment: you'll get better results with a more readable answer.
Comment: @JohnLord I think BA Ute is a reference to the BA chassis format and Ute is short for Utility, which is NZEnglish for a pickup truck body format.
Answer: Why can't you just buy directly from Jasper motors who gives you a way better warranty? They sale rear ends for about $900-1k. Most places here in Tennessee charge about $3-400 to install. I'm buying mine from jasper and having it install all for about $1400 that's with a 3yr warranty from them
Answer: Used diff will only cost $$ u more..go the rebuild...place took mine been in biz 42 years...great job..research who u take ur diff to..
Comment: This is not a forum, you can edit your answers anytime you find it worth editting. You can even edit anyone else's answer as well. Although we usually don't care much about grammar and loose wordings, "Yo-mama" answers are not welcome here as counterproductive. I personally can decode a couple of words you wrote and completely miss the idea you want to share.