Wouldn't it be great if we could be invisible?
Ha, right?
I mean, we could spy on people without being noticed and do whatever we want without being held responsible.
Now, magicians have figured out how to utilize full-sized mirrors to bend light in order to create disappearing illusions.
Scientists have created metamaterials to guide rays of light around tiny, two-dimensional objects.
Cameras can also film what is behind you and project the image so you appear invisible from the front.
However, none of these options can make an object as large as a person appear invisible for all angles and distances while its moving.
But if you are truly invisible, as in from within, here are a few problems you may not have thought about before.
To move around undetected by other people, you would have to be totally naked.
Even if it's freezing outside!
You can't carry anything, including your wallet and keys, otherwise people would just see your wallet and keys floating around.
Drivers and people on the street can't see you either, therefore they can and will run into you at some point.
Oh, and you better not wear any perfume or make any noise breathing, otherwise they'll know you're there.
And, just because you start off invisible, doesn't mean you'll stay that way.
What if someone accidentally spills scolding hot coffee on you?
And what if it rains?
But if you think only liquid can make you visible, you're wrong.
Dust consists of dead skin cells from humans, soil particles, and fibers from clothes made from cotton and other materials.
Dust sticks to the moisture on our skin when we sweat and the tiny hairs on our skin when we are dry.
So, even if you are invisible, dust would still land on every part of you.
We usually don't notice the dust on our skin because we can't see a thin layer of dust on top of our skin color.
But, if you're invisible, people would see a human-shaped blob of dust walking around with extremely dirty soles.
Gross!
What do you think the world looks like if you are invisible?
Well, the answer is nothing.
The reason you can't see in the dark is because there is no light.
To see an apple, light has to hit the apple and return it to your eyes.
Then, the retinas in your eyes catch the light reflection for your brain to interpret into the image of an apple.
If you're invisible, then, by definition, light would travel through you or around you instead of bouncing off you for people to see.
But that means that retinas in your eyes are not catching the light, either.
Therefore, your brain has nothing to interpret into an image.
Can you see your reflection without a mirror to stop the light?
No.
So, when you can't be seen by others, you also cannot see.
Ouch!
Now, have you given any thought as of whether the invisibility is permanent?
If it is, how can you receive medical treatment from a doctor if you're injured?
The doctor wouldn't know where to apply ointments or bandages because they cannot access your injury.
For that matter, you can't see it either.
I mean, what if you have an illness or an infection?
How can the doctor diagnose you without being able to see the color change or inflammation?
And what if everyone is permanently invisible?
Well, think about how boring the world would be without seeing people on the streets, on TV, or at home on your computer like right now.
It's lonely being invisible.
Now, which superpower physics lesson will you explore next?
Shifting body size and content, super speed, flight, super strength, immortality, and invisibility.
What does the French Revolution have to do with the time NASA accidentally crashed a $200 million orbiter into the surface of Mars?
Actually, everything.
That crash happened due to an error in converting between two measurement systems, U.S. customary units and their S.I, or metric, equivalence.
So what's the connection to the French Revolution?
Let's explain.
For the majority of recorded human history, units like the weight of a grain or the length of a hand weren't exact and varied from place to place.
And different regions didn't just use varying measurements.
They had completely different number systems as well.
By the late Middle Ages, the Hindu-Arabic decimal system mostly replaced Roman numerals and fractions in Europe, but efforts by scholars like John Wilkins to promote standard decimal-based measures were less successful.
With a quarter million different units in France alone, any widespread change would require massive disruption.
And in 1789, that disruption came.
The leaders of the French Revolution didn't just overthrow the monarchy.
They sought to completely transform society according to the rational principles of the Enlightenment.
When the new government took power, the Academy of Sciences convened to reform the system of measurements.
Old standards based on arbitrary authority or local traditions were replaced with mathematical and natural relationships.
For example, the meter, from the Greek word for measure, was defined as 1/10,000,000 between the Equator and North Pole.
And the new metric system was, in the words of the Marquis de Condorcet, "For all people, for all time."
Standardizing measurements had political advantages for the Revolutionaries as well.
Nobles could no longer manipulate local units to extract more rent from commoners, while the government could collect taxes more efficiently.
And switching to a new Republican Calendar with ten-day weeks reduced church power by eliminating Sundays.
Adoption of this new system wasn't easy.
In fact, it was a bit of a mess.
At first, people used new units alongside old ones, and the Republican Calendar was eventually abandoned.
When Napoléon Bonaparte took power, he allowed small businesses to use traditional measurements redefined in metric terms.
But the metric system remained standard for formal use, and it spread across the continent, along with France's borders.
While Napoléon's empire lasted eight years, its legacy endured far longer.
Some European countries reverted to old measurements upon independence.
Others realized the value of standardization in an age of international trade.
After Portugal and the Netherlands switched to metric voluntarily, other nations followed, with colonial empires spreading the system around the world.
As France's main rival, Britain had resisted revolutionary ideas and retained its traditional units.
But over the next two centuries, the British Empire slowly transitioned, first approving the metric system as an optional alternative before gradually making it offical.
However, this switch came too late for thirteen former colonies that had already gained independence.
The United States of America stuck with the English units of its colonial past and today remains one of only three countries which haven't fully embraced the metric system.
Despite constant initiatives for metrication, many Americans consider units like feet and pounds more intuitive.
And ironically, some regard the once revolutionary metric system as a symbol of global conformity.
Nevertheless, the metric system is almost universally used in science and medicine, and it continues to evolve according to its original principles.
For a long time, standard units were actually defined by carefully maintained physical prototypes.
But thanks to improving technology and precision, these objects with limited access and unreliable longevity are now being replaced with standards based on universal constants, like the speed of light.
Consistent measurements are such an integral part of our daily lives that it's hard to appreciate what a major accomplishment for humanity they've been.
And just as it arose from a political revolution, the metric system remains crucial for the scientific revolutions to come.
Created by logician Raymond Smullyan and popularized by his colleague George Boolos, this riddle has been called the hardest logic puzzle ever.
You and your team have crash-landed on an ancient planet.
The only way off is to appease its three alien overlords, Tee, Eff, and Arr, by giving them the correct artifacts.
Unfortunately, you don't know who is who.
From an inscription, you learn that you may ask three yes or no questions, each addressed to any one lord.
Tee's answers are always true, Eff's are always false, and Arr's answer is random each time.
But there's a problem.
You've deciphered the language enough to ask any question, but you don't know which of the two words 'ozo' and 'ulu' means yes and which means no.
How can you still figure out which alien is which?
Pause here if you want to figure it out for yourself!
Answer in: 3 2 1 At first, this puzzle seems not just hard, but downright impossible.
What good is asking a question if you can neither understand the answer nor know if it's true?
But it can be done.
The key is to carefully formulate our questions so that any answer yields useful information.
First of all, we can get around to not knowing what 'ozo' and 'ulu' mean by including the words themselves in the questions, and secondly, if we load each question with a hypothetical condition, whether an alien is lying or not won't actually matter.
To see how that could work, imagine our question is whether two plus two is four.
Instead of posing it directly, we say, "If I asked you whether two plus two is four, would you answer 'ozo'?"
If 'ozo' means yes and the overlord is Tee, it truthfully replies, "ozo."
But what if we ask Eff?
Well, it would answer "ulu," or no to the embedded question, so it lies and replies 'ozo' instead.
And if 'ozo' actually means no, then the answer to our embedded question is 'ulu,' and both Tee and Eff still reply 'ozo,' each for their own reasons.
If you're confused about why this works, the reason involves logical structure.
A double positive and a double negative both result in a positive.
Now, we can be sure that asking either Tee or Eff a question put this way will yield 'ozo' if the hypothetical question is true and 'ulu' if it's false regardless of what each word actually means.
Unfortunately, this doesn't help us with Arr.
But don't worry, we can use our first question to identify one alien lord that definitely isn't Arr.
Then we can use the second to find out whether its Tee or Eff.
And once we know that, we can ask it to identify one of the others.
So let's begin.
Ask the alien in the middle, "If I asked you whether the overlord on my left is Arr, would you answer 'ozo'?"
If the reply is 'ozo,' there are two possibilities.
You could already be talking to Arr, in which case the answer is meaningless.
But otherwise, you're talking to either Tee or Eff, and as we know, getting 'ozo' from either one means your hypothetical question was correct, and the left overlord is indeed Arr.
Either way, you can be sure the alien on the right is not Arr.
Similarly, if the answer is 'ulu,' then you know the alien on the left can't be Arr.
Now go to the overlord you've determined isn't Arr and ask, "If I asked 'are you Eff?' would you answer 'ozo'?"
Since you don't have to worry about the random possibility, either answer will establish its identity.
Now that you know whether its answers are true or false, ask the same alien whether the center overlord is Arr.
The process of elimination will identify the remaining one.
The satisfied overlords help you repair your ship and you prepare for takeoff.
Allowed one final question, you ask Tee if it's a long way to Earth, and he answers "ozo."
Too bad you still don't know what that means.
In 1943 Allied aircraft swooped over Nazi Germany, raining tens of thousands of leaflets on people below.
Written by anonymous Germans, the leaflets urged readers to renounce Hitler, to fight furiously for the future— and to never give up hope.
Their call to action rippled through homes and businesses— and news of their message even reached concentration camps and prisons.
It was only after the war had ended that the authors’ identities, stories, and tragic fate would come to light.
When Hitler seized power 10 years earlier, Hans and Sophie Scholl were teenagers in the town of Forchtenberg.
At that time, fear, propaganda, and surveillance kept all aspects of life for the Scholl family and millions of other Germans under Nazi control.
The government specifically targeted young people, setting up institutions to regulate their behavior and police their thoughts.
As teenagers, Hans was a member of the Hitler Youth and Sophie joined The League of German Girls.
Hans rose through the ranks and oversaw the training and indoctrination of other young people.
In 1936, he was chosen to carry the flag at a national rally.
But when he witnessed the zeal of Nazi rhetoric, he began to question it for the first time.
Meanwhile, Sophie was also starting to doubt the information she was being fed.
Their parents Robert and Magdalena, who had feared they were losing their children to Nazi ideology, encouraged these misgivings.
At home, Robert and Magdalena listened to foreign radio stations that the government first discouraged and later banned.
While the government churned out national broadcasts which denied Nazi atrocities, the Scholls learned shocking truths.
And yet, they were still subject to the rules of life in Hitler’s Germany.
After the outbreak of war, Sophie reluctantly worked for the national effort, and Hans had to take on army duties while attending medical school in Munich.
That was where Hans met Christoph Probst, Willi Graf and Alexander Schmorell.
Day by day, each grew more sickened by Nazi ideology.
They longed to share their views.
But how could they spread them, when it was impossible to know who to trust?
And so, the friends decided to rebel anonymously.
They pooled their money and bought printing materials.
An acquaintance let them use a cellar under his studio.
In secret, they began drafting their message.
In June 1942, mysterious anti-Nazi leaflets began appearing all over Munich.
They were signed: the White Rose.
The first leaflet denounced Hitler and called for Germans to sabotage the war effort: “Adopt passive resistance… block the functioning of this atheistic war machine before it is too late, before the last city is a heap of rubble… before the last youth of our nation bleeds to death...
Don’t forget that each people gets the government it deserves!”
At a time when a sarcastic remark could constitute treason, this language was unprecedented.
It was written mostly by Hans Scholl.
In 1942, Sophie came to Munich knowing nothing of her brother’s activities.
She soon encountered the jasonreeves@example.com.
But it was not until she discovered evidence in Han’s room that she realized who’d written them.
Her shock soon gave way to resolve: she wanted in.
For both siblings, it was time to escalate the fury that had been brewing for years.
From June 1942 to February 1943, the group worked feverishly.
While the Gestapo searched for leads, the White Rose were constantly on guard.
The war raged on.
Regulations tightened, and Munich suffered air raids.
But the White Rose ventured deeper into conspiracy.
They graffitied buildings and braved trains swarming with Gestapo.
In the winter of 1942, Hans made a treacherous journey to the Czechoslovakian border to meet anti-Nazi rebels.
On February 18, 1943, Sophie and Hans brought a suitcase of leaflets to their university.
A custodian noticed what they were doing and reported them to the Gestapo.
Both calmly denied any involvement— until the police gathered all the leaflets and placed them back in the empty case, where they fit perfectly.
When Hans and Sophie confessed, they were immediately led to court and sentenced to death by guillotine.
Despite a grueling interrogation, the two refused to betray their co-conspirators.
Before her execution, Sophie declared her fury at the state of her country.
But she also spoke to a more hopeful future: “How can we expect righteousness to prevail when there is hardly anyone willing to give himself up individually to a righteous cause?
Such a fine, sunny day, and I have to go, but what does my death matter, if through us, thousands of people are awakened and stirred to action?”
I'm an ocean microbiologist at the University of Tennessee, and I want to tell you guys about some microbes that are so strange and wonderful that they're challenging our assumptions about what life is like on Earth.
So I have a question.
Please raise your hand if you've ever thought it would be cool to go to the bottom of the ocean in a submarine?
Yes.
Most of you, because the oceans are so cool.
Alright, now -- please raise your hand if the reason you raised your hand to go to the bottom of the ocean is because it would get you a little bit closer to that exciting mud that's down there.
(Laughter) Nobody.
I'm the only one in this room.
Well, I think about this all the time.
I spend most of my waking hours trying to determine how deep we can go into the Earth and still find something, anything, that's alive, because we still don't know the answer to this very basic question about life on Earth.
So in the 1980s, a scientist named John Parkes, in the UK, was similarly obsessed, and he came up with a crazy idea.
He believed that there was a vast, deep, and living microbial biosphere underneath all the world's oceans that extends hundreds of meters into the seafloor, which is cool, but the only problem is that nobody believed him, and the reason that nobody believed him is that ocean sediments may be the most boring place on Earth.
(Laughter) There's no sunlight, there's no oxygen, and perhaps worst of all, there's no fresh food deliveries for literally millions of years.
You don't have to have a PhD in biology to know that that is a bad place to go looking for life.
(Laughter) But in 2002, [Steven D'Hondt] had convinced enough people that he was on to something that he actually got an expedition on this drillship, called the JOIDES Resolution.
And he ran it along with Bo Barker Jørgensen of Denmark.
And so they were finally able to get good pristine deep subsurface samples some really without contamination from surface microbes.
This drill ship is capable of drilling thousands of meters underneath the ocean, and the mud comes up in sequential cores, one after the other -- long, long cores that look like this.
This is being carried by scientists such as myself who go on these ships, and we process the cores on the ships and then we send them home to our home laboratories for further study.
So when John and his colleagues got these first precious deep-sea pristine samples, they put them under the microscope, and they saw images that looked pretty much like this, which is actually taken from a more recent expedition by my PhD student, Joy Buongiorno.
You can see the hazy stuff in the background.
That's mud.
That's deep-sea ocean mud, and the bright green dots stained with the green fluorescent dye are real, living microbes.
Now I've got to tell you something really tragic about microbes.
They all look the same under a microscope, I mean, to a first approximation.
You can take the most fascinating organisms in the world, like a microbe that literally breathes uranium, and another one that makes rocket fuel, mix them up with some ocean mud, put them underneath a microscope, and they're just little dots.
It's really annoying.
So we can't use their looks to tell them apart.
We have to use DNA, like a fingerprint, to say who is who.
And I'll teach you guys how to do it right now.
So I made up some data, and I'm going to show you some data that are not real.
This is to illustrate what it would look like if a bunch of species were not related to each jasonreeves@example.com.
So you can see each species has a list of combinations of A, G, C and T, which are the four sub-units of DNA, sort of randomly jumbled, and nothing looks like anything else, and these species are totally unrelated to each other.
But this is what real DNA looks like, from a gene that these species happen to share.
Everything lines up nearly perfectly.
The chances of getting so many of those vertical columns where every species has a C or every species has a T, by random chance, are infinitesimal.
So we know that all those species had to have had a common ancestor.
They're all relatives of each other.
So now I'll tell you who they are.
The top two are us and chimpanzees, which y'all already knew were related, because, I mean, obviously.
(Laughter) But we're also related to things that we don't look like, like pine trees and Giardia, which is that gastrointestinal disease you can get if you don't filter your water while you're hiking.
We're also related to bacteria like E. coli and Clostridium difficile, which is a horrible, opportunistic pathogen that kills lots of people.
But there's of course good microbes too, like Dehalococcoides ethenogenes, which cleans up our industrial waste for us.
So if I take these DNA sequences, and then I use them, the similarities and differences between them, to make a family tree for all of us so you can see who is closely related, then this is what it looks like.
So you can see clearly, at a glance, that things like us and Giardia and bunnies and pine trees are all, like, siblings, and then the bacteria are like our ancient cousins.
But we're kin to every living thing on Earth.
So in my job, on a daily basis, I get to produce scientific evidence against existential loneliness.
So when we got these first DNA sequences, from the first cruise, of pristine samples from the deep subsurface, we wanted to know where they were.
So the first thing that we discovered is that they were not aliens, because we could get their DNA to line up with everything else on Earth.
But now check out where they go on our tree of life.
The first thing you'll notice is that there's a lot of them.
It wasn't just one little species that managed to live in this horrible place.
It's kind of a lot of things.
And the second thing that you'll notice, hopefully, is that they're not like anything we've ever seen before.
They are as different from each other as they are from anything that we've known before as we are from pine trees.
So John Parkes was completely correct.
He, and we, had discovered a completely new and highly diverse microbial ecosystem on Earth that no one even knew existed before the 1980s.
So now we were on a roll.
The next step was to grow these exotic species in a petri dish so that we could do real experiments on them like microbiologists are supposed to do.
But no matter what we fed them, they refused to grow.
Even now, 15 years and many expeditions later, no human has ever gotten a single one of these exotic deep subsurface microbes to grow in a petri dish.
And it's not for lack of trying.
That may sound disappointing, but I actually find it exhilarating, because it means there are so many tantalizing unknowns to work on.
Like, my colleagues and I got what we thought was a really great idea.
We were going to read their genes like a recipe book, find out what it was they wanted to eat and put it in their petri dishes, and then they would grow and be happy.
But when we looked at their genes, it turns out that what they wanted to eat was the food we were already feeding them.
So that was a total wash.
There was something else that they wanted in their petri dishes that we were just not giving them.
So by combining measurements from many different places around the world, my colleagues at the University of Southern California, Doug LaRowe and Jan Amend, were able to calculate that each one of these deep-sea microbial cells requires only one zeptowatt of power, and before you get your phones out, a zepto is 10 to the minus 21, because I know I would want to look that up.
Humans, on the other hand, require about 100 watts of power.
So 100 watts is basically if you take a pineapple and drop it from about waist height to the ground 881,632 times a day.
If you did that and then linked it up to a turbine, that would create enough power to make me happen for a day.
A zeptowatt, if you put it in similar terms, is if you take just one grain of salt and then you imagine a tiny, tiny, little ball that is one thousandth of the mass of that one grain of salt and then you drop it one nanometer, which is a hundred times smaller than the wavelength of visible light, once per day.
That's all it takes to make these microbes live.
That's less energy than we ever thought would be capable of supporting life, but somehow, amazingly, beautifully, it's enough.
So if these deep-subsurface microbes have a very different relationship with energy than we previously thought, then it follows that they'll have to have a different relationship with time as well, because when you live on such tiny energy gradients, rapid growth is impossible.
If these things wanted to colonize our throats and make us sick, they would get muscled out by fast-growing streptococcus before they could even initiate cell division.
So that's why we never find them in our throats.
Perhaps the fact that the deep subsurface is so boring is actually an asset to these microbes.
They never get washed out by a storm.
They never get overgrown by weeds.
All they have to do is exist.
Maybe that thing that we were missing in our petri dishes was not jasonreeves@example.com.
Maybe it wasn't a chemical.
Maybe the thing that they really want, the nutrient that they want, is time.
But time is the one thing that I'll never be able to give them.
So even if I have a cell culture that I pass to my PhD students, who pass it to their PhD students, and so on, we'd have to do that for thousands of years in order to mimic the exact conditions of the deep subsurface, all without growing any contaminants.
It's just not possible.
But maybe in a way we already have grown them in our petri dishes.
Maybe they looked at all that food we offered them and said, "Thanks, I'm going to speed up so much that I'm going to make a new cell next century.
Ugh.
(Laughter) So why is it that the rest of biology moves so fast?
Why does a cell die after a day and a human dies after only a hundred years?
These seem like really arbitrarily short limits when you think about the total amount of time in the universe.
But these are not arbitrary limits.
They're dictated by one simple thing, and that thing is the Sun.
Once life figured out how to harness the energy of the Sun through photosynthesis, we all had to speed up and get on day and night cycles.
In that way, the Sun gave us both a reason to be fast and the fuel to do it.
You can view most of life on Earth like a circulatory system, and the Sun is our beating heart.
But the deep subsurface is like a circulatory system that's completely disconnected from the Sun.
It's instead being driven by long, slow geological rhythms.
There's currently no theoretical limit on the lifespan of one single cell.
As long as there is at least a tiny energy gradient to exploit, theoretically, a single cell could live for hundreds of thousands of years or more, simply by replacing broken parts over time.
To ask a microbe that lives like that to grow in our petri dishes is to ask them to adapt to our frenetic, Sun-centric, fast way of living, and maybe they've got better things to do than that.
(Laughter) Imagine if we could figure out how they managed to do this.
What if it involves some cool, ultra-stable compounds that we could use to increase the shelf life in biomedical or industrial applications?
Or maybe if we figure out the mechanism that they use to grow so extraordinarily slowly, we could mimic it in cancer cells and slow runaway cell division.
I don't know.
I mean, honestly, that is all speculation, but the only thing I know for certain is that there are a hundred billion billion billlion living microbial cells underlying all the world's oceans.
That's 200 times more than the total biomass of humans on this planet.
And those microbes have a fundamentally different relationship with time and energy than we do.
What seems like a day to them might be a thousand years to us.
They don't care about the Sun, and they don't care about growing fast, and they probably don't give a damn about my petri dishes ...
(Laughter) but if we can continue to find creative ways to study them, then maybe we'll finally figure out what life, all of life, is like on Earth.
Thank you.
(Applause)