Prática de Shadowing: The Most Controversial Idea In Physics - Aprenda a falar inglês com vídeo
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In 1953, the astronomer Fred Hoyle had a problem.
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He was studying how stars make different elements in their cores,
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and he realized that there's much more carbon in the universe than there should be.
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Stars fuse hydrogen into helium and then helium into beryllium-8.
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That part is chill.
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But to get carbon, you need to fuse three helium nuclei together.
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But beryllium-8 is really unstable.
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It falls apart in about 10 to the negative 16th of a second.
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That's one 10 quadrillionth of a second.
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So the third helium nucleus has to fuse with the beryllium in that fraction of a second, and when you run the numbers,
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the reaction is far too slow.
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So according to nuclear physics, stars should make almost no carbon. But clearly they do.
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Carbon is the fourth most abundant element in the universe.
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You and I are made out of carbon.
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Hoyle knew that we were missing something, and predicted that there had to be an excited energy state,
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a resonance, sitting near 7.68 mega electron volts,
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which would vastly increase the chances of three helium nuclei coming together to fuse into carbon.
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He was visiting Caltech at the time and he asked his experimentalist colleagues to look for this resonance.
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And they found it at 7.65 mega electron volts, half a percent off from Hoyle's prediction.
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It is now known as the Hoyle resonance.
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And if we shift the Hoyle resonance up by just a few percent, stars make essentially no carbon.
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down by a similar amount, and they make carbon, but barely any oxygen.
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It's like the dial is set to exactly where it needs to be to produce both carbon and oxygen, which are so essential for life.
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What people don't realize is that the lack of a resonance in oxygen stocks all of that carbon being converted into oxygen.
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There's this balance between a resonance occurring in carbon and a lack of a resonance in oxygen
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means that we've built up that useful carbon atom in the universe.
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And when you look closely at the laws of physics, you keep finding numbers that look dialed in.
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Values where a small change would mean no chemistry, no complexity, no stars or galaxies or us.
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It's weird, it turns up in so many places and the explanations are.. um...
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Well, we'll get to that.
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When you look at the laws of physics, there are the equations and in those equations there are constants.
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Like this is Newtonian gravity and this is the general theory of relativity and they predict how things fall to the ground, how planets move around the Sun,
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etc, etc. Except that they don't.
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Not without this constant.
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Throughout all of our laws of physics are these numbers, right?
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The fundamental constants.
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And the thing is that the mathematics of physics is sterile until you know those constants.
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And the only way that we get those constants is by asking nature.
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So I could give you Newton's law of gravitation, right?
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But there's no way you can calculate the orbit of the moon, how long it's going to take, etc. Until you know how big G is.
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The big G in these equations is the strength of gravity, the universal gravitational constant.
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In our universe, it's around 6.674 times 10 to the negative 11 meters cubed per kilogram per second squared.
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And you can't get this number from the theory.
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It's not something that can be derived, it had to be measured.
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Which Henry Cavendish first did in 1798.
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He suspended two small lead spheres from a torsion wire inside of a sealed shed
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and watched the wire twist as two 350-pound lead bowls pull the small spheres towards them.
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The force he was measuring was about the weight of a dust speck, so the signal was so faint that he had to watch it through a telescope from outside the shed,
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because his own body heat would have stirred up the air so much and swamped the signal from gravity.
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And by measuring how much the wire twisted, he was able to figure out the strength of gravity.
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There's an amazing video about this experiment by Steve Mould, by the way.
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If you haven't seen it, you really should.
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Hey, you might have noticed something.
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Units.
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The meters, the seconds, the kilograms, they're all human inventions and are arbitrary.
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And you're right, but what isn't arbitrary are the ratios between the constants.
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The mass of a proton and the mass of an electron are also constants that we had to measure,
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and a proton has a mass that's a thousand eight hundred and thirty-six times greater than that of an electron, and it doesn't matter what units you are measuring in.
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And, of course, the actual value depends on the units that you use, but you can express combinations of constants in dimensionless ways.
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So there are about 30 of these constants, these dials.
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They aren't set by any of our theories, so in theory, they could be different numbers.
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So the obvious question is, what if they were different numbers?
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What happens when you start turning these dials?
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So, let's turn some dials.
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In our universe, neutrons are heavier than protons by 1.29 MeV,
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which is about 0.14% of a neutron's mass, or two and a half electron masses.
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The difference in their mass is tiny.
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In our universe, a free neutron can decay into a proton, but a free proton is stable.
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And this is really important, because if a proton was heavier than a neutron, the proton would decay into neutrons.
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This means hydrogen atoms would decay, protons would capture their electrons and turn into neutrons.
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A universe without even hydrogen, let alone the rest of the periodic table, is likely very, very boring.
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Just endless neutrons doing basically nothing.
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Another dialogue we can mess with is the strength of the strong force, the fundamental force that keeps atoms together.
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The first step in the chain that powers the Sun is fusing two protons into deuterium.
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Deuterium is bound by just 2.2 mega electron volts, it's barely holding on.
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Weaken the strong force by just a few percent and deuterium falls apart, and the fusion chain never gets started.
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Fusion does not get started.
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The thing that makes stars...
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stars.
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The stars that make every element of the periodic table inside them.
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The stars that burn out and scatter their heavy elements across the universe.
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The stardust that we're made of.
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Those stars.
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If the strong force was just a few percent weaker, we'd have no stars.
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And what you rapidly find is that it's easy to kill a universe.
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And what I mean by that is you can end up with universes that are definitely not going to be habitable.
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You rob them of the key thing that we think is important about life
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and that's complexity to encode information and all this kind of stuff.
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The question then turns to is then, okay, we appeared to live in a universe where we've got constants that allow us to be here.
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And is that telling us something?
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Is there something underlying about the nature of the universe?
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Because we live in a universe that seems to be in some sense special.
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We can also mess with gravity.
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Compared to the other fundamental forces, gravity is pathetically weak.
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Which is why a fridge magnet can beat out the pull of an entire planet.
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The electric repulsion between two protons in a nucleus is about
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10 to the 36 that's a trillion trillion trillion times stronger than the gravitational pull between them.
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So why is gravity so weak compared to the other forces?
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Well, we don't know.
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But if we make it a million times stronger, I know that sounds like a lot, but now it's 10 to the 30 instead of 10 to 36, it's still so much weaker than the other forces.
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Well, in that universe, stars will live for about 10,000 years
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and not 10 billion likely not enough time for complexity or life to arise.
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Okay, let's just mess with one more constant.
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Please indulge me.
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In 1929, Edwin Hubble discovered that the universe was expanding.
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But we have stuff in this universe, and the stuff being acted upon by gravity should be getting pulled in.
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So the thinking was that the faraway galaxies flying away from us should be slowing down.
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But measuring this is really tricky.
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It took another 70 years for us to find this answer.
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Here's how we did it.
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In our universe, we have this particular kind of supernova, called a Type Ia supernova, which occurs when a white dwarf sucks in the matter from another star that it's orbiting next to.
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And at a certain point, around 1.44 solar masses known as the Chandrasekhar limit,
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the electron degeneracy pressure that's keeping the whole structure up gives out.
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The details are interesting and complex as usual and I'll get to it in another video, but what matters here is that these stars explode at basically the same brightness,
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so you can use them as standard candles.
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This is what astronomers call them.
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And the brightness of an object follows the inverse square law.
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A candle that is twice as far away is only a quarter as bright.
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So, if you know how bright the thing that you're measuring actually is, compared to what you measure it to be, you can figure out the distance.
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And you can measure how fast something is moving away from you by seeing how the light is redshifted.
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The light waves that are moving away from you faster get stretched out more.
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In the late 1990s, two teams, the Supernova Cosmology Project, led by Sol Perlmutter out of Berkeley, and the Hi-Z Supernova search team led by Brian Schmidt out of Canberra
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were using this method to measure the rate of the expansion of the universe.
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But type 1a supernovae are rare, so how did they find them?
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Well, they photographed thousands of galaxies and then they came back weeks later, photographed them all again, and had a computer subtract one image from the other.
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If you see a new bright spot appear, it might be a 1a supernova.
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And the results they got were very surprising.
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So surprising that they thought they made a mistake.
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The rate of expansion of the universe wasn't slowing down.
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It was speeding up.
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The cosmological constant was positive.
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There is something that is pushing the universe apart, not just counteracting the pull of gravity, but overpowering it.
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We now call it dark energy, and we're still not sure what it is.
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In 2011, Perlmutter, Schmidt and Rees won the Nobel Prize.
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But the history of the cosmological constant goes back more than a hundred years.
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Back in 1917, Einstein had a problem.
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His own equations insisted that the universe should be expanding or contracting, but everyone knew that it had to be static and eternal.
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So he added a term to the equations by hand, a kind of anti-gravity built into space itself,
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tuned precisely to hold everything still, the cosmological constant.
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Hey, quick side note, there's a story that people say
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that Einstein referred to his addition of the cosmological constant as his biggest blunder,
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and we actually don't have first-hand sources of him saying that.
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There is a book by George Gamow from 1970 and an article from 1956 and also maybe a couple of other scientists,
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a couple of other physicists that have heard him say something like that.
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We don't know if he called it his biggest blunder, but we do know that he hated it.
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In a letter to Georges Lemaitre he wrote, Since I had introduced this lambda term, I had always a bad conscience.
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I had found it very ugly indeed that the field law of gravitation should be composed of two logically independent terms,
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which are connected by addition.
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I cannot help to feel as strongly, and I am unable to believe that such an ugly thing should be realized in nature.
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Which is a shame for Einstein, because such an ugly thing is realized in nature.
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The cosmological constant exists and it seems fine-tuned.
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Anyway, dark energy, what could it be?
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Well, there's an obvious candidate.
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Empty space isn't truly empty.
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Take a box, get rid of every atom, every particle, and then cool it to absolute zero.
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Quantum field theory says that vacuum is still not empty.
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There are virtual particles and antiparticles popping up, buzzing with energy.
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exactly the kind of thing that could potentially push space apart.
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So we know that there is this underlying field of energy in the universe
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which over the last five billion years has come to dominate and is driving the expansion of the universe faster and faster.
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So this dark energy discovered at the end of the 90s.
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And when you do your calculation of quantum field theory about how much dark energy you expect,
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The amount that we have is a teeny sliver compared to what there could be.
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It's one part in 10 to the 120.
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Some ridiculous number.
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The theory predicts
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that the vacuum energy of empty space should be 10 to the 120 times bigger than what we measure in our universe.
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If dark energy is the energy of empty space, which would make sense, we're off by a factor of 10 to the 120.
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It has been called the worst prediction in the history of physics.
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But this dark energy is also fine-tuned.
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A hundred times more than what we measure in our universe and galaxies don't form, or only very small ones.
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And you can rapidly see that if you make it too large, then the universe would be born, and then all the matter in the universe would be spread out,
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such that it would be completely diluted, that you'd never form stars,
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never form galaxies, etc. So you could potentially wind the amount of dark energy up by a factor of, let's say, 100.
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Okay, now you might say, oh, 100, that sounds huge, right?
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A factor of 100 larger.
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But a factor of 100 in 10 to the power of
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120 is still next to nothing right it's a small volume
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so we we there is a little bit of give in there
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but compared to the potential range right there um it's it's it's it's tiny
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so instead of a big galaxy like the milky way
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that you have today you end up with these small compact little blobs of galaxies
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and they are not good places for life
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because you get supernova in there you get black holes in
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there you get all kinds of stuff going on in a small volume, which is part of the reason why the center of our Milky Way is not a good place for life.
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It's too much going on in too small a volume.
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So I say a factor of 100, but the volume is probably smaller than that.
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One of the things that I find wild here is that Steven Weinberg predicted a positive cosmological constant back in 1987,
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a decade before we had the measurement of it.
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He reasoned that because we exist and that galaxies are pretty big,
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we must live in a universe where there is a small but non-zero amount of dark energy, a few times more than the density of matter,
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which is about what we measured.
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I find this paper to be remarkable because it uses the fact that we exist to make a prediction about the universe.
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Weinberg's prediction is based on the existence of us and of galaxies, And so, the value of the cosmological constant must be low enough for galaxies to form.
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And this prediction ended up being basically right.
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I mean, how cool is that?
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But it's not just the constants of nature that allow for complexity to arise.
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We can mess with some other knobs too, for example, the initial conditions.
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Our universe started in a very, very low entropy state.
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This is the whole second law of thermodynamics thing, that over time entropy goes up, things spread out, they become mixed.
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This is why we have the arrow of time.
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Another way of saying low entropy is saying high available energy.
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The ability to do complex, interesting stuff.
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If the universe was born in this high entropy state, you don't get complexity.
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Why is the initial state, why are the initial conditions of the universe such a low entropy state?
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Why was it this way?
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This is super weird.
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Our universe was born in a state where matter was smoothly distributed,
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so it had the potential to collapse and clump together into stars and then into galaxies galaxies.
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So it was born in a low entropy state.
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It was born with lots of possible energy.
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But if the universe had been born instead with all of the matter clumped together and locked into black holes,
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well all of that gravitational energy is gone, right?
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You can't do anything really with black holes.
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You can bring them together, but what are you going to do with that?
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One of the things that we take for granted is the entire existence of the arrow of time.
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Why does time point in one direction?
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It doesn't have to.
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There is nothing in the equations of relativity that tells you which direction time should run in.
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Can you imagine physics if we had time running in both directions?
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That is possibly one of the biggest fine-tuning.
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Also, the dimensions that we live in, three dimensions of space and one of time, are conducive to complexity.
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In two, everything's really boring and in four, well, orbits don't really work.
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And I can't even imagine what two dimensions of time would look like, let alone more.
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I mean, why three dimensions of space and one of time?
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There's nothing in the equations of relativity that says I can't add another minus dt squared term.
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I can add as many as I want and I can do all my laws of physics.
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But what does that mean if you were a being in that universe with multiple dimensions of time?
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So I can play these games, but if I want to then talk about habitability in those universes,
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then I've got to talk about how the laws of physics behave in those universes.
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So how should we think about all of this?
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Well, to some degree, this is obvious, right?
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We're here because we're here.
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Out of all of the possible universes, with all the possible settings of the dials,
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the only ones that ever get noticed are the ones where the dials let observers exist and do the noticing.
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A universe with no stars, no chemistry, no brains, has nobody in it to marvel at how dead it is.
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Douglas Adams, the author of Hitchhiker's Guide,
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wrote about the sentient puddle where after some rain a puddle forms and gains sentience and thinks to itself,
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this is an interesting world I find myself in, an interesting hole I find myself in.
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Fits me rather neatly, doesn't it?
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In fact it fits me staggeringly well.
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Must have been made to have me in it.
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So maybe it's as simple as that.
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Maybe it's just we're here and that's it and stop asking questions and that just doesn't feel satisfying to me.
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It doesn't feel scientific.
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Throughout the whole history of science the stop asking questions things are the way they are that approach hasn't been very successful.
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Being painfully annoyingly curious has been.
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So maybe there is a deeper theory of physics that we're missing that explains why the constants are the way they are,
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why the initial conditions are the way they are, that explains the three dimensions of space and one of time etc etc
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and that would be really cool but it does just push fine-tuning to another level.
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You go look physics is done, there is no freedom.
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These are the ways that the fundamental constants are.
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And you say, right, job done.
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Except job isn't done.
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Why?
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Because the library of possible mathematics is infinite
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and the mathematics used by this universe is a slim volume in an infinite library.
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Why did our universe choose that set of mathematics to describe the universe?
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Or maybe a way to explain all of this is theological.
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If there are all these parameters, all these knobs that seem so fine-tuned for life,
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maybe there's a fine-tuner, a creator that made this universe just so perfect for us.
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So let me just explain the context of the book, right?
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So it's written by myself and Luke Barnes.
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I am an atheist, Luke is a theist.
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And we have seen this argument from both sides.
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For Luke, he sees plenty of people saying that fine-tuning is evidence of a creator.
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For me, who doesn't have that particular hypothesis,
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that this is evidence for something deeper going on with the nature of the universe.
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For me, the notion that saying, if we just do more physics, we'll solve it, I don't think we do.
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I think we just move fine-tune in elsewhere.
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So for me, the thing that helps me sleep at night is the notion of the multiverse, right?
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That there is an unfathomably large collection of other universes where the constants of nature and the initial conditions,
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and maybe even the mathematical structures, are different.
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Some small percentage of them allow for complexity and for life, but most don't.
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And we're one of the lucky ones.
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We live in a fortunate universe.
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We have to let science play out.
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What we shouldn't do is let noisy people shut down the debate because they don't like a concept.
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Right?
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And I've seen plenty of people say, you know, should not talk about the multiverse.
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It's not the way science works.
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Science is playing out and we are not at the end game.
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And a lot of smart people fall into these different camps.
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Hoyle, for example, said, a common sense interpretation of the facts suggests that a super intellect has monkeyed with physics.
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Martin Rees looks at the same data and this pushes him towards the multiverse hypothesis.
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I don't know what to make of this.
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It's why this tab has been open in my brain for a decade.
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I don't even know how seriously to take it.
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Personally, I lean towards the multiverse argument
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because there is a lot of good reasons to take the multiverse hypothesis seriously that's independent of fine-tuning.
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But I just don't know.
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I genuinely don't know what to do with this information.
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I just think it's interesting and really neat and very weird.
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When I worked at Veritasium, we really tried to tell stories that had a clear beginning, middle, and end.
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The setup, the building tension, and then the resolution something that put a nice, neat little bow on the video.
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There is no bow on this video.
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I want to say that I'm sorry that I'm not giving you a resolution here, but I'm just not.
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Humanity does not know the resolutions to some massive, fascinating, consequential problems.
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As John Wheeler famously said, as the island of knowledge grows, so does the shoreline of ignorance.
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When we learn things about the universe, we end up getting more and more questions to ask, more mysteries to unlock.
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That's lovely.
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That's how science works.
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And I like that I've had this problem in my brain for a decade.
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I like that this tab is open in my brain.
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I also like that this is an advanced question to ask.
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This feels like a tremendous success of science to get to
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the point where we are rudely slapped in the face of how fortunate our universe seems to be
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and how strange that is.
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I love being reminded of our insignificance and of our fortune.
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If you want to learn more about cosmological fine-tuning, you just have to read Grant and Luke's book.
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It's really, really approachable and it's beautifully written.
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It's really, really good.
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As always, the reference list is in the description, including a few books that I'd recommend on the topic.
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And if you have a well-paying job and you find the stuff that I make to be valuable, I would really appreciate it if you could subscribe to my Patreon.
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Thank you for being here.
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I'm grateful to share this fortunate universe with you.
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Sobre esta lição
Você está praticando inglês com "The Most Controversial Idea In Physics" usando a técnica de Shadowing.
O que é a Técnica de Shadowing?
Shadowing é uma técnica de aprendizado de idiomas com base científica, originalmente desenvolvida para o treinamento de intérpretes profissionais. O método é simples, mas poderoso: você ouve áudio em inglês nativo e repete imediatamente em voz alta — como uma sombra seguindo o falante com 1-2 segundos de atraso. Pesquisas mostram melhora significativa na precisão da pronúncia, entonação, ritmo, sons conectados, compreensão auditiva e fluência na fala.