Janna Levin on Why Nature May Try Every Physically Possible Idea

Levin begins by pointing to the questions the series takes up: whether everything that is possible in the laws of physics is inevitable, and whether travel to the future or the past could be possible. She says that most of what is out there is in the form of dark energy.

She adds that the end of everything might come through black holes, and that a theory of quantum gravity is where scientists hope to understand these questions. Tyson introduces her as a Claire Tow Professor of Physics and Astronomy at Barnard College of Columbia University.

Tyson says the conversation will cover some of the weirdest and wackiest theories of the universe, which Levin covers in a new series appearing on the StarTalk channel called 'In Theory.' Levin says that is where the big ideas happen and that the hope is nature finds a way.

She recalls a sign on a door at Princeton reading 'Never trust an observation unless it's confirmed by a theory,' which she notes inverts the usual adage that theorists are chastised for not being experimentally verifiable. She says sometimes it takes a few hundred years of patience.

Levin says that the laws of physics tell theorists what is possible, and that people used to imagine nature picked a specific example. She says that over and over again nature kept showing it was rolling the dice and trying different combinations, whether in planets, organisms or stars, because the laws of physics allow more than what is seen at any given moment.

She connects this to evolution as trying again and again under pressure, experimenting with every possibility. She cautions that not all experiments work and not all can be tried on this planet, but suggests that on other planets, or in other universes, more might be tested. Her question, she says, is whether something that is theoretically possible has perhaps been tried by nature, and whether it might be inevitable.

She adds that as a theorist she explores ideas even when she does not know what the experiment or observation will be, or whether it will be possible to make in her lifetime, either because it takes too long or costs too much money.

Levin notes that the solar system has eight planets and that most star systems in the galaxy have multiple planets, with the total reaching into the trillions. Tyson points out that the universe has roughly a trillion galaxies, and the discussion turns to whether every combination might be attempted.

Tyson argues that if Earth is not at the center of the galaxy or the solar system, and is not unique among galaxies, then perhaps it is not unique in having had a big bang. He asks whether this would break the pattern.

Levin responds that the idea of a multiverse becomes a question of language. She asks whether universes might interact or collide, for instance whether the big bang could have been a collision with another universe in the past, or whether universes might be completely disconnected. She says the multiverse is currently indistinct because it is not understood well enough yet.

Tyson invites viewers to check the series out and describes the moment as damn near pre-Copernican, as we are on the cusp of realizing things like other planetary systems. Levin says Copernicus set us right on many things, and that since then the pattern has kept going, with Earth no longer at the center of the solar system.

Levin says she has six episodes, and that the first is about the multiverse. Tyson says the subject of the first installment is the multiverse, and asks how many installments there are.

Levin and Tyson discuss that dark matter and dark energy drive the universe, and that humans are not made of most of what the universe is made of. Levin describes a game in which one imagines being a dark astronomer who sees a galaxy surrounded by a vast halo of dark matter extending hundreds of times beyond the visible stars, and who notes that the visible part is less than 5 percent of what is in the universe, maybe around 15 percent of what is in the galaxy.

Levin says that humans would be like jewels, since they are luminous in ways that dark matter is not, so that against all odds one finds these tiny luminous jewels in a sea of dark matter. Tyson jokes about dark matter aliens putting humans on their jewelry.

Levin recounts that Karl Schwarzschild, writing to Einstein from the Russian front during World War I, had mathematically solved Einstein's equations. Schwarzschild died from an infection contracted on the front within six months of the letter. The solution, which is now called the black hole, took about half a century to receive that name.

Levin says Einstein knew the math was right and was extremely impressed that the solution could be found so simply. However, he thought nature would protect us from their formation and did not believe they would be in the universe.

Levin notes that even though Einstein's own theory and equations gave that result, the equations omitted the fact that matter does not like to be crushed.

Levin describes the lesson as nature figuring out a way to do something that people had considered impossible. She says that nature found a way to form black holes through the collapse of a very massive star, and that Einstein could not foresee how mass could overcome its internal forces. She says that scientific discovery reveals how astoundingly clever nature is, and that science is only catching up in trying to describe it.

Levin says the interesting point is not something nobody imagined, since the premise of the series is that everything in it was imagined. She says that one can conceive of something and then over and over again nature finds a way to do it.

Tyson and Levin joke about Einstein's mistakes and his reluctance toward dark energy, which is in his equations even though he did not like it. Levin describes the scientific achievement as nature being the real genius, with scientists only trying to formalize, describe and understand it.

Levin describes how Newton's gravitational equations describe the Moon orbiting Earth and Earth orbiting the Sun. The same laws apply to the moons of Jupiter orbiting Jupiter, which is not a star. This was a first hint that laws of physics established on Earth may hold in the heavens as well.

Levin says Newton thought of mass as a gravitational charge that big celestial bodies feel against each other, and that mapping that all the way to the sky was a crazy idea at the time.

Tyson describes Newton's gravity as a very simple system of equations that predicted Kepler's laws. He says Einstein then replaces this with a description of curved spacetime, and that Einstein does not treat gravity as a force.

Levin says Einstein struggled to reproduce what Newton could do at low velocities and low energies, where Newtonian gravity was valid and uncontested. She says that if he could not reproduce Newton, he knew he was wrong. The two are not incompatible, since Einstein's theory envelops Newtonian gravity and goes beyond it with predictions that are strictly relativistic.

She points to the bending of light around an eclipse that Eddington saw in 1919, which verified Einstein's general relativity. Tyson remarks that the light would have bent under Newtonian rules, and Levin says what mattered was how much it bent.

Levin and Tyson discuss that astronomers had already figured out that another body was perturbing Mercury's orbit, which they had hypothesized as a planet called Vulcan, lost in the glare of the Sun. Levin says it was quite natural to assume something was perturbing it, but that it was more reasonable to need a completely new law of gravitational physics that transcends Newton.

Levin says Einstein was very devout in his adherence to Newtonian gravity and wanted only to take a step beyond it, and that he said he had heart palpitations when he was able to match the observed result.

Levin says that Newton and Einstein were not simply wrong but incomplete. Newton's laws still work because they were experimentally verified, just as a pedal bike still works after the invention of the electric bike. Any theory beyond Newton must reproduce Newton's laws, and relativity must be reproduced by any theory beyond Einstein.

Levin says that there must be a quantum theory of gravity, because the universe collides at the smallest scales and highest energies with curved spacetime. She describes the current situation as a shotgun marriage between the two, and notes that Einstein wanted to throw out quantum mechanics even though it seems to be the theory that endures.

Levin says that wormholes can be written on paper within relativity but cannot be made in the lab yet, because scientists do not know of energy sources that behave the required way. Some known effects can temporarily trap energy that looks somewhat like negative energy, but no one yet knows how to produce it in a lab.

Levin says the laws of physics do not prevent wormholes, though some conjectures claim that no such energy can exist.

Levin defines a conjecture as a supposition that a law has not yet been discovered but that, when it is, it will adhere to a given principle. Tyson gives the example that a conjecture might be that negative energies are forbidden.

Levin explains that relativity alone allows solutions involving travel backwards in time. Hawking stated what he called the chronology protection conjecture, the idea that once quantum mechanics or quantum gravity is understood, it will protect us from paths that violate chronology. Levin notes that a conjecture is not a law, and not a proof, and that many conjectures have been left behind by later discoveries.

In a lighter exchange, Tyson says Moby Dick was a bomb with vicious reviews, and that Melville died thinking it was his great work. The two then return to a discussion of dimensions and black holes, which Levin says she has written two books about, and Tyson names one of them, The Black Hole Blues.

Asked about so-called ambulance chasing theorists, Levin describes the pattern of a tiny observation that people are not sure about, followed by fifteen papers by theorists trying to fit it. She says this is not her favorite approach, and that the observation may later turn out to be wrong.

Levin says the great theorists are out there, and that the series pays respect to them by honoring deeper ideas whose truth is not yet known, or whether they can be observed or verified. She describes the series as curiosity about whether every idea consistent with the laws of physics might be realized somewhere, sometime.

Levin also considers a question about a theory that predicts something not found in the universe, and says the dominant components driving the universe, dark matter and dark energy, have not been discovered, and that every experimental physicist faces the dilemma of whether to keep looking.