## Guest Post: Chip Sebens on the Many-Interacting-Worlds Approach to Quantum Mechanics

I got to know Charles “Chip” Sebens back in 2012, when he emailed to ask if he could spend the summer at Caltech. Chip is a graduate student in the philosophy department at the University of Michigan, and like many philosophers of physics, knows the technical background behind relativity and quantum mechanics very well. Chip had funding from NSF, and I like talking to philosophers, so I said why not?

We had an extremely productive summer, focusing on our different stances toward quantum mechanics. At the time I was a casual adherent of the Everett (many-worlds) formulation, but had never thought about it carefully. Chip was skeptical, in particular because he thought there were good reasons to believe that EQM should predict equal probabilities for being on any branch of the wave function, rather than the amplitude-squared probabilities of the real-world Born Rule. Fortunately, I won, although the reason I won was mostly because Chip figured out what was going on. We ended up writing a paper explaining why the Born Rule naturally emerges from EQM under some simple assumptions. Now I have graduated from being a casual adherent to a slightly more serious one.

But that doesn’t mean Everett is right, and it’s worth looking at other formulations. Chip was good enough to accept my request that he write a guest blog post about another approach that’s been in the news lately: a “Newtonian” or “Many-Interacting-Worlds” formulation of quantum mechanics, which he has helped to pioneer.

In Newtonian physics objects always have definite locations. They are never in two places at once. To determine how an object will move one simply needs to add up the various forces acting on it and from these calculate the object’s acceleration. This framework is generally taken to be inadequate for explaining the quantum behavior of subatomic particles like electrons and protons. We are told that quantum theory requires us to revise this classical picture of the world, but what picture of reality is supposed to take its place is unclear. There is little consensus on many foundational questions: Is quantum randomness fundamental or a result of our ignorance? Do electrons have well-defined properties before measurement? Is the Schrödinger equation always obeyed? Are there parallel universes?

Some of us feel that the theory is understood well enough to be getting on with. Even though we might not know what electrons are up to when no one is looking, we know how to apply the theory to make predictions for the results of experiments. Much progress has been made―observe the wonder of the standard model―without answering these foundational questions. Perhaps one day with insight gained from new physics we can return to these basic questions. I will call those with such a mindset the doers. Richard Feynman was a doer:

“It will be difficult. But the difficulty really is psychological and exists in the perpetual torment that results from your saying to yourself, ‘But how can it be like that?’ which is a reflection of uncontrolled but utterly vain desire to see it in terms of something familiar. I will not describe it in terms of an analogy with something familiar; I will simply describe it. … I think I can safely say that nobody understands quantum mechanics. … Do not keep saying to yourself, if you can possibly avoid it, ‘But how can it be like that?’ because you will get ‘down the drain’, into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.”

-Feynman, The Character of Physical Law (chapter 6, pg. 129)

In contrast to the doers, there are the dreamers. Dreamers, although they may often use the theory without worrying about its foundations, are unsatisfied with standard presentations of quantum mechanics. They want to know “how it can be like that” and have offered a variety of alternative ways of filling in the details. Doers denigrate the dreamers for being unproductive, getting lost “down the drain.” Dreamers criticize the doers for giving up on one of the central goals of physics, understanding nature, to focus exclusively on another, controlling it. But even by the lights of the doer’s primary mission―being able to make accurate predictions for a wide variety of experiments―there are reasons to dream:

“Suppose you have two theories, A and B, which look completely different psychologically, with different ideas in them and so on, but that all consequences that are computed from each are exactly the same, and both agree with experiment. … how are we going to decide which one is right? There is no way by science, because they both agree with experiment to the same extent. … However, for psychological reasons, in order to guess new theories, these two things may be very far from equivalent, because one gives a man different ideas from the other. By putting the theory in a certain kind of framework you get an idea of what to change. … Therefore psychologically we must keep all the theories in our heads, and every theoretical physicist who is any good knows six or seven different theoretical representations for exactly the same physics.”

-Feynman, The Character of Physical Law (chapter 7, pg. 168)

In the spirit of finding alternative versions of quantum mechanics―whether they agree exactly or only approximately on experimental consequences―let me describe an exciting new option which has recently been proposed by Hall, Deckert, and Wiseman (in Physical Review X) and myself (forthcoming in Philosophy of Science), receiving media attention in: Nature, New Scientist, Cosmos, Huffington Post, Huffington Post Blog, FQXi podcast… Somewhat similar ideas have been put forward by Böstrom, Schiff and Poirier, and Tipler. The new approach seeks to take seriously quantum theory’s hydrodynamic formulation which was developed by Erwin Madelung in the 1920s. Although the proposal is distinct from the many-worlds interpretation, it also involves the postulation of parallel universes. The proposed multiverse picture is not the quantum mechanics of college textbooks, but just because the theory looks so “completely different psychologically” it might aid the development of new physics or new calculational techniques (even if this radical picture of reality ultimately turns out to be incorrect).

Let’s begin with an entirely reasonable question a dreamer might ask about quantum mechanics.

“I understand water waves and sound waves. These waves are made of particles. A sound wave is a compression wave that results from particles of air bunching up in certain regions and vacating other. Waves play a central role in quantum mechanics. Is it possible to understand these waves as being made of some things?”

There are a variety of reasons to think the answer is no, but they can be overcome. In quantum mechanics, the state of a system is described by a wave function Ψ. Consider a single particle in the famous double-slit experiment. In this experiment the one particle initially passes through both slits (in its quantum way) and then at the end is observed hitting somewhere on a screen. The state of the particle is described by a wave function which assigns a complex number to each point in space at each time. The wave function is initially centered on the two slits. Then, as the particle approaches the detection screen, an interference pattern emerges; the particle behaves like a wave.

Figure 1: The evolution of Ψ with the amount of color proportional to the amplitude (a.k.a. magnitude) and the hue indicating the phase of Ψ.

There’s a problem with thinking of the wave as made of something: the wave function assigns strange complex numbers to points in space instead of familiar real numbers. This can be resolved by focusing on |Ψ|2, the squared amplitude of the wave function, which is always a positive real number.

Figure 2: The evolution of |Ψ|2.

We normally think of |Ψ|2 as giving the probability of finding the particle somewhere. But, to entertain the dreamer’s idea about quantum waves, let’s instead think of |Ψ|2 as giving a density of particles. Whereas figure 2 is normally interpreted as showing the evolution of the probability distribution for a single particle, instead understand it as showing the distribution of a large number of particles: initially bunched up at the two slits and later spread out in bands at the detector (figure 3). Although I won’t go into the details here, we can actually understand the way that wave changes in time as resulting from interactions between these particles, from the particles pushing each other around. The Schrödinger equation, which is normally used to describe the way the wave function changes, is then viewed as consequence of this interaction.

Figure 3: The evolution of particles with |Ψ|2 as the density. This animation is meant to help visualize the idea, but don’t take the precise motions of the particles too seriously. Although we know how the particles move en masse, we don’t know precisely how individual particles move.

In solving the problem about complex numbers, we’ve created two new problems: How can there really be a large number of particles if we only ever see one show up on the detector at the end? If |Ψ|2 is now telling us about densities and not probabilities, what does it have to do with probabilities?

Removing a simplification in the standard story will help. Instead of focusing on the wave function of a single particle, let’s consider all particles at once. To describe the state of a collection of particles it turns out we can’t just give each particle its own wave function. This would miss out on an important feature of quantum mechanics: entanglement. The state of one particle may be inextricably linked to the state of another. Instead of having a wave function for each particle, a single universal wave function describes the collection of particles.

The universal wave function takes as input a position for each particle as well as the time. The position of a single particle is given by a point in familiar three dimensional space. The positions of all particles can be given by a single point in a very high dimensional space, configuration space: the first three dimensions of configuration space give the position of particle 1, the next three give the position of particle 2, etc. The universal wave function Ψ assigns a complex number to each point of configuration space at each time.  |Ψ|2 then assigns a positive real number to each point of configuration space (at each time). Can we understand this as a density of some things?

A single point in configuration space specifies the locations of all particles, a way all things might be arranged, a way the world might be. If there is only one world, then only one point in configuration space is special: it accurately captures where all the particles are. If there are many worlds, then many points in configuration space are special: each accurately captures where the particles are in some world. We could describe how densely packed these special points are, which regions of configuration space contain many worlds and which regions contain few. We can understand |Ψ|2 as giving the density of worlds in configuration space. This might seem radical, but it is the natural extension of the answer to the dreamer’s question depicted in figure 3.

Now that we have moved to a theory with many worlds, the first problem above can be answered: The reason that we only see one particle hit the detector in the double-slit experiment is that only one of the particles in figure 3 is in our world. When the particles hit the detection screen at the end we only see our own. The rest of the particles, though not part of our world, do interact with ours. They are responsible for the swerves in our particle’s trajectory. (Because of this feature, Hall, Deckert, and Wiseman have coined the name “Many Interacting Worlds” for the approach.)

Figure 4: The evolution of particles in figure 3 with the particle that lives in our world highlighted.

No matter how knowledgeable and observant you are, you cannot know precisely where every single particle in the universe is located. Put another way, you don’t know where our world is located in configuration space. Since the regions of configuration space where |Ψ|2 is large have more worlds in them and more people like you wondering which world they’re in, you should expect to be in a region of configuration space where|Ψ|2 is large. (Aside: this strategy of counting each copy of oneself as equally likely is not so plausible in the old many-worlds interpretation.) Thus the connection between |Ψ|2 and probability is not a fundamental postulate of the theory, but a result of proper reasoning given this picture of reality.

There is of course much more to the story than what’s been said here. One particularly intriguing consequence of the new approach is that the three sentence characterization of Newtonian physics with which this post began is met. In that sense, this theory makes quantum mechanics look like classical physics. For this reason, in my paper I gave the theory the name “Newtonian Quantum Mechanics.”

Posted in Guest Post, Philosophy, Science | 19 Comments

## Slow Life

Watch and savor this remarkable video by Daniel Stoupin. It shows tiny marine animals in motion — motions that are typically so slow that we would never notice, here enormously sped-up so that humans can appreciate them.

Slow Life from Daniel Stoupin on Vimeo.

I found it at this blog post by Peter Godfrey-Smith, a philosopher of biology. He notes that some kinds of basic processes, like breathing, are likely common to creatures that live at all different timescales; but others, like reaching out and grasping things, might not be open to creatures in the slow domain. Which raises the question: what kinds of motion are available to slow life that we fast-movers can’t experience?

Not all timescales are created equal. In the real world, the size of atoms sets a fundamental length, and chemical reactions set fundamental times, out of which everything larger is composed. We will never find a naturally-occurring life form, here on Earth or elsewhere in the universe, whose heart beats once per zeptosecond. But who knows? Maybe there are beings whose “hearts” beat once per millennium.

Posted in Arts, Science | 11 Comments

## Where Have We Tested Gravity?

General relativity is a rich theory that makes a wide variety of experimental predictions. It’s been tested many ways, and always seems to pass with flying colors. But there’s always the possibility that a different test in a new regime will reveal some anomalous behavior, which would open the door to a revolution in our understanding of gravity. (I didn’t say it was a likely possibility, but you don’t know until you try.)

Not every experiment tests different things; sometimes one set of observations is done with a novel technique, but is actually just re-examining a physical regime that has already been well-explored. So it’s interesting to have a handle on what regimes we have already tested. For GR, that’s not such an easy question; it’s difficult to compare tests like gravitational redshift, the binary pulsar, and Big Bang nucleosynthesis.

So it’s good to see a new paper that at least takes a stab at putting it all together:

Linking Tests of Gravity On All Scales: from the Strong-Field Regime to Cosmology
Tessa Baker, Dimitrios Psaltis, Constantinos Skordis

The current effort to test General Relativity employs multiple disparate formalisms for different observables, obscuring the relations between laboratory, astrophysical and cosmological constraints. To remedy this situation, we develop a parameter space for comparing tests of gravity on all scales in the universe. In particular, we present new methods for linking cosmological large-scale structure, the Cosmic Microwave Background and gravitational waves with classic PPN tests of gravity. Diagrams of this gravitational parameter space reveal a noticeable untested regime. The untested window, which separates small-scale systems from the troubled cosmological regime, could potentially hide the onset of corrections to General Relativity.

The idea is to find a simple way of characterizing different tests of GR so that they can be directly compared. This will always be something of an art as well as a science — the metric tensor has ten independent parameters (six of which are physical, given four coordinates we can choose), and there are a lot of ways they can combine together, so there’s little hope of a parameterization that is both easy to grasp and covers all bases.

Still, you can make some reasonable assumptions and see whether you make progress. Baker et al. have defined two parameters: the “Potential” ε, which roughly tells you how deep the gravitational well is, and the “Curvature” ξ, which tells you how strongly the field is changing through space. Again — these are reasonable things to look at, but not really comprehensive. Nevertheless, you can make a nice plot that shows where different experimental constraints lie in your new parameter space.

The nice thing is that there’s a lot of parameter space that is unexplored! You can think of this plot as a finding chart for experimenters who want to dream up new ways to test our best understanding of gravity in new regimes.

One caveat: it would be extremely surprising indeed if gravity didn’t conform to GR in these regimes. The philosophy of effective field theory gives us a very definite expectation for where our theories should break down: on length scales shorter than where we have tested the theory. It would be weird, although certainly not impossible, for a theory of gravity to work with exquisite precision in our Solar System, but break down on the scales of galaxies or cosmology. It’s not impossible, but that fact should weigh heavily in one’s personal Bayesian priors for finding new physics in this kind of regime. Just another way that Nature makes life challenging for we poor human physicists.

Posted in arxiv, Science | 30 Comments

## Einstein’s Papers Online

If any scientist in recent memory deserves to have every one of their words captured and distributed widely, it’s Albert Einstein. Surprisingly, many of his writings have been hard to get a hold of, especially in English; he wrote an awful lot, and mostly in German. The Einstein Papers Project has been working heroically to correct that, and today marks a major step forward: the release of the Digital Einstein Papers, an open resource that puts the master’s words just a click away.

As Dennis Overbye reports in the NYT, the Einstein Papers Project has so far released 14 of a projected 30 volumes of thick, leather-bound collections of Einstein’s works, as well as companion English translations in paperback. That’s less than half, but it does cover the years 1903-1917 when Einstein was turning physics on its head. You can read On the Electrodynamics of Moving Bodies, where special relativity was introduced in full, or the very short (3 pages!) follow-up Does the Inertia of a Body Depend on Its Energy Content?, where he derived the relation that we would now write as E = mc2. Interestingly, most of Einstein’s earliest papers were on statistical mechanics and the foundations of thermodynamics.

Ten years later he is putting the final touches on general relativity, whose centennial we will be celebrating next year. This masterwork took longer to develop, and Einstein crept up on its final formulation gradually, so you see the development spread out over a number of papers, achieving its ultimate form in The Field Equations of Gravitation in 1915.

What a compelling writer Einstein was! (Not all great scientists are.) Here is the opening of one foundational paper from 1914, The Formal Foundation of the General Theory of Relativity:

In recent years I have worked, in part together with my friend Grossman, on a generalization of the theory of relativity. During these investigations, a kaleidoscopic mixture of postulates from physics and mathematics has been introduced and used as heuristical tools; as a consequence it is not easy to see through and characterize the theory from a formal mathematical point of view, that is, only based on these papers. The primary objective of the present paper is to close this gap. In particular, it has been possible to obtain the equations of the gravitational field in a purely covariance-theoretical manner (section D). I also tried to give simple derivations of the basic laws of absolute differential calculus — in part, they are probably new ones (section B) — in order to allow the reader to get a complete grasp of the theory without having to read other, purely mathematical tracts. As an illustration of the mathematical methods, I derived the (Eulerian) equations of hydrodynamics and the field equations of the electrodynamics of moving bodies (section C). Section E shows that Newton’s theory of gravitation follows from the general theory as an approximation. The most elementary features of the present theory are also derived inasfar as they are characteristic of a Newtonian (static) gravitational field (curvature of light rays, shift of spectral lines).

While Einstein certainly did have help from Grossman and others, to a large extent the theory of general relativity was all his own. It stands in stark contrast to quantum mechanics or almost all modern theories, which have grown up through the collaborative effort of many smart people. We may never again in physics see a paragraph of such sweep and majesty — “Here is my revolutionary theory of the dynamics of space and time, along with a helpful introduction to its mathematical underpinnings, as well as derivations of all the previous laws of physics within this powerful new framework.”

Thanks to everyone at the Einstein Papers project for undertaking this enormous task.

Posted in Science, Words | 34 Comments

## Thanksgiving

This year we give thanks for a technique that is central to both physics and mathematics: the Fourier transform. (We’ve previously given thanks for the Standard Model Lagrangian, Hubble’s Law, the Spin-Statistics Theorem, conservation of momentum, effective field theory, the error bar, gauge symmetry, and Landauer’s Principle.)

Let’s say you want to locate a point in space — for simplicity, on a two-dimensional plane. You could choose a coordinate system (x, y), and then specify the values of those coordinates to pick out your point: (x, y) = (1, 3).

But someone else might want to locate the same point, but they want to use a different coordinate system. That’s fine; points are real, but coordinate systems are just convenient fictions. So your friend uses coordinates (u, v) instead of (x, y). Fortunately, you know the relationship between the two systems: in this case, it’s u = y+x, v = y-x. The new coordinates are rotated (and scaled) with respect to the old ones, and now the point is represented as (u, v) = (4, 2).

Fourier transforms are just a fancy version of changes of coordinates. The difference is that, instead of coordinates on a two-dimensional space, we’re talking about coordinates on an infinite-dimensional space: the space of all functions. (And for technical reasons, Fourier transforms naturally live in the world of complex functions, where the value of the function at any point is a complex number.)

Think of it this way. To specify some function f(x), we give the value of the function f for every value of the variable x. In principle, an infinite number of numbers. But deep down, it’s not that different from giving the location of our point in the plane, which was just two numbers. We can certainly imagine taking the information contained in f(x) and expressing it in a different way, by “rotating the axes.”

That’s what a Fourier transform is. It’s a way of specifying a function that, instead of telling you the value of the function at each point, tells you the amount of variation at each wavelength. Just as we have a formula for switching between (u, v) and (x, y), there are formulas for switching between a function f(x) and its Fourier transform f(ω):

$f(\omega) = \frac{1}{\sqrt{2\pi}} \int dx f(x) e^{-i\omega x}$
$f(x) = \frac{1}{\sqrt{2\pi}} \int d\omega f(\omega) e^{i\omega x}$.

Absorbing those formulas isn’t necessary to get the basic idea. If the function itself looks like a sine wave, it has a specific wavelength, and the Fourier transform is just a delta function (infinity at that particular wavelength, zero everywhere else). If the function is periodic but a bit more complicated, it might have just a few Fourier components.

MIT researchers showing how sine waves can combine to make a square-ish wave.

In general, the Fourier transform f(ω) gives you “the amount of the original function that is periodic with period 2πω.” This is sometimes called the “frequency domain,” since there are obvious applications to signal processing, where we might want to take a signal that has an intensity that varies with time and pick out the relative strength of different frequencies. (Your eyes and ears do this automatically, when they decompose light into colors and sound into pitches. They’re just taking Fourier transforms.) Frequency, of course, is the inverse of wavelength, so it’s equally good to think of the Fourier transform as describing the “length domain.” A cosmologist who studies the large-scale distribution of galaxies will naturally take the Fourier transform of their positions to construct the power spectrum, revealing how much structure there is at different scales.

To my (biased) way of thinking, where Fourier transforms really come into their own is in quantum field theory. QFT tells us that the world is fundamentally made of waves, not particles, and it is extremely convenient to think about those waves by taking their Fourier transforms. (It is literally one of the first things one is told to do in any introduction to QFT.)

But it’s not just convenient, it’s a worldview-changing move. One way of characterizing Ken Wilson’s momentous achievement is to say “physics is organized by length scale.” Phenomena at high masses or energies are associated with short wavelengths, where our low-energy long-wavelength instruments cannot probe. (We need giant machines like the Large Hadron Collider to create high energies, because what we are really curious about are short distances.) But we can construct a perfectly good effective theory of just the wavelengths longer than a certain size — whatever size it is that our theoretical picture can describe. As physics progresses, we bring smaller and smaller length scales under the umbrella of our understanding.

Without Fourier transforms, this entire way of thinking would be inaccessible. We should be very thankful for them — as long as we use them wisely.

Credit: xkcd.

Note that Joseph Fourier, inventor of the transform, is not the same as Charles Fourier, utopian philosopher. Joseph, in addition to his work in math and physics, invented the idea of the greenhouse effect. Sadly that’s not something we should be thankful for right now.

Posted in Math, Science | 26 Comments

## Guest Post by Alessandra Buonanno: Nobel Laureates Call for Release of Iranian Student Omid Kokabee

Usually I start guest posts by remarking on what a pleasure it is to host an article on the topic being discussed. Unfortunately this is a sadder occasion: protesting the unfair detention of Omid Kokabee, a physics graduate student at the University of Texas, who is being imprisoned by the government of Iran. Alessandra Buonanno, who wrote the post, is a distinguished gravitational theorist at the Max Planck Institute for Gravitational Physics and the University of Maryland, as well as a member of the Committee on International Freedom of Scientists of the American Physical Society. This case should be important to everyone, but it’s especially important for physicists to work to protect the rights of students who travel from abroad to study our subject.

Omid Kokabee was arrested at the airport of Teheran in January 2011, just before taking a flight back to the University of Texas at Austin, after spending the winter break with his family. He was accused of communicating with a hostile government and after a trial, in which he was denied contact with a lawyer, he was sentenced to 10 years in Teheran’s Evin prison.

According to a letter written by Omid Kokabee, he was asked to work on classified research, and his arrest and detention was a consequence of his refusal. Since his detention, Kokabee has continued to assert his innocence, claiming that several human rights violations affected his interrogation and trial.

Since 2011, we, the Committee on International Freedom of Scientists (CIFS) of the American Physical Society, have protested the imprisonment of Omid Kokabee. Although this case has received continuous support from several scientific and international human rights organizations, the government of Iran has refused to release Kokabee.

Omid Kokabee has received two prestigious awards:

• The American Physical Society awarded him Andrei Sakharov Prize “For his courage in refusing to use his physics knowledge to work on projects that he deemed harmful to humanity, in the face of extreme physical and psychological pressure.”
• The American Association for the Advancement of Science awarded Kokabee the Scientific Freedom and Responsibility Prize.

Amnesty International (AI) considers Kokabee a prisoner of conscience and has requested his immediate release.

Recently, the Committee of Concerned Scientists (CCS), AI and CIFS, have prepared a letter addressed to the Iranian Supreme Leader Ali Khamenei asking that Omid Kokabee be released immediately. The letter was signed by 31 Nobel-prize laureates. (An additional 13 Nobel Laureates have signed this letter since the Nature blog post. See also this update from APS.)

Unfortunately, earlier last month, Kokabee’s health conditions have deteriorated and he has been denied proper medical care. In response, the President of APS, Malcolm Beasley, has written a letter to the Iranian President Rouhani calling for a medical furlough for Omid Kokabee so that he can receive proper medical treatment. AI has also made further steps and has requested urgent medical care for Kokabee.

Very recently, the Iran’s supreme court has nullified the original conviction of Omid Kokabee and has agreed to reconsider the case. Although this is positive news, it is not clear when the new trial will start. Considering Kokabee’s health conditions, it is very important that he is granted a medical furlough as soon as possible.

More public engagement and awareness is needed to solve this unacceptable case of violation of human rights and freedom of scientific research. You can help by tweeting/blogging about it and responding to this Urgent Action that AI has issued. Please note that the date on the Urgent Action is there to create an avalanche effect; it is not a deadline nor it is the end of action.

Alessandra Buonanno for the American Physical Society’s Committee on International Freedom of Scientists (CIFS).

Posted in Guest Post, Human Rights, Science and Society | 20 Comments

## Unsolicited Advice: Becoming a Science Communicator

Everyone who does science inevitably has “communicating” as part of their job description, even if they’re only communicating with their students and professional colleagues. But many people start down a trajectory of becoming a research scientist, only to discover that it’s the communicating that they are most passionate about. And some of those people might want to take the dramatic step of earning a living doing such communication, whether it’s traditional journalism or something more new-media focused.

So: how does one make the transition from researcher to professional science communicator? Heck if I know. I do a lot of communicating, but it’s not my primary job. You’d be better off looking at this thread from Ed Yong, where he coaxed an impressive number of science writers into telling their origin stories. But lack of expertise has never stopped me from offering advice!

First piece of advice: don’t make the tragic mistake of looking at science communication as a comfortable safety net if academia doesn’t work out. Not only is it an extremely demanding career, but it’s one that is at least as hard as research in terms of actually finding reliable employment — and the career trajectories are far more chancy and unpredictable. There is no tenure for science communicators, and there’s not even a structured path of the form student → postdoc → faculty. Academia’s “up or out” system can be soul-crushing, but so can the “not today, but who knows? Maybe tomorrow!” path to success of the professional writer. It’s great to aspire to being Neil deGrasse Tyson or Mary Roach, but most science communicators don’t reach that level of success, just as most scientists don’t become Marie Curie or Albert Einstein.

Having said all that, here are some tips that might be worth sharing. Continue reading

## Discovering Tesseracts

I still haven’t seen Interstellar yet, but here’s a great interview with Kip Thorne about the movie-making process and what he thinks of the final product. (For a very different view, see Phil Plait [update: now partly recanted].)

One of the things Kip talks about is that the film refers to the concept of a tesseract, which he thought was fun. A tesseract is a four-dimensional version of a cube; you can’t draw it faithfully in two dimensions, but with a little imagination you can get the idea from the picture on the right. Kip mentions that he first heard of the concept of a tesseract in George Gamow’s classic book One, Two, Three… Infinity. Which made me feel momentarily proud, because I remember reading about it there, too — and only later did I find out that many (presumably less sophisticated) people heard of it in Madeleine L’Engle’s equally classic book, A Wrinkle in Time.

But then I caught myself, because (1) it’s stupid to think that reading about something for the first time in a science book rather than a science fantasy is anything to be proud of, and (2) in reality I suspect I first heard about it in Robert Heinlein’s (classic!) short story, “–And He Built a Crooked House.” Which is just as fantastical as L’Engle’s book.

So — where did you first hear the word “tesseract”? A great excuse for a poll! Feel free to elaborate in the comments.

Where did you first discover the word "tesseract"?
Posted in Math, Time, Words | 35 Comments

## Purposeful Distortion

Here is a map, slightly off-kilter but completely recognizable, by Gaicomo Faiella. Can you tell what is special/interesting about it? (Hat tip to Joe Polchinski, and following his lead I won’t reveal the answer in this post — but feel free to leave guesses/spoilers in the comments.)

Posted in Arts, World | 29 Comments

## The Science of Interstellar

The intersection — maybe the union! — of science and sci-fi geekdom is overcome with excitement about the upcoming movie Interstellar, which opens November 7. It’s a collaboration between director Christopher Nolan and physicist Kip Thorne, both heroes within their respective communities. I haven’t seen it yet myself, nor do I know any secret scoop, but there’s good reason to believe that this film will have some of the most realistic physics of any recent blockbuster we’ve seen. If it’s a success, perhaps other filmmakers will take the hint?

Kip, who is my colleague at Caltech (and a former guest-blogger), got into the science-fiction game quite a while back. He helped Carl Sagan with some science advice for his book Contact, later turned into a movie starring Jodie Foster. In particular, Sagan wanted to have some way for his characters to traverse great distances at speeds faster than light, by taking a shortcut through spacetime. Kip recognized that a wormhole was what was called for, but also realized that any form of faster-than-light travel had the possibility of leading to travel backwards in time. Thus was the entire field of wormhole time travel born.

As good as the movie version of Contact was, it still strayed from Sagan’s original vision, as his own complaints show. (“Ellie disgracefully waffles in the face of lightweight theological objections to rationalism…”) Making a big-budget Hollywood film is necessarily a highly collaborative endeavor, and generally turns into a long series of forced compromises. Kip has long been friends with Lynda Obst, an executive producer on Contact, and for years they batted around ideas for a movie that would really get the science right.

Long story short, Lynda and Kip teamed with screenwriter Jonathan Nolan (brother of Christopher), who wrote a draft of a screenplay, and Christopher eventually agreed to direct. I know that Kip has been very closely involved with the script as the film has developed, and he’s done his darnedest to make sure the science is right, or at least plausible. (We don’t actually whether wormholes are allowed by the laws of physics, but we don’t know that they’re not allowed.) But it’s a long journey, and making the best movie possible is the primary goal. Meanwhile, Adam Rogers at Wired has an in-depth look at the science behind the movie, including the (unsurprising, in retrospect) discovery that the super-accurate visualization software available to the Hollywood special-effects team enable the physicists to see things they hadn’t anticipated. Kip predicts that at least a couple of technical papers will come out of their work.

And that’s not all! Kip has a book coming out on the science behind the movie, which I’m sure will be fantastic. And there is also a documentary on “The Science of Interstellar” that will be shown on TV, in which I play a tiny part. Here is the broadcast schedule for that, as I understand it:

SCIENCE
Wednesday, October 29, at 10pm PDT/9c

AHC (American Heroes Channel)
Sunday, November, 2 at 4pm PST/3c (with a repeat on Monday, November 3 at 4am PST/3c)

DISCOVERY
Thursday, November 6, at 11pm PST/10c

Of course, all the accurate science in the world doesn’t help if you’re not telling an interesting story. But with such talented people working together, I think some optimism is justified. Let’s show the world that science and cinema are partners, not antagonists.

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