Sean Carroll

Category: Science

  • Morality, Health, and Science

    In our last discussion of morality and science, an interesting argument was raised in the comments (by rbd and then in more detail by Ben Finney), concerning an analogy between morality and health. Sam Harris has also brought it up. It’s worth responding to because it (1) sounds convincing at first glance, and (2) has exactly the same flaw that the morality-as-science argument has. That’s what a good analogy should do!

    If I can paraphrase, the argument is something like this: “You say that morality isn’t part of science because you don’t know what a `unit of well-being’ is — it’s not something that could in principle be measured by doing an experiment. But one could just as easily say that you don’t know what a `unit of health’ is, and therefore medicine isn’t part of science. The lack of some simple measurable quantity is a simplistic attack against a sophisticated problem.”

    This gets right to the point. Because, in fact, I don’t know what a “unit of health” is, which is why medicine is not — solely — part of science.

    Let me explain what I mean. Obviously we use science all the time when it comes to medicine. Similarly, we should be very ready to use science when it comes to morality — it’s an indispensable part of the endeavor. But in both cases there is a crucial component that lies outside the realm of science.

    Here’s how we do medicine, in a cartoonishly simplified version that is nevertheless good enough for our present purposes. First, we decide what we mean by “healthy.” Then, we use science to try to bring it about.

    That first step is not science, no matter how much science might be involved in the definition. Various measurable quantities certainly belong to the realm of science — height, weight, pulse, blood pressure, lifespan, time in the 40-yard dash, etc. But what we decide to label “healthy” is irreducibly a human judgment, not an empirical measurable. Some people might think that extreme thinness is part of being healthy, while others might prefer a more robust physique. Some people might define health as the state that maximizes life expectancy, while others might put more emphasis on quality of life even at the expense of total years. It matters not a whit what people actually think, of course — even if everyone in the world agreed on what “healthy” meant, it would still be a judgment rather than an empirical measurement. If one contrarian person came up with a different definition, they wouldn’t be “right” or “wrong” in the conventional scientific sense. There is no experiment we could do to answer the question one way or another.

    In the real world, we more or less agree on what constitutes health, so the non-empirical status of this choice isn’t treated as a crucially important philosophical problem. (At least, until you start reading the literature on disability studies, and you realize that what you thought was obvious maybe is not.) We agree on what health is, and we set out to achieve it, and that second part is very much science.

    Morality is exactly the same way, although with somewhat less unanimity in the first step. We agree (or not) on what morality is, and once we do the process of achieving it is very much a scientific issue, in the broad-but-perfectly-valid definition of “science” as “an understanding of how the world works based on empirical data.” Once again, it doesn’t matter whether we agree or not, because that first step is a decision we human beings make, not something we measure out there in the world.

    While both health and morality are human choices rather than empirically measurable quantities, they certainly aren’t random choices. Human beings aren’t blank slates; we have preferences. Most of us would prefer to live longer and be free of aches and pains; these preferences feed into how we choose to define “health.” Likewise for morality. But “we broadly agree on X” is not, and never will be, the same statement as “X is a scientific truth.” Understanding our preferences, turning vague impulses into precise statements, constructing logical frameworks based on them — that’s what the philosophy of medicine/morality is all about.

    The case of morality is actually much more difficult than the case of health, because most interesting moral questions involve tradeoffs between the interests of different people, not only the state of one individual. So even if we could do experiments to establish a unique map between mental states and human well-being, we wouldn’t really be any closer to reducing morality to science. All very fun to think about, though.

  • First Science from Planck

    The Planck Surveyor satellite, a European mission to observe the cosmic microwave background (and various things that get in the way), has released its first science results. 25 papers in all!

    I haven’t absorbed all the goodness as yet, so I’ll just point you to more interesting resources — e.g. blog posts by Peter Coles or Andrew Jaffe, or this BBC article if you prefer your media more mainstream. Note that these are not, for the most part, results about the cosmic microwave background and all the yummy cosmological goodness one hopes to derive therefrom. There’s a lot about dust in our own galaxy, as well as infrared emission from some of the very earliest galaxies in the universe. (Much of this is relevant, of course, to straightening out possible anomalies in the actual CMB.)

    CMB results are expected circa January 2013. That’s when I’ll win my bet with Max Tegmark.

  • Trouble for Dark Energy Space Mission?

    NASA doesn’t have nearly enough money to do what it wants to do. Well, nothing unusual about that. We’ve talked recently about the constraints that budgetary realities are putting on astronomers’ ambitions — here, here, here. Now it’s chickens-coming-home-to-roost time, apparently. Dennis Overbye has an article in the Times (via Brian Schmidt) about how cost overruns on the James Webb Space Telescope — the giant multipurpose infrared satellite into which basket NASA is putting many of its eggs — are forcing dark energy onto the back burner.

    The current NASA vision for dark energy is a mission called WFIRST (Wide-Field Infrared Survey Telescope), which grew out of JDEM (the Joint Dark Energy Mission), which was in turn descended from SNAP (Supernova Acceleration Probe). WFIRST would try to use three different techniques to constrain dark energy parameters — weak lensing, baryon acoustic oscillations, and supernovae. It would also be able to search for exoplanets using microlensing, just as a bonus. But cost overruns on JWST have left NASA with very little money to do ambitious (or even not-very-ambitious) new missions, so WFIRST is now up in the air, despite being judged the highest priority by the National Academy Decadal Survey.

    It looks like the U.S. might try to stay in the dark-energy game by funding a 20% share in Euclid, a planned mission by the European Space Agency. Meanwhile, techniques that try to measure parameters of dark energy without leaving the ground are continuing to improve. So maybe it will end up not being a big deal, and we’ll learn what we need to know anyway. Or maybe we’ll miss out on the opportunity for a transformative discovery. The only thing we know for certain is that it’s not easy to make these tough choices when it comes to planning missions over the course of decades.

  • Scientific Artifacts from the Sky

    I was looking at Google maps at a location near Chicago, so I scooted over to take a look at Fermilab (map). As always, I was struck first by the sheer beauty of the arrangement, and next by how wonderful it is that we human beings would undertake such a massive project just to better understand the laws of nature. And finally, of course, by the irony that it takes something this big to examine particles on very small scales. Blame the wave nature of matter for that: to look at short distances, you need high energies, and that means a whomping big accelerator.

    This moved me to take a look at other giant scientific facilities. Unfortunately CERN puts its accelerators underground, so the Large Hadron Collider doesn’t mark the landscape with enormous circles. Here’s SLAC (map), the largest linear accelerator in the world and claimed to be the world’s straightest object.

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  • Observing the Multiverse (Guest Post)

    It’s a big universe out there — maybe bigger that we think. A lot of people these days are contemplating the possibility that the wider world isn’t just more of the same; it could be that there are regions very different from ours, even with different low-energy laws of physics, outside our observable universe. It’s an old idea, which we now label the “multiverse,” even though we’re talking about regions of space connected to ours. A lot of other people are aghast that this is considered science. Personally I think science talks about unobservable things all the time, and this question is going to be resolved by people doing hard work to make sense of multiverse scenarios rather than by pronouncements about what is or is not science.

    Matt Johnson We’re very happy to have a guest post from one of the people who is doing exactly that hard work — Matt Johnson, who guest-blogged for us before. He and his collaborators just come out two papers that examine the cosmic microwave background, looking for evidence of “bubble collisions.”

    First Observational Tests of Eternal Inflation
    Stephen M. Feeney (UCL), Matthew C. Johnson (Perimeter Institute), Daniel J. Mortlock (Imperial College London), Hiranya V. Peiris (UCL)
    arXiv:11012.1995

    First Observational Tests of Eternal Inflation: Analysis Methods and WMAP 7-Year Results
    Stephen M. Feeney (UCL), Matthew C. Johnson (Perimeter Institute), Daniel J. Mortlock (Imperial College London), Hiranya V. Peiris (UCL)
    arXiv:1012.3667

    The hope is that these other “universes” might not be completely separate from our own — maybe we collided in the past. They’ve done a very careful job going through the data, with intriguing but inconclusive results. (See also Backreaction.)

    Looking for this kind of signature in the CMB is certainly reminiscent of the concentric circles predicted by Gurzadyan and Penrose. But despite the similarities, it’s different in crucial ways — different theory, different phenomenon leading to the signal, different analysis, different conclusions. The road to sorting out this multiverse stuff is long and treacherous, but our brave cosmological explorers will eventually guide us through.

    Here’s Matt.

    ———————————————————————–

    Observing other universes: is this science fiction?

    Perhaps not. Stephen Feeney, Daniel Mortlock, Hiranya Peiris and I recently performed an observational search for the signatures of colliding bubble universes in the cosmic microwave background. Before getting to our results, let me explain some of the back-story.

    The idea that there might be other universes is taken quite seriously in high energy physics and cosmology these days. This is mainly due to the fact that the laws of physics, and the various “fundamental” constants appearing in them, could have been otherwise. More technically worded, there is no unique vacuum in theories of high energy physics that involve spontaneous symmetry breaking, extra dimensions, or supersymmetry. Having a bunch of vacua around is interesting, but to what extent are they actually realized in nature? Surprisingly, when a spacetime region undergoing inflation is metastable, there are cases when all of the vacua in a theory can be realized in different places and at different times. This phenomenon is known as eternal inflation. In an inflating universe, if a region is in a metastable vacuum, bubbles containing different vacua will form. These bubbles then expand, and eat into the original vacuum. However, if the space between bubbles is expanding fast enough, they never merge completely. There is always more volume to convert into different vacua through bubble formation, and the original vacuum never disappears: inflation becomes eternal. In the theory of eternal inflation, our entire observable universe resides inside one of these bubbles. Other bubbles will contain other universes. In this precise sense, many theories of high energy physics seem to predict the existence of other universes.

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  • Farewell, Pioneer Anomaly?

    Here’s an excellent article in Popular Science about the Pioneer anomaly. (Via Dan Vergano on Twitter.) The Pioneer spacecraft, launched in the early 1970’s, have been moseying through the outer regions of the Solar System for quite some time now. But a careful analysis of tracking data indicated that the acceleration of the two spacecraft didn’t quite match what we’d expect from gravity; there appears to be an anomalous acceleration, nearly constant over time and pointing toward the Sun. Many new-physics explanations have been proposed, but it’s always been a difficult scenario to master; it’s very hard to imagine a new force that would account for the Pioneer data but not also show up in observations of the outer planets. (The Voyager spacecraft aren’t as useful for this purpose, as they are guided by tiny thrusters that overwhelm the signal, while the Pioneers float freely and are pointed using gyroscopes.)

    File-Pioneer_11_Saturn_RingsThe most likely explanation has always been that we didn’t completely understand the spacecraft, or the tracking system. Indeed, it’s been recognized for a while that a small imbalance in how the spacecraft radiated heat could account for the acceleration — but that imbalance didn’t seem to be supported by what we knew about the vessels. That may be changing, however. The Popular Science article is a little cagey, but it mentions a new and unprecedentedly thorough analysis by Viktor Toth and Slava Turshyev that should be coming out soon. Here is as much as they would let on:

    Five years have passed. Using the telemetry data, the two scientists created an extremely elaborate “finite element” 3-D computer model of each Pioneer spacecraft, in which the thermal properties of 100,000 positions on their surfaces are independently tracked for the duration of the 30-year mission. Everything there is to know about heat conduction across the spacecraft’s surfaces, as well as the way that heat flow and temperature declined over time as the power of the generators lessened, they know. The results of the telemetry analysis? “The heat recoil force accounts for part of the acceleration,” said Turyshev. They wouldn’t tell me how significant a part. (Turyshev: “We’d like to publish that in the scientific literature.”) But according to Toth, “You can take it to the bank that whatever remains of the anomaly after accounting for that thermal acceleration, it will at most be much less than the canonical value of 8.74 x 10-10 m/s2, and then, mind you, all those wonderful numerical coincidences people talk about are destroyed.”

    Doesn’t look good for people who prefer to imagine that wild new physics is responsible. Not that they will go away — the power of wishful thinking is strong. You can already hear them staking out territory, even before the new report comes out:

    Other physicists are more combative. “Heat? That’s simply not the right explanation. They are wrong,” commented Johan Masreliez, an independent researcher in Washington who supports the expanding spacetime model of cosmology, for which it is crucial that the value of the Pioneer anomaly equals c times H. “But then I’m biased,” he added.

    Even if the new analysis gives a very sensible and believable account of the Pioneer anomaly in terms of very ordinary physics, expect the true believers to hang on for years to come. The rest of us will move on — at least until the next exciting anomaly pops up.

    Also: big props to Natalie Wolchover, who wrote the PopSci piece. Very measured tone, carefully researched and well-written.

  • Translational Invariance and Newton’s God

    Tim Maudlin is writing a two-volume introduction to the philosophy of physics, and I was fortunate enough to get a peek at a draft of Volume One, about space and time. There is one anecdote in there about Leibniz’s objections to Newtonian physics that is worth passing along. This came up in the course of the Leibniz-Clarke correspondence.

    Leibniz was quite fond of proclaiming overarching a priori principles. Perhaps the most famous/infamous is the Principle of Sufficient Reason, which states that everything that happens does so for some good reason. But there was also the Principle of Identity of Indiscernibles, which states that if two things have all the same properties, they are really the same thing. Sounds reasonable enough (although one might worry what qualifies as a “property”), but it can get you in trouble if you take it too far.

    Remember that Newton believed in absolute space — a rigid three-dimensional set of points that forms the arena in which physics takes place. Leibniz, on the other hand, claimed that space should be thought of purely in terms of relations between different points, without any metaphysical baggage of “absoluteness.” (From a modern perspective, Leibniz was closer to correct, given Galilean relativity; but once we allow for spacetime curvature in general relativity, the relational view becomes less useful.)

    So far, so good. The weird part, to modern ears, comes in when we consider Newtonian cosmology. In order to explain matter in the universe, Newton departed from the strict consequences of his Laws of Motion. Instead, he imagined that empty space existed for an infinite period of time, before eventually God decided to create matter in it.

    That’s the part Leibniz couldn’t go along with. He didn’t believe God would work that way, for reasons that amount to what we would now call the translational invariance of space. If God is going to create all this matter in empty space, Leibniz reasons, He has to put it somewhere. But where? Every point is equally good! Therefore there can’t be any “sufficient reason” to create it in one place rather than in some other place. Therefore there must be a deep metaphysical flaw at the heart of Newton’s theory. Interestingly, he didn’t go for “matter has been around forever,” but instead came down on the side of “there is no such thing as absolute space.”

    Maybe he was worried about Boltzmann Brains?

  • Interview on Static Limit

    David Reffkin is a radio host at KUSF in San Francisco. His usual gig is classical music, but once a month he hosts a special called Static Limit where he delves into physics and cosmology. Here’s an interview he did with me a short while back. Right at the beginning we’re talking about this very blog, which I am now using to plug the interview, which is mostly about my book. This is what’s known as “synergy.”

    (Those viewing in an RSS reader, you have to visit the page to click the audio link.)

    David assumes the listeners have been following along previous shows, so we don’t spend too much time defining general relativity and the Big Bang; we go right for the cutting edge. But we also covered a lot of meta ground, about the process of doing physics. He also gave me the most comprehensive list of errata (mostly minor typos) for my book, so I know he read the whole thing!

  • Penrose’s Cyclic Cosmology

    Update: Gurzadyan and Penrose have very quickly put up a response to the analysis papers quoted below. And another paper critical of G&P has appeared, by Amir Hajian.

    Gurzadyan & Penrose Roger Penrose and his collaborator Vahe Gurzadyan made a splash recently by claiming that there was evidence in the cosmic microwave background for a pre-Big-Bang era in the history of the universe. (Here’s the paper.) The evidence takes the form of correlated circles in the cosmic microwave background anisotropies, as pictured here. They claim that they have found such circles at a level of significance much higher than would be predicted in a conventional scenario, where perturbations were random and uncorrelated on various scales.

    That would be pretty amazing, if true. But it looks like it isn’t. Here are two skeptical papers that just appeared on the arxiv. (Hat tip to David Spergel. Peter Coles was an early skeptic.)

    A search for concentric circles in the 7-year WMAP temperature sky maps

    Authors: I. K. Wehus, H. K. Eriksen

    Abstract: In a recent analysis of the 7-year WMAP temperature sky maps, Gurzadyan and Penrose claim to find evidence for violent pre-Big Bang activity in the form of concentric low-variance circles at high statistical significance. In this paper, we perform an independent search for such concentric low-variance circles, employing both chi^2 statistics and matched filters, and compare the results obtained from the 7-year WMAP temperature sky maps with those obtained from LCDM simulations. Our main findings are the following: We do reproduce the claimed ring structures observed in the WMAP data as presented by Gurzadyan and Penrose, thereby verifying their computational procedures. However, the results from our simulations do not agree with those presented by Gurzadyan and Penrose. On the contrary we obtain a substantially larger variance in our simulations, to the extent that the observed WMAP sky maps are fully consistent with the LCDM model as measured by these statistics.

    No evidence for anomalously low variance circles on the sky

    Authors: Adam Moss, Douglas Scott, James P. Zibin

    Abstract: In a recent paper, Gurzadyan & Penrose claim to have found directions on the sky centred on which are circles of anomalously low variance in the cosmic microwave background (CMB). These features are presented as evidence for a particular picture of the very early Universe. We attempted to repeat the analysis of these authors, and we can indeed confirm that such variations do exist in the temperature variance for annuli around points in the data. However, we find that this variation is entirely expected in a sky which contains the usual CMB anisotropies. In other words, properly simulated Gaussian CMB data contain just the sorts of variations claimed. Gurzadyan & Penrose have not found evidence for pre-Big Bang phenomena, but have simply re-discovered that the CMB contains structure.

    The basic message is simple: sure, you can find some circles in the sky if you look there. But they are simply what you would expect from random alignments, not a new signal over and above the usual predictions. The authors here are respected CMB analyzers, and I strongly suspect that they are correct. Which reminds us of an important lesson: analyzing the CMB is hard! It’s a very messy universe out there, and if you don’t take every single source of error correctly into account, you can convince yourself of all sorts of things.

    Just because this particular signal is there doesn’t mean the underlying model — Penrose’s Conformal Cyclic Cosmology (CCC) — isn’t right. I’m all in favor of pre-Big-Bang cosmologies myself, and Penrose more than anyone has been correct in insisting that the low entropy of our early universe is a crucial problem that is not well-addressed in modern cosmology. But I’ve been hesitant because, frankly, I don’t really get it.

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  • Thanksgiving

    This year we give thanks for an idea that is absolutely crucial to how our understanding of nature progresses: effective field theory. (We’ve previously given thanks for the Standard Model Lagrangian, Hubble’s Law, the Spin-Statistics Theorem, and conservation of momentum.)

    “Effective field theory” is a technical term within quantum field theory, but it is associated with a more informal notion of extremely wide applicability. Namely: if we imagine dividing the world into “what happens at very short, microscopic distances” and “what happens at longer, macroscopic distances,” then it is possible to consistently describe the macroscopic world without referring to (or even understanding) the microscopic world. This is not always true, of course — our macroscopic descriptions have very specific domains of applicability, past which the microscopic details begin to matter — but it’s true very often, for a wide variety of situations with direct physical relevance.

    The most basic examples are thermodynamics and fluid mechanics. You can talk about gasses and liquids very well without having any idea that they are made of atoms and molecules. Once you get deep into the details, we start talking about effects for which the atomic granularity really matters; but there is a very definite and useful regime in which it is simply irrelevant that air and water are “really” made of discrete units rather than being continuous fluids. Fluid mechanics is the “effective field theory of molecules” in the macroscopic domain.

    How awesome is that? If it weren’t for the idea of effective field theory, it’s hard to imagine how we would ever make progress in physics. You wouldn’t be able to talk about atmospheric science without knowing all the details of microscopic physics (known in the trade as the ultraviolet completion), all the way down to the Planck scale! Fortunately, the universe is much more kind to us.

    In particle physics, this idea is absolutely central. Protons, neutrons, and pions constitute an effective field theory that describes how quarks and gluons behave over sufficiently large distances. Another great example comes from Enrico Fermi’s theory of the weak interactions. Back in the 1930’s, Fermi proposed a theory that made use of the new “neutrino” particle. It involved processes that looked like this interaction of a proton plus electron converting into a neutron plus neutrino.

    Fermi interaction

    Nowadays we know better. What’s really going on is that the proton is made of two up quarks and a down quark, while the neutron is made of two downs and an up. The electron exchanges a W boson with one of the quarks, converting into an electron neutrino in the process.

    Electroweak interaction

    But the miracle is: it doesn’t matter. Knowing that the weak interactions are “really” carried by W bosons is completely irrelevant, as long as we are concerned only with large distances. In quantum mechanics, large distances correspond to low energies. (Remember that the energy of a wave decreases as its wavelength increases; quantum mechanics is all about waves.) So for low-energy processes, the effective field theory provided by Fermi is all you need to know about the weak interactions.

    The universe is kind, but that kindness comes at a price. Sometimes you want to care about the microscopic realm — for example, if you’re a physicist trying to figure out what is going on down there. When we look at spacetime on length scales of 10-33 centimeters, do we see vibrating strings, or noncommuting matrices, or spin networks, or what? Hard to tell, because it makes no difference at all to the large-distance/low-energy physics we can actually observe.

    That’s okay. A world described by a succession of effective field theories of ever-higher resolution helps us make sense of the world, while leaving physicists plenty of puzzles to think about. Very deserving of our thanksgiving.