Guest Post: Don Page on God and Cosmology

Don Page is one of the world’s leading experts on theoretical gravitational physics and cosmology, as well as a previous guest-blogger around these parts. (There are more world experts in theoretical physics than there are people who have guest-blogged for me, so the latter category is arguably a greater honor.) He is also, somewhat unusually among cosmologists, an Evangelical Christian, and interested in the relationship between cosmology and religious belief.

Longtime readers may have noticed that I’m not very religious myself. But I’m always willing to engage with people with whom I disagree, if the conversation is substantive and proceeds in good faith. I may disagree with Don, but I’m always interested in what he has to say.

Recently Don watched the debate I had with William Lane Craig on “God and Cosmology.” I think these remarks from a devoted Christian who understands the cosmology very well will be of interest to people on either side of the debate.


Open letter to Sean Carroll and William Lane Craig:

I just ran across your debate at the 2014 Greer-Heard Forum, and greatly enjoyed listening to it. Since my own views are often a combination of one or the others of yours (though they also often differ from both of yours), I thought I would give some comments.

I tend to be skeptical of philosophical arguments for the existence of God, since I do not believe there are any that start with assumptions universally accepted. My own attempt at what I call the Optimal Argument for God (one, two, three, four), certainly makes assumptions that only a small fraction of people, and perhaps even only a small fraction of theists, believe in, such as my assumption that the world is the best possible. You know that well, Sean, from my provocative seminar at Caltech in November on “Cosmological Ontology and Epistemology” that included this argument at the end.

I mainly think philosophical arguments might be useful for motivating someone to think about theism in a new way and perhaps raise the prior probability someone might assign to theism. I do think that if one assigns theism not too low a prior probability, the historical evidence for the life, teachings, death, and resurrection of Jesus can lead to a posterior probability for theism (and for Jesus being the Son of God) being quite high. But if one thinks a priori that theism is extremely improbable, then the historical evidence for the Resurrection would be discounted and not lead to a high posterior probability for theism.

I tend to favor a Bayesian approach in which one assigns prior probabilities based on simplicity and then weights these by the likelihoods (the probabilities that different theories assign to our observations) to get, when the product is normalized by dividing by the sum of the products for all theories, the posterior probabilities for the theories. Of course, this is an idealized approach, since we don’t yet have _any_ plausible complete theory for the universe to calculate the conditional probability, given the theory, of any realistic observation.

For me, when I consider evidence from cosmology and physics, I find it remarkable that it seems consistent with all we know that the ultimate theory might be extremely simple and yet lead to sentient experiences such as ours. A Bayesian analysis with Occam’s razor to assign simpler theories higher prior probabilities would favor simpler theories, but the observations we do make preclude the simplest possible theories (such as the theory that nothing concrete exists, or the theory that all logically possible sentient experiences occur with equal probability, which would presumably make ours have zero probability in this theory if there are indeed an infinite number of logically possible sentient experiences). So it seems mysterious why the best theory of the universe (which we don’t have yet) may be extremely simple but yet not maximally simple. I don’t see that naturalism would explain this, though it could well accept it as a brute fact.

One might think that adding the hypothesis that the world (all that exists) includes God would make the theory for the entire world more complex, but it is not obvious that is the case, since it might be that God is even simpler than the universe, so that one would get a simpler explanation starting with God than starting with just the universe. But I agree with your point, Sean, that theism is not very well defined, since for a complete theory of a world that includes God, one would need to specify the nature of God.

For example, I have postulated that God loves mathematical elegance, as well as loving to create sentient beings, so something like this might explain both why the laws of physics, and the quantum state of the universe, and the rules for getting from those to the probabilities of observations, seem much simpler than they might have been, and why there are sentient experiences with a rather high degree of order. However, I admit there is a lot of logically possible variation on what God’s nature could be, so that it seems to me that at least we humans have to take that nature as a brute fact, analogous to the way naturalists would have to take the laws of physics and other aspects of the natural universe as brute facts. I don’t think either theism or naturalism solves this problem, so it seems to me rather a matter of faith which makes more progress toward solving it. That is, theism per se cannot deduce from purely a priori reasoning the full nature of God (e.g., when would He prefer to maintain elegant laws of physics, and when would He prefer to cure someone from cancer in a truly miraculous way that changes the laws of physics), and naturalism per se cannot deduce from purely a priori reasoning the full nature of the universe (e.g., what are the dynamical laws of physics, what are the boundary conditions, what are the rules for getting probabilities, etc.).

In view of these beliefs of mine, I am not convinced that most philosophical arguments for the existence of God are very persuasive. In particular, I am highly skeptical of the Kalam Cosmological Argument, which I shall quote here from one of your slides, Bill:

  1. If the universe began to exist, then there is a transcendent cause
    which brought the universe into existence.
  2. The universe began to exist.
  3. Therefore, there is a transcendent cause which brought the
    universe into existence.

I do not believe that the first premise is metaphysically necessary, and I am also not at all sure that our universe had a beginning. Continue reading

Posted in Guest Post, Religion | 291 Comments

Auction: Multiply-Signed Copy of Why Evolution Is True

Here is a belated but very welcome spinoff of our Moving Naturalism Forward workshop from 2012: Jerry Coyne was clever enough to bring along a copy of his book, Why Evolution Is True, and have all the participants sign it. He subsequently gathered a few more distinguished autographs, and to make it just a bit more beautiful, artist Kelly Houle added some original illustrations. Jerry is now auctioning off the book to benefit Doctors Without Borders. Check it out:

weit2

weit3

Here is the list of signatories:

  • Dan Barker
  • Sean Carroll
  • Jerry Coyne
  • Richard Dawkins
  • Terrence Deacon
  • Simon DeDeo
  • Daniel Dennett
  • Owen Flanagan
  • Anna Laurie Gaylor
  • Rebecca Goldstein
  • Ben Goren
  • Kelly Houle
  • Lawrence Krauss
  • Janna Levin
  • Jennifer Ouellette
  • Massimo Pigliucci
  • Steven Pinker
  • Carolyn Porco
  • Nicholas Pritzker
  • Alex Rosenberg
  • Don Ross
  • Steven Weinberg

Jerry is hoping it will fetch a good price to benefit the charity, so we’re spreading the word. I notice that a baseball signed by Mickey Mantle goes for about $2000. In my opinion a book signed by Steven Weinberg alone should go for even more, so just imagine what this is worth. You have ten days to get your bids in — and if it’s a bit pricey for you personally, I’m sure there’s someone who loves you enough to buy it for you.

Posted in Miscellany | 38 Comments

What Happens Inside the Quantum Wave Function?

Many things can “happen” inside a quantum wave function, of course, including everything that actually does happen — formation of galaxies, origin of life, Lady Gaga concerts, you name it. But given a certain quantum wave function, what actual is happening inside it?

A surprisingly hard problem! Basically because, unlike in classical mechanics, in quantum mechanics the wave function describes superpositions of different possible measurement outcomes. And you can easily cook up situations where a single wave function can be written in many different ways as superpositions of different things. Indeed, it’s inevitable; a humble quantum spin can be written as a superposition of “spinning clockwise” or “spinning counterclockwise” with respect to the z-axis, but it can equally well be written as a superposition of similar behavior with respect to the z-axis, or indeed any axis at all. Which one is “really happening”?

Answer: none of them is “really happening” as opposed to any of the others. The possible measurement outcomes (in this case, spinning clockwise or counterclockwise with respect to some chosen axis) only become “real” when you actually measure the thing. Put more objectively: when the quantum system interacts with a large number of degrees of freedom, becomes entangled with them, and decoherence occurs. But the perfectly general and rigorous picture of all that process is still not completely developed.

So to get some intuition, let’s start with the simplest possible version of the problem: what happens inside a wave function (describing “system” but also “measurement device” and really, the whole universe) that is completely stationary? I.e., what dynamically processes are occurring while the wave function isn’t changing at all?

You’re first guess here — nothing at all “happens” inside a wave function that doesn’t evolve with time — is completely correct. That’s what I explain in the video above, of a talk I gave at the Philosophy of Cosmology workshop in Tenerife. The talk is based on my recent paper with Kim Boddy and Jason Pollack.

Surprisingly, this claim — “nothing is happening if the quantum state isn’t changing with time” — manages to be controversial! People have this idea that a time-independent quantum state has a rich inner life, with civilizations rising and falling within even though the state is literally exactly the same at every moment in time. I’m not precisely sure why. It would be more understandable if that belief got you something good, like an answer to some pressing cosmological problem. But it’s the opposite — believing that all sorts of things are happening inside a time-independent state creates cosmological problems, in particular the Boltzmann Brain problem, where conscious observers keep popping into existence in empty space. So we’re in the funny situation where believing the correct thing — that nothing is happening when the quantum state isn’t changing — solves a problem, and yet some people prefer to believe the incorrect thing, even though that creates problems for them.

Quantum mechanics is a funny thing.

Posted in Science | 60 Comments

From Child Preacher to Adult Humanist

One of the best experiences I had at last year’s Freedom From Religion Foundation convention was listening to this wonderful talk by Anthony Pinn. (Talk begins at 5:40.)

Pinn, growing up outside Buffalo NY, became a preacher in his local church at the ripe young age of 12. Now, there’s nothing an audience of atheists likes better than a story of someone who was devoutly religious and later does an about-face to embrace atheism. (Not an uncommon path, with many possible twists, as you can read in Daniel Dennett and Linda LaScola’s Caught in the Pulpit.) And Pinn gives it to us, hitting all the best notes: being in love with Jesus but also with thinking critically, being surprised to meet theologians who read the Bible as literature rather than as The Word, and ultimately losing his faith entirely while studying at Harvard Divinity School.

But there’s a lot more to his message than a congratulatory triumph of rationality over superstition. Through his life, Pinn has been concerned with the effect that ideas and actions have on real people, especially the African-American community. His mother always reminded him to “move through the world knowing your footsteps matter,” valuable advice no matter what your ontological orientation might be.

This comes out in the Q&A period — often not worth listening to, but in this case it’s the highlight of the presentation. The audience of atheists are looking for yet more self-affirmation, demanding to know why more Blacks haven’t accepted the truth of a secular worldview. Pinn is very frank: naturalism hasn’t yet offered African-Americans a “soft landing.” Too many atheists, he points out, spend a lot of time critiquing religious traditions, and a lot of time patting themselves on the back for being rational and fair-minded, and not nearly enough time constructing something positive, a system of networks and support structures free of the spiritual trappings. It’s a good message for us to hear.

It would have been fantastic to have Anthony at Moving Naturalism Forward. Next time! (Not that there are currently any plans for a next time.)

Posted in Humanity, Religion | 40 Comments

The Big Questions

The other day I mused on Twitter about three big origin questions: the origin of the universe, the origin of life, and the origin of consciousness. Which isn’t to say they are related, just that they’re all interesting and important (and currently nowhere near solved). Physicists have taken stabs at the life question, but (with a few dramatic exceptions) they’ve mostly stayed away from consciousness. Probably for the best.

Here’s Ed Witten giving his own personal — and characteristically sensible — opinion, which is that consciousness is a really knotty problem, although not so difficult that we should start contemplating changing the laws of physics in order to solve it. Though I am more optimistic than he is that we’ll understand it on a reasonable timescale. (Hat tip to Ash Jogalekar.)

Anyone seriously interested in tackling these big questions would be well-served by acknowledging that much (most? almost all?) progress in science is incremental, sneaking up on major discoveries by a series of small steps rather than leaping right to a dramatic new paradigm. Even if you want to understand the origin of the universe, it might behoove you to think about some more specific and tractable problems, like the nature of quantum fluctuations in inflation, or the emergence of spacetime in string theory. If you want to understand the origin of consciousness, it’s a good strategy to think about something like our perception of color, with the idea of working your way up to the more challenging issues.

Conversely, it’s these big questions that attract crackpots like honey attracts flies. I get a lot of emails (and physical letters) from cranks, but they never have a new theory of the branching ratio of the Higgs boson into four leptons; it’s always about the nature of space and time and everything. It’s too easy for anyone to have an opinion about these big questions, whether or not those opinions are worth paying attention to.

All of which leads up to saying: it’s still worth tackling the big questions! Start small, but think big. Because they are so hard, it’s too easy to make fun of attempts to solve the biggest questions, or to imagine that they are irreducibly mysterious and will never be solved. I wouldn’t be at all surprised if we had quite compelling pictures of the origin of the universe, life, and consciousness within the next hundred years. But only if we’re willing to tackle the big problems seriously.

Posted in Science | 71 Comments

Guest Post: An Interview with Jamie Bock of BICEP2

Jamie Bock If you’re reading this you probably know about the BICEP2 experiment, a radio telescope at the South Pole that measured a particular polarization signal known as “B-modes” in the cosmic microwaves background radiation. Cosmologists were very excited at the prospect that the B-modes were the imprint of gravitational waves originating from a period of inflation in the primordial universe; now, with more data from the Planck satellite, it seems plausible that the signal is mostly due to dust in our own galaxy. The measurements that the team reported were completely on-target, but our interpretation of them has changed — we’re still looking for direct evidence for or against inflation.

Here I’m very happy to publish an interview that was carried out with Jamie Bock, a professor of physics at Caltech and a senior research scientist at JPL, who is one of the leaders of the BICEP2 collaboration. It’s a unique look inside the workings of an incredibly challenging scientific effort.


New Results from BICEP2: An Interview with Jamie Bock

What does the new data from Planck tell you? What do you know now?

A scientific race has been under way for more than a decade among a dozen or so experiments trying to measure B-mode polarization, a telltale signature of gravitational waves produced from the time of inflation. Last March, BICEP2 reported a B-mode polarization signal, a twisty polarization pattern measured in a small patch of sky. The amplitude of the signal we measured was surprisingly large, exceeding what we expected for galactic emission. This implied we were seeing a large gravitational wave signal from inflation.

We ruled out galactic synchrotron emission, which comes from electrons spiraling in the magnetic field of the galaxy, using low-frequency data from the WMAP [Wilkinson Microwave Anisotropy Probe] satellite. But there were no data available on polarized galactic dust emission, and we had to use models. These models weren’t starting from zero; they were built on well-known maps of unpolarized dust emission, and, by and large, they predicted that polarized dust emission was a minor constituent of the total signal.

Obviously, the answer here is of great importance for cosmology, and we have always wanted a direct test of galactic emission using data in the same piece of sky so that we can test how much of the BICEP2 signal is cosmological, representing gravitational waves from inflation, and how much is from galactic dust. We did exactly that with galactic synchrotron emission from WMAP because the data were public. But with galactic dust emission, we were stuck, so we initiated a collaboration with the Planck satellite team to estimate and subtract polarized dust emission. Planck has the world’s best data on polarized emission from galactic dust, measured over the entire sky in multiple spectral bands. However, the polarized dust maps were only recently released.

On the other side, BICEP2 gives us the highest-sensitivity data available at 150 GHz to measure the CMB. Interestingly, the two measurements are stronger in combination. We get a big boost in sensitivity by putting them together. Also, the detectors for both projects were designed, built, and tested at Caltech and JPL, so I had a personal interest in seeing that these projects worked together. I’m glad to say the teams worked efficiently and harmoniously together.

What we found is that when we subtract the galaxy, we just see noise; no signal from the CMB is detectable. Formally we can say at least 40 percent of the total BICEP2 signal is dust and less than 60 percent is from inflation.

How do these new data shape your next steps in exploring the earliest moments of the universe?

It is the best we can do right now, but unfortunately the result with Planck is not a very strong test of a possible gravitational wave signal. This is because the process of subtracting galactic emission effectively adds more noise into the analysis, and that noise limits our conclusions. While the inflationary signal is less than 60 percent of the total, that is not terribly informative, leaving many open questions. For example, it is quite possible that the noise prevents us from seeing part of the signal that is cosmological. It is also possible that all of the BICEP2 signal comes from the galaxy. Unfortunately, we cannot say more because the data are simply not precise enough. Our ability to measure polarized galactic dust emission in particular is frustratingly limited.

Figure 1:  Maps of CMB polarization produced by BICEP2 and Keck Array.  The maps show the  ‘E-mode’ polarization pattern, a signal from density variations in the CMB, not gravitational  waves.  The polarization is given by the length and direction of the lines, with a coloring to better  show the sign and amplitude of the E-mode signal.  The tapering toward the edges of the map is  a result of how the instruments observed this region of sky.  While the E-mode pattern is about 6  times brighter than the B-mode signal, it is still quite faint.  Tiny variations of only 1 millionth of  a degree kelvin are faithfully reproduced across these multiple measurements at 150 GHz, and in  new Keck data at 95 GHz still under analysis.  The very slight color shift visible between 150  and 95 GHz is due to the change in the beam size.

Figure 1: Maps of CMB polarization produced by BICEP2 and Keck Array.  The maps show the
‘E-mode’ polarization pattern, a signal from density variations in the CMB, not gravitational
waves.  The polarization is given by the length and direction of the lines, with a coloring to better
show the sign and amplitude of the E-mode signal.  The tapering toward the edges of the map is
a result of how the instruments observed this region of sky.  While the E-mode pattern is about 6
times brighter than the B-mode signal, it is still quite faint.  Tiny variations of only 1 millionth of
a degree kelvin are faithfully reproduced across these multiple measurements at 150 GHz, and in
new Keck data at 95 GHz still under analysis. The very slight color shift visible between 150
and 95 GHz is due to the change in the beam size.

However, there is good news to report. In this analysis, we added new data obtained in 2012–13 from the Keck Array, an instrument with five telescopes and the successor to BICEP2 (see Fig. 1). These data are at the same frequency band as BICEP2—150 GHz—so while they don’t help subtract the galaxy, they do increase the total sensitivity. The Keck Array clearly detects the same signal detected by BICEP2. In fact, every test we can do shows the two are quite consistent, which demonstrates that we are doing these difficult measurements correctly (see Fig. 2). The BICEP2/Keck maps are also the best ever made, with enough sensitivity to detect signals that are a tiny fraction of the total.

A power spectrum of the B-mode polarization signal that plots the strength of the signal as a function of angular frequency.  The data show a signal significantly above what is expected for a universe without gravitational waves, given by the red line.  The excess peaks at angular scales of about 2 degrees.  The independent measurements of BICEP2 and Keck Array shown in red and blue are consistent within the errors, and their combination is shown in black.  Note the sets of points are slightly shifted along the x-axis to avoid overlaps.

Figure 2: A power spectrum of the B-mode polarization signal that plots the strength of the signal as a function of angular frequency. The data show a signal significantly above what is expected for a universe without gravitational waves, given by the red line. The excess peaks at angular scales of about 2 degrees. The independent measurements of BICEP2 and Keck Array shown in red and blue are consistent within the errors, and their combination is shown in black. Note the sets of points are slightly shifted along the x-axis to avoid overlaps.

In addition, Planck’s measurements over the whole sky show the polarized dust is fairly well behaved. For example, the polarized dust has nearly the same spectrum across the sky, so there is every reason to expect we can measure and remove dust cleanly.

To better subtract the galaxy, we need better data. We aren’t going to get more data from Planck because the mission has finished. The best way is to measure the dust ourselves by adding new spectral bands to our own instruments. We are well along in this process already. We added a second band to the Keck Array last year at 95 GHz and a third band this year at 220 GHz. We just installed the new BICEP3 instrument at 95 GHz at the South Pole (see Fig. 3). BICEP3 is single telescope that will soon be as powerful as all five Keck Array telescopes put together. At 95 GHz, Keck and BICEP3 should surpass BICEP2’s 150 GHz sensitivity by the end of this year, and the two will be a very powerful combination indeed. If we switch the Keck Array entirely over to 220 GHz starting next year, we can get a third band to a similar depth.

BICEP3 installed and carrying out calibration measurements off a reflective mirror placed above the receiver. The instrument is housed within a conical reflective ground shield to minimize the brightness contrast between the warm earth and cold space.  This picture was taken at the beginning of the winter season, with no physical access to the station for the next 8 months, when BICEP3 will conduct astronomical observations (Credit:  Sam Harrison

Figure 3: BICEP3 installed and carrying out calibration measurements off a reflective mirror placed above the receiver. The instrument is housed within a conical reflective ground shield to minimize the brightness contrast between the warm earth and cold space. This picture was taken at the beginning of the winter season, with no physical access to the station for the next 8 months, when BICEP3 will conduct astronomical observations (Credit: Sam Harrison)

Finally, this January the SPIDER balloon experiment, which is also searching the CMB for evidence of inflation, completed its first flight, outfitted with comparable sensitivity at 95 and 150 GHz. Because SPIDER floats above the atmosphere (see Fig. 4), we can also measure the sky on larger spatial scales. This all adds up to make the coming years very exciting.

View of the earth and the edge of space, taken from an optical camera on the SPIDER gondola at float altitude shortly after launch. Clearly visible below is Ross Island, with volcanos Mt. Erebus and Mt. Terror and the McMurdo Antarctic base, the Royal Society mountain range to the left, and the edge of the Ross permanent ice shelf.   (Credit:  SPIDER team).

Figure 4: View of the earth and the edge of space, taken from an optical camera on the SPIDER gondola at float altitude shortly after launch. Clearly visible below is Ross Island, with volcanos Mt. Erebus and Mt. Terror and the McMurdo Antarctic base, the Royal Society mountain range to the left, and the edge of the Ross permanent ice shelf. (Credit: SPIDER team).

Why did you make the decision last March to release results? In retrospect, do you regret it?

We knew at the time that any news of a B-mode signal would cause a great stir. We started working on the BICEP2 data in 2010, and our standard for putting out the paper was that we were certain the measurements themselves were correct. It is important to point out that, throughout this episode, our measurements basically have not changed. As I said earlier, the initial BICEP2 measurement agrees with new data from the Keck Array, and both show the same signal. For all we know, the B-mode polarization signal measured by BICEP2 may contain a significant cosmological component—that’s what we need to find out.

The question really is, should we have waited until better data were available on galactic dust? Personally, I think we did the right thing. The field needed to be able to react to our data and test the results independently, as we did in our collaboration with Planck. This process hasn’t ended; it will continue with new data. Also, the searches for inflationary gravitational waves are influenced by these findings, and it is clear that all of the experiments in the field need to focus more resources on measuring the galaxy.

How confident are you that you will ultimately find conclusive evidence for primordial gravitational waves and the signature of cosmic inflation?

I don’t have an opinion about whether or not we will find a gravitational wave signal—that is why we are doing the measurement! But any result is so significant for cosmology that it has to be thoroughly tested by multiple groups. I am confident that the measurements we have made to date are robust, and the new data we need to subtract the galaxy more accurately are starting to pour forth. The immediate path forward is clear: we know how to make these measurements at 150 GHz, and we are already applying the same process to to the new frequencies. Doing the measurements ourselves also means they are uniform so we understand all of the errors, which, in the end, are just as important.

What will it mean for our understanding of the universe if you don’t find the signal?

The goal of this program is to learn how inflation happened. Inflation requires matter-energy with an unusual repulsive property in order to rapidly expand the universe. The physics are almost certainly new and exotic, at energies too high to be accessed with terrestrial particle accelerators. CMB measurements are one of the few ways to get at the inflationary physics, and we need to squeeze them for all they are worth. A gravitational wave signal is very interesting because it tells us about the physical process behind inflation. A detection of the polarization signal at a high level means that the certain models of inflation, perhaps along the lines of the models first developed, are a good explanation.

But here again is the real point: we also learn more about inflation if we can rule out polarization from gravitational waves. No detection at 5 percent or less of the total BICEP2 signal means that inflation is likely more complicated, perhaps involving multiple fields, although there are certainly other possibilities. Either way is a win, and we’ll find out more about what caused the birth of the universe 13.8 billion years ago.

Our team dedicated itself to the pursuit of inflationary polarization 15 years ago fully expecting a long and difficult journey. It is exciting, after all this work, to be at this stage where the polarization data are breaking into new ground, providing more information about gravitational waves than we learned before. The BICEP2 signal was a surprise, and its ultimate resolution is still a work in progress. The data we need to address these questions about inflation are within sight, and whatever the answers are, they are going to be interesting, so stay tuned.

Posted in Guest Post, Science | 10 Comments

I Wanna Live Forever

If you’re one of those people who look the universe in the eyeball without flinching, choosing to accept uncomfortable truths when they are supported by the implacable judgment of Science, then you’ve probably acknowledged that sitting is bad for you. Like, really bad. If you’re not convinced, the conclusions are available in helpful infographic form; here’s an excerpt.

Sitting-Infographic

And, you know, I sit down an awful lot. Doing science, writing, eating, playing poker — my favorite activities are remarkably sitting-based.

So I’ve finally broken down and done something about it. On the good advice of Carl Zimmer, I’ve augmented my desk at work with a Varidesk on top. The desk itself was formerly used by Richard Feynman, so I wasn’t exactly going to give that up and replace it with a standing desk. But this little gizmo lets me spend most of my time at work on my feet instead of sitting on my butt, while preserving the previous furniture.

IMG_1173

It’s a pretty nifty device, actually. Room enough for my laptop, monitor, keyboard, mouse pad, and the requisite few cups for coffee. Most importantly for a lazybones like me, it doesn’t force you to stand up absolutely all the time; gently pull some handles and the whole thing gently settles down to desktop level, ready for your normal chair-bound routine.

IMG_1174

We’ll see how the whole thing goes. It’s one thing to buy something that allows you to stand while working, it’s another to actually do it. But at least I feel like I’m trying to be healthier. I should go have a sundae to celebrate.

Posted in Health, Personal | 34 Comments

The Wrong Objections to the Many-Worlds Interpretation of Quantum Mechanics

Longtime readers know that I’ve made a bit of an effort to help people understand, and perhaps even grow to respect, the Everett or Many-Worlds Interpretation of Quantum Mechanics (MWI) . I’ve even written papers about it. It’s a controversial idea and far from firmly established, but it’s a serious one, and deserves serious discussion.

Which is why I become sad when people continue to misunderstand it. And even sadder when they misunderstand it for what are — let’s face it — obviously wrong reasons. The particular objection I’m thinking of is:

MWI is not a good theory because it’s not testable.

It has appeared recently in this article by Philip Ball — an essay whose snidely aggressive tone is matched only by the consistency with which it is off-base. Worst of all, the piece actually quotes me, explaining why the objection is wrong. So clearly I am either being too obscure, or too polite.

I suspect that almost everyone who makes this objection doesn’t understand MWI at all. This is me trying to be generous, because that’s the only reason I can think of why one would make it. In particular, if you were under the impression that MWI postulated a huge number of unobservable worlds, then you would be perfectly in your rights to make that objection. So I have to think that the objectors actually are under that impression.

An impression that is completely incorrect. The MWI does not postulate a huge number of unobservable worlds, misleading name notwithstanding. (One reason many of us like to call it “Everettian Quantum Mechanics” instead of “Many-Worlds.”)

Now, MWI certainly does predict the existence of a huge number of unobservable worlds. But it doesn’t postulate them. It derives them, from what it does postulate. And the actual postulates of the theory are quite simple indeed:

  1. The world is described by a quantum state, which is an element of a kind of vector space known as Hilbert space.
  2. The quantum state evolves through time in accordance with the Schrödinger equation, with some particular Hamiltonian.

That is, as they say, it. Notice you don’t see anything about worlds in there. The worlds are there whether you like it or not, sitting in Hilbert space, waiting to see whether they become actualized in the course of the evolution. Notice, also, that these postulates are eminently testable — indeed, even falsifiable! And once you make them (and you accept an appropriate “past hypothesis,” just as in statistical mechanics, and are considering a sufficiently richly-interacting system), the worlds happen automatically.

Given that, you can see why the objection is dispiritingly wrong-headed. You don’t hold it against a theory if it makes some predictions that can’t be tested. Every theory does that. You don’t object to general relativity because you can’t be absolutely sure that Einstein’s equation was holding true at some particular event a billion light years away. This distinction between what is postulated (which should be testable) and everything that is derived (which clearly need not be) seems pretty straightforward to me, but is a favorite thing for people to get confused about.

Ah, but the MWI-naysayers say (as Ball actually does say), but every version of quantum mechanics has those two postulates or something like them, so testing them doesn’t really test MWI. So what? If you have a different version of QM (perhaps what Ted Bunn has called a “disappearing-world” interpretation), it must somehow differ from MWI, presumably by either changing the above postulates or adding to them. And in that case, if your theory is well-posed, we can very readily test those proposed changes. In a dynamical-collapse theory, for example, the wave function does not simply evolve according to the Schrödinger equation; it occasionally collapses (duh) in a nonlinear and possibly stochastic fashion. And we can absolutely look for experimental signatures of that deviation, thereby testing the relative adequacy of MWI vs. your collapse theory. Likewise in hidden-variable theories, one could actually experimentally determine the existence of the new variables. Now, it’s true, any such competitor to MWI probably has a limit in which the deviations are very hard to discern — it had better, because so far every experiment is completely compatible with the above two axioms. But that’s hardly the MWI’s fault; just the opposite.

The people who object to MWI because of all those unobservable worlds aren’t really objecting to MWI at all; they just don’t like and/or understand quantum mechanics. Hilbert space is big, regardless of one’s personal feelings on the matter.

Which saddens me, as an MWI proponent, because I am very quick to admit that there are potentially quite good objections to MWI, and I would much rather spend my time discussing those, rather than the silly ones. Despite my efforts and those of others, it’s certainly possible that we don’t have the right understanding of probability in the theory, or why it’s a theory of probability at all. Similarly, despite the efforts of Zurek and others, we don’t have an absolutely airtight understanding of why we see apparent collapses into certain states and not others. Heck, you might be unconvinced that the above postulates really do lead to the existence of distinct worlds, despite the standard decoherence analysis; that would be great, I’d love to see the argument, it might lead to a productive scientific conversation. Should we be worried that decoherence is only an approximate process? How do we pick out quasi-classical realms and histories? Do we, in fact, need a bit more structure than the bare-bones axioms listed above, perhaps something that picks out a preferred set of observables?

All good questions to talk about! Maybe someday the public discourse about MWI will catch up with the discussion that experts have among themselves, evolve past self-congratulatory sneering about all those unobservable worlds, and share in the real pleasure of talking about the issues that matter.

Posted in Science | 112 Comments

Problem Book in Relativity and Gravitation: Free Online!

If I were ever to publish a second edition of Spacetime and Geometry — unlikely, but check back in another ten years — one thing I would like to do would be to increase the number of problems at the end of each chapter. I like the problems that are there, but they certainly could be greater in number. And there is no solutions manual, to the chagrin of numerous professors over the last decade.

What I usually do, when people ask for solutions and/or more problems, is suggest that they dig up a copy of the Problem Book in Relativity and Gravitation by Lightman, Press, Price, and Teukolsky. It’s a wonderful resource, with twenty chapters chock-full of problems, all with complete solutions in the back. A great thing to have for self-study. The book is a bit venerable, dating from 1975, and the typesetting isn’t the most modern; but the basics of GR haven’t changed in that time, and the notation and level are a perfect fit for my book.

And now everyone can have it for free! Where by “now” I mean “for the last five years,” although somehow I never heard of this. Princeton University Press, the publisher, gave permission to put the book online, for which students everywhere should be grateful.

Problem Book in Relativity and Gravitation

If you’re learning (or teaching) general relativity, you owe yourself to check it out.

Posted in Science | 9 Comments

New Course: The Higgs Boson and Beyond

Happy to announce that I have a new course out with The Great Courses (produced by The Teaching Company). This one is called The Higgs Boson and Beyond, and consists of twelve half-hour lectures. I previously have done two other courses for them: Dark Matter and Dark Energy, and Mysteries of Modern Physics: Time. Both of those were 24 lectures each, so this time we’re getting to the good stuff more quickly.

The inspiration for the course was, naturally, the 2012 discovery of the Higgs, and you’ll be unsurprised to learn that there is some overlap with my book The Particle at the End of the Universe. It’s certainly not just me reading the book, though; the lecture format is very different than the written word, and I’ve adjusted the topics and order appropriately. Here’s the lineup:

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  1. The Importance of the Higgs Boson
  2. Quantum Field Theory
  3. Atoms to Particles
  4. The Power of Symmetry
  5. The Higgs Field
  6. Mass and Energy
  7. Colliding Particles
  8. Particle Accelerators and Detectors
  9. The Large Hadron Collider
  10. Capturing the Higgs Boson
  11. Beyond the Standard Model
  12. Frontiers: Higgs in Space

Because it is a course, the presentation here is in a more strictly logical order than it is in the book, starting from quantum field theory and working our way up. It’s still aimed at a completely non-expert audience, though a bit of enthusiasm for physics will be helpful for grappling with the more challenging material. And it’s available in both audio-only or video — but I have to say they did a really nice job with the graphics this time around, so the video is worth having.

And it’s on sale! Don’t know how long that will last, but there’s a big difference between regular prices at The Great Courses and the sale prices. A bargain either way!

Posted in Higgs, Personal | 27 Comments