Boltzmann’s Universe

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Boltzmann’s Brain CV readers, ahead of the curve as usual, are well aware of the notion of Boltzmann’s Brains — see e.g. here, here, and even the original paper here. Now Dennis Overbye has brought the idea to the hoi polloi by way of the New York Times. It’s a good article, but I wanted to emphasize something Dennis says quite explicitly, but (from experience) I know that people tend to jump right past in their enthusiasm:

Nobody in the field believes that this is the way things really work, however.

The point about Boltzmann’s Brains is not that they are a fascinating prediction of an exciting new picture of the multiverse. On the contrary, the point is that they constitute a reductio ad absurdum that is meant to show the silliness of a certain kind of cosmology — one in which the low-entropy universe we see is a statistical fluctuation around an equilibrium state of maximal entropy. According to this argument, in such a universe you would see every kind of statistical fluctuation, and small fluctuations in entropy would be enormously more frequent than large fluctuations. Our universe is a very large fluctuation (see previous post!) but a single brain would only require a relatively small fluctuation. In the set of all such fluctuations, some brains would be embedded in universes like ours, but an enormously larger number would be all by themselves. This theory, therefore, predicts that a typical conscious observer is overwhelmingly likely to be such a brain. But we (or at least I, not sure about you) are not individual Boltzmann brains. So the prediction has been falsified, and that kind of theory is not true. (For arguments along these lines, see papers by Dyson, Kleban, and Susskind, or Albrecht and Sorbo.)

I tend to find this kind of argument fairly persuasive. But the bit about “a typical observer” does raise red flags. In fact, folks like Hartle and Srednicki have explicitly argued that the assumption of our own “typicality” is completely unwarranted. Imagine, they say, two theories of life in the universe, which are basically indistinguishable, except that in one theory there is no life on Jupiter and in the other theory the Jovian atmosphere is inhabited by six trillion intelligent floating Saganite organisms.

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arxiv Find: What is the Entropy of the Universe?

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And the answer is: about 10102, mostly in the form of supermassive black holes. That’s the entropy of the observable part of the universe, at any rate. Or so you will read in this paper by Paul Frampton, Stephen D.H. Hsu, Thomas W. Kephart, and David Reeb, arxiv:0801.1847:

Standard calculations suggest that the entropy of the universe is dominated by black holes, although they comprise only a tiny fraction of its total energy. We give a physical interpretation of this result. Statistical entropy is the logarithm of the number of microstates consistent with the observed macroscopic properties of a system, hence a measure of uncertainty about its precise state. The largest uncertainty in the present and future state of the universe is due to the (unknown) internal microstates of its black holes. We also discuss the qualitative gap between the entropies of black holes and ordinary matter.

It’s easy enough to plug in the Hawking formula for black-hole entropy and add up all the black holes; but there are interesting questions concerning the connection between the entropy of matter configurations and black-hole configurations. They are explored in an earlier paper by Hsu and Reeb, “Black hole entropy, curved space and monsters,” which Steve blogged about here.

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Make the World Better … For Science!

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A couple of simple ways you can make the world a better place without leaving the comfort of your keyboard.

First, the American Physical Society has set up a convenient web page from which you can write to your representatives in Congress to voice your displeasure concerning the unexpected budget cuts that have decimated U.S. physics, particle physics and fusion research especially. As APS President Arthur Bienenstock writes:

Congress wrapped up the Fiscal Year 2008 (FY08) budget just before adjourning for the year. The budget, which wipes out $1 billion in increases approved last summer for the National Science Foundation (NSF), the Department of Energy’s Office of Science (DOE Science) and the NIST laboratories, does irreparable damage to science and abandons the Innovation/Competitiveness initiatives of Congress and the Administration.

While DOE Science programs received a 2.5 percent increase overall (exclusive of earmarks), they will decline by about one percent after inflation. High-energy physics and fusion will feel the greatest pain. High energy physics will likely have to eliminate hundreds of jobs, halt work on both the NOvA, the next step in neutrino physics at FermiLab and partially furlough many remaining employees. The Omnibus bill for FY08 also stopped R&D on the International Linear Collider project, an international high-precision step beyond the Large Hadron Collider, and zeroed out the U.S. contribution to the international ITER project, designed to demonstrate the scientific and technological feasibility of fusion energy. These actions are severely damaging to the U.S. standing in the international scientific community.

Second, Steinn has come up with the clever idea of making our own Presidential Science Debate (just in case the official one doesn’t come to pass, or at least while we’re waiting). There are a pair of upcoming primary debates January 30/31, one for each party, and the Politico is soliciting questions to be asked of the candidates. So let’s flood their inbox with sensible questions! Nothing about boxers v. briefs or whether they believe in the literal reality of transubstatiation — let’s ask about their commitment to basic research, their views on manned vs. robotic exploration of space, the promise of alternative energy sources, what have you.

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Is the Universe a Computer?

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Via the Zeitgeister, a fun panel discussion at the Perimeter Institute between Seth Lloyd, Leonard Susskind, Christopher Fuchs and Sir Tony Leggett, moderated by Bob McDonald of CBC Radio’s Quirks & Quarks program. The topic is “The Physics of Information,” and as anyone familiar with the participants might guess, it’s a lively and provocative discussion.

A few of the panel members tried to pin down Seth Lloyd on one of his favorite catchphrases, “The universe is a computer.” I tackled this one myself at one point, at least half-seriously. If the universe is a computer, what is it computing? Its own evolution, apparently, according to the laws of physics. Tony Leggett got right to the heart of the matter, however, by asking “What kind of process would not count as a computer?” To which Lloyd merely answered, “Yeah, good question.” (But he did have a good line — “If the universe is a computer, why isn’t it running Windows?” Insert your own “blue screen of death” joke here.)

So I tried to look up the definition of a “computer.” You can open a standard text on quantum computation, but “computer” doesn’t appear in the index. The dictionary is either unhelpful — “a device that computes” — or too specific — “an electronic device designed to accept data, perform prescribed mathematical and logical operations at high speed, and display the results of these operations.” Wikipedia tells me that a computer is a machine that manipulates data according to a list of instructions. Again, too specific to include this universe, unless you interpret “machine” to mean “object.”

I think the most general definition of “computer” that would be useful is “a system that takes a set of input and deterministically produces a set of output.” The big assumption being that the same input always produces the same output, but I don’t think that’s overly restrictive for our present purposes. In that sense, the laws of physics act as a computer: given some data in the form of an initial configuration, the laws of physics will evolve the configuration into some output in the form of a final configuration. Setting aside the tricky business of wavefunction collapse, you have something like a computer. I suppose you could argue about whether the laws of physics are “the software” or the computer itself, but I think you are revealing the limitations of the metaphor rather than learning something interesting.

But if we take the metaphor at face value, it makes more sense to me to think of the universe as a calculation rather than as a computer. We have input data in the form of the conditions at early times, and the universe has calculated our current state. It could have been very different, with different input data.

And what precise good does it do to think in this way? Yeah, good question. (Which is not to imply that there isn’t an answer.)

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Again with the De-Lurking

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Posting is slow, partly because of other commitments, and also because my co-bloggers are poopyheads. So this is as good a time as any to resurrect our occasional de-lurking threads, in which loyal readers who tend not to comment on ordinary posts can peek their heads up and introduce themselves. If you see your shadow, it’s six more weeks of winter.

Don’t worry, there are great things ahead, including some potentially very cool guest blogging (you know who you are). And you are welcome to take the opportunity here to advertise important events or links that you think people should know about — for example, Chanda points us to the 2008 joint annual meeting of the National Society for Black Physicists and the National Society of Hispanic Physicists to be held in Washington DC on February 20-24, 2008. And I can point you to the upcoming Categorically Not in Santa Monica on January 27, featuring what promises to be a lively discussion on Hollywood Physics. Stuff like that.

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Code Words

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One of the skills that many successful politicians have is the ability to speak separately to two audiences using the same words. It used to be that you could speak to different groups by just saying different things — go visit them, and tell them what you want them to hear. But these days, the default assumption is that everything you say in every context is up on YouTube the next day, so you have to be more subtle. A great strategy, if you can master it, is to use code words — language that seems sensible but unremarkable to the majority of listeners, but carries special meaning for a particular audience. George W. Bush is a master of the technique, but both winners of last week’s Iowa caucuses have also demonstrated the ability.

For Barack Obama, the particular audience is African-Americans. He rarely brings up race directly, but continually hammers on the theme of bridging divides and bringing people together. The surface appeal is to overcoming the tensions between Blue and Red America, but the parallels with Black and White America are pretty clear. More subtly, he borrows phrases from the civil rights movement — “the fierce urgency of now” — that have powerful resonance for the people who fought in those struggles.

For Mike Huckabee, the particular audience is evangelical Christians. A good example of Huckabee’s use of code words was flagged by Josh Marshall, who picked up on the repeated use of a notion of “vertical thinking.” Without much explanation, Huckabee drops this phrase liberally into his speeches, and it is displayed prominently on his website.

Huckabee vertical thinking

What’s going on there? Marshall found explanations here and here. I suppose context has given away the secret by now, but “vertical thinking” refers to how we conceptualize the role of God as the origin of all things.

vertical thinking

“Horizontal thinking,” meanwhile, is what happens when you leave “Man” to figure it all out by himself.

horizontal thinking

Count me as a committed horizontal thinker. There’s a great benefit to recognizing that it’s we human beings who are conducting an ongoing conversation about how the world works and how we should live our lives, rather than taking instructions from a (literally) higher authority — namely, we can change our minds when we realize that we’ve been making a mistake. If we’re beholden to a set of ancient cryptic mythological texts that were all about reinforcing the prevailing norms at the time, we get stuck with vertical thinking of the form “Wives are to voluntarily submit themselves to their husbands as the head in their marriage.”

Most of we horizontal thinkers didn’t even notice Huckabee’s formulation, I’m sure. It will be interesting to see what happens if he wins another primary or two.

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G’Kar

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Andrew Olmsted was a U.S. soldier who occasionally posted at Obsidian Wings as G’Kar. He was killed yesterday in Iraq. Andrew (who I didn’t know personally) had written a piece with the specific intention of having it posted only in the event of his death. It was posted today by hilzoy.

I write this in part, admittedly, because I would like to think that there’s at least a little something out there to remember me by. Granted, this site will eventually vanish, being ephemeral in a very real sense of the word, but at least for a time it can serve as a tiny record of my contributions to the world. But on a larger scale, for those who knew me well enough to be saddened by my death, especially for those who haven’t known anyone else lost to this war, perhaps my death can serve as a small reminder of the costs of war. Regardless of the merits of this war, or of any war, I think that many of us in America have forgotten that war means death and suffering in wholesale lots. A decision that for most of us in America was academic, whether or not to go to war in Iraq, had very real consequences for hundreds of thousands of people. Yet I was as guilty as anyone of minimizing those very real consequences in lieu of a cold discussion of theoretical merits of war and peace. Now I’m facing some very real consequences of that decision; who says life doesn’t have a sense of humor?

I don’t think the war in Iraq was a good idea. But I have enormous respect and admiration for the people who volunteer and put their lives on the line to serve in the military; they’re not the ones who decide what wars to get into. My heart goes out to Andrew’s friends, colleagues, and family.

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A Form of Not Being Sure

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I bought this print to decorate the wall of my office. I like the art, and the title is “Time’s Arrow,” so how could I resist?

Time’s Arrow by Costa

But I did have a worry: the painting clearly involved text, which I tend to think is an aesthetic mistake — it brings a depressing specificity to what should be an open-ended interpretive process. And here the resolution of the online image was too small for me to make out the words, so what if the text was completely dopey?

Now it has arrived, and here is the main text:

Living is a form of not being sure, not knowing what next or how. The moment you know how, you begin to die a little.

The artist never entirely knows. We guess; we may be wrong, but we take leap after leap in the dark.

I kind of like it.

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