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Wednesday, March 11, 2009

Time after time

Rev. of Sean Carroll, From Eternity to Here:  The Origin of the Universe and the Arrow of Time.  Forthcoming from Dutton (Penguin), 2009.

Time just isn’t what it used to be.  And space has gotten to be a bit of a problem, as well.  When I was a lad, physicists told me that they had these things pretty well figured out: they had discovered material evidence of the Big Bang, they had adjusted their conception of the age and evolution of the universe accordingly, and, having recalculated the universe’s rate of expansion (after Hubble’s disastrous miscalculations threw the field into disarray), they were working on the problem of trying to figure out whether the whole thing would keep expanding forever or would eventually slow down and snap back in a Big Crunch.  The key, they said, lay in finding all the “missing mass” that would enable a Big Crunch to occur, because at the time it looked as if we only had two or three percent of the stuff it would take to bring it all back home.  When I asked them why a Big Crunch, and a cyclical universe, should be preferable to a universe that just keeps going and going, they told me that the idea of a cyclical eternity was more pleasing and comfortable than the idea of a one-off event; and when I asked them what came before the Big Bang, they patted my head and told me that because the Big Bang initiated all space and time, there was no such thing as “before the Big Bang.”

But now they tell me that most of that account of the world is wrong.  For one thing, the expansion of the universe seems to be accelerating, which puts a crimp in the plans of everyone who’d been counting on its eventual collapse; worse still, no one can explain why it is that the universe is different now than it was, say, 14 billion years ago, or why it will be different 14 billion years from now.  For the simple and stupefying fact remains that the laws of physics are reversible; nothing in those laws prevents time from running backwards, and it’s entirely possible to have universes in which conscious entities remember the future and remark offhandedly to each other that you can’t get some eggs without breaking an omelet.  And yet, our universe obeys those reversible laws of physics even though effects follow causes, old age follows youth, and systems move from states of low entropy to states of high entropy.  How can this be?  How might it be otherwise?

It’s above my pay grade, this much I know.  But thanks in part to local fluctuations in my corner of the universe that allow me to read books before they are written (these are known technically as Borges-Boltzmann Waveforms, or more colloquially, “wrinkles in time”), I can reveal that Caltech physicist Sean Carroll will have addressed—if not quite “answered”—these questions in his new book, From Eternity to Here: The Origin of the Universe and the Arrow of Time. (Not to be confused with this superficially similar book, which has been published in parallel universe XGH0046, where Frank Viola gave up a promising baseball career in order to become a Christian writer.)

Carroll will have set himself a difficult task: on the one hand, the questions before him are so fundamental and vexing that they are taken seriously only by cosmologists, sages, and stoners.  How did I get here?  Where does that universe go to?  Why isn’t it the same as it ever was? On the other hand, From Eternity to Here will take its place in a genre that has emerged into prominence over the past few decades, the Popular Explanation of Incomprehensible Physics.  From Steven Weinberg’s The First Three Minutes to Stephen Hawking’s A Brief History of Time to Brian Greene’s The Elegant Universe, such books have appeared roughly once every sunspot cycle, and they usually try to speak to a readership that can’t follow the math but is willing to try to understand why the Second Law of Thermodynamics isn’t just a metaphor for how things fall apart and why the Uncertainty Principle isn’t just a metaphor for how you change things by looking at them.  In other words, the difficulty in writing such books lies in figuring out (1) how much popular misconception needs to be cleared away, (2) how familiar your readers are with things like the light-bulb-in-the-moving-train example, and (3) how much detail you need in order to explain the truly recondite stuff.

For example: one important aspect of Carroll’s argument will have involved the question of how to think about small-scale, anomalous conditions in the universe.  Like us: if indeed the universe is proceeding apace to its eventual heat death, then where do humans come in?  Perhaps, following a provocative suggestion from 19th-century Austrian physicist Ludwig Boltzmann, we might argue that there are potentially vast differences between the macrostate of the universe and a tiny microstate thereof, just as there might conceivably be rooms in which all the fast-moving molecules have congregated in one corner.  The problem with that argument, Carroll will have noted, is that the current state of our microstate is far too complex to be explained by such random fluctuations: all you would really need to make the point is a “Boltzmann Brain” to develop from random molecules somewhere in the universe, form the thought “I think therefore I am, and hey, what’s all this then,” and return to dust again.  Developing an entire biosphere just to spite the forces of entropy seems a bit . . . well, excessive.

Furthermore, Carroll will have rejected the notion that the universe is homogeneous and isotropic.  Instead, he will argue that thanks to something called “spontaneous inflation,” local exceptions to the general rule happen all the time, and that consequently, the universe can be clumpy rather than smooth, and our little corner of it might not look like all the rest.  Carroll may write, “We should certainly entertain the possibility that our observable patch is dramatically unrepresentative of the entire universe, and see where that leads us.” This is deeply counterintuitive; it goes against the Copernican principle, according to which it is a bad idea to think that our immediate surroundings differ appreciably from the rest of the universe, and it relies for its plausibility on some very advanced math.  To put this another way, you know you’re in difficult straits when you hear a physicist say that our standard conception of the Big Bang relies on “classical general relativity,” because when physicists say “classical,” they mean “quaint.” As Carroll may argue:

Most of us suffer under the vague impression—with our intuitions trained by classical general relativity and the innocent-sounding assumption that our local uniformity can be straightforwardly extrapolated across infinity—that the Big Bang singularity is a past boundary to the entire universe, one that must somehow be smoothed out to make sense of the pre-Bang universe.  But the Bang isn’t all that different from future singularities, of the type we’re familiar with from black holes. We don’t really know what’s going on at black-hole singularities, either, but that doesn’t stop us from making sense of what happens from the outside. A black hole forms, settles down, Hawking-radiates, and eventually disappears entirely. Something quasi-singular goes on inside, but it’s just a passing phase, with the outside world going on its merry way.

The Big Bang could have very well been like that, but backwards in time. In other words, our observable patch of expanding universe could be some local region that has a singularity (or whatever quantum effects may resolve it) in the past, but is part of a larger space in which many past-going paths don’t hit that singularity.

Carroll’s larger idea is that ours is one of many not-merely-possible but actually existing universes, that the Big Bang is not the origin of them all, and that in some of them, time may run backwards, forwards, sideways, or not at all.  It is not an utterly alien idea, and Philip Pullman has some fun and games with some aspects of it in the popular book series His Dark Materials.  The passage above, though, seems to dramatize Carroll’s problem quite nicely: the readership imagined here is one that suffers under a vague impression of the Big Bang because its intuitions have been trained by classical general relativity.  How big is this readership, exactly?  And is it expanding?  Carroll’s challenge here lies in disabusing some of his readers of concepts they haven’t gotten to yet, such that he will have had to say, “here’s general relativity, and here are its implications, in layperson’s terms.  OK, well, when it comes to the Big Bang it turns out to be wrong.  So now let me explain quantum gravity, which we don’t quite understand yet.”

It will be a remarkable testimony to Carroll’s skills as a writer and public intellectual that he will have helped to accelerate the expansion of a readership for such things.  Along the way, he will have offered a cogent and compelling explanation for why our universe has such rigid rules about time; he will have suggested that even empty space isn’t empty space; and he will have sketched a picture of a cosmos populated by “baby universes” of all descriptions.  Where are we in that picture?  I won’t say, because I don’t want to give away the beginning.  But I can say that From Eternity to Here will have been a richly rewarding reading experience, even by the exacting standards of the genre, for everyone willing to give it the time.

I didn’t say, because I didn’t want to give away the beginning. Where are we in that picture?  Along the way, he offers a cogent and compelling explanation for why our universe has such rigid rules about time; he suggests that even empty space isn’t empty space; and he sketches a picture of a cosmos populated by “baby universes” of all descriptions. It is a remarkable testimony to Carroll’s skills as a writer and public intellectual that he has helped to accelerate the expansion of a readership for such things.

Carroll’s challenge here lies in disabusing some of his readers of concepts they haven’t gotten to yet, such that he has to say, “here’s general relativity, and here are its implications, in layperson’s terms.  OK, well, when it comes to the Big Bang it turns out to be wrong.  So now let me explain quantum gravity, which we don’t quite understand yet.” And is it expanding?  How big is this readership, exactly?  The passage below, though, seems to dramatize Carroll’s problem quite nicely: the readership imagined here is one that suffers under a vague impression of the Big Bang because its intuitions have been trained by classical general relativity. It is not an utterly alien idea, and Philip Pullman has some fun and games with some aspects of it in the popular book series His Dark Materials.  Carroll’s larger idea is that ours is one of many not-merely-possible but actually existing universes, that the Big Bang is not the origin of them all, and that in some of them, time may run backwards, forwards, sideways, or not at all.

In other words, our observable patch of expanding universe could be some local region that has a singularity (or whatever quantum effects may resolve it) in the past, but is part of a larger space in which many past-going paths don’t hit that singularity. The Big Bang could have very well been like that, but backwards in time.

Something quasi-singular goes on inside, but it’s just a passing phase, with the outside world going on its merry way.  A black hole forms, settles down, Hawking-radiates, and eventually disappears entirely. We don’t really know what’s going on at black-hole singularities, either, but that doesn’t stop us from making sense of what happens from the outside.  But the Bang isn’t all that different from future singularities, of the type we’re familiar with from black holes.  Most of us suffer under the vague impression—with our intuitions trained by classical general relativity and the innocent-sounding assumption that our local uniformity can be straightforwardly extrapolated across infinity—that the Big Bang singularity is a past boundary to the entire universe, one that must somehow be smoothed out to make sense of the pre-Bang universe.

As Carroll argues:  To put this another way, you know you’re in difficult straits when you hear a physicist say that our standard conception of the Big Bang relies on “classical general relativity,” because when physicists say “classical,” they mean “quaint.” This is deeply counterintuitive; it goes against the Copernican principle, according to which it is a bad idea to think that our immediate surroundings differ appreciably from the rest of the universe, and it relies for its plausibility on some very advanced math. Carroll writes, “We should certainly entertain the possibility that our observable patch is dramatically unrepresentative of the entire universe, and see where that leads us.” Instead, he argues that thanks to something called “spontaneous inflation,” local exceptions to the general rule happen all the time, and that consequently, the universe can be clumpy rather than smooth, and our little corner of it might not look like all the rest. Furthermore, Carroll rejects the notion that the universe is homogeneous and isotropic.

Developing an entire biosphere just to spite the forces of entropy seems a bit . . . well, excessive.  The problem with that argument, Carroll notes, is that the current state of our microstate is far too complex to be explained by such random fluctuations: all you would really need to make the point is a “Boltzmann Brain” to develop from random molecules somewhere in the universe, form the thought “I think therefore I am, and hey, what’s all this then,” and return to dust again. Perhaps, following a provocative suggestion from 19th-century Austrian physicist Ludwig Boltzmann, we might argue that there are potentially vast differences between the macrostate of the universe and a tiny microstate thereof, just as there might conceivably be rooms in which all the fast-moving molecules have congregated in one corner. Like us: if indeed the universe is proceeding apace to its eventual heat death, then where do humans come in?  For example: one important aspect of Carroll’s argument involves the question of how to think about small-scale, anomalous conditions in the universe.

In other words, the difficulty in writing such books lies in figuring out (1) how much popular misconception needs to be cleared away, (2) how familiar your readers are with things like the light-bulb-in-the-moving-train example, and (3) how much detail you need in order to explain the truly recondite stuff.  From Steven Weinberg’s The First Three Minutes to Stephen Hawking’s A Brief History of Time to Brian Greene’s The Elegant Universe, such books have appeared roughly once every sunspot cycle, and they usually try to speak to a readership that can’t follow the math but is willing to try to understand why the Second Law of Thermodynamics isn’t just a metaphor for how things fall apart and why the Uncertainty Principle isn’t just a metaphor for how you change things by looking at them.  On the other hand, From Eternity to Here takes its place in a genre that has emerged into prominence over the past few decades, the Popular Explanation of Incomprehensible Physics. Why isn’t it the same as it ever was? Where does that universe go to? How did I get here? Carroll has set himself a difficult task: on the one hand, the questions before him are so fundamental and vexing that they are taken seriously only by cosmologists, sages, and stoners.

(Not to be confused with this superficially similar book, which has been published in parallel universe XGH0046, where Frank Viola gave up a promising baseball career in order to become a Christian writer.) But thanks in part to local fluctuations in my corner of the universe that allow me to read books after they are written (these are known technically as Borges-Boltzmann Waveforms, or more colloquially, “wrinkles in time”), I can reveal that Caltech physicist Sean Carroll has addressed—if not quite “answered”—these questions in his new book, From Eternity to Here: The Origin of the Universe and the Arrow of Time. It’s above my pay grade, this much I know.

How might it be otherwise?  How can this be?  And yet, our universe obeys those reversible laws of physics even though effects follow causes, old age follows youth, and systems move from states of low entropy to states of high entropy. For the simple and stupefying fact remains that the laws of physics are reversible; nothing in those laws prevents time from running backwards, and it’s entirely possible to have universes in which conscious entities remember the future and remark offhandedly to each other that you can’t get some eggs without breaking an omelet. For one thing, the expansion of the universe seems to be accelerating, which puts a crimp in the plans of everyone who’d been counting on its eventual collapse; worse still, no one can explain why it is that the universe is different now than it was, say, 14 billion years ago, or why it will be different 14 billion years from now. But now they tell me that most of that account of the world is wrong.

When I asked them why a Big Crunch, and a cyclical universe, should be preferable to a universe that just keeps going and going, they told me that the idea of a cyclical eternity was more pleasing and comfortable than the idea of a one-off event; and when I asked them what came before the Big Bang, they patted my head and told me that because the Big Bang initiated all space and time, there was no such thing as “before the Big Bang.” The key, they said, lay in finding all the “missing mass” that would enable a Big Crunch to occur, because at the time it looked as if we only had two or three percent of the stuff it would take to bring it all back home.  When I was a lad, physicists told me that they had these things pretty well figured out: they had discovered material evidence of the Big Bang, they had adjusted their conception of the age and evolution of the universe accordingly, and, having recalculated the universe’s rate of expansion (after Hubble’s disastrous miscalculations threw the field into disarray), they were working on the problem of trying to figure out whether the whole thing would keep expanding forever or would eventually slow down and snap back in a Big Crunch.  And space has gotten to be a bit of a problem, as well.  Time just isn’t what it used to be.

x-posted.

Posted by Michael on 03/11 at 08:41 AM
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