Saturday, March 27, 2010

the structure of time

From today:
The accretion process releases vast amounts of energy, and as a result quasars are among the most powerful energy sources known. No one knows for sure, however, how these objects form, how they develop in time, or how exactly their stupendous energies are produced. Because they are so bright, quasars can be seen even when they are very far away, and this combination of being both highly energetic and located at cosmological distances makes them appealing to astronomers trying to figure out the nature of galactic center black holes (our own Milky Way has one) and the conditions in the early universe that prompt these monsters to form.

There are about forty quasars known to be so far away that their light has been traveling toward us for over twelve billion years; in other words, their black holes were already glowing brightly when the universe was very young - less than one billion years old. The question is: do they look like nearby quasars, or are they different somehow? CfA astronomer Yue Shen is a member of an international team of twelve astronomers that has concluded that some remote quasars are very different indeed.

Using the Spitzer Space Telescope's sensitive infrared cameras, the scientists observed twenty-one distant quasars to see whether or not they could detect evidence for hot dust; such dust would be expected if there really is a hot accreting disk of material around a black hole. Indeed, hot dust is a characteristic feature of quasars in the local universe.

Remarkably, as the team reports in this week's issue of Nature, two of the quasars in their study show no evidence for hot dust. The implication is that these galaxies are so primitive (in cosmic terms) that there has not been time for them to make dust, presumably either because there has not been time to form enough of the required constituent chemical elements, or because there has not been time to assemble them into dust grains. The results suggest that these objects date from an epoch in the universe when dust was first being made. Dust is a key catalyst in turning atomic gas into the molecules that facilitate stellar birth and evolution, and this new result is significant not only for quasar research, but also for helping understand how the first few generation of stars in the universe came to be.
I find this wild for some reason. We're asked to think of what a galaxy might be, not only before stars exist but before there is dust. This is a mere 1 billion years after the creation of the universe, a whole 12 or so billion years before the present.

Few people stop to recognize how strange the universe, the whole of physical existence, is. It's worth thinking about.

The furthest back our concept of time, as understood by contemporary physics, allows us to go back is to 10-43 seconds after the "big bang". No one knows what the big bang is or was. It's a theoretical entity derived from the fact that everything in the universe is rushing away from everything else right now—very, very fast. If everything is rushing away from everything else, it stands to reason that if you go wind the clock back, everything was very close to everything else at some point in the distant past, right before it started getting very far apart. According to measurements of the light we receive from special supernovae known as "standard candles", cosmologists argue that the big bang occurred approximately 13.75 billion years ago. That's the point at which all the matter in the universe—about 1.6 x 1060 kilograms, which is about the size of your ass if you attached 60 zeroes to it—occupied less than the space taken up an atom, which is about 1 ångström aka 10-10 meters, which is much smaller even than my ass which itself is very small.

Don't bother trying to imagine it. It's just a number. An intellectual entity. It probably happened, so far as we know it, but there's no reason to believe the typical human imagination is at all adequate to the way the world in fact is.

The universe expanded and cooled a little. Before it cooled, the four forces—electromagnetism, the weak force, the strong force, and gravity—were all basically the same "thing". Again, it's just a mathematical concept. It's not even that, since no one yet has a theory to account for the unity of gravity with the other three forces. Therefore, it's an imagined concept, three steps removed from normal sensuous experience. (Imagination is one step away, mathematical reason another, imagined mathematical theory yet another.)

When it cooled—between 10-43 and 10-36 seconds—gravity separated out from the electromagnetic and strong and weak forces. At this point you have gravity, the Higgs boson (as yet undiscovered), and magnetic monopoles. Magnetic monopoles are so important. We've never discovered one, but inflation theory (see below) predicts they should be especially hard to find. According to Alan Guth, if you could put together about an ounce of magnetic monopoles and a false vacuum, you could create another universe off from this one. Looks like the creation of the universe, at least in theory, is not a divine act. Thankfully the Large Hadron Collider might create magnetic monopoles! If we do create them, it will probably change the world as we know it, but that's a story for another time.

At this point inflation takes place. Inflation implies that the universe went from being about the size of an atom to being, well, the size of the universe in 10-7 seconds (.0000001 seconds). It increased by a factor of about 1078, which is a meaningless number to a human but it's impossibly large. The discovery that the universe inflated is one of the all-time great discoveries in physics. There are a few reasons we know it happened. If you look in any direction in the universe, it's all the same. This implies that everything in the universe was at one point very close together—really, "touching". Otherwise how would everything on the "east" side of the universe have communicated with everything on the "west" side of the universe? (Since they're way too far apart to do any communicating now.) We also know inflation is true because the universe looks completely flat. The universe before 10-36 seconds must have been highly curved. This follow from Einstein's general theory of relativity, according to which, the more shit you have crammed into a 5 lb bag, the more "curved" will be the space it occupies. Curvature of space is hard to grasp, but if you ever played PacMan, it's kind of like when PacMan goes through the portal on the right side of the screen and appears on the left. There's a very high probability the universe is indeed like an extremely big PacMan board in this respect. What's extremely unlikely is that the universe is flat. And yet all our most careful measurements of it show that it is sublimely flat. Inflation explains why. Early on, the universe just got so big that from any observable point on the surface of the universe, it looks flat. Just like from any observable point on the surface of the earth it looks flat. Inflation also explains the bit about monopoles. It predicts there should only be 1 monopole per observable area of the universe. But the actual universe is about 1026 bigger than the observable universe. Hence, we don't see any monopoles. (Doesn't rule out creating them in particle accelerators!)

Time slows down to a crawl after this. You imagine it would, given how big space becomes. It's not until after 10-12 seconds that quarks are allowed to form hadrons (the stuff out of which the crap surrounding us is made).

Yes, we're talking about billion billionths of a second here, very short periods of time, but keep in mind we're working on an exponential scale. 1012 seconds is 1,000,000,000,000 seconds or about 32,000 years (3.2 x 104 years). 1036 seconds is 1,000,000,000,000,000,000,000,000,000,000,000,000 seconds or about 3.1 x 1028 years. So a difference of about 24 orders of magnitude. There's no difference between fractions of a second and factors of a second other than the ordinary human level of perception. Therefore, even though it was trillionths of a second, damn near an eternity passed between inflation and the beginning of the creation of matter. An even greater amount of time was to pass before the universe was cool enough to do anything else like form hydrogen or make dust.

This trend of exponentially greater periods of time between events was to continue. It takes longer to reach the photon epoch (all the light gets released, creating the cosmic background microwave radiation we see today). And it takes longer still to reach the formation of normal matter. Longer than that to create quasars (see above), galaxies, stars, planets, and the rest. The length of time between events increases exponentially.

But finally the exponentially increasing orders of magnitude levels out (from our perspective) and forms an S-shaped curve—when life comes into existence. Now it begins to go in the other direction (picture a bell-shaped curve here). Life exists for 3 billion years before there are eukaryotes. Then in a shorter time there is a difference in sexes. In a shorter time there are body parts (cambrian explosion). A shorter time before that there is life on land. A shorter time before that there are brains. A shorter time before that, creatures who are bipedal and who have opposable thumbs. A shorter time before that, humans. A shorter time before that, art, religion, and thought. A shorter time before that, the death of Socrates. Then the invention of the printing press. Then the invention of the steam engine. Then the computer. Then the internet. Then the sequencing of the human genome.

It might be the case that time is not a neutral, empty medium in which events take place but rather has an intrinsic structure to it. Plato argued that space and matter were the same thing, that the basic background material of the cosmos was something called "chora" which knotted up to form ordinary objects. There are many physicists today who believe that if we probe matter on a fine enough scale, we'll see that Plato's idea is true and point particles are mere configurations of space. Perhaps time is similarly locked in with the events that supposedly unfold in it. In that case the bell-shaped curve does not describe a set of events that happen to occur in time. Instead it describes the structure and perhaps meaning of time itself. In that case human thought is not a mere froth floating on the surface of a vast cosmic ocean—capable of seeing and conceiving of a small part of what is, but incapable of really getting to the bottom of things. Instead, human thought—especially as applied to solving the problems humans encounter, using finite resources—is an efficient cause in the service of a broad cosmological principle. In other words human invention and problem-solving are not mere spandrels, out-of-place with respect to the cold, meaningless cosmos. To think is part of the meaning of time itself, and it is essential to the unfolding purpose of existence.

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