May 24, 2008
Does Time Run Backward in Other Universes?
From Scientific American:
The universe does not look right. That may seem like a strange thing to say, given that cosmologists have very little standard for comparison. How do we know what the universe is supposed to look like? Nevertheless, over the years we have developed a strong intuition for what counts as “natural”—and the universe we see does not qualify.
Make no mistake: cosmologists have put together an incredibly successful picture of what the universe is made of and how it has evolved. Some 14 billion years ago the cosmos was hotter and denser than the interior of a star, and since then it has been cooling off and thinning out as the fabric of space expands. This picture accounts for just about every observation we have made, but a number of unusual features, especially in the early universe, suggest that there is more to the story than we understand.
Among the unnatural aspects of the universe, one stands out: time asymmetry. The microscopic laws of physics that underlie the behavior of the universe do not distinguish between past and future, yet the early universe—hot, dense, homogeneous—is completely different from today’s—cool, dilute, lumpy. The universe started off orderly and has been getting increasingly disorderly ever since.
More here.
Posted by Azra Raza at 10:43 AM | Permalink
Comments
As a lay person, with only an armchair technical understanding, I'm confused by the use of the word "orderly" in the context of the last sentence. "Order" seems to be a very loaded concept, which here is being used to imply something like "regular" or "homogenous", but deeming the current state of the universe "disorderly" seems to belie the implications of the laws of physics. Or at least my understanding of them.
Presumably, "order" is implicitly thermodynamic, so saying that "disorder increases with time" is equivalent to saying that entropy is increasing, which is indeed the case. The local increase of order that we see on our planet is made possible by the sun's energy; if the sun were to switch off tomorrow, all life on Earth would quickly die out. This much is trivial. But I wonder if the corresponding increase in information in life might one day outweigh the dwindling availability of "free" energy from stars in the distant future? Will life find a way to overcome diminishing resources as the expanding universe fades and cools? I guess there's no way for us to know for sure, but it's an interesting question to consider.
Posted by: DavidG | May 24, 2008 2:34:42 PM
Time running backwards? That would imply that the lawyers over there actually pay you to consult with them. That, I refuse to believe.
Posted by: aguy109 | May 24, 2008 4:39:12 PM
This Sean Carroll piece is entertaining, in a Talmudic kind of way ("Why did God create fruits and vegetables on the 2nd day, before there was light to see them with?"). Rather than ask if time can "run backwards" I wonder if it isn't appropriate to finally abandon our notion of time as a fourth "dimension" of space. The spatialization of time is obviously messing up our ability to think constructively about the cosmos.
Nothing has ever been observed "moving" in time; only in space. Likewise there is no "direction" to move in. Whatever its value in developing the 2nd law of thermodynamics, talking generally of "time's arrow" takes the metaphor of temporal motion a little too literally.
Nothing has ever happened "in" the past, and nothing will ever happen "in" the future. Events can only occur in the present. We fix these events in our minds and call them memory or speculation. But past and present are concepts only; they can't be experienced or observed.
Time is such a tenacious illusion for us because we believe so deeply in the permanence of matter. The pencil on my desk is the same pencil that was there an hour ago, and will be there an hour from now (if I don't move it). But particle physics has shown us it is not the same pencil. If we look closely enough, the subatomic waveforms (indeed the molecules themselves) are in constant activity, which our senses and cognition generalize into stillness. In the language of Carroll's piece, we observe macrostates, not microstates.
We know--have known for decades--that "matter" is a convenient fiction; the shadows on the cave wall cast by flickering "waveicles" composed of pure form. Why should time, which none of us has ever observed, be any more sacred?
Posted by: Chris Schoen | May 24, 2008 6:15:12 PM
The microscopic laws of physics that underlie the behavior of the universe do not distinguish between past and future, yet the early universe—hot, dense, homogeneous—is completely different from today’s—cool, dilute, lumpy. The universe started off orderly and has been getting increasingly disorderly ever since.
OMG TOTALLY. Yesterday I noticed that even though I feel less energetic as the day progresses, the numbers on my digital watch get bigger. THE UNIVERSE IS A PARADOX.
Posted by: Nick Smyth | May 25, 2008 12:51:06 AM
Anything real about this moment is not leached away by my conscious mind moving through and beyond it.
Because we can't reinhabit the past it's simple for us to pretend it's gone. Because it's gone from us. But the past is right were it always was, we've moved through it.
Gone from us maybe, but right there where it came into being.
Either that or it was never there at all. Which would leave us kind of hanging.
It seems clearer and clearer that we've been calling time is something we're moving through, and that we've allowed ourselves to be convinced, with no proof but the tacit assertion, that that movement is all time is.
Posted by: Roy Belmont | May 25, 2008 3:37:24 AM
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