Posted on 10/26/2004 7:36:36 PM PDT by ckilmer
Public release date: 26-Oct-2004 [ Print This Article | Close This Window ]
Contact: Steve Koppes skoppes@uchicago.edu 773-702-8366 University of Chicago
Scientists zero in on why time flows in one direction The big bang could be a normal event in the natural evolution of the universe that will happen repeatedly over incredibly vast time scales as the universe expands, empties out and cools off, according to two University of Chicago physicists. "We like to say that the big bang is nothing special in the history of our universe," said Sean Carroll, an Assistant Professor in Physics at the University of Chicago. Carroll and University of Chicago graduate student Jennifer Chen are scheduled to post a paper describing their ideas at http://arxiv.org/ Thursday evening.
Carroll and Chen's research addresses two ambitious questions: why does time flow in only one direction, and could the big bang have arisen from an energy fluctuation in empty space that conforms to the known laws of physics?
The question about the arrow of time has vexed physicists for a century because "for the most part the fundamental laws of physics don't distinguish between past and future. They're time-symmetric," Carroll said.
And closely bound to the issue of time is the concept of entropy, a measure of disorder in the universe. As physicist Ludwig Boltzmann showed a century ago, entropy naturally increases with time. "You can turn an egg into an omelet, but not an omelet into an egg," Carroll said.
But the mystery remains as to why entropy was low in the universe to begin with. The difficulty of that question has long bothered scientists, who most often simply leave it as a puzzle to answer in the future. Carroll and Chen have made an attempt to answer it now.
Previous researchers have approached questions about the big bang with the assumption that entropy in the universe is finite. Carroll and Chen take the opposite approach. "We're postulating that the entropy of the universe is infinite. It could always increase," Chen said.
To successfully explain why the universe looks as it does today, both approaches must accommodate a process called inflation, which is an extension of the big bang theory. Astrophysicists invented inflation theory so that they could explain the universe as it appears today. According to inflation, the universe underwent a period of massive expansion in a fraction of a second after the big bang.
But there's a problem with that scenario: a "skeleton in the closet," Carroll said. To begin inflation, the universe would have encompassed a microscopically tiny patch in an extremely unlikely configuration, not what scientists would expect from a randomly chosen initial condition. Carroll and Chen argue that a generic initial condition is actually likely to resemble cold, empty space-not an obviously favorable starting point for the onset of inflation.
In a universe of finite entropy, some scientists have proposed that a random fluctuation could trigger inflation. This, however, would require the molecules of the universe to fluctuate from a high-entropy state into one of low entropy-a statistical longshot.
"The conditions necessary for inflation are not that easy to start," Carroll said. "There's an argument that it's easier just to have our universe appear from a random fluctuation than to have inflation begin from a random fluctuation."
Carroll and Chen's scenario of infinite entropy is inspired by the finding in 1998 that the universe will expand forever because of a mysterious force called "dark energy." Under these conditions, the natural configuration of the universe is one that is almost empty. "In our current universe, the entropy is growing and the universe is expanding and becoming emptier," Carroll said.
But even empty space has faint traces of energy that fluctuate on the subatomic scale. As suggested previously by Jaume Garriga of Universitat Autonoma de Barcelona and Alexander Vilenkin of Tufts University, these flucuations can generate their own big bangs in tiny areas of the universe, widely separated in time and space. Carroll and Chen extend this idea in dramatic fashion, suggesting that inflation could start "in reverse" in the distant past of our universe, so that time could appear to run backwards (from our perspective) to observers far in our past.
Regardless of the direction they run in, the new universes created in these big bangs will continue the process of increasing entropy. In this never-ending cycle, the universe never achieves equilibrium. If it did achieve equilibrium, nothing would ever happen. There would be no arrow of time.
"There's no state you can go to that is maximal entropy. You can always increase the entropy more by creating a new universe and allowing it to expand and cool off," Carroll explained.
### Images of the authors are available upon request.
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BTTT
I believe in God as much as you do, Jorge...but I don't pretend to fully understand either Him or His creation.
I'm glad you think you've got it nailed down, however. You go, dude...
BTTT
Awww, that's what they said the last time....
I have been reading about time for a long -ahem- time. The more I read, the more confused I become. There is a deep mystery here, one that human minds may not be adequate to unravel or understand.
I've also been reading widely and deeply about Buddhism. Not that a 53-year-old Jew is going to convert. But Cordwainer Smith (perhaps one of the littlest-known and most under-rated of all science fiction writers) referred to the Buddha as "the Saint who defeated time by realizing what it is and stepping aside."
I sent Barbour a list of questions after reading his book twice and he (or his bot) responded: "The questions you pose are deep. I hope to someday soon have time to begin to answer them." I suspect if I'd suggested that time is made of curdled milk, I would have received the same response.
--Boris
You're bad. And funny. Thanks. b.
Actually, it's "Time flies like an arrow. Fruit flies like a banana." Groucho Marx
I hate time!
The only out is that the observations are wrong, e.g. due to error in the experiments. That is very unlikely.
BTW, your final point is kind of in the right direction. Current thinking is that symmetry obtains if parity, change and time are all reversed together.
Along analogous lines, I just learned that when you Google something and you get, say, 2 million hits, Google isn't really finding two million sources. It's seeing how many hits you got over an increment of time. Then it calculates how many hits you should find based on the number of pages out there. Neat.
That's interesting. It takes my dialup a minute to load a webpage, so 2 million hits would be like seeing a vast universe through an infinite bandwidth, which maybe Google has, but at 40 kbaud I don't.
Groan. I have to sign off now because I get a potato clock
5. There are beautiful connections to new pure mathematical structures.
The relation of string theory to mathematics is a huge topic, and I'll comment on it at length at some other time. In brief though, while I think string theory has been an utter disaster for theoretical physics during the past 20 years, it has lead to many interesting things in mathematics. However, most of these interesting things really come from 2d conformal QFT [Quantum Field Theory], and I would argue that it is QFT which is having a huge impact on mathematics, much more so than string theory. Witten's Fields medal was for his work on the relation of QFT to math, not for anything he has done using string theory.
well of course man is made for both time and eternity but ya gotta be real careful about the space between--otherwise you get wierd stuff in the vortices--the spawn of gods and humans-- like the half men half horse centaurs of greek mythology or the half man half elephant men of indian mythology.
anyone with two eyes can see that something went really really wrong there.
Jesus imho did a honking good job bridging that gap.
I always asked myself, why are the rivers flowing and why?! Do they flow a certain way to meet the Ocean/Lake and if it does it why?!
I know it is off the subject but what the hell....
Occam's razor comes to mind ;-)
That being said, on what size and / or mass scales does conventional gravity fail? Quantum (small), relativistic (large), or both, depending? Can you recommend any books on the level of Feynmann's QED or Kip Thorne's works on black holes?
No metaphysical bullshit, please, just pointers to the math...
Perspiring minds want to know...
And how do you get curdled milk without time?
A wise old philosopher called such musings as this as "pouring from the empty, into the void."
Let me know when you dispense with time. I'd like to live forever.
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