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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You've never had a "bad-hair day?"
But neither have "The Man in the High Castle" nor "Our Friends from Frolix 8" nor "Solar Lottery" nor "A Maze of Death" nor "Flow My Tears, The Policeman Said" among others (unless I missed these.)
Not my quote, but it's true in the sense that things at a give time and place cannot affect things outside their own light cone.
Does that include quantum entanglement?
If there is something in this article fresher than about 20 years, I don't see it.
When I shoveled out the driveway again this morning, the snow seemed to fly through the usual eleven dimensions and did not do this spontaneously but by direct action of my will.
The expanded Kaluza-Klein geometry seems to cover the situation.
No metaphysics is necessary.
Metaphysics is not necessary but contingent.
Hard to say. Only you know where you are in your reading of philosophy and physics. All these ideas are quite clear once you have progressed beyond a certain level.
The effect doesn't literally precede the cause in the reference frame in which they occur. But if a distant observer is farther away from the cause than from the effect, he may see the effect first.
Seems to me that science needs physical causality to be presumed for most theories to make sense. Nevertheless, it is not demonstrated for warped space/time and non-locality does point to violations of physical causality. Personally, I believe that extra temporal dimensions are the best explanation for non-locality, Schrodinger's cat, etc.
"All these ideas are quite clear once you have progressed beyond a certain level."
That "certain level" presumably is knowing how these theorists define infinity, entropy, and increase, since their ideas are, from the standpoint of semantics, not clear at all. They are contradictory, rather. b.
Don't worry they will. Seems like I heard another one has been mined for eminent release. Dick's amphetimine fueled imagination has pumped cash into Hollywood for decades.
Thank you for the book titles. I appreciate learning what others are reading, particularly in subjects to which they have given a lot of thought.
I read the original article very early this morning then left the house. Returning, I drove past the tennis club and watched the newly-hired pro giving a lesson. He lofted a tennis ball; it's upward flight stopped when the energy that had propelled it upward dissipated.
The ball seemed to stop in mid-air---the ball=entropy
Then it descended to the point where the pro hit it propelling it down the court. court=infinity
Imagined the ball expanding in size until it filled my field of vision, (increase in entropy) continuing down a court that had lost all measurable boundaries (infinity.)
If entropy "increases" it is no longer entropic, that is, the action of increasing presupposes an expenditure of energy.
Perhaps I am missing something because of their confusion in meaning in describing the phenomena they think they may have discovered.
Have to head out. Thanks again. b.
I think if John Kerry gets elected, we will know this.
He has a plan. I don't know what it is but he does have a plan. "Stronger Universe, Respected in the Universe." He might have it in his website. "Have you driven Kerry lately?"
It is Bush's fault that we don't know this.
Bush's tax cuts to the rich has caused our scientific community to not to know this.
what the astrophysicists are saying these days is that the rate of expansion of the universe is acclerating and not decelerating--which means that some unknown force in the universe is at work--that is, besides the four known forces gravity, electro magnatism, the strong force, and the weak force.
But in this case "force" may not be the correct description of the expansion since we have seen that space itself is maleable in the bent of space that fells the planets into orbit around the sun on the macro level (and the stars around a galactic black hole etc)and on the subatomic level stuff fark quarks in and out of existance like snow on a tv.
honk if you love Jesus
It doesn't as anyone who's ever taken a cost accounting course in night school knows full well. Time can stall and pool around your ankles while you wait for the dreadful boredom to cease.
The inflationary stage of the universe immediately following the Big Bang was driven by gravity. The mass of the universe was near zero and the force of gravity was negative rather than positive as it is now, so inflation happened quickly. We see about 10-30 of the whole universe, the rest being beyond the light horizon. The universe is expanding again, and it is gravity providing the force, a negative force. Gravity is positive locally, and was positive right after inflation, but expansion started up again a few billion years ago, so the large general effect of gravity has become negative again.
Gravity is not explained in detail by Newton's inverse square law, but 11 dimensional string theory may do the trick.
This is only really true if you make certain assumptions about the properties of the system in the abstract. For algorithmically finite systems (like our universe apparently currently is), what you say is generally true and hence why "cause-effect" makes an extremely good heuristic for everything one might normally consider. But there is no particular reason it has to be true under all systems and circumstances. Of course, trying to conceptualize the other theoretical scenarios will generally make your brain core dump...
that can be the name of your new band!
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