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Scientists zero in on why time flows in one direction
eurekalert/University of Chicago ^ | 26-Oct-2004 | Steve Koppes

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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TOPICS: Culture/Society; Miscellaneous; Philosophy
KEYWORDS: bluesky; ghengiskhan; immanualkant; navel; philosphy; physics; science; skyblue; stringtheory; time
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To: the invisib1e hand

Time is a function of Liberal space, as is Newsweek.


81 posted on 10/26/2004 8:02:25 PM PDT by Oberon (What does it take to make government shrink?)
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To: eyespysomething
I question the timing of this study.

Come over here so I can smack you...

82 posted on 10/26/2004 8:02:30 PM PDT by Ichneumon ("...she might as well have been a space alien." - Bill Clinton, on Hillary, "My Life", p. 182)
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To: Oberon

So the Zen master steps up to the hot dog cart and says: "Make me one with everything."


83 posted on 10/26/2004 8:02:47 PM PDT by TheBigB (Please Lord...let Bush win and I promise...no naughty thoughts about Lindsay Lohan for a week.)
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To: timestax

Hey, I'm here to serve...lol


84 posted on 10/26/2004 8:03:04 PM PDT by ApesForEvolution (You will NEVER convince me that Muhammadanism isn't a veil for MASS MURDERS. Save your time...)
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To: the invisib1e hand

Yup!


85 posted on 10/26/2004 8:04:03 PM PDT by ApesForEvolution (You will NEVER convince me that Muhammadanism isn't a veil for MASS MURDERS. Save your time...)
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To: Lady Jag
If it didn't it would slosh.

And sloshing, I might add... would be bad. Filling out my time sheets every week is hard enough without any *sloshing* going on.

Time is simply what God created to keep everything from happening at once.

86 posted on 10/26/2004 8:04:06 PM PDT by Ramius (Time? What time do you think we have?)
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To: timestax

Actually, they filmed one episode of Seinfeld in reverse, so, see, it CAN be done!


87 posted on 10/26/2004 8:04:59 PM PDT by Larry Lucido
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To: ApesForEvolution

. "We like to say that the big bang is nothing special in the history of our universe,"
They like to say anthing that will explain away intelligent design. Hmmmmmmmmmm


88 posted on 10/26/2004 8:05:03 PM PDT by ifeelyourpain
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To: Tax-chick

Err, lady...


89 posted on 10/26/2004 8:05:07 PM PDT by ApesForEvolution (You will NEVER convince me that Muhammadanism isn't a veil for MASS MURDERS. Save your time...)
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To: TheBigB; Oberon

oh, these bits! it must be Henny Youngman night.


90 posted on 10/26/2004 8:05:18 PM PDT by the invisib1e hand (do not remove this tag under penalty of law.)
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To: Shryke

Tempted to ask for a smartassedness ping, just to see what responses we'd get...;)


91 posted on 10/26/2004 8:05:31 PM PDT by TheBigB (Please Lord...let Bush win and I promise...no naughty thoughts about Lindsay Lohan for a week.)
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To: ifeelyourpain

So, you *DID* feel my pain, dint you? lol


92 posted on 10/26/2004 8:06:15 PM PDT by ApesForEvolution (You will NEVER convince me that Muhammadanism isn't a veil for MASS MURDERS. Save your time...)
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To: Larry Lucido

Plus, Superman made time go backwards in his first film.


93 posted on 10/26/2004 8:07:05 PM PDT by TheBigB (Please Lord...let Bush win and I promise...no naughty thoughts about Lindsay Lohan for a week.)
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To: ApesForEvolution
Hey, I'm here to serve

I'll take a Carls'Jr. Cheeseberger, and will gladly pay U in the future

94 posted on 10/26/2004 8:07:15 PM PDT by timestax
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To: TheBigB
So the Zen master steps up to the hot dog cart and says: "Make me one with everything."

And when the Zen master asked for change for his $20.00, the hot dog seller says "Change must come from within."

95 posted on 10/26/2004 8:07:26 PM PDT by Larry Lucido
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To: ckilmer
I think it has something to do with why you can't put toothpaste back in the tube.
96 posted on 10/26/2004 8:07:33 PM PDT by Boiler Plate
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To: ApesForEvolution

I am bitting my lower lip right now


97 posted on 10/26/2004 8:08:22 PM PDT by ifeelyourpain
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To: RightWhale; jennyp

random ping


98 posted on 10/26/2004 8:08:43 PM PDT by aposiopetic
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To: timestax

Ahhh, shoot....it is Tuesday, isn't it?!

You want fries wit dat?


99 posted on 10/26/2004 8:08:56 PM PDT by ApesForEvolution (You will NEVER convince me that Muhammadanism isn't a veil for MASS MURDERS. Save your time...)
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To: Larry Lucido
Actually, they filmed one episode of Seinfeld in reverse, so, see, it CAN be done!

I didn't have time to watch it...Philadelphia Experiment you know!!

100 posted on 10/26/2004 8:09:10 PM PDT by timestax
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