The Nexus commeth!
Posted on 03/19/2005 5:16:19 AM PST by snarks_when_bored
Giant space-time ripples may cause cosmic expansion
* 17:43 18 March 2005
* NewScientist.com news service
* Maggie McKee
Dark energy is not necessary to explain the accelerating expansion of the universe observed by astronomers, suggest controversial new calculations. Instead, gigantic ripples in space-time - larger than the observable universe - may be the cause.
Astronomers have known since the 1920s that space itself has been expanding since the big bang about 14 billion years ago. But in 1998, they discovered the expansion must have sped up about a billion years ago, based on observations of supernovae that appeared farther away than expected.
So cosmologists came up with several exotic explanations, including dark energy - which may be a repulsive property of space itself or an ultra-light particle - and a theory in which gravity behaves differently over large distances.
But current theories overestimate the effect of dark energy by millions of times, and modifying gravity is an "ad hoc" solution, says Antonio Riotto, a cosmologist at the National Institute for Research in Nuclear Physics in Padova, Italy. "There is a big embarrassment about what theory predicts and what we observe," he told New Scientist.
Now, he and a team led by Edward Kolb of the Fermi National Accelerator Laboratory in Batavia, Illinois, US, say they can account for the cosmic speed-up using "inflation" - the widely-accepted theory that describes what happened in the first 10-35 seconds after the big bang. "Our proposal is very conservative - it doesn't invoke any new ingredient to explain the acceleration," Riotto says.
Global universe
During inflation, space itself expanded faster than the speed of light. As it did so, random quantum fluctuations that popped into being produced ripples in space-time. These swelled to fill the entire "global" universe, which is about 10100 times as large as the universe we can see.
Our "observable" universe is confined to a region with a radius of 14 billion light years because only light from within that distance has had time to reach us since the big bang.
The team believes the ripples had little effect on our observable universe for billions of years because the effect of nearby matter overpowered the far-distant ripples. But about a billion years ago, they say, the density of nearby matter became so reduced by the expansion of space that the effect of the ripples began to be felt - as cosmic acceleration.
Kolb explains that the ripples should affect the observable universe because they flowed through all of space during inflation, leaving behind a gravitational wake that can still be felt, if not seen, nearby. "Imagine you're out on the ocean, and it's foggy. You can be affected by very long-wavelength ripples, although you don't actually see the wave - all you feel is the swell moving up and down," he told New Scientist. He adds the ripples are growing with time - which causes the acceleration.
"Tricky" calculations
"I like this idea a lot," says Robert Brandenberger, a cosmologist at McGill University in Montreal, Canada, who predicted a similar effect in 1998. "We are sitting in the trough of a very long-wavelength density wave, which generates something that looks to us like acceleration," he told New Scientist.
But many researchers are not convinced. Sean Carroll, a cosmologist at the University of Chicago, US, says, "I don't really understand what they're doing. But they do have a track record of doing great things in cosmology."
Alan Guth, a cosmologist at the Massachusetts Institute of Technology in Cambridge, US, who pioneered the theory of inflation in the 1980s, also acknowledges the team's record, but is nevertheless "fairly sceptical of the physics this paper is trying to use".
The calculations - which are based on Einstein's General Theory of Relativity - are "very tricky", he says. "As I understand it, when the wavelength of the perturbations gets longer and longer, the effects disappear completely - the ripples would have no effect on the observable universe."
Kolb's team says more observations of supernovae could provide a test of their theory, which predicts how strong the ripples should be. But Guth says it will be "very difficult to make the measurements accurately enough to distinguish this theory from other theories".
The paper has been submitted to Physical Review Letters.
During inflation, space itself expanded faster than the speed of light. As it did so, random quantum fluctuations that popped into being produced ripples in space-time. These swelled to fill the entire "global" universe, which is about 10100 times as large as the universe we can see.
Our "observable" universe is confined to a region with a radius of 14 billion light years because only light from within that distance has had time to reach us since the big bang.
It's not easy to comprehend what scaling up 'small' quantities by a factor of 10100 does. Try it.
Ping
A number like that makes my hair hurt.
Does anything exist in quantities as large as 10 to the 100th power? Are there even that many atoms in the observable universe?
Nope. Last I heard, the total number of elementary particles in the observable universe is something on the order of 1080, give or take a few.
I'm an engineer, but stuff like this makes my brain hurt.
Just as I thought...
Yeah, the idea was so obvious, you didn't even bother to write it up... (smile)
I burp once in a while and I almost never have any warning.
Maybe it was kind of like the sneeze in "The Hitchhiker's Guide to the Galaxy".
"the ripples...flowed through all of space...leaving behind a gravitational wake that can still be felt"
No wonder I feel wobbly!
Bump for later reading.
"Primordial inflation explains why the universe is accelerating today" [Abstract, PDF]
We could ask Jimmah Carter to give us a synopsis in simpler terms.
....Dark energy is not necessary to explain the accelerating expansion of the universe observed by astronomers, suggest controversial new calculations. Instead, gigantic ripples in space-time - larger than the observable universe - may be the cause....Does this explain the dark energy called Hillary?....
...and her gigantic ripples???...
The Nexus commeth!
-b-
You are a Trekkie of the first order. Live long and prosper.
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