Posted on 01/12/2005 11:50:49 AM PST by snarks_when_bored
Big bang sound waves explain galaxy clustering
13:32 12 January 2005 NewScientist.com news service Maggie McKee, San Diego
Sound waves that roared through space after the big bang left behind a subtle imprint in the way galaxies are clustered today, reveal two major studies. The results bolster the standard theory that the universe is flat, and measuring the distance between the sound ripples may provide a new cosmic yardstick to probe the past.
Two independent teams mapping the universe have found that galaxies are currently huddled together slightly more often at distances of 500 million light years as a result of conditions in the early universe. They announced the finding on Tuesday at a meeting of the American Astronomical Society in San Diego, California, US.
The results back the standard models of a flat universe, dominated by dark matter and dark energy, that has been expanding - or undergoing a process of inflation - since the big bang. Generally speaking, the distance between galaxies matches the pattern of sound wave ripples from the early universe.
"The triumph is that the signal is seen at the expected location," says Richard Ellis, an astronomer at the California Institute of Technology, US, and a member of the 2-degree Field Galaxy Redshift Survey (2dF) team.
The discovery is especially powerful because the groups used different observations and statistical techniques to arrive at the same conclusion, says Martin Rees, an astronomer at Cambridge University, UK.
Matching predictions
Astronomers from 2dF studied the locations of 221,000 galaxies using a telescope in Australia. Meanwhile, the Sloan Digital Sky Survey (SDSS) mapped 46,000 bright, red galaxies within six billion light years across an area of sky about 10 times as large with a telescope in New Mexico, US.
The finding agrees well with predictions made 30 years ago about how the nearly featureless infant universe should have matured into the structured place seen today, says Rees. He adds that it dovetails with observations of the big bang's afterglow - called the cosmic microwave background radiation - which supports a universe composed of just 4% normal matter, 25% dark matter, and the rest dark energy.
"The concordant picture we have of the universe is hanging together amazingly well," he says. "In a way, it would be more exciting if we found a glaring inconsistency."
The groups trace the 500 million light-year pattern to the first instants after the universe burst into being 13.7 billion years ago, when mysterious quantum fluctuations bubbled through space. These created pockets of different density in a searing fog of ionised gas and photons that eventually clumped into structures like stars and galaxies.
But early on, when clumps of gas began to collapse and grow, photons trapped in the dense fog exerted an outward pressure that counteracted the growth. These opposing forces set off pressure, or sound, waves that oscillated within the fog.
Freeing photons
But beginning about 400,000 years after the big bang, the universe had expanded and cooled enough for electrons and protons in the fog to start combining into neutral hydrogen. That freed both the photons - which became the ancient "afterglow" of light seen by astronomers - and the trapped sound waves to travel unimpeded through space.
"Instead of ringing, the waves kept going," says Daniel Eisenstein, an SDSS team member at the University of Arizona, US. He says it took about 600,000 years for most of the trapped photons to be freed, so the sound waves from these "overdense" regions would have travelled about 500,000 light years when the ringing stopped.
"That expanding sound wave originates from all points in the universe, like you've taken a handful of gravel and thrown it in a pond," says Eisenstein. The outward ripple from each sound wave grew to be 500 million light years in length because of the expansion of the universe, he says. The birth of galaxies tended to occur at the leading edge of the ripple, where matter was slightly denser and gravitational forces slightly stronger.
But the effect is subtle - galaxies are just 1% more likely to lie 500 million light years away from each other than at other distances, says Eisenstein.
Still, statistical analyses can pick out the effect. Future studies could look for this clustering to probe how the structure of the universe evolved over time. The yardstick could also test the accuracy of "redshift" measurements - upon which astronomical distance estimates are built, says Rees.
The results [of two independent studies] back the standard models of a flat universe, dominated by dark matter and dark energy, that has been expanding - or undergoing a process of inflation - since the big bang.
Ordinary matter—the stuff we're made of—makes up about 4% of the total amount of stuff in the cosmos. The rest of the stuff appears to be 25% dark matter (matter that interacts only gravitationally with itself and ordinary matter) and 71% dark energy (the energy which appears to be responsible for the currently observed acceleration of the expansion of the cosmos).
We're the specks of cinnamon (ordinary matter) on the froth of chocolate cream (dark matter) floating on the surface of the mug's bubbling black coffee (dark energy).
Ping
Maybe I'm dense (I'm no scientist), but I thought sound waves require a medium to travel through. Space (and/or whatever was here before the "Big Bang") doesn't conduct sound because there's nothing there.
Pressure waves propagating through the ionized gas. Sounds are pressure waves propagating through air.
Maybe I oughta read a little slower.
Thanks, I needed that!
So the Universe started with a really big bong?
Sounds that way.
I should also note that the "New Scientist" was what was being read by Dr Radcliffe (the first guy kidnapped) in "The Ipcress File." It's always safer to be careful about reading material.
I'm still trying to grasp the idea that the universe is expanding INTO something. That we are apart of this little bubble in the boil. Thats just plain crazy man:)
I'd forgotten that. Good catch, Doc (and great movie).
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Actually, if the theory of hyperinflation is still widely held, it was more a big pffoot!
So, does this mean that, in space, someone CAN hear you scream?
"No man can find out the work that God maketh from the beginning to the end." Ecclesiastes 3:11.
And I'm life's eclair.
Uh-huh. On the back of a turtle, no doubt.
Are you one of those "flat universers"?
No, but I'm told the flower child movement did.
Like NIN, they'll just go by 2dF.
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