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Echoes Hint At Accelerating Universe Expansion
cr0kin0le writes "400,000 years after the Big Bang, oscillations between gravitationally contracting matter and outward radiation pressure left newly discovered acoustic echoes. Independent teams from U. of Arizona and U. of Durham, England have found circular ripples with wavelengths of 500 million light-years which indirectly imply that universal expansion is accelerating due to dark energy."
Slashdotted at 5 comments. Here's the article text (after a 4 minute wait.)
. asp). The universe's first symphony therefore provides independent evidence that the cosmos is filled with dark energy, which causes the acceleration.
Ultimate Retro: Modern echoes of the early universe
Ron Cowen
Two teams of astronomers have for the first time detected the surviving notes of a cosmic symphony created just after the Big Bang, when the universe was a foggy soup of matter and radiation. The discoverers say that the survival of the acoustic imprint from this early epoch, 13.7 billion years ago, provides compelling new evidence that the blueprint for the present distribution of galaxies was set at the time of the Big Bang by random subatomic fluctuations.
In 1999, researchers detected a specific pattern of acoustic oscillations in the faint, ancient whisper of radiation--the cosmic microwave background--left over from the Big Bang. This week, Shaun Cole of the University of Durham in England and his colleagues announced that they had discerned remnants of that pattern while analyzing data from the Two-Degree Field Redshift Gravity Survey, a large-scale analysis of 220,000 galaxies. The map covers one-twentieth the area of the sky out to a distance of 2 billion light-years from Earth.
Another team, led by Daniel Eisenstein of the University of Arizona in Tucson, examined a subset of 46,000 galaxies from another sky map, the Sloan Digital Sky Survey, which covers one-quarter of the sky.
Each team used a different method of analysis but found the same acoustic pattern. The groups reported their findings this week at a meeting of the American Astronomical Society in San Diego.
The signals are so weak that, to detect them even in large-galaxy surveys, "both groups had to work quite hard," notes cosmologist David N. Spergel of Princeton University. "The result is another important milestone in establishing a standard model for cosmology."
The early universe rang like a bell, notes Spergel. As gravity drew together clumps of atomic matter, radiation--then tightly bound to that matter--exerted an outward pressure. The tug-of-war between gravity's pull and radiation's push generated pressure waves, or acoustic oscillations.
About 400,000 years after the Big Bang, the universe had cooled sufficiently for the radiation to break free from matter and travel unimpeded into space. Now in the form of microwaves, this radiation pervades the universe and provides a snapshot of the cosmos at that early time, ripples and all.
The small size of the fluctuations, both in the microwave background and the galaxy distribution today, provides additional evidence that most of the mass of the universe is composed of dark matter--an exotic, invisible, and primordial material that has never interacted with light and so had never generated sound waves, notes Spergel.
Eisenstein notes that, using the length of the sound waves as a cosmic ruler, astronomers can calculate the universe's expansion. Both of the new studies agree with earlier reports that cosmic expansion is speeding up (SN: 5/22/04, p. 330: http://www.sciencenews.org/articles/20040522/bob9
There are lies, damned lies, and statistics.
at a campus lecture at my college. The professor gave very good evidence that the universe is expanding at an accellerating rate. The devotional was called "Exploding Stars, Expanding Universe."
Unfortunately, the school does not have a transcript of the forum, but you can download it in mp3 format for free
It was, and still remains, a very good talk about the accelerating expansion of the universe.
There's no place like ~/
That's what I thought too, but no. It seems dark energy is stuff we can't see using traditional electromagnetic methods. It seems that vacuum energy may be one of the sources of dark energy- there is energy associated with the vacuum of space. If you place 2 metal plates parallel to each other, there is an energy potential between them caused by the vacuum of space(Casimir effect). Kip Thorne describes how to make a time machine this way with sufficiently large plates. (sufficiently large is pretty fu***n big) Also, you may have read that in deep space subatomic particles pop in and out of existence- this is part of the dark energy, too, and somehow related to vacuum energy. For a mildly technical discussion go to http://www.astro.ucla.edu/~wright/cosmo_constant.h tml
Also, I recommend Brian Greene's "The elegant Universe" for a superb laymans terms description of the state of knowledge and confusion in astrophysics.
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First of all space is not a vacum, although from our point of view (being in a dense atmosphere) it is often considered as such. Secondly, at the time the waves occured, space was much smaller and thus also denser and hotter. What they have observed is just the traces of those waves, not the waves themselves. It like those sand patterns on the beach that you see when the tide is low.
You are partially correct. You need to see at least half of the wave to measure its wavelength. To get the frequency from the wavelength you generally need to know the speed of the wave.
How can they accurately extrapolate a length of 500MLY from about 1LY of data (if indeed they took that length of reading).
I think you are confusing lightyears and years. A lightyear is a unit of length. The astronomers here have measured a wavelength of 500 million lightyears. They didn't take a "lightyear" of data. I'm not sure what you even mean by that. The survey of galaxies they used had to cover a distance of more than 500 MLY in at least one direction. Concerning how they actually found this wave and measured its wavelength, I have not yet seen a detailed journal article nor was I able to attend the AAS meeting where these results were presented, but I can take a guess:
First of all, they are looking at the pattern left over by those accoustic waves. Once the universe cooled enough for matter and radiation to decouple, the push-pull between gravity and radiation pressure disappeared (more or less) and these waves stopped progagating. All that is left are the wave patterns, essentially frozen into the large-scale structure of the universe. They are using the distribution of galaxies to track this structure.
Most likely, they did a 2D Fourier Transformation of a map of the galaxies created from one of the galaxy surveys mentioned in the article and found a statistically significant power at a wavenumber = 1/500 MLY. I'm sure there were other numerical gymnastics they had to perform to get there, but in essence it is just an FT. That is my guess, anyway.
From the linked site: "Today's physicist may start his lecture by convincing the audience that there is no understandable logics behind natural phenomena; it is out of date to look for a common sense picture of the physical reality."
The latter claim (it is out of date to look for a common sense picture of physical reality) is certainly true, and has been true since Newton's time. Newton's theory of gravitation was criticized for being in violation of common sense and being based on "occult qualities".
The former claim is nonsense. No one who is not looking for understandable logic behind natural phenomena is a scientists of any kind, and in hundreds (or possibly thousands) of talks from physicists all over the world I have never heard one so much as hint that they aren't looking for an understandable logic behind natural phenomena.
GR is not "taken as an absolute gospel". It is just a damned good theory, predicting with tremendous precision phenomena on scales of metres (the red shift of Mossbaur gamma rays), hundreds of kilometres (GPS algorithms have GR correction terms), millions of kilometres (precession of Mercury), tens of millions of kilometers (binary pulsars) and millions of light years (large scale structure of the universe.) You don't throw away a theory like that lightly, and any challenging theory has to do at least as well on all the things GR is so very good at.
So far, there is nothing else that even comes close.
--Tom
Blasphemy is a human right. Blasphemophobia kills.
Yes, that is correct. They are looking at the patterns in the distribution of galaxies. They are not detecting radio waves. They are infering accoustic waves (i.e. longitudinal "pressure" waves that propagated through the hot dense matter-radiation soup of the early universe) from the pattern left behind after matter and radiation decoupled. Pretty neat trick, really.
Since it looks like most people here haven't read the journal articles (the sciencenews.org article is pretty light on the details), here's the basic idea:
In the early universe, the universe is mostly smooth except for small density fluctuations. The universe is made up of 3 basic fluids: photons, dark matter, and baryons. Density waves ("acoustic waves") pass through these fluids as far as they can at a given time - in the early universe, the horizon scale is quite small and the waves can't get all that far. Therefore you get horizon-sized acoustic oscillations. Dark matter is pressureless while the photon-baryon fluid isn't, so they react differently to compression... the end result of that is that there are some oscillations on quite large scales that are there because of the baryons.
What these groups have done using two different surveys (the 2 degree Field Galaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky Survey (SDSS - they're using the Luminous Red Galaxy (LRG) subsample)) is look at galaxies at moderate redshift (medians of about 0.1 for 2dFGRS and 0.35 for the SDSS LRG sample) and compute the correlation function (in Dan Eisenstein's paper) or power spectrum (in Shaun Cole's paper). These tell you how clustered galaxies are as a function of how far away they are from each other.
What they both find is that there's a peak around 150 Mpc, exactly as you'd expect for a universe with about 75% vacuum energy and 25% matter, of which about 15% (ie. 15% of 25% = 4% total) is baryonic. The test is pretty sensitive to all of those numbers, and thus provides further evidence that the universe is dominated by a vacuum energy that drives acceleration.
Here's links to preprints of the papers:
[TMB]