Friday, October 26, 2007

Side Exhibits: The Uniform Sky


Above: Inflation's red prediction is ruled out by both COBE and WMAP.

Imitating the popular SETI@Home, a new computing project called Cosmology@Home can use your computer to check if cosmological models actually fit observations. Most of today's myriad "models" are not models but sets of arbitrary parameters. This could be a fun way to use time, but is akin to assigning monkeys the task of recreating Shakespeare. We may find signals from ET's before this project pays off.

Once upon a time humans thought their Earth was centre of the Universe and the planets revolved around us. Anyone observing the planets for any length of time will see that they often appear to move backwards in their orbits. To explain this retrograde motion, astronomers postulated epicycles, wheels within wheels. By the time of Galileo cosmologies had been developed with 60-100 epicycles. The complicated mathematics of epicycles ensured that cosmology was shared by only an elite few. While epicycles could never be proven, they provided physicists with nice careers.

As with the retrograde motion of planets, to see evidence of c slowing one need only look at the sky. Aside from our Sun and Milky Way, the pattern of stars and galaxies is nearly uniform. In the Cosmic Microwave Background, large portions of the sky have nearly the same temperature. Even the ripples seen by WMAP represent temperature variations of less than 1 in 10,000. Large portions of the cosmic horizon appear to have been in contact, indicating a higher primordial speed of light.

When Alan Guth was a struggling postdoc in the 1970's, inflating prices were on everyone's mind. Even for white male physicist, job prospects were not very good. In the theoretical milieu Guth came up with an idea: What if the very early Universe inflated at warp speed, faster than c? Postulating "inflation" at a time of 10^{-35} seconds appeared to solve problems like the cosmic horizon.

Despite decades of work no theorist has a clue how inflation could have started. A universe expanding at many times lightspeed violates both Special Relativity and the First Law of Thermodynamics. Drawing upon the highly theoretical world of particle physics, inflation theorists must infer some sort of "inflaton" or scalar field to get things rolling. In the past 30 years there has been an inflating number of theories: Chaotic inflation, slow-roll inflation, even eternal inflation!

Inflation, like strings, is an untestable hypothesis. We can not time-travel into the first 10^{-35} seconds to observe inflation in action. The energies of the Big Bang are too great for any human experiment to reproduce. Inflation's "predictions" like flatness and homogeneity can be derived from a Theory without ethereal energies. Physicists like Roger Penrose and Nuel Turok wonder if the motivations for inflation are valid. While inflation can never be proved, it has provided physicists with nice careers.

The key prediction of a scale-invariant spectrum is in big trouble. Inflation predicts that temperature fluctuations will be the same at all scales. As observed in the Cosmic Microwave Background, fluctuations are virtually zero above 60 degrees. Like a car running off a curve, this suggests that the Universe is curved not flat. More than a matter of low quadropoles; inflation's red prediction curve is ruled out by both COBE and WMAP. "The supporters of inflation have become too evangelical," Turok declares, "they have no idea why inflation happened but they still believe in it."

When high redshifts of Type Ia supernovae appeared to increase non-linearly, it was the best evidence yet of a changing speed of light. Deftly avoiding a Nobel Prize, physicists inferred another repulsive "dark energy" causing the Universe to accelerate. Earth's formation is theorised to have occured between periods of repulsive nergy, just as Earth is centre of the Universe. There has been another inflation of DE theories, none of which can be proven anytime soon. Even if JDEM is funded it will not return a single track of "dark energy" to prove that it exists.

Despite the seeming long odds, the "GM = tc^3" cosmology has the winning quality of being testable within our lifetimes. Inflation, strings, branes, extra dimensions and "dark energy" all share the convenience of being unprovable. A true Theory makes a prediction that can be tested: The speed of light is slowing down. It is not possible to "prove" experimentally that c is constant, because a more accurate measurement could prove that foolish. It is very possible to prove that c changes. All one needs to do is look at the sky.

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4 Comments:

Blogger mark said...

fascinating, Louise...how is it testable? in a particle accelerator or something? forgive my ignorance..

8:25 AM  
Blogger nige said...

Louise's equation makes a considerable number of testable predictions about cosmology.

Provided that cosmological data keeps coming in, the data will provide increasingly accurate tests on the viability of the theory.

9:02 AM  
Blogger L. Riofrio said...

Hello Mark and nige. If you had an accurate enough c-meter in your lab, you could observe the speed of light slowing. We don't have accurate enough devices now, but will in a few years. As you can see from the past week, there are many indicators of a "c change" in physics.

9:46 AM  
Blogger CarlBrannen said...

Louise, I've got first cut of a guest post for Tommaso, and I'd like you to review it for corrections / accuracy as it deals somewhat with variable speed of light. Send me an email at carl atsign brannenworks dot com and I will send you a copy in reply.

11:03 AM  

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