Multiverse Controversy Heats Up over Gravitational Waves

April 6th, 2014 at 18:48

Organic Consumers Association

The multiverse is one of the most divisive topics in physics, and it just became more so. The major announcement last week of evidence for primordial ripples in spacetime has bolstered a cosmological theory called inflation, and with it, some say, the idea that our universe is one of many universes floating like bubbles in a glass of champagne. Critics of the multiverse hypothesis claim that the idea is untestable—barely even science. But with evidence for inflation theory building up, the multiverse debate is coming to a head.

The big news last week came from the Background Imaging of Cosmic Extragalactic Polarization 2 (BICEP2) experiment at the South Pole, which saw imprints in the cosmic microwave background—the oldest light in the universe, dating from shortly after the big bang—that appear to have been caused by gravitational waves rippling through the fabric of spacetime in the early universe. The finding was heralded as a huge breakthrough, although physicists say confirmation from other experiments will be needed to corroborate the results.

If verified, these gravitational waves would be direct evidence for the theory of inflation, which suggests the universe expanded exponentially in the first fraction of a nanosecond after it was born. If inflation occurred, it would explain many features of our universe, such as the fact that it appears to be fairly smooth, with matter spread evenly in all directions (early inflation would have stretched out any irregularities in the universe).

Inflation might also mean that what we consider the universe—the expanse of everything we could see with the most perfect telescopes—is just one small corner of space, a pocket where inflation stopped and allowed matter to condense, galaxies and stars to form, and life to evolve. Elsewhere, beyond the observable universe, spacetime may still be inflating, with other “bubble” universes forming whenever inflation stops in one location.

This picture is called eternal inflation. “Most inflationary models, almost all, predict that inflation should become eternal,” says Alan Guth, a theoretical physicist at the Massachusetts Institute of Technology (MIT), who first predicted inflation in 1980.

If the BICEP2 results end up proving inflation occurred, then the multiverse may be part of the bargain. “I think the multiverse is a natural consequence of inflation ideas,” says theoretical physicist Frank Wilczek, also at MIT. “If you can start one universe form a very small seed, then other universes could also grow from small seeds. There doesn’t seem to be anything unique about the event we call the big bang. It is a reproducible event that could and would happen again, and again, and again.”

If that is true, it could help explain why our universe seems so special. The mass of the electron, for example, appears to be completely random—this value is not predicted by any known physics. And yet if the electron were any heavier or lighter than it is, atoms could not form, galaxies would be impossible, and life would not exist. The same goes for many other constants of nature, especially the cosmological constant—the theorized, but unverified, source of the so-called dark energy that is propelling the acceleration of the expansion of the universe. If the cosmological constant were different, and dark energy was more or less powerful, the universe would be drastically altered. and life as we know it wouldn’t be possible.

If our universe is the only one in existence, then we need some explanation for why it seems so fine-tuned for us to exist. If it is but one of many, however, then maybe each has different parameters, different constants, and one universe just happened to arrive at the values that enabled life.

Continue reading at http://www.scientificamerican.com/article/multiverse-controversy-inflation-gravitational-waves

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