By Luke Barnes, University of Sydney and Geraint Lewis, University of Sydney | May 14, 2014 09:23pm ET
Captured From: http://www.space.com
The recent BICEP2 observations – of swirls in the polarisation of the cosmic microwave background – have been proclaimed as many things, from evidence of the Big Bang and gravitational waves to something strange called the multiverse.
The multiverse theory is that our universe is but one of a vast, variegated ensemble of other universes. We don’t know how many pieces there are to the multiverse but estimates suggest there many be squillions of them.
But (if they exist) there has not been enough time since our cosmic beginning for light from these other universes to reach us. They are beyond our cosmic horizon and thus in principle unobservable.
How, then, can cosmologists say they have seen evidence of them?
Seeing the unobservable
Unobservable entities aren’t necessarily out-of-bounds for science. For example, protons and neutrons are made of subatomic particles called quarks. While they cannot be observed directly, their existence and properties are inferred from the way particles behave when smashed together.
But there is no such luxury with the multiverse. No signals from from other universes have or will ever bother our telescopes.
While there is some debate about what actually makes a scientific theory, we should at least ask if the multiverse theory is testable? Does it make predictions that we can test in a laboratory or with our telescopes?
The answer is yes, but perhaps not as you’d expect. And the exploration of the multiverse theory involves some very complex, and very controversial, ideas.
The mark of the generator
If your multiverse theory generates its universes via some physical process, then that process may leave its fingerprints on this universe. This is what BICEP2 might have seen.
Cosmologists think that in its earliest stages, the universe underwent an extraordinarily rapid expansion, known as inflation. In many versions of inflation, gravitational waves leave an imprint in fossil radiation, recently observed as characteristic swirls in this ancient light; a successful prediction of inflation.
In some versions of inflation, the process that causes our universe to inflate is expected to produce huge numbers of other universes. Evidence for inflation isn’t exactly direct evidence for the multiverse, but it’s a start. Read More