It’s a great time to be a geek. We’re learning all sorts of extreme stuff. There’s a team led by John Kovac, from the Harvard-Smithsonian Center for Astrophysics, who’ve been beavering away on one of the fundamental questions of modern cosmology. The secret has demanded some extreme research in an extreme place. Antarctica. There’s a telescope there, BICEP2, that’s been collecting data on the cosmic background temperature. Last week, the team published their initial results.
The theory they were testing is as extreme as such things get and goes like this. Straight after the Big Bang, the universe was miniscule and very hot. Then it expanded – unbelievably fast in the first few trillionth trillionths of a second, but then much more slowly. After a while it was cool enough for the particles we know and love today to be formed. This ‘recombination’ epoch occurred perhaps 380,000 years after the Big Bang. One of the outcomes was that photons were released from the plasma fog – physicists call this ‘photon decoupling’.
What couldn’t quite be proven was that the early rate of expansion – ‘inflation’ – had been very high.
But now it has. And the method combines the very best of cool and of geek. This early universe can still be seen, out at the edge of visibility. That initial photon release is called the ‘cosmic microwave background’ (CMB), first predicted in 1948 by Ralph Alpher and others, and observed in 1965 by accident when it interfered with the reception of a radio being built in Bell Laboratories. That started a flurry of research. Its temperature is around 2.725 degrees kelvin, a shade above absolute zero. It’s that temperature because it’s been red-shifted (the wavelengths radiated from it have stretched, because the universe is expanding, and stuff further away gets stretched more). The equation works backwards from today’s CMB temperature, 2.725 degrees Kelvin, thus: Tr = 2.725(1 + z).
The thing is that, way back – we’re talking 13.8 billion years – the universe was a tiny fraction of its current size, and the components were much closer together. Imagine a deflated balloon. Splat paint across the balloon. Now inflate the balloon. See how the paint splats move further apart from each other? But they’re still the original pattern of the splat. In the same sort of way, the CMB background pattern is a snapshot of the way the universe was when ‘photon decoupling’ occurred. It’s crucial to proving the Big Bang theory. It’s long been known that the background is largely homogenous (proving that it was once all in close proximity) but carries tiny irregularities in the pattern (anisotropy). What the BICEP2 team discovered is that the variations are polarised in a swirling pattern, a so-called B-mode.
The reason the radiation is polarised that way is because early inflation was faster than light-speed, and the gravity waves within it were stretched, rippling the fabric of space-time in a particular way and creating the swirls. Discovering the swirls, in short, identifies both the early rate of expansion (which took the universe from a nanometer to 250,000,0000 light years diameter in 0.00000000000000000000000000000001 of a second…I think I counted right…) and gives us an indirect view of gravitational waves for the first time. How cool is that?
What’s a ‘gravitational wave’? They were first predicted nearly a century ago by Albert Einstein, whose General Theory of Relativity’of 1917 was actually a theory of gravity. According to Einstein, space and time are an entwined ‘fabric’. Energy and mass (which, themselves, are the same thing) distort that fabric. Think of a thin rubber sheet (space-time), then drop a marble (mass/energy) into it. The marble will sink, stretching the sheet. Gravitational waves? Einstein’s theory made clear that these waves had to exist. They’re ripples in the fabric.
One of the outcomes of last week’s discovery is the implication that ‘multiverses’ exist. Another is that there is not only a particle to transmit gravity, a ‘graviton’, but also an ‘inflaton’ which pushes the universe apart. Theorists suspect that ‘inflatons’ have a half-life and they were prevalent only in the very early universe.
There’s more to come from this, including new questions. But one thing is certain. Einstein’s been proven right. Again.
Copyright © Matthew Wright 2014
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