ALMOST 14 BILLION years ago, the universe was tiny, tiny place. Suddenly, quantum fluctuations made things a bit wobbly, and what was previously a stable universe just after the Big Bang very quickly became unstable. These fluctuations came from variations in gravity as it came into existence, and triggered the universe to grow very, very rapidly. Whatever size the universe was in one instant, by the next instant it had doubled in size, and doubled again in the instant after that, and so on.
This was the Inflation Epoch of our universe, and the volume of space inside it grew by 10 to the power of 78 times, to the size of … a grapefruit. And it all happened in about a thousandth of a second.
This was all theory up until the weekend, when we finally got the announcement that it really happened.
So why did we think that there should be inflation in the first place? There are a few reasons, but one is this: when we look out into space today it looks the same in all directions – wherever you look there are stars and galaxies spread out throughout the universe. On large scales, everything pretty much looks nice and even. This was all very neat and tidy and lovely until cosmologists delved a bit deeper into the Big Bang idea. Einstein’s work predicted that the period just immediately after the Big Bang should give rise to waves of gravity bouncing through the universe, which in turn would eventually lead to some places having more structures – such as galaxies and clusters of galaxies – or different temperatures than others. But alas, astronomers could see no such thing.
Something wasn’t right.
Two scientists, Alan Guth and Andrew Linde, tackled this problem and came up with a potential solution in the form of inflation, which both agreed with Einstein’s discoveries and explained why we see the universe in the way we do. Hold onto your hats; this is where it gets mind-bending.
During the Inflation Epoch, right at the beginning of time, space itself expanded faster than the speed of light. You may have heard that nothing can travel faster than light, and this is true, but only when it’s something moving through space; when space itself expands extremely quickly, no rules are broken. However, the speed of light places a “horizon” on our universe, which we call the observable universe – that is, we can’t see past that point, because light just hasn’t had enough time to travel from there to here yet. This means that there’s a whole load of stuff beyond this horizon that we just can’t see.
Now, back to those gravitational waves: they first started out as minuscule waves inside the tiny universe, but during this faster-than-light expansion of the universe they grew along with space itself, becoming bigger and bigger, but weaker and weaker as they were stretched, and were pushed out beyond the observable universe. Whatever was left of the waves in the observable universe was too weak to create any strong variations, leaving us with the flat, homogeneous universe we see today.
However, the gravitational waves left their “imprint” on the light of the early universe, and about 400,000 years after the Big Bang that light became free to travel through the universe, unperturbed, with hints of gravitational waves embedded on it. So, if we could detect this imprint on light, we could then show that gravitational waves exist, proving that the Inflation Epoch was real, thereby providing even more evidence for the Big Bang.
And breathe! That’s the hardcore science out of the way.
The team operating the BICEP2 experiment at the South Pole managed to find those signatures in the light from the early history of the universe, showing that inflation is real and providing more evidence for the Big Bang.
What does this mean for cosmology now? Can astronomers just pack up and go home? No way! This is where the fun really begins! Now we know that inflation happened, we now have to figure out just what caused it. At the moment, we just have a hypothetical thing called an inflation that we use as the “trigger” for inflation, but this will soon become a whole new and exciting world for physicists and mathematicians.
Those gravitational waves stem from the quantum fluctuations that arose in the moments after the Big Bang: this means that we now have evidence of quantum gravity, something that has never been observed before. This will be a lot of fun for scientists, too, as merging theories of gravity with quantum physics (like we’ve done with electricity and magnetism in electromagnetism) will give us a more complete view of the universe.
We’ll be able to better understand how gravitational extremes like black holes work, and now we have more solid picture of how massive clusters of galaxies and other cosmological structures form. Maybe, in the future, this will help us tackle new and exciting ideas we haven’t even thought of yet.
Conor Farrell is an avid science enthusiast and studied physics with astronomy at Dublin City University. He now works with Astronomy Ireland to promote all things space-related to a wider audience. In his spare time he writes about science and current affairs, and can be followed on Twitter at @conorsthoughts. Read more of Conor’s columns here.
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