As you've probably heard, yesterday a team of scientists identified evidence of cosmic inflation right after the Big Bang, a finding which helps explain how the entire universe originated. Amazing as that sounds, it's way more important than you even imagine.
To truly grasp the significance, let's start with what exactly it is that the Harvard team found. Forget analogies about ripples in ponds or whatever other over-simplified guff you're read. Here's what actually happened.
Yesterday's results come from analysis of the Cosmic Microwave Background: the thermal radiation left over from when our universe came into being billions of years ago, which is still present as electromagnetic waves zipping through space. They're essentially the oldest waves that can be observed in the universe.
What the Harvard team announced is that they'd observed primordial B-mode polarisation in the microwave background they've been looking at. In English, that means that thermal radiation from the birth of our universe has been distorted, subtly twisted, by gravitational waves that previously had only existed on paper.
That they actually exist reaffirms one of the most foundational principles of modern physics. First predicted by Albert Einstein in 1916, they're tiny ripples—a million times smaller than an atom—that carry energy across the universe. They're an integral part of Einstein's General Theory of Relativity, and the fact we now—for all intents and purposes—have proof of their existence has some profound results.
Yes, we now have solid proof that the Big Bang actually happened. But perhaps more importantly, yesterday's discovery rubbishes the most popular competing theory.
The cyclic model, championed by Neil Turok, director of the Perimeter Institute in Canada, predicted that the universe expanded and contracted over very long cycles. Starting with a Big Bang and ending with a Big Crunch the growth of the universe, Turok reckoned, would be tempered by gravity pulling it pack together in an endless cycle of expansion and contraction.
But the existence of gravitational waves makes it impossible. On BBC Radio 4 this morning, Professor Stephen Hawking explained that the "cyclic universe theory predicts no gravitational waves from the early universe." In fact, Hawking had a bet with Turok that gravitational waves did exist—which he's now calling in. So, a little validation of results aside, we're left with a prime candidate for explaining how our universe began: the inflation model of the Big Bang, where everything grew, for the tiniest fraction of a second at least, at a rate much faster than the speed of light.
With more confidence than ever, then, we know where we come from. We're also, though, now better placed than ever to understand the universe that currently surrounds us. The evidence presented by the Harvard researchers describes the gravitational waves as faint, polarised and distorted by gravitational lensing. That last part is particularly exciting, because gravitational lensing is the key to determining how dark matter manifests itself in our universe.
Put simply, the gravitational force exerted by large objects is enough to bend light subtly, including microwaves like the ones the Harvard scientists have been analysing. The good news is that if we know what's between a source of light and the point from which we're observing it, we can predict how much light should be bent. Any discrepancies can be attributed to the presence of dark matter.
The gravitational lensing of these newly observed waves means that, in theory, we should be able to trace the origins and distributions of dark matter though time, and finally explain how it tangibly affects our universe. That's a big and difficult task that looms ahead, but Doctor Joanne Dunkley from the University of Oxford's Department of Physics recently told me that, if research progressed according to plan, we could expect to see real progress "in the next five to ten years." If anything, this latest finding will speed up that progress considerably.
Remember that, before yesterday, there was no tangible data to explain what happened to the universe until it was over a second old. Now, we can probe it for details of what was happening less than 10 trillion trillion trillionths of a second after everything kicked off. This is, obviously, all wonderful news, so it's no surprise that Andrei Dmitriyevich Linde—one of the main authors of the so happy to hear the news yesterday.
But, as ever, there's one catch. The main benefit of the now-debunked cyclic model was that it neatly sidestepped the fact that all the matter in the universe, every atom around us, had to come from somewhere. As far as it was concerned, everything had been here forever.
The inflation model, however, defines a very clear starting point to our universe, before which there was... well, nobody quite knows. Stephen Hawking's done his best to argue it doesn't matter: "since events before the Big Bang have no observational consequences," he once explained, "one may as well cut them out of the theory, and say that time began at the Big Bang"—the scientific community is yet to buy it en masse.
So while proof of gravitational waves settles many arguments, it brings perhaps the biggest of all to the forefront: what was here before the Big Bang? We may never know. But at least, today, we've got an unprecedented look at what happened just afterwards.
Image by South Pole Telescope