# Tested Explains: What The Heck is Inflation Theory?

Big physics news is always kind of hard to understand. So I called up my favorite theoretical physicist, CalTech’s Sean Carroll, to help explain the theory of inflation for those of us that don’t do physics.

If you were conscious on Monday you probably heard there was big news out of the physics community. So big, in fact, that there’s already talk of Nobel prizes and jokes about Einstein patting himself on the back for being proven right...again. Let’s be honest though, big physics news is always kind of hard to understand. There’s always GeV’s and B-modes and jargon and, well, math. So, in the event that you’d actually like to understand what the heck everybody is talking about right now I called up my favorite theoretical physicist, CalTech’s Sean Carroll, to help explain the theory of inflation for those of us that don’t do physics. Here it is, in the simplest possible terms.

Image credit: California Academy of Sciences

The universe is the same everywhere we look. No matter where we point our telescopes out into the 14 billion light years of space in all directions, we see the same density of stuff. Same amount of matter and number of galaxies. Same gravitational field. The universe is even basically the same temperature everywhere.

The theory is that in the very first fraction of a second after the big bang happened, the universe expanded into existence.

It’s awfully smooth, flat, and uniform -- and there’s gotta be a reason why. Inflation theory explains. Simply put, the theory is that in the very first fraction of a second after the big bang happened, the universe expanded into existence. In other words, everything, everywhere existed all at once and it happened faster than the speed of light.

That’s it. Pretty simple, right? Well, it sounds simple. Until you try to prove that it’s true. Since we can’t go back in time to watch the creation of the universe (whomp whomp), the best way to know that theory is right is to look for leftovers of its aftermath. So scientists have been trying to spot evidence that the rapid inflation of the universe messed with gravity.

It’s not such a complex idea when you think about how easy it is to mess with gravity. The universe has one big gravitational field. Earth, for example, messes with it by spinning around really fast and pulling objects down onto its surface. So, of course, something as massive as the faster-then-the-speed-of-light inflation of the universe would start a fluctuation, or a series of waves, in the gravitational field.

But because gravitational wavelengths are a few billion light years apart (radio wavelengths, for comparison, are about 3,200 feet apart) we can’t detect them directly. We have to detect the effect they have on stuff we can actually see.

One of the things we can see, and also happens to be a result of the big bang, is the cosmic microwave background of the universe. That’s a fancy way of saying radiation left over from the creation of the universe. If the theory of inflation were true, then gravitational waves moving over the radiation would point its photon particles in different directions and create a pattern. They’d basically show the gravitational waves -- like wind blowing over sand and creating ripples. You can’t see the wind, but you know it exists because it left a mark on the sand.

A pattern in the universe’s radiation that proves the gravity field is fluctuating, which makes it extremely likely that the universe expanded into existence right after the big bang.

And that’s a super simplified explanation of what physicists announced that they discovered Monday. A pattern in the universe’s radiation that proves the gravity field is fluctuating, which makes it extremely likely that the universe expanded into existence right after the big bang.

Of course, in physics nothing is ever really proven definitively. First scientists are going to have confirm these findings. And there are other experiments currently ongoing to detect gravitational waves that will eventually chime in. Even once that’s done, it’s possible they will discover some completely, and currently unknown, reason for the existence of gravitational waves (though right now competing theories about them aren’t convincing anybody).

Still, it’s a very exciting time for science. They’ve discovered the first evidence confirming one of physics’ most fundamental ideas. When I chatted with CalTech’s Carroll to help me wrap my brain around these concepts, I asked how he was feeling now that they know this theory could be true. His response: “We feel very excited. In some sense this was more of a surprise than the Higgs. We knew waves were predicted but we didn’t know they’d be this noticeable. If this holds up nature has, for once, been really really nice to us. That’s a very rare thing.”

Bonus: Stanford physics professor Andrei Linde, who was the first to describe the cosmic inflation theory, is surprised by a colleague who tells him that the theory has been proved: