There are two mistakes one can make along the road to truth… not going all the way, and not starting. -Siddhārtha Gautama, a.k.a. Buddha
Last week, I started a new series on The Greatest Story Ever Told, about the origin and evolution of the Universe. In it, I asserted that inflation is the very first thing we can definitively say anything sensible about, and that it happened before the big bang. This runs contrary to a lot of statements out there by a lot of reputable people, including this “timeline” image from Discover Magazine:
Everything else aside, it’s very important to remember where the idea of the Big Bang comes from. What we see today, when we look out at the Universe, is that the farther away things are from us, the faster they move away from us.
The Big Bang, an idea dating back to the 1940s, was a brilliant extrapolation of this idea. If the Universe was smaller, denser, and hotter in the past, George Gamow and his collaborators stated, then a few very interesting things happen.
Far enough in the past, the Universe must have been hot enough to prevent the formation of neutral atoms. If this were true, we should see the leftover radiation that kept the Universe ionized at this time. We not only discovered this, we can measure the temperature fluctuations in this Cosmic Microwave Background, and show them to you.
As you travel further back in time, more interesting things happen at higher and higher energies. (A good part of the new The Greatest Story Ever Told series will be taking you through what those things are and when they happen.) When the big bang was first conceived, the extrapolation went all the way back to a singularity, when all the matter and energy in the Universe was concentrated at a single point, where the expansion was arbitrarily fast, and the temperature was practically infinite.
But when inflation came along, all of that changed. No longer could we extrapolate all the way back to a singularity. If we wound the clock of the Universe backwards, we would discover something remarkable. At some point, about 10-30 seconds before we would anticipate running into that singularity, the Universe instead would undergo inflation (in reverse, if we’re looking backwards), and we have no evidence for anything that came before it.
The Big Bang, instead of being a singularity, is the set of initial conditions of an extremely hot, dense, expanding Universe that exists immediately after the end of inflation.
Was there a singularity before inflation? Possibly, but at this point, we have no way of knowing. Inflation is the first thing we can say anything definitive about, but it definitely comes before what we traditionally call “The Big Bang”. So maybe I should admit that Starts With A Bang isn’t really the starting point of everything, after all, just the start of where our observable Universe comes from.
But the answer to our Q & A for today? Yes, inflation happens before the Big Bang, and ever since its acceptance, has removed the necessity of a singularity at the start.