That Other Inflation

I highlighted this story in the links the other day, but I was really impressed with how clearly the inflation theory is explained:

Even after three decades of hearing her husband explain his theory, though, she admits that she still finds it difficult to grasp both the immensity of the universe that his theory suggests and the tininess of its starting point.
She turns her head to face her husband. “Alan, you used to say it all started from this singularity that was much smaller than an atom and that it got as big as a grapefruit” during inflation. “But now you say it was a marble?”
“That’s right,” he replies. “I’ve changed the grapefruit to a marble.” Then, in response to what sounds like whimsy with metaphors (but which is really the result of refined estimates from certain grand unified theories), he laughs, though Guth laughter is closer to a series of exuberant cackles.
Here, in language that you, Susan, and I can understand, is how Guth’s model of the inflationary universe works: Using the theories of Einstein and others, Guth points out that at extremely high energies, there are forms of matter that upend everything we learned about gravity in high school. Rather than being the ultimate force of attraction that Newton and his falling apple taught us, gravity in this case is an incredibly potent force of repulsion. And that repulsive gravity was the fuel that powered the Big Bang.
The universe is roughly 13.8 billion years old, and it began from a patch of material packed with this repulsive gravity. The patch was, as Susan notes, tiny — one 100-billionth the size of a single proton. But the repulsive gravity was like a magic wand, doubling the patch in size every tenth of a trillionth of a trillionth of a trillionth of a second. And it waved its doubling power over the patch about 100 times in a row, until it got to the size of that marble. All that happened within a hundredth of a billionth of a trillionth of a trillionth of a second. As a point of comparison, the smallest fraction of time that the average human can detect is about one-tenth of a second.
The ingredients of what would become our entire observable universe were packed inside that marble. While the density of ordinary material being put through that kind of exponential expansion would thin out to almost nothing, a quirk of this repulsive-gravity material allowed it to maintain a constant density as it kept growing. But at a certain point — while the universe was still a tiny fraction of a second old — inflation ended. That happened because the repulsive-gravity material was unstable, and, like a radioactive substance, it began to decay. As it decayed, it released energy that produced ordinary particles, which in turn formed the dense, hot “primordial soup.” At that point, after Guth’s model has explained what banged, why it banged, and what happened before it banged, he takes a bow and lets the standard Big Bang theory take over from there.
About a year after Guth joined the MIT faculty in 1980, the “Oh, crap” pit in his stomach finally went away. That’s when he received a preprint of a paper from Andrei Linde, a physicist in Moscow. Linde, who is now at Stanford, had figured out an ingenious way to use inflation to solve the “horizon problem” that had tripped up Guth. “It saved my model,” Guth says now.
Guth and a few colleagues made another big advance the following year in a paper showing that inflation, which remained pure theory, could conceivably be proved. That’s because inflation would have left a unique imprint on the expanding matter of the Big Bang. And this imprint could be seen in the oldest light of the universe — that is, if modern science could build tools sophisticated enough to detect the imprint. But Guth doubted that would happen in his lifetime.

But they did.  And it still doesn't explain where that singularity came from, but, hey, getting from it to the universe is pretty impressive.