True fictions

Once upon a time, the universe blew up.

I say "blew up" not in the sense of an explosion, but rather click-and-dragging the corner of an image outwards to make it bigger. Right after the Big Bang, the universe was a tiny, compact mote. Practically everything that would eventually be anything was bound up not in familiar matter, but in the energy of exotic fields. But it didn't stay that way for long. In a split of a spilt of a split second — a splinter of time so small that more copies of it fit into a second than seconds fit into all time — the universe stretched out so quickly that even light couldn't keep up. By the end, it had grown by a factor of 10³⁰. That's 1,000,000,000,000,000,000,000,000,000,000.

13.8 billion years later, this brief episode of cosmic inflation is still etched into the sky. Were it not for inflation, the universe would be roughly the same everywhere. And like a ball on an infinite, flat plain, it'd have nowhere to "go," no way to do anything other than sit still, forever. But some regions of space are a little denser or a little emptier than others. And when we train radio telescopes on the sky, we see a cosmic quilt of slightly brighter and slightly dimmer patches — tiny fluctuations in the radio afterglow of the Big Bang. Inflation explains the patchwork: quantum fluctuations near the beginning of time that started out tiny got blown up, click-and-drag style, to cosmic scale. Everything else, from stars to intelligences capable of doing cosmology, grew up over the primordial scaffold of disorder created by inflation.

Or did it?

Yesterday on a cycle across town, I played back an old episode of Sean Carroll's Mindscape podcast in which he interviewed Roger Penrose. I mostly associate Penrose with aperiodic tilings, but he's also a Nobel Prize-winning physicist with plenty of thoughts on cosmology. Carroll, a cosmologist, took the interview as a chance to discuss Penrose's ideas about the beginning and end of the universe.

I'd learned cosmic inflation as the story of the Big Bang — a solid scientific truth confirmed by observations of the cosmic microwave background. So you can imagine my shock at hearing Carroll and Penrose talk pretty dismissively about inflationary cosmology. Carroll said he'd place a 50/50 bet on inflation being true. Penrose doesn't buy it at all.