Universe Today
Wouldn't it be nice if the universe had just...always been here?
Don't get me wrong. I love the Big Bang. It has lots of drama, good action, a dying inflation field flooding the young cosmos with light and particles, and the grand central mystery of the singularity sitting right there at the start of everything. It has it all. And it is all so deeply, profoundly annoying. How exactly did it go down? What is inflation, really? Why did it switch off precisely when it did? And the singularity, well, anchoring your entire model of creation on a giant question mark is not what I would call a compelling opening move.
There is a different kind of comfort in imagining a universe that simply always was. Even if it repeats. Even if it runs in cycles. Maybe this particular version of the cosmos isn't doing so great, and you know what, that's fine, because we'll get another shot. Sure, the next one might not come around for another 14 trillion years, but the point is that it comes around at all. And the past stretches back the same way, generation after generation of stars lighting up and burning out in some endless grand wheel. That is a genuinely comforting thought, if you let it be.
The Big Bang offers none of it. The Big Bang is relentlessly, almost rudely linear. This is it. This is the one and only chance the universe gets. It was born, it has already sailed past its glory days, and from here on out there is nothing but expansion into the deepening cold of the vacuum. No encore. No second act. Just a long, slow fade to black.
This linearity is a big part of what made the Big Bang so aggravating to so many people when it first arrived. Plenty of traditions, ancient and modern, religious and philosophical, build their cosmic history out of cycles. Even Christianity has a sort of cycle tucked into it: the flood and Noah and humanity getting handed a clean slate (yes, most people drowned in that story, but it's the thought that counts), and the promise that however miserable your life is right now, a reset is coming. The Big Bang has nothing like that on offer. Just a beginning, a middle, and a cold, quiet end.
So it is no surprise that in the century or so since it was first scribbled down, people have kept trying to bend our cosmology back into a circle. The first person to really go for it was Richard Tolman, working all the way back in the 1930s, right as the standard Big Bang picture was itself just swimming into focus.
Tolman pictured a universe of big bangs followed by big crunches followed by more big bangs (nobody was using those names yet, but it's the same idea). The cosmos expands, slows, stalls, and then falls back in on itself, squeezing down to something unimaginably small and dense before rebounding into a fresh expansion. Over and over. Forever. No first one, no last one, just the eternal heartbeat of a universe that breathes in and breathes out.
It's a beautiful picture. And it falls apart almost immediately, for a reason that has haunted every cyclic model proposed since: entropy.
Entropy, the physicist's bookkeeping for disorder, only ever climbs. It does not reset on its own. So each cycle is forced to inherit all the accumulated mess of the cycle before it. Every bounce starts dirtier than the last, which means every cycle runs a little bigger and a little longer than its predecessor. Now run that movie backward. The cycles get shorter. And smaller. And tidier. Until, inevitably, you arrive at a first one. A beginning. The exact thing the whole scheme was invented to avoid. Tolman worked through the math himself and saw it plainly. His eternal universe still needed a ground floor, some starting point to set the initial entropy, and the moment you concede that, you have quietly let the singularity back in through the side door.
There is a second problem, too. In a crunch, all of that entropy gets crushed back down into a tiny volume with absolutely nowhere to go. You can't hide it. You can't dump it. It just piles up, cycle after cycle, until the books no longer balance.
So for decades it really did look like the Big Bang would have the last laugh. A one-and-done cosmos. Beginning, middle, end, lights out. And every clever attempt to make it cyclic kept smuggling a beginning back in through some unlocked window.
And then, in the late 1970s and early 1980s, something genuinely new walked into the room and scrambled the entire board. A theory so strange that some of the very people who built it would later argue it isn't even a theory at all.
Inflation.
In Part 2, we meet the most successful awkward idea in the history of cosmology, the one that has fended off every challenger for forty years despite barely making sense on paper.
