The Big Crunch

The Big Crunch theory predicts the death of the universe. But that’s probably not what will happen.

The expanding universe

Before talking about the Big Crunch, we need to talk about the Big Bang.

Ever since the Big Bang, the universe has been slowly expanding. The Big Bang, as you probably know, is the event that started our universe. The universe expands, but if you project that expansion backward and apply the general theory of relativity, you end up with a time in the past when the universe was infinitely dense and has an infinite temperature: the Big Bang.

The Big Bang was not an actual bang. Not in the traditional sense. It was not that something actually exploded, but that the universe itself started to rapidly expand from a zero size. Well, expand from something. We don’t actually know if it was the start or not. We can only look back so far, and the closer you get to the actual Big Bang, the less we know. General Relativity brakes down.

The stuff that happened in the first 10-43 seconds after the Big Bang (yes, that’s a fraction of a fraction of a second) is wild. The fundamental forces like gravity and magnetism were one with the forces that keep atoms together. Things like ‘particles’ didn’t exist yet. Instead the universe was super-heated energy soup with a seasoning of undefined laws of nature.

Fast Forward

The first second of the universe was a weird time, with the universe expanding faster than light — light has a fixed speed, but that not constrain the growth potential of a universe, apparently.

Slowly matter formed, with the unexplained quirk that we ended up with a surplus of matter compared to anti-matter. That quirk is what makes us actually able to exist, so yeah for that. But we have no idea why that happened.

As we go from the first seconds and minutes to the first few millennia, things starts to become recognizable for us. Protons and neutrons form and slowly atoms starts to appear. Over the billions of years that follow, the universe has continued to expand until we find ourselves at the current state of things.

The universe is still expanding, but it is big these days, and a lot colder and less energetic than at the start of things.

But what will happen next? That’s where the Big Crunch comes in.

The Big Crunch

The Big Crunch theory is a theory suggesting what will happen to our universe in the distant future. It posits that gravity will make the expansion of the universe stop, then reverse course. Over many billions of years, the universe will collapse in on itself. Eventually, this will result in a giant black hole that will crush everything.

It’s a nice symmetrical theory, and it has led to one of my favorite episodes of the science fiction series Red Dwarf.

Unfortunately, there’s a problem.

The universe is — in fact — only expanding faster over time, not slower, meaning it’s unlikely to start shrinking. This sounds strange, of course. Gravity should be pulling things toward each other, so why are things accelerating away from each other?

Enter dark energy. Dark energy, or vacuum energy is the energy housing in the space between particles, vacuum in other words. Although, ‘no particles’ is a misleading term in the world of quantum mechanics. There is something there, which pops out in certain situations, such as when particles are spontaneously emitted. This vacuum energy is supposedly responsible for the accelerating universe. I say ‘supposedly’ because a lot of this is unproven. I’ve written before about certain conundrums in quantum mechanics, and the need for vacuum energy to explain certain phenomena is one of those.

Heath Death and the Big Rip

An alternative to the Big Crunch is to assume the universe will keep expanding and go from there.

Two things could happen. Eventually the matter and energy of the universe could spread out so far no meaningful thermodynamic reactions can occur. Over time, all parts of the universe would end up at an absolute zero temperature. This is known as the Heat Death of the universe.

Alternatively, the particles of the universe could be pushed far enough apart that they can no longer meaningfully interact. The universe rips itself apart, and nothing happens anymore. This is known as the Big Rip.

The difference is really not that important. It’s like a person getting caught outside in a blizzard and dying. Do they die because their heart stops, or because they freeze to death? Whether the universe ends because particles no longer interact or because the temperature drops to absolute zero matters little. The result is the same.


The death of the universe is very far off, as in billions upon billions of years. We’ll all be long dead by then, and likely the human race will be long gone too. Still, it’s interesting to think about, and makes for interesting possibilities in stories.

Martin Stellinga Written by:

I'm a science fiction and fantasy writer from the Netherlands