When will the Universe end? For the longest time people believed that the Universe was eternal and that it would always exist. Then in the early ’70s most astronomers were convinced by the mounting evidence for a “Big Bang” that there was a beginning to the Universe. For people of that era, the rejection of the eternal Universe was a major conceptual rearrangement but eventually everyone has gotten used to the idea. But most people still do think that the Universe, once created, should last forever.

But there’s a powerful argument based on both the quantum mechanical probability model and the logic of physics done in infinite time that has convinced at least some researchers that the Universe will have an end. And… that there’s an even chance that the end is coming within the lifespan of the Earth and/or Solar System.

“Their argument is deceptively simple and surprisingly powerful. Here’s how it goes. If the universe lasts forever, then any event that can happen, will happen, no matter how unlikely. In fact, this event will happen an infinite number of times.

This leads to a problem. When there are an infinite number of instances of every possible observation, it becomes impossible to determine the probabilities of any of these events occurring. And when that happens, the laws of physics simply don’t apply. They just break down. ‘This is known as the ‘measure problem’ of eternal inflation,’ say Bousso and buddies.

In effect, these guys are saying that the laws of physics abhor an eternal universe.

The only way out of this conundrum is to hypothesise some kind of catastrophe that brings an end to the universe. Then all the probabilities make sense again and the laws of physics regain their power.

When might his be? Bousso and co have crunched the numbers. ‘Time is unlikely to end in our lifetime, but there is a 50% chance that time will end within the next 3.7 billion years,’ they say.”

Read the full article here.

This argument, at least conceptually, isn’t all that different than using Olber’s Paradox to prove that the Universe in not eternal, but has a beginning. (I’ve always been delighted with that btw. It’s so wonderfully elegant to recognize that the dark sky means there was a “Big Bang”.)

The idea that the end is nigh isn’t really terribly surprising either. It’s a consequence of the way statistics work. There’s a similar argument (based on Anthropic reasoning) that our generation is that last generation that will ever exist. Which is a bit troubling until you recognize that each generation has been able to make that argument.

There’s a fuller explanation at the link above – it’s not terribly technical so go and enjoy!