What If the Universe Started to Contract? | Unveiled

What If the Universe Started to Contract?

Ever since the universe began, space has been expanding and spreading out, growing into something bigger and bigger. We’re not exactly sure how or why it does this… or whether it will keep expanding forever. But, if it doesn’t, then what happens when the growth stops, and hits reverse?

This is Unveiled and today we’re answering the extraordinary question; What if the universe started to contract?

The universe is not only expanding at the moment, but it’s accelerating in its expansion. Some galaxies far enough in the distance, in fact, are moving away from us at speeds faster than the speed of light. Scientists are able to work out universal expansion by studying the way that light from distant galaxies changes. In these studies, it appears as though we’re the centre point, and everything is receding away from us… But actually, space isn’t expanding outward from one specific location. If that were the case, we could work it back fairly easily to find the true “centre of the universe”, or where the Big Bang occurred. Really, though, despite its name making it sound as though it was, the Big Bang wasn’t a simple explosion of matter, it was (and is) an expansion… all of which means that, today, space expands everywhere, increasing the distance between any two points.

Before we discovered that universal expansion was accelerating, scientists thought that there was only one way for the universe to stop spreading outwards; it would have to contain enough mass for gravity to eventually overcome the rate of expansion, to force matter to fold back in on itself. Scientists called this amount of matter the Critical Density - it was the point at which everything would change. However, that all changed when we discovered the accelerating rate, which led to theories on Dark Energy - the force usually cited as driving the expansion of the universe. Now for the universe to begin contracting, dark energy would have to either disappear completely, or change how it acts. Given how many unknowns there currently are, there is a possibility that this could happen… with some models predicting that dark energy eventually becomes an “attractive” force (rather than a repulsive one), which would draw the universe back in.

Were that to happen, it probably wouldn’t take us that long to notice it. We can currently see that the universe is clearly expanding because galaxies are redshifted when we observe them, due to the Doppler Effect. When objects move further away, the light that travels from them to the observer is stretched and the frequency is lowered - making it appear “more red”. If something is, instead, moving towards you, however, it appears “more blue” because the light is contracting as it travels, developing a higher, bluer frequency. Unsurprisingly, this is known as “blueshifting”, and if the universe started to contract it’s what we’d see across the cosmos.

In some ways it’s an encouraging thought that everything in the universe would effectively be edging closer to us… but it’s an ominous reality, as well. As the contents of the universe - every galaxy, star, and planet - are pulled inwards, it would appear (from our perspective on Earth) as though we were some kind of supermassive black hole, inescapably dragging every speck of matter toward us. But, were we to somehow relocate to somewhere else in space, then we’d also be met with the same sensation there. Everything in existence would be on a collision course with everything else, meaning the “end of the universe” would now literally be just a matter of time. So, if we were also able to calculate the speed of the contraction, we’d know how long the universe had left to survive… The ultimate doomsday clock would have started ticking.

But is there anything we could do about it? Or even understand about it? Perhaps the first question we’d ask is why expansion stopped in the first place? Something must have happened to the dark energy for it to either change its behaviour or disappear. As it is, dark energy accounts for about sixty-eight percent of the total energy content in the universe - so any change would be a significant one. One possibility is that dark energy could somehow turn itself into dark matter. As it stands, some researchers already think that the opposite is happening; that dark matter is decaying into dark energy, increasing the amount of dark energy in the universe. According to some estimates, dark matter could even one day have disappeared completely, wholly turned into energy, in billions of years’ time. For today’s question though, where the universe contracts, we’d need to see that hypothetical process put into reverse; we’d need to see dark energy transforming into matter, and decreasing.

A little less hypothetically, however, our best guess today (and what most scientific observations infer) is that dark energy is actually a constant force, and that its value never changes. If the universe were to start contracting, and if a contraction results in a drop in dark energy, then that assumption would be blown out of the water straight away. But there are theories on dark energy which do more easily allow for a potential contraction, too - including that dark energy works more like an energy field, called “quintessence”. This “quintessence” also overpowers gravity and (at present) expands the universe… But, if it were to (for some reason) weaken over time, then the ultimate fate of the universe could still be that expansion stops and space “heads back the way it came”.

In popular science, this major turn of cosmological events is called “the Big Crunch”, which is one of many proposed “end of the universe” possibilities. During the “Big Crunch” (which, while estimates vary, could still take billions of years from start to finish), the distance between stars shortens, meaning that it’d grant us on Earth a better-than-ever opportunity to find and meet alien life elsewhere - if it exists. Currently, the speed of light places a boundary on how fast and far we’re able to travel, and the vast, expanding distances between stars means that there are galaxies we will never see or travel to. If the universe were to contract, then with every passing day that would be less and less the case; everything would be drawing closer, allowing us to travel or send communications more easily, effectively and quickly. Becoming an interstellar species would now be an increasingly achievable prospect to the point where, in an unfortunate twist of fate, it could be that we only find proof of other intelligent life once the universe has started destroying itself. Which just wouldn’t be fair, would it!

On the plus side, universal contraction would at least provide more answers to some of life’s other great unknowns. A contraction might be interpreted as proof that there’s a limit to how big the universe can get, which could then be seen as proof that the universe has an “edge”. At the very least, were the universe to revert inwards then we’d know that it does have an endpoint; that it, like everything else in nature, will die and disappear. That’s unless you subscribe to the Big Bounce Theory, which posits that the universe is actually in the midst of an endless cycle of expansion and contraction… so, if it started drawing inwards, all wouldn’t be lost and the universe would recover - not that we humans would know or recall anything about it!

What’s clear is that, if the universe did one day simply start rebounding backwards, then there’d be nothing that life on Earth could do to stop or outrun it - short of somehow relocating to a different universe altogether (if, indeed, different universes even exist!). In reality, we’d be stuck here, waiting for the contraction to reach us and wondering what will happen when it does. Ultimately, all of the particles that form us and our everyday lives would be condensed back to wherever it was we came from in the first place, perhaps with a view of recycling and starting again… perhaps just to spend eternity inside the singularity. And that’s what would happen if the universe started to contract.