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Alone and trapped: this is what will happen when the universe begins to expand at the speed of light

The most accepted theories about the future and the end of our Universe are not too cheerful: they speak of the death of all stars, followed by the slow disintegration of all black holes and an inert and eternal end in which all matter will disappear .

But long before all that another important phenomenon will occur, which is not the end of the universe but it can be for us: the moment when space begins to expand faster than the speed of light. It will be then that humanity will be trapped and the cosmos will be completely unreachable.

If light from other galaxies does not reach us, information does not reach us

Wait: the universe expanding faster than the speed of light? We know that the expansion of the universe is accelerating and therefore the stars and galaxies around us are moving away, but was not the speed of light the maximum speed at which you can travel?

It is, there is no way to travel faster than the speed of light. But it’s one thing to travel relative to space, and something different is that the same fabric of space expands. That expansion is measured differently (in velocity times length), and has no maximum imposed by the laws of physics.

So once the expansion of the universe reaches this point and the galaxies around us are moving away from us faster than the speed of light, what will happen? The answer is a great confinement.

Local group

Our local group, chaired by the Milky Way and Andromeda, will be the only known and observable universe in a few billion years.

Only the stars and galaxies of the local group in which we live, which will remain nearby due to the effects of gravity, will remain accessible. In fact, after billions of years, everything in that local group will converge into one huge galaxy. The light from distant galaxies, unable to reach us, will slowly fade. There will come a time, after many billions of years, when that light will be too dim to see. We will be in the dark.

If a civilization develops during this period, it will not be able to know anything about the universe or its origin. In the sky beyond your great galaxy you will see only blackness, and everything will indicate that this blackness is absolutely infinite. Everything around the cosmos is moving away too fast to be able to travel to it, and not even to be able to see it. The far future will be for large, completely isolated galaxies.

A cannibal universe: the Magellanic Cloud has swallowed up other galaxies on its way to collide with the Milky Way

There is an awful lot of time left for that to happen, and it will happen on such a large time scale that it shouldn’t concern us in the least. Our sky will remain full of stars long after the Sun dies, and human civilization has billions of years to find a way to travel beyond our local group. If we can get to propose it, of course.