I had an email today from one of the authors of “The Five Ages of the Universe“. The book – a pop but respected work by two physicists – divides our universe’s lifetime into five ‘ages’ from the Big Bang era to the final cold emptiness after black holes. It was published a decade ago, and I wanted to know if any of its hypotheses had been disproven or changed.
His answer was scorchingly apocalyptic.
The big development since 1999 has been our partial understanding of dark energy: it’s causing the expansion of the universe to accelerate. While I knew this intellectually, I hadn’t thought about what it means if – as seems to be happening – it doesn’t stop.
This darkly-driven expansion is putting ever-bigger volumes of space between galaxies. And in a startlingly short span of time, that expansion will be happening faster than light.
Now two objects – such as galaxies – moving apart faster than light will be cut off from each other, forever. There is no way anything can cross the span of space between them even in principle. Our little cluster of stars, the Milky Way, is going to end up alone, as other galaxies – in all their splendour and diversity, all those stars and planets to discover and understand – move beyond our causal horizon.
And this starts happening in just a hundred billion years.
Just a hundred billion?
Is that all? Is that really, really all we’ve got?
Given the timescales of the book, that’s only next week or so. The book projects out to 10^145 years, as near as good a definition of ‘forever’ as you’ll find. But long, long before those cold final days, our glorious universe will splinter into a trillion islands, little stellar villages cut off from each other by the most fundamental limit of all. The bubble in which we influence reality will shrink by an unimaginable percentage.
If we don’t have warpdrive or wormholes at that point, it’s all over.
And here’s the really scary part: as long as we’re off this rock, the universe won’t even look that different. It will still be a spacescape of stars and solar systems; the last suns won’t flicker for several tens of trillions of years. There’ll be planets, not yet formed today, thriving around distant suns, and there may be life on them.
But those races yet to evolve will never know us.
Their universes will be smaller than ours, perhaps just single galaxies of a few million stars. And they will never know – indeed, they have no way of ever knowing – that a young race called the humans, just a few hundred billion years earlier, once looked at dust – through Hubble and James Webb – that would one day become a warm, life-spawning planet.
Makes you want to cry, doesn’t it?
Trying so hard to be optimistic, to believe there are no limits to knowledge, that there’s an infinity of space out there to explore. And learning that one day we simply… won’t be able to?
It won’t matter much if you’re planning on remaining earthside, of course: you’ll be able to reach up and touch the sun (suitably attired) in just 7.6bn years, as it becomes a red giant. That’s practically tomorrow. But a few billion years is enough time to build the kind of economies and engines to allow us to spread out across the galaxy, even if we have to do it the old-fashioned way (without warpdrive.) So our local star isn’t the issue here.
The issue is… all those other suns, lost to us forever.
Whole universes pinched off into their separate realities, walled away from each other by the laws of physics. Our universe, giving us a final finger in its last flush of youth.
Less than a second into our universe’s long day of life, we’ll be cut off from the rest of it, forever.
I think I need a hug.