Time travel is definitely impossible

I just wrote a new microfiction story for my Twitter feed:

If time travel were possible, every single star in the entire universe would be surrounded by a fully populated Dyson sphere from its birth.

It's not really a story, but I wrote it to provoke people into to thinking about the ramifications of time travel. In doing so, I came to the logical conclusion that time travel is indeed impossible.

I am no physicist, but I have read a few popular science books from people like Stephen Hawking and Michio Kaku, enough to know the basics of how the universe works. As far as I know, Einstein's theory of relativity does not forbid time travel. Many people believe the laws of physics do not prevent time travel, but perhaps the energy requirements, or radiation levels within a wormhole might be insurmountable as to be pragmatically impossible. There is also the old grandfather paradox to contend with, although some recent ideas suggest that this may not be as much of a problem as we might think, and if the multiverse hypothesis is true, perhaps killing your grandfather just spawns another universe where you exit but your grandfather doesn't.

I love time travel movies like Back to the Future, Bill and Ted and Primer, but I never really gave much thought to whether it might actually be possible or not. Not until I wrote that micro story.

Now I am totally convinced time travel is impossible.

I thought before that it might be impossible, because we have never had any reports of finding evidence, apart from theories that UFOs are humans from the future, or fossilised artefacts which turn out to be 1920s sparkplugs with concretion. Imagine how many time tourists there would have been at the supposed birth of Christ. There is no way temporal police force could wipe out all trace of tourists.


But that was thinking too small. I realised that if time travel were ever invented, travel that is stable and relatively paradox free, then the result would be that the entire universe, for almost its entire life would be completely populated. And technology advances, so more advanced races would constantly be going back to overpower less advanced races, and occupying the same space and time as them. It would just keep going. There would not be a single part of the universe untouched my multiple iterations of civilisations evolving, progressing and travelling back to conquer and settle in the past.

So why don't we see all that? Why can we see stars in the sky, not hidden within Dyson spheres? Why can't we detect radio or other signals from everywhere? Why is our own planet's history untouched by future invaders?

The only conclusion I can come to is that time travel is impossible. This is similar to the fermi paradox, which wonders, if life is so probable, then "where is everyone?" The answer to that night simply be that life is very rare, and that we are the first to evolve sentience. Or that there has been sentience before elsewhere in the universe, but it destroys itself before it can get too fr. Or that there are other civilisatons but they are so far away we haven't detected them yet.

But the time travel problem is more severe. All it takes is for a single sentient species, anywhere in the universe, and at any time in the life of the universe, to invent time travel, and that would instantly fill up the universe with god-like life.

Well, there is another conclusion. Perhaps time travel is possible, but no where and at no time in the life of our universe, past present or future, does a species develop enough technologically to achieve it. Either because it is so hard, or that no species every survives to be technologically advanced enough.

Kind of a sad thought. I'd rather believe time travel is just physically impossible, than believe that no species, including our own ever lasts very long.