# How to travel back in time Part II

So in my last post I described how time travel could be possible within the realm of our physics. When I say within the realm of possibility I mean:

We think wormholes exists

We know there are particles that can travel faster than light.

So given that it is pretty likely we can travel FTL or beyond, how would my proposed FTL work out in reality?

The biggest issue is one of acceleration. Comfortably we want to accelerate no faster than 1g. (9,81 m/s^2). In effect this would make us feel like we have earths gravity. The problem with this though is it would take us 353,7 days to reach light speed.

So some interesting math copied from elsehwere.

Observed from the spaceship, accelerating at 1g would reach 0.77c after 1 year.
Observed from Earth, it would take 1.19 years, and would have travelled 0.56 light years.

After two years on the ship at 1g, you would reach 0.97c, however 3.75 years would have elapsed on Earth and you would have covered 2.90 light years. Viewed from the Earth, your mass would have increased 4x, and you would be a quarter of your size!

After five years on the ship, you would reach 0.99993c. 83.7 years would have elapsed on Earth, and you would have covered 82.7 lightyears. You would stand about an inch high, and have a mass of about 6 tons as seen from Earth, though you would not notice any difference.

After 8 years, you would reach 0.9999998c. 1,840 years would have elapsed on Earth. Great, you are far from what was your home. 400 US presidents came and went. What is more, you are now 1mm high and have a mass of 140 tons.

Nothing to lose now, lets go on, still at 1g…

After 12 years, you would be travelling 0.99999999996 c. By now you would have crossed the galaxy and be 113,000 light years from home. Time is now running 117,000 times more slowly for you than on Earth. You stand 15 microns tall, and your mass is about 9000 tons.

So, in fact you have travelled “faster than light” by covering 113,000 light years in 12 of your years, but well and truly burnt your bridges in doing so.
You have also become a very significant problem for any destination, and would require 12 years too to slow down at 1g, assuming you have survived the deadly blueshifted light and cosmic radiation.

So that’s *just* to get to light speed, not even considering the real problems of deceleration and time passed on earth. Per the quote here, just the acceleration would take up 1840 years on earth. Even if we accelerated faster, we would need to make up for lost time during that acceleration. Let’s say we instantly wound up at 2x FTL after 12 years, we would need an additional 12 years at 2x FTL to arrive at present day, with another 12 to decelerate. At my age, the prospect of coming back to the time I started at 70+ years old isn’t in line with what I’d want to do with time travel.

I started thinking about this the other day because I found the start of a short story I started writing that deals in time travel, but in the lame trope of most sci-fi I took shortcuts. I plan on doing a revision and a rewrite of several chapters to fall into the correct way of time travel.

Humans *might* be able to get to 4-5x FTL if they could be frozen. That’s about the only way I can think of it. It would also take care of the aging in transit issue.