I remember an interesting science fiction short story, about an experimental spaceship that would go faster than the speed of light, like a tachyon. For this reason, the story had to give some tachyon theory.
Normally, to accelerate to the speed of light takes an immense amount of energy. As soon as you cross the speed of light to tachyon space, you still have this vast amount of energy, to get the *slowest* possible tachyon speed. Since you can’t get more energy, to *speed up* in tachyon space you have to give up energy(!) So eventually, the very fastest tachyons have almost no energy of momentum left.
In any event, this spaceship would not accelerate to the speed of light, but with some gizmo, would translate to its energetic equivalent in tachyon space, with the same level of energy.
They figured that they had better be cautious, so would just accelerate for a tiny fraction of a second when they made the jump to tachyon space, and then immediately jump back to normal, sub-light speed space.
Blip! But when they looked out the window all they saw was blackness. They fussed over this a while before they figured out they had traveled so far that they were more than 15 billion light years away from the universe, so its light hadn’t reached that empty space yet.
Using some very careful measurements, they turned their ship around exactly 180 degrees, not an easy trick with no reference points. Then they used twice as much acceleration before going into and coming out of tachyon space.
Luck! They could now see a tiny dot of light in their “rear view mirror”, which was the universe.
The story concluded that it might be some time before they get home.
I enjoy good theoretical science.
The Science Channel has a great show narrated by Morgan Freeman (Yeah I know) covering various lines of theoretical astrophysical thinking.
Interesting story there. I’d like to find and read it. I often wonder if there is like a “wall” at the end of the Universe where say if you took a car and went into it at 100 MPH, what would happen? There is so much we do not know. I remember in the 1990’s when Art Bell had a guest where his theory was that quasars could be “small big bangs” that are adding to our universe and adding to it.