Overall a great episode, other than two plotholes with the science
>!For one, they did the typical "we actually invented a teleporter, because since both the universe, planets, and the ship moves, time travel would land you somewhere else". Every time travel storyline ever does this, but it would have been refreshing to avoid it. Gordon ending up at Earth is explained through sub-conscience, but that doesn't explain the sandwich or the ship.
As for the second one, it seems like the relativistic method used at the end should have more issues with it.
One potential issue is their interpretation of time dilation, which is different from any other I've seen. In this version, they manage to fly at close to 1x speed of light for 400 years while they themselves only experience a few minutes. This is different from other versions I've seen where it would take them 400 years to travel that distance but it would appear more to the outside world. Applying this episode's problem to the more typical approach here would be to have them travel a few light minutes at 0.999etc x light speed, not mess with the whole "need to travel 400 light years" bs.
Even if their interpretation is valid, it's not without issues. Since they moved 400 light years in 400 years (outside perspective) but the ship and crew aged slowly (a few minutes), that leaves the question of fuel if nothing else. It would have to use up 400 years worth it fuel in that time, since that energy was used for powering the engines for 400 lightyears at ~1x speed of light. Even though they experienced it in a few minutes doesn't mean the energy draw didn't happen.<!