Interstellar space contains neutral hydrogen atoms. Hitting a spaceship, they would produce electromagnetic radiation. When the collision speed goes past about 0.25c, the radiation becomes hard gamma rays which are dangerous to living things, and cannot be efficiently shielded against.
At this speed, the time dilation is slightly above 3%, so you're still not going to reach even Alpha Centauri in one human lifetime, or maybe you barely can.
Right, we are never leaving. We should get comfortable here, and take better care of the only habitable planet, rather than doing insane things and justifying that as "Don't worry, we'll make Mars habitable" and other silliness.
Alpha Centauri is only 4.2 light years away. 0.25c is definitely enough to reach it. You could even do a round trip in only your adult years.
Yeah, if you take the highly unlikely and already lethat 0.25c achievability as a given.
That is the context the above comments are talking in.
Well, except that you changed below lethal to already lethal.
A trip there to do… what?
There likely won’t be any planet better than the very low bar of Mars for human habitation, in fact maybe even worse due to binary perturbations.