We spend not enough on space. Most of what tech we now have on Earth-which most take for granted-desktop computers, lasers, masers, cell phones, etc, etc, etc, came out of space research. It has spawned many industries, jobs, health care improvements, recreational advances, and more.

Don't be a sucker all of your life. There is no way to turn back aging without violating The Laws Of Thermodynamics....which nothing can do. Reversing Entropy aint gonna happen in your lifetime.

There is no gravity. The universe sucks. Hahahah!

Nothing in either Newtonian Physics, Einsteinian Relativity, or Quantum Mechanics, forbids time travel...so it is probably possible...but difficult. Dis-believers say that we never experience time going backwards. Believers say that time going backwards is what DeJavu is all about, so we do experience it. The alleged 'Arrow Of Time' may be just a line that physicists came up with so they could dismiss the idea of time travel, and not drive themselves crazy trying to solve the paradoxes it would create. In some theories, the paradoxes take care of themselves. If you go back in time, you may enter a parallel universe / world with alternate yous, etc. So, if you kill your grandpa in that World B, and return to your World A, your gramps in World A is still alive....so no paradox there.

This is the sort of thing we may never learn much about...or maybe we already have, and this world is one created by a time traveler. Perhaps-originally-HItler won WW2, and took over the world, so a physicist from that world's post war era went back in time, arranged for Hitler to lose WW2, and gave us this world as a result. How would we know? It makes for interesting thoughts, and discussions, but it is unlikely that anyone other than a major government would ever have the money to start really investigating it.