What prevents planets from traveling in straight lines through space?

The sun’s gravitational force is very strong. If it were not, a planet would move in a straight line out into space forever. The sun’s gravity pulls the planet toward the sun, which changes the straight line of direction into a curve. This keeps the planet moving in an orbit around the sun.

Why is there no escape altitude?

An orbiting object has not escaped gravity, it is in constant freefall towards the earth. As long as it goes fast enough, it never reaches the ground because the earth curves away beneath it.

Is the universe a straight line?

there are no straight lines in the univere in fact the entire universe is just not straight. if you send a space craft to mars in a straight line then one would see the craft driffting to all aort of directions. one can say the craft fall into different gravitational fields and looses course but that is not the cases.

What would happen if you could travel in a straight line?

If that were the case, if you could travel in a straight line for long enough, you would wind up right back where you started. If you didn’t age, perhaps you could even wind up seeing the back of your own head just by looking for long enough, as your eyes would eventually encounter the light emitted from your own origin.

Is it possible to rotate in space without a jet pack?

Yes, it is possible to rotate in space, without the help of a jet pack or without touching any external object. Your concern might be that you think the astronaut would be violating the conservation of momentum if they suddenly went from a non-rotating state to a rotating state.

Will we ever return to the beginning of the universe?

Unless the Universe repeated on a scale that was less than about 15 billion light years in diameter today, we’d have no way to ever return to our original starting point by traveling in a straight line. The size of our visible Universe (yellow), along with the amount we can reach (magenta).

Is it possible for an astronaut to rotate in space?

Yes, it is possible to rotate in space, without the help of a jet pack or without touching any external object. Your concern might be that you think the astronaut would be violating the conservation of momentum if they suddenly went from a non-rotating state to a rotating state. The key is that the astronaut is not a rigid body.