LOVE the Mick Jagger one!
I typed the following for the last thread then found it closed:
Tabby, Backenette has been incredibly calm and informative throughout this whole thread. I really don’t think that comment was meant to be patronising.
Time travel is possible in theory however you need one of two things to achieve it - faster than light travel or immense gravity.
The reason you hear Brian Cox mention particles associated with time travel is that they’re tiny and some can travel at faster than light speeds in theory. There is just no way you could make something as big as a human, let alone a DeLorean (😂) move that fast. It’s just not possible.
The other way is to actually bend space-time so that two distant points meet in the middle and you jump through. The effect of gravity on time is well known, to the extent that the space station and probes need to run on seperate clocks to compensate for it. We’re talking about seconds here though. The kind of mass you would need to bend space time that much is like a black hole. Also completely out of the reach of Earth technology.
So yes, if someone can find a way to bend space time to that extent without destroying the earth, or propel a person faster than light speed without destroying the person, yes, time travel is theoretically possible. It won’t happen though.
See also ancient aliens. Space is big. Very, very big. Our nearest Star is 4 light years away. That’s 4 years spent travelling at the speed of light. Space ships carrying fleets of aliens are too big to move that fast. Based on current Earth technology that would take us about 100 years, so about 4 generations of people living in space, giving birth in space, and training the next generation to be astronauts so they can breed and die in space, but not before they train the next generation. It’s completely bizarre. Humans certainly wouldn’t be ok ethically doing that to those next generations, but then there’s the money too. No guarantee they would be able to establish a base on a planet near that star, even if one did look habitable from here.
So maybe ancient aliens learned to bend space time? Maybe! But there’s no evidence they were ever here. Pyramids are a very reliable structure. It’s really no wonder they’re found all around the world. Children playing with blocks form these structures independently early on. I don’t think a successful and established ancient civilisation would need alien advice to figure out how to build them.