Is time travel possible?

[SvennoJ]

I don't think time travel is possible but it needs 2 things to work.

We would first need to be able to build a transporter. That is theoretically possible (by way of quantum teleportation) but it needs a receptor on the end. We would need to build the receptor first before we can receive anything from the future.

Secondly we need to be able to send information to the past. That might be theoretically possible using quantum postselection. http://www.telegraph.co.uk/science/7904712/Quantum-time-machine-allows-paradox-free-time-travel.html It sounds to me a bit like building a quantum computer that can predict the future state of itself, and thus pull future information to the past.

Quantum teleportation doesn't seem compatible with qauntum postselection though from what I can tell, plus it's up to semantics whether accurate prediction is the same as pulling information to the past.



Once we have transporters and we send a receptor to Mars, and we find a method for them to work by way of quantum entanglement (which is not bound by the speed of light) we could in theory travel there instantly. Then from there you can watch your own actions from 20 minutes ago by use of a powerful telescope. You can see youserlf step in the transporter and leave. This leads to a paradox instantly, what happens if you decide to travel back within those 20 minutes. You would see yourself arrive back (since you're looking at past events) before you have actually left. Yet then you still have time to change your mind and not got back.

Edit: nvm on the paradox part, by the time you can actually see your decision through the telescope you would have had to have left already. It's all a matter of what your reference point of 'now' is. You can look into the past, not alter it.