Last night at work, we somehow got around to a discussion of time and interstellar travel. I couldn’t do the subjects justice; can anyone here help me to explain these concepts?
No one believed me when I said that a person approaching the speed of light would appear to an outside observer to slow down. Wouldn’t this also mean that suspended animation would be unnecessary when traveling at the speed of… (geez, can I just call it C?) since the traveller’s motion would go to zero also? (and yes, I’m ignoring such things as acceleration and that travelling at C would probably require an infinite amount of energy.)
Last week on PBS, they did a thing on time travel. First off, several physicists claimed that it * could * be possible in the future to go back in time, but it would take an incredible amount of energy.
One physicist suggested that he had proven mathematically that it was impossible for something going back in time to affect the current state of affairs (I think he set up the equation for the case of a ball rolling off a table, back in time and then across its own path; it could not knock itself off its original path.) Did anyone see this, or can someone explain the ideas behind the claim?