Current theory has it that photons have no rest mass and cannot do otherwise than travel at the speed of light. (Of course, there are some speculations that are interesting …).
jrf
Er, that’s not my understanding. Take a look at Does Gravity Travel at the Speed of Light?
jrf
I believe that it’s fair to say that modern physics has pretty much discarded the concept of fields in fundamental explanations. Pretending that there are such things as fields is often conveneient for calculations in those cases where we can be sure (from more fundamental thoeries) that the answers will come out right.
jrf
Cancel, please … I managed to totally misread the original statement.
jrf
BIGmatt asked:
I will have an answer for you two weeks ago ;). Seriously, we are travelling forward in time now, so I think the real question is “Can we travel back in time?”. This question has been batted around a lot. My humble opinion is no. My reason is the classic paradox- What happens if I go back in time and kill my father when he was a child. interestingly, the paradox can be invoked without material travelling back in time. - I decide that in two days I will transmit a message (zero or one) back 24 hours to myself. If the signal I recieve tomorrow is zero then the day after I decide to transmit one and vice versa. I think you can see the problem. OTOH, a paradox does not really rule out the possibilty, it just means we must examine (or reexamine) the theory to try to eliminate it(the paradox not the theory). If we allow faster than light (FTL) travel, we must accept backwards time travel. The theory of relativity assumes light speed is an absoulte limit, but this is not a necesary assumption in that FTL velocities can be substituted in the formulae. You get some weird results. Tachyons (FTL particles) with positive invariant mass (rest mass really does not fit here) will have imaginary relativistic mass. If we allow imaginary invariant mass (and why not?) we get negative relativistic mass, negative imaginary invariant mass gives positive rel. mass.
::whew:: Well, what does this all mean? I do not know. While I think backwards TT is not possible, as I said above, I think you can tell I have thought about it a lot.
Virtually yours,
DrMatrix
Thanks DrMatrix & JonF… the term ‘avalanche’ springs to mind…
DrMatrix:
You’re right when you say that we are always ‘travelling through time’, but whether or not killing your father in the past would kill you ‘now’ depends on causality. If you kill someone crucial to you in the past, does it necessarily mean that you will die? What if by travelling back in time you actually create an entirely new ‘time line’ which bypasses the original one completely.
If this were true, once you travelled back in time, everyone you ‘left behind’ would still carry on the way they were, but in a new time line everyone alive at the point in time where you appeared would go on to live a different future. This would mean that once you went back, there would be no way of travelling back into the future that you came from. It’s also a matter of ‘fate’, and whether or not the events of the future are mapped out already or whether we ‘create’ reality as we go along.
As you may be able to tell, I’ve thought about this a fair amount as well.
Another thing; if as soon as you travel back in time you can create a temporal paradox, which would have presumably very negative effects on all of those involved (perhaps the entire Universe) then wouldn’t that mean that in order for no paradoxes to form then no race in the entire Universe must have the ability to go back in time? It’s either that or the idea that if you go back in time it doesn’t influence the future. Or perhaps something else that I haven’t thought of yet. Hmmm. Any ideas?
“You can have the afternoon off when you die” - Edmund Blackadder