Time Travel Revisited

[XciT]

It has been quite awhile since i've seen a discussion about the idea of time travel and john titor. a recent article i caught on digg today got me thinking about the mad cow issue titor mentioned ( http://digg.com/science/Mad-Cow_Disease_may_Silently_Incubate_in_Humans ) . Just want to see what everyones thoughts are about the whole time travel issue in this day and age.

reference:
http://www.johntitor.com/ (im sure some a few have not read about it)

[Dave]

It has been quite awhile since i've seen a discussion about the idea of time travel and john titor. a recent article i caught on digg today got me thinking about the mad cow issue titor mentioned ( http://digg.com/science/Mad-Cow_Disease_may_Silently_Incubate_in_Humans ) . Just want to see what everyones thoughts are about the whole time travel issue in this day and age.

reference:
http://www.johntitor.com/ (im sure some a few have not read about it)


It's the same as it always has been, a one way street. The topic makes about as mich sense as measuring the IQ of stones.

[senor-turkey-lurkey]

the great war of 2004 failed to happen :(

[Hellsy]

I agree with the philosopher David Lewis-- that time travel, even if possible, wouldn't matter to us in the present. The past includes all the events in the past, including any possible time travelers ahead of time. People travelling to the past would have already been included in it, and thus could not influence the present. It sounds strange, but the past would already include people who travelled back to it, even before they were born in the future.

An interesting question is whether or not you could kill someone required for your existence in the present, by travelling into the past. I agree with this response:

"Can Heloise murder her grandfather? As David Lewis famously remarked, in one sense she can, and in another sense she can’t. The sense in which she can murder her grandfather refers to her ability, her willingness, and her opportunity to do so. But the sense in which she cannot murder her grandfather trumps the sense in which she can. In fact, she does not murder her grandfather because the moments of external time that have already passed are no longer separable. Assuming that events 80 years ago did not include Heloise murdering her grandfather, she cannot create another moment 80 years ago that does. A set of facts is arranged such that it is perfectly appropriate to say that, in one sense, Heloise can murder her grandfather. However, this set of facts is enclosed by the larger set of facts that include the survival of her grandfather. Were Heloise to actually succeed in carrying out her murderous desire, this larger set of facts would contain a contradiction (that her grandfather both is murdered and is not murdered 80 years ago), which is impossible. History remains consistent.

This is also related to Stephen Hawking's view (1992). According to his so-called Chronology Protection Conjecture, he claims that the laws of physics conspire to prevent macroscopic inconsistencies like the grandfather paradox. A "Chronology Protection Agency" works through events like vacuum fluctuations or virtual particles to prevent closed trajectories of spacetime curvature in the negative direction (CTCs). If Hawking is right and many-worlds quantum interpretations are not available, then is time travel to the past still possible? Hawking’s view about consistent history then takes us to the special case of causation paradoxes: the causal loop."

Taken from: http://www.iep.utm.edu/t/timetrav.htm