Dang! What ever will he think up next?? 
No one has “proved” we can go forward or backward in time, as such, but a great many physicists and mathematicians have found solutions to relativistic equations that show time travel is possible…IF our universe is a certain way or other. The infamous Godel, for one, found a solution which was based on the assumption that our universe was rotating. :shrug:
In the interests of this thread I just reread a favorite book of mine called “Hyperspace” wherein many-a-things about time travel are explained. The three “famous” paradoxes of time travel are discussed, and shown how they don’t turn out like we would think they would…in other words, they don’t become paradoxes.
The author sort of summed it up with this: we can only fulfill the past, not change it. I never found time travel paradoxes to be that particularly plausible anyway since I am a fan of the many-worlds interpretation. BUUTTTTT, there was an interesting summary of a time travel short story where a girl ends up being her own mother, father, daughter, son, grandmother, husband, etc etc. Quite interesting.
In science fiction (usually in which references to actual physics theories are minimal to none), I’ve seen three ways of addressing the situation:
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The time traveler goes into the past and changes something–even something very small, like having a seed stick to the time traveler’s sock–and upon returning to the future, discoveres a totallly different future. In other words, tiny changes are magnified, a “butterfly effect” through time.
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The time traveler goes into the past and attempts to change something, only to discover that the past is ridigly unaccomodating to all attempts to change things. Time traveler realizes that all activities he/she performed “in the past” could easily have occurred in the past that is already known about in his/her future, because they weren’t of any particular importance and “make no difference”. So you can go back and do things but not meaningful things.
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The time traveler goes into the past and successfully changes things that would appear to be of great and lasting importance (e.g., killing Adolf Hitler during his childhood) and then moves forward again in time only to discover that something or someone else occurred to occupy the same “niche” or purpose and that the end result is the same (some other person performs essentially the same role as Hitler did and the Holocaust and WW II still take place). So all possible timelines converge towards the future.
OK, speaking as a relativistic physicist here, who’s spent the past 75% of life thus far thinking about time.
First of all, there’s no reason to suppose that a time traveller would age in reverse. In fact, if he did age in reverse, then it would be necessary for all other time-dependent processes in the traveller (thought, digestion, etc.) to reverse as well, and the net result would be a time traveller identical at each point in time to the “original” person, and exactly superimposed on him. This would be completely indistinguishable, from all perspectives, from a non-time travel scenario, so we might as well say that it’s not time travel.
Now, let’s look at some of the physical possibilities. Currently, the method which is considered most plausible by physicists is Thorne’s wormhole method: First, you create a connection between two otherwise separated points in space, then, you cause one of the ends of this connection to age at a different rate than the other end. For instance, if you create the wormhole in the year 2005, and cause one end of the connection to age at half the normal rate, then one end of the hole will be five years old in 2010, and theother will be five years old in 2015. However, the spacetime point corresponding to the five-year old wormhole on one end is still connected to the spacetime point corresponging to the five-year old hole on the other end, so we’ve now got a connection between 2010 and 2015. One of the philosophical advantages to this mechanism is that you can’t travel to a time before the wormhole was produced, so this explains why we don’t see any time travellers here and now. There are, however, other conceivable possibilities being considered, which would, in fact, allow for travel back to an arbitrary time, such as the formation of a “warp bubble” (yes, that’s a real theoretical possibility, though not in quite the same form as presented in Star Trek. The difficulty in any of these plans is that some sort of funky matter with negative mass is necessary to make them work, and we don’t even know if such matter is possible, much less how to produce it.
As to the paradoces (or really the paradox, since they’re all just variations of the same problem): There’s really only three workable explanations. First, and simplest, time travel might be just plain impossible, making the whole thing moot. I believe that this possibility is what Hawking refers to as the “Cosmic censorship principle”. Secondly, it might be possible to travel back in time, and to affect the past, but not to “change” it: If you do something, then that thing was already in the history books as being done, as of when you left. This is the “weak censorship principle”, and is the possibility which I personally consider most likely true, although there is currently no way to prove it (and won’t be, until and unless time travel is actually discovered). The third possibility is that there exist multiple universes, and that any time travel into the past is of necessity into another universe. You can go back to past’ (that’s “past prime”), and kill grandma’, thus preventing the birth of you’, but this has no effect on grandma or you. Currently, there is no scientific way to distinguish between these possibilities.
To re-phrase my first post to this board, we can all travel into the future (try doing anything else) and we can all observe the past (try doing anything else).
ok a stupid question to lighten this up.
On H.G. Wells’s THE TIME MACHINE:
he was sitting in the machine and then the great war covers up his machine and keeps it covered up then he cant stop and go back because at the moment he was stopped he would be encased in stone. so he has to wait for the rock to errode away. but then if too much erroded away he would be hanging in the air and if he stopped he would be dropped. poision air has the same problem.
well if this is all true then you could never travel back in time anyways. right?
First, you would have to wonder if such an event was fixed. If it wasn’t, then anything could’ve happened, which is what the Doctor does: He fixes random points in history that aren’t fixed. If it was fixed, then no one could meddle with it, without a total event collapse. Another thing to consider is, “What did the son do afterwards?” Did he do anything beneficial for the human race that wasn’t supposed to happen?Did he brush it off as cheap voodoo and continue living life? But only me or the Doctor can know if events are fixed. Such as, if I were to die minutes after I post this comment, it may be a fixed in history, or it could be in flux. But I couldn’t cross over my own timeline without ripping a hole in the space time continuum and/or the time vortex.
Wow, this thread just travelled 12 years, 4 months and 15 days forward in time in a single post!
John Titor did. Just ask George Noory.
Interesting - I can’t honestly call this a zombie post, since it didn’t die, but rather leaped forward into the future!
let me point out a few oddities: There’s nothing which clearly in our experience links space and time. This is a problem, as even if you did jump forward or backward in time, you’d have no way of steering to physical locations. Think about it: if you changed your “time position” by 24 hours, you’d end up in the vastness of space elsewhere in our galaxy, unless you were somehow anchored to a specific location. And I have no idea how you’d do that. Note that the wormhole method would work, although that actually might create a permanent frame of reference against which all movement could then be measured…
Huh. That would radically alter how we view space to begin with.
Well, perhaps the concept of time travel is ultimately something we can only speculate upon, and dream about. But it can be a field of fertile and worthy dreams indeed. I would argue that some of the best science fiction ever made comes form the idea of going back or forward to change (fix) history. Ultimately, isn’t the basic theme there that Mankind is (figuratively in reality, literally in the story) stepping outside of the limits and bounds of nature and choosing what the future (present) will become? Time travel stories are inherently speculative, but also arguably very hopeful. They speak to the power and consequence of human choices, and the responsibility we have to make them wisely.
Maybe this was this the way of thinking in the halcyon days of 2001, but in modern times Captain Janeway is the center of that image.
Well, Bill Maher was in a made-for-TV movie in 1988 called Out of Time. He played a cop who as a hobby built high-tech detection gear (none of which worked very well and was subsequently a source for ricidule from his fellow cops) who meets his time-tossed grandson from 2088, played by Bruce Abbott, who is also a cop and routinely uses technology based on his (eventually revered) grandfather’s prototypes.
When the characters meet, Abbott tries to prove his futuristicky origins by warning Maher about Vietnam and Watergate, to little effect.
It was an amusing movie. Pity it didn’t get turned into a TV series.