Time Travel Paradox

i_have_glasses · Apr 15, 2005

If time travel into the past was possible, how would the universe deal with the paradoxes that could be created?(e g I go back and kill my grandfather) This would seem to me to make time travel into the past impossible. Unless somehow the universe would not let paradoxes happen. (e g my grandfather decides to go get his prostate checked and is not home when I arrive to murder him).

yevaud · Apr 15, 2005

Ahh, the "Grandfather" paradox. Love it. That was partially explained away (no proof or evidence for this, just some really weird theoretical musings) by Everett's "Many Worlds" theory. In a quantum sense, everything can, will, and has occurred. Meaning that for every tiny decision you make one way, there must be a corresponding "alternate" time and space where you exist, and *didn't* make that decision. So, the reasoning went, if you were to travel back in time and shoot your Grandparents, it'd have no effect on you - you've just shot one of your alternate's Grandparents, not your own. Therefore no problem with causality. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

alokmohan · Apr 15, 2005

So we can safely time tavel and keep on killing grandfathers,no dearth of stock.

yevaud · Apr 15, 2005

Well, assuming you could figure out how to do so. That's the weirdest thing about the theory. That time travel backwards is prohibited - in your own continuum. But, as the theory goes, travelling "back" to an "earlier time" in an Alternate's history wouldnt be prohibited. So, if you were to travel "back" in time, you would indeed be at another time - in a near-Alternate's past. Lotta "Cross-Time" stories written since Everett came up with his idea in the late 50's. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

alokmohan · Apr 15, 2005

Tell me if it is theoritically possible at all.

yevaud · Apr 15, 2005

I would rather suspect that you're right. There's something inherently wrong about the concept of time-travel. You'd think, if it were possible, we'd see acausal events spontaneously taking place, from time to time. We don't. Besides, when you look at all of the possibles for time travel, they're brilliant, astounding...and completely unworkable. Look at the massive, rotating cylinder concept. Got some spare Neutronium, and a work-crew? Asmiov (I'm fairly certain it was him) said something to the effect of, if there's time travel, then there must be time travellers. Where are they? If it was that easy, we should be overrun by gawking tourists from the future! Hawking's Wave Theory of the Universe also explains the possibility of cross-time travel, inherent in his theory. Although the mechanism of "time travel" would be different here - neccessitating the ability to open stable wormholes between the two continua. Which of course brings us back to "brilliant and utterly unworkable." Still, interesting topic. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

alokmohan · Apr 15, 2005

Hope time travellers from other universes are not hanging around to see our discussions

yevaud · Apr 15, 2005

I'm fairly certain that there are. And there's one or two that I'm convinced are aliens. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

siarad · Apr 15, 2005

<blockquote>In reply to:<hr />In a quantum sense, everything can, will, and has occurred.<hr /></blockquote> Whoa! if everything has occurred you wouldn't go back & kill your grandfather as you'd previously done it. Groundhog day all over & over... <img src="/images/icons/laugh.gif" />

yevaud · Apr 15, 2005

Ummm, sorry. Not quite what I meant by that. In the sense of Quantum uncertainy, all possibles must be considered. That's why QM is probabilistic. All Hawking meant was that to account for the universe as a wave-function, all possibles would have to have occurred, for ours to be so well-designed for us to live in (by designed, I'm not speaking in a religious sense). So - theoretically - there must be a universe in which you didn't just take a sip of juice. And one in which you did. And one in which you spill it. Etc... <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

emperor_of_localgroup · Apr 15, 2005

Its so ramantic. Who says scientists are not romantic. There is no parallel universe, there is no time travel to the past or the future. Just get used to this mundane universe. <div class="Discussion_UserSignature"> Earth is Boring </div>

lewcos · Apr 15, 2005

Only time traveling are the clocks on their way to the stores and the wristwatches on our hands.

alokmohan · Apr 16, 2005

Every honey moon should be time travel.

emperor_of_localgroup · Apr 16, 2005

I liked lewcos and alokmohan's jokes. To other fellow time travelers: I have seen many explanations where time travel is associated with FTL speed. Here is a hypothetical situation, and tell me where is the time travel. I'm here on the earth right now. Suppose there is another world just like ours 100 million light years away in another galaxy. Somehow, someway, I traveled to the distant galaxy in seconds. I looked back to the earth, what do I see? Dinosaurs roaming on the earth. One of them may even be munching on the plants right where my house is. Did I travel to the past? NO. I am still in the present time. All I'm seeing is 'light' from events that took place 100 million years ago. I just beat the 'light' in a 100-million-light-year dash. Light-picture from any event that takes place in the universe spreading out in all directions. If you can have FTL speed you can catch (watch) the light-picture later in time, but there is nothing else you can do. Because it's just light, there is no physical existence, an image in the mirror. In all cases you are catching the old light-shows at the present time. You are not in the past. If speed is concerned in a time travel, remember, we are not traveling in time, we are traveling in spatial dimensions. There is a similar argument by Aetherius on another thread. If some one shows me a negative value of time from a solution of an equation, or derives an equation setting t=-t, that'd not convince me that negative time exists. But i'm open to any new theories. Becuase I have a suspicion Whatever (or Whoever) built this big balloon, there must be some loopholes. IT (or He/She) cant be a total perfectionist. <div class="Discussion_UserSignature"> Earth is Boring </div>

Leovinus · Apr 16, 2005

Imagine a phonograph record playing like time flowing. When the needle gets to a certain point, something in the record itself causes the needle to skip back and scratch the record. Now the record plays differently from now on. Perhaps the paradox could be just that: You go back in time and kill your ancestor. Time flows from that moment in the new timeline and the future hasn't been written yet. However, I think that time travel doesn't make sense to me. The atoms in your body have existed for eons. Before you were born they existed and after you die they will continue to exist. But each and every atom exists in one particular location at any particular time. Now if you do your time travel to the past, your atoms have been removed from the universe of the present where you came from and duplicated in the universe of the past that you travel to. Can we have the same matter in two locations at once? I don't think so. <div class="Discussion_UserSignature"> </div>

i_think · Apr 17, 2005

Yes, how ironic, according to theory the particles in our body were part of the big bang 14 billion years ago, and today with our telescopes we try to look back to the day we were born, meanwhile discussing what is time. How did we get here from there?

siarad · Apr 17, 2005

It's obviously taken energy to move us (our atoms) from their origin to now. I think to move in time would take a similar amount. This is because we are not standing still in space but moving at an indeterminate but high speed. If time travel means somehow going back in time at our present position then it presupposes time has travelled with us around which I can't get my mind.

alokmohan · Apr 17, 2005

Why kill ancestors.We can learn anthropology and use the occasion better.We may attend a marriage ceremony too.

alokmohan · Apr 18, 2005

Time travel is very easy if we have a worm holes.

emperor_of_localgroup · Apr 18, 2005

@eburacum45 I knew someone is going to hit me with my 100-mill light year trip in seconds. But an interesting point is that even if I successfully make that FTL strip, causality is not violated. Then how can the trip itself violate causality? As another post, by alokmohan, pointed out a trip through a wormhole can be a real time trip. I have seen that time cone diagram many times. My personal opinion is the light cone is valid for slower than light objects. We are here more interested in the forbidden regions of the time cone. My another personal opinion, equations for special relativity hold only for objects slower than light (v<c). For v />c, we need modifications of the equations. <div class="Discussion_UserSignature"> Earth is Boring </div>

Saiph · Apr 18, 2005

special relativity also holds for V>>C. In either case, you can approach C, but can't reach it (from either above, or below). <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

pizzaguy · Apr 18, 2005

Asmiov (I'm fairly certain it was him) said something to the effect of, if there's time travel, then there must be time travellers. Where are they? If it was that easy, we should be overrun by gawking tourists from the future! As I have said before, "Back to the Future" style time travel is never gonna happen. How do I know? Because it would have by now.... We would be over-run by travelers, and we'd all already know about it. REMEMBER, when you 'allow' time travel, you remove time itself from the formula. By now, we'd all be time travelers. Never gonna happen. <div class="Discussion_UserSignature"> Note to Dr. Henry: The testosterone shots are working! </div>

alokmohan · Apr 19, 2005

So even if I destroy earth and come back to same earth in another time?Is that what you say?

yevaud · Apr 19, 2005

Not quite. What most people consider to be "Time Travel" is like being a vehicle on a vast superhighway that's always moving in one direction (time moving always forward being represented by the direction). To travel backwards, under this analogy, would be equivalent to turning around on the highway, and moving counter to the flow of traffic. The farther you travel in this direction, the farther "back in time" that you go. But this is effectively impossible, as it would violate numerous strictures of well-grounded science. Under the alternate timeline scenario, you're still a vehicle on that highway, and time travel is still forbidden. But running parallel to your highway is another one that's identical to the nth degree to your own. And you figure out how to jump the gap between the two highways, a la' Evil Kneivel. When you "jump," if your location on the other side is "behind" the flow of traffic, you have effectively traveled "backwards" in time. It's not your own timeline, but otherwise, the history and people are identical. So you can kill your "own" Grandparents. But they're not really yours, just identical in virtually every important detail. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

emperor_of_localgroup · Apr 19, 2005

@stevehw33: We still dont know how does a quantum tunneling work. Its not a miracle. Once you said this tunneling can not be faster than light, but you also said transportation between two space will be FTL, by dividing distance by time. This needs more explanation. On a lighter note, each passenger going by quantum tunneling from milky-way galaxy to andromeda must be assigned a 'probability'. If he doesn't make it, he deserves a full refund. <div class="Discussion_UserSignature"> Earth is Boring </div>

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