How is Time Travel Possible?

Question

One thing that bothers me is the so called "time paradox". For example, what if we go back in time and accidentally kill our grandfather, thus ensuring that we were never born, so how could we go back in time then? One way out of this type of paradox is the realization of the "many worlds" hypothesis but where is the proof for the "many[infinite] universes"?

Answer 1

That all depends on what you mean by "time travel." For instance, quantum science has made fascinating observations regarding the travel of photons (which, rather obviously, are real).

Using the double slit experiment, in which photons upon observation choose a particular discrete path, scientists forced photons from a quasar about 5.4B light-years distant to choose between 2 possible paths -- and in having so done, forced the photons to have chosen that path when they were emitted 5.4 billion years ago. Pretty neat, huh?

The opposite spins of paired photons are affected digitally and simultaneously regardless the distance of their separation, even when only one of them is being acted directly upon -- so, to them, time is a meaningless concept.

As physical beings, we are largely constrained to the 4 basic dimensions (3 spatial dimensions, and time); however there are (depending on the cosmologist with whom you happen to be speaking) 6 or 7 additional dimensions. Unfortunately, scientists can't agree on either (a) the number of dimensions or (b) the properties of the commonly-acknowledged dimensions.

Although we ordinarily perceive time as a forward-moving phenomenon -- and some people might (imho, wrongly) imagine that to qualify as "time travel" -- I think time actually works in both directions (or, technically, in all directions). In other words, the past is a quasi-imaginary construct, as is the future: neither really exists, and yet both exist simultaneously with the present (and therefore, they are also quasi-real).

I'm not really sure how to articulate that so that it's easier to appreciate; I do recognize that it's an exceedingly difficult concept to understand. It may help to imagine that the past is a trans-dimensional concept (as is the future):

If we were trans-dimensional beings, we could move instantly backwards and forwards through "time," without causing any catastrophic "causality loops" or other logic problems -- and we would be able to experience at our respective whims whatever reality we might elect.

The reason there would be no problem with having killed one's own grandfather prior to one's own birth is twofold: (1) in an infinite number of alternative universes, that has already happened, and (2) the past is a quasi-imaginary (and/or quasi-real, depending on your perspective) construct.

Obviously, such possibilities defy orderly expression.

In essence, infinite possibilities exist at every time, and every time exists simultaneously: in our current form, we're merely able to perceive only one possibility at a time (which, by definition, is the present) -- and that binds us in this temporal web.

Even our memories are delimited by earlier perceptions of the then-present, and we are able to make logical and predictive statements regarding the now-future; however, the then-present we each percieve is the now-past for only one of infinite possibilities; the same applies for the now-present and for the foreseeable now-future.

All the other possibilities simultaneously exist, but they are outside our range of perception. This is easier to grasp if you imagine the collision of the cosmological wafers that resulted in what is commonly known as the Big Bang: prior thereto, this universe and this perceived reality did not exist within the multiverse.

So, whenever someone says to you "Remember the future," you can now respond, "I already did."

The "infinite universes" proof is limited to modern cosmological theory: it is the "best fit" explanation yet imagined by scientists, but it is -- technically -- as much an article of faith as is the existence of a Divine superbeing ("god" or "God").

If you're interested in very small (seconds, minutes) alterations in the passage of time, NASA has successfully conducted "local" (near-earth) time-rate experiments in which the passage of time was experienced differently and predictably by identical objects exposed (respectively) to control and variable conditions.

I have heard claims that short jumps to the very near past (much less than a minute) are possible, but I don't recall the details of those experiments. The critical issue, of course, is how the backwards jump was verified.

Answer 2

I agree with you I don't think time travel is possible. You gave a good example. Here's another. Abe Lincoln's assassination caused a lot of problems. We send gunman back and kill John Wilkes Booth and prevent Lincoln's death. How would we then know to go back to prevent it? How would we know about his assassination in the first place? It wouldn't be in the history books or on the History Channel. Another thing if you travel into the future and while there you have a hot dog. When you return to the present what happens to the remains of the meat product that is in your stomach. The animal won't even exist yet in your lifetime. If time travel is possible than a lot of inconsistencies are
possible.

Answer 3

Hi Jargonizer

First, lets see what possibilities exist for backward time travel from theory:

*Special relativity
In relativity time is treated as another dimension like the spatial dimensions (but at right angles to them). In special relativity the space-times are flat (no gravity). In special relativity if an object A travels locally faster than light then to certain other classes of users it will look like A is travelling backwards in time. (For those with some physics study behind them, this can be readily see by plotting a space-like interval on a minkowski chart and then shifting to a new reference frame whose time axis bisects the space-like interval).

* General relativity
IN general relativity gravity introduces curvature into our space-time and we can exploit this curvature to do global (ie non-local) backwards time travel. Remember from above that any faster than light travel will look like time travel to other observers, so warp drives (eg Alcubierre's warp metric), wormholes, etc can be used as "time machines". GR also allows for closed time-like curves under some conditions, meaning a person can trace a path through space-time which leads back to its starting point, hence involving some backward time travel.

* Quantum antimatter
Quantum physics is governed by a special symmetry called CPT symmetry. CPT stands for charge, parity, time. The symmetry means that if I start with a particular particle (say an electron) and I reverse its charge (making it a positron, the antimatter partner of the electron), reverse its parity, and reverse its direction in time (so that it now moves backwards in time) then you end up back where you started. In other words, an electron moving forwards in time is more or less equivalent to a positron moving backwards in time.

*Quantum interpretations
Quantum mechanics is weird. It works (it works very well) but it doesn't make everyday sense. In order to try to understand what is actually going on people use quantum interpretations. There are three major ones, called the Copenhagen interpretation, the Many Universes interpretation, and the Transactional interpretation. Importantly no experiment can distinguish which is "right", you are free to use whichever makes the most sense to you. The first one (copenhagen) is the one generally taught at a university physics course, the second one is the one the public talk about, and the third one is harder to understand (but most interesting in my opinion!). This third one uses backward time travel to confirm the transactions which manifest as quantum interactions.


Now... let's talk about the implications of backward time travel. The prospect of going back in time and altering your future so that you in fact don't exist is called the "Grandfather Paradox" (eg you go back and kill your grandfather before he could conceive your mother/father, but then you don't exist, so how do you go back, etc). There are a number of ways of resolving this paradox. One is, as you mention, using the Many Universes of quantum theory. In this case there is a universe for every possible choice, including one in which you travel back in time to kill your grandfather.

I find the most satisfying explanation is one of causality paradox protection. Suppose you decide to travel back in time to kill your grandfather. The notion is actually absurd, becuase your grandfather has clearly survived to produce your parent. In fact from your perspective, you've already travelled back in time. So what happened? The universe conspires to protect causality paradoxes: something obviously happened to you on your trip back in time which prevented you from killing your grandfather, and no matter how often you go back you won't be able to actually do it *because it didn't happen*. Some physicists suggest that the paradox censorship is actually that time travel can't happen - no time travel, no paradox. My view is that this is only a weak correlation, clearly it is possible for backwards time travel to happen without the paradoxes so the time travel can't be a priori ruled out for this reason.


Hope this helps!
The Chicken

Answer 4

Time Travel is only possible to go forward in time (just in theory only) Einstein said if you traveled to a block hole sat near it for some time and came back everyone on earth would be much older than you ( time is relative).

Answer 5

One way is somehow go faster than thte speed of light, but that only works fo the time traveler forward not backward. Another way is to get close to a black hole, again that would only be time travel forward

Answer 6

Time travel might be possible if we can travel fast enough. In Einstein's theory of relativity it basically states that if we travel really fast then time will slow down, so if we travel fast enough then we might be able to make time go backwards.

Answer 7

Time travel i think is not possible..n is not need...just make sure u giv ur best today so tomorrow u don['t wanna go back to yesterday

Answer 8

there's a like code or formula if u craked u open like a blackhlole that will take u somewhere.maybe the past,future or to the unknow!!

Answer 9

time travel is possible because of the rips in the space time continuum

Answer 10

If there were EVER time travle we would have seen people from the future by now.