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Time Travel for Beginners

Posted by JAZZ SHAW, Assistant Editor in Science & Technology.
Dec 18th, 2008 | Comments

ParallelUniverse.jpgWith the holiday season in full swing, I’m sure that you – like most of us – find your thoughts turning to… time travel. While not practical at this time, explorations of the furthest limits of general relativity and quantum physics bring us to the nearly inescapable conclusion that travel through time is almost certainly possible if we could just manage to get one of those pesky wormholes under control.

“Aha!” I hear you say. “That’s all well and good for you and your fancy pants quantum theory, but you still haven’t explained away the grandfather paradox, have you? So time travel is still rubbish.”

A common objection, and one you should be proud of. But actually, we have worked that one out and today I shall relieve the anxiety of the world and explain it once and for all. The answer is to be found in the parallel universe construction of the multiverse. The theory of parallel universes was first developed by Hugh Everett back in the fifties. There are a potentially infinite number of universes lined up side by side, sometimes bumping into each other, similar in many general ways but unique in the fine details. The concept of “side by side” may trip us up, because they are not separated by some measurable amount of space… they are separated by time.

You see, time and space are wrapped up together too tightly to separate, but they are still useful concepts for this discussion. Whether space is composed of ten or eleven dimensions (depending upon which string theoretician you ask) instead of the normal three, time is sort of locked in place in each universe. And in each one, the “starting point” of time is slightly staggered from the one preceding and the one following. Were we to use a wormhole to travel through time, we would arrive not only in a different time, but in a different, parallel universe of space as well. In fact, through the very act of traveling through the wormhole you would likely spawn an entirely new set of parallel universes, which we can more usefully think of as “timelines.” And this is why the grandfather paradox doesn’t really come into play.

To put it more simply, think of it this way: in order to test the grandfather paradox let’s say you hop through your trusty wormhole and travel back to 1938. You locate your grandfather and shove him down a set of stairs. Now you travel back through the wormhole to 2008 to see if you have disappeared. You have not. Why?

Because in our timeline, you never appeared in 1938 to do anything. Nothing has changed in this universe. If, however, you chose to hang around in the parallel universe where you eliminated your grandpa for eighty years or so, you could see what the world might be like without you. In a similar case, let’s imagine that you decided to travel twenty years into the future and give your future self a rare coin which would then be worth a vastly increased amount of money to ensure your comfortable retirement. If you returned “home” and waited twenty years, a younger you would completely fail to show up to bestow the treasure on you. That’s because the gift was presented in an alternate timeline which is locked into a future reference. In our universe you weren’t there.

There you have it. Time travel is not only possible, but the grandfather paradox is no longer in play. Merry Christmas and enjoy your time traveling.

  • AustinRoth
    The problem with time travel is not the paradox issue. It is, at least for the wormhole solution, the energy requirements to create and maintain one beyond the quantum level, along with the need to harness negative energy and ghost radiation.

    I grew up reading and dreaming of interstellar space flight, time-travel, ect., (still do, in fact), but unfortunately through my studies of physics have come to realize without some new fundamentally different understanding of physics that replaces all current theories, they will always be just dreams.

    I do believe that we have hit the point that the patchwork required to keep the Standard Model working, even as well as it does work, is a clear sign that it is but another set of theories that explain what we can observe now, but there is another, completely different explination underlying physics yet to come.

    A great example of that is Newton's Law of Gravity, which is now known to not be correct at all, but rather is a good enough approximation until you get to very large-scale interstellar calculations. We still use almost all of the time, because it gives answers well within any required margin of error, but fundamentally it is not correct.
  • mikkel
    The alternate dimension theory was always interesting but it creates a far bigger paradox: black holes. The entire concept rests on the idea that gravity is a force that works across dimensions, but if there were all these other dimensions at different points in time then the different sized black holes would leak into the other dimensions and nothing would really be able to exist.

    It's more likely our concept of time and space is wrong.
  • You know what you know until it doesn't work anymore and then you know something else. I think that should be one of the fundamental rules taught about the scientific method.
  • mikkel
    Incidentally, I actually saw Stephen Hawking in person a couple years ago and this is primarily what he talked about. Well only briefly about time travel and more about "branes." They think the other universes are only about 1-2 mm away which is pretty awesome. I actually think there is quite a bit of "evidence" and unanswered questions that make more sense with other universes close by and sometimes I wish I was born like 1000 years later when we might actually know.
  • AustinRoth
    jazz -

    I agree. Even as a student, I was struck on how many times in history all of physics (my field of study) was completely overturned. Yet each generation of physicists, and scientists as a whole, acts as if current knowledge and theories are fundamentally correct, and only need refinement.

    That leads to the current state of affairs, where more and more exotic theories and explanations are required to maintain the current hierarchy.

    Don't even get me started on dark matter and dark energy. That to me is a perfect example of making 'fixes' to theories to fit data that otherwise contradict the current theories . It is like reading about the history of Luminiferous Aether (the Ether).
  • Austin, I should go back and dig up the links to some of our radio shows earlier this year when Cindy and I were lining up an interview with Dr. Neil deGrasse Tyson. I was raging about so called "dark matter" for a solid week after that. Through the history of astrophysics, while trying to figure out how gravity works on vast scales, we came up with theory after theory about how the stars and planets moved. As we became able to make greater and greater observations, the theories fell apart one by one and had to be replaced with new theories and models to explain what we were seeing next. Until now. We see that the stars on the outside rim of the galaxy are moving FAR faster than we predicted they should (if they behaved like our planets do here) but for the first time, instead of going back and fixing the theory to account for the new observations, we apparently decided to FIX THE GALAXY to FIT THE THEORY. So we invented Dark Matter that nobody can find. Drives me insane I tell you.
  • mikkel
    "but for the first time, instead of going back and fixing the theory to account for the new observations, we apparently decided to FIX THE GALAXY to FIT THE THEORY."

    I disagree with that characterization. In fact I think it is the basic M.O. of science to do that. It's not necessarily all bad either.

    I mean look at special relativity. Nearly all of that (I'd say 95%) arose because Lorentz and Poincare attempted to merge Maxwell's electromagnetism laws with observations that the particles displayed amounts of force that didn't make sense based on Newtonian mechanics. So they came up with a transform that was just a fix and then Einstein came along and (without giving credit) simply took the same ideas and hypothesized that maybe it wasn't unique to photons and electrons and was about matter in general. Thus, special relativity!

    However a lot of the behaviors they were trying to explain can be pretty well explained with quantum mechanics. If quantum mechanics as the new theory was developed before special relativity, it's highly possible that they would have just said "well electrons and photons obey quantum mechanics principles and so that explain the discrepancy with Newtonian mechanics.." and they'd be right but that would have made it so the Lorentz transforms wouldn't have been necessary. Well until we expanded our theories about the Universe and developed better technology...but who knows how we would have described things differently.

    I think that science in general is very pro-mechanism rather than contra-observation. By that I mean you can point out flaws in the current model and even eventually convince scientists that they are real, but until you have an alternative mechanism that has positive prediction capabilities that the current model doesn't, then people will just work on refining the existing one. I'm certainly finding this in my own work.
  • AustinRoth
    "but until you have an alternative mechanism that has positive prediction capabilities that the current model doesn't, then people will just work on refining the existing one."

    Absolutely, and there are times that those efforts lead to the new theories. My comment was just a general one about at least admitting the current theories cannot be correct. And to be fair, there is a growing sense of that (lead to string theory among others, but that is another mess of its own), but eventually (and maybe it has already been proposed but is currently not accepted).

    I also agree science cannot stop just because known theories are suspected or even known to be wrong, in the absence of a replacement, as you said. New and valid information still gets generated.
  • Jim_Satterfield
    There is no dark energy, just doppler shifted gravity.
  • So that means that I won't be delivering that Illudium Q-36 Explosive Space Modulator to myself next week?

    Bummer.
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