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Science

How to Build a Time Machine 534

Posted by michael
from the mad-scientist dept.
frank249 writes "The September issue of Scientific American has an article discussing the possibility of time travel. They say that it wouldn't be easy, but it might be possible. It could be a while until we can expand worm holes and tow them to a neutron star but didn't someone say that if it is possible it will happen. If it is impossible it will just take a little longer."
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How to Build a Time Machine

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  • by echucker (570962) on Saturday August 24, 2002 @05:03PM (#4134104) Homepage
    I move we call for a slashback in a few hundred years when this might be possible. ;-)
    • Blockquoth the poster:

      I move we call for a slashback in a few hundred years when this might be possible. ;-)

      I move we call for a slashback a few years ago... :)
  • by Duckz (147715) on Saturday August 24, 2002 @05:03PM (#4134106) Homepage
    Wouldn't the best way to speed up things for this be to leave a post-it note stuck in the files saying "when this is finally invented, please travel back to August 24, 2002AD and provide the HOW-TO."
    --
    Todd
    • This guy [ciudad.com.ar] thinks he can do it with a hand full of parts from Radio Shack. [ciudad.com.ar]
  • Hmm (Score:2, Funny)

    by KanSer (558891)
    As long as you pay the toll...

    "Somebody's gotta go back and get a shitload of dimes!"

  • by bravehamster (44836) on Saturday August 24, 2002 @05:12PM (#4134125) Homepage Journal
    Am I the only one who really wants to see what happens if the universe encountered a true paradox? Would the universe cease to exist? If we assume there are other intelligent species out there (which, given the size of the universe, I'm gonna say is almost a definite), then if time travel is possible then most likely some other species has already invented it, created some sort of paradox, and the universe has continued on. So the whole "universe ceases to exist" thing doesn't seem very likely. Too bad. It would be kind of neat if the Ultimate Weapon was a time travel machine that killed the inventors grandmother.

    • Depends. The problem is that no one really has any good math for disjoint geometries (I'm surprised no one's tried with similar logic to Riemann surfaces, but hey) so it's a little hard to say. That being said though, there's no reason whatsoever to believe that a particle cares whether or not the worldline behind it goes to a consistent universe.

      For instance, think of the Back to the Future scenario. OK, so we know immediately that the "your family is disappearing" bit is bull, since that superscribes an additional time on top of time. Marty only had so much "time" to restore "time"... yah... okay. Would it occur instantly? That would kindof imply that your body cares where it came from - that a break in the worldlines of the particles of your body would somehow "propagate forward" - even if it happened instantaneously, this doesn't make sense - it's another situation where you're describing a "time" on top of "time".

      Bottom line: nah. My guess would be that it would be more like a Riemann surface thing: the action which breaks your past worldline would essentially move you to a different quantum universe. This would (of course) break conservation of energy. Then again, you also are talking about some mega-huge-time-travely-thingy, so I don't think things like "local universe/temporal conservation of energy" would really apply if that thing existed.

      I don't buy time travel into the past. It's too easy to disprove: just state "when I figure out how to build a time machine, I'll come back to this moment and teach myself." The fact that it doesn't happen is pretty good empirical proof.
    • Am I the only one who really wants to see what happens if the universe encountered a true paradox?
      Am I the only one who really doesn't want to see what happens if the universe encountered a true paradox? Let's not, and say we did.

      There was a kid in my second-grade class who really wanted to see what would happen if he stuck a pair of scissors into an electrical outlet one day. The next day, our teacher told us he "moved."

      One man said he didn't want to see what happens when you detonate an atomic bomb, and the people who ridiculed him for passing up a historic opportunity at the Trinity test site have long since died of cancer. At the time, they speculated that there was a possibility the bomb could ignite the atmosphere and kill everyone on the planet, but they went ahead with the test anyway.

      It's always worth asking the questions, but it's not always worth the price of "let's see what happens."

    • Unfortunately there is no such thing as a true paradox. A paradox is merely a problem which exists within the confines of our own mental prejudices. Paradoxes are often created out of our own linguistics or malformed theories.
    • Am I the only one who really wants to see what happens if the universe encountered a true paradox?

      Better be careful, I mean you might figure out what the Universe is actually for and why its here - and if anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.

      Mind you, there is another theory which states that this has already happened.

    • Am I the only one who really wants to see what happens if the universe encountered a true paradox? Would the universe cease to exist? If we assume there are other intelligent species out there (which, given the size of the universe, I'm gonna say is almost a definite), then if time travel is possible then most likely some other species has already invented it, created some sort of paradox, and the universe has continued on. So the whole "universe ceases to exist" thing doesn't seem very likely. Too bad. It would be kind of neat if the Ultimate Weapon was a time travel machine that killed the inventors grandmother

      Larry Niven (the SF author) wrote a story about a time machine as an Ultimate Weapon. However, because the use of the time machine would cause a universe-destroying paradox, the universe wouldn't allow it to be finished. Any civilization that tried to build such a time machine would be wiped out by a supernova or some other kind of natural disaster.

      Thus, the way to use the time machine to destroy your enemies was not to build one yourself, but to convince them to try to build one...

      TheFrood

    • ERROR: Time Travel Constraint
      Violation, Paradox 13.

      1. Cancel Travel

      2. Cancel Universe

      3. Fork Universe

      Response: __

  • I thought the reason that clocks ran faster in the attic than the basement was because of gravity's affect on the MECHANISM rather than gravity's affect on time. Likewise could be said about the atomic clocks. The clock is travelling thru quite a bit more space than it would if it were sitting, could subatomic particles affect it's function and accuracy?
  • Old news. (Score:2, Funny)

    by jellomizer (103300)
    This article was posted years ago.... Oh umm. Wait a minute. Never mind. I never saw this article before. Yea thats it. I never this article before. Realy I have never saw this article. Why are you looking at my third eye funny?

  • Simple (Score:5, Informative)

    by KarmaBitch (562896) on Saturday August 24, 2002 @05:19PM (#4134148)
    Quick lesson in physics for those that don't want to read the article...

    Time travel. Possible? Yes. It happens relativly speaking every day.

    When you get onto an airplane you slow down in time. To say this simply. The faster you go, the slower time moves around you. This was confirmed back in the 1970's using atomic clocks. Although this isn't exactly time travel it's called time dilation which is a product of the general theory of relativity.

    A quick little reference for those not familar with Relativity is a set of lecture notes [uoregon.edu] from a basic astronomy class in U of Oregon.

    For a little more in depth reading I'd look into buying The Large Scale Structure of Space-Time [amazon.com] by Stephen W. Hawking. Or for those that are sadistic you can read Quantum Field Theory in Curved Spacetime and Black Hole Thermodynamics [amazon.com]. That is a collection of lectures from the University of Chicago. Although good in a sense of understanding relativity it kinda takes a tagent into the debate about light being a particle or a wave argument.
    • Re:Simple (Score:2, Interesting)

      by ergo98 (9391)
      When you get onto an airplane you slow down in time. To say this simply. The faster you go, the slower time moves around you. This was confirmed back in the 1970's using atomic clocks. Although this isn't exactly time travel it's called time dilation which is a product of the general theory of relativity.

      One thing I've never understood regarding this involves motion, and what is "absolute zero" in regards to motion. Right now, for instance, the Earth is spinning me around at 1,040mph. At the same time, the Earth is spinning around the sun at 67,000 mph. Our solar system is moving away from nearby stars at the speed of 45,000 mph. My point is that our primitive concept of "speed" is based around the premise of an "absolute zero", but as far as I can tell there is absolutely no way for us to know how fast we are currently moving: All measurements of speed are merely relative-> I drive my car at X speed relative to the surface of the Earth, etc. For all we know, as far as I know (and I'm not a physics buff), the known universe is sliding sideways at 100,000miles per second, and we're totally unaware because it's all relative.

      The point of all of this is the correlation between time and speed seems simplified if it quantifies speed as an absolute metric when as far as I can determine there is no such things: There are only relative speeds.

      Blah, I'm blabbering. There is a point in there somewhere.
      • Everything you just said is precisely why the theory of relativity makes sense. Things move "relative" to other things. There is no "absolute zero" motion.

        Motion is absolute only in relation to a specific frame of reference.

    • Time travel. Possible? Yes. It happens relativly speaking every day.

      Nonsense. Time dilation is not time travel. For whatever it's worth, nothing can move in time, forward or backward. The entire spacetime of relativity is frozen from the infinite past to the infinite future. I'll let the smart ones (i.e., the ones who were not irreparably brainwashed) figure that one out. In the meantime, those of you who are really interested in the truth can take a look at this following link for a complete debunking of time travel and other crackpottery from the physics community. Wild eyed Star-Trek fanatics need not bother.

      Voodoo Physics [sbcglobal.net]

    • has anyone considered that maybe the atomic clock measures time based upon it's velocity? The same goes for quartz.

      Just because a clock measures time by how often an electron moves around a neucleus, how fast a crystal spins, or even how fast c12 decays doesn't mean that I experience time in the same fasion. Be sure you aren't trying to measure time with a ruler and call it evidence that they are related:)

      Also someone asked how do we know what absolute zero velocity is. According to relativity, we can measure this with three rays of light from three non-coplaner axis, we can measure the difference of the phase shifts to determine which way we are moving absolutly. That is unless someone here says that light shining out of a front of a car going at 65mph travels at the c+65mph. (I'm not arguing that it does or doesn't, it's not a fact until it's proven.)
  • by Crispin Cowan (20238) <{moc.nawocnipsirc} {ta} {nipsirc}> on Saturday August 24, 2002 @05:27PM (#4134177) Homepage
    If backward time travel is ever possible, then it has "already" happened. Someone has likely aleady travelled back before August 2002 and done something, we just don't know it.

    Of course, this induces the potential for paradox, causing great cosmological and philosophical consternation. I don't know what will happen if/when someone goes backwards through time, but here's some ideas:

    • The universe forks in two when a paradox is induced.
    • The universe forks in two at the instant the traveller enters history (because at a micro-level, paradox is induced as soon as they appear).
    • Paradox induces a cascading feedback loop of self-modifying universes (each inducing a time-traveller who goes back and causes another chage) until the sequence halts with a universe in which time travel is not developed. My bet is that if time-travel is possible, then this is what has happened, because there is no evidence of time travel.
    Forward time travel is of course possible right now, requiring only some patience :-) Accelerated time travel is also possible due to reletavistic effects and (possibly) cryogenics, allowing you to travel forward in time at some rate greater than 1 second per second.

    Crispin
    ----
    Crispin Cowan, Ph.D.
    Chief Scientist, WireX Communications, Inc. [wirex.com]
    Immunix: [immunix.org] Security Hardened Linux Distribution
    Available for purchase [wirex.com]

    • Woah, woah, woah: all three of the statements you just made superscribe another "timeline" on top of time itself - you can't change a 4D universe - it's there, complete, done, finito. You can't "split" a 4D universe.

      What you COULD say, however, is that all of the Universes were already there, and that when a time traveller enters history, or changes history, he moves into a parallel universe - that is, a Universe which is distinct from his original. Something like a Riemann surface shift. Apparently he gains 2 pi. :)

      However, I don't buy this. It doesn't make sense. Take the example of a person going back and convincing himself not to enter the time machine. OK. He does. Now there are TWO of him in that universe, where before there was only one. Where the heck did that mass come from? (the other universe, yes - but when did we sacrifice local conservation of energy/matter - which we have mountains of observational data for - for "global temporal" conservation of energy/matter - for which we have no observational data for?)

      Taken to its logical extreme, a civilization could turn an "open" universe into a "closed" universe by sacrificing some adjacent quantum reality. To me, this is way beyond the boundaries of what could happen.
    • Forward time travel is of course possible right now

      This is sad. Why does the physics community insist on putting out such unmitigated crackpottery? The truth is that nothing can move in time, forward or backward. The entire spacetime of relativity is changeless, from the infinite past to the infinite future. Karl Popper had a name for it: Einstein's block universe. More details can be found at this site:

      Voodoo Physics [sbcglobal.net]

    • Has anyone ever thought that time travel to the past is more like rewinding a tape. Maybe your interaction with the past is nothing more then a mirror image of already enfolded events. The time traveller would be something more like a ghost floating through time and act as an observer. This would solve all paradoxes simply because travelling to the past is possible but changing it is not. This to me seems more plausible then being able to send something to the past and suddenly popping into existence at that time frame.
    • Paradox induces a cascading feedback loop of self-modifying universes (each inducing a time-traveller who goes back and causes another chage) until the sequence halts with a universe in which time travel is not developed.


      Or the Universe halts with a stack overflow...
  • Maybe this is dorky, but isn't the following evidence that time travel is impossible:

    Since no person from the future has ever come back to say hello to us, wouldn't that imply that time travel will never be invented. Or else it will be invented, but our era in history was just too damn boring for people to come back to visit...

    • If someone did come back from the future and made his/her presence known, then it would become common knowledge that time travel is possible and every physicist in existence would commence working it out, which would result in time travel being invented much earlier than it originally was. That might well mean that by the time our time traveller was born, time travel would be old news and he/she would not be interested in it and would therefore not travel back in time and tell us about it.

      ANY interaction with the past would cause a paradox, and each effect on the past grows more significant as time passes, so if you went far enough in the past and took one breath of air, you could conceivably change the future catastrophically.

      Therefore, I think it's safe to say that even if time travel is possible and if we are not able to refrain from taking such huge risks, we should at least be smart enough not to TELL PEOPLE WE'RE FROM THE FUTURE!!! I mean you might just as well murder your mother before you're born.
  • by doubtless (267357) on Saturday August 24, 2002 @05:31PM (#4134199) Homepage
    is first outlined by physicist Kip Thorn and widely accepted by the scientific community as a real possibility. It is a method which utilise the ability of keeping worm holes open and high speed travel IIRC.

    Black Holes and Time Warps: Einstein's Outragous Legacy by Kip Thorn is perhaps one of the best science books I read, though I didn't really read that many of them. :)
  • I've given this some real thought and if it's possible to time travel at all, it would not be as how we see it in the movies. I'm a philosopher at heart and I think these points have been heard in many different forms:

    • If I could travel back in time, then why would we not have seen people doing so already? Wouldn't travelers from OUR future visit us now?
    • If it is at all possible, then it can't be possible to effect the future or the past-- you may only observe.
    • There are very strong arguements that TIME DOES NOT EXIST. Everything is relative to the observer, and many arguments have been made that suggest that Quantum reality is true-- that all possibilities in the universe are played out and live in discrete "strings" of reality. Sometimes, those strings cross, and you get phenomina such as Deja Vu. Take a lok at the following book: The End of Time, by Julian Barbour. Also, anything by Stephen Hawking.
    • The effects and observations we make concerning time travel may be directly influenced by our transendental means of observation. That is, how we perceive reality is completely based on how we observe it. Really take a second to think about that, because it's one of the most profound concepts I've come accross.

    I just don't see it as a reality. I think what will actually happen is something altogether different-- but not a physical human being traveling into the past to hang out with Babe Ruth. Know whut I mean, vern?

    • Sometimes, those strings cross, and you get phenomina such as Deja Vu.

      OK, I'm gonna get anal here, but Deja Vu is simply your brain incorrectly triggering a memory based on a SIMILAR event. Saying that Deja Vu is evidence of some multi-reality thing is just silly.

  • Anyone else see this in the middle of page 3?

    Censored!
  • Fun trick (Score:5, Funny)

    by mother_superius (227373) <kanu00@yahoo.com> on Saturday August 24, 2002 @05:33PM (#4134208) Homepage
    Wear weird clothes (not weird in the everyday weird people sense, but truly out of place). Walk up to someone (inventing an accent is fun) and ask them what year it is. When they say, puzzled, "2002", get a huge smile and dance a future dance away yelling "it worked, it worked!"

    Fun to confuse people with.

    Just as fun: Dress up like a hippie or something else interesting from the past and change everything accordingly to the past.
  • There's another possibility that was not mentioned in the article, namely, the possibility of different quantum realities. Imagine for an instant, that whatever could happen, does in fact actually happen. Through what what called an Einstein-Rosen bridge (remember the TV show Sliders, the concept does have some scientific merit after all), different quantum realities can be bridged. So, if you go back in time and kill one of your parents, you would still exist because you entered a different reality, one amongst an infinite number of them. Paradox solved. QED.
  • The article says that altering the past is "obviously impossible". But isn't travelling back into the past a way of altering the past? Or was my arrival in the past something that happened back then, before I even made the trip back in time...? Or are such paradoxes impossible, maybe because every possible event in any given time in history exists in its own universe, waiting to happen when the right preceding event occurs? If someone changed what we call the past, would we notice it?
  • Much to my surprise, upon reaching the end of the comments on this story about Time Travel, the random /. quote was:

    And tomorrow will be like today, only more so. -- Isaiah 56:12, New Standard Version

    Freaky. What future bastard is playing with my head??

  • My understanding was that the time dilation effect was from a change in the rate of entropy related in some way to the change in mass. If that's so then you could speed up or slow down entropy, and hence the perceived passage of time, but you can't reverse it. I would think travel to the past would need to reverse entropy in some way. Or I could be wrong, physics class was a LONG time ago.
  • 1. Build a time machine.

    2. ?????

    3. Profit.
  • At last! (Score:2, Funny)

    by paiute (550198)
    With one of these gizmos, I'll be first posting every time!
  • I predict the wormhole concept will be achievable. But there will be one hitch: you will only be able to travel through a wormhole in one direction, and the physical distance you emerge from the wormhole entrance will be equal to or greater than the time it takes to travel at the speed of light to that location.

    Thus, you will be able to go back in time, but even if you then raced at the speed of light back home, you wouldn't be able to arrive before you departed.

    So you'd travel back in time sure enough, but never able to affect your own past. Another way to phrase it would be: you can go back in time, but only someone else's history.

    Of course, you could, say, still go back in time and kill someone in another part of the Galaxy. Maybe terrorist possibilities, etc. Gives a whole new meaning to a leader staying close to his people.

    OK, one more speculation. Wormholes will turn out to repel each other, or maybe wormhole exits and entrances that are close to one another create catastrophic feedback loops, making them impossible.

    Otherwise, you could take the W-80 (Milky Way --> Andromeda) from near Sol, then catch the W-95 (Andromeda--> Millky Way) near Kl'Kithus, which , it turns out, dumps you right out at Sol again.

    And that would make your own past accessible and that's Bad (tm). I guess it could also allow you to go farther and farther into the past by traversing the loop multiple times.

    Of course, it's not clear why someone would want to travel to a time before indoor plumbing or computer games.
  • It's called a bed. Every night I close my eyes and in a moment it is six hours later.
  • Matter can neither be created nor destroyed. So, in the sense of time travel, either to the future or to the past, would we not be introducing new matter into a time by bringing it from another time? If matter can't be created, do the laws of physics allow for matter to be transposed across time?

  • I find it interesting that the article suggests towing a wormhole using a "spaceship, presumably of highly advanced technology" to place a created or expanded wormhole in a powerful gravitational field. Maybe I'm just envisioning this wrong, but I don't know if a wormhole is really what I'd consider to be an "object." Rather, as a rift in spacetime, I'd think would be a thing (for lack of a better word) that is defined by both lack of object, and by objects around it, like the hole in a doughnut, and thus the only way to "move" it would be to alter the objects that surround it, like stretching or shrinking areas of the dough to change the location of the hole with respect to locations on the dough . You can't just grab a hole in a doughnut with a pair of pliers and move it around. In the case of wormholes through spacetime, I'd imagine the way to move a wormhole is to warp the space around it with immensely powerful gravitational fields, folding the space around it and causing it to "fall" to its neutron star target. However, this would certainly require a mastery of gravity far beyond what we have presently attained. When the two ends of the wormhole are created/expanded to macroscopic size, they will need to be separated, with one end taken to a neutron star. Building a tow-ship that can warp the space around a wormhole would require far more knowledge about gravity than we presently possess and far more mastery. Despite being perhaps the most obvious of the fundamental forces of physics, it is probably the least well-understood. Gravitions have never been found in particle accelerators, nor Higgs bosons. Gravitational waves have not been conclusively detected. No coherent theory of quantum gravity exists. We will have to be able to manipulate gravity with the ease that we manipulate electromagnetism if an "interstellar tow truck" is to be built. "Highly advanced technology," indeed!

    Using the neutron star itself to attract one but not the other would be very difficult, but possibly workable- especially if Podkletnov's spinning superconductor gravitational shield works (which it doesn't, that I am sure of). However, you certainly can't use a natural source to reunite the ends once you've "twin clocked" the exit end- the exit is sitting near the surface of a neutron star- so you really won't be able to pull it away with anything less than another neutron star or a black hole, perfectly positioned to make use of the three body problem to slingshot the wormhole out of the star system. Conceivable, but highly unlikely.

    You can't just leave the exit there, either. It would continue to accumulate time difference, so each trip would take you farther from your present time, but actually further and further along in time, since you can never actually travel backwards to before the creation of the exit hole, and since it is in fact still moving forward, albeit slowly, in time. Also, you would leave the exit and find yourself right around the surface of a neutron star, which is a somewhat dangerous location. Worse, you would have to travel at a relativistic velocity to escape the neutron star's monstrous gravity, which means your fast clock would run very slow, so the rest of the universe would be aging faster than you. Also, the nearest neutron star is several light-years away, adding to your return-trip travel time. I'm sure it would be a fantastic adventure, but sort of a waste to fly into a wormhole, travel centuries back in time, and rocket away from a neutron star at nearly the speed of light- only to get back home and find that due to relativistic effects and travel time, you are right back where you started, or even farther along!

    I haven't done the math, but I suspect that sort of scenario could be one of several ways the universe is protected from time travel paradoxes- you can go back in time, but due to relativistic time dilation and the effects of gravitational fields, you can never make it back in time to affect events in the past of your light-cone, preventiing you from creating an inconsistent causal loop.
  • Someone could become very, very rich if this were possible. Let's see, travel back to 1997 and tell your past self to invest in Pets.com, Enron, and Worldcom, but tell your past self to get out by 2000.

    I think Larry and Bill must be time travelers
  • A couple of weeks ago I was in a used bookstore, and happened across a copy of Robert Monroe's [monroeinstitute.org] Far Journeys [amazon.com], which spends a few words on the subject of time travel. Mr. Monroe was one of the first people to write about [amazon.com] Out of Body Experiences [spiritweb.org] in western society. To make what could be a very long post much shorter - time travel is real, it can be experienced - you just need to learn how to leave your physical body behind. OOBE's are just another way to hack your wetware [kuro5hin.org]. To quote the K5 story, "... anything is possible, when you have root access to your mind's /dev/."
  • by TrumpetPower! (190615) <ben@trumpetpower.com> on Saturday August 24, 2002 @07:13PM (#4134528) Homepage

    Time travel isn't possible, except for the everyday kind that your wristwatch measures.

    If time travel were possible, somebody (human, alien, whatever) from the future (perhaps billions of years into the future, or maybe just next week) would have traveled into the past already.

    So, let's consider what can happen. Somebody will travel back in time to before the initial discovery in order to beat the ``original'' researcher to the punch. Now, we've got a cascade of ``inventions'' of the time machine racing backwards through time. Life and time-travel technology reach the earliest time after the Big Bang that the two are sustainable and both are prolifically spread throughout the infant universe. Clearly, that hasn't happened.

    Don't think that some sort of morality would prevent this from happening, either. Time travel is an incredibly powerful weapon; consider what a knife to the throat of the infant Hitler would have done to history, and how many people would leap at the chance, consequences be damned. All it would take is one person to do so...at any time in the next many billion years.

    The instant time travel becomes possible, the only possible method for self-preservation is to race to the beginning. After all, how do you know that some far-distant alien race with souls of pure evil won't do the same just out of spite?

    There's a wonderful quote, and I wish I could remember who said it. ``Time is Nature's way of keeping everything from happening all at once.'' The obvious corollary is that, if you can break time, then everything will happen all at once.

    Some people try to get around this in a few different ways. For one, there's the many-universes ilk: each act of time travel creates a whole new universe. In such a case, all of those universes would be on the same headlong rush to take time travel as early as possible. Besides, think of the incredible amount of energy and information needed to duplicate the universe--but I digress.

    Others try to justify it by saying that it requires huge energy sources or otherwise make it hard. To this I say, ``so''? All you're talking about is a hard engineering project that'll take a lot of time. And--guess what? Even if it takes ten thousand years to build and the energy output of several stars, the payoff is worth it. Again, the alternative is to let somebody else do it...and invite certain disaster.

    I take the mere fact that I'm typing this note as all the proof that I need that time travel is pure fantasy.

    Cheers,

    b&

    • Don't think that some sort of morality would prevent this from happening, either. Time travel is an incredibly powerful weapon; consider what a knife to the throat of the infant Hitler would have done to history, and how many people would leap at the chance, consequences be damned. All it would take is one person to do so...at any time in the next many billion years.
      Someone else would have taken his place. Read Poul Anderson's Time Patrol.
    • by Dr. Manhattan (29720) <sorceror171@gmai[ ]om ['l.c' in gap]> on Saturday August 24, 2002 @10:05PM (#4135011) Homepage
      If time travel were possible, somebody... would have traveled into the past already.

      As has been noted, GR time machines can't go back any further than when they were assembled. So you can't goi back any further than the first one.

      ...consider what a knife to the throat of the infant Hitler would have done to history...

      It's impossible to know. History is chaotic. Consider a simple thing, like weather. That's chaotic, with a lambda on the order of a few days. You appear, kill baby Hitler, disappear. A few days later, it's raining instead of sunny.

      All the weather, subsequently, is different. That affects when people make love; even a small difference in position and timing changes which sperm reaches the egg. The next generation consists of completely different individuals from the one in "our" history. Madonna and Nelson Mandela are never born.

      If you can change the past, then you must, and you can't predict how you will change it.

      I cover all this and more in my time travel page [telocity.com].

  • The Scientific American article notes that traveling into the future is possible and in small ways happens every day. It is the traveling into the past that is really hard. Micheal Crichton in his book and soon to be released movie Timeline [netfirms.com] gives a lengthy explanation of how time travel could be accomplished if we had a quantum computer. It involves 'faxing' someone into a past time through the quantum foam. I thought it was an interesting theory but I don't see how you could destroy someone in the present and reconstruct them in the past if there was not some sort of receiver already in the past. When I first read the book I thought the part about the quantum computer also sounded impossible but it was reported here [slashdot.org] that a practical quantum computer using existing silicon fabrication techniques has already been simulated and could be manufactured in the next year or two so who knows - it might be possible sooner then we think.

    BTW the movie Timeline Movie trailer [crichton-official.com] is out and looks pretty good if you like 13th century adventures mixed in with time travel.

  • homer [as he is being sucked into a blackhole]: there's so much i don't know about astrophysics. i really wish i read that book by that wheelchair guy...
  • Leela: Don't you want to go see the 20th century theme park?

    Fry: ah, if I wanted to go back to the year 2000, I could just have myself frozen again.
  • Check out time travel here. [stanford.edu]

    But seriously. The idea's I've seen on time travel aren't really based on going "back" or "forward" in time, but actually inventing a device which would need a 100% identical device to travel too.

    For example (because sometimes I can't be clear enough): A equal pair of machines would be built. One would be sent into space and likely be sent at speeds approaching light speed. Then we could travel to that device (and back) and use that shortcut to save time in travel, and depending on the speed it flys maybe into the past or whatever.

    Please correct me... I never understood this approach.

    But Feynman Diagrams show that theoretically matter travels back and forth through time all the time.

    But also since we are made of "star dust" we've already sort of time traveled. We are made up of particles (or waves for the cry babies) which existed forever, we can look at ourselves and see the big bang.
  • From the article:
    Indeed, Einstein confessed that he was troubled by the thought that his theory might permit travel into the past under some circumstances.

    What, does he think that the universe revolves around his theories?

  • elsewhen (Score:3, Interesting)

    by epine (68316) on Saturday August 24, 2002 @07:57PM (#4134646)

    The best thing about having a working time machine would be pushing all who find this fascinating into it and sending them elsewhen.

    If time proves to be a complex number, while I would find that fascinating I wouldn't tempted in the slightest to project the terms "backward" or "forward" into a polar coordinate system.

    If there's any virtue at all to a discussion about time travel, it's that you can't determine whether mathematics or linguistics is taking the worst beating.
  • On Time Distortion (Score:3, Interesting)

    by Tokerat (150341) on Sunday August 25, 2002 @03:15AM (#4135761) Journal
    OK, I haven't been good at physics since high school, so I woudl jus tliek to know if I am correct in my understanding:

    1. It is (theoretically) impossible to accelerate to the speed of light, because it would require an infinite amount of energy to do so, so the best we can do is approach the speed of light.
    2. The closer you get to the speed of light, the harder it is to accelerate, because of said energy requirement.
    Wouldn't time distortion then simply occur because things simply could not happen as fast? Your aging, your blood flow, the chemicals flowing between your synapses (this altering preception), the rate at which something burns, the rate electricity moves at, etc. all happen slower than they would if the object where traveling at a lesser speed, because the whole process takes more energy, correct?

    If this is true, what happens when an object comes to a complete halt in space, the absolute zero of velocity, if you will. Could that make a black hole or something?

    IADNAP.
  • Time Travel (Score:4, Informative)

    by evilviper (135110) on Sunday August 25, 2002 @06:39AM (#4136047) Journal
    Here, since no one seems to be putting theories forward, here goes.

    I think of time like a flashlight shining on a wall.
    There is only one point shining at any one time. It may be possible to 'see' into the future, or travel there, but not backwards, namely because the Langoliers have eaten it.

    It certainly is possible to travel faster than light, and will not result in time-travel. As time has shown again and again, there are no limits. Sound, Light, Warp 10, etc. So, this should tell you all one thing...

    NEVER speak in infinitives. You will ALWAYS be proven wrong.

Byte your tongue.

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