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The Science and Physics of Back To the Future 436

Posted by ScuttleMonkey
from the how-many-giga-which? dept.
overthinkingit writes "A scientist has tried to apply serious math and physics, including the Law of Cosines, to analyze how the DeLorean in Back to the Future travels through both Time AND Space: 'in order to pull off the kind of time travel we see in the Back To The Future trilogy — the kind where the traveler is transposed in time, but remains stationary in the same relative position to where he/she left — the DeLorean would have to be an outstanding space ship, in addition to its already laudable work as a time-ship. According to Doc Brown's stopwatch, Einstein the dog travels precisely one minute into the future on this first jump, arriving, relative to their frame of reference, at the same location he left. But how far has this reference frame itself traveled during that one minute?'"
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The Science and Physics of Back To the Future

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  • by oodaloop (1229816) on Monday January 19, 2009 @04:29PM (#26519729)
    how it leaves tracks of fire on asphalt? Or in the air? Never quite understood that part. The rest of the movie, OTOH, makes perfect sense.
  • by Diss Champ (934796) on Monday January 19, 2009 @04:29PM (#26519731)

    The universe really DOES revolve around the earth in the movie universe, so no special measures are necessary beyond "simply" moving in time.

  • by Yvan256 (722131) on Monday January 19, 2009 @04:30PM (#26519735) Homepage Journal

    Since it was in space for 0.0000E+999 seconds, i.e. never.

    It did travel in time and moved from one point to another in the universe (to stay in the same spot on earth) but it didn't "travel in space", hence no need to be a spaceship.

    • by mog007 (677810)

      The earth moves around the sun, which moves around the galactic center, which is moving away from all the other galaxies in the universe.

      • Re: (Score:2, Interesting)

        by Yvan256 (722131)

        Read my post again.

        • by Yvan256 (722131)

          Sure, someone can't bother to actually READ what I wrote and suddenly I'm a troll.

          What part of "It did travel in time and moved from one point to another in the universe (to stay in the same spot on earth)" don't you people understand?

          • Re: (Score:3, Insightful)

            by Bozzio (183974)

            Here, let me help.

            ``It did travel in time and moved from one point to another in the universe (to stay in the same spot on earth ) but it didn't "travel in space", hence no need to be a space ship.''

            He's being pedantic, folks.

            • Re: (Score:3, Funny)

              by sootman (158191)

              A pedant? On Slashdot? How did he make it through the rigorous screening process and obtain an account?

      • by Talderas (1212466) on Monday January 19, 2009 @05:26PM (#26520515)

        Whenever life gets you down, Mrs. Brown,
        And things seem hard or tough,
        And people are stupid, obnoxious or daft,
        And you feel that you've had quite eno-o-o-o-o-ough...

        Just remember that you're standing on a planet that's evolving
        And revolving at nine hundred miles an hour,
        That's orbiting at nineteen miles a second, so it's reckoned,
        A sun that is the source of all our power.
        The sun and you and me and all the stars that we can see
        Are moving at a million miles a day
        In an outer spiral arm, at forty thousand miles an hour,
        Of the galaxy we call the "Milky Way".

        Our galaxy itself contains a hundred billion stars.
        It's a hundred thousand light years side to side.
        It bulges in the middle, sixteen thousand light years thick,
        But out by us, it's just three thousand light years wide.
        We're thirty thousand light years from galactic central point.
        We go 'round every two hundred million years,
        And our galaxy is only one of millions of billions
        In this amazing and expanding universe.

        The universe itself keeps on expanding and expanding
        In all of the directions it can whizz
        As fast as it can go, at the speed of light, you know,
        Twelve million miles a minute, and that's the fastest speed there is.
        So remember, when you're feeling very small and insecure,
        How amazingly unlikely is your birth,
        And pray that there's intelligent life somewhere up in space,
        'Cause there's bugger all down here on Earth.

    • Re: (Score:3, Interesting)

      But it HAS to travel in space. See, space and time are as intertwined a green and grass. Let's skip the over-the-top explanation and illustrate where this mistake is comprehensible. While, in your frame of reference, you are not moving, in the grand scheme of things you are. The earth is rotating and revolving around the sun. The solar system is likely gyrating around something else. This very galaxy is moving as a whole. So many movements going on that no one even thinks of.

      So, think about it... if you mo
      • by shaitand (626655) on Monday January 19, 2009 @04:52PM (#26520043) Journal

        'So, think about it... if you moved through time, forward one minute, and somehow skipped any spatial movement, the earth is going to be AT LEAST 1000 miles away from the point, relative to JUST its movement around the sun. That says nothing about how our solar system is moving through the galaxy or the galaxy moving in the universe.'

        I think you misunderstood his point. Yes being at the same location on earth requires a spacial movement. But in back to the future that movement is instantaneous just as your movement through time is. You never actually occupy the space in between and are never in outer space. There is no reason the delorian must be pressurized or carry oxygen tanks, exercise equipment, etc like a 'space ship'.

      • by EllisDees (268037) on Monday January 19, 2009 @04:56PM (#26520095)

        I think the problem is that there is no universal frame of reference that you are moving through. Sure, the Earth is spinning, the galaxy is rotating, etc. - but without some force acting on whatever is moving through time, it would follow the exact same trajectory as the surface of the planet.

        • by Cederic (9623) on Monday January 19, 2009 @05:12PM (#26520309) Journal

          So when travelling back in time, the car moves forward to where the Earth would be as far into the future as the car went in the past - while the earth in the past hasn't reached where it was in the present yet.

          To go back in time inertia is insufficient.

          • Re: (Score:3, Interesting)

            by harry666t (1062422)
            I think GP means that all movement is relative. Sure, you've got Earth revolving around the sun, sun around the center of the galaxy, center of the galaxy around something bigger, etc. But hey, does the whole universe have a (0,0,0) point which we can effectively measure? What if we're contained in a bigger universe, and our universe is moving exactly so that Earth is always at the (0,0,0)?

            I guess I've gotta take some shrooms and check it out by myself.
          • Re: (Score:3, Interesting)

            by LihTox (754597)

            If conservation of energy still applies in some fashion, then the car wouldn't immediately disappear at one point in time and reappear in the other: it would have to travel along a worldline (that is, it would travel through all intermediate points in time). As it travels, it is reasonably to suppose that it is susceptible to outside forces-- for example, gravity; therefore, the car would stay on Earth for the same reason you stay on Earth. However, if the car can be affected by outside forces, then the c

      • Re: (Score:3, Interesting)

        by snowraver1 (1052510)
        Let me take a shot Yvan. The car does travel trough space, but not through the void of space. The car departs from a mall parking lot, then arrives at the same mall parking lot one minute later. Sure, earth has moved 1000km or so in that time, but you are not thinking fouth dimentionally. The car (and the dog) never experianced that minute, so to the dog in the car, nothing abnormal would have appeared to happen. The car never "Travelled" through space. It was in one location and time, then another.
      • You're assuming that the Delorian is moving through our 4 dimensional universe to get from point A to Point F. What if there was a worm hole/time tunnel/extra dimension that allowed you to go directly from point A to point F with out going through points B ->E? No need for space travel at fantastic speeds.
        • by Yvan256 (722131)

          Please don't add Star Trek DS9 or Stargate theories into the mix, some people already can't understand what I meant in my first post. ;)

    • Re: (Score:3, Insightful)

      by Ephemeriis (315124)

      Since it was in space for 0.0000E+999 seconds, i.e. never.

      It did travel in time and moved from one point to another in the universe (to stay in the same spot on earth) but it didn't "travel in space", hence no need to be a spaceship.

      Seems to me that you're misunderstanding the terminology.

      Nobody is claiming that the DeLorean needs to be able to survive the vacuum of space. Nobody is claiming that it is capable of leaving the Earth's atmosphere.

      The article is referring to the two seperate aspects of spacetime - space, and time. Space as in the distance between two locations. The inches between my keyboard and monitor...the feet between my desk and the door...the miles between my office and my house. That kind of space. Not the inte

      • by Ioldanach (88584) on Monday January 19, 2009 @05:51PM (#26520865)

        If you were to simply remove yourself from the flow of time for a moment, the rest of the universe would keep chugging along. It would leave you behind. The Earth would spin away from you, as well as orbit away from you. When you re-entered the flow of time you'd be in a different place than where you started from.

        That depends a bit on how you remove yourself from the flow of time. First, there's how you stay in one place, and that's only half the problem.

        If you cause all atoms, down to the smallest level, within the envelope of your craft to be trapped in a void that stops experiencing the timestream and doesn't appear to the outside world, but the void itself is still acted upon by the forces of the outside world, then the void should remain in place until the occupants exit at the designated "arrival" time. The downside to this is that the void should be easily detectable, since you're not jumping through space, you're simply pausing your experience of existence until you want to be un-paused.

        Or, as with the latter, the void can be locked to the reference point without actually being interacted with, this would have the same result without being detectable.

        Then again, maybe the craft would be detectable, but only if you knew to look for it and happened to look in just the right spot while it was sitting there, just out of visible space, perhaps creating a gravity and energy signature as if it were dark matter.

        The third method would be to calculate the exact position of the craft based on the earth moving through space at a perfectly predictable rate and somehow teleport (portal, wormhole, stargate, whatever) from your starting point and time to your end point and time. Obviously, if this were the method employed, interplanetary travel would instantly become trivial as a side effect of time travel. (Pern, anyone?)

        I think the middle method is what's implied in the movies, but I'm not sure how you'd get the void to follow the reference frame without being detectable.

        The second half is traveling backward through time as well as forward. With the third method, above, this is part of the same operation, the teleportation method's destination coordinates simply include a time component. (Ok, "simply" is a stretch, but...) For the first two methods, creating a forward moving void is, well, "relatively" trivial compared to causing the void to experience the timestream backwards, and still be locked in the backwards-moving reference.

  • The obvious question is "relative to what"? Once you are moving in time, relativity is out the window. So, I assume, would be any frame of reference in XYZ space. Once you pull of magic in terms of the time position, magic in space positions seems easy. Maybe the whole trick is to change the reference frame, and time travel comes along with the teleportation for free.
    • Exactly. It's quite simple when you reference the original reference point is merely just another reference point in a sea of infinite reference points, which are rendered irrelevant when you remove the 4th dimensional constraint. When moving through time, the only frame of reference neccessary is a clock - which further supports my theory that flavor flav was a time traveler: (proof) [].
    • The obvious question is "relative to what"?

      We are all moving through space relative to the center of the Milky Way Galaxy, but we don't need to be space ships because, relative to the surface of the Earth, we're not moving and and that's the frame of reference we're most interested in. In the Back to the Future movies, the DeLorian moved in time, but stayed close enough to its original position (relative to the Earth) that there wasn't ever a problem. The only time there'd be trouble would be if shiftin

  • by frovingslosh (582462) on Monday January 19, 2009 @04:32PM (#26519761)
    This explains the problem that I have trying to use a stasis field in place of a refrigerator. Every time that I shut down the field the food comes flying out of it real fast! (but fresh)
  • Boiling It Down (Score:4, Interesting)

    by eldavojohn (898314) * < minus bsd> on Monday January 19, 2009 @04:33PM (#26519773) Journal
    First off, there are WAY too many pages to this article for me to read but it looks fun so maybe later.

    But in regards to this, I would like a physicist to boil large problems down to "We can't do X because of the simple problem of Y." Example with Mr. Fusion: We can't do Mr. Fusion because the amount of energy that goes into creating the conditions for fusion outweigh the amount of energy produced. That's something measurable and approachable to me, a starting point.

    If it comes down to the problem requiring a Free Lunch, I'd probably give up early--I'm not one to disobey the laws of thermodynamics.

    In middle school I devoted large amounts of time and reams of paper to developing a formula f(n) to produce the nth prime number (at the time I was searching for O(1) oh how naive I was about mathematical induction!) and it was all because a teacher explained how powerful such a formula would be for encryption and many other things.

    While I (obviously) never solved it, I sure the hell enjoyed the simplified form of a much more complex problem. And on top of that, it kind of set the tone for computer science in my life. Could hoverboards & time machines turn a movie goer into a physicist? Maybe not often but it happens [].
    • by Zironic (1112127)

      When I last read up about fusion it the problem wasn't that it takes too much energy to start the reaction(it does take quite a lot and all current fusion reactors are energy negative and although they're currently building the first energy positive fusion reactor right now in France) but rather the problem is that if you try to make a reaction large enough to produce more energy then you put in it has a tendency to melt the container.

      So basically it has become a material sciences problem where they have to

      • Re: (Score:3, Interesting)

        (IAAPhysicist) The heat load on part of the wall is around 10 MW per square meter. Only the Ariane V rocket has higher power loads, but only for a few seconds. ITER, the one they are building in france, will have a plasma for about half an hour. Yes, it's a materials issue. It's also (still) a problem of plasma stabilities. Control of ELM's is also important. These are sudden outbursts of plasma towards the wall, depositing massive amounts of gas and energy on the wall. At the moment, JET the largest reac
    • Re:Boiling It Down (Score:5, Interesting)

      by thedonger (1317951) on Monday January 19, 2009 @05:19PM (#26520413)

      I spent some time in high school looking for a common form of a 2-digit multiplication trick and wound up deriving the quadratic formula. No one was impressed. So much for public school...

      But back on topic, I think Homer Simpson's time traveling toaster is accurate with regards to the time portion: anything you do while in the past creates an alternate time stream only into which you may move forward. The problem the Simpson's didn't deal with is that if you exist in that new future, you will be a duplicate if you are able to travel forward in time to when you are alive. But I don't think forward time travel is possible since there is not/will not be a future.

      Physical position notwithstanding, BTTF - while fun to watch - can't happen. Once you move backward through time you are screwed.

  • by awitod (453754) on Monday January 19, 2009 @04:34PM (#26519791)

    What you fail to grasp is that the 7th dimension works like quantum sticky tape to hold you in place relative to the things around you as you travel through time. So, you don't really need a space ship because of the relativistic affects of the items around you relative to each other pulling you along. Plus there's the whole inertia thing which requires you to go 88 miles an hour exactly so you always wind up where you started whether you go forward or backward. Try it yourself by drawing two 8's. On is for space space and the other one is for time space.

    Also, don't forget that the velocity has to be in miles per hour, because the metric system is gay.


  • browser that can handle the math...... seems he need to calculate in the slashdot effect...

    • Re: (Score:3, Funny)

      by BobSixtyFour (967533)

      Wrong, as you can CLEARLY see, his server doesn't have the 1.21 Jigawatts necessary to jump OVER the slashdot effect and into your browser.

  • wear your space suit (Score:5, Interesting)

    by v1 (525388) on Monday January 19, 2009 @04:40PM (#26519873) Homepage Journal

    anyone that has (in the past) managed to create a time travel device and has tried it, probably thought they made a disintegration machine, because anything they sent back or forward in time was never seen again. (or before, I suppose)

    Because a second/minute/year/millenia ago that spot was occupied by empty space. The earth is moving very fast through space.

    I've always used that reason to concede that even if we DO make time travel possible, it will be of little practical value.

    Then there's the other snag of transposition... if you say, send yourself back in time, what happens to that volume of space where you arrive? Is it destroyed? And what fills in the void where you left? Or one more expected result is it's transposed with your time's space. Thus all time travel is time swapping, something goes forward and something goes back. Now lets say you do make a time travel machine, and test it without considering the earth-travels-through-space issue... that means whatever you send out, you get a big ball of vacuum back. If it's a very brief travel, you may get a chunk of earth, high pressure ocean, or more likely, high pressure magma. Ouch... hope you got insurance. That'll turn your lab into a disaster area real quick.

    There are so man "problems" with time travel, that it really doesn't matter if its possible or not. It's not useful.

    • by cowscows (103644)

      Couldn't you minimize a lot of these problems by testing your device out in space? Find a location that's mostly empty, and that you would expect to be equally empty at your target time.

      Of course, this assumes some decent space travel technology, but I'd hope by the time humanity has figured out time travel that they've also managed to make spaceflight reasonably accessible.

    • This leads to the series of time machines that provide their own frames of reference, where an object can only travel within the duration for which the machine is "turned on". See the movie "Primer" for an example.

      Of course, this makes me wonder, if a person gets into such a machine at 2PM to travel back to 10AM, what would another person see inside if they entered at 1PM to leave at 11AM? Is the device empty? Do they meet the other traveler? What if the other traveler is themselves?

    • by gardyloo (512791) on Monday January 19, 2009 @05:14PM (#26520339)

      Because a second/minute/year/millenia ago that spot was occupied by empty space. The earth is moving very fast through space.

      You're assuming some immutable aether to give an absolute reference. Why assume that the place the object might appear later in time is some position stationary with respect to Sol, but not to the galaxy? Or the parent supercluster? Or some other object? We've abolished the Machian idea of an absolute reference frame by now.

  • by Sebastopol (189276) on Monday January 19, 2009 @04:41PM (#26519887) Homepage

    as serious math?

    Did a communications major write this?

  • erm, (Score:5, Interesting)

    by Speare (84249) on Monday January 19, 2009 @04:42PM (#26519913) Homepage Journal

    Reference frames don't travel with respect to themselves. By definition.

    However, you could say that we're that much closer/farther from Vega, or in a different season in our Solar orbit, or in a different timezone, etc. Or the Earth's core has counterspun in relation to its own crust. Or tectonic shifts have occurred.

    Just assume the car is locked onto a specific reference frame, such as a given latitude/longitude relative to the Earth's axis of rotation and the nearest large mass: the Earth's crust under the car. And pass the popcorn, it's a movie for chri'sakes.

    • by ShakaUVM (157947)

      >>Reference frames don't travel with respect to themselves. By definition.

      Right. I'm glad someone else noticed that.

      Relativity tells us that there's no absolute velocity. So while we say that the Earth is traveling very fast through space, if we set, say, London as our reference frame, there's no motion at all.

  • by gobbo (567674)

    Time travel stories very very rarely accommodate the notion that an object made independent of the earth's-sol's-milkyway's current position in time/space might fail to match the movements (future or prior) of these systems, and not return to the same spot on earth, never mind even staying in the solar system.

    That always bugs me. Isn't it an obvious problem? Wouldn't your 'magical' explanation of a 'magical' tech need some explanation of it?

    • Re: (Score:3, Insightful)

      by thedonger (1317951)
      Distilling down time travel for the masses requires some dumbification of the minutia. Did you see "Primer"? Excellent, but required a flow chart. That's why the BTTF series was more popular.
    • Before we discovered Relativity it was a problem, but Einstein had made it abundantly clear that it is NOT a problem.

      However, Einstein also showed that gravity is an accelerating reference frame, which might be a problem since then shit is actually moving.

    • Not necessarily. If you can travel through the fourth dimension "instantaneously", there's no real reason you couldn't travel through the first three. Lock the earth as your frame of reference and stay where you are relative to it.

  • by omnilynx (961400) on Monday January 19, 2009 @04:45PM (#26519959)

    But how far has this reference frame itself traveled during that one minute?'

    Relative to what? Relative to itself, it hasn't traveled at all. And since we don't know the mechanism for time travel, there's no reason to use any other reference frame. Really, until we understand how they are supposed to travel through time we can't discuss the interactions of reference frames across time skips.

  • Don't they realize that "it's fiction"?

    They might as well play around with radioactive spiders. Whose turn is it to be bitten today?

    • Well, we CAN play around with radioactive spiders, that's not new.

      Probably would lose more experimental subjects that way, though. I am guessing that the life expectancy of radioactive-spider-bite testers is fairly low. :)

  • Maybe at the moment the DeLorean actually travels through time, it simply moves relative to whatever it's resting on, namely the Earth (or a patch of air) just like Wells' Time Machine is shown as doing in the 1960 film of the same name. Of course, you'd need a little extra handwavium to explain how it also temporarily becomes invisible to an external observer, something to do with causality perhaps...

    Meh! Physicists! It *always* has to be ohhh sooo complex!
  • It's simple - large masses such as the earth curve Spacetime. When the Delorean transits time, its path is bent by this natural curvature of spacetime. This serves to keep the time machine firmly rooted in position as related to that of the Earth, regardless of where (or when) it is at either the departure or destination times. This would also mean that time travel between points not on or in orbit around a large mass would be impossible. So that bootleg script for Back to the Future Part IV: The Search fo
  • Aether Drag (Score:4, Funny)

    by argent (18001) <peter@slashdot.2 ... com minus physic> on Monday January 19, 2009 @04:46PM (#26519977) Homepage Journal

    Since Professor Brown is obviously using Steampunk technology (look at the ending to the final BTTF), it seems clear to me that the solution to this problem is that the Time Machine is carried along in the Earth's "Aether Drag", the distorting effect that any large mass has on the Luminiferous Aether!

  • Couldn't you just tie a tether to the DeLorean, anchor it to the ground, and then make the time jump?
    You arrive at your temporal destination, and the tether would keep you bound to the Earth's surface. It would only have to be long enough for the 88mph ramp up speed.

    However, this means 1 second time jump would result in being physically yanked several kilometers in a split second. Barring astronomical whiplash, this should keep you relatively stationary to the Earth.

    Maybe Timecop did have the better
  • Just remember that you're standing on a planet that's evolving
    And revolving at nine thousand miles an hour.
    It's orbiting at nineteen miles a second, so it's reckoned,
    The sun that is the source of all our power.
    Now the sun, and you and me, and all the stars that we can see,
    Are moving at a million miles a day,
    In the outer spiral arm, at fourteen thousand miles an hour,
    Of a galaxy we call the Milky Way.

    Our galaxy itself contains a hundred million stars;
    It's a hundred thousand light-years side to side;

  • When the DeLorean becomes unstuck from time, it does not actually also become unstuck from space. Since it does not experience time, that means it can't interact with physical objects, but the interactions before and after must be consistent. For example if the DeLorean didn't "move" at all, so the earth moved away from it, that would mean a massive change in its potential energy without any change in time, which requires infinite energy. Thus the point in space where the DeLorean becomes unstuck serves

  • We're talking about time travel, so we get to go a little nuts. Much like when landing in a valley, as long as you're close, you'll fall into it. Call it a funnel you like. So as long as you're generally close the Earth's gravity well will suck you into the same spot that you left -- relative to the gravity well. It's one of those pendulum and gyroscoping effects.

      - Q.E.D.

    (In case it isn't obvious, I know nothing. But love the trilogy.)

  • by retchdog (1319261) on Monday January 19, 2009 @04:59PM (#26520135) Journal

    These kinds of considerations aren't anything new, and injecting them into soft sci-fi like Back to the Future is a waste of time. BttF is enjoyable, though, and does make a great accidental (?) satire of the American dream and hubris. For science, read some Larry Niven or Stanislaw Lem instead.

    For example, Vernor Vinge did something like this, involving teleportation. A teleporter could control both the outcome position and velocity, but velocity was "harder" and took effort proportional to the difference in velocity.

    Therefore, long distance teleports were only feasible along a longitude, and to the opposite latitude, since you had to match momentum or die by either being crushed or flung off into space. The earth's spin matches at lat X long Y, and lat -X long Y, but nowhere else.

    As a result, one of the world's superpowers controlled both semi-polar regions, alternating by season; while the other stuck to the equator.

  • Not just time and space, but you have to arrive with the right velocity, orientation, and spin. If you landed in the future in a DeLorean spinning at 380 rpm on its top and traveling at 483 mph with respect to the local terrain, you might not survive to make your next movie.
  • The science and physics of superman racing the flash.

    "A scientist has tried to apply serious math and physics, including the Law of Cosines, to analyze who would win in a race between superman and the flash"

    In other news, said scientists' funders have threatened to pull their grants citing too much idle time.

  • Now, if this scientist had simply realized that Back to the Future is a fictional movie, he could have saved a lot of time.
  • - Like the unfortunate Federation officers that get stuck in 'phase' after a transporter accident. And all they can successfully interact with is the deck. They go through ceilings, walls, equipment, even Mr. Spock, but not the deck. And of course, they are fortunate to still be able to breath the air, despite not being able to actually move any of it sufficiently to wave at fellow crewmembers and cause them wonderment at the drafts...

    - Or the ghosts that also can walk about on Earth, but sadly cannot he

  • by damburger (981828) on Monday January 19, 2009 @05:27PM (#26520523)

    There is no absolute frame of reference in space or in time. By taking into account the motion of the Earth around the Sun and around its axis, he is arbitrarily picking implying the heliocentric-ecliptic coordinate system is the absolute frame of reference.

    To be honest though, I can't suggest a better way of doing this. The DeLorean can simply pop out of existence in one spot in spacetime and pop into existence at another. If this ability is a given, I'm not sure its necessary to treat travelling through space separately.

  • by actionbastard (1206160) on Monday January 19, 2009 @05:33PM (#26520621)
    Professor Brown explained that Einstein simply 'skipped' over that minute and arrived in the same place at a different time. The DeLorean -and hence Einstein- still had their combined velocities of the reference plane (place) that it had when it did the 'timeskip'; that's why it was still going eighty-eight MPH when it reappeared one minute later. If the combined velocities of the 'time traveler' or the 'place' do not change during his trip, then he simply arrives in the same 'place' just at a different time. However, if the 'place' from which he leaves encounters a sudden change of velocity at the exact moment of departure, then he could return in a very different 'place' upon arrival.
  • Space? (Score:3, Interesting)

    by mosb1000 (710161) <> on Monday January 19, 2009 @06:06PM (#26521085)
    Sometimes I think our understanding of space is even more shaky than our understanding of time. It should be obvious, for example, that distances can only be measured between two objects. So saying that the time ship would need to travel a considerable distance in order to be in the same place is actually rather silly. The distance traveled in space (if that really is distinct from time) is zero if you measure it in any sensible way.

    Why would you measure it from some fictitious "stationary" point in space? What does the word stationary really mean in this context? Would it be important in any physical sense?

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