Forgot your password?
typodupeerror
Space Science

Excursions at the Speed of Light 360

Posted by Zonk
from the nice-bike dept.
D4C5CE writes "S/F fans can finally find out what you really get to see at relativistic velocity, and tourists are one step closer to "doing Europe in a day" in these amazing Space Time Travel simulations of the Theoretical Astrophysics & Computational Physics department at the Institute for Astronomy and Astrophysics Tübingen. They put you in a driver's seat that both Armstrong the Astronaut and Armstrong the Cyclist would equally enjoy, in simulators built to ride a bike at the speed of light."
This discussion has been archived. No new comments can be posted.

Excursions at the Speed of Light

Comments Filter:
  • by MrByte420 (554317) * on Sunday May 15, 2005 @08:58PM (#12539270) Journal
    I'm presently ingrossed in Brian Greene's new book called "The Fabric of the Cosmos" and does a wonderful job at creating lively understandable analogies while sticking to alot of interesting science. He covers the history and philospophy of how problems involving realtivity, time, and space have evolved - stronly reccomend it...
  • G forces (Score:2, Interesting)

    by Turn-X Alphonse (789240) on Sunday May 15, 2005 @08:58PM (#12539271) Journal
    What about the G forces at the speed of light? Does it just rip peoples skin off?
  • Beyond cool! (Score:1, Interesting)

    by Anonymous Coward on Sunday May 15, 2005 @09:01PM (#12539284)
    it has always been difficult to me to understand modern physics since they generally aren't so full of 'seeable' stuff like classical physics. this is a dream come true for a computer guy who wants to know more about the rules of the world around him.
  • Re:G forces (Score:1, Interesting)

    by PoopJuggler (688445) on Sunday May 15, 2005 @09:11PM (#12539338)
    "G-force" is caused by your resistance to acceleration. I would assume that by the time we can travel at the speed of light, we would have solved the whole g-force problem as well..
  • Not that new.. (Score:1, Interesting)

    by Anonymous Coward on Sunday May 15, 2005 @09:18PM (#12539381)
    The idea, while cool, is not that new (although doing it interactively might be). There's always the Relativistic Raytracer [anu.edu.au] (more movies [anu.edu.au]), which has been available since 1997.
  • videos (Score:5, Interesting)

    by commodoresloat (172735) on Sunday May 15, 2005 @09:19PM (#12539385)
    All this does is attempt to simulate the visual distortion that one would perceive when traveling that fast. The videos look like you could be going 100 mph or whatever in terms of speed, but the distortion of the buildings seems to be what they're trying to get across here. The idea that you could have a long enough street lined with similar enough buildings to even perceive this distortion is beyond fantastical, so there doesn't seem to be a whole lot of point to this other than illustrating the notion that there is visual distortion. But I imagine what you would actually see would be much more of a blur.
  • Length contraction? (Score:2, Interesting)

    by Futonchild (875487) on Sunday May 15, 2005 @09:26PM (#12539407)
    I always understood that distances lying on lines parallel to your path (e.g. the length of a passing storefront) got shorter as you approached c. In the video it looks like the storefronts remain a constant length, or maybe even expand, as the speed increases. Am I missing something?
  • Apples and oranges (Score:1, Interesting)

    by Anonymous Coward on Sunday May 15, 2005 @09:38PM (#12539455)
    G Force is a quality of excelloration not speed. If you could excellorate at half a G you'd eventually achieve the speed of light and feel very little excelloration. There are real problems like the mass and the fact even tiny objects can strike with the force of an atomic blast. Achieving light speed is a kind of sucker bet. As you near the speed of light the energy required to continue to excellorate increases. No source of energy known can overcome it's own mass to reach the speed of light. There was a proposal to build an enitre ship out of bags of hydrogen ice so the mass would be reduced as you excellorated and there'd be little wasted mass. Even then I think it was unlikely to hit better than half the speed of light. Antimatter is a good option but still couldn't overcome the mass energy issue. In normal space it's unlikely that speed of light will ever be achieved let alone passed.
  • by tylersoze (789256) on Sunday May 15, 2005 @09:40PM (#12539461)
    They're simulating the *visual* effect which is much different than just the Lorentz transformation because of the differing light travel times from various parts of the object to your eyes. For example, a body actually appears *rotated* instead of just Lorentz contracted.
  • by Anonymous Coward on Sunday May 15, 2005 @09:41PM (#12539462)
    I assume you have also read Steven Hawkings, A Brief History of Time, if so, how does it compare? I only ask as that book is the only one I've read in that field and I found it very interesting. I'm looking for similar.
  • by mnmn (145599) on Sunday May 15, 2005 @09:53PM (#12539505) Homepage
    Sure.

    See light travels at the speed of light. You cant travel faster, or even AT the speed of light.

    But if youre zipping by an object that emits light, and its light doesnt travel in the same direction as you, its speed component in that direction is also slower than the speed of light, and you can catch up and see the object after you're past it.

    Lets try that again.

    Imagine youre on a bike, zipping past a lamppost. The light the lamppost emits travels in all directions. Now take the photos that are emitted in the same direction youre going, at the same time that youre just crossing the lamppost... now youre travelling parallel to that photon, although it beats you in speed.

    However, if the lamppost was say 10m away from you when you zipped past, the photon you'd see is the photon the lamp emits not in the same direction youre travelling, but slightly towards you. If youre travelling north, the photon is travelling northwest, towards you. After youve crossed the lamppost, some distance later, the photon reaches you, because it had to travel a bigger distance, going in your travel direction (north) as well as towards you (west), and we all know the hypotenuse is longer than the base or height.If you travelled faster than the photon's north speed component, you'll see greater than 180 degrees around you... but never 360.
  • No blueshift (Score:5, Interesting)

    by Vilim (615798) <(ryan) (at) (jabberwock.ca)> on Sunday May 15, 2005 @09:53PM (#12539506) Homepage

    They are missing the blueshift you would encounter at that speed. However I guess they couldn't be accurate because wouldn't the frequency would shift to far above the ultraviolet quite quickly?

  • by Asterixian (806481) on Sunday May 15, 2005 @10:17PM (#12539601)
    At forward viewing angles, yes, the images would be blue-shifted, but this doesn't mean everything goes dark. Visible becomes UV, and infrared becomes visible. But this is angle-dependent. Light arriving from behind you is actually red-shifted.

    And yes, pushing several hundred watts per square meter of visible light into the UV range would result in a terrible sunburn.
  • by MAdMaxOr (834679) on Sunday May 15, 2005 @10:25PM (#12539634)
    But the point is that while you are going the speed of light, while time appears normal to you, you will have traveled an infinite distance in that first instant of time in your reference frame.

    Which leads to the observation that you could never stop going the speed of light, because when you decide to hit the brakes X seconds later, you would have traveled an infinite distance. Where would you end up? (Never mind the problem of having to dissipate infinite energy)
  • by 2*2*53*4127 (874924) on Sunday May 15, 2005 @10:37PM (#12539682) Journal
    I can't speak for any of Brian Greene's work- never read it- but if you enjoyed Hawking you NEED to read Sagan's Cosmos.

    Bringing us back on topic, it was a PBS television series as well, and included one show with light speed visualizations at the same (or better) quality than linked to in the article.

    And that was 25 years ago.
  • Re:How long? (Score:3, Interesting)

    by OverflowingBitBucket (464177) on Sunday May 15, 2005 @10:48PM (#12539736) Homepage Journal
    You make some interesting points, but I should point out a couple of things.

    If you are a human, eventually the things in front of you will be blueshifted out of the visible spectrum, and the back will be redshifted, so everything will go 'dark' (light non visible).

    The direction of the shift will depend which way you are facing. Also, bear in mind that although the human-visible spectrum will be shifted out of the human-visible range, depending on your direction, one side of the human-invisible spectrum will be shifted in. So it may not go dark at all, it could even get brighter, depending on how bright the human-invisible component is.

    There will never be a 'boom'

    Regarding the boom, bear in mind that we really haven't gotten anywhere near lightspeed, so we don't know. At one time it was theorised that it was quite impossible to break the sound barrier. It is not only possible but quite likely that our understanding of what happens near lightspeed is inaccurate. What I've said is just my hunch, no doubt what you said, yours as well.
  • by Anonymous Coward on Sunday May 15, 2005 @11:04PM (#12539809)
    OK, I am going to pick nits. At the speed of light, there isn't much point to turning to see the sights. Due to length contraction, everything except directly in front of or behind you is now visible at a 90 degree angle to your path.

    And, due to time dilation, you don't have the ability to decide to turn in your reference frame. Your entire trip at the speed of light must be zero duration in your reference frame to be of finite duration to outside observers.

    Of course, if they simulated those two effects, the bike ride wouldn't be very interesting.
  • Re:G forces (Score:3, Interesting)

    by StikyPad (445176) on Sunday May 15, 2005 @11:43PM (#12539969) Homepage
    They changed C to 30km/h in order to see the relativistic effects without that annoying windburn.
  • Re:G forces (Score:1, Interesting)

    by Anonymous Coward on Monday May 16, 2005 @12:11AM (#12540077)
    We're talking about the speed of light, presumably in space. Not in the atmosphere, not in water, not in Aunt Ester's Fameous Jello Salad, or for that matter in anything else, because even light dosen't travel at the speed of light in *ANY* of those things. Light only travels at the speed of light in a vacuum!

    Next you'll say "in which case, you'll run out of oxygen in about 30 seconds, what with the riding of bicycles in outerspace and all" and then you will deserve to be kicked very hard in the balls.

  • Re:How long? (Score:1, Interesting)

    by Anonymous Coward on Monday May 16, 2005 @12:48AM (#12540193)
    You're right. The rate at which you receive photons goes up as gamma, and the power received goes up as gamma^2 (since the photon energy goes up as gamma too). This is apparent dimensionally: rate of photon reception has units of 1/time, and time gets contracted by time -> time/gamma, so photon reception rate transforms like 1/(time/gamma) = gamma * 1/time, so is multiplied by gamma. Power has units of energy/time, which transforms (gamma energy)/(time/gamma) = gamma^2 energy/time.
  • by Anonymous Coward on Monday May 16, 2005 @01:05AM (#12540307)
    Close. Everywhere collapses into a point around them, such that the distance travelled is none. So, every time you turn on a light, you are causing distortions in the fabric of space/time. And you thought you're dad was just trying to save a couple cents on the electric bill by harping on you to turn the lights off when you weren't using them.
  • by fear025 (763732) on Monday May 16, 2005 @01:20AM (#12540402)
    For people really wanting to see how it would look to travel at the speed of light, you could always try the open source 3d space simulator Celestia [shatters.net].

    I find that watching planets whiz by as you travel at the speed of light is pretty entertaining. I've had some fun just trying to steer with a joystick at this speed.

    Of course, I suppose if you really were going this speed (or even 99.9% of it), you'd see some wierd spectral shifting (or that circular blur effect as in the article's animation), which is not shown by celestia.
  • Re:What? (Score:4, Interesting)

    by Gopal.V (532678) on Monday May 16, 2005 @01:39AM (#12540493) Homepage Journal
    Slow Light [bbc.co.uk] is around 1.6 Kms per hour
  • by loraksus (171574) on Monday May 16, 2005 @01:47AM (#12540530) Homepage
    If you liked the first few chapters of BHOT (the historical stuff, I think the book was re-arranged, so I don't know where he put it), check out "A Short history of nearly everything" by Bill Bryson.
    Very good. As the title suggests, more on more things, developments in chemistry, biology, geology, physics, et al and Bryson keeps it very interesting. Don't bother with the abridged audiobook though (the unabridged is read by the author and is basicallly word for word)
  • by Anonymous Coward on Monday May 16, 2005 @02:08AM (#12540615)
    I have issues with Einstein's theories. While I agree they match what we see, I don't agree that's what's actually happening.

    It'd be like me saying that radios work because they have little people in them singing and playing instruments. They watch the knob from the inside and have a clock to tell what to play. That would explain the behavior, but it raises other problems. Now you might say "well we can open a radio and see what's in it". Gee thanks Cpt Obvious. Now make that radio the size of a quark and maybe you'll get what I mean. We can't look in it (at least yet), so all we have are theories. Give me a million more years of science and your theory will look sillier than my take on radios.
  • Re:No blueshift (Score:2, Interesting)

    by roseblood (631824) on Monday May 16, 2005 @03:21AM (#12540891)
    Well, that might not be true. Travel at close to C, and look in the direction you came from. No blue shift. Big time RED shift. It's all a matter of perspective.
  • by Anonymous Coward on Monday May 16, 2005 @11:05AM (#12543605)
    Einstein believed until the day he died that the entire universe must be predictable down to its smallest scale, however deep that may lie. He couldn't accept that quantum physics was inherently random, and thought that it was just a matter of making precise enough observations of quantum systems to be able to predict them with certainty.

    So, you have a photon. It has no mass, so it always travels at c in a vacuum. Since it travels at c, in its frame of reference the universe has no duration and no length. It is emitted from one atom and absorbed by another instantaneously, from its perspective. Also, the rest of the universe exists outside the photon's light cone (which incidentally, has a zero radius and zero length), so the rest of the universe is therefore completely irrelevant to the photon. Remember also that every frame of reference is perfectly valid.

    This means that for every photon that ever has been or will be emitted by one atom and absorbed by another, there is a relativistic frame of reference in which those two atoms are tangent. That means, for example, that if you turn your naked eye on the light from a star 100 light-years away, photons emitted from that distant sun 100 years ago are striking your retina, and for those photons the entire universe is a single point that bridges the star and your eye instantaneously. It must have therefore been "known" 100 years ago when the photon came into being that it would strike your eye, and therefore by extension the entire universe must be completely deterministic.

    My head hurts thinking about it.
  • by Anonymous Coward on Monday May 16, 2005 @03:37PM (#12546496)
    It does if you use conventional math and logic.

    Don't be absurd. Massless photons themselves are a prediction of a fundamentally non-deterministic theory, quantum electrodynamics. Bell's theorem continues to hold in relativistic form.

    If you're in a relativistic frame which consists of only the single point where a photon emitter and a photon absorber are tangent, then that's that.

    There's no such frame. The emitter and adsorber are at distinct points in the spacetime manifold; however, the distance between them imposed by the additional structure of the spacetime metric is zero. In pseudo-Riemannian geometry, unlike Euclidean geometry, two points with zero distance between them don't have to be the same point.

    The universe between source and destination is not a single point, it's an entire 1-dimensional curve of distinct points all of which are separated by no distance.

    However, even if you were right and there were no points between source and destination, that still wouldn't imply that relativistic quantum mechanics is deterministic. In fact, you can have zero-dimensional non-deterministic quantum theories (consider the quantum theory of a single Ising spin, for instance, or the IKKT matrix model of M-theory).

    When it is emitted and therefore has its own frame of reference, the source and destination of the photon are explicitly defined.

    They are no more explicitly defined than the source and destination of a massive particle.

    Besides which, it's not terribly meaningful to speak of "the frame" of an observer which is not timelike, nor "what that observer sees"; it's not timelike, and you can't associate a clock with it, any more than you can with a spacelike "observer".

    The only difference between the photon's frame and the frames of the emitting and absorbing atoms is how much time passed between the events and what the distance between them was.

    The same is true of a non-null frame of a massive body, too.

    There can't be any doubt as to which atom the photon will eventually strike.

    The photon doesn't have to strike any atom. Just like any other particle in quantum theory, there is a probability amplitude associated with any path of the photon. The trajectory of a real particle is not predetermined, massless or not. Just look at the path integral for the QED Lagrangian!

    Therefore, whether the distance is one micrometer or a billion light-years, the eventual destination of a photon at the time it is created is a known quantity.

    This conclusion does not follow from your premise. It's not logically connected to any known facts about photons. It has nothing to do with the quantum theory of photons.

    But by all means, publish your theory. The Nobel Prize awaits you for proving that relativistic quantum mechanics is deterministic.

    While I'm at it, I may as well correct another of your errors:

    the rest of the universe exists outside the photon's light cone (which incidentally, has a zero radius and zero length), so the rest of the universe is therefore completely irrelevant to the photon

    A light cone is associated with an event, not a worldline. The light cone of a photon at a particular point on its worldline is no different from the light cone of a massive particle at the same event. I have no idea what you mean when you claim that "the rest of the universe is therefore completely irrelevant to the photon", but if that follows from some property of the light cone, it has to apply to massive particles as well.
  • by gbpuckett (572575) on Monday May 16, 2005 @05:01PM (#12547532)
    The way various posts have dealt with time dilation and the Doppler effect as separate issues in relativistic theory shows how people have gotten comfortable with Einstein's theories, rather than do what Einstein did and keep pushing at the gaps in the theories that were current in his day.

    In doing some reading on Einstein's General Theory, I ran across the idea that Einstein's theory of how time dilates in the presence of an intense gravitational field could be proven by a red-shift in light affected by that gravitational field, the light functioning as a "clock" that would shift its spectrum in direct relationship with the gravitational time distortion.

    Fine, I thought. Light does make a pretty reliable and observable clock. So, what does that mean for the Special Theory? Well, for objects moving away from each other, no problem. At relativistic velocities, there would be a red shift, which would fit with Einstein's theory of time dilation. However, since the Special Theory suggests dilation as the only relativistic time distortion caused by high velocity, any blue shift experienced by converging objects is really problematic. Blue-shifted light would indicate a contraction of time, something that the Special Theory doesn't consider at all. But maybe we should.

    Do a few thought problems, and it becomes clear that, at least with regard to velocity, time dilation is but one side of a two-sided Doppler coin.

    The Special Theory is great, but maybe not the last word, even in dealing with just velocity effects. It doesn't pay much attention to vectors. It hints at but doesn't really address the possibility that, when two objects have a relationship of extreme velocity, what is most distorted by relativistic effects is not either object's length, mass, or passage through time, but each object's ability to use light to "observe" the other, particularly with regard to its location and velocity.

    After one hundred years of digesting the Special Theory, we really ought to be doing more than creating more dazzling illustrations of it. It needs correcting and refining, too.

  • by Anonymous Coward on Monday May 16, 2005 @05:24PM (#12547797)
    However, since the Special Theory suggests dilation as the only relativistic time distortion caused by high velocity, any blue shift experienced by converging objects is really problematic. Blue-shifted light would indicate a contraction of time, something that the Special Theory doesn't consider at all. But maybe we should.

    What nonsense. Doppler blueshifting is accounted for in special relativity, and does not imply time contraction. The two effects in SR that influence the observation of light are time dilation and the finite propagation speed of light; blueshift arises from the combination of the two. The time dilation part is separated out using Einstein's synchronized rod/clock procedure.

    The Special Theory is great, but maybe not the last word, even in dealing with just velocity effects. It doesn't pay much attention to vectors.

    You are ignorant beyond belief. SR is wholly a theory of spacetime vectors. Read Spacetime Physics by Taylor and Wheeler and Flat and Curved Space-Times by Ellis and Williams for a discussion of 4-vectors.

    It hints at but doesn't really address the possibility that, when two objects have a relationship of extreme velocity, what is most distorted by relativistic effects is not either object's length, mass, or passage through time, but each object's ability to use light to "observe" the other, particularly with regard to its location and velocity.

    SR doesn't ignore that! The graphics linked to by this very Slashdot article take into account not just the time dilation and length contraction, but the optical distortions due to the propagation of light. See, for instance, Penrose-Terrell rotation and Moebius transformations.

    After one hundred years of digesting the Special Theory, we really ought to be doing more than creating more dazzling illustrations of it. It needs correcting and refining, too.

    The special theory was corrected by the general theory, which in turn is in the process of being corrected by quantum gravity. "Corrections" based on your vast miscomphrension of relativity don't count.

Premature optimization is the root of all evil. -- D.E. Knuth

Working...