Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

FTL: Does time even matter?

  1. Dec 16, 2004 #1
    So, if I'm thinking of this correctly....

    The faster we travel, the slower time progresses for those traveling.
    We go faster, time for us slows down.

    Just for ease of example, let's say the travelers are traveling exactly at c.

    They travel toward a star that is 10LY away - so at c, those who are still at the launch site should expect the travelers to get there in 10 years.

    But how long does it seem to take for the travelers themselves - since time has slowed down for them?

    :bugeye: :bugeye: :bugeye:
  2. jcsd
  3. Dec 16, 2004 #2


    User Avatar

    Staff: Mentor

    It would pretty much seem instantaneous. But you'd have to be careful - you might pick a main sequence star to fly to and and instant later it would go supernova on you!
  4. Dec 16, 2004 #3
    Instantaneous? Does that mean that time seems to stop completely for the travelers when they travel at light speed? So traveling >c would reverse time... means I could throw away those beauty cream product? :rolleyes:

    What about the computers onboard - would they experience the time differential; would the computer clocks slow down as well?
    Last edited: Dec 16, 2004
  5. Dec 17, 2004 #4
    I don't get the instantaneous thing.
    From what I understand of Relativity each would have it's own relative time frame based on the factors of velocity and relation to gravity fields. Thinking about it I guess the velocity at the speed of light could compress the time experience, human and machine alike, to something near instantaneous but I'd imagine the crew would have to somehow be shielded from the actual experience of that velocity in which case the time experience would be based on whatever means you used to buffer the crew and machines from the velocity experience.
    And now my brain hurts lol.
    I think that the the time experience of the crew and machines once outside of the gravitational field becomes more a factor of velocity. The differential between the launch and landing sites is probably more a factor of gravity.
  6. Dec 17, 2004 #5


    User Avatar

    Staff: Mentor

    Remember guys, we're talking hypothetical here. In reality you can't reach C. If you went very, very close to C, your time would slow relative to an outside observer so much that you could get anywhere in the universe almost instantaneously. Due to length contraction, the universe would look slightly larger than a single point to you.

    And remember, this is time itself we're talking - a computer clock and you will experience the same thing: everything would appear normal to you inside your ship, but look out the window and you'll see the entire universe zip by.
  7. Dec 17, 2004 #6
    Hypothetical as all hell ;-)

    With respect I'm not sure you guys really quite have a feeling for the implications of what Russ is explaining to you when he says this is all hypothetical 'cause nothing could move at the speed of light (at least nothing with mass). Since I didn't either maybe I can help.
    Imagine something REALLY tiny and insignificant, like just a single solitary nose hair. You can just blow on something that light and it'll fly off a table top right? In other words it's easy to move at everyday speeds 'cause it doesn't weigh much. A single breath can move it.
    Now I'm making these numbers up (Russ could probably provide real numbers), but these fake ones accurately show in general HOW this works.
    O.k. As things move faster they get heavier (more accurately more massive or difficult to move but you get the idea).
    So now at rest that nose hair weighs practically nothing and a single breath can move it.
    But as its speed increases its mass starts to go up LIKE CRAZY.
    At a half light speed, that same nose hair now weighs as much, and is as difficult to push, as a railroad car.
    (so forget about it moving when you blow on it, you're now going to need something with several THOUSAND horse power to push it any faster)
    At three quarters light speed it weighs as much and is as difficult to push as an entire planet.
    (At this point there isn't an engine in existence, and none I know of even on the drawing boards, big enough to move it any faster)
    At seven eighths light speed it weighs as much and is as difficult to push as an entire GALAXY.
    At fifteen sixteenths the speed of light that very same tiny nose hair weighs as much and is as difficult to push as OUR ENTIRE FRIGGING UNIVERSE!
    And at thirty one thirty seconds light speed it now weighs as much and would be as difficult to push as a gazillion trillion million universes!
    At this point you STILL haven't reached the speed of light yet, you're just close, and even if you could come up with some fantasy "matter/antimatter warp drive engine" powerful enough to push "a gazillion trillion million universes" what in the living HELL would you use to run that engine? ALL the energy in our ENTIRE universe, wouldn't even be the slightest fraction of the amount of energy you'd need to so much as start that puppy let alone get it to idle for a minute or two.
    And you have to keep in mind that what we're talking about here is what it would take just to push a tiny little nose hair up to light speed, so try to imagine what it would take to move an entire human being, let alone some kind of ship full of people and equipment up to those impossibe to attain speeds.
    So this isn't like "breaking the sound barrier" in that maybe, someday in the future, somebody could come up with an engine powerful enough to drive a "starship" up to the speed of light, because it's not a case of not being sophisticated enough technologically to do it, it's a case of something that literally CAN NOT BE DONE, not now, not a thousand years from now, or a million. What the physics is telling you is that the whole idea of trying to build a "starship" with "matter/anti-matter engines", or whatever, powerful enough to push it to light speed (let alone faster), is simply a dead end approach no matter how much time you spend on it, so if you want to get to other stars in less than a single lifetime, you're going to have to come up with some other way of doing it other than pushing a ship with any kind of powerful star drive engine.

    So when Russ says this is all "hypothetical" he means way waaaaay beyond practical, and well into the zone of talking about the aerodynamic load requirements of a pixie's wings in a discussion about how to use pixies to air lift cement trucks into the jungles of the Congo.

    When you ask "what happens when you travel at the speed of light", you're actually asking a nonsensical question about "what happens to something when it gets bigger than infinitely big?". There's no such thing as "BIGGER than infinitely big". The question doesn't really make sense. So when you try to calculate what happens the answers don't make any more sense than the question does, which is why you get answers like...
    Time stops from your perspective.
    You become thinner than having no thickness at all in the direction of travel.
    And your mass approaches infinity.

    Zat help at all?
    Last edited: Dec 17, 2004
  8. Dec 17, 2004 #7

    If we eventually find a way to tunnel through the light barrier, what will we find?

    Will the effective inertial mass decrease with increasing velocity?

    Will time speed up again with increasing velocity?

  9. Dec 17, 2004 #8
    Again, with respect...

    ... I think you're missing the point juju.

    The whole point is that there really is no such thing as "tunneling through the light barrier".
    There's no kind of "barrier" to have to "tunnel through". When you talk about "barriers" it implies that there's something you can figure out how to break down or blast your way through. But there is no "barrier" to overcome. At least not in any kind of physical sense.

    I'm not trying to make fun of you, or make you look dumb, *I* sure didn't understand this whole idea at first either.
    Maybe if you try to explain to us what you picture in your head as the "light barrier" that you're trying to "tunnel through" one of us can help.
  10. Dec 18, 2004 #9
    Re: instantaneous

    It is eminantly possible to travel at light speed after all light does it and it has mass :wink: if you instantaneously achieve light speed, I.e with no real intervening time period, you can achieve it's speed, will we ever do so? yes?? It's only a matter of time :rolleyes:
  11. Dec 20, 2004 #10

    Everyone's comments have been very helpful and thanks!

    But, we are connecting the FTL 'barrier' to Einstein's theories, yes?

    I see the only real reason we're not already going FTL is because of one man, one human... theory. Just because a few things have been ' proven' mathematically doesn't mean it's 100% correct, nor does it mean that Einstein's theories are now Law.

    I had someone somewhere tell me that just because my theories could be explained with math equasions, didn't mean they were correct - I use that same quote here. There has got to be another way around this, and I think if we stop limiting out thinking to E=mc^2, we'll see another picture.
  12. Dec 20, 2004 #11
    Hi Artic Fox,

    I agree. Just because a theory (even one well-documented) says that we can't do something, that doesn't mean we can't.

    I think that a startrek-like warp field is possible and may be realized sooner than anyone believes.

    I would also like to say that it appears weird to me that anyone would want to be stuck forever in the confines of limiting theories. The only real adventure in science is the possibility of the unknown.

    As my favorite quote from AE says "Imagination is more important than knowledge."

    Last edited: Dec 20, 2004
  13. Dec 20, 2004 #12
    What if space and time could change, so that if you went near a certain object, you might get larger or smaller, or experience a faster or slower rate of time? If saw someone going near this object, you would see them move slower and slower, and maybe get smaller and smaller, until you couldn't watch them any more. You could come back after fifty years, and still see them, a tiny microscopic point, moving very very slowly.

    But then if you went near that object yourself, you would not feel like you were slowing down at all, in fact you would not feel any different at all from the way you "normally" feel. Then, if you had a change of heart and turned back again, you would see the world you left speeding up and moving very very fast, until, by the time you returned entirely, hundreds of years might have passed. You would have been away for maybe a year, but when you get back again, hundreds of years have gone by.

    Then what if you did not turn back at all, but just kept on going toward the object? Maybe the whole universe we know would get old and die, but you would still be going forward. Maybe new universes would form.

    It is true, I think, that we cannot push an eyelash that hard. No onboard engine will ever probably fly a ship to near light speed. But, maybe we don't have to push. Maybe there are places in space where we could just fall all the way to light speed, as if falling toward some huge but immensely far away object. Maybe it would be like falling off a waterfall in a barrel. The barrel doesn't need an engine to push it faster and faster, it just falls.

    And then, what if you had an engine like that proposed by the scientist Freeman Dyson. True, your mass would be greater, but so would the mass that you use for fuel. You would not notice that your fuel wasn't giving you the same push as before. Nothing would seem to change for you, except your view of the world you left behind. That would recede into a point, very very hot and very very fast, and you could not go back there again. If you went back to the "same" place, you would arrive there at a very different time from the one you knew when you left. There is really nothing in physics stopping us from exploring the universe. The only problem, aside from the technical ones of life in deep spacetime, is that once you decided to go, you could never return. The price of immortality is eternal exhile.

  14. Dec 22, 2004 #13
    I quite well understand that it's hypothetical and that there is a great problem of reaching that speed which is why I brought up the need to shield the passengers and ship from the effects of the velocity. When Arctic asked the question I wasn't realising that (s)he was refering to the speed of light with "c" but just assumed "c" meant a constant speed undefined.
  15. Dec 24, 2004 #14
    Good thinking people, outside the envelope,just say yes we can travel faster than light and then go out and proove it 'swhat makes a good doctor of philosophy :smile: Thinking outside the envelope, after all if your travelling at the speed of light and some one observes u from outsside holding a lantern how fast is the light travelling :smile: anyone got any ideas about the twins paradox?

    We can travel faster than light scientists have observed sub atomic particles that appear to move back wards in time to anhialate themselves or did I dream it? :confused:

    The answers in the post :tongue:
  16. Dec 29, 2004 #15


    User Avatar
    Homework Helper

    I don't understand something. Let's say we have some sort of advanced fusion engine on board the spacecraft.

    At a speed of 0.999c relative to the Earth, the spacecraft would appear to have the mass of a "gazillion" Universes or whatever. But the nuclear fuel woud go up in mass by the same factor and the extractable energy would still be related by E = mc^2.

    From the rest frame of the ship, the remaining nuclear fuel would only have its rest mass, but the ship would be at rest mass too. As far as the ship itself is concerned, there is no great difficulty in accelerating itself further to 0.9999c, for example.

    Is my logic totally off ?

  17. Jan 8, 2005 #16
    what about light going in a curved or spiraling path? Would not that be faster than a straight line? Therei is no matter in the universe, only energy. Light=Energy.
  18. Jan 9, 2005 #17
    The same thing happens at the event horizon of a black hole. The far away observer never sees the local observer pass through the event horizon, while the local observer passes easily through the event horizon.

    In your example, the ship could possibly accelerate as long as it's fuel lasted even beyond the speed of light, relative to some absolute spacial reference frame. However, the observer at rest would never see the spaceship break the light barrier. However, time dilation due to relative observed velocity, would account for the increased velocity of the spaceship.

  19. Apr 8, 2005 #18
    How long would it seem to be for the travellers? General concensus seems to be that the travellers would experience no passage of time on their ten year journey at the speed of light. This makes sense to me and here's why.

    Imagine if this traveller has a telescope with them on this journey that is powerful enough to view the Earth in detail from 10 light years distance. If they are moving at the speed of light and looking back at Earth as they do so they would see no change. They would be moving along at the same speed as the light that as being reflected from the Earth. They would perceive no movement from the time that they began to move at the speed of light. When they come to a speed relative to that of the Earth then they would move through time at the same speed. It would all seem instantaneous to the traveller who would be able to look back at the smoke on the launch pad, so to speak. However, the light that the traveller is viewing has been travelling for 10 years along with him and back on Earth everyone is ten years in the travellers future. The actions that people take on Earth today, the traveller will see in 10 years time. It makes sense to me that the laws of the universe would balance the experience of the consciousness with that of the senses.

    When we watch a sunset, in reality the sun has already set about seven minutes ago, the time it takes for light from the sun to reach the Earth. When we look at the stars at the edge of our galaxy we are actually seeing those stars as they were billions of years ago. Yet if you were to throw a baseball at the image of a star 10 billion light years away it would eventually strike that star even though its actual location could be on the other side of the galaxy.

    As far as things moving at and beyond the speed of light, most people seem to believe that it is not possible within reality. It is a scientific view we can only make judgements based on what our senses can tell us. If an event cannot be observed and measured then how can we make a rational decision? Anything moving faster or slower than the speed of light in relation to the observer would take on different dimensional properties. How can you measure velocity if there is no time? How can you measure change in scale when both the observer and the object change at the same rate? It doesn't make sense from a mathematical point of view. Despite this I still mantain that the velocity of light is exactly the velocity of the observer, but matter and energy can only exist in the contemporary 3D if their velocities are within +/- the velocity of light in relation to the observer.

    What was the question?
  20. Apr 23, 2005 #19
    The reason why Einstein faced consternation in all of his attempts at deriving at a "Unified Field Theory" is that he omitted the influence (Electromagnetic, Kinetic and otherwise) of the power of the human mind and the forces of one's will against an object....
  21. Apr 23, 2005 #20

    What if you pointed the telescope at your destination.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook