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Near light speed space travel

  1. Sep 1, 2011 #1
    note: I will be brief, I previously attempted to post this thread and was logged out while writing a wall of text, I do not have the energy to get it all down again.

    - Is near light speed space travel theoretically viable due to time dilation (traveler covering light years while potentially experiencing very little time passing) As I interpret the physics, a person could travel less than light speed yet experience faster than light speed travel. I assume that this is probably equivelent to a first day dumb question in the average lecture hall, or that I have made a leap based on lack of understanding.

    - Are the obstacles and limitations of achieving near light speed theoretically surmountable (e.i. acceleration stress, energy requirements, method of propulsion) I have watched many a documentary that has raised the subject of space travel and then ignored time dilation in favor of warp engines and leprechauns, I assume there is a good reason for this.

    I suspect it's highly likely that I have misunderstood some key concepts to arrive at this point, but it's the subject of many a daydream and I appreceate any insight even if it's the cold hard reality check I fully anticipate :D
  2. jcsd
  3. Sep 1, 2011 #2


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    yes, traveling to a planet several billion light-years away at a velocity that is arbitrary close to c, you might experience just a few years (or even just hours - depends on how insanely fast are you flying) but the planet you wanted to visit may be long gone out of existence by the time you get there.. - so not practical at all.
  4. Sep 1, 2011 #3
    Suck it up soldier...

    There are no dumb questions only dumb answers.

    Yes and no...

    I expect so but keep asking questions.
  5. Sep 1, 2011 #4


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    Hi there!
    The phrase 'travel at less than light speed yet experience faster than light speed travel' is quite confusing, and I think it confounds the basic issue. If we shoot a rocket off at 0.99c relative to us towards a planet one light year away, according to us the rocket will take ~1yr to get there. However, according to those on board the rocket, only a few months will have passed by their own personal clocks. This is how time dilation comes into relativistic space travel. Saying that those on board the spaceship 'experienced FTL' is incorrect and worse, confusing.

    Yes, the obstacles are surmountable, although extremely difficult to solve when we try to create the kind of sci-fi scenarios we are all exposed to. The reason time dilation is never (or almost never) mentioned when space travel appears in TV or whatnot is because it is a damn pain and completely shatters the Star Trek idea of some unified galactic federation. Planets 100 light years apart must wait at least 100 years for a space ship to arrive, so communication takes place on a timescale of approximately two hundred years! Even though those on board might have only experienced a few hours (in the most extreme case), they will arrive to a much different world than they were expecting. Some authors do illustrate this concept, a good popular example being Ender's Game.

    To circumvent the time dilation problem, often times people deal with warp drives or wormholes, which do not experience time dilation but are generally grounded in much more speculative physics. That is, we know for sure that there is nothing impossible about sending a ship to alpha centauri at relativistic speeds (in principle), but whether or not creating a wormhole/warpdrive is possible is still an open question.
  6. Sep 1, 2011 #5

    Thanks. Yeah that is it.
  7. Sep 1, 2011 #6
    Thanks for the swift responses! This has been a bit of a thorn in my brain ever since I watched a docu by Michiio Kaku about space travel and was left slightly dissapointed (even moreso than the one about lightsabers) I see the point that it is a tough pill to swallow versus 'neater' concepts like warp drives and wormholes and I had considered that this might be the case.

    With regards to 'experiencing FTLS', I should say that the specific wording here is the result of my lack of understanding of how moving at close to light speed effects how one percieves light. I vaguely recall something about vision narrowing and blue shift, but I assume whatever does happen prevents you from 'seeing' planets and stars simply zip past at FTL from time dilation. I guess if one percieved space via... spidey sense... or something, they could percieve travel relative to objects in space that would seem to them to break the speed barrier? (My brazen insertion of the Marvel universe into relativity is just a way to sidestep Einstein's laws and explain the reason behind my misuse of terms :p)
  8. Sep 1, 2011 #7
    The two approaches to long space flights have quite different problems. The time dilation method has, as others have said, has the problem of communications and things being maybe millions of years different by the time you get there. Also there is the practical problems of shielding the ship from the incoming radiation from running into all that diffuse but ever present intergalactic material.

    The wormhole/warp thing has tremendous problems with causality.
  9. Sep 1, 2011 #8


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    Well, while the ship is coasting along at a constant speed, those on board will observe time to be passing much more slowly outside the ship. This is the essential feature in the 'twin paradox' you might wish to look up. Only when the ship accelerates/decelerates does time behave funny.

    As another general note, while wormholes quite obviously admit causality issues, warp drives in general do not.
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