Faster Than Light Communication/Transportation Not Possible?

  • Thread starter Gold Barz
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  • #26
this is a topic of faster than light travel and no one here is discussing UFO's, the Bible (moses goign to mt. sinai entering a chariot of fire... and coming out with the 10 commandments [ a ufo ] ) or anything like that? what's up? no one here believes in UFO's? there is some type of faster than light travel or teleportation goig on in the universe. Our laws and theories are in their infancy... as are we as humanity... and people are dismissing faster than light travel? btw i saw something earlier that someone posted about sending something out that is faster than light and then having a detonator button and destroying it before it was sent out?! speed of light does not propogate time in any way, that is false, just because you are moving extremely fast does not mean time goes in reverse.
 
  • #27
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dgoodpasture2005 said:
btw i saw something earlier that someone posted about sending something out that is faster than light and then having a detonator button and destroying it before it was sent out?! speed of light does not propogate time in any way, that is false, just because you are moving extremely fast does not mean time goes in reverse.
If you are moving faster than the speed of light in one person's reference frame, then it is easy to construct a reference frame in which you are traveling back in time. The quote came from d'Inverno, a well respected special relativity text book.
 
  • #28
ellipse... if me and you are at my house... and i hypothetically have a craft that can travel at 300 times the speed of light... and i leave... and my destination is 300 light years away... and i travel there, and then back, it will take me two years ... i will not come back or get there before i leave.. speed of light in no way propogates time or dismisses FTL travel. I'm glad that your text book is well respected... but i respect my logic more. Time travel is impossible, and traveling faster than light is not going to make it possible. When i leave to a destination it will still take time, i will just arrive faster.. but not before i left.
 
  • #29
pervect
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dgoodpasture2005 said:
ellipse... if me and you are at my house... and i hypothetically have a craft that can travel at 300 times the speed of light... and i leave... and my destination is 300 light years away... and i travel there, and then back, it will take me two years ... i will not come back or get there before i leave.. speed of light in no way propogates time or dismisses FTL travel. I'm glad that your text book is well respected... but i respect my logic more. Time travel is impossible, and traveling faster than light is not going to make it possible. When i leave to a destination it will still take time, i will just arrive faster.. but not before i left.
If you travel at 300c in one inertial frame, you will appear to be travelling backwards in time in another inertial frame moving with respect to first.

This is a mathematical consequence of the Lorentz transform.

You can logically have FTL without time travel, but it requires violating the principles of relativity to do so. The simplest way is to define some "preferred frame" in which your FTL drive operates. The principle of a preferred frame means that your FTL drive does not respect the laws of relativity, and it prevents the time travel problem.

To go back in time before you arrived with a FTL drive that respects the principles of relativity by travelling at 300c relative to the "rest frame" of the space-drive engine before it was engaged, all you'd need to do is to travel a long distance at 300c, turn on a conventional space-drive engines to change your velocity and shift to a different inertial frame, and then travel back to your original position in space with your FTL drive.

You might take a look at the "Relativity and FTL travel FAQ" for more information.

http://www.physicsguy.com/ftl/html/FTL_part4.html#part:ftl

This goes into the FTL problem, and talks about the "preferred frame" solution.

A quote to illustrate the proper section of this long document:

In short, for any signal sent FTL in one frame of reference, another frame of reference can be found in which that signal actually traveled backwards in time, thus violating causality in that frame.
Wormholes are a possible way around the FTL/causality barrier. It's not that wormholes can't become time machines under the right circumstances - relativity suggests that they can. But there is a plausible "cosmic censorship" option which makes the wormholes self-destruct when they attempt to become time machines.

See for instance

http://www.npl.washington.edu/AV/altvw69.html

Hawking has suggested that while Nature does not abhor a vacuum She may very well abhor a time machine. His calculations indicate that vacuum fluctuations of drastically increasing energy, rather like the audio feedback we experience with a PA system when we bring a microphone too close to the speaker, will arise just as the wormhole connection becomes "timelike".
 
  • #30
thanks for the links, i'll have some reading to do... but still, my mind does not grasp any concept of time rewinding itself... time always moves forward... speed does not propogate time, no matter how fast i travel it will still take time, even if it's 0.00000000000000000000000000000000000000000001 of a nano second, i will never travel fast enough to go in reverse, this logic is backwards to me... maybe i just need to be a little more open minded, but the prospect of traveling back in time eludes my logic and comprehension of time... i have read no where that the speed of light controls time. I will definitely read about the Lorentz transform and differnent inertail frames... but it still eludes me for the time being that from anyones vantage point... looking at an object traveling faster than light would make it appear to be going back in time in any way, it would just be traveling extremely fast.. then again i still have some reading to do.. i'll get back at you later after i am done, thank you for the links and your co-operation pervect... appreciated deeply ;)
 
  • #31
okay i've read about half of it... and everything is saying that the speed of light controls time... why does this not make sense to me? If i am watching someone travel at .99c and i am here on earth and i can look into his ship at a clock inside of his ship, and watch it the whole trip, i'd see exactly how long it would take, and our times would be running the same... would they not? if he is traveling at the speed of light, and his destination is one light year away, and i am able to view his clock from here on earth the whole time(trip), he will still arrive in a year... and it will also take me a year of observation.. therefore our times are running at exactly the same pace? i don't see where this slowing of time comes into affect... or if i do, i don't see how it makes any sense... especially with that explanation i just gave, our time still runs at the same speed, even relative to each other.
 
  • #32
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dgoodpasture2005 said:
okay i've read about half of it... and everything is saying that the speed of light controls time... why does this not make sense to me? If i am watching someone travel at .99c and i am here on earth and i can look into his ship at a clock inside of his ship, and watch it the whole trip, i'd see exactly how long it would take, and our times would be running the same... would they not? if he is traveling at the speed of light, and his destination is one light year away, and i am able to view his clock from here on earth the whole time(trip), he will still arrive in a year... and it will also take me a year of observation.. therefore our times are running at exactly the same pace? i don't see where this slowing of time comes into affect... or if i do, i don't see how it makes any sense... especially with that explanation i just gave, our time still runs at the same speed, even relative to each other.
What you are reading about is Einstein's special theory of relativity. It is counter-intuitive at first, but the good news is it can actually start to make a lot of sense once you convince yourself that Einstein's two postulates ("postulate" is another word for "assumption") are correct. Einstein's two postulates are:

(1) All inertial reference frames are equivalent for the description of the laws of nature.
(2) The speed of light is the same in all inertial reference frames.

The second postulate is one of the hardest to accept, but it has been adequately verified by experiment. No matter how fast you move, light always moves at the same speed. As a result of this second postulate, we find that the way nature allows the speed of light to be the same in any reference frame is by shortenning our perception of length (length contraction) and slowing down our clocks (time dilation).

For a good, layman description of the special theory of relativity, read Robert Geroch's General relativity from A to B. I have not read this personally, but have seen it recommended enough on these forums for me to feel sure it is a good source. For a slightly more advanced approach, I would read Einstein's Relativity: The Special and General Theory (if you have graduated from high school, and feel up to the challenge, you should be able to understand this in an appreciative way -- it has very little math, but enough for you to play with, and it's all basic algebra). This has helped me a lot personally because a lot of things in relativity seem so outrageous when you first hear them (especially the relativity of simultaneity) that it helped reading from a physicist as prominent as Einstein himself, because you're much more likely to accept what he says rather than think he may not know what he's talking about. That has been my personal experience, anyway. Einstein also liked understanding things conceptually, so he explains in a conceptual manner. (You can find it online here ( http://www.bartleby.com/173/ ) or also in most book stores with a physics section ... or a local library) If you would like to try a textbook, refer here ( http://math.ucr.edu/home/baez/physics/Administrivia/rel_booklist.html#intro_sr ) for a list of respected relativity textbook authors and what level textbook may suit you best.

And welcome to Einstein's wonderful world of relativity!
 
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  • #33
You know I heard allot of this before and will I'm just not buying it. Why is everyone so quick to ftl is impossible. I see a one problem with Einstein theory. If mass changes with the speed of an object, then is mass a virable? With out know what interaction makes this happen I think it is a bit much to say FTL is not possible. If one day we find the cause of this change in mass it might be possible to change the mass of an object to nothing, Einstein own theory say mass is not a constain nor is time. Would this not mean once we have a better understand of both, that both time and mass could be changed to make FTL possible, or do we keep doing as we have been doing, and say everything impossible? Another good one, is the people who says there no way to get around gravity or there not antigravity, they are sure that it is impossible yet nobody know what cause gravity. How do you know it is impossible when you don't why is possible?
 
  • #34
Ich
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As long as SR´s first postulate and the relativity of simultatneity hold, FTL leads inevitably to causality violations and is therefore considered impossible.
However, if you assume some sort of Hyperspace which violates the first postulate, you can avoid these inconsistencies - FTL would become logically possible. Still I guess you would have a hard time implementing eg energy conservation or gravitation in such a theory.
 

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