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Why is faster than light travel so bizarrely 'addressed'

  1. May 15, 2009 #1


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    Hello everyone,

    The topic of superluminal flight has intrigued me for decades but coming from an engineering background and not a strong physics background (although I have studied physics), I am finding the notions about how to possibly achieve such a system quite difficult to accept.

    In a nutshell, all this talk of bending 'space/time', expanding space behind and shrinking space in front of a starship and discussions of dark matter and wormholes laced with exotic matter seem most odd indeed. I wonder how many other people who read of these topics question whether they actually exist in reality and are merely created to explain away something which hasn't as yet been physically created.

    Certainly engineering in many ways is directly derived from physics, but so much of engineering is based on real life application. I feel that conventional rocketry is coming to its near end, as the system has almost achieved its peak of efficiency and shouldn't even be thought of when considering 'proper' distances due to the level of propellant needed etc. So for true interplanetary missions, a bold new approach needs to be created. It is clear that atomic or nuclear energy based power plants will be the next step forward in spacecraft propulsion. Ultimately, a matter/antimatter reactor will be the final goal - this seems to me to be the most logical approach. And as related technologies connected with safe human space travel expand, sooner or later, mankind will be faced with the great light speed barrier.

    Yet, the problem I have with all of these incredible sounding theories is what do they mean in the physical universe and how would they physically work in reality? This has always been a massive problem with truly advanced subjects. For example, the current 'system' for possible FTL travel requires a starship to expand space behind and shrink space in front of it. Analogies have it being likened to a surfer on a large wave, where the wave carries the surfer. Analogies are great, but when someone states that space/time is expanded or shrunk, what does that practically mean? How is space actually expanded? What technology would actually do that? To me and many others, space is a vacuum filled with all sorts of natural matter in varying quantities, but mostly it is empty space. What is there to expand? Talking of expanding space to theoretically satisfy a need is all well and good but in reality, to me, such a notion is not a real one. If I am sitting in my living room and I want to get a beer from the fridge in my kitchen 30ft away, by expanding the space behind me etc, does that mean I can open the door from my seat because it physically pulls the entire kitchen towards me?

    There are so many strange ideas associated with FTL travel that I wonder if the true ability to pursue such a technology (now or decades into the future) will be ignored in favour of bizarre ideas that will always be years into the future no matter how advanced we get. For example :-

    The idea that time starts to slow down as a spacecraft approaches light speed is a concept I find most strange. Why would time 'slow down' just because you were approaching what is to all intents and purposes, just a very high speed? But this is a topic for another time as this is very interesting in its own right.

    Anyway, I would like to end this first post by stating that this discussion is not about ridiculing physics at all, far from it. It is a very important point this. I just wanted to ask questions and raise some professional alternatives/views to the current theories regarding FTL, how it could work and its associated components.


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  3. May 15, 2009 #2


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    Hello, and welcome.

    Even the matter/antimatter approach requires that the mass of the fuel carried by the rocket must be a several orders of magnitude greater than the mass of the ship. That's a problem with all the "rocket" technologies actually. I don't remember the details, but there's a calculation in "The physics of Star Trek" if you're interested. (What I mean by a "rocket" is a ship that's propelling itself in one direction by throwing stuff in the opposite direction).

    General relativity is built up around an equation (Einstein's equation) that tells us the relationship between the geometry of the universe and its content of matter. To "curve" spacetime, or just space, means to change what paths freely falling particles would take through the vacuum. This is definitely not science fiction. Experiments have proved that the predictions of GR are much better than the predictions of Newton's theory. (Yes, I consider an astronomical observation an "experiment").

    The particular geometry we need to create for "warp speed" requires that we use the existence of a type of matter that has never been observed, not even indirectly. So it's not very realistic. Even if this matter exists, it would probably be absurdly difficult to distribute it the way it needs to be distributed to produce the warp speed geometry.

    Expanding the space behind you isn't going to help, but maybe contracting the space between you and the refrigerator. Hm, I'm going to have to think about that.

    This is one of the easiest things in special relativity. It's counterintuitive, but not at all controversial. It's as standard as things get in physics. You're right that it's a topic worthy of its own thread. (There are many such threads already). I suggest that you try to read the relevant pages of some text on relativity first, and then ask more specific questions about it.
  4. May 15, 2009 #3


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    This is a problem that doesn't exist. Engineers will not ever have the propulsion technology necessary to even begin to worry about the limitation of C getting in their way. Ie, if technology advances enough that someday we are able to propel our spacecraft 1000 times the speed we can now, they'll only be going 4% of the speed of light.
  5. May 16, 2009 #4


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    The way I imagine things is this. If I'm traveling near the speed of light, and someone shines a laser past me, everything (time) around me outside my frame of reference has to speed up in order for light to remain the same speed. Of course, the opposite of this is everything around me remaining the same, except time for me is slowing down, allowing light to remain the same speed. I like to imagine it as a kind of fast forward for my surroundings, imagine a particle of solid matter with no constant properties. Then imagine a photon which has to be and has proven to be constant in a vacuum. The photon has to remain the same speed, it can't just speed up and slow down relative to stationary observers, time it's self has to drive the photon forward to keep up with you, including any stationary observers.

    It's not the most educated way of putting things, but I hope it can put the idea into perspective for you...
    Last edited: May 16, 2009
  6. May 17, 2009 #5
    If you did a survey and asked people if they thought FTL speed would ever be possible I'm sure a very high proportion would say yes.
    The only thing that would indicate that FTL speed is unlikely is that we would be overrun with aliens dropping in from distant galaxies and that doesn't appear to be the case.
  7. May 17, 2009 #6


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    Sure, but what if you asked scientists? The vast majority would say no.
    Well that and the fact that the laws of physics prohibit it. :rolleyes:
  8. May 18, 2009 #7
    Image you are a snail at one corner of a large (2-dimensional) sheet of tarpaulin and you want to get to the opposite corner. That would take ages. But imagine you could fold the 2D tarpaulin so that the opposite corners became adjacent. You could then crawl across and then unfold the tarp back to its flat position. Even though you crawled very slow, you have travelled a huge distance in a short time.

    Now, imagine taking 3D space and folding it in a fourth dimension ?

    Hmmm - interesting concept, a good one for the science fiction novels, maybe not so hot to achieve in practice : )
  9. May 21, 2009 #8


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    Dear all,

    Thanks for the varied responses - most interesting.

    I therefore have some questions I'd like to ask. I've looked for answers in numerous books etc yet no-one can seem to give a simple straight answer - so maybe you can help!

    1) What exactly is space-time? (as practical as you can please!)
    2) What exactly is meant by curving/bending/warping this space/time?
    3) How exactly would you go about curving/bending/warping space-time? (i'm talking theoretically here and assuming technology is not an issue)

  10. May 21, 2009 #9
    Just to start the ball rolling ..

    1) 'Space-time' was devised as a mechanism to assist in predicting or calculating the position of a moving body in space at any particular moment. As I understand it makes things easier - mathematically speaking.

    2) The curvature of spacetime is a way of explaining the Equivalence principle, whereby gravity and inertia (acceleration) are thought of as one and the same effect. The difficulty was to explain how we could be standing on earth, not moving yet experiencing this acceleration as though we were accelerating upwards in a lift at 1g. The way to do this is to distort time and modify what is considered a straight line and the mathematics drop into place, and there you have it - gravity.

    3) Spacetime is naturally distorted by matter. Probably all particles distort spacetime to a greater or lesser extent. The search for the Higgs boson, considered the holy grail of spacetime distortion, could, if it exists be a dominant factor.
    If you wanted to distort spacetime and technology not a problem, then get a large lump of matter the size of the moon and an equally large lump of antimatter and join them together.
  11. May 21, 2009 #10


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    These questions are really difficult to answer in simple terms. For example, the mathematical model of spacetime is a 4-dimensional smooth manifold with a Lorentzian metric. It would take a very long time to explain what that means. Its most important feature is that it's an abstract set of points that's equipped with a bunch of functions (coordinate systems) that take points in spacetime (events) to 4-tuples of real numbers (coordinates). It's also equipped with something called a metric tensor which represents various geometric properties of spacetime, including curvature. Curvature is even more difficult to explain than manifolds, but one of the characteristics of a curved manifold is that the sum of the interior angles of a triangle isn't 180°.

    I suspect that you intended question 1 to be a question about the real world rather than the mathematical model. In that case, the answer is that science can't tell us what spacetime really is, or what anything really is actually. Theories just make predictions about results of experiments, and experiments just tell us how accurate those predictions are. It isn't possible to find out what something "really is".
  12. May 24, 2009 #11
    Russ posted
    "Engineers will not ever have the propulsion technology necessary to even begin to worry about the limitation of C getting in their way."

    Russ has posted some great stuff here...that is NOT one!!

    ...it's myopic. Looking back to the early 1800's it was supposed by "scientists" that a train could never go fast because people would not be able to breath....

    While I accept "c" as an upper speed limit in conventional (classical) discussions, I also know there has never before in history been a "consensus" that has been initially correct....as an example Einstein believed the unibverse was static and that black holes were "impossible"...

    I looked at perhaps 50 "established facts" myself over history and NONE, not one, was correct....I was NOT trying to prove that, I just investigated tosee how accurate scientists have been over time.....ALL first theories were proved false or at least partially incorrect....

    we already know general relativity CAN NOT be correct because quantum mechanics conflicts with it and is an extremely successful theory of the very small...
    just consider that 95 or 96% of the universe is "dark"...we don't even know what it is........dark energy and dark matter...and have only a basic understanding of the other 4%and we think we are so smart...!!!
  13. May 25, 2009 #12
    I believe there are a few "somewhat" realistic propulsion ideas floating around. The first propulsion device is able to displace or cancel out gravity by rotating a superconducting disc at very high speeds. Somehow getting all the electrons to line up together cancels out gravity. I'm unsure how well this would be used in the middle of empty space where no matter (gravity) exists, but this idea was intriguing enough that the goverment snatched up a few of the leading scientists in this area a few years ago (The lead scientist was from the University of Alabama and was about to start a company called AC gravity before she got a $500,000 grant to continue her research privately. The second is to bend/fold space. To curve space enough to make traveling somewhere worth while you would need to accelerate a large amount of mass at relativistic speeds. One way you might do this in the future would be to use some kind of condensed matter or superfluid and use magnetic fields to accelerate it around a torus. (Superfluids have no viscosity and thus can be accelerated to extremely high speeds - where the only thing you would be fighting is the increase in mass due to special relativity) Keep in mind current condensates are comprised of only a couple thousand atoms using laser traps - we're a long ways off from trapping enough to be able to manipulate space and time enough to see it. The last option that is unknown to us all but not to nature is the mechanism responsible for the expansion of the universe. Something is curently working (seemingly) at every point in space pushing everything away from everything. This force or whatever it is obvioulsy doesnt require any matter to work and may be used instead bring two points closer together once it's understood.
  14. May 25, 2009 #13
    i believe the concept of FTL travel is so "bazaar" because, think about it, how are you supposed to arrive at a destination before the image of your self does? the concept is a difficult one to grasp a hold of. However i do believe that FTL travel is a realistic goal, and hope to someday be in the forefront of the technology.
  15. May 25, 2009 #14


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    The Podkletnov effect has NEVER been reproduced or shown to be valid. It is a fringe physics at best, and someone's imagination at worst.

    I will remind everyone of our https://www.physicsforums.com/showthread.php?t=5374", especially our policy on speculative theory. Previous threads on this topic have had to be closed or deleted. Failure to abide by our rules will result in this thread ending with the same fate. So it is your decision.

    Last edited by a moderator: Apr 24, 2017
  16. May 25, 2009 #15
    Hello all.

    I read from time to time details of marvellous technological breakthroughs, proposed or already on the drawing board, regarding FTL travel. I wonder why these marvels usually come from people with little knowledge of physics and an aversion to mathematics. But there again, perhaps I'm just an old cynic.

  17. May 25, 2009 #16
    I think this example isn't as constructive as people think it is. If I were a human standing on one corner of a tarpaulin that is very large and I wanted to reach the other corner quickly, by your methaphor, I should just fold the tarpaulin and take one step to the other corner and then unfold the tarpaulin. How would I do this folding? I could walk to the other corner, pick it up and drag it back to my original corner, but then I would have done twice the work I needed to do and would have already been at my destination. I could phone someone and at the other corner and they could bring it to me, but this would take as long as me walking to their corner. Also, in 4D, communication is only as fast as the speed of light, so I wouldn't be able to "tell" the corner of space that I wanted to fold towards me what to do faster than the speed of light, thereby disallowing faster than light travel by bending space.

    As an engineer, I understand the frustrations of the OP. You can't just go around bending space-time and warping things and making matter-antimatter reactions in the same way you can build a jet engine to attach to a thing with wings to get somewhere fast. I'm not saying it's impossible, but it's so intangible, especially for practically thinking engineers who would have to build the things that physicists are theorising.
  18. May 25, 2009 #17


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    But that's sort of the state of things. It's somewhat amazing that "FTL" according to GR would even be possible -- and if you have to figure out how something is possible before you can figure out how it might be done intentionally, let alone reduce it to an engineering problem!
  19. May 26, 2009 #18
    I'd be happy if we could be technologically advanced enough to produce waste free (minimum or useful "waste") energy over the entire globe in my lifetime. I'll leave the FTL devices to the coming generations.
  20. May 26, 2009 #19
    We are advanced enough.
    Only problem: money.

    FTL devices are in our reach, but we need more courage to test the fuel. I think the next world war will solve the problen. It is unavoidable, becouse our current economy model is not working.
    If you will think in action=reaction way, you will get nowhere.
    As an example : atomic chain reaction. We put in less, we get out more.
    Matter-Antimatter -> how much energy does it take to create some of these?

    What about subatomic chain reaction? Is this possible? Who will be brave enough to make an experiment?

    I hate theoreticians / sci-fi writers / ecoterrorists.

    Last edited: May 26, 2009
  21. May 26, 2009 #20
    That’s not exactly how it works. I'm trying finish a video of what FTL travel would look like and it's quite fascinating - it actually resembles particle creation/annihilation processes. For example imagine a speeding bullet flying right by your eyeball at 2c. If it were possible for you to even see it, the first image of the bullet will arrive at your eye perpendicular to your line of sight – when it’s right in front of your eye barely missing it. This is because the light from the bullet from where it was first fired has not had time to catch up. It’s too complicated for me to explain without confusing you (and me as well), I will just say that 2 bullets emerge from this initial point both moving forward and backward. The backward moving bullet is composed of light catching up from where it was first fired, the bullet moving forward is from bullet once it crossed your eye. The backward image of the bullet moves at 2c and the forward bullet moves strangely at 0.67c forward! Very weird, but the false image of the bullet moving back towards the gun represents the bullets true velocity. I should also note that if the bullet were symetric, there would be no way of knowing which way the bullet went unless you did the math.
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