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Idea's for FTL and Space travel

  1. Mar 14, 2012 #1
    Hello Everyone this is my first post on the forums and I want to share my ideas on what FTL is how it would possibly work. Now first thing is that I choose this part of the forum because of what FTL would involve. Now I am 14 who greatly interested in mechanical and electrical engineering and physics and I may get a few things wrong so bare with me......

    SO I know that FTL travel is currently impossible with todays technology and the standard model of physics. Most theoies and ideas depict using a worm hole to get to point A to point to point b. Also in Sci-fi which i am making a small connection to there is this idea of hyperspace in which it is used in the Alien series. Not the starwars light speed type. But anyways in Alien the FTL drive is called a "Tachyon Shunt" which can move the ship at .4 lightyears but is travaling relivant to time in normal space. This speed is affected by mass by a ratio of 5000000 TON to .1 lightyears a day (so 20000000 ton cargo= .1 lightyears a day. These numbers when it comes to other sci-fi movie's one's seem slightly more realistic that starwars and startrek but let me know what you think.
     
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  3. Mar 15, 2012 #2
    So you are writing sci-fi stories? It really depends on what you want to do. Personally I find the stories where spaceships move at sub-light speeds to be much more interesting,not only physics-wise but also from the point of storytelling. Books by Alastair Reynolds are a good example of this being used very effectively.

    From a storytelling point of view, it doesn't matter at all what you decide to call your ftl-technology. Just decide how fast you want it to go, and you're done! If you want something more "realistic", you can consider wormholes or Alcubierre drive.
     
  4. Mar 15, 2012 #3
    No I am not trying at all to make a sci-fi story what so ever. I am just see what real concepts would be as simular to in Alien. In fact it was called most realistic sci-fi for space travel by Popular Mechanics magizine. Also I have thought it could be a Alcubierre drive that was used since FTL in the series was not instant travel. If you or anyone else is inquired on the forum I can give the spec's of the ships. I do also realize that this Sci-Fi and not real life but I LOVE to make connections to them.
     
  5. Mar 15, 2012 #4
    I am not really familiar with the Alien universe, but I remember that they fell into cryogenic sleep. That part is fairly realistic, since even one thing you could theoretically do is exploit relativistic time dilation (the principle that states that time slows down as you move faster) and travel at very high speeds while ageing "only a little", because of the combination of cryogenic sleep and time dilation (of course if we are talking about traveling light-years, that should still be enough time to kill you for large enough distances :tongue:).

    On a more realistic page, the problem with any kind of FTL space travel concept is mainly threefold:

    - It requires unreal amounts of energy to accelerate anything with meaningful mass (like a spaceship) to velocities that even approach the speed of light.
    - Even in space, at that velocity there would be serious friction between particles and the spacecraft. Furthermore, as the spaceship gains kinetic energy, its atoms will start being able to simply fly away, because of the excess energy they now possess.
    - There is no known technological way to manufacture a spacecraft that can withstand the theoretical gravitational effects involved when travelling through a wormhole (even if it can somehow get near one).

    So, in short, we lack the means to power that sort of spacecraft, and we lack the materials that can withstand the phenomena involved in travelling at those velocities!

    The conflict is that SciFi always implies serious breakthroughs in physics and technology. Even if it is stated that the spaceship possesses a very powerful engine, that in itself is not enough to justify FTL or close to light speed travel. Without discoveries that drastically change our knowledge of physics, the spaceship would simply fall apart.

    A good example would be if we discovered to way to cancel out gravity using very little (or no energy). If for instance the spacecraft could be made out of a special material that does not interact with gravity (and ideally shields everything it contains from external gravitational fields), then it might be able to go through a wormhole. Of course, the only thing that we currently know that has this property is light, so you can see how unrealistic it seems at our current level of technology. Furthermore, even light can be trapped in a black hole, so that discovery alone would not enable us to do everything. We need, in fact, a series of breakthroughs!

    Finally, despite how much we would want to, it is quite likely that we will never be able to travel outside the solar system and live to tell the story. The physical laws might simply not allow it :)
     
    Last edited: Mar 15, 2012
  6. Mar 15, 2012 #5

    PAllen

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    true
    Friction isn't the issue, it is damage. On a long journey at even .9c, hitting a single 1 gram fragment would hit your ship with the energy of the Nagasaki nuclear bomb.

    Your comment about atoms flying off is all wrong. Everything relative to the ship is perfectly normal. The energy they have relative to something else is completely irrelevant. Kinetic energy is frame dependent, and in the rocket the atoms have no extra KE at all.
    .
    The more basic issue is that wormholes and alcubierre drive require negative energy in large amounts. There is no basis in observation or currently known theory to believe that such exists.
    The fall apart bit is false, as noted.
     
  7. Mar 15, 2012 #6

    PAllen

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    Monstrous energy isn't the issue for wormholes or Alcubiere drive. It is negative energy, which doesn't exist at all by observation or currently known theory outside of inherently local, small, quantum field effects (Casimir Effect). There are inequalities true of such effects that (by present theory) preclude wormholes and Alcubiere in principle. Of course, one can speculate on outside current theory.
     
  8. Mar 15, 2012 #7

    PAllen

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    Anything else precluded even more fundamentally. Again, you can have anything you want in a universe with your own rules. But there is no way to discuss it scientifically - you have ruled out the foundations of known science. In this universe, it appears very unlikely that even 'reasonably close to light speed' is plausible.
     
    Last edited: Mar 15, 2012
  9. Mar 15, 2012 #8
    Isn't this the definition of friction though? Collision with surrounding particles?

    For an ideal vacuum, I stand corrected :shy: However, this is a phenomenon caused by increase in temperature (which is why early supersonic aircraft wing metals used to start melting at high velocities). If you were to accelerate something at such velocities, wouldn't the difference between the frame that the rocket is and the free particles, be such that the temperature created because of the impacts will cause this effect?

    This comment was summing up the statement that the materials cannot withstand the impact of particles and that if the spaceship is near a gravitational field so strong that it distorts space, then the steep gravitational gradients would take the ship apart. Is this incorrect?
     
  10. Mar 15, 2012 #9

    PAllen

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    I guess you could argue this. At some speed, average density of interstellar molecules would be a problem. However, for a long journey, the rare speck of matter (rather than interstellar medium treated as gas) will become dangerous at much slower speeds. Thus, for interstellar medium to become problematic, you might need .999999c. For one rare speck of dust to be problem, you need only .9c. But on a long journey, it becomes likely for a rare event to happen.
     
  11. Mar 15, 2012 #10

    Ryan_m_b

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    Welcome to the forums. Currently only wormholes and the Alcubierre drive are entertained in the literature i.e. there is speculative theoretical work on how it might be possible. Things like hyperspace or tachyonic drives have no basis in reality.
    This is pure science fiction; it doesn't matter how much power you put into a propulsion system it will never reach the speed of light. Furthermore there are no proposals that I am aware of for a fusion reactor that can operate at 2 terawatts, commercial reactors operate at 100-1000x less than that.
     
  12. Mar 15, 2012 #11

    Matterwave

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    One should note that the Alcubierre drive is "closest to reality" of any of these Sci-Fi concepts. It is the only one, as far as I know, which has a real scientific paper published on it. Even then, it's existence requires exotic forms of matter as yet undiscovered, and so is no more than a "what if" at this point.

    Additionally, the power level needed to accelerate conventionally to .9c is ridiculous. 2 terawatts is nothing compared to it. Given a spaceship of ~2000tons (not very large for a space-ship), it would take, even without relativistic corrections, 7E22 joules of energy to get it to .9c. This means you'd have to accelerate the ship for 1100 years at 2 terawatts to get it to that speed.
     
  13. Mar 16, 2012 #12
    It has scientific papers published on it because it can be formulated within general relativity. This has nothing to do with being "close to reality" :-)
     
  14. Mar 16, 2012 #13

    Matterwave

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    Do you know of one which is "closer to reality"? FTL transportation I mean.
     
  15. Mar 16, 2012 #14
    But by close to reality we conventionally mean that there is no obvious violation of physical laws. The Alcubierre drive does agree with our current knowledge of physics. It is still considered impossible, but it agrees with what we know. Hyperspace concepts etc. usually do not :wink:

    Btw,
    this is very illuminating, thank you!
     
  16. Mar 16, 2012 #15

    PAllen

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    Actually it does violate physical law. Exotic matter doesn't exist classically; in QFT it is subject to inequalities that rule out Alcubierre drive. What one can say is that it doesn't violate one theory taken in isolation - GR. But then, GR itself says matter with negative energy is required. We turn to our theories of matter, and find this is impossible, or impossible on the scale required.
     
  17. Mar 16, 2012 #16
    Yes, but since the original 1994 (?) paper, there have been revisions of the model, and the mass equivalent of the energy required has dropped quite a bit, compared to the original, so it's reasonable to assume that in a few hundred years there may actually be a "viable" model. I am obviously not an expert, so it's very interesting to hear that QFT rules out the Alcubierre drive!

    You are right of course about exotic matter, although I believe that dark matter is also considered to be exotic matter, and it does exist (probably :tongue:). But anyhow, the theory demands negative mass, which has never been observed. I thought, however, that antimatter has not yet been conclusively proven to have positive mass, so there may be a window after all:tongue:
     
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