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Faster Than Light Communication/Transportation Not Possible?

  1. Aug 5, 2005 #1
    Because if it is then it could cause problems with causality. Or is it possible but our "laws" are still incomplete?
  2. jcsd
  3. Aug 5, 2005 #2
    Well if we follow current laws of physics you would need an infinite amount of energy to go faster than light. That is what they told me when I asked the same question. BUT, whenever we thought that something is impossible or that we are in some way special in the universe we were wrong. Imagine of you told to the smartest man in 15th century that there will be a space station or that we will send robots to Mars...He wouldn't believe you. If you say to the smartest man today that there will be a machines that go 10 times the speed of light in 2200. He would say to you that that is impossible, but we all know that human knowledge is growing now faster than ever, and if we don't destroy each other we might see machines that take us to the next galaxy in the matter of days, or something like that incomprehensible today.
  4. Aug 5, 2005 #3
    Yes, faster than light communication would cause major problems with causality. To quote d'Inverno (1992, page 22):
  5. Aug 6, 2005 #4


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    It is unlikely the 'laws' are that incomplete. There are compelling mathematical arguments forbidding faster than light communication.
  6. Aug 6, 2005 #5


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    Our 'laws' are definitely incomplete, or science would be at a standstill and we would know everything. That particular law, however, is pretty firmly entrenched. New laws, as they are discovered, don't negate the old ones; they expand upon them. Old theories fall by the wayside all of the time, but it isn't considered a 'law' unless it's inviolable.
  7. Aug 6, 2005 #6
    Faster than light communication is possilble through Quantum Entanglement, though no one knows how??. The idea of quantum teleportation uses this principle....
    Yet, it does not conflict with the core principle of Special Relativity.
  8. Aug 6, 2005 #7
    Good question,

    scroll down to the Faster than light communication entry

    Your answer is in there

  9. Aug 6, 2005 #8


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    No, you can't actually use quantum entanglement to send messages faster than light. With quantum teleportation, you need to send a classical signal (speed of light or slower) between the two locations in order for the quantum state to be correctly "teleported".
  10. Aug 6, 2005 #9


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    True, in the case of quantum entaglement, you are not sending a signal from receptor A to receptor B faster than the speed of light, you are transmitting information about the state of the partner particle at the other receptor faster than the speed of light. If the emitter of the entangled particles is exactly in the center of the path between the receptors of the particles, receptor A "knows" the state of the particle at receptor B in half the time that it would take for a classical transmission between A and B. In this way, receptors A and B can share a bit of information at twice the speed of light. If the receptor A is very close to the emitter and recepter B is 100 times farther away, receptor A would get it's relevant information about the state of the entangled particle at receptor B at about 100 times the speed of light (far before the entangled particle ever gets to B), while receptor B would receive information about the particle at receptor A at just a little faster than the speed of light.
  11. Aug 6, 2005 #10
    So it looks like it is not possible?
  12. Aug 7, 2005 #11


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    Not true. You can know all the "laws of chess" and still not be a master.

    Also, the line between "theory" and "law" is pretty meaningless. It is more a matter of social convention than any real difference between the two. For example, we seek of Newton's Law of Gravity, but Einstein's Theory of General Relativity. We have the theory of evolution, and Murphy's Law (OK that was a cheap shot).
  13. Aug 7, 2005 #12


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    No. All of the information about the state of the particles came from the emitter, and that information was sufficient for observer A to determine what observer B would see, without requiring any sort of transmission of information from observer B.

    Anyways, observers A and B will indeed have a shared bit of information. However, that usage of shared is not the same as that of the following sentence: "A knew something and shared that information with B, and now B knows it too!" If A wants to impart knowledge to B, he has to do it with a light-speed signal, just like everybody else.
  14. Aug 7, 2005 #13
    Another problem with entanglement is that you should have the partner particle @ the desired destination first, which means, slower than light transportation of that particle..
    u can have a 'Morse code' type of information transmitted like, spin=clockwise=1 & spin=counter-clockwise=0...
    decode using binary language of 10101010... :biggrin:
  15. Aug 7, 2005 #14


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    It really depends on your interpretation of QM. In a hidden-variables interpetation like Bohmian mechanics, it is true that the particles are affecting one another's state faster-than-light. In the transactional interpetation you might say that the measurement of one particle had a backwards-in-time influence on the other's state when the two were created. And the many-worlds interpetation tries to explain everything about entanglement without any FTL or backwards-in-time influences, by way of each observer locally splitting into multiple copies during a measurement and the copies in different locations not being matched up until a signal has had time to pass between them. I came up with a simple example to show how in principle a many-worlds-type interpretation can explain the Bell inequality, although in the actual many-worlds interpretation the relation between probability and "number of copies" is not so clear as in my example:
    He doesn't know the state of the other particle, he just knows that if the other experimenter measures along the same axis he did, he'll always get the opposite spin, but if he measures along a different axis, he only knows the probability the other experimenter got the opposite spin, which will be lower than a local hidden-variables theory would lead him to expect. The only difference between the classical case here is that the probabilities are lower than expected if the two experimenters measure different things. For example, suppose I build two boxes which each have three doors behind them, and behind each door is either a black ball or a white ball; I always make sure that if door #1 of the first box has a black ball then door #1 of the second box will have a white ball, and so forth. Also, I install an auto-locking mechanism so as soon as one door is opened the others become impossible to open. Now if I send the two boxes in opposite directions, and you will receive the box in one location at the same time your friend will receive the box at another, then you know that if both you and your friend open the same door of your respective boxes, you will see opposite-colored balls--but obviously this does not involve any FTL information transmission! You also know that if one box contains three white balls and the other contains three black balls, then if you and your friend open different doors, there's a 1/1 chance you'll see opposite colored balls; on the other hand, if your box contains 1 ball of color A and 2 balls of color B, while your friend's contains 2 of color A and 1 of color B, then if you open different doors, the chance you will see opposite colors is (1/3 chance you pick door with color-A ball)*(0/3 chance your friend's door has color-B ball) + (2/3 chance you pick door with color-B ball)*(1/2 chance your friend's door has color-A ball) = 1/3. So if you and your friend pick different doors, then no matter what scheme I used to pick the colors behind each door, a local-hidden-variables theory implies that when you two pick different doors the chance of getting opposite-colored balls must be between 1/3 and 1/1. So if you did this experiment a bunch of times and then got together with your friend to compare notes afterwards, you'd be pretty surprised if, when looking at trials where you both picked different doors, you only found opposite colors on 1/4 of these trials! This is the mystery of entanglement, but you can see that before the two experimenters actually get together to compare notes, the readings of one experimenter don't give her any FTL information about the readings of the other, no more so than in the boxes-with-three-doors experiment.
  16. Aug 7, 2005 #15


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    That's not quite the same situation. Knowing all of the laws of chess gives one the potential to become a master if other factors don't prevent it. In terms related to your own occupation... someone with a photographic memory can know every law on the books in the world. That gives him the potential to be the best lawyer in the world. If, however, he can't apply them in an intelligent manner he'll never win a case.

    My interpretation of the the difference is that a theory becomes a law when it has proven itself to be unbreakable.

    Newton's Law of Gravity has been proven unbreakable within the framework to which it applies. You can stand around dropping bricks for the rest of your life and every single one of them is going to hit the ground in accordance with that law. Einsteinian and quantum gravity don't negate that law, they supplement it. Think of them as being like ammendments to your constitution.
    The Theory of GR is still being tested. Also, the proven fact of Evolution is more or less a law. The theories relate to what mechanisms and time-scales are most likely true.
  17. Aug 7, 2005 #16


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    A law describes something we see; it describes what happens. It is simply a quantified observation.

    eg. There is no 'alternate' Law of Gravity. The Law of Gravity simply describes what every scientist on every planet in the universe will jot down on her notepad. They will all describe what speed objects fall and what speed the Moon revolves. Generalizing, they will all arrive at G=(m2*m1)/r^2. It's not negotiable.

    OTOH, a theory attempts to describe how or why.

    Every one of those scientists on those planets could have a different theory about how/why objects fall or how/why their moon revolves (gravity particles, warped space-time, invisible tendrils), all of which can be negotiated and refuted.

    In fact, I'll boil that down:

    A law describes something; a theory tries to explain it.
    Last edited: Aug 7, 2005
  18. Aug 7, 2005 #17


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    That distinction doesn't make any sense to me. Are you saying Newtonian gravity is a "law" because it just describes what happens, while General relativity is a "theory" because it describes why? Seems to me that GR just describes what happens too--it doesn't say why matter/energy curves spacetime, or why objects moving in curved spacetime follow geodesic paths, it just says that's what happens, and the predictions you get from this match observations. All of physics is just about mathematical models that make certain predictions, it doesn't deal with meta-explanations of why this model makes accurate predictions but that model doesn't.

    Note item 17 on physicist John Baez's crackpot index:
    Likewise, Feynman talks about the issue of whether we need a "mechanism" to explain why a particular abstract mathematical theory works in chapter 2 of his book "The Character of Physical Law", which is entitled "The Relation of Mathematics to Physics":
    Last edited: Aug 8, 2005
  19. Aug 7, 2005 #18
    Then why do general relativity's predictions deviate from Newtonian gravity's predictions? For an example, look to the perihelion shift in Mercury's orbit, which cannot be explained by Newton's Law of gravity. Obviously, Newton's laws are wrong if applied to the orbit of Mercury.
    Last edited: Aug 7, 2005
  20. Aug 8, 2005 #19
    In our now actual life experiences, it very seems that it is impossible. I ever read a book the writer is a Cambridge University professor, he thinks that speed can faster than light speed, he put much hypothesis, but I feel the book's hypothesis is impossible and fantastic. I now have no enough reasons to believe Einstein's hypothesis is wrong, so I trust his idea.
  21. Aug 8, 2005 #20
    This kind of discussion bothers me sometimes. I mean, at what point do we decide our laws are incomplete ? What is incomplete ? For example, general relativity allows for time reversal to be applied in the mathematical framework. When applied to the (correct :wink: ) physics of black holes (eg : Schwarzschild metric or Kerr metric for rorating black holes AND the Einstein equation) we get the white holes (the vomoting stars), yet we have not yet found such white holes. When combined with black holes we get the famous worm holes. The problems involved with these are legendary, yet GR is proven to be very correct. You see my point ?

    Just because mathematically, something makes sense, it does not mean that physically it is also ok. You can find similar situations with QM.

    Even, you can turn this around. Look at renormalization theory in QFT, in order to fit physical reality, we perform some mathematical tricks that are merely interpretative, though mathematically not correct. However, when holding on to such a system, we are ablt to describe the quark behaviour and we are able to describe quasi all atomic phenomena with incredible accuracy.

    I say we just need to be pragmatic about this and hold on to the hole falsification process. If we don't do that, all structure is lost

    Just my two cents

    marlon o:)
    Last edited: Aug 8, 2005
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