wondering about faster than light signals

Discussion in 'Physics & Math' started by nanok, Dec 18, 2001.

  1. Dreamsa Dare to Dream! Registered Senior Member

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    125
    Adam...

    A rigid body is one that does not deform during its motion. The distance between any two points in the rigid body remains fixed.
    But for that large rod it is inevitable that it will deform on pushing.

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    Talking about a rigid rod is not applicable here! I think!

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    Maybe I am wrong!

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    Last edited: Dec 27, 2001
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  3. tetra Hello Registered Senior Member

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    Solids involve crystalline lattice, which is bound at the atomic level. If you were trying to move gas, then it would be the speed of sound.
     
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  5. Brainz0 Registered Senior Member

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    Lattice, shmattice

    Atoms contacting atoms = sound waves, whether in solids, liquids, gas, or plasma. Same diff.

    Here's an old poem for your amusement:

    There was a young lady named Bright,
    Who could travel much faster than light.
    She took off one day
    In a relative way
    And came back on the previous night!
     
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  7. Dreamsa Dare to Dream! Registered Senior Member

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    Hi!

    The vibrations in the crystal lattice are just sound waves!

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  8. tetra Hello Registered Senior Member

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    no, they are bound atomicly. There is no space inbetween them, and sound involves two unconnected atoms hitting each other.
     
  9. Brainz0 Registered Senior Member

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    Tetra, tetra, tetra...

    "Bound atomicly" is peculiar grammar and spelling, and irrelevant physics. There is no such thing as rigid contact at the atomic level, in the sense we are used to thinking of it at the macro (usual, human, visible) scale. Atoms are in constant motion with regard to each other, in elastic bonds if a solid, temporary loose bonds in a liquid, in independent motion in gas, and complex electrostatic and magnetic patterns in a plasma.

    The "surfaces" of atoms are electron clouds which are shared to greater or lesser degree with nearby atoms, and they stretch, vibrate, change and dissolve gazillions of times a second. The only atomic structures bound as units are the newly created Bose-Einstein condensates, at microscopically low temperatures, which are in the same quantum state; they are sometimes called "superatoms."
     
    Last edited: Dec 28, 2001
  10. NAPALM Registered Member

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    1
    Hey guys!
    Don't you think it's not too interesting arguing which one is the speed of light or sound in the rod.
    Our physics doesn't know any signals that can travel faster that light.
    So, our problem is to think about existence of such signals.
    I guess the clue is in our measuring instruments, that just can't register any super-light speed.
    It's the same as we can't see objects smaller than light wavelength...

    Maybe anyone has any suggestions about super-lightspeed, or super-timepropagating stuff. With our technology we can only imagine such things, but using science.
    I guess neutrino is very suspicious for this topic, what do you think? And btw, gravity is a cornerstone in this problem, for sure.
     
  11. Brainz0 Registered Senior Member

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    Not neutrinos

    Their travel time from known supernovas etc. has been measured. They travel at lightspeed.

    There are many measurements of such effects as slowing of time and mass increase which have in fact been made with large objects and small particles which verify the increase of mass and other predicted changes at near lightspeed.

    At this time, any and all FTL technologies are fairy tales, with no backing in science, other than tachyons. Unfortunately, they are theoretical particles which travel only faster than light, and go backwards in time...so by the time you decide to use them, it's too late (if you do, you would already have seen the results in the past).

    I love sci-fi, but see zero prospect for FTL in any current scientific models. The posts on this and other threads and topics which talk about it are obvious babble by hopeful but uneducated writers. Sorry 'bout that.
     
  12. Adam §Þ@ç€ MØnk€¥ Registered Senior Member

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    7,415
    I thought the light from stars and other such things was travelling at C (300 million m/s or whatever) divided by the refractive index of space? Coz it isn't a void up there. It's chockas with dust, gas, all sorts of crap. Gravitational forces, EM fields, all sorts of things which affect the passage of EM signals.

    Was Lijun Wangs experiment at NEC not evidence of a signal moving faster than light? As far as I know, there has not yet been any disproof of his experiment. Also, the former head of Australia's CSIRO, who lives around the corner from me, told me of another experiment involving the transmission of the old "Mary had a little lamb" signal via FTL microwaves; that, he said, had also not yet been disproven.


    http://www.neci.nec.com/homepages/lwan/

    http://physicsweb.org/article/news/4/7/8/1
     
  13. Brainz0 Registered Senior Member

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    Science, Philosophy of

    Ever heard of Popper? He's a prominent philosopher of science. I like his attitude. He says that any scientific assertion ("law") is a testable, disprovable statement which has not yet been disproven or shown to have exemptions despite thorough, competent attempts to do so.

    It is important to compare every scientific statement to this standard. Where most pseudoscientific statements fall down is in not being testable or not having been subject to competent attempts to disprove them.

    None of the FTL or time reversal assertions you make qualify under any of these standards.
     
    Last edited: Dec 31, 2001
  14. Dreamsa Dare to Dream! Registered Senior Member

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    125
    Hi!

    The experiment described in Adam's post actually do not vilate the special relativity as said in the article. Does anyone know the explanation?

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    What is the difference between 'phase velocity' and 'group velocity'?

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  15. flamethrower Junior Registered Senior Member

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    No FTL

    Was Lijun Wangs experiment at NEC not evidence of a signal moving faster than light?

    No. It was simply a re-shaping of a light pulse. No FTL occured and no information transfered. The entire process is predicted from Relativity. NEC was terribly embarrassed by the misunderstanding.

    http://www.salon.com/people/feature/2000/08/03/light/
     
  16. flamethrower Junior Registered Senior Member

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  17. Adam §Þ@ç€ MØnk€¥ Registered Senior Member

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    If the electrons are moving at C, and somehow the effect is moving faster than C, whay is that not a signal? Any change in state at the far end constitutes a signal. If something registers at all, regardless of what it is, that's a 1. If nothing registers, it's a 0. So even if you can't send a tune through as PART of the signal, the binary changing of state at the other end should still exist. You don't NEED to send the tune as part of the signal if there is any change of state at the afr end which can be interpreted AT THAT END. Or not? Can someone explain the difference?
     
  18. James R Just this guy, you know? Staff Member

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    30,376
    Adam,

    Imagine you're transmitting a continuous Zero signal, by any method you like. Then, you decide to switch to a One signal. The time it takes for the receiver to know that Zero has gone to One is limited by the distance between source and receiver and the speed of light. There is no existing experiment and theoretically no way to make the change from Zero to One propagate faster than the speed of light.
     
  19. Dreamsa Dare to Dream! Registered Senior Member

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    125
    Hi!

    So what does the experiment by Wang mean?

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    That fuzzy thing with speed greater than speed of light!

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  20. Adam §Þ@ç€ MØnk€¥ Registered Senior Member

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    Anyone got anything interesting to say about these things I have seen on various websites (some of you will probably know what I'm talking about):
    - Superluminal scissors idea.
    - Spin around on the spot at night, and relative to you the moon moves around faster than light.

    And other such things mentioned on many websites. This is all new stuff for me still. I must say, from what I already know and what the teachers tell me, there seem to be many very large holes in our understanding of physics. I have all these questions in class, and the teacher always says "Nobody knows yet."
     
  21. James R Just this guy, you know? Staff Member

    Messages:
    30,376
    Dreamsa,

    <i>So what does the experiment by Wang mean?</i>

    There a pulse made up of many different frequencies of light travelled faster than the "normal" speed of light. The explanation is to do with a phenomenon called <i>anomalous refraction</i> in a specially prepared atomic medium. The individual waves making up the pulse all travel at different speeds, giving the impression of the pulse moving faster than light. This is possible because the component waves themselves <i>can</i> move faster than light. That is quite normal and not contrary to relativity since they carry no signal.

    It's a little complicated to explain in detail, but I might try a little later on.


    Adam:

    <i>Spin around on the spot at night, and relative to you the moon moves around faster than light.</i>

    Yes, but the important thing is that no information moves from the moon to you faster than the speed of light.
     
  22. Brainz0 Registered Senior Member

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    Moving Spots of Light

    James R....
    Exactly. And no information can be transferred between two points on the moon or, say, between two stars by having an illuminated spot swing between them.

    I don't know how fast the scan point on a CRT screen can move, but regardless of such "apparent" motion, there is no transfer of matter, energy, or information between separated points of the screen.
     
  23. nanok Registered Senior Member

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    30
    Wow you guys made this topic complicated, but I was thinking somemore and I thought when mankind discovers the smallest building block of them all (the higgs or whatever it will be) couldn't you theoretically line them up, touching each side to the next, therefore creating a rigid structure that doesn't flex because there are no atoms or smaller pieces inside of each particle to compress and hit the next..........
     

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