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Massive objects going 99.9% speed of light.

  1. Jan 19, 2005 #1
    Found this interesting, is this for real?

  2. jcsd
  3. Jan 19, 2005 #2
    I read this as the article taking this as proof that particles cannot travel at the speed of light, but would it be possible to measure a particle travelling at, or faster, than the speed of light? While I don't agree with the moving backward in time theories, it would an object moving that fast would be tricky to detect.
  4. Jan 19, 2005 #3
    I wouldn't have thought that measuring the speed of something moving fester than the speed of light would be difficult. You see the particle at point A, you see the particle at point B, find the distance between the points and the time it took to move that far and you have your speed.

    Assuming that it is possible for something to travel faster than light, it should be possible for that object to interact with light, much like if a concorde were to fly by at Mach 2 you'd probably notice even if you were looking the other way and could only hear it.
  5. Jan 19, 2005 #4


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    come on you two, there is nothing here about particles traveling the speed of light (much less faster)

    mapper asked, "is this for real"

    certainly as far as I know it is, as regards what you quoted, it is real

    I cant vouch for the details but this is essentially a familiar story

    man-made acclerators accelerate particles like
    protons to speeds very close to light
    and have for decades

    and cosmic ray energies have been measured at 50 joules and up,
    that has been known for decades too,
    and a proton going so fast it has a kinetic energy of 50 joules has to be
    going 99.999999..... percent of speed of light (many nines...)

    all this does is confirm the special relativity theory which is the basis of the belief that c is a universal speed limit.

    THAT COULD BE WRONG and in fact maybe things do go faster than c, but all the evidence that mapper is giving us is not indicating any violation of ordinary special rel. In what you are discussing there is no requirement to change the usual picture.
  6. Jan 19, 2005 #5


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    With faster than light speed, the problem is in the math. In relativity, you end up with division by zero when any form of mass reaches the speed of light. This sort of occurence is typically called an unphysical result - meaning it does not actually occur in the physical universe. Objects made of ordinary mass can only travel up to, but not as fast as light. Objects made of imaginary mass [square root of a negative number], could travel at any speed, down to but never as slow as light. So, mathematically, there is no type of mass that can travel precisely at the speed of light. That privelege is strictly reserved for massless particles, which are forbidden to travel at any speed other than light. I suppose in principle you could accelerate ordinary mass up to the speed of light, convert it to photons, then convert the photons to imaginary mass and resume accelerating to your hearts content. Aside from the fact there is no theory to suggest such a conversion is possible, I doubt it would be a pleasant experience. Reassembling reformed particles back into the original configuration would be a quite a task and require a really big computer.
  7. Jan 19, 2005 #6


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    Does the article mention the mass of the plasma blobs in blazars? I mean, I would assume this statement:
    is refering to the rest mass of the blob. At 99.9c, the mass should be many thousands of times greater, shouldn't it?
  8. Jan 19, 2005 #7
    So what would be so simple about measuring the speed of the Concorde if you could only use sound marks to "See" where it was?
    The BOOM you just heard started right next to you and then traveled out and away from you in both directions. You'd need to listen close for a Doppler effect just to figure out which way it was going.

    If there was something to go by us at >c. The "Light boom" from a warp speed ship interacting with space dust would give a light trail extending out in both directions, appearing near us and then going off in two directions.

    For all the looking in space we've done having not seen such an event is partial confirmation of SR on its own. Even if you don't trust the math of SR yet.
  9. Jan 20, 2005 #8
    Layman with a stupid question.

    The article doesn't mention what this near-light velocity is relative to.
    Is going 0.999c wrt the "blazar" or wrt the Earth? Both?

    I understand that light is going c wrt to every frame of reference,
    but what about matter moving close to c?
  10. Jan 21, 2005 #9


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    With respect to earth. The velocity is derived from the observed [from earth] doppler shift.The speed of light is relative to the object in motion and the observer. If another object was traveling in the same direction and speed as the blazar jet, the blazar jet would appear to be stationary to that observer. However, to that observer, just about everything else in the universe would appear to be going darn near the speed of light.
  11. Jan 22, 2005 #10
    This is a good question, since the expansion of the universe complicates things. If the recession velocity of the blazar isn't too great, say 0.3c then it doesn't much matter since using special relativity we get 0.999c-0.3c=0.998c

    However, cosmologists use the proper time of objects moving with the expansion as a time coordinate, leading to a coordinate system which is not consistent with special relativity. In particular, the blazar might be moving away from us at twice the speed light - so if the jet has a relative velocity towards us of 0.999c then what is the resultant velocity?

    In fact it is likely to be blueshifted, as is shown in http://arxiv.org/abs/astro-ph/?0104349, but whether it's moving towards us or away from us is a debatable point. My feeling is that the cosmologist's coordinate system is unsuitable to describe velocities of distant objects. I've discussed this further on my website: http://www.chronon.org/Articles/milne_cosmology.html
    Last edited by a moderator: Apr 21, 2017
  12. Jan 26, 2005 #11
    This is actually wrong. If the particle is moving faster than the speed of light you will see it at point B before you see it at point A!
  13. Jan 26, 2005 #12


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    Any such cosmologists do not understand relativity.
    .999c, if you do the math.
    Not really. Cosmological redshift does not go away that easily.
    What cosmologist's coordinate system are you talking about? Are you saying redshift does not mean distance? If so, please cite examples of high redshift objects observed superimposed in front of lower redshifted objects at Z>1. Even a single, high quality example would be appreciated.
  14. Jan 26, 2005 #13
    The diagram on Ned Wright's website at http://www.astro.ucla.edu/~wright/cosmo_03.htm#MSTD shows the sort of coordinate system in general use by cosmologists. I would say that this wasn't compatible with special relativity because (1) some objects are travelling faster than c and (2) the speed of light is not constant. In fact looking at the red line as a possible light beam, we see it first moving away from us, and then towards us.
    The example I had in mind was of a blazar receding from us, but with a jet coming out of the blazar at 0.999c wrt the blazar. The question is what is the resultant velocity of the jet wrt us. I admit that the original quote had particles moving wrt us at 0.999c, in which case maybe the question should be turned round to ask what velocity they originally had wrt the emitting object.
    The paper quoted shows that such a jet would be blueshifted. I would explain this by saying that the blazar was actually receding from us at less than 0.999c, and so the jet was approaching us. Some would say that the blazar is receding at 2c, so the jet is also receding at 1.001c, and the blueshift is some strange 'cosmological' effect.
    Goodness me, No. I'm saying that I prefer a coordinate system where the upper limit of velocities is c, and the redshift/velocity relation is given by the special relativistic formula.
    Last edited: Jan 26, 2005
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