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Relativistic velocities of uncharged particles 
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#1
Jan1406, 08:22 PM

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Since relativity theory requires that the value of c be the same for all observed physical processes regardless of relative velocity, it seems reasonable to hypothesize that matter that has no electromagnetic interaction with the rest of the universe may be accelerated to arbitrarily high velocities. Examples of such matter are neutrons and neutron stars, and hypothetical causes of superlight speeds might be the gravitational force exerted by a supermassive black hole.
Is there anything about relativity theory that is inconsistent with this hypothesis? Testing it would probably be difficult, since all pertinent matter would necessarily be "dark". I presume the prevailing assumption is that relativity theory applies to all matter, but if that assumption were lifted for eletrically neutral particles, would it allow for a selfconsistent mathematical model of black hole merger? 


#2
Jan1406, 08:49 PM

P: 932

Firstly, it's not only the electromagnetic interaction that propagates at the speed of light  all information has the maximum speed c, and so we expect all interactions to be limited by this speed.
The special theory tells us that all massless objects must necessarily move at this maximal speed in all reference frames. All other objects can move at various speeds less than this, depending on the reference frame. 


#3
Jan1506, 01:04 AM

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Neutrinos undergo no electromagnetic interactions at all, only weak interactions. However, they have never (to my knowledge) been observed to travel faster than [itex]c[/itex]. 


#4
Jan1506, 02:01 AM

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Relativistic velocities of uncharged particles
Relativity says that *all* particles obey the Lorentz transform, not just particles that interact electromagnetically. 


#5
Jan1706, 02:16 AM

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#6
Jan1906, 02:41 AM

P: 30

Hi everybody! I'm very new to this forum but I have read almost all of the posts and I find the discussion here very interesting, although I don't understand some of it ;)
My question, or better doubt is about the possibilities of detection of velocities grater then “c”. If a body travels with v > c is it possible to detect it? I think that it is not. I think that such a body doesn’t exist for us. For instance  if you send a light signal towards a body which is traveling with v>c the signal will never reach this body – the body will never detect the signal! So, maybe there are particles that travel with speeds greater than “c” but we are not able to detect them? Sorry about my English Sheyr 


#7
Jan1906, 05:21 AM

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No. For example: you see the flash of a Supernova in visible light, and at the same time you detect a flash of neutrinos. Both sorts of particles obviously traveled the same distance in the same time. So they must travel at the same speed.



#8
Jan1906, 10:24 AM

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P: 8,147

But there is a possible exception; If the mass of a particle is a complex number, it can consistently move faster than light. In fact it must travel faster than light; trying to slow down to c gives exactly the same energygoingtoinfinity condition that trying to speed up to c does for realmass particles. So particles with [tex]m^2 < 0[/tex] entered physical theory and were dubbed tachyons, from a Greek word for fast. Subsequently the tachyon has had a checkered history in string theory; first they turned up and weren't wanted, then physicists found how to get rid of them and were happy, then they turned up again at a deeper level (string field theory) and by this time physicists knew how to deal with them and accepted them. They are theorized to collapse the vacuum to a lower energy state. But all this is PURE THEORY! Tachyons have NEVER been observed. 


#9
Jan1906, 10:52 AM

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It is also true that "seeing" something is not the only way of detecting it. If there were an object moving directly away from us, faster than light, we could detect it through its effect (gravitational for example) on other objects. (Your English is excellent far better than my {put language of your choice here}.) 


#10
Jan1906, 01:11 PM

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#11
Jan1906, 08:35 PM

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If something with positive mass hypothetically moved with a velocity faster than c, and hypothetically gravity waves propagated faster than c, then the only method of observing such a thing would be by its gravitational influence, e.g. one black hole on another black hole on a third thing that emits radiation (which we could conceivably detect with current instrumentation). 


#12
Jan1906, 09:07 PM

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P: 6,246

A measurement was done a fewof years ago by Fomalont and Kopeikin when a quasar passed behind Jupiter. Fomalont and Kopeikin claimed that this experiemnt showed that the speed of light and and the speed of gravity are the same. Clifford Will disagreed, saying that Fomalont and kopeikin's experiment didn't actually measure the speed of gravity. In general relativity, the speed of gravity and the speed of light are the same, so an alternative to general relativity is needed to even talk about a difference. Steve Carlip has written a nice paper on this. The interpretation of what was measured depends on the which (class of) alternatives is used. This is subtle stuff, and one of Carlip's conclusions is that for a certain class of models that have different speeds for gravity and light, measurements have yet to reach the sensitivity required to measure the difference. Regards, George 


#13
Jan2106, 03:34 AM

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#14
Jan2106, 03:55 AM

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#15
Jan2106, 07:21 AM

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Zz. 


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