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Speed of Light May Not Be Constant


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#1    Render

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Posted 30 April 2013 - 08:34 AM

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The speed of light is constant, or so textbooks say. But some scientists are exploring the possibility that this cosmic speed limit changes, a consequence of the nature of the vacuum of space.
The definition of the speed of light has some broader implications for fields such as cosmology and astronomy, which assume a stable velocity for light over time. For instance, the speed of light comes up when measuring the fine structure constant (alpha), which defines the strength of the electromagnetic force. And a varying light speed would change the strengths of molecular bonds and the density of nuclear matter itself.
A non-constant speed of light could mean that estimates of the size of the universe might be off. (Unfortunately, it won't necessarily mean we can travel faster than light, because the effects of physics theories such as relativity are a consequence of light's velocity). [10 Implications of Faster-Than-Light Travel]

http://www.livescien...t-constant.html

Edited by Render, 30 April 2013 - 08:35 AM.


#2    Frank Merton

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Posted 30 April 2013 - 08:48 AM

We already know that the speed of light changes in a medium other than vacuum.  What we are seeing here is the possibility that it also changes in different "kinds" of vacuum.  (It now being known that a vacuum is not at all what the ordinary person thinks it is).  I also read the bit about how this could influence estimates of the size of the universe, but have to think this is some journalist writing about stuff he knows not about.  What does "the size of the universe" mean?


#3    Render

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Posted 30 April 2013 - 09:15 AM

View PostFrank Merton, on 30 April 2013 - 08:48 AM, said:

We already know that the speed of light changes in a medium other than vacuum.  What we are seeing here is the possibility that it also changes in different "kinds" of vacuum.  (It now being known that a vacuum is not at all what the ordinary person thinks it is).  I also read the bit about how this could influence estimates of the size of the universe, but have to think this is some journalist writing about stuff he knows not about.  What does "the size of the universe" mean?

I think the journalist hints at something worth thinking about ... that you are overlooking because you do not understand.
Expansion of the universe holds in it the observation that galaxies are moving further away from us and each other, at a certain speed.
The Hubble constant tells us that for every megaparsec of distance between two galaxies, the apparent speed at which the galaxies move apart from each other is greater by 71 kilometers per second.
Since we know that the speed of light is around 300,000 kilometers per second, you can calculate how far away two galaxies must be in order to be moving away from each other faster than the speed of light.
If the speed of light is not constant this throws a curveball in the calculations. So maybe they're wrong at how fast inflation is happening and also how far along this inflation is.


#4    Frank Merton

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Posted 30 April 2013 - 10:21 AM

What you are talking about is not "the size of the universe."  That is the expression I object to.  I doubt that there is any such thing.  We can talk about the size of the "observable universe" if you want, and a change in the C would probably effect our measurement of that, but not of the universe as a whole.

You also misuse the term "inflation."  What is going on now is the expansion of space-time at a reasonable moderate rate that allows things like galaxies to form.  "Inflation" is used for a very early exponential expansion of space-time that in an extremely short time blew the initial universe up to something unimaginable.


#5    sepulchrave

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Posted 30 April 2013 - 04:19 PM

This seems a bit suspect to me. A preprint of the first paper is available on arXiv, the second paper is open access.

I definitely agree with Jay Wacker's statements at the end of the original article; I also think that Feynman diagrams are the correct way of talking about vacuum fluctuations, not the approach the authors used.

View PostFrank Merton, on 30 April 2013 - 08:48 AM, said:

We already know that the speed of light changes in a medium other than vacuum.  What we are seeing here is the possibility that it also changes in different "kinds" of vacuum.  (It now being known that a vacuum is not at all what the ordinary person thinks it is).
This is what the authors are saying, but I don't see how this is relevant.

The ``speed of light'' is presumably in the same category as the ``bare rest mass'' or ``bare charge'' of a particle. Because of fluctuations in the quantum vacuum (or the material the object is propagating through) the ``bare rest mass'' and ``bare charge'' cannot be measured directly. Rather the sum influence of the various fluctuations is incorporated into the renormalized mass and charge.

I assume the same could be true of the speed of light, but I think the ``bare speed of light'' is still the critical theoretical parameter, just like the ``bare rest mass'' and ``bare charge'' are critical for calculating the behaviour of a particle in an arbitrary situation.

So the ``bare speed of light'' is the relevant constant; if that changed over time or space it would affect ``the physics''. But I think the ``renormalized speed of light'' in a particular vacuum would be no more significant than the speed of light in, say, glass.

View PostFrank Merton, on 30 April 2013 - 08:48 AM, said:

I also read the bit about how this could influence estimates of the size of the universe, but have to think this is some journalist writing about stuff he knows not about.
I agree with you here, I couldn't find any discussion about that in the actual papers either.


#6    keithisco

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Posted 30 April 2013 - 08:43 PM

What i find interesting is that the the paper is quite open about the Caveats contained within it. It impresses with the fact that the Summations are only estimations (and suggests that several particle - anti particle pairs in excess of 58GeV are yet to be discovered) and therefore greater fidelity can be obtained only through greater fundamental physics experimentation.

Inferred is also the modelled result that Quantum Vacua does not exist (just as physical vacuum does not exist) and that the fundament on which the Speed of Light is based is in fact, incorrect because the requirements for a vacuum is not sufficiently well described.

Overall a very good paper but lacking in Fidelity


#7    Babe Ruth

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Posted 01 May 2013 - 12:25 PM

How does the knowledge gained from the Hadron collider effect this?

I read that the validty of the Higgs boson among other things means that there is no longer a mathematical restriction on exceeding the speed of light.  Does that sound right?


#8    sepulchrave

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Posted 01 May 2013 - 03:47 PM

View PostBabe Ruth, on 01 May 2013 - 12:25 PM, said:

How does the knowledge gained from the Hadron collider effect this?
I don't think it does.

View PostBabe Ruth, on 01 May 2013 - 12:25 PM, said:

I read that the validty of the Higgs boson among other things means that there is no longer a mathematical restriction on exceeding the speed of light.  Does that sound right?
It doesn't sound right to me. Whether or not the Higgs mechanism is the correct explanation of why some particles have mass (and technically, only inertial mass) shouldn't have any bearing on the wave propagation speed in a medium.


#9    keithisco

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Posted 01 May 2013 - 09:29 PM

I do not see any difference between inertial mass and passive - active gravitational mass. Why is this important?


#10    sepulchrave

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Posted 01 May 2013 - 11:23 PM

View Postkeithisco, on 01 May 2013 - 09:29 PM, said:

I do not see any difference between inertial mass and passive - active gravitational mass. Why is this important?

Inertial mass is the property of an object that resists changes in motion, i.e. in the equation F = ma.

Gravitational mass is the property of an object that reacts to gravitational force, i.e. the ``gravitational charge'' analogous to ``electric charge''.
Active gravitational mass is the property of an object that can generate a gravitational field, passive gravitational mass is the property of an object that can respond to a gravitational field.

Classical gravitational force is exactly analogous to electric force, so for two objects with passive gravitational masses p1, p2, active gravitational masses q1, q2, and inertial masses m1, m2 separated by a distance r with the appropriate scaling factor k, the forces and accelerations of each object (a1, a2) will be:

Force experienced by object 1 in response to object 2:

F12 = k p1q2 r-2 = m1a1

Force experienced by object 2 in response to object 1:

F21 = k q1p2 r-2 = m2 a2


(Actually we don't even need to know the equation for the force, we can just write some arbitrary force F12(p1,q2) without given an explicit expression.)

Now if Newton's laws of motion are correct, we expect F12 = F21, and therefore p1 = q1, and p2 = q2; i.e. active gravitational mass and passive gravitational mass are identical.

And if the equivalence principle is correct, we expect m1 = q1 = p1.

Certainly it seems that the gravitational masses and inertial masses are identical, and it makes a good deal of theoretical sense for it to be this way.

But experimental tests have been done in the past and will continue to be done (as equipment gets better) to see if there are any discrepancies.

Your comment is very topical because there is another thread about whether antimatter exerts ``negative gravity''; in this case it doesn't really sense to have negative inertial mass, because then the object has negative kinetic energy (in some derivations, anyway). So I expect if antimatter exerts ``negative gravity'', it is because in that case q = p = -m.

--------- EDITED TO ADD:
I also think it is important to distinguish inertial mass from gravitational mass in terms of the Higgs boson because the Higgs mechanism does not explain where gravity comes from (or why it exists).

The Higgs mechanism imbues some bosons and fermions with mass in a solely kinetic sense.

Now I am fairly sure the equivalence principle is correct, and therefore the inertial mass created by the Higgs field is intimately linked with gravity, but so far there is absolutely no theoretical connection between the two.

The discovery of the Higgs boson, and the subsequent verification of the Higgs mechanism, explains why particles have mass. It does not explain why massive particles have gravity. Sometimes this distinction is lost on people.

Edited by sepulchrave, 01 May 2013 - 11:27 PM.


#11    third_eye

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Posted 02 May 2013 - 09:10 AM

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(Actually we don't even need to know the equation for the force, we can just write some arbitrary force F12(p1,q2) without given an explicit expression.)


can I have a cupcake instead ?
:blush:


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It does not explain why massive particles have gravity. Sometimes this distinction is lost on people.

... but now is found ... thanks :tu:

Edited by third_eye, 02 May 2013 - 09:11 AM.

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dancing in the ebb and flow of attention, more present than the breath, I find the origins of my illusions, only the dreamer is gone ~ the dream never ends
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#12    Zeta Reticulum

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Posted 03 May 2013 - 08:48 AM

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"Einstein showed that Newton's theory of gravity is flawed and incomplete, e.g. gravity is not a force, but rather a curvature of space-time which bends the paths of zero-mass photons. Is Einstein's Theory of Relativity also flawed and incomplete? Einstein's theory says nothing about the relation of quantum mechanics to gravity. It does not explain the underlying unity of all forces. It does not acknowledge or explain the reality of dark matter. So, be wary of all those who say that travel faster than the speed of light is impossible because of Einstein's theory. Einstein was not an all-knowing god, and his theory is not the final word on reality. He claimed, most would now say wrongly, that quantum mechanics with its probabilistic underpinning is flawed because "God does not play dice with the universe."

So, if we continue to experiment with Higgs bosons and the Higgs field, some physicist yet unborn may gain enough insight to develop a new theory which shows that Einstein's original theory is flawed and incomplete just like Newton's. The probability is high that such a new theory will allow for faster than light space travel. We know so very little about how the universe is truly put together."

Source: http://answers.yahoo...06221935AAoEVAp

Edited by Waspie_Dwarf, 03 May 2013 - 10:15 AM.
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