Speed of individual photons cannot exceed speed of light in a vacuum

On 27/07/2011 12:16 PM, dlzc wrote:
I'm wondering if individual photons do exceed the speed of
light, but we just don't detect them as they get filtered out
by the direction of time? That is to say that time polarizes
the photons.

Quantum mechanics has "real propagating" photons as a series of
virtual photons. So maybe the question is moot.

I've always been a little puzzled by this statement. What is the
difference between virtual photons and real ones? Aren't all virtual
photons real at some point? Is it just the amount of time that they are
in existence before being terminated?


Yousuf Khan

On Jul 26, 12:07*pm, Yousuf Khan wrote:
BBC News - Time travel: Light speed results cast fresh doubtshttp://www.bbc.co.uk/news/science-environment-14289114

"Now, a paper in Physical Review Letters shows that individual photons
too are limited to the vacuum speed limit.

That means that photons maintain the principle of causality laid out in
Einstein's theory of special relativity - that is, an event's effect
cannot precede its cause by traveling faster than light. It is violation
of this causality that would, in principle, permit time travel.

While the limit in vacuum is a fixed number - some 300,000km per second
- the speed of light can vary widely in different materials. "

Well, that will hold forever on Earth, since it's a circular
definition of cause,

Bu, whether it holds in advanced alien science it a different
question.

On Jul 26, 9:07*am, Yousuf Khan wrote:
BBC News - Time travel: Light speed results cast fresh doubtshttp://www.bbc.co.uk/news/science-environment-14289114

"Now, a paper in Physical Review Letters shows that individual photons
too are limited to the vacuum speed limit.

That means that photons maintain the principle of causality laid out in
Einstein's theory of special relativity - that is, an event's effect
cannot precede its cause by traveling faster than light. It is violation
of this causality that would, in principle, permit time travel.

While the limit in vacuum is a fixed number - some 300,000km per second
- the speed of light can vary widely in different materials. "

If the speed/velocity of light speeds up with having less medium, then
what's holding our photons back at merely the dull roar of 300,000 km/
sec? (which is kinda slow)

http://translate.google.com/#
Brad Guth, Brad_Guth, Brad.Guth, BradGuth, BG / “Guth Usenet”

On Jul 26, 2:49*pm, Sam Wormley wrote:
On 7/26/11 11:07 AM, Yousuf Khan wrote:

BBC News - Time travel: Light speed results cast fresh doubts
http://www.bbc.co.uk/news/science-environment-14289114

Experiment shows time travel impossible
* *http://www.abc.net.au/science/articl...25/3277064.htm

Hong Kong physicists say they have proved that a single photon obeys
Einstein's theory that nothing can travel faster than the speed of
light, demonstrating that time travel is impossible.

See:http://www.abc.net.au/science/articl...25/3277064.htm

So what's filling up the IGM that's keeping our photons down to only
300,000 km/sec?

Obviously the IGM isn't nearly as empty as we've been told. So why
don't you start earning your keep by telling us what's out there?

http://translate.google.com/#
Brad Guth, Brad_Guth, Brad.Guth, BradGuth, BG / “Guth Usenet”

On 7/27/2011 1:31 PM, Yousuf Khan wrote:
On 27/07/2011 12:16 PM, dlzc wrote:
I'm wondering if individual photons do exceed the speed of
light, but we just don't detect them as they get filtered out
by the direction of time? That is to say that time polarizes
the photons.

Quantum mechanics has "real propagating" photons as a series of
virtual photons. So maybe the question is moot.

I've always been a little puzzled by this statement. What is the
difference between virtual photons and real ones? Aren't all virtual
photons real at some point? Is it just the amount of time that they are
in existence before being terminated?

It's a legitimate question, although I would invite you to turn around
the statement a little to say that all real photons are in fact virtual.
Virtual photons can be reasonably be characterized as off mass-shell.
This just shifts the question to be, how far off mass-shell do you have
to be to be considered off mass-shell? Any particle with a finite
lifetime (as ANY detected photon necessarily is) therefore exhibits an
energy (and hence an invariant mass) spread, due to the uncertainty
principle.

It really is a matter of degree, or if you like, an arbitrary boundary.

On 7/27/2011 3:14 PM, Brad Guth wrote:


So what's filling up the IGM that's keeping our photons down to only
300,000 km/sec?


It's worse than that. In units that make physical sense, the speed of
light is 1.

It's one because there is a finite speed limit, and 1 is the most
natural finite number. Which number would you think would be more
appropriate than 1?

If you're asking why there is ANY finite speed limit at all, and why the
speed of light can't be infinite, the answer is that *all* causal
connections are bound by the structure of spacetime to be within a cone
of slope 1.

On 7/27/11 11:16 AM, dlzc wrote:
Quantum mechanics has "real propagating" photons as a series of
virtual photons. So maybe the question is moot.

David A. Smith


David, is some accessible material for the layman concerning
"real propagating" photons as a series of virtual photons?

Thanks,
-Sam

On 7/27/11 3:09 PM, Brad Guth wrote:


If the speed/velocity of light speeds up with having less medium, then
what's holding our photons back at merely the dull roar of 300,000 km/
sec? (which is kinda slow)



Brad, throw away the concept of medium, or at least replace it
the the "fabric" of space-time.

On 7/27/2011 4:28 PM, Sam Wormley wrote:
On 7/27/11 11:16 AM, dlzc wrote:
Quantum mechanics has "real propagating" photons as a series of
virtual photons. So maybe the question is moot.

David A. Smith


David, is some accessible material for the layman concerning
"real propagating" photons as a series of virtual photons?

Thanks,
-Sam


I think David is simply pointing out that what we observe in reality are
not bare particles but "dressed" ones. That is, the measured properties
of these particles (like the anomalous magnetic moment of the muon, for
example) do not jive with calculations unless those calculations treat
them as dressed ones. Dressed particles necessarily include loop
contributions, where the original particle disappears, is replaced by a
virtual particle-antiparticle pair, and then the pair annihilates to
produce another particle like the first. Thus, the real, dressed
particle is at least to some order a series of virtual particles
interspersed by loops.

On 7/27/11 4:34 PM, PD wrote:
On 7/27/2011 4:28 PM, Sam Wormley wrote:
On 7/27/11 11:16 AM, dlzc wrote:
Quantum mechanics has "real propagating" photons as a series of
virtual photons. So maybe the question is moot.

David A. Smith


David, is some accessible material for the layman concerning
"real propagating" photons as a series of virtual photons?

Thanks,
-Sam


I think David is simply pointing out that what we observe in reality are
not bare particles but "dressed" ones. That is, the measured properties
of these particles (like the anomalous magnetic moment of the muon, for
example) do not jive with calculations unless those calculations treat
them as dressed ones. Dressed particles necessarily include loop
contributions, where the original particle disappears, is replaced by a
virtual particle-antiparticle pair, and then the pair annihilates to
produce another particle like the first. Thus, the real, dressed
particle is at least to some order a series of virtual particles
interspersed by loops.

Thanks PD.
-Sam