Science
Related: About this forumNew Studies Suggest the Speed of Light is Variable
According to the Alpha Galileo Foundation, Two new studies slotted for publication in the European Physical Journal D demonstrate that the speed of light is actually variable. The authors of the studies include March Urban of the University of Paris-Sud, along with Gerd Leuchs and Luis L. Sanchez-Soto from the Max Planck Institute for the Physics of Light in Erlangen, Germany.
A major part of the discussion in both studies is the nature of a vacuum, which on a quantum level is not, as most believe, empty. Rather, it is filled with the particle pairs.
First, Urban and his team propose that there are in fact a limited number of particle pairs including electron-positron or quark-antiquark pairs within a vacuum. This opens the possibility that the speed of light can then fluctuate at a level independent of the energy of each light quantom or photon. In other words, the speed of light would depend on the vacuum properties of space and time.
In their study, Leuchs and Sanchez-Soto found that variations in the speed of light can reveal the number of charged elementary particles in any given space. If correct, the value of the speed of light can then be combined with the value of vacuum impedance in order to determine the total number of charged elementary particles that exist in nature.
http://www.natureworldnews.com/articles/1010/20130325/speed-of-light-variable.htm
longship
(40,416 posts)The earth really is 6,000 years old!! The literal truth of the Bible is vindicated by science!
A variable speed of light falsifies all of biology and all of any other physics so we get to make up any shit we want!
Furthermore, Hitler thought the speed of light was constant!!!!!!
You see! The inevitable Conservapedia entry writes itself. No intelligence or education required (only being the evil spawn of Phyllis Schlafly).
Demo_Chris
(6,234 posts)Dragonbreathp9d
(2,542 posts)loudsue
(14,087 posts)bananas
(27,509 posts)The article in the OP didn't have a direct link to the alphagalileo article so I searched for it.
Ephemeral vacuum particles induce speed-of-light fluctuations
25 March 2013 Springer Science+Business Media
New research shows that the speed of light may not be fixed after all, but rather fluctuates
<snip>
Full bibliographic information
M. Urban et al. (2013), The quantum vacuum as the origin of the speed of light, European Physical Journal D, DOI 10.1140/epjd/e2013-30578-7
Gerd Leuchs and Luis L. Sánchez-Soto (2013), A sum rule for charged elementary particles, European Physical Journal D, DOI 10.1140/epjd/e2013-30577-8
bananas
(27,509 posts)Jim__
(14,077 posts)The speed of light is usually given as a linear measure. From the paper cited in the OP:
Is that because the light is not actually travelling through a true vacuum and so the wave properties of light have to be accounted for in the distance that the light is traveling?
caraher
(6,278 posts)The actual claim reads,
?_T ? 5 10^?2 (fs) (m)^?1/2
In other words, in their model they estimate the fluctuation in the time it takes for a photon to transit a distance L varies with with the square root (not the square) of the distance. So there would be a fluctuation whose standard deviation is 50 attoseconds for a photon traversing 1 m, 500 attoseconds over a 100 m distance, etc.
Jim__
(14,077 posts)caraher
(6,278 posts)A sum rule for charged elementary particles
Lobos Motl is pretty steamed about the hype both papers receive and dismisses them both as crackpot nonsense.
Jim__
(14,077 posts)Maybe if I knew who Lobos Motl was, I would know better than to ask. But, I don't, so ... I have some specific questions about the paper on the speed of light.
About that paper, Motl says:
The paper is proposing that their model can be empirically tested:
We show that the vacuum permeability ?0 and permittivity
?0 may originate from the magnetization and the polarization of continuously appearing and
disappearing fermion pairs. We then show that if we simply model the propagation of the photon in vacuum as a
series of transient captures within these ephemeral pairs, we can derive a finite photon velocity. Requiring
that this velocity is equal to the speed of light constrains our model of vacuum. Within this approach,
the propagation of a photon is a statistical process at scales much larger than the Planck scale. Therefore
we expect its time of flight to fluctuate. We propose an experimental test of this prediction
So Motl is saying that the speed of light is tautologically constant. The authors say that the vacuum is not really
empty causing a statistical variance to the speed of light through a vacuum. If the instruments exist, it would seem
that this could be tested. If the paper is right, then the definition of a meter would have to be adjusted. If the
variance in the speed of light is due to interaction between photons and these particles, does this have any
implications for the Theory of Relativity?
This is what I get from reading the different articles and not understanding the physics of it all.
caraher
(6,278 posts)I haven't done more than skim them, so it's fair to say that I wouldn't condemn them in the terms Lubos does. Yet.
Lubos Motl is an interesting character. He's a former Harvard faculty member and string theorist with utterly abhorrent politics. He definitely has the training to evaluate this work; at the same time, he never lets the facts stand in the way of boldly pronouncing his opinion (as in his skepticism regarding global climate change).
caraher
(6,278 posts)I agree with Lubos. While they talk about deriving electromagnetic properties of the vacuum from quantum theory and some basic information about fermion properties, the paper reflects a very peculiar understanding of both basic quantum mechanics and classical electrodynamics, and basically ignores the most successful theory in physics, quantum electrodynamics.
For example, the authors suggest there is something counterintuitive about the fact that a parallel-plate capacitor with a vacuum between the plates has a finite, rather than zero, capacitance. They claim that the only way to explain this nonzero capacitance is through polarization of the vacuum:
This is almost complete nonsense! They do give a qualitatively decent explanation of why inserting a dielectric material between the plates of a capacitor does increase the capacitance; however, it is utterly false that the capacitance would go to zero in the absence of a material between the plates.
There are many elementary mistakes of this nature in the paper. It's rubbish.
caraher
(6,278 posts)They don't even do the basic math correctly on their experimental test proposal. Yes, the standard deviation for the jitter in propagation time, under their theory, for 30 round-trips in a 100 m evacuated tube would be about 4 fs. But if you are using a 9 fs duration pulse and randomize the travel times via a process whose spread is about 4 fs, you estimate the broadening of the pulse not by the sum of those two times but by adding them in quadrature (that is, by taking the square root of the sum of the squares). So leaving aside some more fussing about the difference between full width at half maximum (the usual way of talking about short pulses) and the standard deviation of a distribution of times, the effect would be to take a 9 fs pulse and make it more like sqrt(9^2 + 4^2)=sqrt(97)=9.8 fs, not 13 fs.
The reason you have to add in quadrature is that whether a given photon in the pulse arrives earlier or later would be random for each photon in the pulse, whether it's in the leading edge or trailing edge of the pulse. Some of the early photons will be delayed and some of the late photons will arrive earlier than expected. Their calculation would be accurate if the leading edge photons always arrived sooner than they would without this broadening and the trailing photons were always delayed.
Jim__
(14,077 posts)dimbear
(6,271 posts)Bound to be cited soon.
Fantastic Anarchist
(7,309 posts)I remember reading several theories on VSL 15 years ago. I especially remember a bright new physicist who came up with his own - can't remember his name - he was from Portugal, if I recall.
caraher
(6,278 posts)You're probably thinking of Joao Magueijo who wrote "Faster than the Speed of Light"
It's a very entertaining read, as much for his critique of how theoretical physics functions as a profession as for the theories he describes.
The difference is that Magueijo knows what he's talking about. These folks seem to be very naive, at best, in their approach.
Fantastic Anarchist
(7,309 posts)Thanks for the link.
Wounded Bear
(58,670 posts)that the density of the universe (the "vacuum of space" is variable. It has long been shown how the SOL varies in differing media.
I don't see how this shows a variation in the basic SOL.
caraher
(6,278 posts)You have a good approach to thinking about this, but I think there's even less to it than meets the eye. In one of the papers it's clear that their model include no "bare" speed of light. Instead, they posit that the propagation time of light consists of something like the sum of the lifetimes of all the virtual particles one might expect to encounter along a light beam's path.
The conventional way of talking about this, that you've picked up on, would still result in the speed of light equal to "c" in the limit of taking the density of your medium to zero. The usual index of refraction arises from the interaction of light with real particles (with virtual particles coming into the picture only in the sense that those interactions can be described by QED). And you never get light traveling faster than c.
By contrast, in this work, the transit time for light has a random element, and can be either faster or slower than c.