### The speed of light in a vacuum may not be a constant after all

##### April 25, 2013

Two *European Physical Journal D* papers challenge established wisdom about the nature of vacuum.

In one paper, Marcel Urban from the University of Paris-Sud and colleagues identified a quantum-level mechanism for interpreting vacuum as being filled with pairs of virtual particles with fluctuating energy values.

As a result, the inherent characteristics of vacuum, such as the speed of light, may not be a constant after all, but fluctuate.

**A quantum mechanism**

Meanwhile, in another study, Gerd Leuchs and Luis L. Sánchez-Soto, from the Max Planck Institute for the Physics of Light, suggest that physical constants, such as the speed of light and the impedance of free space (377 ohms), are indications of the total number of elementary particles in nature.

Vacuum is one of the most intriguing concepts in physics. When observed at the quantum level, vacuum is not empty. It is filled with continuously appearing and disappearing particle pairs such as electron-positron or quark-antiquark pairs. These ephemeral particles are real particles, but their lifetimes are extremely short.

In their study, Urban and colleagues established, for the first time, a detailed quantum mechanism that would explain the magnetization and polarization of the vacuum, referred to as vacuum permeability and permittivity, and the finite speed of light. This finding is relevant because it suggests the existence of a limited number of ephemeral particles per unit volume in a vacuum.

**Why the speed of light may not be fixed**

As a result, there is a theoretical possibility that the speed of light is not fixed, as conventional physics has assumed. Instead, it could fluctuate at a level independent of the energy of each light quantum, or photon, and greater than fluctuations induced by quantum-level gravity.

The speed of light would be dependent on variations in the vacuum properties of space or time. The fluctuations of the photon propagation time are estimated to be on the order of 50 attoseconds per square meter of crossed vacuum, which might be testable with the help of new ultra-fast lasers.

Leuchs and Sanchez-Soto, on the other hand, modeled virtual charged particle pairs as electric dipoles responsible for the polarization of the vacuum. They found that a specific property of vacuum called the impedance, which is crucial to determining the speed of light, depends only on the sum of the square of the electric charges of particles but not on their masses.

If their idea is correct, the value of the speed of light combined with the value of vacuum impedance gives an indication of the total number of charged elementary particles existing in nature. Experimental results support this hypothesis.

### References:

- M. Urban et al., The quantum vacuum as the origin of the speed of light,
*European Physical Journal D*, 2013, DOI: 10.1140/epjd/e2013-30578-7 - M. Urban et al., The quantum vacuum as the origin of the speed of light,
*arXiv*, 2013, arxiv.org/abs/1302.6165 - Gerd Leuchs, Luis L. Sánchez-Soto, , A sum rule for charged elementary particles,
*European Physical Journal D*, 2013, DOI: 10.1140/epjd/e2013-30577-8 (open access) - Gerd Leuchs, Luis L. Sánchez-Soto, , A sum rule for charged elementary particles,
*arXiv*, 2013, arxiv.org/abs/1301.3923

## comments 21

June 12, 2016by GatorALLin

so as we send messages to Mars and back to control our rovers or get data on Earth, can’t we test how fast those messages arrive and actually measure the speed of light with real data vs. our assumptions about a vacuum or true vacuum of space? I can appreciate that in a perfect vacuum the max speed of light fits the calculations and in the real word uses must be just a tiny bit slower, and over billions of light years must add up to make a difference. I know that when we posted up atomic clocks on airplanes to test how time may slow down we could prove it, but for an earthling that lives to be 100 years old and flew in a plane at 550 mph 100% of their life, the total measured time vs. a twin on the earth standing still for those same 100 years, would equal about 1/10th of a second, or so little actual time difference it seems silly to try and ponder how this would prove useful for earthlings at slow speeds we seem stuck at. Maybe we can send a few dozen tardigrades to alpha centauri with the Breakthrough StarShot mission and get that up to 20% the speed of light. Anyhow, my real question was how does this change our calculations on how fast the universe may be moving apart by things not locked together with gravity, so as space expands and our calculations on that are best guesses on redshift, then are those calculations all off and by how much?

October 5, 2013by nilesh

Is it possible that we can resolve differences in perception? One new findings has the mathematical details in combinatorial form as calculus cannot be applied in simultaneous time domains where the interval is zero.. Isn’t the reason that space is not recognised and defined as a real continuum containing real components. If that was done then the next logical step would have shown that all manifestation must be a holographic state of those components. These components in space are dynamic as they interactively oscillate at an axiomatic rate of 296575969 cycles per axiomatic cycle of 10 interactions. isn’t it tru that two such components oscillate together or simultaneously the rate density increases and appears as a holographic phenomena ? Numerical axioms derived Space comprises components (real elemental matter) at a critical density of 3.6 E minus 25 kgs/ cu. m. The components are in a dynamic interactive state of perpetual harmonic oscillations at a stress frequency of 2.965E +8 cycles/ sec with a1 meter wavelength. It is axiomatic and constant. When due to acceleration the stress frequency increases the formation of particles with mass occurs. At a mass of 9.5 E minus 35 kgs (Neutrino) it starts to become detectable and at 6.6 E minus 34 kgs it forms a quanta as a light and then on is visible. Light and Neutrinos are stress holograms on the basic dynamic components. That is why two opposing light waves do not collide and get destroyed/ Holograms change forms only. So a galaxy at boundary in Neutrino states and becomes light photons as density increases towards its center (by compression) . Pls investigate & explore further http://www.kpaillavastu.com

July 1, 2013by timeless

If Einstein said clockspeed is based on the speed of light, and the speed of light is subject to random quantum fluctuations, then doesn’t that mean that time is subject to random fluctuations? Doesn’t that mean that there is some finite probability that time will slow down by any imaginable amount? Maybe even stop?

That’s randomness in physics. Check out my paper for a hint of randomness in mathematics.

July 1, 2013by Editor

And what is your paper?

July 1, 2013by timeless

The paper is on a formula to find the nth prime that makes use of the randomness in the primes. The paper is being hosted by William Stein at the University of Washington in Seattle.

http://tiny.cc/randompi

April 27, 2013by Ray Fleming

This is good work but they have still failed to identify the physical mechanism, as permeability alone does not explain the real physical mechanics.

The virtual dipoles of the quantum vacuum interact with each other producing van der Waals forces. In this case it is the van der Waals torque of the vacuum that inhibits the rotation of the photon’s electric field, thus giving light a maximum velocity in a vacuum and slower velocities in regions of space where the torque is greater, such as within bodies of transparent matter and near large bodies of matter. We should be able to derive the speed of light from first principles by calculating the van der Waals torque of the vacuum.

Einstein’s assumption that the speed of light is constant between all observers is false. The speed of light changes due to the van der Waals torque of the local vacuum, and space is not dilated or curved. The speed of light is only constant in a perfect vacuum and only when measured relative to the zero point field rest frame (which is the same as the CBR rest frame).

April 26, 2013by Dirk Bruere

“per square meter”?

April 26, 2013by denis

To DougW:

If we have a 3+ dimensional space and virtual particles are considered as real particle crossing our 3D *slice* and the extra dimensions are not compactified at plank scale then there are some questions:

1) Why the distribution of time that any virtual particle spends in our particular 3D slice is not uniform but is rather limited to very short times?

2) The real-virtual particle should have mass and charges so they should interact with particles sticked to our 3D slice and we could detect it

3) The extra dimensions should have effect on the way the field potentials are spreading from the source of charge, so if there are extra dimensions the force of gravity and EM fields should decay faster

But if we consider the extra dimensions as compactified manifolds then we are talking string theory.

April 25, 2013by Sanjeev Sabhlok

I invite your attention to my amateur comments here, for whatever these are worth: http://sabhlokcity.com/2013/04/evidence-that-observed-photons-could-be-self-selected-so-we-incorrectly-imagine-fixed-speed-of-light/

April 25, 2013by ProfessorZ

Does this mean if a photon could somehow avoid or clear the particle pairs ahead of it as it travels through vacuum, would there be no limit to its speed?

It still wouldn’t be faster-than-light travel, but at least we could have faster-than-light communication.

April 25, 2013by Derek

Well, if we eventually develop the capability of disassembling a person and storing all the relevant information in computer memory, we could then beam that data to a receiver on a distant world, which could then use that information to reassemble the person exactly as he was. Thus…faster-than-light travel.

July 1, 2013by Ian Clarke

But that still doesn’t help us physically expand into the universe at or above c when we’re busy turning dumb matter into computronium. That is, unless we can remotely manipulate matter by the mere use of communications (i.e. remote creation of self-replicating nanobots by means of ≥SoL matter manipulating tunnelling data streams).

Possible? :)

April 25, 2013by DougW

How can it be that even in light of now-known facts such as vacuum space being “filled with continuously appearing and disappearing particle pairs” we still have scientists denying the existence of additional dimensions? WHERE DO THEY THINK THESE PARTICLES ARE COMING FROM??? Any simple model of 4+ dimensional space would inherently include particles that move ‘through’ the particular dimension we inhabit, thus seemingly ‘appearing and disappearing’ as described (think of our universe as a 2-dimensional sheet of glass in a 3-D universe, photons would seeming ‘appear’ and ‘disappear’ as they move through this universe…).

April 25, 2013by Giulio Prisco

Doug, no scientist denies the utility of additional dimensions to build better models of reality. We have phase spaces with dimension 6 times the number of particles in a system since Hamilton, and there are plenty of theories with extra dimensions “rolled up” on a quantum scale. Some theories have infinite dimensions.

Mathematical models with extra dimensions are generally accepted, and produce experimentally valid results. As a positivist I prefer to stop at the models without thinking of”ultimate realities” beyond the models.

April 25, 2013by Giulio Prisco

By analogy with the speed of light in a medium, the speed of light in vacuum should depend on something, and the quantum scale microstructure of the fabric of spacetime is the obvious candidate.

On the other hand, most of today’s fundamental physics depends on the speed of light in vacuum being a constant, so even small variations would require radical changes in physical theories.

Deviations from the value of c may be smaller than what we have been able to measure so far, and it will be interesting to watch for attempts to validate this theoretical result experimentally.

Perhaps c, the constant that appears in most of the equations of fundamental physics, is really the speed of light in an idealized, very void vacuum, away from all strong fields including gravity (readers of Egan’s Schild’s Ladder will be familiar with this concept) and not realized in the pedestrian forms of vacuum accessible to us. Based on this I would predict that the real speed of light in vacuum is always less than c.

April 25, 2013by DougW

The speed of light in a vacuum can still be constant if you expand the definition of vacuum to include more than the dimensions we can currently measure. What these experiments may actually be telling us is that what we think of as vacuum is often only ‘empty’ in our specific perceivable value of an additional dimension. There may well be matter close enough to impact the speed of light, but located in a place where we can not perceive it. Again, how does one explain ‘particles appearing and disappearing’, a pretty direct violation of several major laws, including the supposedly irrefutable 2nd law of thermodynamics? The obvious answer is that this matter was already there, just in a state which we could not detect, and it ‘moved’ to a state we could detect. The 2nd law is preserved by the redefinition of the ‘closed system’ that includes these appearing/disappearing particles…

April 25, 2013by Cloudswrest

“By analogy with the speed of light in a medium, the speed of light in vacuum should depend on something”

True, but so does the size of atoms and molecular bonds, etc. For example, if the permittivity went up, the speed of light would go down, but Coulumb’s constant would go up and atoms would get smaller, so light would take less time to cross the atom … The point I’m getting at is it doesn’t matter if the vacuum speed of light varies. Whatever it is our existence is normalized in terms of it, so it always looks the same to us locally.

April 25, 2013by Ralph Dratman

Objects in vacuum are closer than they appear.

April 25, 2013by Eric Balingit

I have held the notion for several years that matter is nothing more than knots tied in empty space, as though the bending of space through different dimensions creates fields that either attract, repel or have no effect on each other, and as such, these fields can be rendered into configurations that get ‘stuck’ or do not easily come untied – particles – where as waves are of course propagating fluctuations in the space metric. If space is bent, or stretched, as in the quantum flux, then it makes sense that light, a form of bending or perhaps knotting, would travel more slowly through it, following the convoluted shape of the space it travels through, interacting with that shape along the way.

June 7, 2013by Penny St. James

I also had that intuition after reading about string theory and the extra curled up dimensions.

April 25, 2013by Khannea Suntzu

The universe may not be a smooth expanding medium. The cosmos may in fact me as turbulent as a river on the macro macro level. We may simply have a skewed perspective because we are still jostling about after we just tumbled down the waterfall.