# Speed of Light in a Vacuum is Variable **URL:** \ **Category:** Factual Questions\ **Created:** [March 25, 2013, 8:44pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946 "2013-03-25T20:44:38Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![barbitu8](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@barbitu8](https://boards.straightdope.com/u/barbitu8)\ **Post date:** [March 25, 2013, 8:44pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/1 "2013-03-25T20:44:38Z")
> **[New Studies Suggest the Speed of Light is Variable](https://www.natureworldnews.com/articles/1010/20130325/speed-of-light-variable.htm)** > > Two studies that are going to appear in the European Physical Journal D suggest that the speed of light is not the constant we always thought it was. Does this mean that some particles can accelerate to a speed faster than the speed of light? ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [March 25, 2013, 9:04pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/2 "2013-03-25T21:04:37Z")
I didn’t read it that way. The speed of light in and of itself isn’t that important. It is known that light travels at different speeds in different mediums. Researchers have been able to slow it down to a crawl or even stop it in recent years. What is important is the constant _C_ (the speed limit of the universe). Light is one of the things believed to travel at _C_ at least in a vacuum but this article is saying that we may not know as much about vacuums as we thought. A vacuum may not be just the absence of anything but consist of quantum particle pairs that may not always be the same. I believe they are saying that conditions within a vacuum may vary and therefore so would the light that travels threw it. _C_ itself would not be violated. The differences would slow light down but at varying levels. These differences would still be incredibly tiny but may be measurable with the latest equipment and might be importance for theoretical physics but not in everyday practical terms. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [March 25, 2013, 9:04pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/3 "2013-03-25T21:04:39Z")
There are two ways to talk about the speed of light, and they usually get confused. Call C the constant that is used in E=MC[sup]2[/sup]. It is fixed and independent of nature. Call c the local speed of light, the speed at which light moves through a physical object. This varies with every possible transparent object. We know that c is always \< C. Shine a beam of light through a diamond and it will slow considerably. Shine it through the vacuum of interstellar space and it will slow down only by a tiny bit, depending on how many particles still remain. That article appears to say that creation of virtual particles from the vacuum energy has an effect on light that is measurable even if all other particles have been removed. You can use that to measure how many particles actually remain in a supposed vacuum. But nothing is accelerating faster than C. It’s all about local speed, c. ---
**Author:** ![colonial](https://avatars.discourse-cdn.com/v4/letter/c/34f0e0/32.png) [@colonial](https://boards.straightdope.com/u/colonial)\ **Post date:** [March 25, 2013, 9:12pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/4 "2013-03-25T21:12:08Z")
> [@barbitu8](#): > > [New Studies Suggest the Speed of Light is Variable](http://www.natureworldnews.com/articles/1010/20130325/speed-of-light-variable.htm) > Does this mean that some particles can accelerate to a speed faster than the speed of light? No. It means the speed of light may be slowed by 1/several 100 millions of a second, not due to its intrinsic nature, but due to interference from particles whose presence prevents there from being a true vaccum. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 25, 2013, 10:28pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/5 "2013-03-25T22:28:46Z")
Ten quatloos says that this research is rescinded, disproven, or otherwise superseded within a year. Probably six months. ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [March 25, 2013, 11:13pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/6 "2013-03-25T23:13:05Z")
This could be huge. It could tell us the nature of particle pairs in the zero point field and their density distribution. That would give us mass. From that would determine to what extent if any the quantum vacuum contributes to either dark energy or dark matter. Dark matter obviously because of the additional mass, but dark energy since the particles are particle-anti-particle pairs which annihilate. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [March 26, 2013, 3:54pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/7 "2013-03-26T15:54:03Z")
> [@Exapno\_Mapcase](#): > > There are two ways to talk about the speed of light, and they usually get confused. > > Call C the constant that is used in E=MC[sup]2[/sup]. It is fixed and independent of nature. > > Call c the local speed of light, the speed at which light moves through a physical object. This varies with every possible transparent object. > > We know that c is always \< C. Shine a beam of light through a diamond and it will slow considerably. Shine it through the vacuum of interstellar space and it will slow down only by a tiny bit, depending on how many particles still remain. > > That article appears to say that creation of virtual particles from the vacuum energy has an effect on light that is measurable even if all other particles have been removed. You can use that to measure how many particles actually remain in a supposed vacuum. > > But nothing is accelerating faster than C. It’s all about local speed, c. Is there any way of calculating C from other measurable constants and comparing the observed c to it? ---
**Author:** ![barbitu8](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@barbitu8](https://boards.straightdope.com/u/barbitu8)\ **Post date:** [March 26, 2013, 8:00pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/8 "2013-03-26T20:00:58Z")
> [@Exapno\_Mapcase](#): > > There are two ways to talk about the speed of light, and they usually get confused. > > Call C the constant that is used in E=MC[sup]2[/sup]. It is fixed and independent of nature. > > Call c the local speed of light, the speed at which light moves through a physical object. This varies with every possible transparent object. > > We know that c is always \< C. Shine a beam of light through a diamond and it will slow considerably. Shine it through the vacuum of interstellar space and it will slow down only by a tiny bit, depending on how many particles still remain. > > That article appears to say that creation of virtual particles from the vacuum energy has an effect on light that is measurable even if all other particles have been removed. You can use that to measure how many particles actually remain in a supposed vacuum. > > But nothing is accelerating faster than C. It’s all about local speed, c. I don’t get the distinction. The speed of light (abbreviated in all texts as “c”) is approx. 186,300 miles per sec in a vacuum. However, there is no absolute vacuum. Even the “vacuum” of outer space has virtual particles, which, as you note, slightly lowers the speed. The denser the medium through which light travels, the greater the effect on its speed. “C” stands for “constant” because its speed is not relative to the movement of anything else, not because it has a constant speed in all mediums. > [@](#): > > 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. As deltasigma pointed out, the importance of the article is that it may be a lead in to determine the nature of dark matter and dark energy. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [March 26, 2013, 8:10pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/9 "2013-03-26T20:10:59Z")
> [@deltasigma](#): > > This could be huge. It could tell us the nature of particle pairs in the zero point field and their density distribution. That would give us mass. From that would determine to what extent if any the quantum vacuum contributes to either dark energy or dark matter. Dark matter obviously because of the additional mass, but dark energy since the particles are particle-anti-particle pairs which annihilate. Could you break this down a little? What does this have to do with mass, for instance? And how exactly do you think dark energy and matter comes in at all? ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [March 26, 2013, 8:25pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/10 "2013-03-26T20:25:55Z")
Ah, you’re probably referring to the idea that vacuum fluctuations don’t necessarily have to be conceived of as virtual particle pairs perhaps? However we know that vacuum energy contributes to the mass of particles. [In fact, it makes up 99% of it.](http://www.newscientist.com/article/dn16095-its-confirmed-matter-is-merely-vacuum-fluctuations.html) [edit:](http://en.wikipedia.org/wiki/Proton#Quarks_and_the_mass_of_the_proton) > [@](#): > > In [quantum chromodynamics](http://en.wikipedia.org/wiki/Quantum_chromodynamics), the modern theory of the nuclear force, most of the mass of the proton and the [neutron](http://en.wikipedia.org/wiki/Neutron) is explained by special relativity. The mass of the proton is about 80-100 times greater than the sum of the rest masses of the [quarks](http://en.wikipedia.org/wiki/Quark) that make it up, while the [gluons](http://en.wikipedia.org/wiki/Gluon) have zero rest mass. The extra energy of the [quarks](http://en.wikipedia.org/wiki/Quarks) and [gluons](http://en.wikipedia.org/wiki/Gluon) in a region within a proton, as compared to the rest energy of the quarks alone in the [QCD vacuum](http://en.wikipedia.org/wiki/QCD_vacuum), accounts for almost 99% of the mass. The rest mass of the proton is, thus, the [invariant mass](http://en.wikipedia.org/wiki/Invariant_mass) of the system of moving quarks and gluons that make up the particle, and, in such systems, even the energy of massless particles is [still measured](http://en.wikipedia.org/wiki/Mass-energy_equivalence#Fast-moving_objects_and_systems_of_objects) as part of the rest mass of the system. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [March 26, 2013, 8:52pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/11 "2013-03-26T20:52:52Z")
> [@deltasigma](#): > > Ah, you’re probably referring to the idea that vacuum fluctuations don’t necessarily have to be conceived of as virtual particle pairs perhaps? > > However we know that vacuum energy contributes to the mass of particles. [In fact, it makes up 99% of it.](http://www.newscientist.com/article/dn16095-its-confirmed-matter-is-merely-vacuum-fluctuations.html) This doesn’t really say that. Basically, taking into account virtual quark-antiquark pairs improves the numbers from being accurate up to 90% to being accurate up to 98%: > [@](#): > > Without the quarks, earlier simulations got the proton mass wrong by about 10%. With them, Dürr gets a figure within 2% of the value measured by experiments. And this is no surprise. The idea is basically that most of the mass of a composite particle is contained in its binding energy; those calculations merely get a better estimate of this binding energy. And I’m afraid I still don’t see what any of this has to do with the vacuum speed of light, or dark matter/energy… ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [March 26, 2013, 8:56pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/12 "2013-03-26T20:56:52Z")
> [@Half\_Man\_Half\_Wit](#): > > This doesn’t really say that. Basically, taking into account virtual quark-antiquark pairs improves the numbers from being accurate up to 90% to being accurate up to 98%: > > And this is no surprise. The idea is basically that most of the mass of a composite particle is contained in its binding energy; those calculations merely get a better estimate of this binding energy. And I’m afraid I still don’t see what any of this has to do with the vacuum speed of light, or dark matter/energy… But that binding energy exists in a state of constantly annihilating sea quarks. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [March 26, 2013, 9:09pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/13 "2013-03-26T21:09:20Z")
> [@deltasigma](#): > > But that binding energy exists in a state of constantly annihilating sea quarks. Meaning what for dark matter or energy, and depending how on the speed of light? ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [March 26, 2013, 9:11pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/14 "2013-03-26T21:11:16Z")
> [@Half\_Man\_Half\_Wit](#): > > Meaning what for dark matter or energy, and depending how on the speed of light? That vacuum fluctuations have mass, energy or both. ---
**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\ **Post date:** [March 28, 2013, 6:16pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/15 "2013-03-28T18:16:18Z")
I read the paper, and while it was obviously beyond my undergraduate physics level, I was struck by a number of things. If different photons in a beam travel at different speeds because they interact with different numbers of fermion pairs along the way, how does a laser remain coherent? How can interferometry in general work? There’s a line in the paper that caught my eye: “this mechanism relies on the notion of an absolute frame for the vacuum at rest”. Hmm. Aether? It appears that the authors are proposing a form of interaction between photons and these quantum-fluctuation fermion pairs that operates by some novel mechanism not seen before. Is that a fair assessment? ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [March 28, 2013, 7:52pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/16 "2013-03-28T19:52:53Z")
I’m just guessing here but maybe the issue is that the differences in speed are so vanishingly small that they couldn’t be detected previously. From the OP link - > [@](#): > > In all, the fluctuations in time are estimated to be somewhere around the realm of 50 attoseconds per square meter (scientists estimate that it takes 320 attoseconds for electrons to transfer between atoms) and may in fact be testable with the help of ultra-fast lasers. Up until this point, light was considered to move at a constant 186,000 miles per second. ---
**Author:** ![Martin\_Hogbin](https://avatars.discourse-cdn.com/v4/letter/m/58f4c7/32.png) [@Martin\_Hogbin](https://boards.straightdope.com/u/Martin_Hogbin)\ **Post date:** [March 29, 2013, 12:35pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/17 "2013-03-29T12:35:35Z")
This is a somewhat speculative research paper, yet to published and certainly unverified experientially. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [March 29, 2013, 9:14pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/18 "2013-03-29T21:14:12Z")
> [@barbitu8](#): > > I don’t get the distinction. The speed of light (abbreviated in all texts as “c”) is approx. 186,300 miles per sec in a vacuum. However, there is no absolute vacuum. Even the “vacuum” of outer space has virtual particles, which, as you note, slightly lowers the speed. The denser the medium through which light travels, the greater the effect on its speed. “C” stands for “constant” because its speed is not relative to the movement of anything else, not because it has a constant speed in all mediums. C is not the speed of light. C is the speed limit of the universe. When in a vacuum, light travels at C, when not in a vacuum, light travels at a speed less than C. If the researchers have discovered that light travels slower than C through a vacuum, it has no effect on the nature of C. Therefore although it may be possible that there is some particle that can travel faster than light through a vacuum, it does not mean that the particle can travel faster than C through a vacuum. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [March 30, 2013, 11:55am UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/19 "2013-03-30T11:55:52Z")
> [@Half\_Man\_Half\_Wit](#): > > Could you break this down a little? What does this have to do with mass, for instance? And how exactly do you think dark energy and matter comes in at all? The density of the vacuum nearby isn’t precisely what determines c. c is related tot he permeability and permittivity, which makes sense as the e/m wave is affected by the e and m properties of the material… ---
**Author:** ![davidm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidm/32/225_2.png) [@davidm](https://boards.straightdope.com/u/davidm)\ **Post date:** [March 30, 2013, 2:10pm UTC](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946/20 "2013-03-30T14:10:25Z")
This is probably a very dumb question. The variation is tiny. Is it so tiny that it isn’t meaningful even at large distances? Could it affect, for example, calculations of the size of the universe or the distance of very distant astronomical objects? [Next page](https://boards.straightdope.com/t/speed-of-light-in-a-vacuum-is-variable/653946.md?page=2)