# Lightspeed variable say intellectuels français

French researchers have proposed a mechanism by which the observed speed of light might not be the constant we think it is: it could, in fact, vary at the attosecond level. It's not, however, time to reach for the “the old boffins were wrong!” template, because their reasoning is actually elegant and simple: we know that …

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1. #### Pedantry ahoy!

The researchers also say their theory

Come, now. You mean hypothesis, surely?

2. #### Hmmm....

Well, I don't yet get much vibes from this, but this is a bizarre line:

> That “quantum noise” is a spooky property that looks like the Universe is watching us back

It's not "spooky" at all and the Universe is certainly NOT "watching" anything, be it our back or anything else.

The base physical machinery "just" accounts for the infinite number of possibilities that it might evolve in time, then very quickly drops those that interfere destructively as you scale-out. No magic involved, just loss of the classical "one timeline" straightjacket. Said machinery does not correspond to anything that one can build or actually observe on the macrolevel, but it's still not "spooky", it's just "amazingly extravagant in computational power (which remains mostly inaccessible)".

1. #### Re: Hmmm....

Can anyone smell that?? I'm sure I can smell bullshit.

If you don't think that particles and antiparticles appearing and annihilating each other out of a quantum soup of pure energy is spooky as well as being scientifically intuiging then you either don't understand it or you think you understand it. Which is not the same as understanding it.

I call bullshit.

3. #### I will save you the wikipedia lookup on Attoseconds

Attosecond

An attosecond is an SI unit of time equal to 10−18 of a second. (one quintillionth of a second).[1] For context, an attosecond is to a second what a second is to about 31.71 billion years, or twice the age of the universe.[2][3]

The word "attosecond" is formed by the prefix atto and the unit second. Atto- was made from the Danish word for eighteen (atten).[4] Its symbol is as.

An attosecond is equal to 1000 zeptoseconds, or 1/1000 of a femtosecond. Because the next higher SI unit for time is the femtosecond (10−15 seconds), durations of 10−17 s and 10−16 s will typically be expressed as tens or hundreds of attoseconds:

Shorter times

1 attosecond – the time it takes for light to travel the length of three hydrogen atoms.

12 attoseconds – record for shortest time interval measured as of 12 May 2010.[5]

24 attoseconds – the atomic unit of time.

67 attoseconds – the shortest pulses of laser light yet created.[6]

100 attoseconds - fastest ever view of molecular motion[7]

200 attoseconds (approximately) – half-life of beryllium-8, maximum time available for the triple-alpha process for the synthesis of carbon and heavier elements in stars.

320 attoseconds – estimated time it takes electrons to transfer between atoms.[8]

1. #### Re: I will save you the wikipedia lookup on Attoseconds

I'll see your attosecond and raise you a zeptosecond.

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2. #### Can you spare me the trip, too?

> 12 attoseconds – record for shortest time interval measured as of 12 May 2010.

Yeah, right! How do they know they measured it accurately?

1. #### Re: Can you spare me the trip, too?

What I don't understand is the speed per square meter. What does that mean?

1. #### 50 attoseconds per square meter of crossed vacuum

That quote is a mistake. The paper itself states that the fluctuation time varies in proportion to the square root of the travelled distance. The effect gets proportionally smaller the further you go, nothing to do with any square metre of crossed vacuum.

2. #### Re: Can you spare me the trip, too?

she said she wouldn’t tell anyone!

3. #### Re: Can you spare me the trip, too?

I thought the shortest possible time was the New-York second: the time between the traffic light turning green in front of you and the yellow cab behind you honking its horn.

Mine is the one with "The Long Dark Teatime of the Soul" in the pocket

4. A famous French philosopher* once remarked: "Whenever I feel I have written something particularly profound, I first translate it into English to see if it makes any sense at all".

* Anyone know who? My Google powers are weak ...

5. I think this could definitely be categorised as "no shit, Sherlock". Space isn't quite a vacuum even without quantum funkiness.

Nice to see some people trying to measure the perturbations though. Good luck, and all that.

1. #### Re: "no shit, Sherlock"

Clearly, you are one of Leuchs, Villar, or Sanchez-Soto who published a similar idea in 2010 (ref 1 of this here paper). If not - well, where was your paper on the idea, eh?

1. #### Re: "no shit, Sherlock"

I figured this out as a child and just thought it was obvious.

Space is not really a vacuum, therefore why should the speed of light in space be the speed of light in a vacuum?

1. #### Re: "no shit, Sherlock"

"Space is not really a vacuum, therefore why should the speed of light in space be the speed of light in a vacuum?"

I think what they're saying is only indirectly related to with the speed of light in space. It sounds like the theoretical speed of light in a vacuum is different from the actual speed of light in vacuum, even assuming that the vacuum is "perfect". This is a bit different from "space actually contains stuff".

2. #### Re: My Paper?

I'm studying computer games technology. My professional/academic interest in physics goes as far as "can I simulate this using OpenGL/GLUT/Ogre/XNA?"

The rest I'll leave to the Proper Boffins.

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3. #### 10 billion light years between interactions? Sounds good enough to me

The mean free path of a photon in intergalactic space is about 10 billion light years. Is that good enough for you to count as a vacuum, without the quantum funkiness?

1. #### Re: 10 billion light years between interactions? Sounds good enough to me

As I understand it this is referring to a photon hitting "something" (solid). The article is relating to the traversal of photons through vacuum space and their interactions with fundamental particles that "pop in and out of existence". It's sometimes easier to think of "vacuum" as a zero state much like the surface of boiling water - taken on a wide average it's flat, but as you get closer to the scale of the boiling there are peaks and troughs.

1. #### Re: 10 billion light years between interactions? Sounds good enough to me

"The article is relating to the traversal of photons through vacuum space and their interactions with fundamental particles that "pop in and out of existence". "

That's the quantum bit that was referred to. The original poster (unless I got it wrong) was stating that because he realised that you could find hydrogen atoms and the like in deep space, it wasn't a perfect vacuum. I suspect that the boffins involved are well aware of this but because the MFP is measured in light years, didn't really worry about that and instead concentrated on the quantum bit.

2. #### Re: 10 billion light years between interactions? Sounds good enough to me

>Is that good enough for you to count as a vacuum, without the quantum funkiness?

Not for me - presumably it's still interacting with dark matter/souls of dead nice people/stacked turtles or whatever.

6. I don't buy it. Not as stated anyway. Would kinda make mockery of the uncertainty.

1. Are you sure?

7. How quick are them extremely fast lasers then?

1. #### Ultrafast Lasers

http://en.wikipedia.org/wiki/Ultrafast_laser_spectroscopy

tl;dr: ultrafast refers to the pulse time, not the propagation time.

2. #### Answer: Almost 3 hundred thousand km/sec

... that is assuming proper vacuum, of course.

Just in case you meant 'short' when you said 'quick': the shortest reproducible attosecond pulses have a duration of some 50-100 as, corresponding to 100*10e-18 m * 3e8 m/s = 10 nm. That's an awfully short amount of space or time.

1. #### Re: Answer: Almost 3 hundred thousand km/sec

I thought the point of the story is that there is no proper vacuum.

8. #### Attosecond

Noun: The length of time Windows 8 looks like a good idea.

1. #### Re: Attosecond

It's no use posting anonymously Eadon, we all know it's you.

2. #### Re: Attosecond

This prefix also explains certain practices at jobs that I've held: The "AttoBoy" is now defined as the amount of reward one earns for going above and beyond to get the job done under nearly impossible constraints.

I was going to use the "Joke Alert" icon but, sadly, it isn't really...

1. #### Re: Attosecond

The "AttoBoy" is now defined as the amount of reward...

Yes, very good. Now tell the one about the herd with 1e12 bulls.

9. #### Maybe the speed of light in a vacuum IS infinite

.....but its all that quantum suds stuff that slows it down.

Come to that, maybe matter is just REALLY dense quantum suds.

1. #### Re: Maybe the speed of light in a vacuum IS infinite

Unlikely, as that would make a real buggery of the Maxwell equations and indeed the Lorentz transformations, not to mention that the impact on the Minkowski space-time metric would imply that *all* intervals were time-like, what with the light-cones being flat and all.

1. #### Definitely not infinite

It cannot be infinite. The best way to think of this paper is that there is a fundamental maximum speed in the universe defined by the properties of space-time. Then there is the speed of light. Generally these two values are so incredibly close to each other that we can think of them as one and the same. However light interacts with the virtual particles in vacuum and so sometimes has a speed which almost imperceptibly less than the fundamental maximum. Essentially this is the same effect as the slower speed of light in water where photons interact with the water molecules and so are slowed down.

2. #### Re: Maybe the speed of light in a vacuum IS infinite

I'm glad to see this comment was voted down. That restores my faith in the inherent irrationality and foolishness of people. For a minute there I thought the Reg readership might be getting more sensible.

Carry on!

10. #### Good

Expecting a atto hard drive soon, perhaps a Atto Intel inside too.

Bye the way, meaningful results tend to start with random guessing, one of our best assets in fact.

1. #### Re: Good

Indeed! Random guessing is the foundation on which all science is built.

1. #### Re: Good

Random guessing is the foundation on which all science is built.

What a load of utter rubbish.

The portion of scientific epistemology that includes "guessing" (hypothesizing) at all is not based on "random guessing", unless you're using some mechanical device with a source of physical randomness to select interpretations from the set of all possible. It's based on formulating a hypothesis consistent with and relevant to initial observations. If it weren't, there would be an overwhelming probability of starting with irrelevant nonsense, and empirical and formal techniques would have no basis on which to refine the hypothesis.

1. #### Re: Good

MonteCarlo simulations.

nuff said.

11. #### re. "...the permissivity of vacuum,..."

That would be 'permittivity' in English. It may be that 'permissivity' is the French word.

12. #### But you can't tell if your ruler is wrong

if the only thing to check it with is your ruler.

13. ...which might be testable with the help of new ultra-fast lasers.

They've finally worked out how to apply the grease to the light then?

14. #### Slightly OT

But I've always thought that C being a fixed value irregardless of the velocity of it's source really shouts "simulation; some calculations have been simplified to ease rendering"

1. #### Re: Slightly OT

No. If you use Maxwell's equations to describe an electric wave, then you will find it travels through the vacuum with the speed 1/√(μ0ϵ0). It's first year degree stuff.

In Special Relativity, Einstein takes it as axiomatic that c is constant and works out the consequences. But the existence of a maximum speed for massless particles (e.g. photons) emerges naturally in General Relativity. In both theories, travelling faster than the maximum speed means travelling backwards in time.

1. #### Re: Slightly OT

"Yes, maximum speed, see equations here and here, has to be like this or universe would become orders of magnitude more complicated, will be internally consistent, unlikely anyone will notice."

It's like the pre rendered star box drama all over again.

2. #### Re: Slightly OT

"No. If you use Maxwell's equations to describe an electric wave, then you will find it travels through the vacuum with the speed 1/√(μ0ϵ0). It's first year degree stuff."

Not in media studies, I'll wager.

1. #### Re: Slightly OT

Not in media studies, I'll wager.

I'd hope they'd teach that "irregardless" is not a word, even there, though...

3. #### Re: Slightly OT

"In both theories, travelling faster than the maximum speed means travelling backwards in time."

Surely if you travel faster than light you could see "back in time", in the same way that being able to travel faster than sound would (ignoring the practicalities) enable you to hear past events that you'd already heard. But that doesn't count as time travel for me in either case.

15. #### Bang goes Star Trek

"Bridge to engine room: warp factor, erm, whatever!"

16. #### V. Interesting

Consider 2 photons passing a line A close together (but far enough apart so you can tell which is which) at exactly the same time, passing through empty (as empty as it gets) space and then being detected when they cross another line B (parallel to A)

On the face of it you would expect them to pass B at the same time.

These guys say not so.

What is the speed of light - is it when the first photon hits or the second/last one?

I always wondered why photos of distant galaxies looked blurry - over v.v. long distances instantaneous events will be 'smeared' according to this.

1. #### Re: V. Interesting

"I always wondered why photos of distant galaxies looked blurry "

I think they are blurry like a bacteria on an adjacent mountain would look blurry

17. #### Very interesting. Surprising people have not looked into this before

Historically there has been the properties of the permeability permittivity (useful for capacitor design) of free space and the (derived) impedance of free.

All have measurable values but no one knew why they had those values (it's one of those "stop asking stupid questions, memorize the values and get back to work" conversations).

Given that it's been know the vacuum is subject to quantum fluctuations for decades it's surprising no one seems to calculated the implication what happens if a photon hits one (or more?) of these particles in transit. Just because they don't stay around for long does not mean that they are not "real" while they are here.

Even more amazing laser technology is at (or close) to being able to measure this effect.

Note that practically it would not change much. We would have to change the definition of the speed of a light in a vacuum to mean a vacuum with no virtual particles (which AFAIK is a complete abstraction).

Now if the rate and density of virtual particles remains constant then this just means you need to compute the speed of light slow down but if either varies then things could get muchmore interesting.

BTW GPS propagation already corrects for some quantum effects so this could improve navigation accuracy, especially over long distances or high speeds (but probably nothing moving slower than a serious fraction of the speed of light or ranges of several AU).

Thumbs up for picking up the ball and running with this.

18. #### Why is this news?

Back in high school chemistry (!), we discussed how light passing through various mediums (OK, pedants: media — but no jokes about the press or TV, please) has different speeds. (This was in relation to Cherenkov radiation). Therefore, if vacuums are not truly vacuums nor consistently adulterated, it follows that the speed of light will similarly vary.

19. #### Proust was right

Ils sont a la recherche du temps perdu.

Merci. Je vais chercher mon manteau.

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