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back to article Speed of light slower than we thought? Probably not

With the simple headline “Einstein was wrong”, yet another piece of questionable physics has garnered world attention. It starts with this kind of canned statement, which originated at Phys.org and apparently arose from this uncritical write-up at the Medium-hosted Physics at Arxiv blog. To quote Physics at Arxiv, “James …

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Did Einstein predict the speed of light?

Or was it Maxwell and his silver hammer?

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Boffin

Re: Did Einstein predict the speed of light?

Einstein recognised the significance of what Maxwell had stumbled upon (and proved) - that the speed of light is a constant - no matter what, not relative to anything (people kept asking the question 'constant relative to what what?'. Einstein through his theories of relativity explained why it isn't relative to anything.

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Re: Did Einstein predict the speed of light?

Sorry - exactly wrong. SOL is always constant relative to an observer. So you get the same value regardless of whether you're moving towards or away from it. Unlike tennis balls.

Best way to get a reputation in science would be to disprove Einstein, so it's no wonder people keep trying. Which shouldn't be taken as me saying don't try, just be pretty damn sure before you publish.

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One of these things is not the same as the other...

The travel time of a beam of light/photons and the speed of light in a vacuum can be different. Because you can "stop" the beam/photon and re-emit it. A neutrino though is less likely to be interfered with as it is so small and weakly interacts.

Basically, it's the difference in the theoretical limit "my car can do 150mph" and the "but I'm stuck in traffic doing 1mph" limit. :P

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Coat

Re: One of these things is not the same as the other...

What is the maximum velocity of your car* in a vacuum?

*while being driven by a sheep, of course.

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Boffin

Re: One of these things is not the same as the other...

Zero - unless it's one of those new fangled electric horseless carriages.

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@Martin Budden: Re: One of these things is not the same as the other...

"What is the maximum velocity of your car* in a vacuum? *while being driven by a sheep, of course."

Assume the sheep is a sphere...

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Re: One of these things is not the same as the other...

Umm. IIRC light can be refracted by gravitational masses, but neutrinos...what path do they take?

Well they have mass so should also be bent by strong gravitational fields en passant, but to the same extent?

My A-level physics gives up at this point.

Also light slows down when passing through matter, but neutrinos do not I believe?

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Re: @Martin Budden: One of these things is not the same as the other...

The sheep is in a vacuum. Spherical, cube, what difference does it make?

(Never the less made me laugth.)

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Re: @Martin Budden: One of these things is not the same as the other...

The sheep is in a vacuum. Spherical, cube, what difference does it make?

Moment of inertia and angular momentum. Think, man, think!

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Re: @Martin Budden: One of these things is not the same as the other...

"Assume the sheep is a sphere..."

... with zero rest mass, neutral charge and a spin of 1/2.

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Re: One of these things is not the same as the other...

The thought occurred to me that we are observing a small fraction of a milliradian(?) of the light coming from the SN. Suppose it took 7.7 hours for the light to find a clear path through the debris from the SN, but the neutrinos weren't hampered at all by the debris. Simple explanation, no?

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Re: One of these things is not the same as the other...

That is the actual theory so far. That the neutrinos escape before the light as the light gets caught up in debris, clouds etc.

No idea why I got downvotes. If I misspell something, or get some facts and details wrong, please correct me, I'm no genius that is for sure and not afraid to be told so.

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Ok, so they're fine-tuning the speed of light, that means that the measuring equipment and techniques in early-ish 1900's wasn't as good as 2014. Yes, that's shocking, but true - 100 years DOES make a difference to accuracy.

That doesn't make Einstein "wrong", he just didn't factor in some guy farting in Thailand, to affect the weather in Canada.

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Not really, the speed of light is very well established. Actually the speed of light is so well established, that it is defined as a constant and will never ever change from 299,792.458km/s. Any differences in measurement will not change c, instead it would change the definition of a metre.

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I think the conjecture is that the photons were emitted at the same time as the neutrinos but were slower to reach us.

If so, that's not saying so much that the 'speed of light' - as a constant - is not quite as big a number as was thought but saying that the speed of light (in a vacuum) is no longer the ultimate speed limit. I.e. - neutrinos move faster than the 'speed of light'.

Revising a measurement is one thing, but saying that that measurement no longer represents what you thought it did is quite another.

Is that the gist?

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That's an interesting point: while I agree that a metre is defined as the distance light travels in a vacuum in 1/299,792,458th of a second, arguably a metre as it exists at this point in time is more important than the accuracy of that calculation, in terms of the impact to society as a whole. i.e., if we (hypothetically) did discover that the speed of light is slightly different (as John suggested), wouldn't it make more sense to change that formula to keep the metre the same, rather than having to adjust all of our measurements?

Too early?

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Even if we're not quite right about the speed of light, any correction would be very small. We do have almost 100 years of measuring it, and the results are all pretty similar.

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Perhaps the Neutrino's took a short cut?

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Silly question...

I don't know much about this stuff but do neutrinos get effected by gravity as much as light? If light is bent by gravitational pull, surely light would have further to travel than the neutrino which has more of a direct route.

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Re: Silly question...

As I understand it, light (photons) are not affected by gravity. Space itself is distorted by gravity and so it looks as if light is deviating from a straight-line path.

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Re: Silly question...

Light is affected by gravity - that's why there are 'black holes'.

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Re: Silly question...

Photons and pretty much everything else is affected by gravity because gravity distorts the very spacetime continuum itself. Large clusters of distant galaxies act as a 'gravitational lens', for example, distorting the image of galaxies that lie beyond them.

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Headmaster

Re: Silly question...

Mutatis mutandis....

I thought Reg readers would have been aware that 'what is' and 'what our models of it are' were in fact different things.

"The map is not the territory"

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Re: Silly question...

@frank ly

Within General Relativity, gravity is not really a force in the same way as, say, the electro-magnetic force - it is more a result of the curvature of spacetime by massive bodies.

Essentially, the Newtonian idea of the 'force' of gravity is (under Einstein) simply a manifestation of the curvature of spacetime, as influenced by mass or, more precisely, the 'stress-energy tensor', which is effectively a combination of mass, energy and momentum.

In other words, the curvature of spacetime that results in the apparent 'bending' of light is gravity.

Of course, Neutrinos are affected by gravity too! (And would be even if they were massless.)

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Re: Silly question...

At low relative speeds, Einstein's equations effectively reduce down to the Newtonian formulation of mass acting on mass. This works fine for celestial bodies moving at tiny fractions of c - the Earth, for example orbits the sun at ~1/1000 c. Of course, Newton's model can't account for light because light moves at 100% of c!

Thus, light is not affected by gravity as modelled by Newton but that model was explained by Einstein as essentially a special case of the larger picture, which is General Relativity.

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Boffin

Re: Silly question...

Both are affected by gravity but

- neutrinos hardly interact and go 'straight out'

-light will interact with any matter in and around the supernova and will take some time to get out. How long depends on a lot of detailed understanding that we might not have got right.

for example photon diffusion time (getting absorbed, re-emitted in random walk style ) from the sun's core to its surface is estimated to be about 170,000 years, despite its radius being about 2.3 light seconds.

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Re: The map is not the territory

Thumbs up for the Van Vogt / Korzybski reference.

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A basic misunderstanding of supernovae

Franson has based his work on a conundrum raised by an old supernova explosion: that when supernova SN 1987A was observed in 1987, neutrinos were spotted 7.7 hours before the event became visible when photons arrived.

While we do not completely understand the physics underlying a supernova (the simulations show the shock wave stalling a few milliseconds after it rebounds from the collapsed core), scientists do pretty much agree that:

1. The neutrinos are generated during the initial core collapse;

2. The photons are generated when the shock wave reaches the surface of the star; and

3. The two preceding events are separated by several hours.

I guess Franson must have assumed that everything happens instantly. Just shows what an idiot he is.

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Re: I guess Franson must have assumed ...

If it's on the arXiv, you dont have to guess. You can go check it yourself. Or indeed you can check the open access article itself, using the links in the Reg article.

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Re: I guess Franson must have assumed ...

As you could have too instead of posting about it..... Gander meet sauce.

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Anonymous Coward

Re: A basic misunderstanding of supernovae

There's certainly an idiot here, but it's not Franson.

If you'd read anything beyond the El Reg write up -- you don't even need to read the original paper, even some of the "Einstein wrong!!!" press reports got this part right -- you would know that this El Reg's cockup, not Franson's.

Yes, it's well known that there should be some hours between the arrival of the neutrinos and the photons. The problem with SN1987A is that the difference is several hours longer than our best theories of supernovae say it should be. Franson's proposal deals with that discrepancy quite neatly.

Whether he's correct remains to be seen, but if we're going to call somebody an idiot, I nominate the person who used the words "guess" and "assume" about a well-established physicist rather than read one link deeper.

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Re: A basic misunderstanding of supernovae

Franson isn't questioning the speed of light. What he is actually saying, is that over those sort of distances, you can't consider space to be a true vaccum - you have to take into account quantum mechanical effects. Only an idiot would accuse him of being an idiot without first bothering to RTFM.

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Re: A basic misunderstanding of supernovae

Ahhh... so he is "just" (though said in context, a lot of hard work goes into improving data and results) improving the theory and info about why the light takes so long to reach us. Not replacing it entirely (as that would be going against established observations and theories).

I do wonder, what other effects can the quantum mechanics, this "no true vacuum" cause?

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Joke

If gravity bends light...

then does heat bend light? And, is the speed of darkness just slightly faster than the speed of light? I've never been able to hit the light switch and be under the covers before it's dark!

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Joke

Re: If gravity bends light...

Of course Einstein was wrong - this whole "photon" malarkey will soon go the way of the Aether, once people finally realize the whole process is about dark being sucked instead of light being emitted...

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Re: If gravity bends light...

Does heat bend light?

In its own way, yes, it does. An oasis mirage would be one example. Hot air and cool air have differing refractive indexes, which bends an incoming light ray by varying amounts.

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Re: does heat bend light?

heat is energy, and energy bends spacetime, and light beams follow curved paths in curved spacetime. So yes, heat does bend light.

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Re: If gravity bends light...

The speed of dark is obviously faster than the speed of light as you can demonstrate with a simple experiment:

Open your closet door. You can see light enter the closet, but dark moves so fast that you can't see it leave.

As for the heat question, Radiant heat is just another form of light, but shiftier, as it doesn't let us see it. Who knows what it's up to.

Conductive heat is just agitated matter. Some photons, usually from the shifty Radiant heat mentioned above, seek to keep matter agitated. Most respectable photons just move a little faster when they see agitated matter, they don't want to get involved.

Convective heat is just conductive heat trying to escape the gravity of the situation, therefore the same rules apply to it.

Sexual heat is the odd situation where intellect has shifted from between one set of limbs to between the other pair. This may cause passing photons to stop and stare, usually yelling "Get a Room!"

So, as you can see there is no easy answer to that question... Er, what was it again?

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Re: If gravity bends light...

Move the light switch to be under the covers.

Not that big of a deal.

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Anonymous Coward

Re: If gravity bends light...

"And, is the speed of darkness just slightly faster than the speed of light?"

Cosmic distances are fascinating. The light from our sun takes a finite time to reach us. If it disappeared suddenly - we wouldn't know until about 8 minutes later. What really knots my mind is that apparently the effects of the sun's gravity would also only disappear after that time.

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Re: If gravity bends light...

The comment about dark sucking is straying close to the theories of De Selby and his "dark particles" (a prize to the first person to identify the reference)

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Joke

Re: If gravity bends light...

I believe they would be coincident...? Although, it would be a fascinating experiment....

Planet pool, anyone?

P.

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Re: If gravity bends light...

"Light thinks it travels faster than anything but it is wrong. No matter how fast light travels it finds the darkness has always got there first, and is waiting for it."

Reaper Man, by Terry Pratchett

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Re: If gravity bends light...

The Dalkey Archive -- Flann O'Brien -- wonderful madness.

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Anonymous Coward

Re: If gravity bends light...

The Dalkey Archive by Flann O'Brien --- quite brilliant madness

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Headmaster

What am I reading?

"His conclusion, in this paper at IOP, is that both Einstein's prediction of the speed of light – 299,792,458 metres per second in a vacuum – is wrong"

1) Einstein didn't "predict" the speed of light. That speed has to be measured. It is always 1.

2) He correctly posited that the most elegant way out of the pretzel-shaped contortions that physicists were making to adapt their theories to the logical implications of electromagnetism and the absence of any experimental sign of an absolute rest system in which light was moving was to go whole hog and posit that the speed of light must be the same in all reference systems. Which means that durations and lengths differ between reference systems

3) Quantum mechanics comes in later, whereby you can have "faster than light" events in the small (resolved by changing to antiparticles in other reference frames) and the world-famous "entanglements" (which have nothing to do with any speed at all, except the speed of thought).

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Alien

Tsk!

It's all relative in it?

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Re: Tsk!

A mother generally.

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