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Evidence of a Correction To the Speed of Light
KentuckyFC writes: In the early hours of the morning on 24 February 1987, a neutrino detector deep beneath Mont Blanc in northern Italy picked up a sudden burst of neutrinos. Three hours later, neutrino detectors at two other locations picked up a second burst. These turned out to have been produced by the collapse of the core of a star in the Large Magellanic Cloud that orbits our galaxy. And sure enough, some 4.7 hours after this, astronomers noticed the tell-tale brightening of a blue supergiant in that region, as it became a supernova, now known as SN1987a. But why the delay of 7.7 hours from the first burst of neutrinos to the arrival of the photons? Astrophysicists soon realized that since neutrinos rarely interact with ordinary matter, they can escape from the star's core immediately. By contrast, photons have to diffuse through the star, a process that would have delayed them by about 3 hours. That accounts for some of the delay but what of the rest? Now one physicist has the answer: the speed of light through space requires a correction.
As a photon travels through space, there is a finite chance that it will form an electron-positron pair. This pair exists for only a brief period of time and then goes on to recombine creating another photon which continues along the same path. This is a well-known process called vacuum polarization. The new idea is that the gravitational potential of the Milky Way must influence the electron-positron pair because they have mass. This changes the energy of the virtual electron-positron pair, which in turn produces a small change in the energy and speed of the photon. And since the analogous effect on neutrinos is negligible, light will travel more slowly than them through a gravitational potential. According to the new calculations which combine quantum electrodynamics with general relativity, the change in speed accounts more or less exactly for the mysterious time difference.
There's an alternative explanation. Space-Time could have non-zero viscosity, and slow down photons.
There are a lot of reasons to consider that space might have a viscosity. For one thing, it would neatly explain the expansion of the universe, without the necessity of invoking dark matter and dark energy.
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(however, the apparent local time when you see this post may differ based on the apparently non-constant nature of c )
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do they correct the idealized, or do they correct the observed?
Neither. You cannot correct the speed of light, because it isn't measured, it is DEFINED as EXACTLY 299,792,458 meters per second. So it is not the speed of light that needs to be updated, but the length of the meter.
It is the average speed of the light over very large distances that needs a correction, to account for the portions of travel where the light, well, is not light. The photons still move at 2.99x10^8m/s. It's the electrons and positrons that move slower.
...is "more or less exactly" ?
Modest doubt is called the beacon of the wise. - William Shakespeare
Presumably this happens all the time for light so what we've measured as the speed of light is correct, it's just that the true universal speed limit is higher and only neutrinos travel that fast. So we should find out that speed and use the speed of neutrinos when doing relativistic corrections.
The time period over which pair production-annhilation occurs might be a small part of the correction here, but from my quick reading of TFA, I think the key phrase is "This results in a small correction to the angular frequency of a photon and thus its velocity," where velocity is the key word. Velocity of course is a vector quantity, consisting of both a speed (c) and a direction. The key aspect here is the direction; when the pair recombines, the total energy of the system is slightly different as the positron-electron pair is affected by gravity and thus may pick up a small positive or negative acceleration from the gravitational potential they are traveling through. When they recombine this will be reflected in the new velocity (c d) of the resultant photon, which is not exactly the same as the photon prior to pair production. At least thats what I got, but I'm the wrong kind of doctor to be an expert in this. Any PhD's wanna weigh in and correct me, please do!
Or it could be a badly written summary and article that completely misrepresent what is being stated.
If every science journalist on the planet were to spontaneously combust, not only would it introduce a whole new physical phenomenon, it would cause the average IQ of the planet to jump by at least 5 points.
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Wait until you see these guys split up a bill for lunch.
There seems to me to be a slight error in the original article. Neutrinos have been determined to possess mass. It is only a slight amount of mass, but it precludes them from being able to travel at exactly the speed of light. How close to light-speed do they normally travel? I can't say. But it is reasonable to think that the distance from Supernova 1987A to Earth should have led to a slightly later arrival time, for neutrinos, than if they had actually traveled at light-speed.
The preceding relates to another thing, the quantum-mechanical mechanism for interfering with the actual speed of light. Those pairs of virtual particles that form also have mass. That means, while they temporarily exist, they also cannot be traveling at exactly light-speed; they have to be traveling slightly slower.
The photons still move at 2.99x10^8m/s. It's the electrons and positrons that move slower.
This whole premise sounds wrong and needs data to confirm it. The problem is that the article is wrong to claim that neutrinos move at the speed of light - they have a non-zero mass and so must move slower than this. However their mass is incredibly small (probably ~100,000 times less than an electron - so small that we have not actually measured it yet!) so they move very close to the speed of light. What sounds dodgy is that they are claiming that the primary effect of the non-zero neutrino mass is negligible while the secondary effect of the zero-mass photon coupling to virtual electron-positron pairs is more significant. A quick back of the envelope calculation suggests that the neutrino mass could cause a ~30 minute delay in the neutrino arrival over such a distance.
In addition they are basing this on being able to accurately calculate the scattering delay time of photons in a super nova. Less than a decade ago super nova models could not even get the star to explode (the explosion was not powerful enough and was overcome by gravity) so I have a hard time believing that they have perfected things to the extent where can really give a reliable number for the scattering delay time.
As usual extraordinary claims require extraordinary evidence and so far there is much of the former and none of the latter. Although it is also possible that the article is completely misrepresenting the claims but if so it is doing an even worse job of it that you suggest!
You have this the wrong way around. The speed of light is not defined, it is a universal constant. It is the length of the meter that is defined based on a combination of this constant, and the international standard of time. So you are correct that if light turned out to travel slower, the length of the meter would be slightly shorter, and the speed of light would still be exactly 299792458 meter per second. This would be according to the new length of the meter though, when expressed in the old length (which is what the poster is implicitly asking for), it would most certainly be less, and could be given as such.
Of course the truth is that the speed of light is perfectly fine as it is. It's just that light isn't always exactly 'light' when it travels through space.
Genuine question - this seems like an interesting thing, but as someone whose expertise in physics is incredibly limited, is there anyone who would be willing to provide an "explain it like I'm five" version for an individual like myself who is interested in understanding the speed differences observed in the particles?
Thanks, internet!
None of this is the issue; speed of light stays constant, as does distance measurements. What changes is the understanding of the stability of a photon of light in a vacuum and the effect of this instability on travel time while passing near a gravitational well.
So while it's a photon of light, it travels light speed. When the energy converts to kinetic energy for a breather, it is affected by the gravitational pull, in a manner significantly stronger than a neutrino is affected. When it then flops back to being a photon, it is once again traveling at the speed of light.
What intrigues me about this is that this will also have implications regarding relativity, as every time the light flips state, it is essentially anchoring itself to a location in space from which the next photon flop can take its bearing. My mind can't quite grasp the further implications of this right now, but it could really mess with observation of light from a moving point (which all points are).
The recalibration is mostly on how we project distances based on light measurements; it's now become significantly trickier, as we need to account for gravity at specific moments.
Franson's idea, as I understand it, is that during the small window between creation and annihilation, the massive particles are under the influence of gravity, which bleeds off energy. When the pair recombines, it results in a reduced velocity of the photon.
Now, as I understand it, reducing the energy of a photon would merely reduce its frequency (red-shifting), not affect its actual velocity.
However, over long distances, the total time required for a photon to travel distance X would thus be slightly more than X/c, based on the proportion of time spent as a pair of massive particles, rather than as a massless photon. From a statistical perspective, this yields an average velocity of slightly less than /c/ (the speed of light in a vaccuum).
This seems reasonable to me, at least at first.
mrsquid0 raises an issue, though: Photons in the visible light range are not sufficiently energetic to create an electron-positron pair. I do not know if the photons in question were in the visible light range or not.
NoNonAlphaCharsHere also raises an important point: the electron-positron pair *cannot* travel at the speed of light. In fact, he/she raises an even better idea than Franson; my reading of Franson's explanation is that gravity is slowing down the particles (gravity field behind the photon), but there's just as much opportunity for gravity to *speed up* the particles (gravity field in front of the photon).
Now, I don't feel like doing all the math for this one little message, so here are the things I would consider before taking this article (and the original paper) at face value:
Ah, this is getting off topic, but your comment raised a question in my mind. Suppose the light is blue shifted for an observer approaching it so that it does have the energy to form an electron-positron pair, but for another observer not approaching it as fast, it doesn't have the energy. Might one observer see the pair formation while the other did not?
In theory, theory and practice are the same; in practice they're different. (Yogi Berra & A. Einstein)
Okay, let's say you have two cars, a Porsche and an NSX (representing a photon and a neutrino, respectively). Both are limited by the same speed limit, which they always travel at (the speed of light).
Well, due to some weird quantum mechanics, every so often that Porsche splits into a pair of motorcycles, because apparently they got bought by Wayne Enterprises or something (in actuality, they split into an electron and anti-electron). They almost immediately join back together (forming a photon again), but while they're motorcycles, they are affected by wind (gravity). They still can't break the speed limit, but sometimes it slows them down just a bit.
When you're traveling almost literally between galaxies, that little bit of slowdown for tiny snippets of time can really make a difference. In this case, the NSX made it here a few hours earlier.
An easier example of this: light moves much slower than c in glass, or in water. The open question is: does light move non-trivially slower than c in the vacuum of space (which is not an idealized vacuum).
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I think you are confusing neutrinos, which have been known for a while, with tachyons, which are speculative and haven't been detected. Neutrinos don't move faster than light.
The summary (and linked article) do a poor job of explaining the process and imply some change in the speed of light (there isn't one). The problem with the article (http://arxiv.org/abs/1111.6986) is that it ignores a bunch of more relevant data: Fermi-LAT observed photons from the same GRB over a very wide energy range placing an extremely good limit on effects like this proposed in the article (http://arxiv.org/abs/1305.3463).
Furthermore this is NOT new; the original article was posted in 2011 and only recently published in the "New Journal of Physics" which has apparently only published 16 volumes and I believe has had its email permanently redirected to my spam box.
Finally why do people link to Medium and not the actual article for physic related news items? We have demanded open, free access to all our papers since the birth of the internet (I speak as a physicist). Do everyone a favor and find the arxiv link and include it in your summary when submitting physics stories to Slashdot.
When 1987A happened, it is fair to say that an enormous amount of attention was placed on those neutrinos - >> 1 paper per neutrino. The report of an earlier neutrino burst from the Mt Blanc LSD was discussed at length - see Arnett 1987 Table 1 for the time line.
The facts are these - the optical supernova could not be accurately timed, it wasn't bright at Feb 23.10 and it was at 2 / 23.443. The Mt Blanc LSD burst was at 2 / 23.12, while the other two detectors had a mutual burst at 2 / 23.316. Note that both neutrino bursts occurred before the optical SN was detected, and also that none of the other detected picked up the Mt Blanc LSD burst.
All of this has been known a long time, and numerous theories have been introduced to explain it.
- formation of a nlack hole (from the neutron star)
- formation of a quark star (from the neutron star)
- the Mt Blanc data were unrelated to the SN (that appears to be Arnett's viewpoint).
So, this is another explanation, and not a super compelling one to me. It will clearly never be proven from the SN 1987A data - the next such close supernova should have a lot of neutrino data, and maybe will resolve the issue.
If you reverse the polarity of the neutrino beam, you might be able to detect the tachyon pulse that's out of phase with normal matter!
In my conception (which may be flawed; I came to this conclusion after university physics classes that I didn't always understand as well as I should have, and these were 20+ years ago), the speed of light is governed by "the rate at which things can happen".
Electromagnetic waves propogate because a changing electric field produces a changing magnetic field which produces a changing electric field, etc. For reasons that I can't remember these changing fields occur in a slightly offset position each time, so that the fields move through space as they create each other.
If causes and effects could occur at an infinite rate, the waves would move infinitely fast; but since there always has to be a time gap between a cause and an effect, there is a fixed upper bounds for the rate at which these fields can produce each other.
There is also a fixed lower bounds on the minimum offset that can occur between the electric and magnetic fields.
So what you have is essentially effects occurring as quickly as possible over distances as small as possible. The ratio of the smallest possible time between a cause and an effect, and the smallest possible distance between an electric field and the magnetic field it produces and vice versa is ... the speed of light.
So why can't light go faster than c? Two reasons really: a) things "can't happen" faster than the cause-effect relationship of a magnetic field producing an electric field, and vice-versa; and b) distances between an electric field and the magnetic field it produces, and vice-versa, can't be smaller.
I vaguely remember that this is related to one of the cool aspects of Calculus - the ability to take the ratio of an infinitesimally small number to another infinitesimally small number, each expressed as a limit approaching zero, and get a calculatable, real number result.
In this case, if you take the limit as distance approaches zero, divided by time as it approaches zero, you get the speed of light - the ratio of two infinitesimally small numbers (the smallest unit of distance over the smallest unit of time).
Anyway that's how I explain it to myself.
None of your questions can be answered by science. Science is a great tool, but can't answer "why" things are the way they are. Just be grateful it is not different, otherwise we wouldn't even be here to ask the questions.
Similarly, asking what happened before the big bang is meaningless. Stephen Hawking puts it beautifully:
Since events before the Big Bang have no observational consequences, one may as well cut them out of the theory, and say that time began at the Big Bang. Events before the Big Bang, are simply not defined, because there's no way one could measure what happened at them.
This doesn't mean you can't enjoy pondering these questions if that's what you want to do, but do so with full realization you're now in the realm of philosophy, religion, and mysticism - not science.
and oh by the way photons can momentarily turn into other shit on their journeys yet somehow neutrinos can't.
I don't study particle physics, but from what I understand, for photons or neutrinos to "turn into other shit", they need to interact with something -- such as the particles they create, atomic nuclei, etc. Photons interact through electromagnetic forces -- which is the strongest force out there. In contrast, neutrinos interact via the weak force. As you might guess, that force is very weak. That's why neutrinos are so hard to detect.
Since photons interact with "other shit" via a much stronger force than neutrinos, photons are much, much, much more likely to "turn into other shit" than neutrinos are.
So, sorry internet troll, this isn't "cherry picking"; it's science. Deal with it.
Agreed. But that's kind of my point. It's easy to wonder why light has to be bounded by a maximum speed because we can easily ask "why not faster"? For me it makes it clearer that there are fundamental aspects of physics/reality at work here to keep in mind that it's really the ratio of the smallest distance to the shortest time.
Yes, you do then have to ask "why is there a smallest distance" and "why is there a shortest time", but at least for these questions, I have an answer I can live with: because there has to be a separation between cause and effect, so there has to be a shortest time in between which two things can happen. If the time that it takes for an electric field to propogate a magnetic field and vice versa, which has no time component as far as I remember in the equations governing how this happens, has nothing limiting it to happening with a shorter time duration between the cause and the effect (which I believe is true, at least according to electromegnetic theory), then this is the shortest time.
A similar argument can be applied to explaining why there is a shortest distance.
So basically, for me, it is more directly meaningful to think of there being a smallest possible time increment (because there *must be*, otherwise zeno's paradox and all that), and a shortest possible distance (once again because there *must be*, for the same reason), than to think of there being a limit to the speed of light, which otherwise logically I can't understand, except in the terms that I described in this and in my prior post.