neutrinos travel at a velocity 20 parts per million above the speed of light

[ASH]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

ASH, do you have a take on Garrett Lisi and his E8 Theory of Everything? Crackpot? Genius in the making? Wrong, but usefully so? Etc etc etc. Can't get a handle what the serious physics folks think of him, but when he first presented his paper it seemed like he had at least got their attention.

He sounds to me like a "normal" particle physicist. He has a Ph.D. in theoretical physics from a good school, so he's not even approaching the problem "from outside the system", as it were. As far as I can tell, he is using the usual theoretical tools to approach the problem, albeit possibly in an innovative way. The only thing odd about him is his life style. He isn't claiming to re-write the rule book or revolutionize physics (by, say, throwing out foundations like quantum mechanics or relativity), and he's not spouting nonsense or non sequiturs. Instead, working within a well-established framework, he is saying he thinks he's made some progress on a problem of great significance that physicists have been hacking away at for decades. It seems to me that his ideas are attracting the normal type of criticism and analysis that meet similar theories advanced by others.

I remember seeing a cartoon, possibly by Sheldon Glashow, that satirized the mathematical search for grand unified theories. It was something to the effect of "Step 1: Choose a symmetry group. Step 2: Break symmetry. Step 3: Calculate particles and masses. Wash, rinse, repeat." Anyway, when I was a teenager in the late 80's and early 90's, I used to avidly read popularizations of particle physics -- and it's like nothing has changed. Hyping the latest and greatest would-be unification theory is the bread and butter of popular science publications and television shows. There were the Grand Unified Theories of the 1980's which predicted proton decay (which was not observed)... super-string theory (still a going concern, I think, but increasingly a kludge)... twistors...

The amazing success of electro-weak unification, which was based on the mathematics of symmetry groups, established the basic mathematical way to unify physics. Glashow found the correct symmetry groups that describe electromagnetism and the weak nuclear force in a single theory, something denoted SU(2)xU(1), back in 1961; the theory of electro-weak unification based on this symmetry was completed in 1968. Ever since then, particle physics has been about identifying symmetry groups that might describe the particles and forces we observe, working out what other particles and forces are implied by the symmetry, and then looking for those undiscovered particles with an accelerator. Glashow shared the 1979 Nobel prize in physics for electro-weak unification before the new particles the theory predicted were directly detected (in 1983), because indirect evidence was observed in 1973. But basically, the particle physics community has done nothing but crank out different combinations of symmetry groups, searching for patterns that match what we observe experimentally, for longer than I've been alive. Lisi's E8 is another variation on this theme. Based on reading the Wikipedia article on it, Lisi hasn't been able to predict particle masses with his theory yet, so that is one barrier to testing it. On the other hand, his theory does at least predict the number and type of particles, so if the LHC sees something that doesn't fit Lisi's pattern, it could falsify Lisi's theory. The general bet right now is that the parts of the universe we don't know what are (dark matter; dark energy) are most likely related to the undiscovered particles associated with one of the symmetries like E8. But there are tons of different competing theories, and so far no winners. One of the latest pieces of news is that the LHC isn't seeing evidence of supersymmetry, which had been one of the leading contenders.

[Starving Steve]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

If a neutrino can travel faster than the speed of light, then a neutrino would arrive to me before the light from its starting gate reaches me to indicate that the neutrino has left to begin its journey. So does that mean that the neutrino went backward in time since the speed of light binds all of the information in the universe together? Or what does this mean? Something like a neutrino arrives before it has departed. How so?

As usual, I am lost.

[ASH]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

If a neutrino can travel faster than the speed of light, then a neutrino would arrive to me before the light from its starting gate reaches me to indicate that the neutrino has left to begin its journey. So does that mean that the neutrino went backward in time since the speed of light binds all of the information in the universe together? Or what does this mean? Something like a neutrino arrives before it has departed. How so?

I'm not sure there's a really intuitive way to understand the implications for causality of faster-than-light-in-vacuum travel. The usual way to work through a problem like this is to carefully define the space-time coordinates of a pair of events in one inertial reference frame, and then work out the coordinates of the same events when viewed from a different reference frame that is moving relative to the first one. If you do this, you can find situations where faster-than-light travel results in an effect preceding its cause.

Mathematically, the Lorentz transformations are algebraic recipes for converting coordinates from one "point of view" in special relativity to the coordinates observed from another. So, given the Lorentz transformations, you can read how transmitting information faster than light (which could include sending a physical particle faster than light) breaks causality here. But that is only going to be satisfying if you're comfortable that the Lorentz transformations themselves make sense.

The only intuitively appealing way to look at special relativity that I've encountered is the geometrical interpretation I described earlier in this thread -- the stuff about the space-time interval between two events remaining the same, regardless of one's state of motion. The Lorentz transformations fit into that picture, but at some point, there is enough algebra between the intuitively-appealing physical picture and the interesting implication that handy-wavy explanations aren't that satisfying.

[ocelotl]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

I'm not trying to be an "all knower" about this, since my background in theoretical physics is a bit limited, but a systematic error of 60 ns is enough to show in repeated experiments and to be easily detected even with OXCO time bases... And on this I'm taking personal experience with VSAT modems on field. Maybe measurement mistakes are enough to cover this discrepancy on the lab. We must wait for confirmation, or use a larger distance base.

[Alvaro Spain]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

No -- nothing at all, including particles without rest mass.



Why c is regarded as an upper limit on speed[/URL] is a bit too complicated to describe well in text (and honestly, 17 years after taking special relativity, I didn't retain the details of the argument as well as the stuff about the interval), but it relates to the same basic geometry.

27 years have passed since I studied special relativity at the university, and you can safely assume that I remember almost nothing of it. But, if you allow me a simple question, is not c as an upper limit on speed an axiom (or principle) of the theory and not a deduction from it?

[ASH]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

27 years have passed since I studied special relativity at the university, and you can safely assume that I remember almost nothing of it. But, if you allow me a simple question, is not c as an upper limit on speed an axiom (or principle) of the theory and not a deduction from it?

It is an axiom of the theory that c has the same value in all inertial reference frames, but c as an upper limit on the speed at which you can transmit information is a deduction. The way the theory is usually developed, you start by assuming that c is invariant, and use that assumption to derive coordinate transformations between inertial reference frames. Then, using those coordinate transformations, you can show that faster-than-light transmission of information can lead to violations of causality.

One reason I like the "c as a unit conversion factor" viewpoint is that a geometric interpretation of the invariant space-time interval makes more intuitive sense than arbitrarily deciding that c is a special speed that is the same in all inertial reference frames. It makes sense that a unit conversion factor doesn't depend upon your state of motion, and that there's something like a "distance" in space-time that is the same, regardless of how you are moving. But historically, I think the constancy of c was the starting point for developing special relativity, and the geometric interpretation is something that was discovered along the way.

[ASH]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

There is a short write-up about different approaches to formulating special relativity here.

As the link notes:

As formulated by Albert Einstein in 1905, the theory of special relativity was based on two main postulates:

1. The principle of relativity — The form of a physical law is the same in any inertial frame.

2. The speed of light is constant — In all inertial frames, the speed of light c is the same whether the light is emitted from a source at rest or in motion. (Note this does not apply in non-inertial frames, indeed between accelerating frames the speed of light cannot be constant. Although it can be applied in non-inertial frames if an observer is confined to making local measurements.)

The geometric description I favor is in terms of Minkowski space-time, which was a reformulation dating from about 1907.

I was previously unaware of the work of Jong-Ping Hsu and Leonardo Hsu, but in reading this Wikipedia article, I see that the geometric formulation that stresses the role of c as a unit conversion factor is formally called Taiji relativity. This is probably because Hsu and Hsu wrote up their formulation in about 1996, after I had already taken special relativity in college (in 1994). But as the article notes, other physicists -- including the pair who wrote my college relativity textbook -- had already made the basic connection, which is why I was aware of the concept. It's kind of neat that although the nuts and bolts of what special relativity says hasn't really changed in 100 years, it was still being reinterpreted when I was in school.

Anyway, if I understand the history correctly, special relativity started out primarily as an exercise in algebra: writing down coordinate transformations between different inertial reference frames, assuming that the speed of light and the laws of physics are the same in all inertial reference frames. A bit later, it dawned upon Minkowski that the coordinate transformations implied some mixing about what was a separation in time versus a separation in space, depending upon one's state of motion, and this motivated thinking about space and time as a unified playing field. And general relativity, which came along in 1916, was both an extension of the postulates of relativity to accelerating reference frames and an explicitly geometric description of gravity. The role of geometry in general relativity is probably why physicists later emphasized the geometric interpretation of special relativity, even though it started out as a matter mostly of algebra.

[Jam]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

It is an axiom of the theory that c has the same value in all inertial reference frames [...]. The way the theory is usually developed, you start by assuming that c is invariant, and use that assumption to derive coordinate transformations between inertial reference frames.

While it is true that Lorentz transformation is often derived assuming constant c, there exists an approach that uses a (much) weaker assumptions and obtains constant c as a consequence, rather than an assumption. See http://en.wikipedia.org/wiki/Lorentz...oup_postulates or http://www.eecis.udel.edu/~murakows/lorentz/lorentz4/lorentz4.html. Eqs. (2.10) and (2.11) in http://www.eecis.udel.edu/~murakows/lorentz/lorentz4/node2.html is where the presence of a constant first emerges.
This way of obtaining Lorentz transformation is particularly revealing since you realize that the only postulates are:
1. The principle of relativity; i.e., there is no such thing as 'absolute' motion--only relative motion between observers (reference frames) makes physical sense.
2. Space is isotropic; it looks the same no matter which way you turn.
Augmenting the above with the postulate of simplicity leads to the special relativity formulas as one of only three options, and gives constant c as a free bonus.
So, if someone calls (special) relativity into question, they better understand what they are up against since they would have to either give up simplicity, or (re)introduce the idea of absolute motion, or introduce spatial anisotropy.
The down side is that you actually have to do some math to fully understand and appreciate the limitations imposed by the postulates above.

One reason I like the "c as a unit conversion factor" viewpoint is that a geometric interpretation of the invariant space-time interval makes more intuitive sense than arbitrarily deciding that c is a special speed that is the same in all inertial reference frames. It makes sense that a unit conversion factor doesn't depend upon your state of motion, and that there's something like a "distance" in space-time that is the same, regardless of how you are moving. But historically, I think the constancy of c was the starting point for developing special relativity, and the geometric interpretation is something that was discovered along the way.

Clearly, invariant space-time interval is also a consequence of the postulates above.

[ASH]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

While it is true that Lorentz transformation is often derived assuming constant c, there exists an approach that uses a (much) weaker assumptions and obtains constant c as a consequence, rather than an assumption. See http://en.wikipedia.org/wiki/Lorentz...oup_postulates or http://www.eecis.udel.edu/~murakows/lorentz/lorentz4/lorentz4.html. Eqs. (2.10) and (2.11) in http://www.eecis.udel.edu/~murakows/lorentz/lorentz4/node2.html is where the presence of a constant first emerges.
This way of obtaining Lorentz transformation is particularly revealing since you realize that the only postulates are:
1. The principle of relativity; i.e., there is no such thing as 'absolute' motion--only relative motion between observers (reference frames) makes physical sense.
2. Space is isotropic; it looks the same no matter which way you turn.
Augmenting the above with the postulate of simplicity leads to the special relativity formulas as one of only three options, and gives constant c as a free bonus.
So, if someone calls (special) relativity into question, they better understand what they are up against since they would have to either give up simplicity, or (re)introduce the idea of absolute motion, or introduce spatial anisotropy.
The down side is that you actually have to do some math to fully understand and appreciate the limitations imposed by the postulates above.


Clearly, invariant space-time interval is also a consequence of the postulates above.

[ASH]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

I'm not trying to be an "all knower" about this, since my background in theoretical physics is a bit limited, but a systematic error of 60 ns is enough to show in repeated experiments and to be easily detected even with OXCO time bases... And on this I'm taking personal experience with VSAT modems on field. Maybe measurement mistakes are enough to cover this discrepancy on the lab. We must wait for confirmation, or use a larger distance base.

I'm not up on all the details of their experiment, but they were transmitting neutrinos through the earth's crust, since the lab that detects the neutrinos is 730 km away in Italy, and is over the horizon. They didn't actually fire off synchronized neutrino and optical pulses, and time which signal arrived first. Instead, they timed the departure and arrival of the neutrino pulses, and measured the distance between start and finish to get the velocity. It's a much less direct "race" than the case of SN1987A, which produced both a neutrino pulse and an optical flash (and that over a much larger distance base). Based on CERN's press release, they were relying upon their ability to measure the straight-line distance through the earth's crust in order to figure out the speed of the neutrinos:

"In order to perform this study, the OPERA Collaboration teamed up with experts in metrology from CERN and other institutions to perform a series of high precision measurements of the distance between the source and the detector, and of the neutrinos’ time of flight. The distance between the origin of the neutrino beam and OPERA was measured with an uncertainty of 20 cm over the 730 km travel path. The neutrinos’ time of flight was determined with an accuracy of less than 10 nanoseconds by using sophisticated instruments including advanced GPS systems and atomic clocks. The time response of all elements of the CNGS beam line and of the OPERA detector has also been measured with great precision."

Anyway, the SN1987A data proves that electron anti-neutrinos don't travel faster than light over long distances in vacuum. The CERN work is with muon-neutrinos traveling through matter. Most of the speculation I've read about what this could be, if it is real, centers on the possibility of the neutrinos taking a "short cut" associated with the presence of matter, rather than violating the speed of light. But I guess we'll see if the experiment can be reproduced.

[Ghent12]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

Well 60 ns at the speed of light is roughly 18 meters of length. I wonder... Is there a spare 18 meters of "cable" running through the detection equipment unaccounted for?

[we_are_toast]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

Those weird faster-than-light neutrinos that CERN thought they saw last month may have just gotten slowed down to a speed that'll keep them from completely destroying physics as we know it. In an ironic twist, the very theory that these neutrinos would have disproved may explain exactly what happened.

Back in September, physicists ran an experiment where they sent bunches of neutrinos from Switzerland to Italy and measured how long the particles took to make the trip. Over 15,000 experiments, the neutrinos consistently arrived about 60 nanoseconds early, which means 60 nanoseconds faster than the speed of light. Einstein's special theory of relativity says this should be impossible: nothing can travel faster than light.

The fact that the experiment gave the same result so many times suggested that one of two things was true: either the neutrinos really were speeding past light itself and heralding a new era of physics, or there was some fundamental flaw with the experiment, which was much more likely. It's now looking as though the faster-than-light result was a fundamental flaw, and appropriately enough, it's a flaw that actually helps to reinforce relativity rather than question it.

...

To understand how relativity altered the neutrino experiment, it helps to pretend that we're hanging out on one of those GPS satellites, watching the Earth go by underneath you. Remember, from the reference frame of someone on the satellite, we're not moving, but the Earth is. As the neutrino experiment goes by, we start timing one of the neutrinos as it exits the source in Switzerland. Meanwhile, the detector in Italy is moving just as fast as the rest of the Earth, and from our perspective it's moving towards the source. This means that the neutrino will have a slightly shorter distance to travel than it would if the experiment were stationary. We stop timing the neutrino when it arrives in Italy, and calculate that it moves at a speed that's comfortably below the speed of light.

"That makes sense," we say, and send the start time and the stop time down to our colleagues on Earth, who take one look at our numbers and freak out. "That doesn't make sense," they say. "There's no way that a neutrino could have covered the distance we're measuring down here in the time you measured up there without going faster than light!"

And they're totally, 100% correct, because the distance that the neutrinos had to travel in their reference frame is longer than the distance that the neutrinos had to travel in our reference frame, because in our reference frame, the detector was moving towards the source. In other words, the GPS clock is bang on the nose, but since the clock is in a different reference frame, you have to compensate for relativity if you're going to use it to make highly accurate measurements.

...

http://dvice.com/archives/2011/10/speedy-neutrino.php

[ASH]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

Curiouser and curiouser...

The experiment has been repeated, with tighter neutrino bunches at CERN. It will still be awhile before there's data from independent experiments...

The team which found that neutrinos may travel faster than light has carried out an improved version of their experiment - and confirmed the result.

...

Initial analysis of the work by the wider scientific community argued that the relatively long-lasting bunches of neutrinos could introduce a significant error into the measurement.

Those bunches lasted 10 millionths of a second - 160 times longer than the discrepancy the team initially reported in the neutrinos' travel time.

To address that, scientists at Cern adjusted the way in which the proton beams were produced, resulting in bunches just three billionths of a second long.

When the Opera team ran the improved experiment 20 times, they found almost exactly the same result.

...

Next year, teams working on two other experiments at Gran Sasso experiments - Borexino and Icarus - will begin independent cross-checks of Opera's results.

The US Minos experiment and Japan's T2K experiment will also test the observations. It is likely to be several months before they report back.

The newer result is based on just 20 detections. Also, if there is some sort of systematic error in the measurement, then repeating it on the same equipment doesn't prove anything. One story on the new result mentions the possibility of signal propagation timing errors caused by aging materials:

The latest result is consistent with the one presented in September, but both could still be wrong. Precision measurements of this sort are fraught with difficulty and other sources of error may have crept in. For instance, when a neutrino strikes the detector in Gran Sasso, that signal has to travel 8km through a waveguide before a timing measurement can be made. The properties of the waveguide were last measured three years ago. Any changes to those properties—caused by ageing of the plastic of which it is made, say—could lead to an overestimate of the time it took the signal to run the length of it, and thus to an underestimate of neutrinos' actual time of flight.

[we_are_toast]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

Brian Greene expressed a great deal of skepticism about these results and says the vast majority of his colleagues are skeptical as well. He talked about the extreme difficulties of taking measurements for the experiment. One of his points for skepticism was the the precision needed to measure the distance from the neutrino transmitter and the neutrino receiver.

http://www.npr.org/player/v2/mediaPl...53&m=142518934

By the way, Dr. Greene has an excellent 4 part series running on PBS's NOVA called "the Fabric of the Cosmos".

[ocelotl]

Re: neutrinos travel at a velocity 20 parts per million above the speed of light

Well 60 ns at the speed of light is roughly 18 meters of length. I wonder... Is there a spare 18 meters of "cable" running through the detection equipment unaccounted for?

We have to check if the delays at both the emission and detection circuitry are taken into account, In copper, signal waves (not electrons, and that is explained here) propagate at a lower speed than light (read here). Also we have to take into account the delays caused by parasitic impedances and the junctions on semiconductors (an example here), and all these add up and can be measured. It all may be just a few picofarads and a few nanohenries and the junctions may add several nanoseconds (read here, and here), but at the time scale considered in the experiment, it all counts.

Brian Greene expressed a great deal of skepticism about these results and says the vast majority of his colleagues are skeptical as well. He talked about the extreme difficulties of taking measurements for the experiment. One of his points for skepticism was the the precision needed to measure the distance from the neutrino transmitter and the neutrino receiver.

http://www.npr.org/player/v2/mediaPl...53&m=142518934

By the way, Dr. Greene has an excellent 4 part series running on PBS's NOVA called "the Fabric of the Cosmos".

We also have to take into account that the detector is in a different Earth Crust plate than the transmitter, and thus, even with decimeter resolution GPS measurement, magnetic fields within the Alps range can alter the radio signal propagation that has to follow a longer path (due to both the Earth's curvature and the lack of plain terrain between emitter and the receiver) than the neutrinos, as has been posted before.