I have been prompted to write this blog, instead of chilling with a glass of wine after a busy week and watching a movie on TV, because of the flurry of comments via email and Twitter that I have received today regarding the latest news from the Opera neutrino experiment.
It’s entirely my own fault. After the first announcement back in September I volunteered on Twitter, then on BBC television to eat my boxer shorts on live TV if this result is proven to be right. Now, many people mistakenly believe that this second repeated experiment is the confirmation needed for me to fetch the ketchup.
Let me begin by making two statements that I hope are very clear and that I can refer back to if necessary:
- The result from Opera is still only a measurement, not a discovery
- I would absolutely love it if it were true and particles could indeed travel faster than light. It’s heaven for physicists because it means the whole of modern physics is back up for grabs again. We would need something to replace Einstein’s theories of relativity or at least a way of fixing them.
OK, so, briefly, what is all the fuss about? Well, neutrinos are tiny elementary particles that are almost weightless and which pretty much ignore the presence of all other matter. We all have millions of neutrinos streaming through our bodies that arrive from space, mainly from the Sun. And they do this even at night because those neutrinos can pass right through the whole of the earth (when the sun is on the other side) before coming up through the ground, up our feet and leaving to continue through space. Now, neutrinos are so light that they are able to travel almost at the speed of light. We know there are three types of neutrinos (electron neutrinos, muon neutrinos and tau neutrinos). I won’t go into the technical details. Basically, the most common, the electron neutrinos are produced in what is known as beta decay inside the nuclei of atoms.
The Opera experiment involved timing a beam of mostly muon neutrinos between their point of origin at CERN in Geneva and the arrival point at a the Grand Sasso Lab in Italy (which has special detectors than can capture these elusive particles. The travel distance is 730 kilometers and the neutrinos appear to be able to cover this at a speed faster than light. Basically, they arrive 20 billionths of second sooner than light would were it travelling in a vacuum. Of course, even though these neutrinos are travelling underground, it’s as though they are moving through empty space since they don’t interact or bump into anything.
Maximum speed limit
There is nothing that annoys people more about Einstein’s theory of relativity than its claim that nothing can travel faster than light. Why can we not conceive of anything moving at a speed of over a billion kilometres per hour? Granted, this is a stupendously high speed to which nothing that we know of (apart from subatomic particles) can get close, but special relativity seems to be saying that the laws of nature forbid anything from going faster.
This is hard to stomach if you haven’t followed the logical steps and the careful experimental tests of Einstein’s relativity. I do not plan to go through the details but will instead try and give a flavour of why physicists are so confident that there is a universal speed limit. You see in a sense it is not light that is so special that it holds the speed record, but rather that way space and time themselves are intertwined in our universe implies that there is a maximum speed limit beyond which those laws of physics break down. In our universe this speed happens to be 299,792,458 metres per second, or 186,282 miles per second. Light, because it has no mass, is able to travel at this speed. In fact, in the vacuum of empty space, light is unable to speed up or slow down but is constrained to always move at this speed.
There are a number of ways to explain why the speed of light is the upper speed possible in our universe. One method is by using algebra. (Oh great, you’re thinking, that will really convince me; a load of equations full of Greek symbols is just what is needed to put my mind at rest.) I will not go into all the gory details. Suffice it to say that, in special relativity, speeds get added up in a very strange way.
It also turns out that the faster an object moves the heavier it becomes, and the harder it gets to make it go even faster. The closer it gets to the speed of light, the larger its momentum becomes, but this is by virtue of its increasing mass, not its velocity. Consider what happens to an object’s mass when it moves very fast. The single most important consequence of the equations of special relativity is how mass and energy are related. Einstein showed that mass can be converted into energy and vice versa. The two are related through the equation E=mc2, which tells us how much energy is locked up in any given mass. The c stands for the speed of light, and thus the quantity c2 (the speed of light times itself) is a very large number indeed and explains how we can get so much energy out of a small amount of mass. This equation suggests that that we can think of mass as frozen energy.
Since a moving object also has energy due its motion (called its kinetic energy), its total energy will be the sum of the energy frozen as mass when it is not moving plus its kinetic energy. The faster it moves the more energy it has. This means that the real mass of an object will be due to its frozen energy plus the energy due to its motion. Most of the time the frozen energy of an object (its mass) is so much more than the energy of its motion that we can ignore the latter and take the mass to be constant. But as the speed approaches that of light the kinetic energy becomes so great it can exceed the frozen energy. Thus the mass of a fast moving object is much greater than its mass when stationary.
You can now see the problem of trying to attain light speed. Imagine an accelerating train engine pulling a single carriage. What if, for every ten kilometres per hour faster that it goes, another carriage is added. It would therefore have to work harder just to maintain its speed. The faster it goes the more carriages it has to pull, and the more power it needs. In the same way, the faster a body moves the heavier it will seem, and the harder it will be to make it go any faster. To accelerate it up to the speed of light would require an infinite amount of energy, which is impossible.
Finally, the real real real clincher is this: If anything can travel faster than light in our frame of reference, then we will always be able to find another frame of reference (i.e. another perspective from someone moving relative to us) in which it will appear to be moving backwards in time. Remember of course that if Einstein is right then all frames of reference are equally valid (all motion is relative). In this new frame, causality is violated – that is, causes have to come before their effects, otherwise we are left with a paradox. For instance, if A were to shoot B with a faster than light bullet, then it will appear to some observers as though the bullet is moving backwards from B to A’s gun. That is B is shot before A pulls the trigger, so he could decide not to after B is shot!!
See how crazy violation of causality is, and just how much this neutrino experiment needs to explain away???
Could Einstein have been wrong?
Ultimately, the speed of light being the maximum speed limit is written into the fabric of reality itself. But what if we’re wrong? Is there a way of understanding this result? The simple answer is that we cannot with our current theories and understanding. We would need to overhaul the whole of modern physics, and we would need to find a way of explaining away the thousands of other experiments that over the past century have all confirmed that nothing can go faster than light. We may have to bring back the aether, or modify Einstein’s equations. We would have to explain why no other neutrino experiment showed such a result, and why none of the trillions of neutrinos coming from supernovae manage to exceed light speed.
So, yes of course Einstein could be wrong. The whole point of a scientific theory is that it is there to be shot down – to be shown to be false by new experimental evidence or to be replaced with a better, more accurate or more profound theory that explains more about the universe. But… extraordinary claims require extraordinary evidence, and Einstein’s ideas have been checked too carefully for too long for one experiment to come along and destroy all that. But of course that is all it would take if this experiment is proved correct.
Nobel prize winner, Sheldon Glashow, together with Andrew Cohen have predicted that such faster-than-light neutrinos would have to be radiating electrons and their antiparticles, positrons, all along their route from CERN to Grand Sasso via a process called vacuum Cerenkov radiation and hence lose energy. This is not seen. It’s a bit like an aircraft that manages to break the sound barrier silently and without a sonic boom. It just isn’t possible folks.
So, what would it take for it to be possible. I reckon there are two possibilities (there are other more exotic ones that are rather too speculative):
a) Einstein was wrong and there is an aether: technically, what is known as Lorentz invariance is violated here and there is a preferred frame of reference.
b) Einstein was wrong and Lorentz invariance has to be modified: technically, there may be nonlinear correction terms in the mass-energy relation.
I am not prepared yet to buy into these, or notions of tachyons (hypothetical faster than light particles), or wormholes as shortcuts through space-time or replacing the electroweak theory, etc. All this technical hot air basically means I prefer to appeal for now to Occam’s razor and go for the simplest explanation: there is still an error in the experiment.
So what could be wrong with the experiment?
I should say that this experiment is a highly complex one and has been carried out with the utmost care and attention to detail. I am a theoretical physicist not an experimentalist so I certainly refuse to insult my colleagues at CERN and Grand Sasso by trying to point out where they may have gone wrong. They know where uncertainties still lie. So far, they have ruled out one potential source of systematic error.
Not all the scientists involved in the experiment wanted to sign the paper because they were themselves yet to be convinced. After this second check, four of the physicists who had not signed the paper in September now agreed to sign it, but four more who had signed the first one now asked for their names to be removed from the new one.
Having said this, here are a few potential problems:
1. The neutrinos are produced via a complex process: protons from the SPS at CERN are fired in pulses at a carbon target, producing new particles: pions and kaons, which decay to produce muons and neutrinos. The muons are stopped in detectors while the neutrinos continue on to Italy. The start of their journey time is itself not recorded directly but is started from the timing of the proton beam and so the long process has to be subtracted away from total time to leave just neutrino’s travel time.
2. At both ends there are complicated electronics that may contain tiny systematic timing errors.
3. The timing has to be done via GPS satellite. We know that GPS systems only work if we carefully take into account Einstein’s theory of relativity. It seems strange to me that Einstein’s equations (both special and general relativity) need to be taken into account to measure something that is proving them wrong. It just doesn’t make sense. In any case, the experimenters haven’t ruled out an error in the GPS relativistic timing.
What next?
The experiment needs to be re-run independently by other particle physics laboratories, and plans are currently underway for this to take place in Japan and the US, but it will take some months at least.
I am happy to eat my boxers on live TV. It would be a small price to pay for the thrill of so much new physics. But let’s not be too hasty just yet, eh?
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Potential problem 3 struck me as well, can’t have it both ways right!
The Cerenkov radiation issue is interesting, not seen that mentioned before.
Isn’t the distance corresponding to the timing discrepancy about the same as the size/length of the target, are we less sure of the mechanism of pion kaon production than special relativity?
Jim
I’m not sure that potential problem 3 is such an issue; it just confirms that any replacement theory would have to encompass all the existing experimental support for Einstein’s relativity.
All this “FTL neutrino implies SR is wrong and causality is broken” nonsense I’ve been subjected to is extremely annoying. http://www.guardian.co.uk/discussion/comment-permalink/13051532
(“is” -> “has been”)
For posterity, I’ll note that this is a comment linking to a comment linking to a comment linking to papers! (But it’s very interesting.)
Heh! Yes – sorry about that. I’ve actually put direct links to the two papers on arXiv in another comment below.
Chapeau Jim. Thanks for bringing the debate back down to Earth. The speed of light isn’t the maximum speed of light for the sake of satisfying some upper limit figure: it is at heart of the very definition of matter-energy conversion. You may even leave aside Einstein’s theory of relativity. It is his equation E=mc^2 that matters in this instance. Funny we tend to forget that the great man graced science and humanity with this equation well before the mathematisation of relativity (with the help of Mankowski). Is any one suggesting that “energy” should be ruled out of neutrinos or vice versa? Come on.
I have a doubt.
Why the “speed limit” must be the speed of light and not a slightly different speed, (speed of neutrinos, for instance)?
This is because the particles of light, photons, are massless. Since they have no mass, they move through space as fast as possible, and experience no time.
Neutrinos, on the other hand, do have mass, so they cannnot (should not) move as fast as their no-mass cousins.
Assuming Einstein’s equations are right in order to prove them wrong is just standard practice for a “reductio ad absurdum” argument, is it not?
Oh, by the way, “koans” ≠ “kaons”.
Well explained prof. can’t wait for the result of independent experiments in US and/or Japan. If such a thing turn out true, I think results from LHC experiments would be entirely useless until a physics is re-written.
one question though:
Would it be possible the laws of nature change as time passes by?
Ehsan
so far and at this point, nothing to raise eyebrows about. A lot still needs to be done to bring down what Einstein left for us. Thanks Prof, I’m completely convinced!
The possibility of our laws of physics changing with time would be an interesting concept to ponder. If this were true then physicists would likely begin studying the laws of these changes instead of just physics at the present, such that they can prepare for the physics that are yet to come.
I’m sure there’s an awesome sci-fi novel in there.
If the scientists are right that neutrinos are faster than light, then contrary to what most experts believe in, neutrinos do not have any mass. And since they do not interact or interact as strongly as photons to the numerous types of particles, antiparticles, matter, dark matter, virtual particles and gravity in a vacuum, they are not slowed down by these entities as in the case of light. Therefore they should be able to move faster than light. The C in Einstein’s equation should be the speed of neutrinos in a vacuum!
Actually, the particle or entitiy that has no mass, no charge and absolutely do not react or interact with anything in this universe should hold the ultimate speed record. Unfortunately, it is by definition impossible to detect.
Alternatively, if neutrinos do have a tiny mass, then the speed of light in an absolute vacuum where there are none of those numerous types of energy, particles, matter, gravity etc. is in fact much higher than the 300,006 km/sec of the speed of the measured neutrinos. In other words, C > 300,006 km/sec and the neutrinos have not exceeded the real unimpeded speed of light. The speed of light that we have been measuring is not the maximum speed that light is capable of if it is not slowed down by the numerous “things” that really exist in a so called vacuum.
For instance if we were to imagine that we all live in a block of glass, and if we were to measure the speed of light, we would find that the speed is only 70% of the present accepted value of the speed of light in a vacuum and that of neutrinos which are not slowed down by the glass atoms will still be at 300,006 km/s.
Light doesn’t always travel at the same speed, true, that’s how lenses work.
And actually particles can travel faster than light, if the light is slowed down, lie in water, that’s how Cerekov radiation comes about.
I don’t think you can just adjust the maximum speed in special relativity, replace c by some other slightly larger value, and be consistent, the speed limit has that value and light must necessarily travel at that speed in a vacuum.
Jim
Sorry, should read. “like in water”
Jim
“I don’t think you can just adjust the maximum speed in special relativity, replace c by some other slightly larger value, and be consistent, the speed limit has that value and light must necessarily travel at that speed in a vacuum.”
That’s all very true – the invariant speed of SR is c etc. and nothing is ever going to change that – but, contrary to popular belief, SR isn’t necessarily a (local) theory of everything:
http://arxiv.org/abs/gr-qc/0107091
http://arxiv.org/abs/1005.1614
“the numerous types of particles, antiparticles, matter, dark matter, virtual particles and gravity in a vacuum”
As far as I know, there are no particles/matter (anti-, dark, or normal) in a vacuum. Gravity is an attraction of masses, and since there is nothing with mass in a vacuum, there should also be no gravity. There are virtual particles, but from what I understand, they shouldnt affect the passing through of photons/neutrinos.
As for massless neutrinos, observations of supernova 1987A indicate that neutrinos do have mass, and it is likely less than 16 eV. If neutrinos moved faster than photons, we would have measured the neutrinos much earlier than we did.
To be very frank, I do not think that any scientist has ever been able to created a perfect vacuum on planet earth that does not contain even a molecule or an atom of matter! This can only be created in the imagination. It is well known that a so-called perfect vacuum has an intrinsic vacuum impedence and what I am trying to say is that the impedence of neutrinos in a vacuum is less than that of photons in the vacuum and as such has a great advantange as far as speed is concerned. In fact if the vacuum impedence to a massless particle like a photon were zero, the speed would be infinity!
And I forgot to mention that the effects of the gravity in a vacuum come from the planets, stars and galaxies and not just from the minute amount of matter in the vacuum itself.
If we assume that that the vacuum impedence of photons is 1 unit (the vacuum impedence of other electromagnetic forces = 376 ohms), then knowing the peculiar nature of neutrinos, the vacuum impedence of neutrinos is probably less than 1 unit and as such it has a great speed advantage.
Jim,
I generally agree with you. As an engineer, I remain a little sceptical with the overall accuracy of the measurements. They are reporting a speed of 1.0000237 c (or faster by just 0.00246 % c).
I do have a question, and I would be very interested in your thoughts and comments. With such a small relative difference in speed reported, how do we factor in Heisenberg’s Uncertainty principle ? I searched through the updated paper, and found no reference to Heisenberg.
On a related issue (!!), I tend to liken this reported result with the amazingly close finish to the Melbourne Cup horse race earlier this month … The photo-finish appeared to show a “nose hair” between the first two horses, circa 1-2mm difference ! I reckoned that it should have been called a “dead heat”, because the apparent gap on the frame could be impacted by inter-frame uncertainty, or even a slight parallax error, but I digress
Get ready to eat those shorts…but it’s ok…google “edible underwear” and it will be a pleasure..lol!!
How is the distance that the neutrinos travel calculated? Is it a straight line between the 2 points? Do neutrinos have to follow curved space time or do they go directly from a to b?
“Do neutrinos have to follow curved space time or do they go directly from a to b?”
If not via curved space-time, what route would be more direct?
A straight line I guess. (but that can’t be the case because they would have to disappear from space-time and then re-appear at the other end).
I love the idea of carbon bombarded by protons giving off quanta of zen
What about that X Factor though? Helluva show. You guys see it last night?
hahahha
Hi Jim
Tiny typo in “2. At both ends there are complicated electronics that mat contain tiny systematic timing errors.”
Should be “may contain”.
Nice explanation.
Why, if they can detect the neutrinos arriving, can they not detect them leaving by the same or similar means?
This *cant* be right. Think of all the sci-fi that has to be re-done from FTL to FTN (Faster than Neutrinospeed).
It just cant be done. hehe
As i recall, gravity also travels at lightspeed. Maybe it’s worth to re-measure?
This talk of light “travelling in a vacuum” departs from the fundamental standpoint of Faraday, Maxwell and (early) Einstein that space-filling fields are physical, as the formulation of Steven Weinberg, Logunov etc. of a real energy tensor for the gravitational field. Light travels not in a vacuum but in that field and waves in it, as well as in the electromagnetic (e-m) field.
If neutrinos have mass, they would likewise be travelling in the gravitational field and they would Cherenkov radiate in that field. But if they are massless like ‘photons’, but not perturbations of the electromagnetic field, they would be perturbations of a third space-filling ‘neutrinic’field. As that has an energy density, it automatically enters Einstein’s equation (ie. the Einstein-Hilbert unified field equation).
So physics can accommodate neutrinos faster-than-light without the drastic overthrow that Jim warns of – and in a way as Alice suspects (http://crisisinphysics.wordpress.com) that might force him to eat his boxers.
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Typical. If I had a nickel for every time a theoretical physicist declined to eat his underwear on TV because of special relativity…
The sideffects of quantum entanglement have causal effects that are faster than light. Or not?
–
Offtopic: Did someone hear about Burkhard Heim, what do you think about this person?
Found http://www.heim-theory.com/
“The whole point of a scientific theory is that it is there to be shot down – to be shown to be false by new experimental evidence or to be replaced with a better, more accurate or more profound theory that explains more about the universe. ”
Absolutely! Shame it doesn’t work out quite like that in the realm of climate science.
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Can somebody help me with the apparent violation of causality mentioned by Jim? He said in some reference frames, a shooter firing a supraluminal bullet would appear to receive the bullet into his gun rather than emit it, and the shooter could change his mind about shooting after his victim drops dead, causing a paradox. But the causal chain involving free will only needs to apply in the shooter’s frame of reference. A spectator in a moving frame would look at the shooter and see nothing that violates any law of physics. I don’t see a true paradox, just something that we are not accustomed to.
“But the causal chain involving free will only needs to apply in the shooter’s frame of reference.”
The fact that it doesn’t necessarily is the paradox! Consider a similar example: A shoots B in one inertial frame with a superluminal bullet. In another inertial frame, C passes B at the moment of B’s demise and immediately shoots another superluminal bullet at A which reaches and kills A before A pulls/pulled the trigger. If you look at the spacetime diagram on page 12 of this you can see that such a paradoxical situation can be arranged if ‘hard’ superluminal motion is allowed.
Oops! I seem to have got the link syntax wrong. The diagram is on page 12 of this: http://arxiv.org/abs/gr-qc/0107091
I am not quite convinced with your A shoots B argument, where you said that A would be able to decide not to pull the trigger after he shot B.
From what I understand, let A have a normal gun with a normal bullet (and not the one with speed of light) and say he is shooting B with it.
Assume that A is looking at his hand pulling the trigger through a medium other than vacuum through which the speed of light is so slow that bullet can reach B faster than light travelling through this medium reaches A’s eyes.
In this case again when A shoots, B would have been shot before A actually sees that he has pulled the trigger, but this does not mean that A can reverse his action. What we are only saying is that A comes to know of his action much later than it has already been done?
(The same situation could also have been created if A were looking at the trigger being pulled through a streamed video which had some delay)
I don’t see this as any violation of the laws of physics. Since the action has already been done there is no way to undo it. Yes, A came to know of it later but that’s all there’s to it.
This causality rule is really funny. Imagine that maximum speed of information is speed of sound. Then you are sitting in a trench and soldier next to you gets hit, after some time you hear gunshot. Omg causality rule is broken. B gets killed before A pulls the trigger. Can A change his mind after B is killed?
Nothing in the universe is perfect, regardless of how we like to think. Einstein was a theoretical physicist not a god and he does not dictate the way the universe works, having said that, E=MC^2 may in reality turn out to be E=MC^2+1 for all we know. Without the benefit of experimental data at the time that was the best that he could do. I say the law still exists we just need to add the 1.
Before we all shoot our mouths off, let another lab perform the experiment and get the data, only then will Jim need to get the soy sauce out.
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Now what would happen if it was possible for a particle to have negative mass…
If these neutrinos are moving backwards through time, then perhaps we should call them oldtrinos.
Jim, I think you should eat your boxers and if you are right and these results are flawed you can rest assure that no one will travel back from the future to stop you.
Hey Jim, how do you like your shorts cooked? Rare, medium, or well done?
Given that the timing side seems like it could be correct (atomic clocks, satellites etc) ,
what about the accuracy of the distance measurement.
I just wondered how did they estimate the straight line distance through the Earth rather than around the curvature of the Earth’s surface.
I reckon about a 17.98 metres error would explain the speed anomaly.
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Some great replies to Jim’s wonderful explanation and opinion.
Some very funny replies too eg. Bob Lyons ‘Oldtrinos’!
I liked Steve Jone’s question..’ Now what would happen if it was possible for a particle to have negative mass…’.
It’s certainly an interesting notion to contemplate this experimental data as being ‘correct’. In science nothing is ruled out or, closed to reinvestigation no matter the historical crowns of achievements.
The ‘measurement problem’ here is so open to variations and unknown,s it’s a sure bet that it may manifest to explain the apparent ‘anomaly’. But… I hope not!
I can’t wait to hear how further experimentations go and, the brilliant minds club together in trying to resolve this, if it’s an abnormal reading.
I have my own theories but, they are only speculations.
Dear Professor Jim Al-Khalifi,
If we believe that neutrinos do have a mass from the point of creation of the neutrino to the point of detection, as such they should react to gravity and would form an extremely dense layer of orbiting neutrinos around every black hole because of their immense speed and their superior numbers in this universe.
I wonder if anyone has found such a layer of orbiting neutrinos around a black hole.