“I knew I was going to take the wrong train….”

…”so I left early.”

Thus sayeth that noted neutrino expert Yogi Berra, Bb.D.

Because humankind cannot live by politics alone, here’s a bit of an off-angle reaction to the biggest news in physics since Big Al (as I thought of him through a decade of film-and-book making/writing on the good Dr. Einstein) looked out of his window and wondered what would happen if the roofer he was watching slipped and fell.  Before the poor fellow hit the pavement, of course.

That would be the announcement last Friday that an Italian team of physicists sent a beam of neutrinos from the CERN high energy physics facilty on the Franco-Swiss border through the Alps to a detector in the Italian national physics lab in Gran Sasso, a journey of almost 460 miles (~730 km).  The newsworthy bit was that the experimenters measured the speed with which some 16,000 or so neutrinos covered that distance, and found that it very slightly exceeded the speed of light, “c”  — the canonical limit within Einstein’s special theory of relativity that nothing may exceed.*

The effect detected by the experiment, known as OPERA, was small:  1 part in about 40,000 greater than c.  But any breaking of the light barrier is a huge deal.  If the result stands up, we’re in for a fun ride.  There will be lots of new physics to be found.  Good initial reactions can be found all over the physics blogosphere — try this, or this to get started.

For my part, as someone who’s been observing physics from the outside since I first grew fascinated with Einstein’s work in the late 1980s, I’m reminded a bit of the last decade of the nineteenth century.  In 1894 the (to-be) Nobel laureate A. A. Michelson famously told an audience at the University of Chicago that

The more important fundamental laws and facts of physical science have all been discovered, and these are now so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote.

Timing is everything:  in  1895, just one year after Michelson gave his speech Wilhelm Röntgen discovered X-rays, and it was off to the races into the 20th century revolutions in physics.

Recently, folks may have been forgiven for feeling at least a little bit of what Michelson did, as by the 1990s, every major relevant experiment over the previous couple of decades had confirmed the details of the Standard Model of particle physics.

That theory is not complete.   It does not encompass General Relativity, Einstein’s theory of gravity, for example, and it has a just the whiff of an ad hoc quality to it.  It has troubled a fair number of observers that the Standard Model comes with a number of dials (parameters) that have to be set by hand, as it were, to make all the sums come out right.

For all that, the theory proved for decades to be astonishingly powerful:  those twenty or so parameters have paid for themselves with hundreds — thousands, really — successful predictions.  But the frustrating bit has been that for many, many years, very clever people have tried and failed  to find something that the Model got wrong that would lead to a more comprehensive picture of reality.  Physics, if not confined to what Michelson quoted a colleague as saying — measurements of the sixth decimal place — seemed to some to be grasping for something to liven up the joint again.†

And then, of course, we got dark matter.  Dark matter has been hanging around for a while — roughly forty years, ever since Vera Rubin first measured motions in distant galaxies that implied the presence of much more mass than could be accounted for by the available luminescent matter —  stars.  We’re still waiting for a definitive understanding of what all that mass is made of.

More recently, dark energy (or a non-zero cosmological constant, if you prefer) appeared on the scene — a yet more challenging observation. Dark energy was first detected by a pair of teams measuring the light from a particular type of supernova. Reporting in 1998 and 1999, they confirmed that the universe is expanding at an accelerating pace — and putting that information into the framework of Big Bang cosmology generated an astonishing number:  about three quarters of the stuff in the universe — the sum of mass and energy present within the cosmos– comes i the form of whatever this dark energy turns out to be.


In other words:  we live in interesting times.  And thankfully, some such circumstances — those outside of politics — are actually interesting as in fun, rather than applying the usual torque that line evokes.

There are huge, significant new problems out there, with at least some real prospect of observational discoveries that could lead to major shifts in our understanding of the cosmos we call home.  This neutrino result would lead to another such shift — if it holds up — and it would thus stand both as an example of virtuoso measurement and as a great big sloppy kiss of an invitation to theorists who will have to rethink special relativity — for a century one of the fundamental principals of existence, a fact of life in the universe so fundamental that any physical result had to conform to it or fail.

To be sure, there’s a good way to go yet before we plunk the leaders of the OPERA team into sedan chairs and bear them off in triumph to Stockholm.  As of four or five days into the era of superluminal neutrinos, no one has found an obvious killing flaw in the work, but it’s a complicated experiment, and confirmation would be so consequential that every physicist I’ve talked to or read has cautioned me not to bet the rent money on it.

(Thanks xkcd)

But even as we wait — probably not too long, as these things go — for another experimental team to reproduce or demolish this initial finding, we can enjoy the one certain decay product of a collision between theoretical physics and the Twitterverse.

That would be neutrino jokes (perhaps an acquired taste).  Hence these, gathered by the L.A. Times.  (h/t @JenLucPiquant).

My favorite (also plumped by regular commenter SiubhanDuinne in a previous thread):

We don’t allow faster than light neutrinos in here, said the bartender. A neutrino walks into a bar.

Yeah.  An acquired taste.

*There is a history of theoretical musings about faster-than-light particles that predates this experiment, but such particles, dubbed tachyons, are understood never to slow to the speed of light.  In this conception, the speed of light is a limit that can be approached from either side — below or above — but never crossed.  So, for those of us in the slow lane, the  cartoon description of the speed of light as a speed limit has been close enough to right to do the job.  We do live in interesting times.

†The “sixth decimal point” statement has earned Michelson a lot of ridicule over the years.  Certainly, it was bad luck indeed to provide such a quotable quote just one year before the gaudy show-stopper of X-rays.  But on reading this paper (pdf) on Michelson’s thinking about measurement, I’m reminded he’s at least partly the victim of a bad rap.  In his 1894 speech he expressly pointed out that two problems pressing on physicists at the time were the “constitution of matter and the ether and the true mechanism of light” — in other words, the questions that lead directly to both relativity and the quantum theory.  (Thanks to Ed Bertschinger for discussing this point with me; he is not to blame for any use I made of his knowledge.)

And though Michelson was clearly wrong in the import of his statement — the “nothing left but the details” suggestion — still, as a master of meticulous experimental technique, he can be credited with a deep, and clearly correct idea:  high precision measurement was and remains the probe through which new phenomena could be discovered.  The neutrino experiment that has prompted all this hullabaloo may indeed be the latest example of the power of experimental acuity to evoke genuinely new insights.

Image:  Joseph Wright of Derby, The Orrery, c. 1766.

Vincent van Gogh, Starry Night over the Rhone, 1888.  (Predictable, I know — but a variation on the usual, and a gorgeous painting).


72 replies
  1. 1
    singfoom says:

    Ah the scientific method. If this holds up under tests from other scientists, that’s going to be really interesting.

    I got nothing else, except to quote Of Montreal: “Physics makes us all its bitches”

  2. 2
    joes527 says:

    wait wait … That neutrino joke is just a recycled tachyon joke.

    Or is it a tachyon joke from the future? I’m so confused.

  3. 3
    Cermet says:

    First off, lets correct a misconception – no law of physics is violated by faster than light travel. Only that any such photon/particle must have both negative energy and momentum (yes, it can have a real rest mass.) The issue with such faster than light speeds is that we can’t really measure anything that exhibits those rather strange properties.
    (The only ‘impossible thing’ is that any particle with rest energy can never go the exact speed of light – faster, maybe, at that speed – never.)

    Second – what is the speed of light. For most measurements, within the error bars over the last sixty years, the speed of light has been found to be different between each of these measurement methods even after taking the error bars into consideration… a strange issue never resolved.

    General relativity cannot explain why an electrically charged particle not in motion but in a gravity field does not radiate – a major failing.

    Lets not pretend this neutrino experiment is raising a major issue that is unique or special in this field.

  4. 4

    I read about this … that a particle traveled faster than the speed of light, heretofore believed to be impossible.

    This means we’re saved! We CAN travel to one of those planets they just discovered that’s like earth! BEAM ME UP!

  5. 5
    IrishGirl says:

    I have some dumb, non-scientific questions (coming from a very mediocre physics student in college).

    If the measurement must be that precise, does that mean they are more likely to be off? Are they really capable of measuring something that accurately? (I would assume they’d calibrated and verified their instruments but I’m never one to overlook the obvious). Also I had some stupid idea in my head, probably from a movie, that as matter approaches the speed of light, it actually becomes pure energy or light…is this true or is it a boiled down explanation of something much more complicated? Did the neutrino survive the acceleration process? Was it destroyed or mutated?

    Sorry for asking dumb questions but I’m curious and sadly uninformed.

  6. 6
    JPL says:

    It is fascinating and it will be interesting to see if it’s confirmed.
    From the LATimes
    -I’m going to tweet my neutrino joke yesterday.

  7. 7
    MBunge says:

    I don’t know if real scientists ever believed this, but I have noticed a conviction among science literate laypeople that we basically have the universe figured out and all that’s left is filling in the details. Even after science had to pull the concepts of Dark Matter and Dark Energy completely out of its collective ass to explain why reality conflicted with its theories on an epic scale.


  8. 8
    Alex S. says:

    I’ve only got the knowledge of an interested bystander, but I think that Einstein’s equation of relativity truly is correct. I guess there must be something else involved that created these results, a different effect. Maybe a wormhole effect or extra dimensions, or something else that does not disprove Einstein but instead opens up a whole new world. That would be the result I’d like to see the most. But even if it turns out to be nothing but an error, I agree with Tom that we live in interesting times. For example, I think that we will be able to prove the existence of extraterrestrial life within 30 years – even if it’s just bacteria emitting …whatever they emit…

  9. 9
    S. cerevisiae says:

    But where’s my starship? Get with it, physicists!

  10. 10

    I love the idea that the silly neutrinos traveled faster than light. Such a surprise!

    And think about how many surprises lie ahead of us.

    The pursuit of knowledge and understanding is like a neverending story. It goes on and on and . . .

  11. 11
    redshirt says:

    I am confident – very – that despite our towering collective scientific knowledge, we’ve only scratched the surface of our reality. As a quick proof – according to current estimates, only 4% of the mass of the universe is observable matter. The rest is “dark matter”, and by far the greatest remainder is “Dark Energy”.

    Does it seem like we’re done when we confidently proclaim we’re really not sure about 96% of the mass of the Universe?

    Much more work to be done.

  12. 12
    RossInDetroit says:

    The speed of light was experimentally determined to within 1.4% of its true value over 280 years ago. By people who were unaware of the neutrinos continuously passing through their bodies.

  13. 13
    Freddie deBoer says:

    I appreciate the reference to the Michaelson-Morley experiment, because it highlights an important aspect of relativity: the theoretical framework was inspired by an experimental result that was unable to fit the conventional model. Which may or may not happen here.

  14. 14
    Lysana says:

    @MBunge: That is indeed an issue. It’s been a source of argument when religion comes up. I know many an atheist who treats science as akin to a religion. It has all the answers, it’s just missing a bit here and there and will settle on those answers soon and there’s no room for a deity or spirits or anything else we can’t weigh or measure right now. Meanwhile, I remember scientists who treat science too much in that fashion tend to be shown up by people who remember that questions must always be asked. A false certainty is a limiting thing no matter what you base it on.

  15. 15
    gnomedad says:

    Asked in a previous thread, but maybe I’ll have better luck here: is there a thought experiment that demonstrates how FTL signalling would violate causality. I mean a real paradox, not just observing an effect before its cause.

  16. 16
    SiubhanDuinne says:

    My fuel tank is almost empty, so I’m going to drive extra fast in order to get to the gas station sooner, before I run out altogether.

    Tom, I figured you were well acquainted with the bartender joke, but I appreciate the hat tip anyhow (probably would have been actually funnier if I had called it a neutrino instead of a neutron, not that I’d recognize either one if they accosted me on the street).

    I once knew a pair of cats named Michelson and Morley.

  17. 17
    Emma says:

    When I was small I used to get these really awful ear infections that would keep me awake for nights. My father used to take me out to the yard and we would sit in a big rocking chair and he would show me the stars. My fascination with all things cosmological dates to that time. I actually “wheeee’d” in my office when I read about the neutrino experiment.

  18. 18
    gnomedad says:

    @Alex S.:

    I’ve only got the knowledge of an interested bystander, but I think that Einstein’s equation of relativity truly is correct.

    As is often pointed out, GPS requires corrections from both general and special relativity. On the other hand, relativity is incompatible with quantum mechanics in realms where both are necessary. There’s no way relativity can be flat-out “wrong”; eventually it will be a special case of a broader theory.

  19. 19
    JustPete says:

    Absolutely fascinating subject and deserves more widely distributed review. I especially like the XKCD and Michelson references. Well done summary.

  20. 20
    Cermet says:

    @IrishGirl: As any particle with rest mass approaches the speed of light, its total momentum approaches infinity (by deduction, its mass must go to infinity.) Of course, its energy also must go to infinity. Hence, no particle with rest mass can go the speed of light – notice this says nothing about faster than the speed of light. That is covered in my easier post.

  21. 21
    RossInDetroit says:

    Coincidentally, I’ve been reading

    Understanding Einstein’s Theories of Relativity: Man’s New Perspective on the Cosmos

    That’s hours of my time I don’t want to have wasted.
    So I have a horse in this race, so to speak.

  22. 22
    Samara Morgan says:

    great great post, dr. levenson.

    i admire people that can popularize Real Science sooooo much.
    Speaking of, Reamde.
    game theory, evolutionary economics, and Warcrack.
    its epic.

  23. 23
    Lockewasright says:

    Do neutrinos have mass to begin with?

  24. 24
    eyelessgame says:

    At this point it’s much more likely to be some sort of systematic experimental error.

    The most obvious direct experimental counter to this (the theoretical and indirect experimental counters are prodigious, but let’s pretend those don’t matter) is that we didn’t get a blast of neutrinos from SN1987A in 1983 (at a one in 40000 advantage, the neutrinos would have been 4 years ahead of the light by the time both reached us). We did get the neutrinos *slightly* before the light, but that’s attributable to the light having to claw out of the center of the explosion through the star, while the neutrinos weren’t stopped by normal matter, so they got a jump of an hour or so, and kept it.

    But if neutrinos really can move superluminally, we have three possible explanations: relativity is wrong (basically impossible), causality is wrong (wouldn’t we already know?) or our understanding of space-time is incomplete in some way that we didn’t expect (that one is exciting and not outside plausibility).

  25. 25
    JPL says:

    My ex’s brother wrote a book in which he states that most current evidence is misinterpreted. I didn’t read his book but it was about the Theory of Elementary Waves. With my limited knowledge, I pretty much said that’s nice.

  26. 26
    Cermet says:

    @Lockewasright: Yes, but the value is so tiny no one can, as yet, measure it. The reason it has to have rest mass is because it can change its ‘flavor’ (type of neutrino) and that is impossible if it does not have a finite rest mass.

  27. 27
    RossInDetroit says:

    Light travels at different speeds in different materials. Do neutrinos act the same way? If they do, perhaps the wrong factor was used for the transmission medium. I know it was supposed to be vacuum, but maybe it was vacuumier than they thought it was and the neutrinos were behaving normally for that medium.
    Just a thought completely unsupported by research…

  28. 28
    Davis X. Machina says:


    I once knew a pair of cats named Michelson and Morley.

    Naming pairs of things make some people goofy. As a lad I had a neighbor who had a catamaran with the hulls separately named and painted — “Scharnhorst” and ‘Gneisenau”

  29. 29
    a hip hop artist from Idaho (fka Bella Q) says:


    our understanding of space-time is incomplete in some way that we didn’t expect

    That one gets my vote, if neutrinos really can move superluminally. Which is, of course, a rather large if at this point. Actually, it gets my vote even if they can’t, heh.

  30. 30
    The Pale Scot says:

    Couldn’t this be some sort of quantum tunneling? That’s the thing I thought of.

  31. 31
    Cermet says:

    @RossInDetroit: As I read the results, the answer is no. The neutrino’s traveled the distance faster than light could in vacuum over the same distance. Hence, the neutrino’s appeared to travel faster than light in vacuum and that is not allowed. Also, the speed of light is ‘known’ to a few decimals and the neutrino’s travel 6 km/s faster so it was well outside the error bars for the known speed of light. For the experiment itself, it measured accuracy was to six sigma, which means it was very accurate compared to the measured value (error such that the odds of their measured value being wrong (outside the error bars)was only one chance in a million – rather good to say the least.

  32. 32
    JGabriel says:


    Do neutrinos have mass to begin with?

    [Pauses for thought]

    Define begin.


  33. 33
    dmsilev says:


    Do neutrinos have mass to begin with?

    Short answer: Yes, but we don’t know how much.

    Longer answer: There are three types of neutrinos, and it turns out that we can measure the difference in masses between the various types to fairly high precision (due to an oddball effect known as flavor oscillation), so if we could measure the mass of any one of the types, we’d get the numbers for all three. Unfortunately, the best we can do is say “it’s really small”. It’s possible that one of the three types does has mass zero, and the other two have non-zero mass, but that offends physicists’ sense of elegance, so the usual assumption is that all three have non-zero mass.

  34. 34
    Cermet says:

    @The Pale Scot: As I understand ‘quantum tunneling’, that requires the scale be on the size of atomic dimensions and the distance for this experiment covered a few hundred kilometers. Quantum effects just are not seen on those scales.

  35. 35
    Francis says:

    So, is dark matter neutrinos?

  36. 36
    RossInDetroit says:

    Dark matter seems to interact only with gravity and not with any other known forces.

  37. 37
    RossInDetroit says:

    A weird thing about dark matter is that when they attempt to determine its distribution in the vicinity of a galaxy by studying the effect of its gravitational influence they find that its distribution is different from the normal visible matter. The galaxy – stars, dust, gas – has one shape and the nimbus of dark matter near it has a different shape.

  38. 38
    SiubhanDuinne says:

    @Davis X. Machina:

    Naming pairs of things make some people goofy. As a lad I had a neighbor who had a catamaran with the hulls separately named and painted —“Scharnhorst” and ‘Gneisenau”

    I admit, that sent me on a quick expedition to the Magical Land of Google. Now that I’ve had my passport stamped, that’s funny.

  39. 39
    Brother Shotgun of Sweet Reason says:

    Oh, and the neutrino is the best example of the *political* subatomic particle:

    No mass*
    No charge
    Just spin

    *OK OK, it’s got miniscule mass.

  40. 40
    Donald says:

    ” is there a thought experiment that demonstrates how FTL signalling would violate causality. I mean a real paradox, not just observing an effect before its cause.”

    Yeah. It’s the standard grandfather paradox. A sends a message to B with tachyons. B sends a reply back to A. If B is moving away from A at a great enough speed (but still under the speed of light–he doesn’t need to be a tachyon himself), the reply could arrive at A before A sends his message. There could be a bomb at A wired to blow up when a tachyonic message is received, so you’d have the standard SF problem of someone going back in time and preventing his or her own birth.

    Whether any of this would apply if these neutrinos are going faster than light I don’t know. As the links provided above point out, the theorists would have to think long and hard about how Einstein’s theories need to be modified.

  41. 41
  42. 42
    Richard S says:

    Was it Michelson or Morley who died believing that their own almost perfect, and in fact, correct results were in error?

  43. 43
    Cermet says:

    @Donald: I have never read or seen a real example by anyone that shows how ‘going faster than light’ creates the possibility that you could kill your parents/grandparents or self before leaving on your ship/etc. The only example I have ever worked out is that causality of a single event will not be consentient between two observers that are at different locations and/or traveling at different speeds (but neither are accelerating.) I’d love to see a real example with clocks worked out. Only stories that are never based on a clear example. If you have such a link, please make it available! I’d love to finally see how that works!!! Thanks. (I hope it isn’t one of those everyone knows it but no one has ever really worked it out things … )

  44. 44
    Marty says:

    @Cermet: Our understanding of causality is violated by faster-than-light travel. How that would translate into going back in time and killing your great grandparents etc. is rather speculative. But within special relativity, if an event A precedes another event B in one frame of reference then it will precede B in any and all other frames of reference. So if A is the cause of B then all observers must agree that A is the cause of B. But special relativity assumes that the speed of light is the fastest possible speed – and so if this is wrong then the constancy of causality fails. That’s the problem.

    As for the neutrino experiment, major earth-shaking physics results come out every five or ten years. Sometimes they prove correct (high Tc superconductivity) but they are often found to be irreproducible. Think of fifth-force experiments from a few years back. These experiments are difficult and they involve a lot of precision analysis. It’s just a fact that some of the best experimental results will eventually prove to be wrong.

  45. 45
    KCinDC says:

    I’m having flashbacks to the “cold fusion” brouhaha when I was in grad school.

  46. 46
    Ron says:

    @Cermet: What is true is that according to special relativity, it would take an infinite amount of energy to accelerate a particle from below light speed to super-light speeds.

  47. 47
    Brother Shotgun of Sweet Reason says:

    @Ron: OK, so as near as I can understand it all we need to do is Drill Here Drill Now and we’ve got FTL solved? Amirite??

  48. 48
    Bill E Pilgrim says:

    the Franco-Swiss border through the Alps to a detector in the Italian national physics lab

    I’m certain that this was an error in measurement. Having lived in Italy, I can assure you that nothing has ever arrived early for an appointment there.

  49. 49
    Cermet says:

    @Ron: A common missunderstanding – it would take an infinite amount of energy to accelerate a particle that has rest mass to light speed.

    A minor but important point relative (ok, a bad pun) to a particle going faster than light – energy is finite (but negative!)

  50. 50
    Cermet says:

    @Marty: I agree and have done that calculation:hence, my confusion about that result so many people (in physics, no less) have claimed over the years. So, faster than light signals do NOT in any way allow someone to violate the orginal ’cause’, only cause two experimentors to disagree about when an effect created a given ’cause’. So I guess that example (about time travel) is just BS that has just been going around as a old republican tale. Wish that wasn’t the case because it would be fun, otherwise.

  51. 51
    Jebediah says:

    I for one am not surprised at all that neutrinos might travel faster than light. Everyone knows that there are just some particles that can’t be trusted to follow the rules.
    And don’t call me a particle-ist! Some of my best friends are neutrinos!

  52. 52
    Elie says:

    @Bill E Pilgrim:

    YOU get the LOL award, sir! I completely agree with your conclusion as well….:-)

  53. 53
    dfphil says:

    Sean Carroll’s post at Cosmic Variance on this linked above is quite good. Having read (but not carefully) the preprint on the arxiv about the measurement, the authors are very careful with timing (common view GPS between the two sites and old fashioned surveying into the tunnels to get the distance to 20 cm and the timing down to nanoseconds) but the most likely problem (which I’m sure they’ve thought about carefully already) is taking the 10 microsecond pulse of neutrinos they generate at CERN and understanding it well enough to see the reported 60 nanosecond deviations. That pulse of neutrinos has an ugly shape (again, as the authors show in detail) that is hard to subdivide. I’d bet a really nice dinner that they’re wrong but not a whole month’s rent.

    If these results hold up, the most likely interpretation would be a violation of Lorentz Invariance and hence Einstein would be subtly wrong. However, this would not – as Sean describes – lead to problems with causality.

    More parenthetically, we now have tests of the standard model at 12 significant digits (the spin of the electron) that are in good agreement with the standard model. Michaelson would be proud!

  54. 54

    Perfect point to “whip out” Starry Night Prime.
    Great fucking post.


  55. 55
    smintheus says:

    It wasn’t really a fair experiment though, was it, when neutrinos can travel through the center of the earth and light cannot.

  56. 56
    El Cid says:

    The important question is which Biblical verse was being spelled out by the rebel FTL neutrinos, and how will the Al Gore mafia keep this information silent?

  57. 57
    delphi_ote says:

    Wake me up when another lab or two replicates this result. THEN it’s worth worrying about completely rewriting our understanding of the fundamental laws of nature.

  58. 58
    Bago says:

    You just need a few million credits worth of eezo. By applying the Mass Effect generated from the element zero core, you can reduce the mass of the ship and break the relativity constraints and achieve FTL travel. However, if you REALLY want to scoot around the galaxy, you’re going to need a Mass Relay.



  59. 59
    Yutsano says:

    @delphi_ote: Is there another lab on the planet that can though? I think the main reason CERN could pull this off was because of the size of the collider.

  60. 60
    THE says:


    Do neutrinos have mass to begin with?

    Neutrinos have mass? I didn’t even know they were Catholic.

  61. 61
    THE says:

    Sorry. That was an old physics joke.

    If I tried to really speculate — A more serious answer would be that I am not sure that this would be that revolutionary if it were true.

    It just means that the maximum speed “c” that appears in the Lorentz transforms is not the actual speed of light. i.e. Light travels slightly slower than the actual maximum speed.

    Now the agreement between the speed of light and the maximum speed c would still have to be very close, or you would not be able to account for all the experimental successes of relativity over the last century.

    So we have to ask ourselves: What is it that slows light down by a small fraction, so that it travels at just below the maximum speed?

    There are a couple of possibilities: Perhaps the photon has a tiny mass? But current experimental limits are very tight and I think it would be hard to accommodate it.

    Another possibility is that the photon is a complex particle and there is another force that actually mediates the electromagnetic (gauge) interaction with the vacuum. This additional field would be responsible for the photon traveling slightly below the maximum speed. In other words the Lorentz symmetry would be a broken symmetry with respect to the electromagnetic force.

    This is not that different to how light travels slower in a medium like glass or water. It is responsible for the bending of light and the “index of refraction”. It would mean that the vacuum (or “our” vacuum) was slightly refractive compared to some hypothetical “true” vacuum.

    One could imagine a perfectly symmetrical vacuum where gravity was the only force. In that vacuum, forces would propagate at the maximum speed c.

    In our much richer and complex vacuum, there are many additional forces and the observed “effective” forces travel slightly slower than the maximum speed.

    This is always assuming that the experiments are validated of course.

  62. 62
    mclaren says:

    Your example with Roentgen is a bad one, since James Clerk Maxwell’s electromagnetic equations predicted electromagnetic radiation back in 1865. When X rays shows up, scientists were relieved because as high-frequency electromagnetic radiation, they confirmed Maxwell’s equations.

    A better example might be Becquerel’s discovery of radioactivity. It was thought prior to that point that atoms were indestrucible and eternal.

    Another example would be Max Planck’s hypothesis that energy comes in quanta. That was entirely unexpected. However, Planck made that guess in 1905, about 10 years later than Michaelson’s statement.

    I’m betting the experiment won’t be confirmed. An error of 20 feet in the measurement of the distance would explain the result.

  63. 63
    jayackroyd says:

    I heard about this live, at Virtually Speaking. My guest that night was Lee Smolin, a physicist who works on quantum gravity.


    He said that the consensus, and his view, was the experiment is wrong–not to mention @mclaren.

  64. 64
    Ordovician Bighorn Dolomite (formerly rarely seen poster Fe E) says:

    @Davis X. Machina:

    Oh wow–I did NOT expect a German naval reference in Balloon Juice this morning.

    I’m not positive that this will win the thread, but you clearly deserve extra points for tangential randomness!

  65. 65
    jayackroyd says:

    Also, it was nice to see xkcd cited in the NYTimes article about the experiment.

  66. 66
    Tone in DC says:

    Recidivistic particles. They belong in a verrrrry small max security prison (damn, they’ll just travel right through it).

  67. 67
    Donald says:

    Cermet–The story I gave you wasn’t about people killing their own ancestors, but it was about a tachyon transmitter killing itself in a way that was equally paradoxical. A sends message to B, B replies, B’s reply arrives before A sends message, and A blows up. So A initiated a chain of events that caused A to cease to exist before A could initiate the chain of events that caused A to cease to exist.

    If I knew how to draw diagrams in one of these boxes I could show it to you in a space time diagram.

  68. 68
    Donald says:

    I didn’t have time to read it through (lunch hour is up), but I think this link describes the example I was talking about–


  69. 69
    samson says:

    @THE: I thought light was affected by gravity – the ol’ “not even light can escape a black hole …” Do we think vacuums exist where no gravitational force exists? If there is a miniscule tug of gravity onthe photons, maybe this is what keeps them slightly under the theoretical speed limit. You’d have to set up your vacuum at one of theose equipoise points where gravitational pulls all equal out and run light through there.

    Or what about neutrinos themselves? Can we exclude them from vacuums? If not, and they have mass, maybe they slow down photons a tiny bit?

    Sorry to babble. I’m no scientist, but your post intrigued me.

  70. 70
    THE says:


    Do we think vacuums exist where no gravitational force exists?

    Light is affected by gravity. In General Relativity, gravity arises from the curvature of spacetime, the speed of light doesn’t change though. Any sufficiently small patch of spacetime will look approximately flat to a free falling observer, and you will recover the ordinary laws of flat space physics locally. Light follows a path which is locally straight (which is to say a geodesic) but which is globally curved because the spacetime itself is curved.

    Even free falling into a large stationary black hole you don’t perceive anything different locally, until you are right near the central singularity and then intense tidal forces tear you apart. Which is to say the different parts of you are pulled in different directions because spacetime there is so intensely curved.

    I’m treating neutrinos as just another kind of quantum field. Neutrinos do seem to have a very small mass. Neutrinos have no electric charge so they don’t really interact with light — Neutrinos hardly interact with anything.

  71. 71
    Michael Sullivan says:

    The real irony of Michelson’s statement is that it came 8 years after his own result which demanded an explanation — that ultimately led to special relativity. When he made that statement, the mechanics of light and what kind of model made sense to explain it’s unchanging velocity were still a completely open question. You had Lorentz equations that could work as a model, but it took Einstein to put together the physical theory that gave that model enough sense to make real predictions.

  72. 72
    Ab_Normal says:

    @Bago: delurking late to give you much love for that. I was thinking, “Well, first we need to get to Mars, then find the Prothean ruins…”

Comments are closed.