A couple people have written to tell me about the new BBC Faster Than the Speed of Light? documentary on superluminal neutrinos which evidently featured trademark hype from string theorist Mike Duff about how string theory could explain this. For better or worse, I don’t think I have access to the show from the US, although I’m sure that sooner or later it will arrive on our shores.
Update: Philip Gibbs has more here.
Update: The BBC program is now on Youtube, see here.
I watched this tonight and can confirm that it did include stringy hype. The entire last segment was given over to a speculation that neutrinos might travel in the bulk in a braneworld scenario and thus appear to be travelling faster than light to those of us who are stuck on a brane. I’ve never heard anyone propose that anything other than gravity might operate in the bulk, so this seems like an extreme example of opportunism to me. Of course, I am not an expert on braneworld scenarios, so I could be wrong about this. Nevertheless, to claim that the OPERA result might be evidence for string theory seems quite a stretch to me.
To be fair, the documentary did include a reasonable amount of discussion of the possible errors in analysis of the OPERA result, but, apart from some vague talk about tachyons, this stringy explanation was the only serious alternative mentioned. There was not even any discussion of the possibility that Lorentz invariance might be violated.
The presenter claims that the mass changes if the speed of the body is increased – moreover he claims that this follows from Special Relativity. He is a mathematician so perhaps this is why he does not realise how false that statement is. A mass is a Lorentz invariant – it cannot be changed by Lorentz transformations (like a boost) – what changes is the 4-momentum.
Not everyone equates “mass” with “rest mass”. It is okay to say that speed changes mass.
Don’t criticize this program if you have not seen it. It gives a very balanced view of the theory and experiment. Mike Duff explains in hypothetical terms the idea of how extra dimensions could explain the effect and then makes a very clear statement that he does not believe that this is the right explanation. There is no hype.
no, it is not ok to say “the speed changes mass”. The numerical equivalence between the gravitational mass and the inertial mass is the reason why “M times \gamma” has no physical meaning i.e. cannot be called a mass. You will not increase the gravitational field of a body by increasing its velocity.
Do you similarly object to people saying that speed changes length, or speed changes time?
I do not wish to argue it here, except to point out that both views are common and tenable, as explained by John Baez and Wikipedia. It is silly to complain about the BBC, when many physicists and textbooks say the same thing.
Back in the day, people did tend to refer to the “relativistic mass” rather than the relativistic momentum. This is because the momentum for a particle with non-zero mass is given by
p = gamma*m_0*v
so sometimes people would consider the combination gamma*m_0 to be the relativistic mass as opposed to the invariant mass m_0. From a practical point of view, it’s just semantics. From the theoretical point of view, it is more technically correct to speak of the relativistic momentum rather than the relativistic mass.
No Roger, I am not objecting to length contraction and time delays.
Gravitational mass m_g is equal to m_0(rest mass, inertial) and not to m_0*gamma therefore the statement “the speed changes mass” is not true (as it would imply that m_g is speed dependent which is clearly not the case). Note that the equality m_g=m_0 is empirical therefore the statement “the speed changes mass” would contradict the (Eötvös) experiment.
may c j, what you have is an argument for a definition that some textbooks use, and some don’t. The concept of relativistic mass is just as legitimate as the FitzGerald contraction. You could likewise argue that the lengths do not really contract, but it appears that way when measured in another frame. There are some advantages to saying that the mass changes, but you ignore those.
Better hype: Hints of supersymmetry seen at the LHC, according to Matt Strassler:
Please, enough about relativistic mass.
@ Henry Bolden
What Strassler actually *says* is,
“There’s absolutely no evidence at this point that this has anything to do with supersymmetry. ZERO. So keep that in mind.”
So it seems a little unfair to attribute SUSY hype to him, on this score at least.
In fact, Mike Duff said that, having worked on the concept of extra Dimensions for 30 years, he’d be very pleased if the Opera result provided experimental confirmation for them.
But he also said that he didn’t think this was the case.
So there wasn’t really any hype involved; no more so than any other theoretical conjectures that would arise were it confirmed that neutrinos were indeed superluminal particles. Which would be pretty paradigm shifting, if true.
Marcus du Sautoy pointed out that none of the attempts to find measurement errors in the results had produced a quantitiative explanation for the excess speed calculated. But I think it was made before Ronald van Elburg’s paper on the subject, which does seem to provide such an explanation – ironically one that confirms Einstein’s theory rather than refuting it.