* Ahem * Well, not quite. (Note: FTL = Faster Than Light)
The first image, taken in 2007, of a neutrino interaction. The neutrino, coming from the left of the figure following an interaction, produces several particles identified by their tracks in the detecting 'brick'. Credit: INFN (Italian National Institute of Nuclear Physics)
Not entirely, at least.
Those of you watching the science news today may have noticed an awful lot of excited wittering about results being published today which suggest the neutrinos may have broken the speed of light.
Please note the use of ‘may’ there.
First, a brief note on neutrinos themselves. My favourites of the subatomic particles*, they are virtually massless, seldom interact with, well, anything (making them tricky as hell to detect), and on top of it all, have a pretty fascinating discovery story, at least some of which involves enormous underground pools of bleach.
They’re similar to electrons, in fact, except for the intriguing characteristic of having no electrical charge. How’re they made? By nuclear reactions and certain kinds radioactive decay – our sun, for example, pumps out a fairly respectable number of them, but at least some of our experiments actually involve our making them, and pointing detectors in their direction**.
Oh, and also? Neutrino detectors are seriously, seriously beautiful and involve some wonderful chemistry/physics. Examples include IceCUBE!, Super-K, and MINOS.
Now, on to the Science of the Day.
Nothing, at least according to one of Einstein’s equations (you know, the one beginning e=…), can travel faster than the speed of light in a vacuum (light travels slower in dense media***). However, scientists on the Opera (Oscillation Project with Emulsion-tRacking Apparatus) experiment are announcing today, at Cern, that they appear to have results showing neutrinos doing exactly that.
And it’s got everyone extremely excited because, well, it could overturn causality – the idea that cause comes before effect. We’re talking _time travel_ here, people. And having to fundemtnally relook at our understanding of physics.
Amusingly, though, it does, finally, allow us the following joke (thanks @rmi!):
“We don’t allow FTL neutrinos here”, said the barman. A neutrino walks into a bar.
Over the last three years, our somewhat-bemused scientists have been watching the arrival of some 15,000 neutrinos, and noticed that they were arriving slightly faster than they should. Apparently, some 60 billionths of a second earlier, with an error margin of plus/minus 10 billionths of a second. This in a 730km, 2.4 millisecond (ish) trip.
At this point, I’m going to quote from the Guardian:
The measurement amounts to the neutrinos travelling faster than the speed of light by a fraction of 20 parts per million. Since the speed of light is 299,792,458 metres per second, the neutrinos were evidently travelling at 299,798,454 metres per second.
Physicists can claim a discovery if the chances of their result being a fluke of statistics are greater than five standard deviations, or less than one in a few million. The Gran Sasso team’s result is six standard deviations.
To everyone’s credit, the scientists involved are being very careful to point out that they are not, as yet, claiming to have overturned any equations whatsoever, and are asking their colleagues to help them either verify the results, or figure out what happened. Which is pretty awesome :)
And there are a number of alternate hypotheses floating around for the result. Perhaps they took a shortcut through some other dimensions, for example. Perhaps the ultimate speed isn’t that of light, but of neutrinos, and something’s slowing light down more than we thought.
And, in a really fun conversation thread on Facebook, Ethan Dicks said the following:
For comparison, when I was at IceCube, three sigma results were trivialized, but four sigma is where you start to think about publishing. If they want to support overturning a simple and fundamental thing like the speed of light, six sigma is not overkill.
Not having seen their evidence yet, I would initially wonder if the neutrinos didn’t take some “shortcut” during the muon-tau oscillation. After all, the important phrase is nothing can go faster than light *in its medium*. If the neutrinos are doing something unfathomably bizarre, perhaps the speed of light still holds, but we don’t understand the medium or the path the neutrinos took.
I’d bet on some flavor of “hyperspace” before I’d bet on time travel.
Ethan’s a former researcher and three-time South Pole Winter-over for the University of Wisconsin-Madison and the IceCube Collaboration. He ran AMANDA for a while, then then helped install and run IceCube for a bit, too.
And perhaps it’s nothing at all: a fluke, or some new interesting effect.
Either way, we’ll be watching closely!
The paper can be found here, and Cern’s doing a webcast, too. I _would_ link to all the coverage out there, but there’s tonnes of it, and you have Google :)
* They’re like the ninjas of the subatomic particle world. Very, _very_ sneaky. Also, I get the impression, rather diffident. And, possibly, they may help explain why our universe favours matter over antimatter (they can change ‘flavour’ from muon neutrino to electron neutrino). Thanks to Seth for alerting me to that one.
** Yes, I am paraphrasing :)
*** I’m forbearing from making any puns here about poor media reportage and shining the light of knowledge onto things
It’s worth noting that arXiv isn’t peer-reviewed, much as I absolutely love the papers posted thereon :)
Also, I’d like to know who’s driving the media frenzy on this – the scientists? Cern? The media itself? Because at the moment, the news is actually ‘we have something interesting which we cannot currently explain’. Yes, it’s _very_ interesting, but still… I’d have been far more interested to hear about this once it’s been through all the checks and balances the scientific community will go through over these results. If it turns out to be an error, I’m concerned there’ll be the inevitable chorus of ‘naughty scientists, wasting our money and time, blah blah blah’. So yes – is this actually _responsible_ science reporting?