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Author Topic: Faster than light neutrinos?  (Read 13202 times)

Offline JP

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Faster than light neutrinos?
« on: 22/09/2011 22:31:40 »
Ok, this isn't really a question.  It's more of a discussion topic.  I don't know if you've seen the news, but apparently scientists at CERN claim to have seen particles (neutrinos) moving faster than the speed of light.  This would obviously be a big deal, since it would cause major problems for special relativity.

Here's a link to the news:
http://www.reuters.com/article/2011/09/22/science-light-idUSL5E7KM4CW20110922

And here's a link to tomorrow's talk (streamed live on the web):
http://indico.cern.ch/conferenceDisplay.py?confId=155620

So... are we going to have to rethink relativity or is this a case of an error in the measurements?
« Last Edit: 23/09/2011 01:57:42 by JP »


 

Offline Geezer

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Re: Faster than light neutrinos?
« Reply #1 on: 23/09/2011 00:23:29 »
They don't seem to be much faster. Maybe it's because they have negative mass ;D
 

Offline CPT ArkAngel

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Faster than light neutrinos?
« Reply #2 on: 23/09/2011 03:38:48 »
I don't think so Geezer. It is probably a question of interactions. Neutrinos are less interacting with the environment than photons. But are they going faster than C? That's the question...  :o
 

Offline CZARCAR

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Offline MikeS

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Faster than light neutrinos?
« Reply #4 on: 23/09/2011 08:11:19 »
"Light would have covered the distance in around 2.4 thousandths of a second, but the neutrinos took 60 nanoseconds -- or 60 billionths of a second -- less than light beams would have taken."

It reads like it wasn't a direct comparison between light and neutrinos but was based on the theoretical speed of light.  Maybe, the affect is due to a local gravitational anomaly (time dilation).  There's a lot of rock in that area! ;)
« Last Edit: 23/09/2011 09:03:43 by MikeS »
 

Offline MikeS

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Faster than light neutrinos?
« Reply #5 on: 23/09/2011 09:01:06 »
They don't seem to be much faster. Maybe it's because they have negative mass ;D

If they had negative mass then they would be going backward in time.

Thinks [:0]
If they were going backwards in time then they would have arrived before they left! 
Presumably that would have been noticed.
« Last Edit: 23/09/2011 09:06:13 by MikeS »
 

Offline Soul Surfer

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Faster than light neutrinos?
« Reply #6 on: 23/09/2011 09:06:08 »
Most probably its a slight directional error or geometrical error.  I'm not sure of the geometry of the situation the size of the source and detectors but the time error represents a distance of about 60 feet in a total distance of 500 miles.  

There is one other interesting factor.  Neutrinos change between types all the time this is probably a quantum mechanical tunnelling process.  Now there are strong reasons to believe that tunnelling takes zero time and if the particles are in slightly different positions along their track before and after each tunnelling happens it might just be possible to get from A to B a little bit faster.

It may also be an energy thing because there are also some slight suspicions that very high energy gamma rays travel at a slightly different speed to lower energy ones.
 

Offline imatfaal

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Faster than light neutrinos?
« Reply #7 on: 23/09/2011 09:30:35 »
I hope it is the tunnelling (or other unexpected thing) rather than a mismeasurement - but I am pretty certain it will be an experimental/datahandling error.
 

Offline Nizzle

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Faster than light neutrinos?
« Reply #8 on: 23/09/2011 11:02:46 »
Maybe the neutrino's had the wind in their back  :P

On a more serious note: When was the last time that they measured that distance to San Grasso, Italy? It looks to me to be a geographical/geometrical error as Soul Surfer already mentioned..
 

Offline imatfaal

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Faster than light neutrinos?
« Reply #9 on: 23/09/2011 14:21:43 »
http://imgs.xkcd.com/comics/neutrinos.png




kudos to randall for being so quick and h/t to swansont
 

Offline JP

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Faster than light neutrinos?
« Reply #10 on: 23/09/2011 14:39:35 »
I hope it is the tunnelling (or other unexpected thing) rather than a mismeasurement - but I am pretty certain it will be an experimental/datahandling error.

Yeah, it probably is just an error in measurement, but it would be great if it turned out to be real, opening up a whole lot of new physics. 

On second though, we can't have anyone overturning the mainstream orthodoxy.  Deploy the thought police!
 

Offline imatfaal

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Faster than light neutrinos?
« Reply #11 on: 23/09/2011 14:42:18 »
There are men in grey suits approaching my door and black helicopters circling above - what have you done to me JP?
 

Offline imatfaal

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Faster than light neutrinos?
« Reply #12 on: 23/09/2011 14:52:14 »
webcast at cern in 7 mins

http://webcast.web.cern.ch/webcast/
 

Offline Geezer

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Faster than light neutrinos?
« Reply #13 on: 23/09/2011 17:31:28 »
Bet they used Google Earth to measure the distance  ;D

(A small error in their measurement of the Earth's curvature would account for the difference.)
« Last Edit: 23/09/2011 17:34:48 by Geezer »
 

Offline JP

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Faster than light neutrinos?
« Reply #14 on: 23/09/2011 17:42:33 »
I had the talk on in the background while working.

From what I could understand, they used very precise techniques borrowed from geodesy to characterize the expected time of flight.  Things had to be so precise that they couldn't just use GPS to determine distances.  They also accounted for possible GR effects (time dilation), so any error from GR was expected to be several orders of magnitude below the discrepancy they saw. 

When they publish their results, it will no doubt be pored over by experts in geodesy to find possible sources of error.  At the same time, others will be looking for independent ways to check their results.

And of course, the big problem is that if neutrinos do travel faster than light, we should see neutrinos from distant supernovae arriving years ahead of the light.  We don't see this--so that has to be explained.
 

Offline Geezer

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Faster than light neutrinos?
« Reply #15 on: 23/09/2011 18:02:32 »
They only have to be a few inches off in their distance calculation to account for the observation. The problem is that there is no direct method to measure the distance and there are too many variables that can affect the result when it is measured indirectly.

If they did it "line of sight" between the tops of two mountains and got the same result, I'd get excited.

I think the more likely conclusion is that we will discover people have been selling real estate that isn't real :D
« Last Edit: 23/09/2011 18:06:29 by Geezer »
 

Offline JP

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Faster than light neutrinos?
« Reply #16 on: 23/09/2011 18:32:40 »
Yes, but that's trivializing the effort that went into computing the significance of their measurement.  If you believe the experts in geodesy, this kind of measurement is well understood, and it's not a case that there are "too many variables."  These measurements are usually painstakingly accurate with (hopefully all) possible sources of error accounted for.  I'm clueless on this myself, but I trust they know that they're doing.

I still do think it's an error, but it's likely something subtle.  When they fix that subtle point, the measurement will probably be just as precise, but fall into line with what they expect.

On a related point, my knee jerk reaction to these kinds of ultra-precise measurements is always that they can't be possible, since you're talking about precision that boggle the mind.  I recall seeing some talks by folks at NIST about ultra-precise measurements of time, down to the attosecond (10-18 seconds) scale!  At some point, unless you're an expert in the field, you just have to trust that they know how to account for errors. 
 

Offline Geezer

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Faster than light neutrinos?
« Reply #17 on: 23/09/2011 19:04:09 »
It's a geometry problem. They are trying to determine the length of a chord from the length of an arc where the chord is very close to the arc. A very small error in the determination of the radius of the arc will result in quite a large error (relatively) in the chord length. If the curvature (or gravitational field) of the Earth between the two points is not quite what they think, it could easily produce quite a large difference in the chord length.

I'm sure their measurements of the transit time were highly accurate, but they are relying on other people's data to determine the distance.

If they could determine the distance by shooting a light beam between two points, they would be in much better shape. 
 

Offline Geezer

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Faster than light neutrinos?
« Reply #18 on: 23/09/2011 19:32:05 »
Another way of thinking about it is that they have produced a super accurate method of determining the straight line distance between any two points on the Earth's surface. Nobody was able to do that directly before now. Those distances have always been estimated from indirect measurements.

I'm willing to bet we will discover the distance estimates have sufficient uncertainty to account for the observed results. Bear in mind that the geodesic experts are hardly likely to admit that the guys at Cern just proved they screwed up :D

Just to up the ante a bit, there is a well known expression that seems to describe this situation rather well,

"Garbage in, garbage out."
« Last Edit: 23/09/2011 20:10:19 by Geezer »
 

Offline Waldo Pepper

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Faster than light neutrinos?
« Reply #19 on: 23/09/2011 20:35:13 »
Most probably its a slight directional error or geometrical error.  I'm not sure of the geometry of the situation the size of the source and detectors but the time error represents a distance of about 60 feet in a total distance of 500 miles.  

There is one other interesting factor.  Neutrinos change between types all the time this is probably a quantum mechanical tunnelling process.  Now there are strong reasons to believe that tunnelling takes zero time and if the particles are in slightly different positions along their track before and after each tunnelling happens it might just be possible to get from A to B a little bit faster.

It may also be an energy thing because there are also some slight suspicions that very high energy gamma rays travel at a slightly different speed to lower energy ones.

I would like to think in this day and age that scientists need to be a little smarter before contradicting Albert Einstein. Even if it's a little problem with school geometry.

 

Offline CZARCAR

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Faster than light neutrinos?
« Reply #20 on: 23/09/2011 21:07:51 »
mAYBE ITS A NEWTRINO?
 

Offline lightarrow

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Faster than light neutrinos?
« Reply #21 on: 23/09/2011 21:10:03 »
On a more serious note: When was the last time that they measured that distance to San Grasso, Italy?
Gran Sasso.
"Gran" --> "Grande" = Big
"Sasso" = Rock.
 

Offline JP

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Faster than light neutrinos?
« Reply #22 on: 23/09/2011 22:29:37 »
Geezer, it's rather pointless to argue over whether they made a mistake in measuring distance or not, since we don't have their data.  (And I highly doubt if we're experts enough to offer any useful comments if we did have their distance measurement data).  They claim that by using GPS units placed in tunnels and optical triangulation, they have an accuracy of 20 cm.  They also say that's the largest source of error in the measurement, so no doubt it's been checked and rechecked many times.  (I'd put even money on the error being somewhere else that they didn't check as thoroughly.)

You can check out that section of their talk, where they (roughly) explain their techniques.  Click the link in the first post to check out the talk, and it's on slides 32-33.  Actually, even if you don't want to listen to the talk, it's worth checking out just for the cool web interface they have.  You can click on each slide and it brings up a picture of the slide along with a video of the presenter during the portion of the talk for which that slide was shown.

But there's always a slim chance they discovered something new, and since they did a very thorough job of checking their work, it will no doubt be taken seriously and rechecked by others who are a bit more expert than us.  :)
 

Offline CPT ArkAngel

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Faster than light neutrinos?
« Reply #23 on: 23/09/2011 23:09:37 »
 

Offline Geezer

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Faster than light neutrinos?
« Reply #24 on: 23/09/2011 23:20:35 »
Geezer, it's rather pointless to argue over whether they made a mistake in measuring distance or not, since we don't have their data.  (And I highly doubt if we're experts enough to offer any useful comments if we did have their distance measurement data).  They claim that by using GPS units placed in tunnels and optical triangulation, they have an accuracy of 20 cm.  They also say that's the largest source of error in the measurement, so no doubt it's been checked and rechecked many times.  (I'd put even money on the error being somewhere else that they didn't check as thoroughly.)

You can check out that section of their talk, where they (roughly) explain their techniques.  Click the link in the first post to check out the talk, and it's on slides 32-33.  Actually, even if you don't want to listen to the talk, it's worth checking out just for the cool web interface they have.  You can click on each slide and it brings up a picture of the slide along with a video of the presenter during the portion of the talk for which that slide was shown.

But there's always a slim chance they discovered something new, and since they did a very thorough job of checking their work, it will no doubt be taken seriously and rechecked by others who are a bit more expert than us.  :)

JP -  It's not so much a question of distance. It's a question of radius (or angles if you prefer).

The arc length is very short. A very small change in radius will produce a significant change in chord length. If the Earth's surface between the two points turns out to be slightly more curved than the value they used, the real chord length will be shortened significantly. I suppose I'll have to listen to the thing to find out how they determined the radius. If it's based on GPS data, I think they are up a tree.

As you tell us often, extraordinary claims require extrordinary evidence. Mr Ocam tells us that the simplest explanation probably applies. It's very difficult to measure the chord length accurately (unless, of course, you use neutrinos), therefore............

 

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Faster than light neutrinos?
« Reply #24 on: 23/09/2011 23:20:35 »

 

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