CERN team claims measurement of neutrino speed >c

divvydan

Hi everyone, interested newbie.

Was sent a link today to a page that explains why the result was wrong statistically (http://johncostella.webs.com/neutrino-blunder.pdf).

Leaving aside any concern on the background of the person involved, I was left unconvinced by the argument put forward but I don't know enough to be able be definitive about it.

Could one of the more knowledgeable people (particularly in statistics) have a quick read and post their thoughts?

Vanadium 50

According to the Costella paper, if I want to measure the distance between the left end of a piece of wood and a point to its left, it depends on how long the piece of wood extends to the right. That's nonsense.

TrickyDicky

The fact is that if we leave aside the systematic error as the most likely cause of this, this is the point where the search must be and surely will be centered by serious theorists long time before they even seriously consider something's wrong with relativity. (the media is a different matter, all newpapers I've seen have already decided "Einstein was wrong").
As hamster 143 correctly answered the "FTL neutrinos" are assumed to be neutrinos because they are expected to be the neutrinos coming from the accelerator (measuring the time distributions of protons for each extraction for which neutrino interactions are observed in the detector) based on measured neutrino interaction time distributions. These statistical results can't completely rule out for instance that the "arriving" neutrinos' signal is due to some local neutrino-like interaction totally unrelated to the proton accelerator.

kfmfe04

in one of the videos about OPERA, I saw a mention of fiber carrying light along the path - assuming that this light is subject to the same mass distributions as you ghc mentioned, couldn't you work backward with this fiber as the calibration point for c, and determine if the neutrinos have traveled faster than the photons in this fiber?

Vanadium 50

When the accelerator is on, they see neutrinos. When it's off, they don't. That's pretty convincing.

DevilsAvocado

Could you please help me out here (because I’m about to lose my mind [almost])...

IF something is moving faster than light then the Lorentz factor γ (using c as a constant) must be somewhat 'adjusted', right? The Lorentz factor appears in several equations in Special Relativity, including time dilation, right? Time dilation is used in the GPS system to adjust the clocks involved for relativistic effects, right?


Lorentz factor as a function of velocity

So, how can we trust the GPS timing if we at the same time are looking for data that will 'overthrow' the scientific foundation the system is built on?? I don’t get it...


Please note: I know that I’m wrong (to many extremely smart people around to miss this), I just can’t see it myself...

TrickyDicky

It is not as simple as that and anyone who has bothered to look up the paper or knows about neutrino detection knows it, so you ought to know.
If experimental error is not found,the very detection of neutrinos 60ns before they should if they were coming from the accelerator should make you consider this possibility, unless you are one of those speculating about the fall of modern physics as we know it.

Vanadium 50

That's exactly how it's done. You have the neutrino beam produced for a fraction of a second every SPS cycle, and the detector sees more events - substantially more - in this period than at other times. Furthermore, this tracks the accelerator operation at all time periods. Machine off for a week? No neutrinos that week.

You can see it graphically in the paper; figure 11.

keji8341

It is more convincing that experiments for both neutrino and photon are done based on the same clock synchronization. The key point is the clock synchronization.

xeryx35

GPS compensates for time dilation, if you read the paper.

In any case, I feel that this may be a statistical anomaly, as there have been no real follow-up observations. And unlike much of the Internet, I do not think that this in any way disproves relativity, just in the way that relativity itself did not disprove Newton.

Relativity may have a few permutations, but the theory will only become refined further, rather than disproven entirely. However, 99.9999999% of the time, relativity holds true, just as Newtonian mechanics held true for pretty much all of the world of everyday experience. No-one considers the advent of relativity a "nail in the coffin" for Newton's ideas.

Furthermore, the news media has ignored one key line in the paper announcing the results:

The paper later goes on to say that the measurements were normalized, but the truth remains that no individual neutrino was clocked at FTL velocities. Obviously the lamestream needs to ignore anything which will dampen the sensationalism.

PeterDonis

Since the clock synchronization is done using GPS, I would assume that it is in the frame GPS uses, which is an Earth Centered Inertial (ECI) frame:

http://en.wikipedia.org/wiki/Earth-centered_inertial

I don't remember seeing an explicit statement to that effect in the paper, though.

TrickyDicky

This is the statistical process I referred to

This might be misleading, neutrinos are detected in a location at some rate at all times, regardless the existence of beams directed to that location.

f95toli

The reason why we trust it is because it has been tested to many times. The GPS system is compensated both for SR and GR effects; UTC time uses a "normalized" geodesic sphere to compensate for local differences in speed and position.
Note that GPS time is NOT the same thing as UTC, but the former is disciplined to the latter.

Now, there are several methods for time transfer; although the two methods that currently used are (as far as I know) based on transfer via satellites. One methods uses GPS, the second geostationary satellites that are not part of the GPS system, the latter system is more accurate than the GPS.
It is also possible to transfer time using optical fibres etc; but that is as far as I know only done for experiments with optical clocks; the latter are several orders of magnitude better than cesium clocks (and will one day replace the cesium clocks as time standards) and current time transfer methods are not good enough.

The main point here is that UTC and associated methods are very well established (old, if you like), if you visit a modern NMI you will find that many if them have clocks that are much better than the clocks that are part of the UTC. Hence, comparing two clocks using the UTC in the way it was done in this experiment is -if not easy- so at least routine.

Also, note that both PTB and METAS were involved and they certainly know what they are doing, the clocks were properly calibrated and the result checked by a movable time transfer device.

Hence, it is extremely unlikely that the error (and I agree that it is probably a systematic error) comes from problems with the clocks.

I should point out that I am not involved in time metrology (although in my experiments I use methods from frequency metrology), most of what I know about this I've learned from collegues who work on clocks and time transfer (talks etc) so take what I've written in this thread with a pinch of salt.

PeterDonis

They didn't do a corresponding experiment with photons (as someone mentioned in an earlier post in this thread, that would require cutting a 730 km vacuum tunnel between CERN and OPERA). They calculated what the time of flight for a photon should be based on the GPS-determined positions of the source and detection points. That is subject to a number of uncertainties, but so far I don't think anyone in this thread has found one that is potentially large enough to shorten the actual distance (as compared to the calculated distance) by 18 meters.

IttyBittyBit

That's because they didn't clock neutrinos individually at all. Your argument is invalid.

Greg Bernhardt

Let me repeat the reminder yet again.

Before posting in this thread, we'd like to ask readers to read three things:

1. The PF Rules. Don't forget the section on overly speculative posts.
2. The paper http://arxiv.org/abs/1109.4897
3. The previous posts in this thread

dan_b

Read the article, and they were careful. That being said:

a) The 8.3 km fiber optic, including Tx and Rx circuits, has some temperature coefficient of group delay. Since the GD is ROM 30 us, and they desire a couple ns cal error, then was the temperature at the cal times close enough to the temperature at pulse measurement times?
b) Would like to know more detail on how the digitizer time stamping was done. Concern is with front end latencies. My sense is they probably did fine here, but it would put everybody to sleep actually explaining it.
c) What if the proton pulse shape has a good-size temperature coefficient? Then will the pulse shape statistical treatment they did still work and not lead to errors? Because the pulse, 10 us long, might then give problems with the way they modeled it if it varies quite slowly.