# Thread: Speed of light exceeded??

1. Originally Posted by Jeff Root
Obviously. It is the reason why we are talking about it.
The straight line between two points on Earth's surface is
shorter than the great circle geodesic between those two
points. The geodesic is curved because it is on Earth's
surface. The straight line goes through the Earth.
I.e. it goes outside the space within which the great circle is a geodesic, which is the 2d space which is the surface of the Earth.

Thanks for making my point.

The way we're looking at is that a great circle is a straight line, the surface of the earth is a curved space, and the only way to take a shortcut is to leave the space it exists in.

And you're assuming an outside Euclidean space is a normal spot to look from, despite the Universe not being one.

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Originally Posted by Ara Pacis
I think the confusion is that the term geodesic is used both
for mathematics and for the physical properties of earth.
That would be a possible confusion, but the confusion I have
been railing against is even simpler than that. Really simple.
Calling a curved line "straight" is not only confusing, it is
obviously wrong. At best, it is an analogy. Straight lines are
analogous to curved geodesics in many ways.

The confusion most likely to occur in this context doesn't
appear to have happened yet. It is very similar to the possible
confusion you point out, which has to do with terms. The more
likely confusion has to do with what those terms refer to.

A geodesic on Earth's surface is the shortest path between
two points on the surface. It is a curve. A straight line
between those two points goes through the Earth. It is of
course shorter than the geodesic on the surface. The path
that light would take if it could travel through the Earth much
more nearly approximates a straight line than the geodesic
on the Earth's surface, but it is in fact a curved geodesic.
It is curved by Earth's gravity. But the amount of curvature
is very, very slight. Immeasurably slight, as far as I know.

The question is: Could the geodesic path taken by real
neutrinos somehow be shorter than the geodesic path
that light theoretically would take?

-- Jeff, in Minneapolis

3. Originally Posted by Jeff Root
That would be a possible confusion, but the confusion I have
been railing against is even simpler than that. Really simple.
Calling a curved line "straight" is not only confusing, it is
obviously wrong. At best, it is an analogy. Straight lines are
analogous to curved geodesics in many ways.
But it's only curved when you look at it from an outside that doesn't exist in the relevant space.
Originally Posted by Jeff Root
The question is: Could the geodesic path taken by real
neutrinos somehow be shorter than the geodesic path
that light theoretically would take?
And the answer would be no, not without taking a shortcut outside of space-time.

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Originally Posted by HenrikOlsen
Originally Posted by Jeff Root
The straight line between two points on Earth's surface is
shorter than the great circle geodesic between those two
points. The geodesic is curved because it is on Earth's
surface. The straight line goes through the Earth.
I think I found where we talk past each other, it's in our
choices of which way of looking at it is "normally".

To me, the relevant spots from which to look at the line are the
points on the line itself, every other spot has the potential of
giving a distorted impression of what's going on with the line.
You are choosing a specific, extremely limited range of
locations from which to view the line, in order to hide the
line's curvature. I am allowing lines to be viewed from any
location. That viewing does not introduce distortion.
It reveals any curvature the line has.

Originally Posted by HenrikOlsen
"Seen from outside" is an arbitrary sweet spot which can
distort what is going on.
Obviously that is false.

Originally Posted by HenrikOlsen
A great circle is straight in the sense that matters for
people travelling along it.
Exactly! It is straight in a sense. And for some people.

It isn't *actually* straight, and the sense in which it *is*
straight doesn't apply to most points of view.

-- Jeff, in Minneapolis

5. Oh well. Looks like we're at an impasse. You keep insisting it's more relevant to look at it from the outside, I think the only relevant (for physics) point of view is from within the space where things are happening.

If you want to look at the world from some imaginary 5 dimensional space the Universe might conceivably be embedded in, feel free. Within this Universe it's straight lines.

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Henrik,

The arcs in this HST image are of gravitationally-lensed light
from galaxies far beyond the Abell 2218 cluster. The galaxies
are directly behind the cluster, but we see the light off to the
sides. The light paths are curved in a way that we can see
without having to go "outside" our Universe into some higher
dimension.

http://apod.nasa.gov/apod/image/0110/a2218c_hst_big.jpg

Likewise, we can measure Shapiro delay without having to
go into some higher dimension.

-- Jeff, in Minneapolis

7. Originally Posted by Strange
Yes, and no more of that here, unless very directly related to the topic of this thread. Jeff Root has been infracted for the post following my earlier note.

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The spacetime curvature and Shapiro delay which Pete
suggested as a possible explanation for the apparently
anomalous travel time of neutrinos is obviously relevant.
Such an explanation depends on the actual path taken
by the neutrinos to be shorter than the hypothetical
path calculated for light. Since spacetime near Earth's
surface is "curved" by Earth's gravity, the hypothetical
path calculated for light is curved. The possibility then
arises that the path for neutrinos might somehow be
less curved than that hypothetical path for light.

That is all that Pete was suggesting, and I agree that
it is a very good suggestion. I think it should be given
a deeper examination rather than being dismissed out
of hand simply because the path of a light ray is
considered to be the shortest possible path.

-- Jeff, in Minneapolis

9. It's not "considered" to be the shortest, it IS the shortest path possible in that space. You need to leave the Universe to have a shorter path.

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As I understand the situation now, there
was a measurement campaign to get the surface
distance between the two labs then a calculation
of the chord distance through the Earth. The
time of travel for light was used to get a time
of flight. If this included the Shapiro delay
then the discrepancy is 60 nsecs. If not then
it is about 50 nsecs I think.

The actual path is downhill then uphill a bit.
So not exactly Earth grazing. Light would follow
a null geodesic, no arguments. Neutrinos would,
we think, follow timelike geodesics from what
has been said here. The question is what is the
difference in time here and how might it relate
to the discrepancy. I was remembering that Soldner
showed a material particle delected half that
of light if it went at lightspeed. Whether this
might still hold given the complete GR picture
I dont know.

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Originally Posted by Jeff Root
....... Since spacetime near Earth's
surface is "curved" by Earth's gravity, the hypothetical
path calculated for light is curved. The possibility then
arises that the path for neutrinos might somehow be
less curved than that hypothetical path for light.

............
-- Jeff, in Minneapolis
First off... I'm blissfully ignorant so be gentle......

And so... would space-time be more or less curved at Earth's surface than closer to the center of the earth? Space-time would be a bit more curved as one moves deeper/closer to the center of the earth, yes? And if two points were separated by space-time of 1x, then those same two points being separated by <1x (due to bending of space-time under the influence of gravity)would be closer together, which would produce lower transit time if the speed was the same.
..........so basically we have a localized wormhole kinda thing going on.

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That is a very good question. I agree that the curvature is
greater a bit closer to Earth's center than it is at the surface.
I think it is greatest where the gravitational field strength is
greatest, though I may easily be wrong about that. The field
strength is greatest at the boundary between the dense outer
core and the less dense lower mantle. It increases slightly
from the surface to the boundary between the upper mantle
and lower mantle, then drops very, very slightly in the upper
part of the lower mantle, but then gradually rises again to a
peak at the boundary between the lower mantle and outer
core. From that peak it falls rapidly to zero at the center.

I think you got the results of the curvature backwards.
Greater curvature (greater gravitational field strength) means
that two points in space are farther apart along a geodesic in
spacetime, and longer transit time between them: A longer
Shapiro delay.

-- Jeff, in Minneapolis

13. Originally Posted by HenrikOlsen
It's not "considered" to be the shortest, it IS the shortest path possible in that space. You need to leave the Universe to have a shorter path.
Now I have a question. Is that definition due to the speed of light being "considered" to be the speed limit? Assume, for the moment, that the results mean that neutrinos did travel faster than light, does that affect what would then be considered the "shortest path possible in that space"? Or would it suggest that indeed, the neutrinos "left the universe to have a shorter path"? Or would we just need to adapt the definition to include neutrino paths to be shorter?

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Originally Posted by Ara Pacis
Now I have a question. Is that definition due to the speed of light being "considered" to be the speed limit? Assume, for the moment, that the results mean that neutrinos did travel faster than light, does that affect what would then be considered the "shortest path possible in that space"? Or would it suggest that indeed, the neutrinos "left the universe to have a shorter path"? Or would we just need to adapt the definition to include neutrino paths to be shorter?
I think that one thing that Henrik forgets (or may not realize) is that it is the shortest path, if there are no Lorentz symmetry violations. Both Special and General Relativity require that there be no Lorentz symmetry violations(General Relativity only locally). This makes sense after all, as the Lorentz transformations (and the general Poincare transformations which they are a part of) are a manifestation of Lorentz symmetry. IF Lorentz symmetry is not valid, then a geodesic in GR does not necessarily describe the shortest path, as the math and concepts used in GR are not necessarily exactly correct (they would be close, much as Newtonian gravity is close to, but not exactly correct when compared to GR). In these cases, there can be shorter paths (somehow, I can't see how it would work) which means c is not the limit we think it is.

Of course, the main reason most physicists are leery of the OPERA results is simply due to the amount of experimental verification that SR has and the values that have been found forming very tight constraints on any Lorentz violations. The latest values I've found for constraining a Lorentz violation are 10-31 GeV for a neutron, 10-27 GeV for a proton. Electrons have constrained a Lorentz violation to 10-31 GeV also. The value for neutrinos is less than 10-23 GeV and the best constraint is for polarization of photons at 10-43. It's hard to see how the OPERA results are correct, unless all the Lorentz violation experiments are wrong, which seems to be a longshot. Here is a paper that lists all the Lorentz and CPT (which is equivalent to Lorentz) violation tests and the constraining values, along with the list of the experiments done.

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I would guess that the tests for neutrino violation of Lorentz
symmetry were all done with neutrinos coming out of a reactor
or accelerator, before they had a chance to change flavor.
The long path of the neutrinos through the ground would seem
to be what must make the difference in the OPERA results if
the apparent difference is real. I'm guessing that the observed
neutrinos did change flavor.

-- Jeff, in Minneapolis

16. Hi All;

There may be a rational explanation along these lines of enquiry, provided one prepares oneself for the ‘quantum leap’ into a fifth dimension, afforded by M-Theory.

Along the lines of causality violation, a five dimensional model was proposed in Dec 2011, which allowed Closed Timelike Curves (CTCs), and derived them as solutions to the geodesic equations of motion. In the extra dimensional model, certain ‘modes’ of ‘gauge singlets’ are permitted to travel through CTCs via paths in the extra dimensional bulk (of M-Theory). From our brane’s perspective, the paper says that some of these ‘modes’ would appear to travel travel backwards in time. The premature arrival and departures, seem to still be bound by momentum conservation, (which is the good news part).

The aims of the paper are:
First of all, we seek a class of CTCs embedded in a single compactified extra dimension. We require the CTCs to be geodesic paths, so that physical particles will become negative-time travelers. Secondly, we ensure that this class of CTCs is free of undesirable pathologies. Thirdly, we ask whether particles traversing these CTC geodesics may reveal unique signatures in large detectors such as ATLAS and CMS at the LHC.
They also offer a way around the standard time paradoxes (Grandfather, Bootstrap and Unitary):

the standard paradoxes (described below) are ameliorated, as no macro objects can get transported back in time.
Apparently, the ‘shortcut’ mechanism has been used before, and it doesn’t necessarily guarantee a CTC although CTCs are also a natural outcome of the mathematical derivation ...
Exactly this mechanism has been invoked as a solution to the cosmological horizon problem without inflation [27]. Although this leads to an apparent causality violation from the brane’s point of view, the full 5D theory may be completely causal. Superluminal travel through extradimensional “shortcuts” generally doesn’t guarantee a CTC. To obtain a CTC, one needs the light cone in a t-versus-r diagram to tip below the horizontal r axis for part of the path. Then, for this part of the path, travel along r is truly progressing along negative time. When the positive time part of the path is added, one has a CTC if the net travel time is negative.
Also, this paper appeared in July 2011, as a possible theoretical explanation of leptogenesis of neutrinos which includes CPT violation, but seems also to ‘not cause problems with the solar, atmospheric and reactor neutrino data’.

Despite the crucial significance of CPT symmetry in the conventional quantum field theory, it has been shown that string interactions may induce couplings between Lorentz tensors and fermions in the low- energy 4D effective lagrangian [1]. When the appropriate components of these Lorentz tensors acquire non-zero vacuum expectation values, they lead to a spontaneous CPT violation.
Both of these papers seem extraordinarily clever to me, and make for interesting reading.
Please note also, I am happy to say that I am probably not capable of much deeper discussions into the intricacies behind the concepts, but I have found that a quick read seems to lead to a deeper-than-TV-documentary level of understanding of how M/String Theory is capable of explaining what, in the case of the OPERA experiments, will probably ultimately turn out to be experimental ‘issues’ anyway.

Best Regards.

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I just thought I would put down another few
thoughts following on from my previous and I
admit straight away they may be totally off
the wall.

The route between the two labs is a bit downhill
then uphill. Suppose it is a bit more downhill
than uphill from the shape of the Earth and what
Jeff says about the matter just below the surface
of the Earth. Then a matter particle may have
some residual extra speed.

Then I speculate about the "baseline" speed of
neutrinos being c, the speed of light. Could this
be added too? I do not know if this is totally
balderdash in GR. Perhaps the description
Marjariana particles has a let out. (and that
spelling is probably totally wrong) Lets
look up Paulis' first theory of neutrinos where
he specified small particles at c!

So 60 nsecs is a roller coaster phenomenon!

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Originally Posted by Jeff Root
............
I think you got the results of the curvature backwards.
Greater curvature (greater gravitational field strength) means
that two points in space are farther apart along a geodesic in
spacetime, and longer transit time between them: A longer
Shapiro delay.

-- Jeff, in Minneapolis
OK...so curvature is then the wrong word for what I'm envisioning. Perhaps "warping" would be a better descriptive term? "Compressed" is really what I'm thinking but somehow that doesn't seem appropriate.... space/time being "compressed" by gravity? ...squeezed?....

Point being.... if I imagine two points that are 1x apart in two dimension, as in two dots on a piece of paper....and then we bend/fold the piece of paper... the two dots are still separated by the same number/amount of cellulose molecules with respect to that piece of paper, but not so with respect to the third dimension that allows us to bend/fold the paper.
Similarly, two points on the globe separated by 1x distance with respect to the "matter" between them...but under two variant sets of gravity...the actual space/time between the two points could change based on the gravity having varying values. ....? ..as in folding the paper.

This seems so elementary as to be silly to post... so I assume it's simply a matter of my own ignorance on this. ...but I do appreciate you guys educating me.

This seems so elementary as to be silly to post... so I assume it's simply a matter of my own ignorance on this. ...but I do appreciate you guys educating me.
Actually, it is one of the more speculative explanations proposed.
http://www.newscientist.com/article/...ght-speed.html

ETA:
Another theoretical argument against the result, based on conservation of energy: http://www.newscientist.com/article/dn21328
Interestingly, the "extra dimensions" thing gets a mention again.

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Originally Posted by Jeff Root
I think you got the results of the curvature backwards.
Greater curvature (greater gravitational field strength) means
that two points in space are farther apart along a geodesic in
spacetime, and longer transit time between them: A longer
Shapiro delay.
OK...so curvature is then the wrong word for what I'm
envisioning. Perhaps "warping" would be a better descriptive
term? "Compressed" is really what I'm thinking but somehow
that doesn't seem appropriate.... space/time being
"compressed" by gravity? ...squeezed?....
"Curvature", "warping", and "stretching" are all commonly
used to describe the effect of mass-energy on spacetime.
It is the opposite of compression. It is very much like the
analogy of a heavy object sitting on a rubber sheet: The
weight of the object stretches the rubber, increasing the
distance between two points on the sheet which are at
different distances from the object. Note that the analogy
is ironic in that it uses gravity to explain something about
how gravity works!

Point being.... if I imagine two points that are 1x apart in two
dimension, as in two dots on a piece of paper....and then we
bend/fold the piece of paper... the two dots are still separated
by the same number/amount of cellulose molecules with
respect to that piece of paper, but not so with respect to the
third dimension that allows us to bend/fold the paper.
Similarly, two points on the globe separated by 1x distance
with respect to the "matter" between them...but under two
variant sets of gravity...the actual space/time between the
two points could change based on the gravity having varying
values. ....? ..as in folding the paper.

This seems so elementary as to be silly to post... so I assume
it's simply a matter of my own ignorance on this. ...but I do
appreciate you guys educating me.
Whether a curved paper is analogous to the curvature of
spacetime is not at all elementary. You need to look at the
actual "direction" of the curvature, which is hard to do since
it is not a direction in space. It isn't even a fourth spatial
dimension. The fourth dimension of general relativity is
time. At one level, I think your analogy is okay: it suggests
in a vague way how space can be curved and distances
between things can change because of that curvature.
At another level, though, it isn't sufficiently detailed to get
the changes in distances in the right direction. Analogies
always fail in that way at some level.

-- Jeff, in Minneapolis

21. Faulty optical cable connecting to the GPS !!

Credible, or not ?

Now, according to a breaking news article by Edwin Cartlidge on AAAS’ ScienceInsider, the neutrinos may be cleared of any speed violations.

“According to sources familiar with the experiment, the 60 nanoseconds discrepancy appears to come from a bad connection between a fiber optic cable that connects to the GPS receiver used to correct the timing of the neutrinos’ flight and an electronic card in a computer,” Cartlidge reported.
Regards

22. I was just going to post that. I'm wondering if that applied to all tests? Were they still using that same hardware for timing in the recent follow-up tests?

23. I read there's to be a press conference on this tomorrow. I hope they share the "debugging" process that led them to find this, was it just a "hey, let's measure this part" or a methodical approach to verify everything?

24. Originally Posted by Selfsim
... Credible, or not ?
As the others have said "we'll see". There are a number of similar experiments with different distances and energies that will happen this year. I took the FTL neutrinos as unlikely but unknown till later experiments. I'll take the faulty cable to the atomic clock as likely but uncertain until later experiments.

25. Yep .. I agree with Antoniseb. Have to wait and see (again).

(Seems like it might be a fairly embarrassing possibility for the OPERA team, though).

Regards

26. This image of Johnny immediately came to mind.

"Just kidding!"

27. I couldn't find the direct link to to the OPERA press release that Nature News Blog claims to have but presumably it's real and in it, the OPERA team seems to suggest they've located two possible errors - which might, if I read the text correctly, cancel each other out:
http://blogs.nature.com/news/2012/02...le-errors.html

They do promise "an extensive report on the above mentioned verifications and results will be shortly made available to the scientific committees and agencies".

Some commentary:
http://cosmiclog.msnbc.msn.com/_news...an-light-setup
http://scienceblogs.com/startswithab...e_gig_is_u.php

28. Originally Posted by Selfsim
It is not clear to me how a faulty connection could be the cause and, according to this New Scientist article, it ain't that simple.
Originally Posted by NS
However CERN spokesman James Gillies told me, "It's not quite as simple as that....There's a possible explanation, but we will not know for sure until further tests have been made with beam."

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Not a surprise. It was inconsistent with the results from SN1987a....that the neutrinos were pretty much coincident with the optical display,given a time lag for the kinematics of the expanding fireball, after ~170,000 years...and of other physical effects. They would have been hours/days early.That and throwing out Special Relativity, causality and Lorentz Invariance in one fell swoop seemed entirely unlikely.
I'll betcha a hot fudge sundae....both photons and neutrinos will be found to travel identically...born at c, travel at c, die at c...within all experimental limits in every repeatable experiment, for the next 20 years, should I live to pay/collect, the bet. Pete

SEE: c http://en.wikipedia.org/wiki/Speed_of_light

P.S. As for the author, Mr. Major....I'm not dropping my plans for WARP drive, as long as WARP 10 is c,and not ever to be seen... discussed many moons ago with Zep. Cochran on AOL's Astronomy Club. A computer made that all disappear when Stuart Goldman was moderating the forum....circa 1994-5. pete

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