Good post Eric.
Merged Puzzling results from CERN
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It isn't constant. Take a look at this report on a super-accurate optical clock. It's so precise that you can see two of these clocks losing synchronisation when they're separated by only a foot of vertical elevation. Now take a look at wiki re time dilation, and note the bit that says consider a simple clock consisting of two mirrors A and B, between which a light pulse is bouncing. When you simplify the optical clocks to parallel-mirror light clocks, they lose synchronisation when they're separated by a vertical foot too. This is essentially what's happening:
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Think about the evidence, and think about the light beams as if they're racehorses. Ask yourself if they're really going at the same constant speed.
I think it's significant for a different reason, along the lines of "neutrinos are more like photons than people think".
What makes it special is that we use the local motion of light to define the second and the metre, which we then use to measure the local motion of light. Hence we always measure 299,792,458 m/s.
sol invictus
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Light moves at constant speed in all inertial reference frames. The rest frame of the earth is non-inertial because of its gravity (and because it's rotating). But that was - supposedly - taken into account by OPERA.
Supposedly. 730km and 20 parts per million means we're only talking of a distance of 14.6 metres. It isn't much. Not enough to get excited about. But I think they were right to go public, because other people do find it exciting. It's real experimental physics, with a result that ought to be laid out on the table rather than buried by peer-review because it's unexpected.
I agree with this bit. Pity they haven't done this yet! (As far as I know). It should certainly include making the raw data available, with full details of their own analysis.
sol invictus
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Unfortunately, experimental collaborations almost never make their raw data publicly available.
Part of that is because it would actually be almost useless in raw form - you'd need a lot of information about the detector, the electronics, how and when the data was collected, etc. to do any meaningful analysis of it. But the other part is purely territorial.
Patrick1000
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My point is not, was not, about "speed"/velocity per se
My point is not, was not, about "speed"/velocity per se. The absoute number is irrelevant in a sense. The speed of light is taken as constant in special relativity axiomatically. If the measured speed is "faster/slower" who cares? But if the speed/velocity is found to vary in important contexts, in unexpected ways, then we may have something new and important. What matters is if somehow the CERN result SUBSTANTIVELY UNDERMINES EINSTEIN'S SPECIAL RELATIVITY POSTULATE/AXIOM. THEN, IT IS A HUGE DEAL!
My point is not, was not, about "speed"/velocity per se. The absoute number is irrelevant in a sense. The speed of light is taken as constant in special relativity axiomatically. If the measured speed is "faster/slower" who cares? But if the speed/velocity is found to vary in important contexts, in unexpected ways, then we may have something new and important. What matters is if somehow the CERN result SUBSTANTIVELY UNDERMINES EINSTEIN'S SPECIAL RELATIVITY POSTULATE/AXIOM. THEN, IT IS A HUGE DEAL!
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Any chance we can get back on topic, guys?
1911: If we call the velocity of light at the origin of co-ordinates co, then the velocity of light c at a place with the gravitation potential Φ will be given by the relation c = co(1 + Φ/c²).
1912: On the other hand I am of the view that the principle of the constancy of the velocity of light can be maintained only insofar as one restricts oneself to spatio-temporal regions of constant gravitational potential.
1913: I arrived at the result that the velocity of light is not to be regarded as independent of the gravitational potential. Thus the principle of the constancy of the velocity of light is incompatible with the equivalence hypothesis.
1915: the writer of these lines is of the opinion that the theory of relativity is still in need of generalization, in the sense that the principle of the constancy of the velocity of light is to be abandoned.
1916: In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust.
What he actually said in 1916 was die Ausbreitungs-geschwindigkeit des Lichtes mit dem Orte variiert which translates to the speed of light varies with the locality.
But show this to people, show them those light clocks, and for some strange reason they insist that the speed of light is constant. That's the huge deal.
Everybody. Think about what I said about neutrinos being more like photons than people think. Then just suppose OPERA had been measuring the speed of photons rather than neutrinos.
Einstein substantively undermined his special relativity postulate:
1911: If we call the velocity of light at the origin of co-ordinates co, then the velocity of light c at a place with the gravitation potential Φ will be given by the relation c = co(1 + Φ/c²).
1912: On the other hand I am of the view that the principle of the constancy of the velocity of light can be maintained only insofar as one restricts oneself to spatio-temporal regions of constant gravitational potential.
1913: I arrived at the result that the velocity of light is not to be regarded as independent of the gravitational potential. Thus the principle of the constancy of the velocity of light is incompatible with the equivalence hypothesis.
1915: the writer of these lines is of the opinion that the theory of relativity is still in need of generalization, in the sense that the principle of the constancy of the velocity of light is to be abandoned.
1916: In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust.
What he actually said in 1916 was die Ausbreitungs-geschwindigkeit des Lichtes mit dem Orte variiert which translates to the speed of light varies with the locality.
But show this to people, show them those light clocks, and for some strange reason they insist that the speed of light is constant. That's the huge deal.
sol invictus
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Farsight, this is all perfectly understood by physicists. There is no confusion about it, and hasn't since about 1916. The words one uses to describe mathematical results are sometimes confusing to people that can't do or don't understand the math, that's true. But the math itself is established and unambiguous. There is no "huge deal"; that's in your head.
And in this case, the math of relativity tells us that neutrinos could not have propagated from CERN to Gran Sasso in the time they measured. Therefore either relativity is wrong or the experiment is wrong. That's all there is to it.
Sol is right, Farsight. OPERA's claim is that the neutrinos arrive 60 nanoseconds in advance of the actual predicted arrival time ... not in advance of "the speed of light and the geometry that you'd have used if you hadn't known GR."
Everything we know about GR, including the effects Einstein is referring to in those 1916 quotes (Shapiro delay and whatnot), is included in the prediction already.
Everything we know about GR, including the effects Einstein is referring to in those 1916 quotes (Shapiro delay and whatnot), is included in the prediction already.
Starts with a Bang has an interesting post on what happens next:
http://scienceblogs.com/startswithabang/2011/10/a_test_for_neutrinos_put_up_or.php
http://scienceblogs.com/startswithabang/2011/10/a_test_for_neutrinos_put_up_or.php
kalen
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Thanks for the link. That is very informative. I also very much like the follow-up test that is proposed.
Don't hide behind mathematics and intellectual arrogance. Make it crystal clear to Patrick. He thinks it's a huge deal. Tell him the room he's in is a non-inertial reference frame in which the speed of light varies. Just like everywhere else. As for what physicists understand, see Is The Speed of Light Constant? on Baez’s website, which ends up saying Finally, we come to the conclusion that the speed of light is not only observed to be constant; in the light of well tested theories of physics, it does not even make any sense to say that it varies. Also see Note on Varying Speed of Light Cosmologies where Ellis finishes up saying On the standard view, these various roles are tightly integrated together in a coherent package in which the speed of light does not vary.
sol invictus
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If the results of OPERA are accurate, it is a huge deal, as I said in what I thought was a pretty clear way. People "insisting that the speed of light is constant" is not a huge deal, because they are correct under a certain definition of "speed" (a good such definition is, a quantity measured locally in units of meters/seconds).
Here's the context of that quote, which is perfectly correct and agrees precisely with what I said above (I've bolded a few bits you might learn something from reading):
Steve Carlip/Chris Will said:
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sol invictus
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There are two ways to look at that.
One is, gravity exerts a force on light, and light responds by accelerating. So yes.
The other is, gravity is not a force at all, it's the curvature of spacetime. Light in vacuum (and anything else that's freely moving) follows the shortest path through a curved spacetime. The shortest path is what you'd usually call a straight line, with no acceleration. Since the spacetime is curved, the path looks curved, but it really is the shortest path.
The second view explains certain fundamental facts, like that inertial and gravitational mass seem to be exactly identical. The first works OK too.
How does it know to pick the shortest path?
Is there something about the shortest path that is actually different from all other paths? (Except for length, I mean. There's no way for light to "know" which path is shortest until it gets to the end. A path is only shortest when viewed from the end, so unless light knows where it's going from the start, how does it choose which path to take?
It must be in some sense "easier" at every point, for light to go one way and not another.
Or it goes every way and we just measure one.
Is there something about the shortest path that is actually different from all other paths? (Except for length, I mean. There's no way for light to "know" which path is shortest until it gets to the end. A path is only shortest when viewed from the end, so unless light knows where it's going from the start, how does it choose which path to take?
It must be in some sense "easier" at every point, for light to go one way and not another.
Or it goes every way and we just measure one.
sol invictus
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Good question, and my fault for not being clear. It follows a local version of "shortest path" - which actually might not be the shortest path between two distant end points. For instance the shortest path on the surface of the earth between London and Paris is the obvious one leaving London going more or less southeast, but there's another "straight" (in the local sense) path connecting them that leaves London going northwest, wraps around the globe, and arrives at Paris. Light could follow the analog of either of those.
Sometimes, the local version of shortest path is always also the global version. For instance, on a flat piece of paper, the local version just means straight lines. For any pair of points on any such line, the line is the shortest path between them. But that's not true on the surface of a sphere as the above example shows, nor is it always true in curved spacetime.
There's a disturbingly teleological aspect to the concept of a shortest route.
To say an object follows a straight line (or any shortest course through a space) we need to know where it started and where it is going.
Imagine I'm walking across a flat plane- a field, say.
I start at point 1 and walk to point 2 where I change direction and walk to point 3.
An observer can say I took the shortest route from 1 to 2 and from 2 to 3- but not from 1 to 3, because I changed direction at 2.
As a conscious entity I can say that I set out to go to 3, so the course I took was not, at any point, the shortest possible - but there MUST always exist a point 2 - and as any 2 points are linkable by a straight line, I am constrained to follow that line whether I want to or not, because if I changed course every inch between points 1 and 2, then there must exist a new point 2, closer to point 1, which I DID reach by the shortest distance possible. In short, no matter what convolutions my course follows, it is a linked chain of straight lines, of possibly very short length- each of them a shortest possible course . On a quantum scale, such line segments may approach the Plank length, yet still, between each two points, there exists a "straight line".
Is this all that is meant by saying that light follows straight lines in spacetime?
Or is this too incoherent to make sense?
To say an object follows a straight line (or any shortest course through a space) we need to know where it started and where it is going.
Imagine I'm walking across a flat plane- a field, say.
I start at point 1 and walk to point 2 where I change direction and walk to point 3.
An observer can say I took the shortest route from 1 to 2 and from 2 to 3- but not from 1 to 3, because I changed direction at 2.
As a conscious entity I can say that I set out to go to 3, so the course I took was not, at any point, the shortest possible - but there MUST always exist a point 2 - and as any 2 points are linkable by a straight line, I am constrained to follow that line whether I want to or not, because if I changed course every inch between points 1 and 2, then there must exist a new point 2, closer to point 1, which I DID reach by the shortest distance possible. In short, no matter what convolutions my course follows, it is a linked chain of straight lines, of possibly very short length- each of them a shortest possible course . On a quantum scale, such line segments may approach the Plank length, yet still, between each two points, there exists a "straight line".
Is this all that is meant by saying that light follows straight lines in spacetime?
Or is this too incoherent to make sense?
Belz...
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So, has modern science been overturned, yet ?