Cautionary Tale From Neutrinoland
There’s one main reason I don’t care how many non-experts rail against topics like we see with global warming or evolution. It’s because they are NOT EXPERTS. When you get into the details, science is subtle and tricky, and even though you might understand the big chunks, there comes a point where the non-expert — even a very intelligent one — will be out of his or her depth.
I offer up an example from the brouhaha of the month, the neutrino experiment. (I trust I don’t have to say no, not that one, the other one.) Followup: FTL neutrinos explained? Not so fast, folks.
There are two issues here. One is the paper itself on which Phil is commenting; the author seems to assume that the GPS satellite use for synchronization is always traveling in the same direction as it passes over the experiment, which I don’t think is the case. But I’m not a GPS expert. The second is that if this purported timing offset weren’t already accounted for in GPS receivers, it would show up as a positioning error. 1 nanosecond is 1 foot, roughly. (3 ns is a meter). So from just this one source we’re talking 10 – 11 meters of error. GPS does better than that. It’s kind of silly to assume that this wouldn’t be accounted for in setting up the system. So my initial reaction is that it’s bunk.
The second part is what Phil posts
I had thought of something like this as well. CERN and OPERA are at different latitudes, and since the Earth rotates, they are moving around the Earth’s axis at different speeds. Could that be it? I did the math, and the answer is no. Too bad; it would’ve been fun to be the person to have figured this out!
As I’ve mentioned at least once before, the rotation of the earth has no effect on clocks. The rotation causes deformation of the earth (we are oblate spheroid, mighty mighty oblate spheroid) and it turns out that the slowing from the kinematic time dilation is offset by a speedup cause by being slightly higher in the gravity well. So on the geoid, clocks all run at the same rate, and you only have to account for elevation changes.
It’s not surprising that an astronomer wouldn’t know that. Hell, I didn’t know that for the first few years I worked with clocks, and when I asked the question, the people I talked to weren’t sure why latitude corrections weren’t necessary. I went and found the answer in Neil Ashby’s “Relativity in the Global Positioning System”
Considering clocks at two different latitudes, the one further north will be closer to the earth’s center because of the flattening – it will therefore be more redshifted. However, it is also closer to the axis of rotation, and going more slowly, so it suffers less second-order Doppler shift. The earth’s oblateness gives rise to an important quadrupole correction. This combination of effects cancels exactly on the reference surface.
What does all this mean? Smart people outside of their field will not be familiar with subtle but very important effects. They may, as happened here, raise what seem to be legitimate objections that are well-know to people who actually work in the field.
SFN RSS
Well said.
Excellent points. The devil is in the details. And the details are often subtle and understood by those who are experts in THAT field. Generalizations and assumptions by smart people who are not experts in that field can lead to reasonably sounding arguments which are flawed.
Reminds me of arguments against global warming.
Generalizations, indeed, are quite a risky business. Such as the comparison of the theory of relativity and global warming “science.” Doctor: cure thyself of such generalizations.
If you’re trying to sell that global warming is simple and everyone understands it, I’m not buying.
Physics Today 58(3) 34 (2005)
Time passage, equator vs. poles.
Cf: Longitudinal and transverse mass
Phys. Rev. 129(6) 2371 (1963)
Transverse Doppler effect in an ultracentrufuge hub vs. rim is inert toward rate of time passage.
yes,i like.
Hmmm, it is “interesting” that something like Earth oblateness (which has to depend on the Earth’s material, it can’t be an intrinsic geometric relation to a given rate of rotation) would *exactly* (I suppose, FAPP) cancel the motional time dilation. A coincidence, like the apparent size of Sun and Moon being equal?
I think it’s true of any planet that is free to deform. The surface will be a gravitational equipotential.
that assumes the surface is the equilibrium surface.
it is not.
(all mountains crumble into the sea, etc)
The geoid — basically mean seal level — is an equipotential. If you are on the geoid, your clock rate does not change.
I wonder if there could be subtle interplay between the calculations that the GPS satellites do to correct for geoid deviations and the calculations that the experimenters are making. If the experimenters have not taken into account all the corrections the GPS satellites are making maybe they are correcting for something they didn’t need to, giving a systematic error. Not likely, but one area to look at. http://en.wikipedia.org/wiki/Geoid
The thing is that people do time transfer with GPS common-view at the nanosecond level. The method is pretty well established, though it is certainly possible to make errors. It’s my understanding that they consulted with the PTB, the German standards lab, which makes a fundamental timing error unlikely.