On 11-10-14 02:53 PM, Daniel Rocha wrote:
As far as I know, each GPS device sycs with several different
satellites, or clocks, at least 3, and also corrections for
gravitational effects from general relativity.
That's not the point. The GPS system could be absolutely perfect and
the problem would still exist.
The point is they're using a time value which is "universal". An
observer hanging in space, stationary, directly over the pole, looking
down at GPS receivers all over the Earth would see that, at a given
moment, they /all showed the same time/ (modulo time zone changes).
/And that's wrong!/
If you time the speed of light using two clocks set that way, you'll
find that it's anisotropic -- it's faster one way than the other. Note
well: The observer hanging in space would say that the reason is that
your start and end point were in motion, and the light had to travel
farther one way than the other. An observer comoving with the Earth's
surface, on the other hand, would say the two clocks were /not properly
synced/ -- relativity of simultaneity was not properly accounted for in
setting them.
In other words, if you sync your clocks using the GPS system, then
you've automatically failed to take account of the motion of the Earth's
surface.
Maybe their problem was more subtle than this, but it doesn't sound like it.
2011/10/14 Stephen A. Lawrence <[email protected] <mailto:[email protected]>>
OMG -- of course! You can't synchronize (all) clocks on the
Earth's surface -- it's a rotating frame, and Sagnac comes around
and bites you on the bumm if you try! Yet by using the GPS
satellite signals, which are available everywhere, they were doing
essentially that: using a "universal" time value, which doesn't
produce a sensible result on the Earth's surface.
Using clocks in another frame (the GPS clocks) to synchronize the
clocks in the rotating frame (on the surface of the earth) just
adds confusion, it doesn't avoid the problem, which is
fundamental. In particular, if you sync your (rotating) clocks
with an external source, then when you measure light speed you
find it's anisotropic -- it's faster one way than the other.
The only way to deal with it an experiment like this it is to pick
just two clocks and E-sync them using point-to-point two-way light
travel (or use some other source, but then figure out what the
E-sync times would have been and use the computed values).
Apparently, they didn't do that.
When I say it's "fundamental", I mean that if you use two-way
light signals to sync pairs of clocks on the Earth's surface, and
you do it for a chain of pairs of clocks reaching all the way
around the Earth, you will find the clocks at the beginning and
the end of the chain are stubbornly out of sync, even though the
clocks all the way back along the chain were in sync. And you
can't avoid it by using some other clock source.
See, for example,
http://www.physicsinsights.org/sagnac_1.html
On 11-10-14 01:42 PM, Terry Blanton wrote:
On Fri, Sep 23, 2011 at 10:30 AM, Terry
Blanton<[email protected] <mailto:[email protected]>> wrote:
Don't bury Einstein yet:
http://www.newscientist.com/article/dn20957-dimensionhop-may-allow-neutrinos-to-cheat-light-speed.html
"Sher also mentions a third option: that the measurement
is correct.
Some theories posit that there are extra, hidden
dimensions beyond the
familiar four (three of space, one of time). It's possible
that the
speedy neutrinos tunnel through these extra dimensions,
reducing the
distance they have to travel to get to the target. This
would explain
the measurement without requiring the speed of light to be
broken."
Those neutrinos probably knew a short cut in the other 6
dimensions.
Well it wasn't extra dimensions. It was relativity itself. They
needed entangled clocks!
http://www.technologyreview.com/blog/arxiv/27260/?p1=blogs
"Faster-Than-Light Neutrino Puzzle Claimed Solved by Special
Relativity"
T
