MMX and the earth's rotational sagnac

  • #1
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Main Question or Discussion Point

MMX proves light is isotropic in all directions.

Hand held GPS units apply the earth rotational sagnac correction which means light is not isotropic in all directions at the unit from the satellites.

If a hand held GPS unit is placed at the same location as an MMX experiment, one experiment proves light is isotropic in all directions and the other concludes it is not.

Yet both of these results prove SR.

How is that?
 
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Answers and Replies

  • #2
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Hand held GPS units apply the earth rotational correction
Do you have a reference for this?

Since you have trouble understanding basic SR concepts I suspect you may have trouble understanding any such reference and any explanations you get here.
 
  • #3
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Do you have a reference for this?

Since you have trouble understanding basic SR concepts I suspect you may have trouble understanding any such reference and any explanations you get here.
Thanks for the flaming. I have a few links.


GPS and sagnac
http://relativity.livingreviews.org/Articles/lrr-2003-1/ [Broken]

Because Earth rotates, Sagnac effect is large enough in the GPS and the clocks can’t be synchronized in the rotating frame and there is necessity for different approach to synchronize the clocks. In the GPS synchronization is performed in the Earth-Centered Inertial frame using constancy of speed of light.
http://www.phy.syr.edu/courses/PHY312.03Spring/GPS/GPS.html [Broken]

GPS observation processing must also compensate for another relativistic effect, the Sagnac effect. The GPS time scale is defined in an inertial system but observations are processed in an Earth-centered, Earth-fixed (co-rotating) system, a system in which simultaneity is not uniquely defined.

Read more: http://www.articlesbase.com/gps-articles/about-gps-223087.html#ixzz1AgD2Ds8w
Under Creative Commons License: Attribution
Allan et al., Science, 228 (1985), pg 69.They observed the Sagnac effect using GPS satellite signals observed simultaneously at multiple locations around the world. See GPS.
http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#Sagnac

Signals
from a single GPS satellite in common view of receivers at the two locations
provide enough information to determine the time difference between the two
local clocks. The Sagnac effect is very important in making such comparisons,
as it can amount to hundreds of nanoseconds, depending on the geometry. In
1984 GPS satellites 3, 4, 6, and 8 were used in simultaneous common view
between three pairs of earth timing centers, to accomplish closure in performing
an around-the-world Sagnac experiment. The centers were the National
Bureau of Standards (NBS) in Boulder, CO, Physikalisch-Technische Bundesanstalt
(PTB) in Braunschweig, West Germany, and Tokyo Astronomical Observatory
(TAO). The size of the Sagnac correction varied from 240 to 350 ns.
Enough data were collected to perform 90 independent circumnavigations. The
actual mean value of the residual obtained after adding the three pairs of time
differences was 5 ns, which was less than 2 percent of the magnitude of the
calculated total Sagnac effect [4].
http://www.ipgp.fr/~tarantola/Files/Professional/GPS/Ashby_2003.pdf
 
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  • #4
DrGreg
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The Sagnac effect applies only to light which travels around a closed loop that encloses a non-zero area, for example a circle, triangle or square. In the MMX experiment, light travelled in a straight line there-and-back enclosing zero area, so the Sagnac effect was irrelevant.
 
  • #5
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The Sagnac effect applies only to light which travels around a closed loop that encloses a non-zero area, for example a circle, triangle or square. In the MMX experiment, light travelled in a straight line there-and-back enclosing zero area, so the Sagnac effect was irrelevant.
Indeed.
Given a sagnac correction is applied to a GPS unit and clearly the signal did not travel around in a closed loop, then why do mainstream papers apply this correction to GPS?
 
  • #6
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The Sagnac effect applies only to light which travels around a closed loop that encloses a non-zero area, for example a circle, triangle or square. In the MMX experiment, light travelled in a straight line there-and-back enclosing zero area, so the Sagnac effect was irrelevant.

Geez, I missed this on first read. Light travels in straight lines only in ECI. That is why the sagnac must be applied in ECEF. Light aberration is applied in ECEF , the location of the MMX experiment, based on the earth's rotation.

Therefore, although one's brain may think the light is moving in the MMX arms in straight lines because the arm are straight, in fact the arms are moving in ECEF and hence, light is moving at an angle in the MMX arms. This is proven everyday by GPS.
 
  • #7
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5,032
In the GPS synchronization is performed in the Earth-Centered Inertial frame using constancy of speed of light.
That seems to explicitly contradict your assertion that GPS handheld units use a Sagnac correction. The citations that you provided that actually detected Sagnac effect using GPS did so via a system of multiple recievers at different locations on the earth, certainly not a Sagnac correction embedded in a hand held unit.
 
  • #8
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That seems to explicitly contradict your assertion that GPS handheld units use a Sagnac correction. The citations that you provided that actually detected Sagnac effect using GPS did so via a system of multiple recievers at different locations on the earth, certainly not a Sagnac correction embedded in a hand held unit.
In the GPS synchronization is performed in the Earth-Centered Inertial frame using constancy of speed of light.
Yes, I thought that would trip you up. Synchronization is performed in ECEF for the hand held units, not ECI. In ECI, light is measured c in all directions.

The links reveal the sagnac effect to receivers on the ground as you admit. So how would you apply triangulation to determine position without considering the sagnac effect since it has been scientifically proven and you agree? Actually Ashby confesses the sagnac effect is applied to the units.


For atomic clocks in satellites, it is most convenient to consider the motions as they would be observed in the local ECI frame. Then the Sagnac effect becomes irrelevant. (The Sagnac effect on moving ground-based receivers must still be considered.)
http://relativity.livingreviews.org/Articles/lrr-2003-1/ [Broken]

Chapter 5.
 
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  • #9
28,763
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Synchronization is performed in ECEF for the hand held units
Not according to your citation.
 
  • #10
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That seems to explicitly contradict your assertion that GPS handheld units use a Sagnac correction. The citations that you provided that actually detected Sagnac effect using GPS did so via a system of multiple recievers at different locations on the earth, certainly not a Sagnac correction embedded in a hand held unit.
This may help you.

Sagac Effect.
--- Maximum Value 133ns
--- Correction applied to receiver.
http://www.intalek.com/Index/Projects/Research/gps.ppt
 
  • #11
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  • #12
The MMX allows for a margin of error due to such effects, but the Sagnac effect would be insignificant. The experimenters were trying to find a difference in times for the light pulse to traverse each arm due to the Earth's motion. The Earth travels around the sun at a speed of appromimately 1 / 10000 the speed of light, so the experimenters thought this would make a difference. The difference in times expected between an arm aimed into the Earth's motion and the other aimed perpendicularly to it would be d / (c - v) in the direction of the Earth's motion and d / (c + v) against, while the time either way along the perpendicular arm would be d / sqrt(c^2 - v^2), where d is the length of the arms of let's say 1 meter, giving a difference in times of

(d / (c + v) + d / (c - v)) - 2 d / sqt(c^2 - v^2)

= (d / c) [1 / (1 + v/c) + 1 / (1 - v/c) - 2 / sqrt(1 - (v/c)^2)]

= 3.33 * 10^(-17) seconds

For a maximum difference in times with the Sagnac effect, let's say the light pulses travel completely around the perimeter of the MM apparatus in opposite directions, so the area covered is A = 1 m^2. The apparatus would rotate at the same rate as the Earth. The difference in times for the light pulses will be 4 A w / c^2, where w is the rotational speed of the Earth where w = 2 pi / (24 hours) = 1 / (13751 sec), so we have a difference in times of just 3.232 * 10^(-21) seconds. The difference with the Sagnac effect is still 4 orders of magnitude smaller than the expected value, and that is with the maximum effect of having the pulses travel all the way around, which would be nowhere near that otherwise. So while the Sagnac and other effects might not allow the result of the MMX to be precisely null, it is nowhere near what the experimenters were looking for and expecting with the motion of the Earth. Of course as well as this, the Sagnac effect deals with rotation, not inertial motion. Only inertial frames measure an isotropic speed of light, but even non-inertial frames are well within the margin of error for subtle issues such as the Sagnac effect as compared to what would otherwise be expected.
 
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  • #13
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The MMX allows for a margin of error due to such effects, but the Sagnac effect would be insignificant. The experimenters were trying to find a difference in times for the light pulse to traverse each arm due to the Earth's motion. The Earth travels around the sun at a speed of appromimately 1 / 10000 the speed of light, so the experimenters thought this would make a difference. The difference in times expected between an arm aimed into the Earth's motion and the other aimed perpendicularly to it would be d / (c - v) in the direction of the Earth's motion and d / (c + v) against, while the time either way along the perpendicular arm would be d / sqrt(c^2 - v^2), where d is the length of the arms of let's say 1 meter, giving a difference in times of

(d / (c + v) + d / (c - v)) - 2 d / sqt(c^2 - v^2)

= (d / c) [1 / (1 + v/c) + 1 / (1 - v/c) - 2 / sqrt(1 - (v/c)^2)]

= 3.33 * 10^(-17) seconds

For a maximum difference in times with the Sagnac effect, let's say the light pulses travel completely around the perimeter of the MM apparatus in opposite directions, so the area covered is A = 1 m^2. The apparatus would rotate at the same rate as the Earth. The difference in times for the light pulses will be 4 A w / c^2, where w is the rotational speed of the Earth where w = 2 pi / (24 hours) = 1 / (13751 sec), so we have a difference in times of just 3.232 * 10^(-21) seconds. The difference with the Sagnac effect is still 4 orders of magnitude smaller than the expected value, and that is with the maximum effect of having the pulses travel all the way around, which would be nowhere near that otherwise. So while the Sagnac and other effects might not allow the result of the MMX to be precisely null, it is nowhere near what the experimenters were looking for and expecting with the absolute motion of the Earth. Of course as well as this, the Sagnac effect deals with rotation, not inertial motion. Only inertial frames measure an isotropic speed of light, but even non-inertial frames are well within the margin of error for subtle issues such as the Sagnac effect as compared to what would otherwise be expected.
Nice post.


The Michelson-Morley Experiment (the MMX)
The Michelson-Morley experiment (MMX) was intended to measure the velocity of the Earth relative to the “lumeniferous æther” which was at the time presumed to carry electromagnetic phenomena. The failure of it and the other early experiments to actually observe the Earth's motion through the æther became significant in promoting the acceptance of Einstein's theory of Special Relativity, as it was appreciated from early on that Einstein's approach (via symmetry) was more elegant and parsimonious of assumptions than were other approaches (e.g. those of Maxwell, Hertz, Stokes, Fresnel, Lorentz, Ritz, and Abraham).
http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html

The fact is, the null result supported relativity.

Those that understand basic math understand the result cannot be null.

So, a null MMX has been used to prove SR. But, it is not actually null.
 
  • #14
JesseM
Science Advisor
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The fact is, the null result supported relativity.

Those that understand basic math understand the result cannot be null.

So, a null MMX has been used to prove SR. But, it is not actually null.
Seems like another case of reviving an old argument you raised on another forum:

http://www.sciforums.com/showthread.php?t=105408&page=25

If someone just doesn't understand some mainstream conclusions they can of course ask questions, but the rules here don't allow for aggressively disputing mainstream results in SR as you did on the other forum and appear to be doing above, make sure to read the IMPORTANT! Read before posting thread.
 
  • #15
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Seems like another case of reviving an old argument you raised on another forum:

http://www.sciforums.com/showthread.php?t=105408&page=25

If someone just doesn't understand some mainstream conclusions they can of course ask questions, but the rules here don't allow for aggressively disputing mainstream results in SR as you did on the other forum and appear to be doing above, make sure to read the IMPORTANT! Read before posting thread.
Uh, what mainstream am I disputing? The sagnac correction is a mainsteam fact. I agree with the modern experiments of GPS with distances to measure correctly.

Please be specific on what mainstream I am disputing.

If you are disputing the mainstream fact of the sagnac correction in GPS, I have supplied many many many mainstream papers for that experimentally verified position.

Please indicate your position so I can understand.
 
  • #16
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Seems like another case of reviving an old argument you raised on another forum:

http://www.sciforums.com/showthread.php?t=105408&page=25

If someone just doesn't understand some mainstream conclusions they can of course ask questions, but the rules here don't allow for aggressively disputing mainstream results in SR as you did on the other forum and appear to be doing above, make sure to read the IMPORTANT! Read before posting thread.
I read my stuff over there. I can't see where I am refuting any GPS facts. Can you please prove your flat earth accusations? I support the conclusions of modern non-flat earth GPS experimental data and did in all my posts here and there that I have proven with the most accepted mainstream links.

Perhaps you can be more specific.
 
  • #17
Nice post.
Thanks.


The fact is, the null result supported relativity.

Those that understand basic math understand the result cannot be null.

So, a null MMX has been used to prove SR. But, it is not actually null.
The expected effect resulting solely from the inertial motion was not found. Other insignificant effects due to rotation or anything else do not apply as they are not what MMX was intended to measure, so do not affect the overall outcome of the experiment for inertial motion only.
 
  • #18
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Thanks.


The expected effect resulting solely from the inertial motion was not found. Other insignificant effects due to rotation or anything else do not apply as they are not what MMX was intended to measure.
Again nice post.

6 months ago, you could find many links that claimed MMX supported isotropic light.

Try to look now. There are none. Therefore, MMX does not prove lorentz invariance and if any readers believe this, look for it.

If anyone finds a mainstream paper of flat earth times, I have a modern one based on verified GPS data waiting to counter.

So, here is the bottom line, what does MMX prove? Nothing.

So, what is the experimental basis of special relativity without MMX?
 
  • #19
Again nice post.
Thanks again. :smile:

6 months ago, you could find many links that claimed MMX supported isotropic light.

Try to look now. There are none. Therefore, MMX does not prove lorentz invariance and if any readers believe this, look for it.
A lesser number of links showing that MMX supports Lorentz invariance means it's not true? That doesn't sound right. :smile:

So, here is the bottom line, what does MMX prove? Nothing.

So, what is the experimental basis of special relativity without MMX?
It proves that light can be measured isotropically in any arbitrary inertial frame, since it travels away and back with the same two way time over the same distance in any direction. From there, SR follows.
 
  • #20
PAllen
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Again nice post.

6 months ago, you could find many links that claimed MMX supported isotropic light.

Try to look now. There are none. Therefore, MMX does not prove lorentz invariance and if any readers believe this, look for it.

If anyone finds a mainstream paper of flat earth times, I have a modern one based on verified GPS data waiting to counter.

So, here is the bottom line, what does MMX prove? Nothing.

So, what is the experimental basis of special relativity without MMX?
See: https://www.physicsforums.com/showthread.php?t=229034

Harping on this like harping on the relatively well accepted fact the first measurement of light bending in an eclipse was swamped by experimental errors; ignoring hundreds of additional tests of GR of enormously greater precision; same goes for SR.

Please desist.
 
  • #21
JesseM
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Uh, what mainstream am I disputing?
That the MMX (and other more recent experiments of the same type) is evidence for SR because SR predicts a null result. Aren't you disputing this claim?

(note, I'm not saying the rotation of the Earth has precisely zero effect on what we should predict for the MMX to an infinite number of decimal places, just that any rotational effect is too miniscule to change the fact that SR predicts a null result to within the limits of experimental error).
 
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  • #22
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See: https://www.physicsforums.com/showthread.php?t=229034

Harping on this like harping on the relatively well accepted fact the first measurement of light bending in an eclipse was swamped by experimental errors; ignoring hundreds of additional tests of GR of enormously greater precision; same goes for SR.

Please desist.
I want to desist. But that would mean I need to toss all of the GPS evidence proven everyday in the trash.

GPS proves light is not isotropic in the ECEF frame everyday. Do you refute the mainstream evidence?
 
  • #23
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A lesser number of links showing that MMX supports Lorentz invariance means it's not true? That doesn't sound right. :smile:
No, there was a paper that has been accepted modernly and refutes MMX using GPS data. It is even at Microsoft's publishing outlet.

It proves that light can be measured isotropically in any arbitrary inertial frame, since it travels away and back with the same two way time over the same distance in any direction. From there, SR follows.
You cannot claim ECEF sagnac is true and MMX proves isotropy.
 
  • #24
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That the MMX (and other more recent experiments of the same type) is evidence for SR because SR predicts a null result.

(note, I'm not saying the rotation of the Earth has precisely zero effect on what we should predict for the MMX to an infinite number of decimal places, just that any rotational effect is too miniscule to change the fact that SR predicts a null result to within the limits of experimental error).
Why don't you show me links that MMX proves light is isotropic in post GPS papers. I want to see them.
 
  • #25
JesseM
Science Advisor
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Why don't you show me links that MMX proves light is isotropic in post GPS papers. I want to see them.
Try searching "Michelson-Morley" on google books, you'll find plenty of books more recent than the GPS system (which dates to 1973).
 

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