Shapiro effect ? Speed of gravity waves and light ?

Sep 2019
54
5
Azores
I have recently come across the Shapiro effect and I have not been able to find anything conclusive to refute its claims of gravity slowing down light.

If the Shapiro effect is correct and light does slow down in a gravity field, then surely the same would be true in a gravity wave. When the black hole mergers were detected by Ligo back in 2017 at the same time as light from the explosion caused by the BH merger. Did that gravity wave really travel at c or did it slow down the light that was travelling with the gravity wave.

I am correct in thinking the only thing that can be ascertained is that the light traveled at the same speed as the gravity wave, which MIGHT not have been at c.
 

topsquark

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Apr 2008
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On the dance floor, baby!
Light "slows down" when it passes through a transparent solid. (ie. refraction.) In the same way a gravity wave should also slow down as it passes through matter.

On the other hand, in free space both light and gravitons travel at the speed of light.

-Dan
 
May 2014
147
13
Poole, UK
I have recently come across the Shapiro effect and I have not been able to find anything conclusive to refute its claims of gravity slowing down light.
You won't be able to. See these Einstein quotes:

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”.

1914: “In the case where we drop the postulate of the constancy of the velocity of light, there exists, a priori, no privileged coordinate systems.”

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”.

1920: “Second, this consequence shows that the law of the constancy of the speed of light no longer holds, according to the general theory of relativity, in spaces that have gravitational fields. As a simple geometric consideration shows, the curvature of light rays occurs only in spaces where the speed of light is spatially variable”.

If the Shapiro effect is correct and light does slow down in a gravity field, then surely the same would be true in a gravity wave. When the black hole mergers were detected by Ligo back in 2017 at the same time as light from the explosion caused by the BH merger. Did that gravity wave really travel at c or did it slow down the light that was travelling with the gravity wave.
I imagine it moved at the same speed as a light wave. However the speed of a light wave varies with gravitational potential. For some reason people say this isn't mainstream, even though Einstein said it repeatedly, and it's right there in Shapiro's paper:

ShapiroScreenshot.jpg

I am correct in thinking the only thing that can be ascertained is that the light traveled at the same speed as the gravity wave, which MIGHT not have been at c.
Not quite. Light travels at the speed of light, which is c. But c varies. See Is The Speed of Light Everywhere the Same? by PhysicsFAQ editor Don Koks. He says this

"Light speeds up as it ascends from floor to ceiling, and it slows down as it descends from ceiling to floor; it's not like a ball that slows on the way up and goes faster on the way down. Light travels faster near the ceiling than near the floor. But where you are, you always measure it to travel at c; no matter where you place yourself, the mechanism that runs the clock you're using to measure the light's speed will speed up or slow down precisely in step with what the light is doing. If you're fixed to the ceiling, you measure light that is right next to you to travel at c. And if you're fixed to the floor, you measure light that is right next to you to travel at c. But if you are on the floor, you maintain that light travels faster than c near the ceiling. And if you're on the ceiling, you maintain that light travels slower than c near the floor".
 
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Sep 2019
54
5
Azores
@Farsight from your link.

To an engineer explaining the constancy of light as an instrumentation issue makes real sense.

"But the SI definition highlights the point that we need first to be very clear about what we mean by constancy of the speed of light, before we answer our question. We have to state what we are going to use as our standard ruler and our standard clock when we measure c. In principle, we could get a very different answer using measurements based on laboratory experiments, from the one we get using astronomical observations. (One of the first measurements of the speed of light was derived from observed changes in the timing of the eclipses of Jupiter's moons by Olaus Roemer in 1676.) We could, for example, take the definitions of the units as they stood between 1967 and 1983. Then, the metre was defined as 1,650,763.73 wavelengths of the reddish-orange light from a krypton-86 source, and the second was defined (then as now) as 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of caesium-133. Unlike the previous definitions, these depend on absolute physical quantities which apply everywhere and at any time. Can we tell if the speed of light is constant in those units? "

The speed of light will also be constant using caesum 133. Time will slow for caesium in a gravitational field as it would with any other clock. therefore c remains constant. Correct?

Therefore viewing the curvature of space as a contraction of space slowing down time then viewing the expansion of space due to cosmological (not so) constant, space time speeds up > during the inflationary stage of the universe preceding the big bang, time may have been a lot faster and light may have travelled more than 3x10^8m in every one of our seconds today. So when theories state light may have gone faster than c in our reference frame during inflation is this what they are driving at?

From your link > The subject of inertial reference frames, along with why the writer seems to think a photon may have as yet some undetectable mass, which does sound a bit fringe physics. All things have inertia, they dont acquire mass until they are accelerated, so why does a photon need mass?

Edit: how can distance be measured to blackholes merging when the speed of light slows down as it moves towards us. When the gravity wave recedes, the speed of light is back to normal.
 
Sep 2019
54
5
Azores
@dan

Do you agree with Farsights link. speed of light varies and for different observers, and therefore so do distances?
 
Jun 2016
1,239
588
England
One does tend to get into circular arguments when measuring time, and distance, and the speed of light,
since c and time and space are totally intertwined.
I have seen suggestions that the linking of the maximum speed limit to the speed of light is somewhat misleading.
The maximum speed limit of the universe is a fundamental property of spacetime,
It is also the speed that light travels at (in a vacuum) and the speed that gravity waves travel at (in a vacuum),
However it is the light waves and gravity waves obeying this fundamental property of spacetime, not a property of light.

The maximum speed limit (as observed by an outside observer) will depend on the local geometry of the spacetime being traversed (by a light ray for example)
A light ray traversing a region close to a large mass will be traversing a region of "curved" spacetime.
In the field of reference of the light ray, it will be travelling at the maximum speed.
However to an observer outside this curved region of spacetime, the speed will appear to not be the maximum speed.

Try this analogy:
An observer on the moon uses a powerful telescope to watch a plane travelling from Europe to America.
To the people on the plane they are travelling at 600mph, relative to the ground.
The observer on the moon will see that the starting point and the ending point subtend a particular angle at his telescope.
Knowing the diameter of the Earth, the observer will be able to calculate the distance traveled and thus, (given the time taken for the journey) the speed.
However, if the observer just assumes a straight line between the two airports (ie. neglects to include the curvature of the earth)
then the speed determined by the observer will not be 600mph.
 
May 2014
147
13
Poole, UK
@Farsight from your link.

To an engineer explaining the constancy of light as an instrumentation issue makes real sense.

"But the SI definition highlights the point that we need first to be very clear about what we mean by constancy of the speed of light, before we answer our question. We have to state what we are going to use as our standard ruler and our standard clock when we measure c. In principle, we could get a very different answer using measurements based on laboratory experiments, from the one we get using astronomical observations. (One of the first measurements of the speed of light was derived from observed changes in the timing of the eclipses of Jupiter's moons by Olaus Roemer in 1676.) We could, for example, take the definitions of the units as they stood between 1967 and 1983. Then, the metre was defined as 1,650,763.73 wavelengths of the reddish-orange light from a krypton-86 source, and the second was defined (then as now) as 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of caesium-133. Unlike the previous definitions, these depend on absolute physical quantities which apply everywhere and at any time. Can we tell if the speed of light is constant in those units? "

The speed of light will also be constant using caesum 133. Time will slow for caesium in a gravitational field as it would with any other clock. therefore c remains constant. Correct?
No, it isn't constant. What happens is that people use the local motion of light to define their second and their metre, and then use the second and the metre to measure the local motion of light. Then they claim the speed of light is constant even though it isn't. It is the height of foolishness. It is a tautology. See [0705.4507] Comments on "Note on varying speed of light theories".

Therefore viewing the curvature of space as a contraction of space slowing down time then viewing the expansion of space due to cosmological (not so) constant, space time speeds up > during the inflationary stage of the universe preceding the big bang, time may have been a lot faster and light may have travelled more than 3x10^8m in every one of our seconds today. So when theories state light may have gone faster than c in our reference frame during inflation is this what they are driving at?
I don't know I'm afraid. I'm not a big fan of inflation.

From your link > The subject of inertial reference frames, along with why the writer seems to think a photon may have as yet some undetectable mass, which does sound a bit fringe physics. All things have inertia, they dont acquire mass until they are accelerated, so why does a photon need mass?
A photon doesn't have any rest mass. However it has a non-zero inertial mass. This is why in the last line of Einstein's E=mc² paper says radiation conveys inertia between the emitting and absorbing bodies:

Edit: how can distance be measured to blackholes merging when the speed of light slows down as it moves towards us. When the gravity wave recedes, the speed of light is back to normal.
I don't think it can.
 
Sep 2019
54
5
Azores
No, it isn't constant. What happens is that people use the local motion of light to define their second and their metre, and then use the second and the metre to measure the local motion of light. Then they claim the speed of light is constant even though it isn't. It is the height of foolishness. It is a tautology. See [0705.4507] Comments on "Note on varying speed of light theories".
Light is measured as constant due to the clock rates changing speeds and and rulers changing lengths in different reference frames. Can you suggest another method measuring light speed to show it is not constant.

I don't know I'm afraid. I'm not a big fan of inflation.
Inflation is standard model, what would you replace it with Hoyles universe, Cosmic Cyclic Cosmology What

A photon doesn't have any rest mass. However it has a non-zero inertial mass. This is why in the last line of Einstein's E=mc² paper says radiation conveys inertia between the emitting and absorbing bodies:
Thats what I think I said Photons have inertia also Einstein stated E^2=(mc^2)^2+(pc)^2 the E=mc² is an abbreviation

I don't think it can.
Without constant light speed a lot of theories appear a bit wobbly. Are you saying the standard model view of the universe is wrong? If so how so?
 
Sep 2019
54
5
Azores
One does tend to get into circular arguments when measuring time, and distance, and the speed of light,
since c and time and space are totally intertwined.
I have seen suggestions that the linking of the maximum speed limit to the speed of light is somewhat misleading.
The maximum speed limit of the universe is a fundamental property of spacetime,
It is also the speed that light travels at (in a vacuum) and the speed that gravity waves travel at (in a vacuum),
However it is the light waves and gravity waves obeying this fundamental property of spacetime, not a property of light.
I am a little concerned that I might be being mislead, in some subtle way by Farsight. Is the explanation ref variable light speed correctthe explaining Shapiro effect. I follow the argument and it seems plausible.

If the speed of light in the vacuum is not constant away from gravitational sources ie in an expanding space, possibly expanding at different rates, then does this not make the measurements look a little more difficult.
 

topsquark

Forum Staff
Apr 2008
3,007
635
On the dance floor, baby!
I'm not certain how farsight is getting his information. As he seems to know more about it than I do I'm not going to generally address any point but this: The speed of light is invariant no matter what local space-time distortions there may be in the vicinity. It is true that a photon in a gravitational field will be red shifted, but that's an apparent loss of energy not a loss in speed.

-Dan