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# Michelson Morley And Gravitational Lensing Question

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engcat;

In GR, by definition, by a rule, which is the equivalence principle, a light that follows a curved path is in an accelerated frame. Gravitional lensing proves.
In SR, by definition, light cannot be in an accelerated frame. it follows a straight line!
Which is it? It cannot be both.

SR was the 'special' version, which did not include significant gravitational effects.

Inertial ref.frames have inertial motion or constant velocity.

GR is used for significant gravitational effects.

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This has different interpretstions , but the general consensus is that light can accelerarate. If you want me to go into more details let me know.

I do.  We know light accelerates because of gravitational lensing.   That's the theoretical paradox with SR.

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I do.  We know light accelerates because of gravitational lensing.   That's the theoretical paradox with SR.

The constancy of the speed of light is a fundamental foundation of relativity, gravitational lensing also comes with an observed time delay (Shapiro time delay).

The lensing effect is created by slowing down light in a medium, or by making the 'medium' longer or shorter (same effect as slowing light down, making space longer). That's basic optics, that's how a lens works.

It is not the light being influenced by gravity, that's not how relativity works, gravity changes space, and light moves through space, it's not the gravity doing anything to the light. The question then is what does gravity do to space?

Shapiro time delay (and gravitational lensing) shows us that it takes longer time for light to move through space in a gravitational field, so if light moves at a constant speed, the only way for it to take longer time, is for space to be longer.

The only question is, 'is the longer time taken because space is curved, or is it a longer time because space itself is longer?'

Gravitational shift of light, (red shifted from a higher gravity state) indicates to me that the light is generated in longer space, so has a longer wavelength (red shifted), because it was created in longer space. It takes more time for light to move through relative longer space.

Ask yourself, if you think space is curved, what property of space do you plot on a graph that gives you that curvature? In other words, what about space is curved?

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I do. We know light accelerates because of gravitational lensing. That's the theoretical paradox with SR.

Two situations, possibly three arise in GR Forget SR for now because it was "special due to an incompleteness" when involving curvature. In GR (by strong postulation) that anything following a curved path say round the geodesic of a planet due to a slingshot must accelerate. But according to the postulate of the constancy of the speed of light,it seems contradictory. But relativity is not a one way street. The peculiar thing is that anyone who could approach the speed of light to 99℅ of its own speed, suggests light must always accelerate according to the observers frame in order to maintain the axiom set by relativity that the speed of light is always measured moving at such a speed. Its also believed that photon cannot reach a speed of light from some initial position without an acceleration involved, but the rate of acceleration cannot change in such a way that the photon can exceed the universal speed limit.

Nevertheless,the key words to remember that acceleration and a rate of change in acceleration are two different things. An electron only emits radiation for instance, when there is a rate of change in the acceleration. In the same sense, from a photons point of view, it has no inertial frame and so cannot in principle have a rate of change on its own acceleration. But this does not exclude that it cannot have a sense of acceleration, only that time appears infinitely paused because it lacks an inertial frame. In some theories studied, the speed of light could equally have been faster or slower in the early universe. If it was slower, then parameters have changed allowing it to accelerate or decelerate in the past cone, as some interesting viewpoints.

Edited by Dubbelosix
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In GR, by definition, by a rule, which is the equivalence principle, a light that follows a curved path is in an accelerated frame. Gravitional lensing proves.

In SR, by definition, light cannot be in an accelerated frame. it follows a straight line!

Which is it? It cannot be both.

Light follows a straight line in an inertial frame, not an accelerated one. It isn't both because an object is either accelerating or inertial, not both.

Although it gets interesting when you try to use Mach's principle which to me is basically the idea that accelerationis also relative.

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Light follows a straight line in an inertial frame, not an accelerated one. It isn't both because an object is either accelerating or inertial, not both.

Although it gets interesting when you try to use Mach's principle which to me is basically the idea that accelerationis also relative.

Then, if that is true, the theory says there are no local accelerated frames anywhere? Which would mean there are no local gravitational frames, which would mean that gravity is just a visual appearance from a local observer's viewpoint.  Which we now is not the case, we know it here on earth, in the environment of the MM experiment.  And that is a paradox.

Edited by engcat
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Then, if that is true, the theory says there are no local accelerated frames anywhere? Which would mean there are no local gravitational frames, which would mean that gravity is just a visual appearance from a local observer's viewpoint.  Which we now is not the case, we know it here on earth, in the environment of the MM experiment.  And that is a paradox.

Huh?

SR deals with inertial frames free from gravity, so light follows straight pasths in SR.

GR deals with gravity as objects (including light) following curved paths. How is that a paradox?

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Huh?

SR deals with inertial frames free from gravity, so light follows straight pasths in SR.

GR deals with gravity as objects (including light) following curved paths. How is that a paradox?

Does GR gravitational constant not have constant speed of light?

Does SR paper not say: "... and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocity c ..."?

The topic here is the part about definite speed of light, not about frames of reference.  The light is the topic, that part of sentence in the SR paper.

Edited by engcat
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Does GR gravitational constant not have constant speed of light?

Does SR paper not say: "... and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocity c ..."?

The topic here is the part about definite speed of light, not about frames of reference.  The light is the topic, that part of sentence in the SR paper.

The foundation principle of general and special relativity is the 'constancy of the speed of light', without light having a constant speed we don't know anything, and nothing makes sense.

Also: all varying the speed of light does is very the size of space and everything in that space, SO, if you had our universe in a box on your lab bench and were looking at it from your own separate space and time, and you could vary the speed of light in our universe on your lab bench, (with a big knob).

The universe on your bench would just get bigger as you lower the speed of light and smaller as you increase the speed of light, but for us in the universe nothing would change, including the speed of light!

So no, the speed of light is constant, and it is the fastest anything can go, because it moves through ALL space (length, distance) that exists at the point in space.

Matter cannot move through all available space length, because matter produces its own contribution to that length and matter cannot have a velocity in it's own space.

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Does GR gravitational constant not have constant speed of light?

Does SR paper not say: "... and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocity c ..."?

The topic here is the part about definite speed of light, not about frames of reference.  The light is the topic, that part of sentence in the SR paper.

General relativity explicitly states that the local speed of light is always c, allowing that the average speed of light along a finite distance is not necessarily c.

By “local” what is meant is, at a particular point along the light path.

I don’t know how you feel about analogies, maybe give this one a try?

You can visualize this by suspending a string from two points pulling it taut, so it is absolutely straight between the two points. If you imagine light travelling between the two points in a straight line, along the string, that would be analogous to light travelling in an inertial frame, with constant speed c everywhere on the path and also with an average speed c between the points.

Now if you release some of the tension, the span of string between the support points will hang according to the pull of gravity. The string will hang as a catenary; a hyperbolic curve analogous to a non-inertial frame. If you now imagine light travelling between the two points along the longer curved path, it will obviously take longer to travel from one point to the other. The average speed of light between the two points is now less than c. However, at the two support points nothing has changed, so the local speed at these points is still c. In fact, the local speed, taken at any point along the curve is still c.

There is no paradox once you realize what is meant by local speed and average speed. It is the average coordinate speed of light between two points that may be different from c; but the local speed of light measured at a point is always c.

This paper explains the concept of an average speed of light propagating between two points in non-inertial frames far better than my analogy.

Edited by OceanBreeze
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General relativity explicitly states that the local speed of light is always c, allowing that the average speed of light along a finite distance is not necessarily c.

By “local” what is meant is, at a particular point along the light path.

I don’t know how you feel about analogies, maybe give this one a try?

You can visualize this by suspending a string from two points pulling it taut, so it is absolutely straight between the two points. If you imagine light travelling between the two points in a straight line, along the string, that would be analogous to light travelling in an inertial frame, with constant speed c everywhere on the path and also with an average speed c between the points.

Now if you release some of the tension, the span of string between the support points will hang according to the pull of gravity. The string will hang as a catenary; a hyperbolic curve analogous to a non-inertial frame. If you now imagine light travelling between the two points along the longer curved path, it will obviously take longer to travel from one point to the other. The average speed of light between the two points is now less than c. However, at the two support points nothing has changed, so the local speed at these points is still c. In fact, the local speed, taken at any point along the curve is still c.

There is no paradox once you realize what is meant by local speed and average speed. It is the average coordinate speed of light between two points that may be different from c; but the local speed of light measured at a point is always c.

You have to be a bit careful about talking about 'average' speed of light, which is a constant speed, so it has no 'average'. What you are describing with your string analogy is light staying at a constant speed over a longer path. (the extra length of the curved string),

This just means you cannot remotely, only locally, because your clocks and your measure of time are different.

So a clock ticks a bit quicker on the top of Mt Everest relative to the surface of the earth, but both points would measure the speed of light as c, but the length of time is different.

In that case if I could measure the speed of light at the surface of the earth using Everest time, the speed of light would be faster, because it is going the same distance in shorter (Everest) time.

It's about the length of space, be it from curved space, or from stretched (flat) space the end result is the same

The important thing you get from this is that the length of space varies in a relative fashion (either stretched or curved), and we know this because at any point the speed of light remains the same.

So 1. We know the length of time varies (from both GR and SR), and 2. The speed of light is the same REGARDLESS of the different length of time.

The only way for that to work is for the length of space (either from curvature or stretching) varies along with time.

Different length of path will show a 'travel time' that is or could be different from what you expect in your position in that length value, but at all times the light does not ever deviate from that one and only speed.

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• 3 weeks later...

Yes, the constancy of the speed of light is the very foundation of relativity, if that is wrong, you have nothing to work with. Also, there is no such thing as anything 'devoid of a gravitational field' in our universe.

The reason why there is an apparent change in the speed of light in a non-vacuum is due to the longer path the light travels (at c), not the value of c changing.

It's sort of like the Hubble constant, if it is not constant and changes from place to place then you might as well throw out the whole model, because everything stops making sense.

"Longer path that light travels?" What rubbish do you speak?  Here you are hopping from on foot to the other, from one claim to the next just to keep your precious Relativity in tact. Truth is its obvious self contradictory and therefore invalid.

If spacetime is curved, then that curved path IS THE ONLY PATH POSSIBLE TO OBSERVE.  You don' get to draw imaginary "straight lines" anymore, claiming that these are shorter, that this explains contentedly how light speed is not constant, yet it still is. "I want my cake and eat it too!" this is baby thinking.  Einstein's theories are rubbish, get over it.

And when you do throw out the "whole model" then things actually do begin to make sense again.

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I do.  We know light accelerates because of gravitational lensing.   That's the theoretical paradox with SR.

WE don't "KNOW" anything of the sort.  Some theorise that this maybe whats happening, and they assume its correct.

Gravitational Lensing is an "interpretation of observations", its not PROOF of anything. It could be the result of many things, they ASSUME and HOPE its Gravitational  lensing to support their hypothesis.

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The only way for that to work is for the length of space (either from curvature or stretching) varies along with time.

Well this is a wrong statement here.  Really? the ONLY way it could work is the irrational way, that's full of paradoxes and contradictory claims?

Seems that this proposed way would be the FIRST proposal to be rejected as a possibly correct "way it could work".

A better way does not have "shrinking distances and dilating times or increasing Mass."

A better way does not have the nothingness of space needing to be magically "curved" while the  places we inhabit are clearly all well described as Cartesian or 3D space.

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