Didn't I say that earlier?
Spacetime geometry is the gravitational field, and light follows geodesics in curved spacetime that we see as gravity.
a story about special relativity,who can explain it？
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Spacetime geometry is the gravitational field, and light follows geodesics in curved spacetime that we see as gravity.
Yes, so the assumption that the speed of light is constant is wrong. Light is only held by the gravitational field of the earth, and the speed of light measured anywhere on the earth is constant.
The speed of light on the earth is superimposed on the speed of the earth's revolution around the sun. The speed of light relative to the earth does not change, but the speed of light has always changed relative to other things in space.
The Morley experiment could not be explained by classical physical theory at that time, so Einstein put forward the hypothesis of "the speed of light is constant" and put forward special theory of relativity. But this theory lasted only 2 years. Einstein proposed the general theory of relativity, questioned the "constant speed of light", and rejected this assumption. I also mentioned this history in my previous post.
There’s a Wikipedia article on the Variable Speed of Light, which is often abbreviated to VSL. If you take a look at an old version dating from 2014, you can see a section entitled Einstein’s VSL attempt in 1911. This says Einstein first mentioned a variable speed of light in 1907 and reconsidered the idea more thoroughly in 1911. However it then goes on to say Einstein abandoned the idea in 1912 because it only predicted half the deflection of light by the Sun. However it isn’t true. Einstein didn’t abandon the idea. That’s why you can find him saying the same thing year after year:
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”.
The last quote is the English translation of what Einstein said in German in 1916: “die Ausbreitungsge-schwindigkeit des Lichtes mit dem Orte variiert”. That translates to “the propagation speed of light with the place varies”. Einstein never did abandon his variable speed of light. The people who tell you that grew up before the Einstein digital papers were online. The general relativity they were taught wasn’t the same as Einstein’s.
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Write4U
Valued Senior Member
Lol, sorry I tagged it to your post.
I just thought Einstein's "man in the box" might be pertinent to the discussion of gravitational relativity (refraction?) in general..
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Einstein said the speed of light is constant in 1905 when he was doing special relativity, but by 1907 he was broadening his horizons and looking into what would become general relativity. That’s when he wrote a paper on the relativity principle and the conclusions drawn from it. He used Φ (phi) to denote gravitational potential, and he said this: “These equations too have the same form as the corresponding equations of the nonaccelerated or gravitation-free space; however, c is here replaced by the value c[1 + γξ/c²] = c[1 + Φ/c²]. From this it follows that those light rays that do not propagate along the ξ-axis are bent by the gravitational field”. Only two years after his special relativity postulate, there’s Einstein talking about a speed of light that varies with gravitational potential. This wasn’t some one-off. He said the same thing in 1911. That’s when he wrote a paper on the influence of gravity on the propagation of light. He said this: “If c₀ denotes the velocity of light at the coordinate origin, then the velocity of light c at a point with a gravitation potential Φ will be given by the relation c = c₀(1 + Φ/c²). The principle of the constancy of the velocity of light does not hold in this theory in the formulation in which it is normally used as the basis of the ordinary theory of relativity”. He said the principle of the constancy of the velocity of light does not hold. And it’s clear from the context that the word velocity is as per “high velocity bullet”. It’s the common usage as opposed to the vector quantity. Einstein was talking about the speed of light, which is why he was referring to c.
We need to understand this history. The special relativity is a mathematical game based on the assumption of "the speed of light is constant" and based on Lorentz transformation.
Einstein's theory of general relativity is a relatively perfect model of physics and mathematics, which is worthy of our serious study. But we should give up the special relativity and classify it as a mathematical game. And the speed of light does not change, which is really not science.
We need to understand this history. The special relativity is a mathematical game based on the assumption of "the speed of light is constant" and based on Lorentz transformation.
Einstein's theory of general relativity is a relatively perfect model of physics and mathematics, which is worthy of our serious study. But we should give up the special relativity and classify it as a mathematical game. And the speed of light does not change, which is really not science.
The special theory of relativity is already one of the contents of the Olympic physics competition. This is very scary. It will put these outstanding students into trouble and destroy their normal thinking about physics. As a teacher, I am worried, so I must do something. That's what I'm doing.
I know a lot of physicists here, such as Janus, Write4U,paddoboy, Halc,(Q), etc. I am very happy to meet you. The collision with your thinking is a feeling similar to watching the final of the European Champions Cup, which is great.
I know a lot of physicists here, such as Janus, Write4U,paddoboy, Halc,(Q), etc. I am very happy to meet you. The collision with your thinking is a feeling similar to watching the final of the European Champions Cup, which is great.
Halc
Registered Senior Member
Oh, it is pertinent to the general discussion. That's why SR (that makes the constant light speed premise) only holds for the special case of uniform gravitational fields.
It's well known that light speed at c is only a locally measured constant, and hence why light beamed to the moon and reflected back does the round trip in less time than the total distance/c. Not much faster, but measurably so.
Yes, refraction is responsible for some of the bending of light around an object, but not all of it, so an explanation based purely on refraction can be falsified.
Halc, looks like we have reached an agreement.
These special relativity formulas are based on the constant speed of light:
w = (u + x) / (1 + ux / c^2)
t '= t (1-v^2 / c^2)
They are all mathematical games. They are not laws or truth.
Light on the earth is held by a gravitational field, and the speed of light measured anywhere on the surface of the earth is constant. The speed of light is superimposed on the speed of the gravitational field (that is, the speed of the earth's revolution around the sun).
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No, the speed of light is constant, any variation as measured from an outside FoR, simply allows for a longer "curved"path it has travelled...you know, geodesics.
I'm happy to meet you to, and I'm not a physicist, but I still say you are wrong.
That's confusing to put it mildly. but the speed of light ''on" Earth, is the same as it is anywhere else..."c"
And the speed of gravity is the same as light as far as we know. The curvature of spacetime caused by the mass of the Earth as it orbits the Sun, follows the Earth at the same speed of Earth's orbit.
If the light is aimed at the center of the planet, is the geodesic a straight line or a curve? A geodesic is a trajectory you see. The reason for this trajectory is the non-uniformity of the gravitational field.
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It's hard to illustrate a 3D/4D concept in 2D....but that is a good question. A geodesic simply put, is the shortest path between two points or observers. I would say a photon directed at the center of a planet would like the defintion of a geodesic, follow the shortest path.
Here are some illustrations of light bearing near a massive object in 2D
or in the presence of a strong gravitational field and strong gravitational lensing, we get what we call an Einstein cross, as follows...
https://en.wikipedia.org/wiki/Geodesics_in_general_relativity
In general relativity, a geodesic generalizes the notion of a "straight line" to curved spacetime. Importantly, the world line of a particle free from all external, non-gravitational forces is a particular type of geodesic. In other words, a freely moving or falling particle always moves along a geodesic.
In general relativity, gravity can be regarded as not a force but a consequence of a curved spacetime geometry where the source of curvature is the stress–energy tensor (representing matter, for instance). Thus, for example, the path of a planet orbiting a star is the projection of a geodesic of the curved four-dimensional (4-D) spacetime geometry around the star onto three-dimensional (3-D) space.
In general relativity, a geodesic generalizes the notion of a "straight line" to curved spacetime. Importantly, the world line of a particle free from all external, non-gravitational forces is a particular type of geodesic. In other words, a freely moving or falling particle always moves along a geodesic.
In general relativity, gravity can be regarded as not a force but a consequence of a curved spacetime geometry where the source of curvature is the stress–energy tensor (representing matter, for instance). Thus, for example, the path of a planet orbiting a star is the projection of a geodesic of the curved four-dimensional (4-D) spacetime geometry around the star onto three-dimensional (3-D) space.
https://photos.app.goo.gl/jDgewZHgjeCPr4jG9
The strength of the gravitational field at a position X in space is not only related to the mass of the planet and the distance between them, but also to the relative speed of X and the planet's relative motion. This is a bit similar to the Doppler effect. If the planet is near the position X, the intensity of the gravitational field X will be greater than when it is relatively stationary. When the planet is away from the position X, the intensity of the gravitational field X will be less than their relative static intensity. The intensity of the gravitational field affects the speed of light. The stronger the gravitational field, the slower the speed of light, and the weaker the gravitational field, the faster the speed of light. If light enters a space with a constant gravitational field, the speed of light will no longer change.
I often mention that the speed of light on the earth is superimposed on the speed of the earth's revolution around the sun. The root cause of this superposition is that the gravitational field becomes stronger or weaker due to the relative speed of the earth and space, which affects the speed of light.
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Have you ever thought that it would be easier to analyze this process with a moving gravitational field, and Newton's classical mechanics can calculate the planetary trajectory. This trajectory is exactly the geodesic described by general relativity. Although this deviation will be small relative to the stationary gravitational field, it is sufficient to explain Mercury's precession.
Compared with the general relativity model, Newton's law of gravity model is easier to understand, and it can also accurately calculate the trajectory of the celestial body.
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Write4U
Valued Senior Member
But we are talking about Light, not about massive objects. The SOL in a vacuum is a constant.
https://en.wikipedia.org/wiki/Theory_of_relativity
If you run up an escalator that is moving @ SOL, you do not get to the top any faster than if you stand still...
The light is similar, I described it in # post 253.But we are talking about Light, not about massive objects. The SOL in a vacuum is a constant.
If you run up an escalator that is moving @ SOL, you do not get to the top any faster than if you stand still...
The assumption that the speed of light does not change is not accepted by Einstein himself. I described it in # post 242 , #post 244.
I have stated many times that the speed of light measured on the surface of the earth is constant. But this cannot be concluded that the speed of light is constant.I described it in # post 253, 247...
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Write4U
Valued Senior Member
Well, obviously light does not behave in a gravitational field as is illustrated. That pertains to massive objects only, which are subject to the gravitational pull between two massive objects.
I am out of my depth here, but it seems to me that a photon's mass is acquired by its momentum but that this kinetic mass is not subject to gravitational pull, but only restricted to follow the geodesics of the warped spacetime itself, but never gets caught in a gravitational well to form an orbit.
This might possibly occur in a Black Hole where the spacetime geodesics themselves fold into themselves?
Don't ask me to prove any of this....
If you return to Newtonian mechanics, your scientific path will be smooth.Well, obviously light does not behave in a gravitational field as is illustrated. That pertains to massive objects only, which are subject to the gravitational pull between two massive objects.
https://photos.app.goo.gl/LbJoTK2q5dX11TBe7
There are usually two reasons that can cause the object's motion path to bend. One is the velocity caused by the force in the vertical direction, and the other is the refraction caused by the unevenness of the medium or the unevenness of the field. Then the bending of the light is probably caused by the latter. The sun is surrounded by the gravitational field. The gravitational field is stronger as it goes inside. When light passes through the gravitational field of the sun, the light is bent similarly to refraction due to the unevenness of the gravitational field. The curvature of this path is different from the curvature caused by the direct action of gravity on an object. Therefore, it is not appropriate to calculate the bending angle of light using the classic flat throw theory.
https://photos.app.goo.gl/fcHk2UjEQufwdmw1A
This is because the theory of flat throw thinks that there is a co-directional acceleration process under the pull of gravity at the beginning, before the acceleration caused by gravity becomes negative, the light will be farther away from the sun and the influence of gravity will be smaller. The deflection angle will also be smaller. This is the reason why the angle of light deflection calculated by the classic flat throw theory is too small. Newtonian mechanics is not wrong, but this time it was not used correctly.
The rotation of the earth does not affect the strength of the gravity field. We should consider the revolution of the earth around the sun, and the gravitational field moves with the earth. The data we calculated are basically consistent with the experimental observation data given by Janus. But Janus thinks that the gravitational field of the earth is too weak to affect the bending of light, which is wrong.
Light deflected by just 0.0006 arc-seconds =1.667*10^-7 degree. This is the observation data given by Janus.
The earth's angular speed : 360/365*24*60*60 = 1.1415*10^- 5 degree/s.This is my calculated angular speed of the Earth's revolution around the sun.
If the time of light passing through the earth is 0.01 seconds, about 3000 km,the angle of rotation of the earth is 1.1415*10^- 7 degree. It can't be ignored!
I am out of my depth here, but it seems to me that a photon's mass is acquired by its momentum but that this kinetic mass is not subject to gravitational pull, but only restricted to follow the geodesics of the warped spacetime itself, but never gets caught in a gravitational well to form an orbit.
This might possibly occur in a Black Hole where the spacetime geodesics themselves fold into themselves?
Don't ask me to prove any of this....
Gravitational fields still perform well on light. I described it in # post 170 and #post 253.
When it comes to the mass of a photon, I need to explain the mass energy equation, which can also be easily derived using Newtonian mechanics.
https://photos.app.goo.gl/Xv4ZAMkQwtERC1fYA
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Halc
Registered Senior Member
All light (and any other inertial object) follows a geodesic through spacetime, per GR. Where it is aimed has nothing to do with it. A geodesic is always a straight line in the coordinate space in which it is defined. That means if you toss a paper wad into the trash across the room, and discounting air friction, the wad of paper traces a straight line through spacetime. This is true even for the slow, hi-arced shot and the faster attempt that follows a different path through space, but both straight lines through spacetime.
A wad of paper sitting in a trash can does not trace a geodesic because a force is acting upon it, curving its worldline from any geodesic. Most of the time, there is only one geodesic in spacetime between any two events, but this is not always the case.