# The Speed of Light is Not Constant

... You missed the point that distance contracts as time dilates, and vice versa...
We've been over this umpteen times now. The second changes with gravitational potential, the horizontal metre doesn't. We all know that the "coordinate" speed of light varies in a gravitational field. In the room you're in. Hence it's the speed of light varying in a gravitational field. Hence one NIST optical clock goes slower than the other. When the light goes slower the second is bigger. But the metre is the distance travelled by light in vacuum in 1⁄299,792,458th of a second. The slower light and the bigger second cancel each other out, leaving the metre unchanged.

Unfortunately, length contraction in heavy ion colliders, free electron lasers, and contraction in Penrose-Terrell Rotations are some junk, Farsight, wont address.

But he has a gif!

We've been over this umpteen times now. The second changes with gravitational potential, the horizontal metre doesn't. We all know that the "coordinate" speed of light varies in a gravitational field. In the room you're in. Hence it's the speed of light varying in a gravitational field. Hence one NIST optical clock goes slower than the other. When the light goes slower the second is bigger. But the metre is the distance travelled by light in vacuum in 1⁄299,792,458th of a second. The slower light and the bigger second cancel each other out, leaving the metre unchanged.

I think this is wrong.

Think about moving a light clock from higher up in your lab (on Earth) to lower down. As you do so, the coordinate distance between the two mirrors of the light clock increases. The speed of light remains constant. Light takes longer to travel the larger distance between the mirrors, so the clock "ticks" slower.

The point I was making was the speed of light is constant across all space-time references. I can accept this. However, the wavelength and the frequency of these same photons are not invariant across all references. How is it possible for only part of the photon to be invariant across all frames, while part of it is variant in each frame (wavelength and frequency)? This is what is observed and is not postulated.

It appears the discussion fixates on the proven thing thereby avoiding discussion of this anomaly. To me, this anomaly indicates two references at the same time, for the same phenomena, one which does not change and other which can change.

The classic analogy, to help explain the double slit experiment, is a ship (particle) and its wake (wave).

Relative to the ship and wake analogy, if you ever went to the beach and watched the waves, their height is a function of the terrain below. This would suggest than when the space-time well is shallow or deep, this changes the terrain of the wave/wake. Say we have a boat with a shallow hull making a wake, with an underground terrain, below the water, with peaks and valleys, this will impact the waves but not the boat.

Say we did the double slit experiment but change the space-time terrain under the waves. This is easier to explain if we assume the speed of light is the ground state of the universe.

The point I was making was the speed of light is constant across all space-time references. I can accept this.

Correct, "c" is invariant for any and all frames.

However, the wavelength and the frequency of these same photons are not invariant across all references. How is it possible for only part of the photon to be invariant across all frames, while part of it is variant in each frame (wavelength and frequency)?

Spacetime is not invariant from one reference frame to another. "Part of the photon" is not variant. The space and time ARE variant, the thing the photon is moving through. The frequency (time) and wavelength (space) are dependent on the observer's frame, not on the photon's frame. An observer can not observe from within a photon's frame. A photon does not experience time or distance.

It appears the discussion fixates on the proven thing thereby avoiding discussion of this anomaly. To me, this anomaly indicates two references at the same time, for the same phenomena, one which does not change and other which can change.

It's not an anomaly. It would only be an anomaly if it did something inconsistent with the predictions. The descriptions, observations, and experimental attributes conform exquisitely with the predictions SR & GR.

The space and time ARE variant, the thing the photon is moving through. The frequency (time) and wavelength (space) are dependent on the observer's frame, not on the photon's frame. An observer can not observe from within a photon's frame. A photon does not experience time or distance.

Exactly, one part of the photon's observational output, attributed to its wave nature, is impacted by space and time; red shift. But the particle aspect is not impacted by space and time, since the speed of light does not change.

If you think in terms of red shift and blue shift, these shifts subtract and add energy, respectively, with respect to the original photons. The speed of light does not change, so this loss or gain of energy, via the wave, is not connected to the kinetic energy of the particle. Only the wave can lose or gain energy since the speed will not change. The question is why do we have this division of the photon? I am not questioning GR and its ability to correlate. I am asking why does part of the photon interact with inertial reference, while another aspect is unaffected?

This is question is easier to answer if we assume the speed of light is the ground state of the universe. This premise is inferred from potential energy spontaneously moving from higher to lower energy. Our universe net forms energy (lower potential) from matter (higher potential). If matter was the ground state our universe would flow in the direction off making more matter.

If we assume the C ground state of the universe, part of the photon remains in the ground state of the C reference, while part of the same phenomena is connected to inertial references which is at higher potential. Energy is the bridge between matter and the C ground state, touching both.

Photons are not entirely, in the C ground state, even though they move at C, since an aspect of the photon, connected to the wave, stills shows characteristics which interact with inertial references of space and time.

This is question is easier to answer if we assume the speed of light is the ground state of the universe. This premise is inferred from potential energy spontaneously moving from higher to lower energy.

Saying that c (or as you call it 'C') is the ground state is nonsense. It makes no sense to say a speed is the ground state of the universe, now does it?

Our universe net forms energy (lower potential) from matter (higher potential). If matter was the ground state our universe would flow in the direction off making more matter.

Just after the big bang there was no matter in the universe, there was only energy. As the universe expanded and cooled matter formed from the energy, which sort of negates your postulate doesn't it?

Exactly, one part of the photon's observational output, attributed to its wave nature, is impacted by space and time; red shift. But the particle aspect is not impacted by space and time, since the speed of light does not change.

If you think in terms of red shift and blue shift, these shifts subtract and add energy, respectively, with respect to the original photons. The speed of light does not change, so this loss or gain of energy, via the wave, is not connected to the kinetic energy of the particle. Only the wave can lose or gain energy since the speed will not change. The question is why do we have this division of the photon? I am not questioning GR and its ability to correlate. I am asking why does part of the photon interact with inertial reference, while another aspect is unaffected?

Nothing in the photon changes, what changes is the photon's environment. Time & space change for the observer depending on reference frame. A photon does not experience time or space.

This is question is easier to answer if we assume the speed of light is the ground state of the universe. This premise is inferred from potential energy spontaneously moving from higher to lower energy. Our universe net forms energy (lower potential) from matter (higher potential). If matter was the ground state our universe would flow in the direction off making more matter.

I have no idea what that means. "Ground state", what does that mean as applied to the universe? Or spacetime? Are you speaking of a quantum vacuum state? Or what?

If we assume the C ground state of the universe, part of the photon remains in the ground state of the C reference, while part of the same phenomena is connected to inertial references which is at higher potential. Energy is the bridge between matter and the C ground state, touching both.

Again what do you mean by "ground state of the universe. You can assume "c" is anything ya want to assume it, but all observational and theoretical results shows that "c" is "c" and is invariant everywhere and anywhere. So whatever you mean by "ground state" should be referred to as "c"'s ONLY state. A photon at any speed other than "c" does not exist.

Photons are not entirely, in the C ground state, even though they move at C, since an aspect of the photon, connected to the wave, stills shows characteristics which interact with inertial references of space and time.

You see the photon changing some aspect. That is incorrect. The only thing that changes is the spacetime the photon is passing through, and those aspects are dependent on the OBSERVER'S frame. Not the frame the of the photon. You can not observe from the photon's frame. You can not look at spacetime through the photon's "eyes". The photon doesn't experience time or space.

deleted

Last edited:
Maxila said: I couldn't agree more; however speed is a function of distance/time and what we call dilated time is really unequal unit values between perspectives.

Even if that were a plausible argument, the dilation of time is offset by the contraction of length, and vice versa. So the argument hits a brick wall anyway.

You have yet to explain how you arrived at the conclusion that length is constant across frames. That is contradicted by gravitational lensing.

You misunderstood me, of course there is length contraction, I was stating that between all frames the unit of length is considered the same (i.e. a meter = meter’ or a km=km’). So quite the opposite is true where two frames disagree on both time and length they must also value any speed including c relative to their own d/t value, otherwise c would not be invariant to their own perspective of time and distance since c is defined by c=d/t; and I agree with the evidence that c is invariant for observers in all frames.

You missed the point that distance contracts as time dilates, and vice versa.

When did you decide to throw out all observations of length dilation/contraction?

You made incorrect assumptions that we both can likely bear some blame for; I was probably not clear or thorough enough, and you were probably too ready to jump to conclusions and criticize without making much effort to analyze what was said. I am fully aware of length contracting in proportion to time dilation.

In an empirical role time is speed, and speed is time, they are inseparable and coincident, as could be seen in any empirical experiment or observation one could devise. That is exactly why length must contract in proportion to time relative to another observer’s frame; if it did not contract then for a frame experiencing an increased gravity or motion there would be a discrepancy between its perception of time & speed to length. Length contraction is how c remains c when they disagree on time, which by its empirical characteristics is also a disagreement on relative speed to length too.

Time and speed are two descriptions of one phenomenon (a change of position and its magnitude relative to a distance) they function equally as a ratio to a distance as in t=d/s or s=d/t the value for “t” or “s” is only dependent on the ratio of d/s for time, or d/t for speed (i.e. c=300,000km/second, or c=600,000/2 seconds, or 1second=300,000km/c, or 1 second=600,000km/2c …) So when length contracts both time and speed contract to maintainthe same relative value of their ratio to a distance.

Maxila said: in that role it is always a ratio of two physical quantities in a change of position and its magnitude relative to a distance (the quantities are a distance/magnitude).

In the first place it's the derivative of length with respect to time.

That’s what I’ve shown, except I’m also showing that both speed and time (empirically) encompass the same physical quantities that cannot be separated (a magnitude of change relative to distance). Stating speed only as a derivative of length with respect to time implies time can exist without speed (motion) and empirically it cannot they are coincident, they exist together as a derivative of length in any empirical examination.

Last edited:
No, it isn't circular, and it is in line with Einstein and the evidence, and it does make a difference. You can actually understand things that appeared to be some intractable mystery, and you're left blinking at just how simple they are. What's circular is saying the speed of light is the same at different altitudes because we use the motion of light to define the second and the metre, and then use them to measure the motion of light.

How do we know light slows down near the sun and why? Scattering from density? But that does not affect speed , just direction.
I do know that it may take a photon years to escape the interior of the sun, then reach earth in 8 seconds. But that has nothing to do with the speed of the photon.

In any case, IMHOM, time is a non causal result (a by-product), so it cannot be used as an active part in any equation about the speed of light which is a "constant". It is impossible to have an inconsistent constant.

I think this is wrong. Think about moving a light clock from higher up in your lab (on Earth) to lower down. As you do so, the coordinate distance between the two mirrors of the light clock increases. The speed of light remains constant. Light takes longer to travel the larger distance between the mirrors, so the clock "ticks" slower.
This would mean the distance at black hole event horizon goes infinite, and doesn't square with the coordinate speed of light going to zero.

...but all observational and theoretical results shows that "c" is "c" and is invariant everywhere and anywhere...
It's a tautology, Declan. Just like Magueijo and Moffat said. And the coordinate speed of light varies in a gravitational field. In the room you're in.

Declan Lunny said:
...a photon at any speed other than "c" does not exist.
Yes it does. Check out photon effective mass.

Declan Lunny said:
...That is incorrect. The only thing that changes is the spacetime the photon is passing through...
The photon passes through space. Spacetime is a static mathematical model that depicts space at all times.

...You misunderstood me, of course there is length contraction...
Amazingly Maxila, it doesn't work the way people think. If you're in your gedanken spaceship and you step on the gas, things in this universe don't change. You do. And then things in this universe then look shorter to you. Think about it.

How do we know light slows down near the sun and why?
We call it the Shapiro delay. You send a radar pulse to Venus and back. When the line between the Earth and Venus skims the Sun, there's a delay. Some will tell you this is all because the signal has further to travel, but it isn't true. If they insist that it is, ask them about black holes. The delay occurs because the coordinate speed of light is lower near the Sun. The light just goes slower near the Sun.

Write4U said:
Scattering from density? But that does not affect speed, just direction.
It's not scattering. But it can be likened to refraction, hence gravitational lensing. See the OP and look at Ned Wright's web page.

Write4U said:
I do know that it may take a photon years to escape the interior of the sun, then reach earth in 8 seconds. But that has nothing to do with the speed of the photon.
No problem.

Write4U said:
IMHOM, time is a non causal result (a by-product), so it cannot be used as an active part in any equation about the speed of light which is a "constant". It is impossible to have an inconsistent constant.
That's right. It isn't constant. Just like Einstein said.

We call it the Shapiro delay. You send a radar pulse to Venus and back. When the line between the Earth and Venus skims the Sun, there's a delay. Some will tell you this is all because the signal has further to travel, but it isn't true. If they insist that it is, ask them about black holes. The delay occurs because the coordinate speed of light is lower near the Sun. The light just goes slower near the Sun.

It's not scattering. But it can be likened to refraction, hence gravitational lensing. See the OP and look at Ned Wright's web page.

No problem.

That's right. It isn't constant. Just like Einstein said.

When you say the signal has further to travel you can just say the sun has more points to travel through. You can move the points together near the sun, and so light doesn't have further to travel it has more point to travel through. That's more like Christmas tree lights, and you have wire between each lightbulb. Now near the sun you move the lightbulbs closer together, and you have more lightbulbs to turn on. So you strobe the whole thing like a Christmas tree, and you see light slow down there.

The light just goes slower when it's nearer the Sun. It's that simple.

The light just goes slower when it's nearer the Sun. It's that simple.

Well Christmas tree lights I think are an exact analogy of the model. Entangled particles are said to travel through wormholes. I use the wire as the wormhole. I use holes between the wires as the bulbs. I use tachyons for electricity. I spin the tachyons in the holes for photons. So an exact analogy works best. The distance between the points around the sun is shrunk, so the wires become shorter. So more bulbs occupy that space. You get a bright white light.. the sun. You get the holes moving inwards.. gravity, and the bending of spacetime. You get a good model I think.

No, you don't. There are no wormholes. There are no tachyons. It's just space and light, not a Christmas tree lights.

So it looks like I got Farsight to bail on the rest of his threads, but I didn't seal-up this one. Lets see if we can take care of that...

Let's make sure we're discussing the right issue here. This is what he said in the OP:
Farsight said:
And the whopper is this: the speed of light is not constant.

This goes against the grain of what people say about relativity.
The first statement is are too non-specific, not differentiating between measured (proper/local) speed of light and coordinate speed of light or between SR and GR. SO:
-The measured/local/proper speed of light is a constant in SR and GR.
-The coordinate speed of light is frame dependent.

Later in the same post:
The coordinate speed of light is the speed of light. The measured speed of light isn't.
The first sentence is vauge: the measured speed is the measured speed and the coordinate speed is the coordinate speed. But when most people just say "the speed of light" without qualifier, they are referring to the measured speed, not the coordinate speed. Why do they say it? Why is this of value? Because the measured speed is a constant and it is used in equations. So it is a useful number to know.

Further, it doesn't make sense to say "the coordinate speed of light is the speed of light". Why? Because that's the speed of light someone else tells you they see in your location. That doesn't always have any value for you, particularly if you aren't communicating with anyone else or if you are performing a task that doesn't require it (such as calculating time dilation or calibrating GPS clocks). Worse, different people will claim different coordinate speeds of light for the same location. In other words: every location has an infinite number of different coordinate speeds of light. So the coordinate speed of light can't be "the speed of light" because there isn't just one, even for an individual location.

That's how the speed of ligth works (in a nutshell) in Relativity. That's what people who understand it say about it. There is no conflict here except perhaps that Farsight is using non-standard terminology to try to create conflict where none exists. But that still makes it just a conflict over terminology and not a conflict over science.

So, Farsight, if you want to keep saying "the speed of light is not constant" and mean the coordinate speed of light is not constant, fine. I disagree with your terminology, but the science is correct once we translate it into the accepted terminology....er...except insofar as you won't be able to apply this correctly in other areas, such as your light clock animation. But we'll get to that later if necessary.

So then with that out of the way:
Yes, we all agree that the coordinate speed of light is variable. Do you agree that the local/proper/measured speed of light is constant in measurements and in GR and was constant in measurements and in GR even before the recursive definitions of the units were created?

One might notice that Farsight never directly addressed this issue in the thread brucep started for the sole purpose of discussing the issue. Why? Because the title of the thread is unambiguous ("The reason the speed of light is an invariant local measurement in GR"), so it doesn't allow for Farsight's misdirection. It didn't allow for Farsight to argue about whether "the speed of light" is referring to the coordinate or local/proper speed. That's why I'm pretty certain Farsight is doing this on purpose. He knows the truth and is just trolling this for fun: he's not a real crackpot, he's just pretending to be one for fun.

Incidentally, this is the same tactic Trapped uses to try to trick people into agreeing with him that we are being visited by aliens. He uses "UFO" to mean aliens when it doesn't. Farsight isn't trying to trick people into agreeing with him though: he's just trying to make messes. Also incidentally and ironically, he seems to have tripped-up RJ - who is a real crackpot - with this word game.