# The Speed of Light is Not Constant

Sorry, left out the detail of accelerating in a vacuum and a narrow beam of ligt placed perpendicular to the directio of travel so that the light beam would enter the box at right angles and potentially the shortest distance to the opposite wall. Yet the reality to the man in the box was that the light was curving and actually traveled a longer distance and struck the opposite wall at a lower point, in the same amount of time as if it the box were stationary and the light would be a straight line.

And @ Russ_Watters, I was young and my father had a book on Einstein which gave me my first glimpse into into the wonders of physics.

I appreciate all responses as I am trying to find a balanced worldview, based on Natural Laws and mathematical constants.

I don't think you understand what I was telling you. The light itself was traveling in an arc, and the box was changing distance from the start point, and it was changing the rate at which it traveled distance in space.

Everything has to be layed out at the same time. You can't jumble little facts here and there and try to assemble them and make it work. Doesn't work that way. It has to be EXACT, because nature is exact.

I don't think you understand what I was telling you. The light itself was traveling in an arc, and the box was changing distance from the start point, and it was changing the rate at which it traveled distance in space.

Everything has to be layed out at the same time. You can't jumble little facts here and there and try to assemble them and make it work. Doesn't work that way. It has to be EXACT, because nature is exact.

Yes to the man in the box the light actually travelled at an arc. and struck the opposite wall at a lower point. But the light was always travelling in a straight line and struck the projected opposite point. Come to think of it it was in reference to Relativity. It's been a long time.

The General Theory of Relativity

The Special Theory of Relativity describes the events which take place in a universe with no gravity. In 1916, Einstein published his General Theory of Relativity with the help of his friend and mathematician Marcel Grossman.

Before this theory, each object was thought to have gravitational and inertial mass. Gravitational mass was the weight, or effect of gravity on the object. Inertial mass was the measure of how much force had to be applied to the object to accelerate it a certain amount. Einstein realized that these two masses were equal, thus each object had only one value for its mass.

Einstein also saw no difference between how a gravitational field affected an object and how a moving frame of reference affected an object. For instance, if a man was in a closed box that was accelerated at a uniform rate, he could drop a ball and see it fall to the floor. His body would also be pulled toward the bottom of the box and he would assume that a gravitational field was pulling both him and the ball toward the side of the box he called the floor. In a few minutes, the box would attain an incredible speed but the man in the box would not know it. This box is illustrated in the following example.
http://library.thinkquest.org/29033/history/einsteinbox.jpg

Figure 4: The effect of a moving frame of reference on an object. To an observer outside of the box, the yellow ball looks as if it stays in the same place but the box moves. To an observer inside the box, the ball would look as it is falling, or being acted on by a gravitational field.

Close enough?

But the light was always travelling in a straight line and struck the projected opposite point.

No, that is your imagination at work. The light was NOT traveling in a straight line when it entered the box.

I don't think you understand what I was telling you. The light itself was traveling in an arc, and the box was changing distance from the start point, and it was changing the rate at which it traveled distance in space.

Everything has to be layed out at the same time. You can't jumble little facts here and there and try to assemble them and make it work. Doesn't work that way. It has to be EXACT, because nature is exact.

No, that is your imagination at work. The light was NOT traveling in a straight line when it entered the box.

From a local FoR, the light travels in a straight line......
From any remote FoR, the light travels in a downward arc, along with the box/lift and whatever else is in the box/lift.
All FoR's are valid.

I think I have a way to settle the argument. Farsight is saying that time itself is not variable, only that physical clocks run at different rates in different gravities. But we can force some clocks to run at the same rates. So here is an experiment that is quite practical IMO. One clock will be a stable crystal oscillator and the other a phase-locked VCO that is locked to the crystal oscillator. We are forcing the two clocks to run at the same rate with a phase-lock. Position the crystal clock on the floor and the phase-locked VCO near the ceiling. If time is not variable then the clocks should be locked in phase if measured at the height of the phase detector (ceiling) in the PLL or measured at the crystal on the floor. But if time is really variable then the measurement made at the height of the crystal oscillator (floor) then the phase should drift. I don't know what the phase drift rate would be but you could run the experiment for days or even years with a frequency counter in A/B mode. It seems so simple. Am I missing something?
I think so. If you force two oscillators to run at the same rate, that's exactly what you do. It doesn't prove anything.

Please explain the difference between a locally curved field and a local inhomogeneous field. If a field is affected in any way by the presence of a massive body is that not defined as an inhomogeneity in that field. If that field is a gravitational field, why would it not qualify as an inhomogeneity?
We need to go back a bit. People say a gravitational field is curved space when they ought to say curved spacetime. Take a look at Einstein's 1929 History of Field Theory. Down near the bottom he was talking about electromagnetic and gravitational fields. He said this:

"It can, however, scarcely be imagined that empty space has conditions or states of two essentially different kinds, and it is natural to suspect that this only appears to be so because the structure of the physical continuum is not completely described by the Riemannian metric".

Note that a field is a state of space. Now look at Einstein's 1920 Leyden Address where he's talking about gravity:

"This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that 'empty space' in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials gμν), has, I think, finally disposed of the view that space is physically empty".

For a gravitational field, he's saying space is inhomogeneous. Now think about space in the room you're in. Because it's inhomogeneous, your pencil falls down. The local force of gravity relates to the slope on the "bowling ball" depiction here. If space is very inhomogeneous, your pencil accelerates quickly. A long way up in space, space is less inhomogeneous so a pencil doesn't accelerate quickly. When you plot the inhomogeneity what you see is a curve, which is curved spacetime. For a gravitational field, space isn't curved, there's a curvature in your plot of the inhomogeneity of space.

Maxila said:
I’ve always thought using only the term “invariant” for the speed of light, caused confusion. Of course it will always be measured in a vacuum by every direct observer to be 300,000 k/s (rounded). But the term doesn’t make it clear that 300,000 k/s is relative to the space-time the observer is in…
I think you are trying to over think a rather simple property of SR & GR. Stated as simply as possible: All observers will find that the speed of light is the same, regardless of whether they are looking at light in their own reference frame or someone else's reference frame. Everyone will measure it speed as 3 x 10^8 m/s. Any light they measure from whatever source will be just that. What differences they will observe which ARE frame dependent are time dilation and space contraction. But light they will all agree on. It is invariant because it is same to all observers and doesn't need any adjustment to relate one frame to another.
That's what they say, Declan. But it doesn't square with what Einstein said. And more importantly it doesn't square with the evidence of optical clocks in the room you're in. Or the Shapiro delay.

The point was and is that optical clocks are not measuring the speed of light, so they are providing no direct evidence that the speed of light is either constant or variable.
They're clocking up some regular cyclical motion. Not the flow of time. So if one clock goes slower than the other that motion is going slower. It's that simple.

OnlyMe said:
You keep using this example attached to a pong like graphic and claim it proves something about the speed of light. Re-read your own last response and point to direct evidence of any value for the speed of light.
The graphic depicts parallel-mirror light clocks. The NIST optical clocks lose synchronisation when one is 30cm above the other. Parallel-mirror light clocks will too. And the metre doesn't change. There is no horizontal length contraction.

OnlyMe said:
Or any experiment using optical or even cesium clocks to measure the speed of light, where the experiments are sufficiently separated in a gravitational field that they measure the speed of light to be anything other than constant. I suspect any real experimental confirmation will have to wait until someday the speed of light in vacuum is measured somewhere far from the surface of a gravitationally significant mass.., using an appropriately accurate clock which can also be shown to be gravitationally time dilated.
Read the OP. The motion of light is used to define the second and the metre. Which are then used to measure the motion of light. So no matter how fast the light moves you always get the same answer. It's a tautology.

So the top clock is rotating with the earth at the same rotational velocity as the bottom clock? In other words, if the two clocks both rotate exactly one earth rotation, then the top clock traveled a further distance than the bottom clock in one rotation of the earth, right?
Right. But like I said previously, you could do all this stuff on a planet that isn't rotating.

What I find curious is the fact that the "existence of time" as an independent dimension is fact. As far as I know there is not a shred of proof of that claim.

We use the term "time" only in relation to an action in a geometric "field" or "space". But like the claim of a god, no one has actually proven that time does exist independent of space and without measurable action time cannot emerge as a property of measurement.

I have never heard anyone able to disprove that time is a "result" and emerges along with the action of the field or object. I am not arguing against the accepted relationship between space and time. I am questioning the assumption of the passage of time in the absence of space or action.
Well said that man. This thread follows on from a thread about time, see the OP at Time Travel is Science Fiction.

Farsight:

They're clocking up some regular cyclical motion. Not the flow of time. So if one clock goes slower than the other that motion is going slower. It's that simple.

But the motion could be going slower because time is going slower.

The graphic depicts parallel-mirror light clocks. The NIST optical clocks lose synchronisation when one is 30cm above the other. Parallel-mirror light clocks will too. And the metre doesn't change. There is no horizontal length contraction.

I'm not sure about that, due to the relativity of simultaneity issues involved in defining lengths in the two different reference frames (of the top and bottom clocks).

Can you please justify your claim that there is no horizontal length contraction?

The motion of light is used to define the second and the metre. Which are then used to measure the motion of light. So no matter how fast the light moves you always get the same answer. It's a tautology.

The second is defined independently of light. You said so yourself. We define the second by counting oscillations in caesium atoms.

The metre is defined with reference to the speed of light, which is a defined constant. Ask Motor Daddy. He's very fond of pointing this out.

There's an assumption that the metre and the second are both defined in a local reference frame, with the caesium clock at rest relative to the observer.

The speed of light may not be measured as constant by an accelerating observer, of where the spacetime is not flat.

But the motion could be going slower because time is going slower.
Time going slower is a figure of speech. Things move, things like cogs and light and planets and people. When all things around us go slower we say time is going slower, but there isn't any actual thing called time that's going fast or slow or anywhere. A clock doesn't actually measure the flow of time, or the passage of time. It clocks up some kind of motion. When it goes slower it's because that motion is going slower. The rate of motion is lower. People say the coordinate speed of light is lower, but it's more than that.

James R said:
I'm not sure about that, due to the relativity of simultaneity issues involved in defining lengths in the two different reference frames (of the top and bottom clocks).
The definition of length doesn't change. See the OP. When the light goes slower the second is bigger, then the slower light and the bigger second cancel each other out and the metre is unchanged.

James R said:
Can you please justify your claim that there is no horizontal length contraction?
See above. And if there was, the lower clock would run faster, not slower.

James R said:
The second is defined independently of light. You said so yourself. We define the second by counting oscillations in caesium atoms.
No, it's the duration of 9,192,631,770 periods of radiation. The hyperfine spin-flip causes this radiation, but we aren't counting spin-flips.

James R said:
The metre is defined with reference to the speed of light, which is a defined constant. Ask Motor Daddy. He's very fond of pointing this out.
It's a defined constant, but it isn't constant. Look at the gif. There's no horizontal length contraction. The lower clock goes slower.

James R said:
There's an assumption that the metre and the second are both defined in a local reference frame, with the caesium clock at rest relative to the observer.
And that definition isn't good enough for the room you're in. because those two NIST optical clocks don't stay synchronised.

James R said:
The speed of light may not be measured as constant by an accelerating observer, of where the spacetime is not flat.
Sure thing. And it may not be measured as constant by a guy in a room.

Has Farsight proposed an experiment to overturn all other experiments done in nearly a hundred years of relativity, or is he just going to constantly post his evaluation of a gif?

Since his ego is tied in with his self published, non peer reviewed product for sale, I cry foul and conflict of interest. Hell, I would be adamant that drunken aliens abducted people in the Bermuda Triangle if I could make a buck.

Good question, in case Farsight has you on ignore:
Has Farsight proposed an experiment to overturn all other experiments done in nearly a hundred years of relativity, or is he just going to constantly post his evaluation of a gif?

No, it's the duration of 9,192,631,770 periods of radiation. The hyperfine spin-flip causes this radiation, but we aren't counting spin-flips.
If the radiation is caused by spin-flips, then it is the spin-flips that determine how many periods of radiation we count. Ie, if the spin-flips slow down, then the radiation gets redder.
It's a defined constant, but it isn't constant. Look at the gif. There's no horizontal length contraction. The lower clock goes slower.

Your argument is a lot like saying we don't see clocks, we only see the light they reflect and therefore it is the light they reflect that determines the tick-rate.
The lower clock goes slower, but the graphic is wrong on the reason why. You seem to be confusing the linear speed of a photon (which is what a light clock thought experiment uses) with the photon's frequency (which is what an atomic clock uses).
Sure thing. And it may not be measured as constant by a guy in a room.
Under what conditions? Define such an experiment.

And just to be clear here, your thesis is this:
Measured differences in the rate of passage of time at different elevations are an illusion caused by a varying speed of light.

Am I correct that that is your thesis?

Farsight:

Time going slower is a figure of speech. Things move, things like cogs and light and planets and people. When all things around us go slower we say time is going slower...

So we're having a semantic argument that is of no special consequence. There's no operational way to distinguish between time slowing down and all motion slowing down. In fact, it sounds like you're saying they're the same thing.

No, it's the duration of 9,192,631,770 periods of radiation. The hyperfine spin-flip causes this radiation, but we aren't counting spin-flips.

Is this important to your argument in some way?

It's a defined constant, but it isn't constant. Look at the gif. There's no horizontal length contraction. The lower clock goes slower.

Yes, I agree it goes slower.

Sure thing. And it may not be measured as constant by a guy in a room.

The spacetime in the NIST lab is curved, so there's more space at the bottom clock than at the top one (if you're talking light clocks). Therefore, light takes longer to cross the gap. But we like to assume we're in a flat spacetime, so it looks to us as if light has slowed down.

Or something like that.

If the speed of light is same in all frames of references, then why do the wavelength and frequency of light change with reference? Does this mean that only the light particle moves at C, but its wave nature, via wavelength and frequency, by not being the same in all references, is not at C?

Not being the same in all references is an artifact of inertial. Only the speed of light is the same in all references. This division between inertial and the speed of light seems clear cut by observing variable versus fixed. So if wavelength and frequency is not the same in all references it is not at speed of light since light speed of the same in all references. Does this means that the wave-particle duality of light is connected to energy existing in both the consistent speed of light (particle) reference and the variable inertial reference (wavelength and frequency) at the same time?

This would explain the intuition that light is not always at C, since wavelength/variable is variable with reference.