The Speed of Light is Not Constant

[paddoboy]

Anyway, a neutral pion decays into two gamma rays $$\pi ^0\to \gamma +\gamma$$ ie light. In 1964 at CERN whether these pions were moving at 0.999 75c or stationary in the lab, the gamma rays that came from them were all measured to be the same speed.

Farsight is out to lunch like no other on this one. He may be challenging that light is not an electromagnetic wave that travels at a finite speed, or he wants to re-write Maxwell's equations.

Missed that beer w/Straw...
Nice example and quite valid. [on both counts] nudge nudge wink wink

 

[Declan Lunny]

Here’s the idea: a medium, whatever it is, is made up of molecules. When a photon (light particle) hits a molecule it is sometimes absorbed. Its energy is turned into raised electron-energy-levels, or vibrations and flexing, or movement. In short order (very short order) the photon is spit out of the other side, none the worse for wear.

In between molecules light still travels at light speed. It’s just that, with all those molecules around, it’s always darting ahead, getting absorbed, pausing for a moment, then being re-emitted. On the scale we’re used too, this happens so much and so fast that you don’t notice the starting-and-stopping. Instead you notice an average slowing of the light.

That is, if light always takes about 33% longer to travel through water than air (and it does) due to absorption and re-emission, you’d say “ah, light travels slower through water!”. The fact that that isn’t quite the case is rarely important.

For a defender of the mainstream and enforcer of the tested theory, you sure seem to like making up "theory" out of thin air. Everything you just said it wrong. The light isn't being absorbed and re-emitted as it passes through a lens, it is slowing down. ACTUALLY moving slower. This is not even the slightest bit controversial, it is the most basic of well established physics.

You shouldn't try so hard in your "defender" role. Because the really basic stuff you need to know is something you have tried to skip. Instead of you doing one of those things you call "word salads", you should have taken the time to do what I suggested, in the same amount of time you could have discovered some very cool, useful and interesting physics.

It's not the particle construct of the photon that causes this thing to happen, the slowing, it is the wave role of the photon which is slowed. If you "idea" were correct, it would be density dependent, which it is not. Some dense materials transmit a lot of light, and some very rarefied materials are opaque.

 

[paddoboy]

For a defender of the mainstream and enforcer of the tested theory, you sure seem to like making up "theory" out of thin air. Everything you just said it wrong. The light isn't being absorbed and re-emitted as it passes through a lens, it is slowing down. ACTUALLY moving slower. This is not even the slightest bit controversial, it is the most basic of well established physics.

No, I don't believe it is wrong...This maybe another one of these perception things
Anyway you argue it out with the link...

http://www.ccmr.cornell.edu/education/ask/?quid=918


OK, I am pretty busy at this time, but so far there is some support for your position.....again, could this just be a way of perceiving/looking at things on face value...

Here is another for my position......

An electromagnetic wave (i.e., a light wave) is produced by a vibrating electric charge. As the wave moves through the vacuum of empty space, it travels at a speed of c (3 x 108 m/s). This value is the speed of light in a vacuum. When the wave impinges upon a particle of matter, the energy is absorbed and sets electrons within the atoms into vibrational motion. If the frequency of the electromagnetic wave does not match the resonant frequency of vibration of the electron, then the energy is reemitted in the form of an electromagnetic wave. This new electromagnetic wave has the same frequency as the original wave and it too will travel at a speed of c through the empty space between atoms. The newly emitted light wave continues to move through the interatomic space until it impinges upon a neighboring particle. The energy is absorbed by this new particle and sets the electrons of its atoms into vibration motion. And once more, if there is no match between the frequency of the electromagnetic wave and the resonant frequency of the electron, the energy is reemitted in the form of a new electromagnetic wave. The cycle of absorption and reemission continues as the energy is transported from particle to particle through the bulk of a medium. Every photon (bundle of electromagnetic energy) travels between the interatomic void at a speed of c; yet time delay involved in the process of being absorbed and reemitted by the atoms of the material lowers the net speed of transport from one end of the medium to the other. Subsequently, the net speed of an electromagnetic wave in any medium is somewhat less than its speed in a vacuum - c (3 x 108 m/s).


http://www.physicsclassroom.com/class/refrn/u14l1d.cfm

 

[OnlyMe]

And as a newbie, you need cut out the unwarranted crap....As you are now no doubt aware, I'm not making up anything out of thin air.
The view I present is supported on at least two links.
And the "pick up lines" [defender of the mainstream and enforcer of tested theory] you seem to have aquired, are those used by the 4 or 5 pushing the anti mainstream position, and naturally wallow in whatever derision they can get their paws onto.
The position I presented in the BH thread was well supported by the more intelligent on the forum, but being more wise then I, they got rather bored and tired of the continued anti mainstream crap, from at least 5 sources, and left the thread alone as it descended into chaos.
You should first study the history of the lengthy thread and you will see what I mean.

Have a good day anyway.

Paddoboy, those explanations are theoretic and come out of QM where empty space is truly empty space. As such it is concluded that if a ray of light, passes through a transparent medium without the process described, as it is still traveling through empty space it should still be measured to travel at c. So to account for the change in velocity it must be time delayed by an interaction with the electrons of the atoms in the medium, through a process of absorption and reemission.

The problem is that, that explanation assumes that space is truly just empty . . . nothingness.

Now recall an earlier question I never addressed,

Reality is another question I agree.
Suffice to say, I have a broad outlook as to what is real or what isn't. Just because we cannot see, touch, smell something, does not mean it is not real.
Do you see space/time as real?
If you answer no to that, then tell me what GP-B was measuring to incredible precision.

If the empty space in the vicinity of the GP-B satellite were true empty nothingness how then could space be drug along by the motion of planet and star?

Space is either a dynamic partner to mass in a dance we experience as gravitation, or it is simply an empty box that everything else moves within.

It becomes very problematic when QM and and GR are commingled. That point was the intent of a couple of my earlier posts.

If space is a dynamic counterpart to gravitationally significant masses moving within it, then the vacuum cannot be thought of as empty and the passage of light through any empty space cannot be thought of as unaffected by the dynamics of the space it passes through.

So the results of the GP-B experiment suggests that space does interact dynamically with mass.., and proximity plays a part in to what extent.

How then might the very close proximity of the mass of atom and molecule in transparent mediums affect the dynamics of the empty spaces in between?

I don't know why light slows down in transparent mediums other than vacuum, just that it does. I don't even know that c is in fact universally constant in vacuum. It's velocity has only ever been accurately measured in vacuum within the limitation of our local gravitational field, at or near the surface of the earth. The universal constant c, remains an a priori assumption. And it will remain so until we at some time in the future experimentally measure the velocity of light in vacuum some distance from the surface of the earth with a gravitationally time dilated clock.

My intent here has not been to challenge or refute any aspect of SR or GR. It is to once again attempt to draw that line in the sand that separates what we know because we have experimentally proven it and what we accept as an a prior fact because the underlying theory has been exceedingly successful, many other predictions having been experimentally proven.

All of that to say your reference though accepted to some extent by a portion of the "mainstream", are theoretical. As far as I am aware they have never been experimentally verified and proven.

 

[paddoboy]

It becomes very problematic when QM and and GR are commingled. That point was the intent of a couple of my earlier posts.

All of that to say your reference though accepted to some extent by a portion of the "mainstream", are theoretical. As far as I am aware they have never been experimentally verified and proven.

Interesting coherent post OnlyMe...You need to give lessons to one or two others that seem to post in more inane gobbldydook fashion.

I don't really see it though as mixing QM and GR....Rightly or wrongly I see it as more an explanation via particle physics, which I think can be distinguished from QM.
Either way, as I mentioned in my post to Declan, there is support for his position as well as mine.
That also holds true for Hawking Radiation...
That also holds true for aspects of what some claim to be abstractions in cosmology, and which others see as having reality.
So we have a dilemma of sorts.

Again while not agreeing entirely with your own stance, I do see the differences in thinking as minor and pedant.


Still when we get down to the nitty gritty of things, this thread was a red herring to add to the anti GR BH forces, along with the time thread :shrug:


Again, good clear concise coherent post.

 

[Farsight]

That is wrong. That is why "c" is specified as "in a vacuum". Light does slow down as it passes through a medium. That is the basis of the entire field of optics. Various mediums slow it by different amount. That is why lenses work. That is how a prism works. It is just one of those 1st Principles that everyone should know as second nature. There is nothing controversial about it all. It's experimentally demonstrated in all introductory physics labs. Google up refraction and dispersal. There are tons of materials available.

You will know all about gravitational lensing, Declan. Have a look at this: Inhomogeneous Vacuum: An Alternative Interpretation of Curved Spacetime. Then take a look at Einstein's 1920 Leyden Address:

"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."

 

[James R]

Farsight:

It's more than that James. The speed of light in the room you're in is not constant as measured by you.

It is true that there's some curvature of spacetime in the room I'm in.

Only it isn't. If it was, those two NIST optical clocks, one 30cm above the other, would run at the same rate.

The problem there is one of time in different reference frames, not a change in the speed of light.

See the quotes in the OP. Take Einstein seriously.

I do. All but one of your quotes was prior to 1916, when Einstein published his general theory. So, we see him groping towards it gradually, up until the last statement you quoted. Of course, in 1916, there was still a lot that Einstein didn't understand about the implications of his own theory. We've had almost 100 years since then to get a handle on it all.

 

[Farsight]

It is true that there's some curvature of spacetime in the room I'm in.

But look at this depiction of gravitational potential. It's like the bowling-ball analogy. Now zoom in to a small portion of it. Your pencil falls down because of the gradient, the first derivative of potential. Spacetime curvature is the second derivative. It isn't why your pencil falls down.

The problem there is one of time in different reference frames, not a change in the speed of light.

We've already established that a clock doesn't actually measure the flow of time, it "clocks up" some kind of regular cyclical motion and shows you a cumulative result called "the time". And that two optical clocks in the room you're in don't stay synchronised when one's 30cm above the other. Have we also mentioned that a reference frame is an abstract thing? Optical clocks aren't.

I do. All but one of your quotes was prior to 1916, when Einstein published his general theory. So, we see him groping towards it gradually, up until the last statement you quoted. Of course, in 1916, there was still a lot that Einstein didn't understand about the implications of his own theory. We've had almost 100 years since then to get a handle on it all.

But "you" haven't. You've screwed it up. Now you flatly contradict Einstein, but you won't admit it. Take a look at this Baez article by Philip Gibbs. See the general relativity section where he says this:

"Since Einstein talks of velocity (a vector quantity: speed with direction) rather than speed alone, it is not clear that he meant the speed will change, but the reference to special relativity suggests that he did mean so. This interpretation is perfectly valid and makes good physical sense..."

Now see the last line:

"Finally, we come to the conclusion that the speed of light is not only observed to be constant; in the light of well tested theories of physics, it does not even make any sense to say that it varies".

So what Einstein said makes sense, but it doesn't? Yes, screwed up is the word. Look at the OP again. Look at the gif:

Image credit: Brian McPherson

It's an exaggeration, but it is not misleading. Now, are you seriously saying the speed of light is constant?

 

[James R]

Farsight:

But look at this depiction of gravitational potential. It's like the bowling-ball analogy. Now zoom in to a small portion of it. Your pencil falls down because of the gradient, the first derivative of potential. Spacetime curvature is the second derivative. It isn't why your pencil falls down.

You seem to be referring to a Newtonian-type potential. General relativity is a bit different.

I agree with what you say in the Newtonian sense.

We've already established that a clock doesn't actually measure the flow of time, it "clocks up" some kind of regular cyclical motion and shows you a cumulative result called "the time".

Yes, and we use that regular cyclical motion to define what we mean by time. Time is what clocks measure. Counting time is counting the ticks of a clock.

And that two optical clocks in the room you're in don't stay synchronised when one's 30cm above the other. Have we also mentioned that a reference frame is an abstract thing? Optical clocks aren't.

It is well understood why clocks above one another don't stay in sync. Time goes slower lower down in a gravitational well.

But "you" haven't. You've screwed it up.

I'm mostly agreeing with you. Does that mean you screwed up too?

Now you flatly contradict Einstein, but you won't admit it. Take a look at this Baez article by Philip Gibbs. See the general relativity section where he says this:

"Since Einstein talks of velocity (a vector quantity: speed with direction) rather than speed alone, it is not clear that he meant the speed will change, but the reference to special relativity suggests that he did mean so. This interpretation is perfectly valid and makes good physical sense..."

I agree with this.

Now see the last line:

"Finally, we come to the conclusion that the speed of light is not only observed to be constant; in the light of well tested theories of physics, it does not even make any sense to say that it varies".

So what Einstein said makes sense, but it doesn't?

Did you read the whole article?

Yes, screwed up is the word. Look at the OP again. Look at the gif:

Image credit: Brian McPherson

It's an exaggeration, but it is not misleading. Now, are you seriously saying the speed of light is constant?

I already told you. Locally it is constant (and by "locally" I mean in a small enough region where we can take spacetime to be approximately flat). With sensitive enough measuring equipment, that 30 cm vertical gap may well mean that you need two locally flat reference frames instead of one. And so, an observer looking from a distance sees one light clock tick slower than the other one. And, indeed, from the point of view of this distant observer, the speed of light does not appear to be constant.

I said all this in my first reply to this topic, didn't I?

We agree with one another, don't we?

 

[Declan Lunny]

And as a newbie, you need cut out the unwarranted crap....

Oh my, well I guess I need to do that thing.

As you are now no doubt aware, I'm not making up anything out of thin air.

No? Well just because you read an op-ed piece on what the "speed of light is through a medium" doesn't mean you understand the argument.

The photon's motion through a medium can only be taken as "abstract" if you are going to present it as an "instantaneous" velocity. The motion can only have any meaning by describing it "Point A" to "Point B" and the time it takes to get there. The reason for that is a "Photon" (as a particle) can never have it's instantaneous velocity known. Never, ever, it is not possible.

The view I present is supported on at least two links.

Geared to trying to elucidate for the uninformed general reader. As is too often the case, they don't present the whole story.

And the "pick up lines" [defender of the mainstream and enforcer of tested theory] you seem to have aquired, are those used by the 4 or 5 pushing the anti mainstream position, and naturally wallow in whatever derision they can get their paws onto.

I came up with that "pick up lines" completely independently and had not seen someone else use it. That in itself should suggest something about your presentation and demeanor.

The position I presented in the BH thread was well supported by the more intelligent on the forum, but being more wise then I, they got rather bored and tired of the continued anti mainstream crap, from at least 5 sources, and left the thread alone as it descended into chaos.

Does that not suggest anything to you? You chose to play into the anti-mainstreamers, game,,, probably just as they intended that you do. There is a phrase about that,,,, uh, well, it will come to me,,,, oh yeah, it has something to do with feeding and such,,,,,

You should first study the history of the lengthy thread and you will see what I mean.

Have a good day anyway.

I always do, I always do. And you have a good day also.

 

[Captain Kremmen]

This diagram is wrong, I think.
Shouldn't the lower bats be closer together if they are in a stronger gravity field?

 

[Beer w/Straw]

Paradigm shifts in physics come through gif interpretation.

Sorry, I had to say it.

 

[Waiter_2001]

I imagine the speed of light varies when moving through different mediums i.e. air or glass (glass=slower.) Hence when light passes through a prism (glass) we find a spectrum (colours).

 

[Farsight]

This diagram is wrong, I think.
Shouldn't the lower bats be closer together if they are in a stronger gravity field?

No. And note that the strength of the gravitational field relates to the gradient in your plot of clock rates. The lower "bats" represent a parallel mirror light clock which like the NIST optical clock runs slower at a lower gravitational potential.

 

[Motor Daddy]

No. And note that the strength of the gravitational field relates to the gradient in your plot of clock rates. The lower "bats" represent a parallel mirror light clock which like the NIST optical clock runs slower at a lower gravitational potential.

Farsight, Is that top pic just floating in space up there?

 

[Farsight]

You seem to be referring to a Newtonian-type potential. General relativity is a bit different.

Sure thing. That image was a just nice big version of the "bowling ball analogy", akin to the picture on the right on the wiki Riemann curvature tensor page.

I agree with what you say in the Newtonian sense.

Good stuff. Another time maybe we can talk about Newton's thoughts on gravity.

Yes, and we use that regular cyclical motion to define what we mean by time. Time is what clocks measure. Counting time is counting the ticks of a clock.

No problem with that. Now watch this:

It is well understood why clocks above one another don't stay in sync. Time goes slower lower down in a gravitational well.

No. That regular cyclic motion goes slower. And when it's a light clock, it's the motion of light going slower.

I'm mostly agreeing with you. Does that mean you screwed up too?

No. This is what I wanted. I come out with a series of mundane simple things that are easy to agree with because they match Einstein and the evidence, and I make my case one easy step at a time.

I agree with this.

Cookin' on gas.

Did you read the whole article?

Yes. And I've talked to editor Don Koks about it. And I've tried to talk to Philip Gibbs about it.

I already told you. Locally it is constant (and by "locally" I mean in a small enough region where we can take spacetime to be approximately flat). With sensitive enough measuring equipment, that 30 cm vertical gap may well mean that you need two locally flat reference frames instead of one.

Noted. We should talk about the principle of equivalence another time.

And so, an observer looking from a distance sees one light clock tick slower than the other one. And, indeed, from the point of view of this distant observer, the speed of light does not appear to be constant

Yep. Only it isn't a distant observer. You're the observer. Those NIST optical clocks are in front of you. In the room you're in. And yes, the speed of light does not appear to be constant. Because it isn't.

I said all this in my first reply to this topic, didn't I? We agree with one another, don't we?

Yes and yes. And I'm sure we'll continue to do so. Time for the next step methinks. Another thread. Gravity works like this.

 

[Russ_Watters]

This diagram is wrong, I think.
Shouldn't the lower bats be closer together if they are in a stronger gravity field?

The light clock is an SR thought experiment, not a GR thought experiment, so Farsight creates the confusion he is after by misapplying and vaguely defining it.

But the probable answer to your question is no, you have it backwards: the speed of light should be the same which therefore means the distance is LARGER. This is because the curvature of space curves (and therefore lengthens) what appears to be a straight path.

So by ignoring GR in his analysis of GR, Farsight obliquely attacks SR. See?

 

[OnlyMe]

... Those NIST optical clocks are in front of you. In the room you're in. And yes, the speed of light does not appear to be constant. Because it isn't.

To start, I don't have a position here re: the variable speed of light issue. But it has for a long time bothered me that it seems a theoretical leap to connect an atomic ground state optical frequency rate, with the speed of light, even where the emission of a photon is associated with electron transions. Locally all light/photons have the same speed in vacuum reguardless of their frequency, or the ground state frequency of the emitting atom.

Might you reconsider your statement in the above quote with respect to the following?

Those NIST optical clocks are not based on or measuring the speed of light. They are based on ground state optical frequencies.

They do say something about how the optical frequencies of specific atoms are affected by location in a gravity well, but not so much about the speed of light... The implied application of a frequency change, to a change in the speed of light, seems to me to remain based on the underlying theory. May be true or may not, it does not seem to have been directly measured, relative to location in a gravity well, the velocity of light that is.

And aren't those optical clocks only used to set a standard for the second IOW to set other clocks? They don't actually keep time theirselves. Mostly they would just up the accuracy from cesium/microwave frequency clocks, as a standard to adjust or set something like a hydrogen maser...?

 

[Farsight]

Farsight, Is that top pic just floating in space up there?

Huh? The gif is a parallel-mirror light-clock idealised exaggeration of the NIST optical clocks, which run at noticeably different rates when separated by a vertical distance of 30cm.

The light clock is an SR thought experiment, not a GR thought experiment, so Farsight creates the confusion he is after by misapplying and vaguely defining it.

I'm giving you clarity Russ. A light clock runs slower when it's lower just like any other clock. Apart from a pendulum clock of course, where the clock rate depends on strength of field rather than gravitational potential.

But the probable answer to your question is no, you have it backwards: the speed of light should be the same which therefore means the distance is LARGER. This is because the curvature of space curves (and therefore lengthens) what appears to be a straight path.

Only it doesn't. Here Russ, have a look at this Baez article. See this bit: "Note: not the curvature of space, but of spacetime. The distinction is crucial." Space isn't curved. Your plot of clock rates is curved.

So by ignoring GR in his analysis of GR, Farsight obliquely attacks SR. See?

No way. How many times do I have to say it? I root for relativity. I'm the one quoting Einstein. I'm the one fighting cargo-cult science and ignorance and Emperor's New Clothes woo.

 

[Russ_Watters]

Farsight, you do know that no one believes that (that you are a champion of Relativity), right? I don't even think most of us believe you believe it. This is just a game you are playing.

Still: be clear here: you do NOT accept SR's constancy of light speed postulate, right?

Also, the Baez article: more out of context quotes (that is a key part of your game). Yes, space is curved. That quote means it isn't JUST space that is curved.