The WHY of speed of light vs. the FACT thereof

[bcrowell]

The causality I have in mind is the notion that the act of measuring one particle determines the state of that particle and the state of a distant particle. The measurement is thus the cause; the effect is the combination of states [spin up and spin down, e.g.] taken on by the two particles.

OK. Your use of the word "causality" is then different from mine, and probably different from that of every physicist in the world. In particular, your idea of causality implies that the order of cause and effect depends on the frame of the observer. This is an undesirable feature for a definition of causality, which is why nobody else uses the word to include examples like this one.

I read through the full page.

Reading through a page of links is not the same as understanding the physics in the links.

There is a sticky at the top of this forum, titled "FAQ: Experimental Basis of Special Relativity." Every experiment in that sticky constitutes empirical evidence that causality is satisfied, as predicted by SR.

I don't think there were any experiments in the list which dealt with entangled particles.

But this would only be relevant if others accepted your nonstandard definition of causality.

If one accepts the premise that the measurement of a particle is a cause and the state of a distant (non-local) particle is an effect of that cause, then it seems true on the face of it that the effect of the cause has propagated at a speed faster than c.

But nobody else accepts this premise as falling within the definition of "causality," which has a technical definition in physics. For example, I know you're currently studying Spacetime Physics, by Taylor and Wheeler. Have you gotten to section 6.3 yet? It has a clear discussion of causality, and it makes it clear that causality is frame-independent ("Cause and effect preserved by light cone"), which would be inconsistent with your notion of causality.

 

[yuiop]

If one accepts the premise that the measurement of a particle is a cause and the state of a distant (non-local) particle is an effect of that cause, then it seems true on the face of it that the effect of the cause has propagated at a speed faster than c.

In the case of entangled particles, it is hard to distinguish cause from effect as opposed to the causal interactions of macroscopic particles. For example if someone loads a bullet into a gun and fires it at some else so that the bullet ends up in victims's head, then we can reasonably say the that firing the gun is the cause and the victims head exploding and subsequent death is the effect. We never observe the opposite, i.e. dead body coming back to life and ejecting a bullet from its brain that ends up in the breach of a gun. The firing of the gun is indisputably the cause and the demise of the victim is indisputably the effect. Now things are not so clear in quantum mechanics. Alice observing up spin in an entangled particle might be described as the cause of Bob observing down spin in the other entangled particle. However it is equally likely that Bob observing down spin in his particle is the cause of Alice observing up spin so it not at all clear which is the cause and which is the effect as both observations have equal statistical likelihood. Even in a single instance of an entanglement experiment, different observers with relative velocity will disagree on which observer observation was the cause and which observers observation was the effect. There is no violation of entropy change or reversal of the "arrow of time." In the case of quantum observations, cause and effect are complete mirror images of each other and it does not matter which order they happen in, so it hard to claim that entanglement experiments contradict the normal light speed relationship between cause and effect. Also as I said before, EPR type experiments with entangled photons can not be used to pass any information from one observer to another at greater than light speed.

 

[GregAshmore]

Having a definition of a word certainly is a precondition if you want to make meaningful statements using the word. If I were to try to discuss my opinion about "the distinction between farglmoger and our measurement of farglmoger" wouldn't you consider it necessary for me to define "farglmoger"?

If you can't define "real" then stop using the word. Otherwise you are literally writing nonsense.

I'm afraid we will have to disagree on this point. I readily understood all of the authors who were brash enough to discuss the subject of reality without first defining 'real'. The reason I was able to understand their meaning (to within a reasonably small margin of error) is that they were discussing reality, in which we all live (to one degree or another), and not 'farglmoger', with which no one has any experience.

 

[Dale]

I readily understood all of the authors who were brash enough to discuss the subject of reality without first defining 'real'. The reason I was able to understand their meaning (to within a reasonably small margin of error) is that they were discussing reality, in which we all live

If understanding the word is so easy for you then why is defining it so difficult? I believe it is because you do not understand it as well as you think you do and are simply deluding yourself. How can you even talk about a "reasonably small margin of error" for something that you cannot even define enough to measure?

Your posts are nonsense because you cannot define a key term.

and not 'farglmoger', with which no one has any experience.

And who do you think has experience with "reality" as distinct from our measurements of "reality"?

 

[GregAshmore]

OK. Your use of the word "causality" is then different from mine, and probably different from that of every physicist in the world. In particular, your idea of causality implies that the order of cause and effect depends on the frame of the observer. This is an undesirable feature for a definition of causality, which is why nobody else uses the word to include examples like this one.

I don't know enough to disagree with you, but I will observe that, as the experiments have been described to me, the two "stations" at which the entangled particles are measured are in the same frame. If so, then the cause and the effect are in the same frame.

While I understand from personal experience the need to properly understand and use technical terms, it is also true that most technical terms may be used to adequately communicate, without rigorous adherence to their formal definitions. In the books which I have read so far, it has been necessary for the authors to speak with less precision than they might otherwise, because those books were written for a general audience, not as college textbooks.

Of course, Einstein saw fit to use the less-than-precise, "spooky action at a distance", and still communicated very well.

I believe that I have correctly expressed the concept of "cause and effect", or "determinism", as it has been used by these authors in their explanations of the concept of fundamental probability.

This is not to say that I can continue being imprecise in my use of technical terms. As you know, I am working toward a technical grounding in relativity. If I live through that, I'll see what I can do in quantum mechanics.

It happens that my interest in these subjects, apart from the fact that I'm a nerd, is the relationship between scientific theories and reality. This explains why I keep coming back to the subject--and it is the driver for learning to handle the subjects with some degree of technical understanding.

But nobody else accepts this premise as falling within the definition of "causality," which has a technical definition in physics. For example, I know you're currently studying Spacetime Physics, by Taylor and Wheeler. Have you gotten to section 6.3 yet? It has a clear discussion of causality, and it makes it clear that causality is frame-independent ("Cause and effect preserved by light cone"), which would be inconsistent with your notion of causality.

No, I'm not to 6.3 yet. Again, without presuming to disagree with your assertion, I note that the association of cause and effect with the light cone assumes (as I understand it) that no information can be transmitted faster than the speed of light. But that is precisely the conundrum which quantum entanglement presents to us: the [seeming] transmission of information at speeds faster than light.

I am well aware, again from experience in other endeavors, that one must learn how to do things in the established way before one can seriously consider alternate approaches. (Which is why I was wrong to use the word 'contradict' in those three posts. But I was so sure...)

 

[GregAshmore]

If understanding the word is so easy for you then why is defining it so difficult? I believe it is because you do not understand it as well as you think you do and are simply deluding yourself. How can you even talk about a "reasonably small margin of error" for something that you cannot even define enough to measure?

Your posts are nonsense because you cannot define a key term.

I guess I'll just fall in line behind those other spouters of nonsense--all of whom are much smarter than I, and have much better credentials for writing the nonsense that they do.

And who do you think has experience with "reality" as distinct from our measurements of "reality"?

Everyone. There are many things which I know are real, but have never measured because they are not subject measurement. Indeed, they are similar to the photon in that the attempt to measure them destroys them. Some of these things I would not consider to be purely "physical", but the materialist would. So on the materialist's terms, I am certain of the reality of physical things which cannot be measured.

More along the lines of our discussion, we don't know what we don't know. So long as our knowledge of nature is incomplete, there is (in my opinion) an undeniable distinction between reality and our measurement of reality. As I mentioned in another post, that distinction takes on practical importance when we act at the limits of our knowledge. In those circumstances, reality has a way of biting us in the butt.

 

[JesseM]

I don't know enough to disagree with you, but I will observe that, as the experiments have been described to me, the two "stations" at which the entangled particles are measured are in the same frame. If so, then the cause and the effect are in the same frame.

Events aren't "in" any frame! A frame is just a coordinate system, a way of labeling events with position and time coordinates, nothing more. Any set of events can be described in any frame you like, and for a given set of initial conditions all frames make the same predictions about local events at later times, that's a basic principle of relativity.

I believe that I have correctly expressed the concept of "cause and effect", or "determinism", as it has been used by these authors in their explanations of the concept of fundamental probability.

What specific quotes by these authors are you thinking of? Surely you realize that you may have misunderstood, so if you give a quote then others who are more familiar with the technical details of the theory may be able to give you an alternate interpretation more in line with what the theory actually says.

No, I'm not to 6.3 yet. Again, without presuming to disagree with your assertion, I note that the association of cause and effect with the light cone assumes (as I understand it) that no information can be transmitted faster than the speed of light. But that is precisely the conundrum which quantum entanglement presents to us: the [seeming] transmission of information at speeds faster than light.

It's been proven that there's no way to exploit quantum entanglement to transmit messages FTL. If you believe in "hidden variables" (like the idea that particles have well-defined positions at all times, even when not measured), then quantum entanglement may suggest "hidden" FTL influences between these hidden variables, but there are other interpretations of QM which don't involve such hidden variables. Incidentally, if you want a simple explanation of why quantum statistics rule out any "local hidden variables" explanation, see my post #8 on this thread.

 

[Dale]

I guess I'll just fall in line behind those other spouters of nonsense--all of whom are much smarter than I, and have much better credentials for writing the nonsense that they do.

Appeal to authority is a fallacy, regardless of how smart and well credentialed the authorities. It is also an attempt to avoid an issue where you know you have taken an untenable position.

Everyone. There are many things which I know are real, but have never measured because they are not subject measurement.

I am going to call BS on this. There is nothing which anyone knows is real which has never been measured, certainly not if you are speaking scientifically. If you are not speaking scientifically then I would remind you about the forum rules that you agreed to. This is not a forum for philosophically or religiously motivated speculation.

More along the lines of our discussion, we don't know what we don't know.

First you assert some mysterious knowledge of reality independent of observation and then you talk about the limits of knowledge. That is a pretty rapid turn around, and I am much more supportive of this second position than your previous one.

there is (in my opinion) an undeniable distinction between reality and our measurement of reality.

If it is so undeniable then how come you can't even tell me clearly what you mean?

 

[GregAshmore]

Appeal to authority is a fallacy, regardless of how smart and well credentialed the authorities. It is also an attempt to avoid an issue where you know you have taken an untenable position.

I am going to call BS on this. There is nothing which anyone knows is real which has never been measured, certainly not if you are speaking scientifically. If you are not speaking scientifically then I would remind you about the forum rules that you agreed to. This is not a forum for philosophically or religiously motivated speculation.

Please define "science" so that I will know when I have crossed the boundary. (You will observe, I hope, that I have been careful not to actually cross the boundary as I understand it, in spite of the fact that you have not rigorously defined science.)

If any hint of philosophical speculation is out of order on this forum, then this thread is out of order. Simply define any discussion of reality as philosophical, and we can be done.

The problem with that approach is that an understanding of reality was a primary motivator for Einstein as he developed the theory. Not coincidentally, the theory challenges our intuitive conception of reality--this is no doubt why the theory is of interest to so many non-physicists. So I don't know how one would go about separating a discussion of reality from the discussion of relativity.

I have taken note of your earlier dismissal of the concept of reality--"whatever that is"--and thus have refrained from wasting my time trying to define it. I expected that no definition of reality would satisfy you.

Now I see that you do have at least a negative conception of reality--a thing cannot be known to be real if it has not been measured. On that much we can agree, at least in the lab.

First you assert some mysterious knowledge of reality independent of observation and then you talk about the limits of knowledge. That is a pretty rapid turn around, and I am much more supportive of this second position than your previous one.

If it is so undeniable then how come you can't even tell me clearly what you mean?

I contend that the universe exists apart from, and distinct from, our measurement of it. Thus, so long as our measurements give us an incomplete or distorted view of the universe, there exists some portion of reality which is unknown to us. In that context, the question as to whether the length contraction of SR is real or merely apparent ought to be clear enough.

You have chosen to dismiss such questions on the basis that no experiment can be devised which will answer them. This is a logical fallacy. Our inability to answer a question does not invalidate the question. Furthermore, your response assumes that our technology will never improve to the point where we can devise experiments which will answer such questions. It is precisely that over-confidence in our current understanding which motivates my questions.

In my view, our inability to answer questions as to how closely our conception of reality conforms to reality is a sign of weakness in our theories. I do not mean any disrespect for what has been accomplished; I do suggest that we should recognize that the residual ignorance leaves open the possibility that we are wrong to some degree.

Take the photon for example. What happens in the interval between the creation of a photon and its destruction? We have developed an equation which expresses the probability of the various modes of its destruction, but that equation is not the real photon. What is the reality of the photon's existence as it travels through spacetime? Or does it pass through spacetime in a sort of zombie state, becoming truly real only as it is destroyed? I can't answer these questions--but they are valid questions nonetheless.

What is to say that our ignorance of the nature of the photon's "being" will not manifest itself in some practical way as our technology advances? Is it wise to make sweeping claims about the nature of the universe on the basis that we cannot measure it? I don't think so.

How many particles can seethe on the head of a pin?

 

[Dale]

Please define "science" so that I will know when I have crossed the boundary. (You will observe, I hope, that I have been careful not to actually cross the boundary as I understand it, in spite of the fact that you have not rigorously defined science.)

Unlike you, when I use an important term I am always willing to provide a definition. Science is the body of knowledge obtained by using the scientific method. I can also explain the scientific method if you need, but the key elements are theories and experiments. If an idea is, in principle, not experimentally testable then it cannot be scientific and therefore does not belong on this forum.

The problem with that approach is that an understanding of reality was a primary motivator for Einstein as he developed the theory. Not coincidentally, the theory challenges our intuitive conception of reality--this is no doubt why the theory is of interest to so many non-physicists. So I don't know how one would go about separating a discussion of reality from the discussion of relativity.

Easy. Don't use terms you can't define.

Our inability to answer a question does not invalidate the question.

Maybe not, but your inability to even formulate the question certainly does invalidate it.

 

[GregAshmore]

Unlike you, when I use an important term I am always willing to provide a definition. Science is the body of knowledge obtained by using the scientific method. I can also explain the scientific method if you need, but the key elements are theories and experiments. If an idea is, in principle, not experimentally testable then it cannot be scientific and therefore does not belong on this forum.

Easy. Don't use terms you can't define.

Maybe not, but your inability to even formulate the question certainly does invalidate it.

I've taken a couple of days to think about this. Two thoughts:

1. The fact that I have not provided a clear positive definition of reality--"Reality is..."--is a consequence of my conception of reality. I start with the notion that our knowledge is limited, that there is more to the physical universe than we have been able to measure. Given that assumption, a comprehensive definition of physical reality is probably out of reach, because one cannot define positively what one does not know. The best I can do (at this point) is a tautology: Reality is what is. I'm not happy with that; I doubt that you are.

On the other hand, it is undeniable (in my view) that our knowledge is limited. That being the case, there is some portion of reality which is beyond us, at least for the moment.

2. The scientific community has a tendency to blur--or at times ignore--the line between aspects of a theory which are backed up by direct measurement and those which are inferred from those measurements. In other words, scientists tend to treat their theories as completely "real", forgetting that our knowledge of reality is limited.

Example: Bruce Schumm, in "Deep Down Things", says, "The charge of the electron, theorists tell us, is infinite. But they also tell us that no experiment you ever mount will measure that infinity." Yet several pages later he concludes the discussion with, "It must be right." To which I must respond, "Really?"

 

[AdrianZ]

I didn't read the whole topic and I'm not a theoretical physicist, but I think It's only an assumption. if I'm not making a mistake, Einstein based his special theory of relativity on two assumptions, the first one is the equivalence principle for inertial frames and the second one was the speed of light is invariant for all observers in inertial frames. the second assumption was added to escape from the idea of an existing ether. in fact equations of Einstein's special relativity had been developed by Lorentz many years before but because Lorentz believed in ether he gave wrong interpretations of the equations, Einstein said there is no need to insist on the existence of ether when it's not easy or maybe impossible to prove its existence therefore he added the 2nd assumption as an experimental FACT to develop his theory. I think asking why "the speed of light is constant for all inertial frames" is like asking why the equivalence principle is true which is not a question that you can ask from scientists. maybe philosophers would like to talk about such questions, but scientists don't.

 

[Hawkwind]

The value for the speed of light in vacuum is a historical artefact.
It is the consequence of an unfortunate choice of units. In better chosen systems of units accounting for the equivalence of space and time, c is without dimension having the value 1.

http://en.wikipedia.org/wiki/Natural_units

 

[ghwellsjr]

I didn't read the whole topic and I'm not a theoretical physicist, but I think It's only an assumption. if I'm not making a mistake, Einstein based his special theory of relativity on two assumptions, the first one is the equivalence principle for inertial frames and the second one was the speed of light is invariant for all observers in inertial frames. the second assumption was added to escape from the idea of an existing ether. in fact equations of Einstein's special relativity had been developed by Lorentz many years before but because Lorentz believed in ether he gave wrong interpretations of the equations, Einstein said there is no need to insist on the existence of ether when it's not easy or maybe impossible to prove its existence therefore he added the 2nd assumption as an experimental FACT to develop his theory. I think asking why "the speed of light is constant for all inertial frames" is like asking why the equivalence principle is true which is not a question that you can ask from scientists. maybe philosophers would like to talk about such questions, but scientists don't.

Lorentz did not give wrong interpretations of the equations but you are right that Einstein said there is no need to insist on the existence of ether but you are not right when you say that his 2nd assumption is an experimental FACT. It is not and never can be. It is an assumption which doesn't matter if it is true or not. What is an experimental fact is the round trip speed of light is a constant. The 2nd postulate is that both halves of that round trip are the same which can not be measured or demonstrated to be either true or false.

It is no more possible to disprove the existence of the ether than it is to prove the existence of the ether. In fact, what Einstein's second postulate says is that you can assume that ANY inertial frame IS the one and only absolute ether frame.

 

[matheinste]

Lorentz did not give wrong interpretations of the equations but you are right that Einstein said there is no need to insist on the existence of ether but you are not right when you say that is 2nd assumption is an experimental FACT. It is not and never can be. It is an assumption which doesn't matter if it is true or not. What is an experimental fact is the round trip speed of light is a constant. The 2nd postulate is that both halves of that round trip are the same which can not be measured or demonstrated to be either true or false.

It is no more possible to disprove the existence of the ether than it is to prove the existence of the ether. In fact, what Einstein's second postulate says is that you can assume that ANY inertial frame IS the one and only absolute ether frame.

The quote below is from Craig and Smith, Einstein, Relativity and Absolte Simultaneity, page 14. An intereting read if you can overlook the religeous agenda. These are purported to be Lorentz's own words regarding SR and the undecideable choice between the Lorentz and Einstein views of the ether.

""One thus comes to the same results as when one in agreement with Einstein and Minkowski denies the existence of the aether and the true time and treats all coordinate systems as equivalent. Which of the two modes of thought one may agree with is best left to the individual.""

(Lorentz 1934)

Matheinste.

 

[Dale]

I've taken a couple of days to think about this. Two thoughts:

1. The fact that I have not provided a clear positive definition of reality--"Reality is..."--is a consequence of my conception of reality. I start with the notion that our knowledge is limited, that there is more to the physical universe than we have been able to measure. Given that assumption, a comprehensive definition of physical reality is probably out of reach, because one cannot define positively what one does not know. The best I can do (at this point) is a tautology: Reality is what is. I'm not happy with that; I doubt that you are.

Thanks for making that effort here. Interestingly, in all of the conversations I have had with people about defining "reality" this is only the second time that someone has actually proposed a definition, so I do appreciate having a relatively productive discussion.

I am glad that you are not happy with that definition. The big problem scientifically is that there is no clear experiment that can be used to determine "what is", particularly in the context of how you want to use the term "reality". So your definition would be a philosophical definition rather than a scientific definition. That is fine but doesn't belong on this forum. The only definition I can come up with for "reality" is religious so it doesn't belong here either which is why I avoid the term on this forum so carefully.

2. The scientific community has a tendency to blur--or at times ignore--the line between aspects of a theory which are backed up by direct measurement and those which are inferred from those measurements. In other words, scientists tend to treat their theories as completely "real", forgetting that our knowledge of reality is limited.

Sure, but that is the nature of science and inductive reasoning. We make an experiment and then we generalize the results into a theory that predicts the outcome of experiments we have not yet performed. A theory that was simply a catalog of experimental results and made no predictions would be a pretty useless theory.

It certainly is possible that if we did the Hafele-Keating experiment in airplanes painted neon pink instead of white that we would get a different result. Should we therefore hesitate to make statements about time dilation on neon pink aircraft? Well, we have a theory that accurately describes the result obtained on white aircraft (and all other results obtained to date) and according to that theory the color of the paint for the aircraft will not change the result. So we have good reason to believe that we know the result for neon-pink aircraft even though it has not been tested.

 

[AdrianZ]

Lorentz did not give wrong interpretations of the equations but you are right that Einstein said there is no need to insist on the existence of ether but you are not right when you say that his 2nd assumption is an experimental FACT. It is not and never can be. It is an assumption which doesn't matter if it is true or not. What is an experimental fact is the round trip speed of light is a constant. The 2nd postulate is that both halves of that round trip are the same which can not be measured or demonstrated to be either true or false.

It is no more possible to disprove the existence of the ether than it is to prove the existence of the ether. In fact, what Einstein's second postulate says is that you can assume that ANY inertial frame IS the one and only absolute ether frame.

what I claimed is based on the book "Introduction to Special Relativity" by Robert Resnick. if Lorentz had given a correct interpretation of the equations then the credit of the theory would've gone to him not Albert Einstein. the results of experiments like the Michelson-Morley experiment, the Fizeau experiment and many others leaded to the development of different theories like like the FitzGerald-Lorentz contraction theory, but all of those theories failed to justify later experiments. the only theory that has been proved right in all experiments so far is Einstein's special theory of relativity which is also mathematical consistent and can be simplified to Newtonian mechanics when v/c approaches zero.

about our inability of proving/disproving the existence of Aether, I think you are right. that's why I used "maybe" in my sentence. but we have many experiments against the idea of Aether, including the Michelson-Morley experiment. therefore we can't deny the possibility of an existing ether, but we can surely deny the theories developed based on the ether postulate through experiments.

 

[GregAshmore]

Thanks for making that effort here. Interestingly, in all of the conversations I have had with people about defining "reality" this is only the second time that someone has actually proposed a definition, so I do appreciate having a relatively productive discussion.

I am glad that you are not happy with that definition. The big problem scientifically is that there is no clear experiment that can be used to determine "what is", particularly in the context of how you want to use the term "reality". So your definition would be a philosophical definition rather than a scientific definition. That is fine but doesn't belong on this forum. The only definition I can come up with for "reality" is religious so it doesn't belong here either which is why I avoid the term on this forum so carefully.

Sure, but that is the nature of science and inductive reasoning. We make an experiment and then we generalize the results into a theory that predicts the outcome of experiments we have not yet performed. A theory that was simply a catalog of experimental results and made no predictions would be a pretty useless theory.

It certainly is possible that if we did the Hafele-Keating experiment in airplanes painted neon pink instead of white that we would get a different result. Should we therefore hesitate to make statements about time dilation on neon pink aircraft? Well, we have a theory that accurately describes the result obtained on white aircraft (and all other results obtained to date) and according to that theory the color of the paint for the aircraft will not change the result. So we have good reason to believe that we know the result for neon-pink aircraft even though it has not been tested.

Granted that a theory which makes no predictions is of little value. However, the claims of scientists should be scientific--falsifiable in principle. I chose the example of infinite charge on the electron because even the claimants know that the claim is not falsifiable. The adherents to that part of the theory believe something to be real which cannot be measured.

Early on, I found such claims to be an impediment to acceptance of the theory. I felt that the whole body of work--which seems half crazy to the newbie anyway--was of the same character as those unscientific claims.

I'm headed back into Taylor-Wheeler. It's time for me to learn how to work with the theory, not just read about it.

 

[Dale]

the claims of scientists should be scientific--falsifiable in principle.

I agree completely.

I'm headed back into Taylor-Wheeler. It's time for me to learn how to work with the theory, not just read about it.

Always a good choice. Please let us know if you get stuck at some point.

 

[phyti]

Since the speed of light c, can be derived from the permittivity and permeability constants of the vacuum, why can't the constant c result from the properties of space?
GR models gravity as the effect of mass deforming space, and quantum theory deals with vacuum fluctuations.
Space is something by virtue of its properties.

 

[Buckethead]

... It is not and never can be. It is an assumption which doesn't matter if it is true or not. What is an experimental fact is the round trip speed of light is a constant. The 2nd postulate is that both halves of that round trip are the same which can not be measured or demonstrated to be either true or false.

It is no more possible to disprove the existence of the ether than it is to prove the existence of the ether. In fact, what Einstein's second postulate says is that you can assume that ANY inertial frame IS the one and only absolute ether frame.

This is one of the most interesting, succinct and profound comments I have read on this forum. If it could be stated more concisely I would create a huge banner in 1000 pt text and hang it on the wall in my office. Nice job!

 

[grav-universe]

This is one of the most interesting, succinct and profound comments I have read on this forum. If it could be stated more concisely I would create a huge banner in 1000 pt text and hang it on the wall in my office. Nice job!

Yes, I also agree that was very well put indeed.

 

[ghwellsjr]

what I claimed is based on the book "Introduction to Special Relativity" by Robert Resnick. if Lorentz had given a correct interpretation of the equations then the credit of the theory would've gone to him not Albert Einstein. the results of experiments like the Michelson-Morley experiment, the Fizeau experiment and many others leaded to the development of different theories like like the FitzGerald-Lorentz contraction theory, but all of those theories failed to justify later experiments. the only theory that has been proved right in all experiments so far is Einstein's special theory of relativity which is also mathematical consistent and can be simplified to Newtonian mechanics when v/c approaches zero.

about our inability of proving/disproving the existence of Aether, I think you are right. that's why I used "maybe" in my sentence. but we have many experiments against the idea of Aether, including the Michelson-Morley experiment. therefore we can't deny the possibility of an existing ether, but we can surely deny the theories developed based on the ether postulate through experiments.

I don't suppose you could provide exact quotes from your book that make statements such as "Lorentz gave a wrong interpretation of his equations" or "experiments have proven SR correct and other theories incorrect" or "we can deny ether based on experiments"? Please?

I like what you said in your first post about Lorentz believing in æther while Einstein said there was no need to insist on the existence of æther. In other words, Lorentz felt the need to always pick a reference frame in which he was never at rest with respect to the æther so that MMX would experience length contraction and time dilation (because there was little chance that he could be at rest in the absolute æther frame) while Einstein said its OK to always assume that MMX is at rest in the absolute æther frame and everyone else that is moving are the ones that are experiencing length contraction and time dilation. It's that difference that made Einstein stand out from all the others and why he deserves all the credit for Special Relativity.

But you should acknowledge that if Special Relativity is an accurate description of reality, and that it affirms every inertial reference frame as being exactly like an absolute æther rest frame, then it certainly cannot be used to deny that an absolute æther rest frame could exist (but known only to Mother Nature).

 

[yossell]

Having a definition of a word certainly is a precondition if you want to make meaningful statements using the word. If I were to try to discuss my opinion about "the distinction between farglmoger and our measurement of farglmoger" wouldn't you consider it necessary for me to define "farglmoger"?

If you can't define "real" then stop using the word. Otherwise you are literally writing nonsense.

Unless one allows circular definitions - which wouldn't help - I don't see how one can insist that all terms must be definable. Eventually, a chain of definitions must come to an end.

I don't know how to define away the logical constants `and', `or', `there is', `for all', nor the mathematical notion `set'.

 

[Dale]

Unless one allows circular definitions - which wouldn't help - I don't see how one can insist that all terms must be definable. Eventually, a chain of definitions must come to an end.

Sure, but I am not looking for a chain of definitions and would even be OK with a rather circular definition of reality as long as it were something that could be measured or otherwise determined experimentally. My objection isn't about constructing a minimal axiomatization of the word "reality" but rather constructing an operational definition that would be relevant to a scientific discussion instead of a philosophical or religious discussion.

 

[AdrianZ]

I don't suppose you could provide exact quotes from your book that make statements such as "Lorentz gave a wrong interpretation of his equations" or "experiments have proven SR correct and other theories incorrect" or "we can deny ether based on experiments"? Please?

I like what you said in your first post about Lorentz believing in æther while Einstein said there was no need to insist on the existence of æther. In other words, Lorentz felt the need to always pick a reference frame in which he was never at rest with respect to the æther so that MMX would experience length contraction and time dilation (because there was little chance that he could be at rest in the absolute æther frame) while Einstein said its OK to always assume that MMX is at rest in the absolute æther frame and everyone else that is moving are the ones that are experiencing length contraction and time dilation. It's that difference that made Einstein stand out from all the others and why he deserves all the credit for Special Relativity.

But you should acknowledge that if Special Relativity is an accurate description of reality, and that it affirms every inertial reference frame as being exactly like an absolute æther rest frame, then it certainly cannot be used to deny that an absolute æther rest frame could exist (but known only to Mother Nature).

according to the book I mentioned, Lorentz talked about length-contraction, not time dilation. if you claim Lorentz had come up with a consistent theory explaining time dilation and invariant light speed please provide resources verifying your claim.

I didn't say the existence of Aether can be denied, I said if we pose a theory based on the idea of Aether, we can do experiments to check the predictions of the theory and if it fails, the theory will be rejected. That's what we have done so far. what I meant was "all other theories based on the Idea of Aether before the SR had been rejected through experiments and Einstein's special theory of relativity was the only theory that successfully solved the contradictions between Maxwell's equations and Newtonian mechanics".

 

[Domenico Mico]

I appreciate the responses, although some are beyond my ken - IANAP. However, their net net still seems to be (1) it is because it is, and (2) that's the way the math requires it. For some reason, I don't have the same problem with time being flexible (two seemingly incongruent sides of the same coin?). It's all amusing as heck.

Hi, JoeShiner,
One more answer for you. This is how I see it. Once upon a time there was a monopole which, as Faraday wanted, generated an electric field which in turn generated a magnetic field which in turn etc... etc...
It appears that both of them at the starting line were full of energy and behaved like a bull at the gates with the end result that one second later, just before the end, we find them again, but this time they both are breathless. At the end of the run there it is: the surviving magnetic component is so tired that is unable to generate a further electric field and puts the final touch at the speed of light. The story ends, I think, with a somewhat undulating magnetic component joining, in its extremely weak conditions, his predecessors for the make-up of our expanding universe.

 

[harrylin]

what I claimed is based on the book "Introduction to Special Relativity" by Robert Resnick. if Lorentz had given a correct interpretation of the equations then the credit of the theory would've gone to him not Albert Einstein. the results of experiments like the Michelson-Morley experiment, the Fizeau experiment and many others leaded to the development of different theories like like the FitzGerald-Lorentz contraction theory, but all of those theories failed to justify later experiments. the only theory that has been proved right in all experiments so far is Einstein's special theory of relativity which is also mathematical consistent and can be simplified to Newtonian mechanics when v/c approaches zero.

about our inability of proving/disproving the existence of Aether, I think you are right. that's why I used "maybe" in my sentence. but we have many experiments against the idea of Aether, including the Michelson-Morley experiment. therefore we can't deny the possibility of an existing ether, but we can surely deny the theories developed based on the ether postulate through experiments.

Actually that is very inaccurate, as it's quite the opposite (but it's not your fault). Different book writers credited Einstein and Lorentz differently. And this is what Einstein admitted in 1907, discussing what then became known as the Lorentz-Einstein theory:

"We [...] assume that the clocks can be adjusted in such a way that
the propagation velocity of every light ray in vacuum - measured by
means of these clocks - becomes everywhere equal to a universal
constant c, provided that the coordinate system is not accelerated.
[..this] "principle of the constancy of the velocity of light," is at
least for a coordinate system in a certain state of motion [..] made
plausible by the confirmation through experiment of the Lorentz theory
[1895], which is based on the assumption of an ether that is
absolutely at rest".
- http://www.soso.ch/wissen/hist/SRT/E-1907.pdf

I will elaborate on that clarification by Einstein in a direct reply to the OP, as it is very helpful to understand the "WHY".

 

[harrylin]

I have puzzled over a couple of things relating to the speed of light as a constant to all observers. I fully recognize that it has been demonstrated to be so, and that those demonstrations have been confirmed by facts such as the existence and workability of GPS; however, these go much more to the FACT THAT the speed of light is a constant. I also recognize that, mathematically speaking (and I'm no math whiz), it MUST be a constant, since "somethin's got to give"; however, these do not satisfy my need to understand WHY the speed of light is a constant; or, put another way, HOW CAN IT BE that the speed is constant? I mean, everything else "gives" - the cars on the highway going toward one another or passing one another... and the trains, the planes, etc., but not light. HOW is it happening? Is light scrunching up or stretching out somehow as it needs to (but not as to speed [?!]), to the various and relevant observers?

As an aside - With reference to various experiments that have been conducted involving gravitational effects on time using atomic clocks aboard airplanes, if a quantum entanglement experiment was conducted involving photons that are "on" two different airplanes at two different gravitational states (and tied to atomic clocks, of course), what would be the result?

BTW, I am not a physicist and perhaps have no business at all sticking my nose in, but if some of you more well versed in these matters than I might take pity on me (and provide a bit of forgiveness of my ignorance, and benefit of the doubt, I'd be most appreciative). Thank you!

Hi Joe, several people have in part answered your question but if I did not overlook it, they forgot to mention clock synchronization.

First of all, in GPS the speed of your GPS receiver relative to a GPS radio signal is NOT constant, but exactly like you expect from cars and airplanes etc (in modern jargon, the closing velocity is c-v). In GPS, the Earth is a single system in which clocks everywhere are synchronized in agreement with each other.

What you probably can picture is Lorentz's model to explain light propagation. In that model, light is a wave in a medium and its speed is independent of the speed of the source. Moving objects in that medium slightly deform and clocks slightly slow down, but those are small effects that are not the main issue for replying your question that seems to focus on the one-way speed of light.

To measure the one-way speed, we have a light ray that propagates from one clock in the lab to another clock.

Funny enough, you can find any speed you like, depending on how you synchronize your clocks. In relativity, if you set up an independent measurement system then you typically use light or radio waves to synchronize your clocks; when you measure the same speed both ways, then you have synchronized your clocks!

Probably you can imagine that in a moving system, light takes longer in the forward direction than in the backward direction; and that by adjusting the clocks, you can make the measured speed equal in both directions. That speed would be very slightly less than c if the lab did not very slightly contract; those two effects exactly cancel.

With that explanation, light is not scrunching up or stretching out somehow, but objects are slightly affected; and the main explanation to your question is that clocks of independent systems are synchronized in such a way that the measured speed is again c.

I hope that this explains to you or some others "how it can be" that the speed that is measured in systems that move relative to each other, is constant.

Einstein clarified it as follows:

"We [...] assume that the clocks can be adjusted in such a way that
the propagation velocity of every light ray in vacuum - measured by
means of these clocks - becomes everywhere equal to a universal
constant c [..]
[this] "principle of the constancy of the velocity of light," is [..] made
plausible by the confirmation through experiment of the Lorentz theory
[1895], which is based on the assumption of an ether that is
absolutely at rest".
- http://www.soso.ch/wissen/hist/SRT/E-1907.pdf

And from my rather limited knowledge of quantum entanglement, the results should be independent of gravitational potential.