Actual earth measurement contradicts measurement predicted by special relativity

[ghwellsjr]

So, then it would be unambiguous to say "it is a frame-independent fact that one clock has physically aged less than the other when they reunite"?

 

[JesseM]

So, then it would be unambiguous to say "it is a frame-independent fact that one clock has physically aged less than the other when they reunite"?

I would say it's unambiguous, yes.

 

[Dale]

So, then it would be unambiguous to say "it is a frame-independent fact that one clock has physically aged less than the other when they reunite"?

I would get rid of the word "physically" here also. It doesn't add anything other than confusion.

 

[JesseM]

Humor aside, chronon's post does offer a good way of thinking about time dilation. Just like Chronon and his friend disagree as to who is making better progress, clocks in relative motion will disagree as to which one is runner slower.

We can even apply this analogy to the twin paradox. Let's assume that while Chronon kept walking in a straight line, his friend, at some point makes a 90 degree turn that has him heading towards chronon's path. Upon intersecting chronon's path, he then turns again to walk in the sam direction as chronon. Would not he and chronon agree that he is now behind chronon? ( even though on the second leg of his trip he would still maintain that he was making better progress than chronon)

Is this not similar to the way that someone can travel away from the Earth at some high fraction of speed and then return to find that he has aged less than everyone on Earth, even though while going out and coming back he determined that time on Earth went slower than it did for him?

I also expanded on this type of geometric analogy in [post=2972720]this post[/post], there are even more parallels with relativity than the ones that have been mentioned so far.

 

[ghwellsjr]

Dalespam, what unconfusing, unambiguous word would you use in place of physically?

 

[JesseM]

Dalespam, what unconfusing, unambiguous word would you use in place of physically?

Why does any word need to be in its place? Do you think there is some alternate frame-dependent notion of "aging" other than proper time, so that the statement "it is a frame-independent fact that one clock has aged less than the other when they reunite" would be too ambiguous?

 

[Dale]

Dalespam, what unconfusing, unambiguous word would you use in place of physically?

What do you mean by "physically"?

If you can answer that then use those words, if you cannot answer that (as I cannot in any useful way) then why would you say it at all?

EDIT: JesseM beat me to it! But his post is along the lines of what I was thinking. The statement was clear and unambiguous without the word "physically". It seems to be just an unnecessary and useless filler word in that statement.

 

[ghwellsjr]

There are plenty of people on this forum that think the idea of clocks running at different rates just because there is a relative speed between them is an illusion, an artifact, a measurement error, or otherwise not real. What do you tell them?

 

[JesseM]

There are plenty of people on this forum that think the idea of clocks running at different rates just because there is a relative speed between them is an illusion, an artifact, a measurement error, or otherwise not real. What do you tell them?

Can you define "illusion" and like terms? The rate at which any clock is running at is not frame-independent like the total elapsed time on a clock between two events on its worldline. Would you say that a frame-dependent quantity is "an illusion, an artifact, a measurement error, or otherwise not real"?

 

[yuiop]

There are plenty of people on this forum that think the idea of clocks running at different rates just because there is a relative speed between them is an illusion, an artifact, a measurement error, or otherwise not real. What do you tell them?

I agree with this sentiment because you often see people asking if the differential clock readings in the twins paradox would actually cause differential biological ageing, which of course it does (when you have a frame independent differential in elapsed proper times).

As a side question, would it reasonable to assume there always some ambiguity in the differential ageing of two clocks unless the initial and final measurements are made only when the clocks are right alongside each other?

For example, if the traveling twin (Bob) is 3/4 of the way home, the stay at home twin (Alice) might decide to take a trip and follow a path through spacetime such that when they eventually reunite, Alice could conceivably be the younger twin.

 

[Dale]

There are plenty of people on this forum that think the idea of clocks running at different rates just because there is a relative speed between them is an illusion, an artifact, a measurement error, or otherwise not real. What do you tell them?

I tell them that it is a measurable, frame-dependent effect. I try to let them decide how to categorize such things as illusion, or real, etc. since I don't feel comfortable with any such terms.

 

[ghwellsjr]

There are plenty of people on this forum that think the idea of clocks running at different rates just because there is a relative speed between them is an illusion, an artifact, a measurement error, or otherwise not real. What do you tell them?

Can you define "illusion" and like terms? The rate at which any clock is running at is not frame-independent like the total elapsed time on a clock between two events on its worldline. Would you say that a frame-dependent quantity is "an illusion, an artifact, a measurement error, or otherwise not real"?

I didn't say "the rate at which any clock is running at", which I agree is not frame-independent. I said "clocks running at different rates [with] a relative speed between them", which is frame independent (except in special cases), but more generally, I say, whenever a clock accelerates, its tick rate changes, which is a frame-independent truth, just like the clocks having different times on them when they re-unite. And so I say this is not an illusion, it is a frame-independent physical truth.

 

[Dale]

And so I say this is not an illusion, it is a frame-independent physical truth.

Then why not just say "frame-independent" instead of words like "illusion", "real", and "physical"? It is not only what you mean, but it is unambiguous.

 

[JesseM]

I didn't say "the rate at which any clock is running at", which I agree is not frame-independent. I said "clocks running at different rates [with] a relative speed between them", which is frame independent

I don't think it's a normal use of the terminology to say a verbal proposition is "frame independent", I've only ever seen physicists refer to frame-independent quantities like the elapsed proper time between two events on a given worldline. And even if you want to define "frame independent" more broadly, I'd say that for some fact to be frame-independent it must be true in all coordinate systems, not just inertial ones. You could construct a non-inertial coordinate system where two clocks have different coordinate velocities but are both ticking at the same rate relative to coordinate time.

but more generally, I say, whenever a clock accelerates, its tick rate changes, which is a frame-independent truth

Both criticisms above apply to this too.

just like the clocks having different times on them when they re-unite.

This example is unlike the first two in the sense that it's not vulnerable to either of my criticisms above. If you want to avoid my first criticism you can just talk about the amount of proper time that elapses on each clock's worldline between the two local meetings, and of course the second criticism doesn't apply either since even non-inertial coordinate systems agree about the proper time between two events on any given worldline.

 

[GregAshmore]

No, I wouldn't say that because "physically" is an ambiguous word.

I am not suggesting or implying anything, please don't read anything into it. I am simply trying to get GregAshmore to clarify his ambiguous question.

My question is indeed ambiguous. Some of that ambiguity will probably be cleared up by experience. However, in my opinion a good deal of the ambiguity is tightly bound to the nature of light.

The fundamental question is whether there is a difference between perception (measurement) and reality. In the case of length contraction, does a measured reduction in length imply an actual reduction in length?

It is easy enough to say that we don't know how to define reality apart from measurement. I appreciate that point of view, but cannot be satisfied with it philosophically. My dissatisfaction would become a very practical matter if you were to ask me to travel with you on a round trip to Canopus.

In ch. 4 of Taylor-Wheeler, discussing a trip to Canopus:

Dr. Bright sits back in his chair with a smile, obviously believing that he has disposed of all objections single-handedly. "Yes," we conclude, "about the reality of the effect there is no question."

This without a single experiment involving round trip high-speed travel. And with a number of unanswered questions even closer to home.

Take the muon experiments, for example. As impressive as the data are, we are still missing key bits of information. It is one thing to speculate about the readings on clocks in the muon frame; to have actual measurements is another. I understand that the numbers all work out on paper, and I have a deep sense (due to my own sluggishness, if nothing else) of the genius of Einstein in developing the theory. But without more data, I don't see that we can rule out the possibility of other explanations for our measurements.

Born spends over eleven pages discussing appearance and reality in SR. With regard to length contraction he says, "We do not mean to say that a body which is moving in a straight line with respect to an inertial system S "undergoes a change", although it actually changes its situation with respect to S." A few paragraphs later he concludes, "It is only the strip as a manifold of world points (events) which has physical reality, and not the cross section. Thus the contraction [the body seen in cross section] is only a consequence of our way of regarding things and is not a change of a physical reality."

Born's language is very clear, yet I doubt that he has escaped the ambiguity inherent in the subject.

 

[Dale]

The fundamental question is whether there is a difference between perception (measurement) and reality. In the case of length contraction, does a measured reduction in length imply an actual reduction in length?

I think you have only swapped the ambiguous word "physically" with the ambiguous words "reality" and "actual". Again, what sort of experiment could we perform to determine if something is "real", "physical", or "actual"?

It is easy enough to say that we don't know how to define reality apart from measurement. I appreciate that point of view, but cannot be satisfied with it philosophically.

It is not the goal of science to satisfy people's philosophical pre-conceptions about "reality" (whatever that means). The goal of science is to accurately predict the results of experiments. If you cannot be satisfied with that then you want something other than science.

But without more data, I don't see that we can rule out the possibility of other explanations for our measurements.

I agree, it is always possible to come up with an infinite number of explanations for any given set of measurements simply by adding things that cannot yet be measured.

 

[ghwellsjr]

There are plenty of people on this forum that think the idea of clocks running at different rates just because there is a relative speed between them is an illusion, an artifact, a measurement error, or otherwise not real. What do you tell them?

I tell them that it is a measurable, frame-dependent effect. I try to let them decide how to categorize such things as illusion, or real, etc. since I don't feel comfortable with any such terms.

With two identical clocks in relative motion, what effect is measurable but also frame-dependent?

 

[GregAshmore]

It is not the goal of science to satisfy people's philosophical pre-conceptions about "reality" (whatever that means). The goal of science is to accurately predict the results of experiments. If you cannot be satisfied with that then you want something other than science.

I agree with the sentence in bold. And yet, it is difficult to imagine that one's view of reality can be entirely separated from the theories and experiments of science. Certainly, Einstein's approach was that science and reality are closely intertwined, perhaps even synonymous. For my own part, I would be satisfied with a science that not only accurately predicts the outcome of experiments (in something more than a statistical chart) but also gives me confidence that I understand physical reality. I do not seek to have my preconceived notions of reality satisfied; I would simply like to have confidence that I understand what reality is. If you are not so motivated, that's fine.

I agree, it is always possible to come up with an infinite number of explanations for any given set of measurements simply by adding things that cannot yet be measured.

Actually, I have not proposed any non-standard values for the physical characteristics which we have not yet measured. What I have suggested is that when and if we do make those measurements, the results may surprise us. If that happens--and it wouldn't be the first time such a thing has happened--we will have to revise our theories. It seems to me that it would be wise to leave a little wiggle room when we speak of such things as round trips to Canopus in a single lifetime.

Just a thought, as an example. What confidence do we have that large bodies will maintain their integrity as they approach light speed?

 

[ghwellsjr]

I'd say that for some fact to be frame-independent it must be true in all coordinate systems, not just inertial ones. You could construct a non-inertial coordinate system where two clocks have different coordinate velocities but are both ticking at the same rate relative to coordinate time.

I was thinking of the situation where one clock never accelerates and a second clock accelerates in an arbitrary manner and I claim the second clock is experiencing a change in its tick rate while it is accelerating. Are you suggesting that because we can use the non-inertial frame in which the second clock is always at rest, that it therefore experiences no change in its tick rate? If so, what do you then say about the first clock's tick rate? If not, then are you saying the second clock's tick rate is changing?

 

[ghwellsjr]

Just a thought, as an example. What confidence do we have that large bodies will maintain their integrity as they approach light speed?

They could if nothing got in their way but unfortunately, the universe is full of particles which will make them feel like they are being subjected to machine gun fire and which will destroy them. Sorry.

 

[JesseM]

I was thinking of the situation where one clock never accelerates and a second clock accelerates in an arbitrary manner and I claim the second clock is experiencing a change in its tick rate while it is accelerating. Are you suggesting that because we can use the non-inertial frame in which the second clock is always at rest

What do you mean "the" non-inertial frame in which the second clock is at rest? There are an infinite number of them! Take a spacetime diagram drawn from the perspective of an inertial frame, draw on some arbitrary curves to treat as surfaces of simultaneity and some other arbitrary curves crisscrossing the first set to treat as curves of constant position coordinate, resulting in some sort of distorted grid, and that can be the basis of a valid non-inertial coordinate system (see for example the final animated diagram near the bottom of this page). So you can always pick one where the surfaces of simultaneity are defined so that if a surface passes through the worldline of clock #1 when it reads a time of T, then that same surface also passes through the worldline of clock #2 when it reads a time of T. And you can also draw some curves of constant position coordinate that coincide with the worldlines of the two clocks for any section of the worldlines where they don't cross. So, the clocks will each be at rest in this coordinate in those sections of their worldlines, and they will each show the same reading at any time-coordinate in those sections.

 

[Dale]

For my own part, I would be satisfied with a science that not only accurately predicts the outcome of experiments (in something more than a statistical chart) but also gives me confidence that I understand physical reality.

Then you don't want science, you want religion or philosophy. Science has no means to interrogate "physical reality" other than through the outcome of experiments.

What I have suggested is that when and if we do make those measurements, the results may surprise us. If that happens--and it wouldn't be the first time such a thing has happened--we will have to revise our theories.

Certainly, and when such data is acquired then we will revise our theories. No big deal. As you say, it has happened several times before. That is what science does.

In the meantime we cannot scientifically choose one particular theory with untested "wiggle room" over another. As mentioned earlier, there are an infinite number of such wiggle parameters we could add, and all have the same experimental support. That is why we apply Occham's razor and use the theory with the least wiggle room.

 

[Dale]

With two identical clocks in relative motion, what effect is measurable but also frame-dependent?

Well, to have a pair of frames you need not just two identical clocks in relative motion, but two systems of synchronized clocks in relative motion. Then the rate of the other clocks is frame-dependent and measurable.

 

[ghwellsjr]

So you can always pick one where the surfaces of simultaneity are defined so that if a surface passes through the worldline of clock #1 when it reads a time of T, then that same surface also passes through the worldline of clock #2 when it reads a time of T. And you can also draw some curves of constant position coordinate that coincide with the worldlines of the two clocks for any section of the worldlines where they don't cross. So, the clocks will each be at rest in this coordinate in those sections of their worldlines, and they will each show the same reading at any time-coordinate in those sections.

If you are saying that we must have several different such non-inertial frames, separated by when their worldlines cross, then what are saying about the clocks in terms of their aging rates and times when we have to switch from one frame to the next?

 

[ghwellsjr]

Well, to have a pair of frames you need not just two identical clocks in relative motion, but two systems of synchronized clocks in relative motion. Then the rate of the other clocks is frame-dependent and measurable.

But I thought all the synchronized clocks in each frame were defined to have the same time on them because we cannot measure the one-way speed of light.

 

[JesseM]

If you are saying that we must have several different such non-inertial frames, separated by when their worldlines cross,

I don't quite understand what you mean by "separated by when their worldlines cross". The point about worldline crossing is that obviously you can't have a non-inertial frame that says they remain a constant nonzero distance apart even at the point where their worldlines cross (since all frames, inertial and non-inertial, agree about local events like crossings of worldlines), but beyond that, if you pick any arbitrary event A after the crossing on the first worldline, and another arbitrary event B after the crossing on the second worldline, you can always find a non-inertial frame where both clocks are at rest and ticking at the same rate relative to coordinate time starting at the time of A and B.

then what are saying about the clocks in terms of their aging rates and times when we have to switch from one frame to the next?

Not sure I understand this either, why would we "have to" switch from one frame to another? We can derive the values of all frame-independent quantities (like readings on any measuring device) using a single frame. Obviously we can re-analyze the same situation in multiple frames if we wish, the different frames will make the same predictions about frame-independent quantities but may (or may not) give different answers about frame-dependent quantities like the tick rates of clocks relative to coordinate time.

 

[Dale]

But I thought all the synchronized clocks in each frame were defined to have the same time on them because we cannot measure the one-way speed of light.

Yes, and the result of using this definition (the Einstein synchronization convention) is frame variant. This is known as the relativity of simultaneity. I assume that we have no disagreement about that and that you understand the topic well.

 

[Passionflower]

I was thinking of the situation where one clock never accelerates and a second clock accelerates in an arbitrary manner and I claim the second clock is experiencing a change in its tick rate while it is accelerating.

That is correct.

If two clocks A and B at at relative rest at event X and B accelerates away while A remains inertial then B runs slower wrt A.

 

[JesseM]

That is correct.

If two clocks A and B at at relative rest at event X and B accelerates away while A remains inertial then B runs slower wrt A.

Only if by "runs slower wrt A" you mean "runs slower in the inertial frame where A is at rest". Since we're discussing frame-dependent vs. frame-independent facts on this thread, it should be pointed out that even if we restrict the discussion to inertial frames, there will be frames where B is running faster than A after B accelerates.

 

[ghwellsjr]

Only if by "runs slower wrt A" you mean "runs slower in the inertial frame where A is at rest". Since we're discussing frame-dependent vs. frame-independent facts on this thread, it should be pointed out that even if we restrict the discussion to inertial frames, there will be frames where B is running faster than A after B accelerates.

What do you mean "the" inertial frame where A is at rest? There are an infinite number of them!

Sorry--I just couldn't help myself.

 

[Passionflower]

Only if by "runs slower wrt A" you mean "runs slower in the inertial frame where A is at rest". Since we're discussing frame-dependent vs. frame-independent facts on this thread, it should be pointed out that even if we restrict the discussion to inertial frames, there will be frames where B is running faster than A after B accelerates.

I am only talking about clock A and B. I did not mention clock C, D, E and F right?

 

[GregAshmore]

They could if nothing got in their way but unfortunately, the universe is full of particles which will make them feel like they are being subjected to machine gun fire and which will destroy them. Sorry.

And yet T-W assure their students that a 20-year round trip to Canopus is a no-brainer.

Actually, I don't know of any experimental evidence to support your assertion that they could if nothing got in their way.

 

[JesseM]

What do you mean "the" inertial frame where A is at rest? There are an infinite number of them!

Sorry--I just couldn't help myself.

OK, but it's a normal convention to talk about "the" inertial frame where a given inertial object is at rest, unlike with non-inertial frames. I suppose the reason is that although you have a choice of where to place the origin and how to orient the spatial axes, this will make no difference to most of the frame-dependent quantities we're interested in like speed and rate of time dilation.

 

[JesseM]

I am only talking about clock A and B. I did not mention clock C, D, E and F right?

I am talking about coordinate systems, not physical objects. You are free to use any coordinate system you like to analyze a problem, it makes no difference whether or not any of the physical objects (like clocks) are at rest in the coordinate system you have chosen. You are no more limited to coordinate systems where one of the objects is at rest than you are limited to coordinate systems where the spatial origin coincides with one of the objects.

 

[GregAshmore]

Then you don't want science, you want religion or philosophy. Science has no means to interrogate "physical reality" other than through the outcome of experiments.

Certainly, and when such data is acquired then we will revise our theories. No big deal. As you say, it has happened several times before. That is what science does.

In the meantime we cannot scientifically choose one particular theory with untested "wiggle room" over another. As mentioned earlier, there are an infinite number of such wiggle parameters we could add, and all have the same experimental support. That is why we apply Occham's razor and use the theory with the least wiggle room.

But we needn't pretend that we know more than we do--and a lot of that goes on. A good example is the assertion by T-W there can be no question about the feasibility in principle of a round trip to Canopus in 20 years.

Not only do we assert the truth of things we have never measured, we assert the non-existence of things based on measurements which we don't understand. Here I have in mind the denial of cause for quantum events, even though we are not able to directly measure the phenomena about which we make such a sweeping assertion.