Measurement Problem in Einstein's Relativity

[Varon]

In Quantum Mechanics, there are measurement problems and you have many interpretations like Copenhagen, Many Worlds, de Broglie/Bohm mechanics, etc. Are there also measurement problems in Einstein Special Relativity for instance? Can't we consider the following:

Spacetime in Relativity is like Hilbert Space in QM.
In QM, you have the problem of how definite outcomes or collapse from Hilbert Space occurs.
In SR, maybe the equivalent is how "the "observer" who is forced by his concept of "now" to create a coordinate system separating experience into space and time."? I got this idea from our poster Rap. According to him:

"I think there is a measurement problem, even in special relativity. Special relativity presents a bunch of particles, world lines, etc. which exist in a "frozen" spacetime, and puts constraints on the spacetime geometry of these world lines. Then comes the "observer" who is forced by his concept of "now" to create a coordinate system separating experience into space and time. To predict your or any other observer's experience, move yourself or the hypothetical observer along their world line at the speed of light. This whole measurement scenario brings in elements outside of special relativity, including the vague idea of "consciousness", similar to the situation in QM. How can there be "motion" when time has been subsumed into spacetime?

Also, what if we carry the "Wigner's friend" problem to SR? We conclude that the observer we are observing has no "choice", their development in time is determined. Do I, the outside observer, have choice then? This is "Laplace's demon" which exists in classical physics as well. Is there a counterfactual definiteness problem in SR, ignoring QM?"

~~~~~~~~~~~~~~~~~~~

What do you think? If you don't think there is any measurement problem in SR unlike QM. State your reasons why. Also please elaborate if you think there is also measurement problem in SR. Thanks.

 

[PAllen]

In Quantum Mechanics, there are measurement problems and you have many interpretations like Copenhagen, Many Worlds, de Broglie/Bohm mechanics, etc. Are there also measurement problems in Einstein Special Relativity for instance? Can't we consider the following:

Spacetime in Relativity is like Hilbert Space in QM.
In QM, you have the problem of how definite outcomes or collapse from Hilbert Space occurs.
In SR, maybe the equivalent is how "the "observer" who is forced by his concept of "now" to create a coordinate system separating experience into space and time."? I got this idea from our poster Rap. According to him:

"I think there is a measurement problem, even in special relativity. Special relativity presents a bunch of particles, world lines, etc. which exist in a "frozen" spacetime, and puts constraints on the spacetime geometry of these world lines. Then comes the "observer" who is forced by his concept of "now" to create a coordinate system separating experience into space and time. To predict your or any other observer's experience, move yourself or the hypothetical observer along their world line at the speed of light. This whole measurement scenario brings in elements outside of special relativity, including the vague idea of "consciousness", similar to the situation in QM. How can there be "motion" when time has been subsumed into spacetime?

Also, what if we carry the "Wigner's friend" problem to SR? We conclude that the observer we are observing has no "choice", their development in time is determined. Do I, the outside observer, have choice then? This is "Laplace's demon" which exists in classical physics as well. Is there a counterfactual definiteness problem in SR, ignoring QM?"

~~~~~~~~~~~~~~~~~~~

What do you think? If you don't think there is any measurement problem in SR unlike QM. State your reasons why. Also please elaborate if you think there is also measurement problem in SR. Thanks.

I think this is nonsense. To the extent you care to believe there is measurement problem in quantum mechanics, it revolves around how a particular state is selected (or observed) from a superposition of states. Classical SR and GR (as opposed to quantum field theory) has nothing remotely like this. An observer, or measurement doesn't change anything. Positing no observers or measurements, changes nothing about the model.

More specifically, no observer is forced to use any coordinate system. No measurement depends on either the coordinate system or the presence of the observer. There is no 'Wigner's friend' issue at all.

If you were more specific, a more specific answer could be given. But what you say just seems completely silly to me.

 

[bobc2]

Interesting questions you raise, Varon. If you could sharpen your picture of the universe/space-time (or 4-D space) model you have in mind there might be some attempts to respond to your questions.

 

[Varon]

I think this is nonsense. To the extent you care to believe there is measurement problem in quantum mechanics, it revolves around how a particular state is selected (or observed) from a superposition of states. Classical SR and GR (as opposed to quantum field theory) has nothing remotely like this. An observer, or measurement doesn't change anything. Positing no observers or measurements, changes nothing about the model.

More specifically, no observer is forced to use any coordinate system. No measurement depends on either the coordinate system or the presence of the observer. There is no 'Wigner's friend' issue at all.

If you were more specific, a more specific answer could be given. But what you say just seems completely silly to me.

Oh. Maybe it is not a measurement problem exactly. But more of a problem of how the Spacetime translate into Space and Time in our world. I took the analogy of Hilbert Space collapsing states into definite position and momentum as Spacetime collapsing into definite Space and Time. That's it. So how does Spacetime collapse into our Space and Time. Maybe there are different interpretations of this. I think Lee Smolin has one where spacetime is more like events or something (i forgot exactly what he said).

 

[PAllen]

Oh. Maybe it is not a measurement problem exactly. But more of a problem of how the Spacetime translate into Space and Time in our world. I took the analogy of Hilbert Space collapsing states into definite position and momentum as Spacetime collapsing into definite Space and Time. That's it. So how does Spacetime collapse into our Space and Time. Maybe there are different interpretations of this. I think Lee Smolin has one where spacetime is more like events or something (i forgot exactly what he said).

Ok, that's getting better. There is an arbitrary character to how spacetime is divided into space and time. However, unlike QM there is no change (if you believe in wave function collapse) or appearance of change (if you don't) in making a choice. In the real world, making a choice means choosing conventions for simultaneity and distance measurement (for example). But nothing changes from these choices. You could make two at the same time and compare them, choose one today another tomorrow, nothing changes (or appears to change) as in quantum mechanics. Your failure to choose any convention or make any measurement also doesn't change anything. So I continue to see that as very different from quantum mechanics.

 

[Dale]

It doesn't collapse. We just draw different lines on it and label them "here" and "there" or "now" and "then".

 

[Varon]

Ok, that's getting better. There is an arbitrary character to how spacetime is divided into space and time. However, unlike QM there is no change (if you believe in wave function collapse) or appearance of change (if you don't) in making a choice. In the real world, making a choice means choosing conventions for simultaneity and distance measurement (for example). But nothing changes from these choices. You could make two at the same time and compare them, choose one today another tomorrow, nothing changes (or appears to change) as in quantum mechanics. Your failure to choose any convention or make any measurement also doesn't change anything. So I continue to see that as very different from quantum mechanics.

Ok. So how does Spacetime become Space and Time in our world? While sitting in this chair typing this message in the computer. I don't move in geodesics or experience light speed velocity at the worldline.

 

[bobc2]

Ok. So how does Spacetime become Space and Time in our world? While sitting in this chair typing this message in the computer. I don't move in geodesics or experience light speed velocity at the worldline.

That seems like a rather metaphysical or philosophical question. How would you answer that for yourself? And how do you know that you are not experiencing light speed motion along your worldline? Does physics (or do physicists) really try to answer that?

 

[Dale]

So how does Spacetime become Space and Time in our world?

Somebody arbitrarily draws an imaginary set of lines in spacetime and says "that is space" or "that is time".

 

[PAllen]

Ok. So how does Spacetime become Space and Time in our world? While sitting in this chair typing this message in the computer. I don't move in geodesics or experience light speed velocity at the worldline.

It doesn't become anything. How does the world become kilometers or miles? You choose, and can choose both, if you want. No change to accessible reality occurs. Similarly, you can choose, simultaneously, to report measurements 'earth centered', 'sun centered', or 'CMB centered'. These will foliate space and time slightly differently, but all are conventions that you can simultaneously choose or not. Further, the outcome of any measurement or what you 'see with your eyes' eyes is unaffected by any of these choices.

I think the key thing to focus on is that, classically, in SR and GR, there is only one possible outcome to any measurement. In QM, the evolution of accessible reality following a measurement depends on the outcome of the measurement, which was in principle un-determined; and further, it is not completely settled what constitutes a measurement.

 

[ZealScience]

I think in Relativity, space-time is one thing is because of that measuring space without time is meaningless, and wise-versa. Space time are different, though they are related to each other closely. Like one would die 100 years later, but one would not die walking 100 km south. Time change is associated with entropy increase, but space is clearly not. So I think what make "experience into space and time" you asked, is because that they have different properties really.

 

[Varon]

How about Gravity. Time is so different from Space. Yet they were united by Einstein and Minkowski... and latter curved by the EFE equations.. then came an emergence Gravity. This is elegant mathematically.. but we experience time passes by as we walk across space. We can't perceive this spacetime curvature as actually happening. So what's a good way to visualize or imagine it as actually happening if you are trying to convince me that Spacetime is not just mathematical tool but actually our world where we walk right in the manifold.

 

[ZealScience]

How about Gravity. Time is so different from Space. Yet they were united by Einstein and Minkowski... and latter curved by the EFE equations.. then came an emergence Gravity. This is elegant mathematically.. but we experience time passes by as we walk across space. We can't perceive this spacetime curvature as actually happening. So what's a good way to visualize or imagine it as actually happening if you are trying to convince me that Spacetime is not just mathematical tool but actually our world where we walk right in the manifold.

I said that they are united is because that they cannot leave each other, so uniting the two is just summing then up by their relationships. I think what makes them different is that there is no clear recognition of the relationships between them in our conciousness, the relationships are so trivial, that we can never detect them on earth, and humans evolve to adapt to environment. There is no point in recognising such miniscule difference. Suppose that speed of light is 100km/h or imagine that people are living on black holes (if possible of course), where the effect is enormous, I guess there would be a better interpretation of them by our minds.

 

[PAllen]

How about Gravity. Time is so different from Space. Yet they were united by Einstein and Minkowski... and latter curved by the EFE equations.. then came an emergence Gravity. This is elegant mathematically.. but we experience time passes by as we walk across space. We can't perceive this spacetime curvature as actually happening. So what's a good way to visualize or imagine it as actually happening if you are trying to convince me that Spacetime is not just mathematical tool but actually our world where we walk right in the manifold.

These are completely different questions. I have no interest in convincing you of the reality spacetime, as that is philosophy, not physics. You can (and a number of major physicists have: Fock, Weinberg sometimes) use and interpret GR with no notion of curved spacetime. For that matter, it is unprovable whether either space or time 'really exist'. Space, especially, can be argued to be a construct of learned mental processing (I experience only a sequence of visual images and tactile sensations; anything more is derived).

What I don't see is any analog of the QM measurement issue in SR or GR. Stating it slightly differently, there are genuine differences of opinion about how a system including a 'classical' measuring device should be analyzed as a whole (in isolation). There is no equivalent issue or disagreement in SR or GR.

 

[PAllen]

As the OP seems to broadening the issue, an anticipatory response:

1) Are there philosophic and interpretational issues in SR and GR? Yes. Are there unsolved theoretical issues in classical GR? Yes.

2) Is there any issue that corresponds in any meaningful way to measurement issues in QM? Not that I can see, and no plausible case for such a correspondence has been made so far on this thread.

 

[Varon]

These are completely different questions. I have no interest in convincing you of the reality spacetime, as that is philosophy, not physics. You can (and a number of major physicists have: Fock, Weinberg sometimes) use and interpret GR with no notion of curved spacetime. For that matter, it is unprovable whether either space or time 'really exist'. Space, especially, can be argued to be a construct of learned mental processing (I experience only a sequence of visual images and tactile sensations; anything more is derived).

What I don't see is any analog of the QM measurement issue in SR or GR. Stating it slightly differently, there are genuine differences of opinion about how a system including a 'classical' measuring device should be analyzed as a whole (in isolation). There is no equivalent issue or disagreement in SR or GR.

You said "it is unprovable whether either space or time 'really exist'." This means it is possible Spacetime is just emergence of something. Now if you use the law of that more primary theory. Then one can say tele transport objects from say Asia to United States in 2 seconds. That is. Right now. Quantum Teleportation only transfer information. It doesn't teleport the whole particle but just information. So it is possible that using a more primary theory we still haven't understood. One can teleport the entire particle to other side of world. Right? Or is there a theorem that categorically state this is impossible no matter what the more primary theory is because it has to always use Spacetime?

 

[Matterwave]

No theory can make blanket statements on what can or cannot be said in a more fundamental theory. Indeed, what about the possibility that this "theory of everything" negates the act of observation itself, and thereby invalidates hundreds of years of experimental tests? Such thoughts not really productive to entertain within the realm of current physics.

 

[Dale]

We can't perceive this spacetime curvature as actually happening.

Sure you can. Any time you see the tide come in you see space-time curvature actually happening.

You are saying a lot of nonsense. Just because you are confused about relativity doesn't mean the theory is flawed.

 

[Varon]

Sure you can. Any time you see the tide come in you see space-time curvature actually happening.

You are saying a lot of nonsense. Just because you are confused about relativity doesn't mean the theory is flawed.

I mentioned all this because I was reading particle physicist Victor Stenger book called The Fallacy of Fine Tuning. He mentioned inside:

"Most people, including most physicists, believe that the models and "laws" of physics directly described reality. That is, the objects in these models actually exist outside the paper they are written on and the concepts they contain refer directly to true aspects of the world.

further he said:

"Since the spacetime model is a human invention, so must be the dimensionality of space-time. We choose it to be three because it fits the data. In the M-theory we choose it to be eleven. We use whatever works, but that does not mean reality is exactly that way in one-to-one correspondence.

The same thing can be said about the geometry of space. That's our invention, too. It happens to be non-Euclidean in Einstein's beautiful model, but perhaps someday a simpler, Euclidean model will be found with gravity treated in a different way"

~~~~~~~~~~~~~

Victor Stenger is a retired particle physicist. It is after his his book that I got the idea Spacetime being curved and all that may be just mathematical trick and someday.. Euclidean model will be found that may explain all the trick. Bottomline is. It seems divided amongst physicists whether Spacetime correspond to reality or just human invention and math trick. Right? Or are you saying Victor Stenger is wrong? Pls. elaborate.

 

[Dale]

It seems divided amongst physicists whether Spacetime correspond to reality or just human invention and math trick.

Luckily, nature doesn't seem divided on the subject, and hers is the only vote that counts.

If you can come up with an experiment to test whether "spacetime correspond to reality" or is just a "math trick" then you would have something scientifically worthwhile. Otherwise all you have is philosophical whining.

 

[PAllen]

Overdue for this to be moved to philosophy?

 

[Dale]

I agree, but I do feel bad that the philosophy forum seems to be a dumping ground for all of the useless threads.

The reason that these "reality or math" threads bother me is that whatever the ultimate theory of everything is, it will have to reduce to relativity in the appropriate limits. So relativity is here to stay, one way or another, just as classical mechanics hasn't disappeared after more than a century of relativity.