How do we know some particles don't exist until measured?

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  • #51
If physicists don't deal with reality than neither to chemists and biologists, which is of course nonsense. The natural sciences deal with reality, i.e., with the objectively observable facts of nature.

Psychology of course does not deal with reality but studies all kinds of imaginations of the human mind. The part of the natural sciences most related to psychology is neurology and brain research.
Hello vanhees:

I think you misread my posts.

I was qualifying my statement about physics being the study of reality... which needed correction as physics studies reality at certain levels (chemists are scientists who study reality at the level of chemistry, biologists are scientists which study reality at the level of biology, etc).

I tend to agree with your sentiments, however, since human beings are real, and if one generously allows that at least SOME psychologists are scientists, they study that part of reality which is human psychology. The fact that humans have imagination or are even sometimes psychotic, etc. is of course some part of reality which scientists want to understand, and those scientists are called psychologists.

Cheers!
 
  • #53
zonde
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Psychology of course does not deal with reality but studies all kinds of imaginations of the human mind.
Responses given by individuals in controlled experimental settings are "objectively observable facts of nature".
 
  • #54
vanhees71
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Point taken, but would you take psychology as a natural science? I'd be more modest and say that the natural sciences are still not advanced enough to claim that, although modern brain research is quite far already in this direction.
 
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Responses given by individuals in controlled experimental settings are "objectively observable facts of nature".
I don't think research psychologists would describe self-reports this way at all. Self reports by subjects participating in a psychological study must first be recorded or transcribed in some fashion; this immediately distances them from the original context of their utterance, thus introducing the possibility of error - e.g. misrepresentation, over-simplification of context, typos, etc. Once transcribed, self reports must then be scored or otherwise interpreted vis-a-vis the study proposal. Interpretations themselves are liable to being wrong & are often disputed by persons critiquing the study, who often point to alternative models or explanations. Also, statistics are typically brought to bear as part of interpretation, which introduces a further level of dispute & general messiness. And a further problem is that the "controlled" lab conditions may themselves be a source of error, e.g. subjects may give dishonest answers in an effort to please the experimenters.

One consequence of all this is that replication is said to be much more difficult in the soft sciences, including psychology, than it is in the hard sciences. This would further confirm that self-reports as gathered in a psychology experiment can't be considered equivalent to the sort of data typically gathered in a physics experiment.
 
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  • #56
zonde
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Point taken, but would you take psychology as a natural science? I'd be more modest and say that the natural sciences are still not advanced enough to claim that, although modern brain research is quite far already in this direction.
I suppose that there are topics in (cognitive) psychology that are rather close to "hard science". But I agree that in general psychology is "soft science".
I don't know about particular examples of modern research in psychology so I can't give more than just opinion.
 
  • #57
zonde
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I don't think research psychologists would describe self-reports this way at all.
Yes, I would not associate self-reports with "hard science". But what I had on mind was rather responses that require very little/no interpretation. Something like memory test.
 
  • #58
Boing3000
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Although I generally agree with your general opinion on "reality" I have to disagree with the fact you present that as rational. It is a choice, a belief, a leap of faith.

Reality exists, independent of anyone's thoughts or wishes,
As already mentioned, this is kind of circular. You present here an axiom, a definition for reality, which is fine. But by that very same definition reality is absolutely dependent on everyone thoughts and wishes to use observations and not suppositions or wishful thinking.
So if you don't see the moon, don't ascribe it properties. It would be as foolish as attributing it some "nonexistence". That's all there is to it, rationally speaking.
Also, even if you observe it, be wary, because that image is one second old, so there is a possibility some alien prankster may have stolen the moon already, or that all this is just in "your head" matrix (the movie)-like.
So you can philosophically be rational only at the cost off non-denying obvious possibilities (which makes great sci-fi material by the way)

and although it may be difficult to describe reality. "non-existence" simply not the way to characterize anything.
But "unknown" is the only way to describe "reality", as this great prankster explains remarkably

Whatever a particle is, whatever properties it has at various times of measurement and non-measurement does not negate that it is what it is, or that it IS, (until such time as it isn't such as annihilation ... but then it changes form into other particles..).
But this is the question: "what is a particle ?". Whatever is not a valid word for ascribing it properties, unkown is better. What QFT tells us is that it correspond to probability wave into some multidimensional space made of particle fields. Yet, we don't observe that. We never observe that. We even observe that some of those properties are shared between distant(entangled) particle... So whatever this is, it still is a great observed mystery.

And particle can spawn into existence just by taping in the gravitational field energy (like in stars, but apparently also from the even horizon of black hole). This kind of energy in "classic" field is quite diffuse, so I suppose you would agree that those "transformations" are also pretty weird.
 
  • #59
Boing3000
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There's also nothing in QT leading to the conclusion that unobserved entities don't exist.
What bothers me more is that everybody in the physics community (except maybe the Bohm'ian) seems to accept that reality is stochastic (not chaotic)

OK, if I had to put the life of my cat on the line, but having to choose some pixel of the screen (of a x-slit experiment) where to put my photon receptor triggering poison, I would certainly use QM to put it where the waves cancel.

Problem is, there is one photon, and I like my cat, I would like to be more certain than this...
 
  • #60
Paul Colby
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What bothers me more is that everybody in the physics community (except maybe the Bohm'ian) seems to accept that reality is stochastic (not chaotic)
It is what is observed to be the case, no? Philosophy typically doesn't handle limiting cases very well which is why discussions like never really end satisfactorily. Day to day life is the limit of many stochastic processes involving huge numbers of degrees of freedom. This was true even classically with real materials at real temperatures. The idealized Newtonian view is gone for good and I do not morn it.
 
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  • #61
Boing3000
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It is what is observed to be the case, no?
Who knows ? That's the gist of my question. They are somewhat indistinguishable from afar. But even though there are mathematical tools/theories to kind of detect some sort of chaos from "noise", I haven't read a lot of paper that try to do that on "equally" prepared quantum state.

Day to day life is the limit of many stochastic processes involving huge numbers of degrees of freedom.
My take on the subject is that very simple and totally linear system are totally unpredictable. In fact everything in the universe seems to be chaotic, the only exception being QM (hmm sorry) non-existing-collapase". My question is: could quantum "dice" be attributed to some kind of inner/hidden chaotic process whose only visible "tip of the iceberg" would be "probability", while in fact it could be for example be the double pendulum tip x-position (as a basic analogy).
I can't remember how string theory was suppose to reproduce QFT, nor if all it's 11+ dimensions was in "real" space, and not "probability/Hilbert" space.

This was true even classically with real materials at real temperatures. The idealized Newtonian view is gone for good and I do not morn it.
My neither. And I don't know what Newton has to do with that, but I think he would have had no problem with a Planck value being real... because THAT is observed.
 
  • #62
Paul Colby
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My question is: could quantum "dice" be attributed to some kind of inner/hidden chaotic process whose only visible "tip of the iceberg" would be "probability", while in fact it could be for example be the double pendulum tip x-position (as a basic analogy).
The answer is - first supply an observational meaning to your question. This would imply a theory in which QM is replaced with an equivalent theory that allows your question to be framed and verified in terms of experiments that may be performed. It seems to me the answer is clearly no because QM already restricts you to only certain types of measurements.
 
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  • #63
Boing3000
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The answer is - first supply an observational meaning to your question.
This is quite obvious from my previous post. Use the same experiments has before (all of them) but focusing on the noise part of the data (for example in a two slit experiment the distance between in "dot", relative to time, space, energy level and whatnot... (and all combined) and using the current mathematical knowledge to sniff out chaos (use a google search)

I don't say it is easy, re-using one of the example above, it may be like trying to guess that there is a brain composed of neurons inside people's head, just by using the tool of psychology (hard observation about people, but not using neuroscience/biological scanner)

The tool and experiment in question are probably to be more informed by subtle technique (like those of quantum computing) and maybe new math instead of giant hammer like the LHC.

This would imply a theory in which QM is replaced with an equivalent theory that allows your question to be framed and verified in terms of experiments that may be performed.
Of course, that's how science work. I see no reason why QM(QFT actually) could not be superset like all those before.
Right now QM theory can say NOTHING on what a single photon would do in an experiment. Actually QM says the photon may well go take a trip to Betelgeuse and back.
I can perform easily an experiment with one photon. I would like to have a theory usable in such a case.

It seems to me the answer is clearly no because QM already restricts you to only certain types of measurements.
I think you have things backward here. We don't care what theory says. We care about what nature says, and theory must abide by it. Rationally speaking there is not a lot of alternatives:
1) There may not be any better physical theory, and everybody should convert to psychology or philosophy (were there is clearly work to do:wink:)
2) There may be a lot of better theory (Occam's wise) but with identical predictive power
3) There may be a lot more to discover about both theory and nature.

I think all evidence point to the thirds option (like all scientists search for a GUT, or solve zillon'th of other mysteries, or don't know what 75% of the universe mass is made of)
 
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  • #65
Paul Colby
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This is quite obvious from my previous post.
I rest my case. No observational meaning has been supplied. Doing so implies a theoretical definition within the confines of current theory or within a new theory. I see none. This must be followed by the detailed design of an experimental test of said theory. I must have missed it. This test would have then have to be performed. If all this was done, you wouldn't have a question you'd have an answer.
 
  • #66
Boing3000
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I rest my case. No observational meaning has been supplied. Doing so implies a theoretical definition within the confines of current theory or within a new theory.
I don't follow you. Meaning does not have to be supplied to do observations. You measure things. These generally are numbers popping out of experimental apparatus (in all sorts of way/units). In the case of a double slit experiment, time an place of arrival of object are those numbers.
If you need an even more simple setup just measure a polarized stream of photon with a second filter at 45°. It gives you a random stream of pass/don't pass 010011101011101010. All QM say is its 0.5 on average. Yet there are tons of tool able to analyses such stream of bits to try to detect non-randomness.

I see none. This must be followed by the detailed design of an experimental test of said theory. I must have missed it.
Any link of my previous post would have done. This one maybe ?
In computer "science" we use test suite on pseudo-random generator based on chaotic function. This is based on a lot of math and a lot of research because those are involved in many critical processes (like cryptography) or less critical (but equally rewarding) like games. Are you denying those math/theory exist ?

This test would have then have to be performed. If all this was done, you wouldn't have a question you'd have an answer.
Err yes, hence my question, to the knowledgeable peoples on this site. You don't know any, me neither. I hope other people may have ...

The closest thing in QM(interpretation) would be the Bohm'ian pilot wave which is deterministic, yet give "pseudo-random" results for reasons that seem to me to be identical to chaotic ones (sensibility to starting values).

Any good read/research on this particular topic surely exist...
 
  • #67
Paul Colby
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Are you denying those math/theory exist ?
yes, in the sense that we are discussing physics. Defining a quantitative statistical measure for non-randomness is not a new concept. One can search for non-randomness in actual data, like photon counting experiments. Discovering such would be of potential interest if it can be shown to be fundamental and not just some instrumentation issue. However, a theoretical motivation to do so isn't apparent. If it is in your view[1], by all means have at it.

[1] I've had more than a passing interest in doing things like this. I've looked at using photon statistics in an exoplanet detection scheme. Needless to say, light just doesn't behave in a way that supports anything remotely like what is needed. (actually, this isn't quite true. One could use a star as a passive radar for exoplanets but good luck at getting the technology and S/N above the quantum limit.)
 
  • #68
Paul Colby
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The closest thing in QM(interpretation) would be the Bohm'ian pilot wave which is deterministic, yet give "pseudo-random" results for reasons that seem to me to be identical to chaotic ones (sensibility to starting values).
So, what do these say about your tests for non-randomness? Since pilot waves and such are just conceptual window dressing on QM it likely agrees with QM. My guess would be QM would predict no such deviation from randomness except in situation where extensive preparation of the state vector is involved. The only interesting result from a physics perspective would be a failure of QM and not simply an additional verification of QM.
 
  • #69
Boing3000
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yes, in the sense that we are discussing physics.
As far as I understand, physics theories are entirely based on math. There is plenty of threads here and elsewhere that pretend that quantum mechanics could have actually been discovered purely as an extension of probability theory. And, for example, I don't think such a simple notion as standard deviation is irrelevant to discussing physics, especially in the context of QM which cannot do without. I am also discussing physics, and you also obviously also are. So your "yes" makes no sense to me.

Defining a quantitative statistical measure for non-randomness is not a new concept. One can search for non-randomness in actual data, like photon counting experiments.
That is exactly my points. That's why I am surprised that I never see articles which dig deeper that side of thing. Again, as far as I know, every "classical" law of nature so far, will lead to chaotic solutions. Even the orbits of tree body system will turn out to be chaotic at scale large enough. The universe seem to behave in "non-linear" way in every simple instance. QM seems to not care (does not have to actually, that's kind of the purpose of its formulation).

Discovering such would be of potential interest if it can be shown to be fundamental and not just some instrumentation issue. However, a theoretical motivation to do so isn't apparent. If it is in your view[1], by all means have at it.
The theoretical motivation is obviously to settle one of the debate about "hidden variable", trough actual experiments.

[1] I've had more than a passing interest in doing things like this. I've looked at using photon statistics in an exoplanet detection scheme. Needless to say, light just doesn't behave in a way that supports anything remotely like what is needed. (actually, this isn't quite true. One could use a star as a passive radar for exoplanets but good luck at getting the technology and S/N above the quantum limit.)
That's very interesting ! But I was thinking a more simple, minimalist, controlled environment. Photon having crossed LY of space may be "noised" beyond redemption :cry:

So, what do these say about your tests for non-randomness? Since pilot waves and such are just conceptual window dressing on QM it likely agrees with QM
Window dressing ? Well I was under the impression that's a definitive pretty old extension to QM that obviously agrees with it. (and was so before its recent "revival")

The only interesting result from a physics perspective would be a failure of QM and not simply an additional verification of QM.
QM fails to say anything about where a single photon lands. I think an extension that would allow us to fine tune the "initial state"(and maybe other thing) such as to be sure that every odd photons in a double slit experiment land on the top half of the screen would be quite a revolution...
 
  • #70
Paul Colby
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As far as I understand, physics theories are entirely based on math.
Theory amounts to only half of physics if I'm being generous. Mathematics is only half of theory if I'm being equally liberal. My comments have been aimed at physics as a complete subject. When I refer to making a quantifiable statement this is intended to apply both experimentally and within the theory.
 
  • #71
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The thread seems to leave its initial question more and more, which by its nature must tend to become philosophical anyway if terms like existence or reality are involved. Also "physics is based on math" is definitely another philosophical question which is entirely based on based on. It is a bit like saying English is entirely based on roman letters.

Therefore I'll close the discussion here.
 
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