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

[vanhees71]

I agree with everything in the above quote of @Demystifier.

QM (or rather QT, because I consider relativistic QFT as the most fundamental theory, not non-relativistic QM) is incomplete, as all our theories, because there's no rigorous foundation of relativistic QFT and not even a working consistent physicist's way to describe the quantum aspects of the gravitational interaction.

There's also nothing in QT leading to the conclusion that unobserved entities don't exist. I don't discuss the word "reality" anymore, because it's not clearly enough defined to discuss it in a way not leading to misunderstandings and a lot of useless gibberish.

Finally, I believe that the sciences and humanities nowadays have reached such a degree of speciality that there's no way to make any progress without specializing in a subject. My choice was (theoretical) physics and not philosophy, because I could make much sense of the former but nearly none of the latter.

 

[ObjectivelyRational]

I agree with everything in the above quote of @Demystifier.

QM (or rather QT, because I consider relativistic QFT as the most fundamental theory, not non-relativistic QM) is incomplete, as all our theories, because there's no rigorous foundation of relativistic QFT and not even a working consistent physicist's way to describe the quantum aspects of the gravitational interaction.

There's also nothing in QT leading to the conclusion that unobserved entities don't exist. I don't discuss the word "reality" anymore, because it's not clearly enough defined to discuss it in a way not leading to misunderstandings and a lot of useless gibberish.

Finally, I believe that the sciences and humanities nowadays have reached such a degree of speciality that there's no way to make any progress without specializing in a subject. My choice was (theoretical) physics and not philosophy, because I could make much sense of the former but nearly none of the latter.

Good points but I would urge you not to give up on reality or existence. As scientists physicists are tasked with understanding reality, describing aspects (physical, observable etc) of existence.

Back to the OP.
The error is fundamental and not the fault of any physicist qua physicist, but the symptom of very bad philosophy, that accepts the possibility that a thing can be and not be at the same time.

Reality exists, independent of anyone's thoughts or wishes, and although it may be difficult to describe reality. "non-existence" simply not the way to characterize anything. 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..).

If a particle does not possesses a definite position, momentum, or any other quantity/property, that does not mean it does not exist, (in fact the expectation value is not zero). If it can and/or does change into another particle or convert into energy, that is not an expression of its not existing, it is a consequence of it existing, and transforming, becoming, behaving according to what it is. If at anyone time it were not, it simply would not exhibit anything ever again... a particle which "went out" of existence between measurements would be a sheer nothing... and surely we would never measure it again... and also conservation laws would certainly be violated.

Particles (I am including the field not just a particular particle) "not existing" is simply an impossibility. Our understanding of what existence means cannot be so erroneous so as to contradict reality, it has to include it because that is what exists (reality is all that exists) and we need to accept it. Particles may change form, their properties may be indeterminate, but no thing exhibits "non-existence".

 

[eltodesukane]

I don't know if I am right, but I have read about how some particles do not even exist until measured. How would we know this?

You have to reverse the question: how would you know it exist? You only know if you observe it.
Just like in a Pokemon game I used to play. I walk the path and when I'm in view of the hospital, nurse Joy is at the window waving at me. Was nurse Joy already at the window before the hospital came into view? Was the hospital already there while it was nowhere to be seen?
If I a red square is slowly flashing on my computer screen, does the red square exist when it is not there?

 

[DrChinese]

1. ... a particle which "went out" of existence between measurements would be a sheer nothing... and surely we would never measure it again... and also conservation laws would certainly be violated.

2. Particles (I am including the field not just a particular particle) "not existing" is simply an impossibility. Our understanding of what existence means cannot be so erroneous so as to contradict reality, it has to include it because that is what exists (reality is all that exists) and we need to accept it. Particles may change form, their properties may be indeterminate, but no thing exhibits "non-existence".

1. Generally, there is no sense in QM that a particle actually ceases to exist between measurements. Precisely because of conservation issues as you mention.

2. And my above statement (1.) would NOT also apply to quantum properties. Their existence between measurements is questionable in a variety of situations, depending on your preferred interpretation.

Your statement 2 is actually circular: you assume that which you seek to prove. I appreciate it is eminently reasonable, but the consequences of Bell's Theorem leave the question open for now.

 

[ObjectivelyRational]

1. Generally, there is no sense in QM that a particle actually ceases to exist between measurements. Precisely because of conservation issues as you mention.

2. And my above statement (1.) would NOT also apply to quantum properties. Their existence between measurements is questionable in a variety of situations, depending on your preferred interpretation.

Your statement 2 is actually circular: you assume that which you seek to prove. I appreciate it is eminently reasonable, but the consequences of Bell's Theorem leave the question open for now.

Sorry if I worded something to appear circular. That was not my intent. It might look circular due to my attempt to address the broad issues with narrow examples.

Physics is a study of what IS. An attempt to study "what is not" would be futile because "what is not" cannot have any consequence and cannot exhibit any property.

So then, in the study of things: things change forms but nothing disappears completely from existence, so whatever one studies, it can change but it cannot disappear into nothing which is what is implied by saying a particle "does not exist" (temporarily). In fact it has some form, perhaps indeterminate, perhaps a mix of energy or multiple particles/multiple states, perhaps even in a form which is bizzare, nonlocal, or difficult to comprehend, but it would be incorrect to claim it literally does not exist.

That's my point. I hope that does not come off as circular! :)

 

[Paul Colby]

Physics is a study of what IS.

A definition I prefer is along the lines, physics is a study of quantifiable natural phenomena. "Existence", "the way thing are" are all pretty obscure if define at all. Make these quantifiable or measurable phenomena and the discussion becomes well grounded at least operationally IMO.

 

[ObjectivelyRational]

A definition I prefer is along the lines, physics is a study of quantifiable natural phenomena. "Existence", "the way thing are" are all pretty obscure if define at all. Make these quantifiable or measurable phenomena and the discussion becomes well grounded at least operationally IMO.

True.

I agree in principle. Although apart from subjective first person experience - i.e. the hard problem of "consciousness", there simply IS not much other than "quantifiable natural phenomena" (arbitrary assertions notwithstanding) :)

 

[ObjectivelyRational]

True.

I agree in principle. Although apart from subjective first person experience - i.e. the hard problem of "consciousness", there simply IS not much other than "quantifiable natural phenomena" (arbitrary assertions notwithstanding) :)

Paul your point is well taken... Physicists also do not deal with reality at the level of biology, chemistry, and psychology etc. As a science it tends to be focused on the fundamentals i.e. physical (a little circular I know) phenomena which are quantifiable. (implicitly all phenomena are "natural" i.e. exhibited by nature/reality as it is)

 

[physika]

I don't know if I am right, but I have read about how some particles do not even exist until measured. How would we know this?

IMO, a question of properties, not, of existing or not (objects)

What is measured?
.- Properties.

Without objects, there are no properties.
CFD.

 

[Paul Colby]

Without objects, there are no properties.

Yes, but how is "object" defined. One might argue an optical photon is not an object in the same sense as a ball bearing is. One may speak of photon properties in general but for an individual photon one can only claim to know what some it's "properties" were at measurement. Furthermore, these "properties" depend very strongly on the experiment under discussion. Photon statistics are very much a property of the source rather than photons themselves which are very very different than ball bearings. IMO these types of questions should be addressed within the context of physical theory and not before.

 

[David Lewis]

...some particles do not even exist until measured. How would we know this?

"Particle" in this context means something that exhibits particle properties. Particle-like properties are undefined until the quantum interacts with something.

 

[vanhees71]

Paul your point is well taken... Physicists also do not deal with reality at the level of biology, chemistry, and psychology etc. As a science it tends to be focused on the fundamentals i.e. physical (a little circular I know) phenomena which are quantifiable. (implicitly all phenomena are "natural" i.e. exhibited by nature/reality as it is)

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.

 

[Paul Colby]

"Particle" in this context means something that exhibits particle properties.

Define particle properties? As I've pointed out previously, ball bearings and photons don't share the same properties even if we neglect mass and spin.

 

[David Lewis]

Without objects, there are no properties.

You're right, but sometimes the properties are not intrinsic solely to the object itself but rather belong to a system consisting of the object, and something else with which it interacts.

 

[Denis]

You shouldn't take this particle disappearing thing too seriously - the Copenhagen interpretation is simply agnostic about whether the moon exists when you are not looking at it.

The problem is that, at least in the form defended by Bohr, it is far from agnostic about it. If Bohr would have been agnostic about it, there would have been no issue at all about completeness. Bohr would have to be agnostic about completeness too.
Of course, Copenhagen is not bad at all from a pragmatic point of view. But one had to get rid of the positivist baggage to make it useful instead of confusing.

 

[ObjectivelyRational]

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!

 

[vanhees71]

Well, even without being psychotic, our senses are often not very reliable tools for objective observations. This is due to the fact that many sensations are due to "data processing" in our brains. An interesting example can be found here:

http://www.dailymail.co.uk/sciencet...tical-illusion-say-shows-brain-makes-see.html

 

[zonde]

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".

 

[vanhees71]

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.

 

[UsableThought]

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.

 

[zonde]

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.

 

[zonde]

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.

 

[Boing3000]

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.

 

[Boing3000]

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...

 

[Paul Colby]

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.

 

[Boing3000]

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.

 

[Paul Colby]

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.

 

[Boing3000]

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)
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)

 

[ObjectivelyRational]

So whatever this is, it still is

My exact point. Thank you.

 

[Paul Colby]

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.

 

[Boing3000]

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...

 

[Paul Colby]

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.)

 

[Paul Colby]

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.

 

[Boing3000]

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

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...

 

[Paul Colby]

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.