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

[romsofia]

In the usual sense it has gone so I don't see your point.

Thanks
Bill

My point was in response to this thread, particles don't exist outside of a minkowski spacetime, so OP needs to be more specific on "where" the measurement/particle is taking place. Even then, as I pointed out in my post, I take the position with Davies that particles have no meaning without a particle detector. So do particles exist before measurement? The answer, from my point of view, is an easy no. Particles make no sense "except in the context of a specified particle detector measurement."

 

[atyy]

Has this Bohmian formalism been consistently extended to a completely relativistic many particle formalism? Can this be said for an equivalent replacement for LQFT and the standard model? If not it's just more hot air in the quantum swirl. To be a viable replacement for what exists now these things must be shown first. A theory which replaces any of the QM formalism with something with measurable differences must first be consistent with all the physics that is known. This is required before it can be taken seriously.

The standard model is not known to be fully relativistic and many aspects can be notionally replaced by non-relativistically by lattice models, eg. https://arxiv.org/abs/cond-mat/0407140, https://arxiv.org/abs/1409.7414. The major gap is a lattice model that incorporates all aspects of chiral fermions and their interactions is still an open problem.

 

[Paul Colby]

The standard model is not known to be fully relativistic

If by fully one means compatible with GR then nothing is completely. The standard model is Lorentz invariant last I checked though people talk about non-invariant mods. QM is at the roots of so many known and verified things. A replacement/mod of QM has a big bar to meet. Seems prudent to check these known things first. Hence my question, is there a Bohmian replacement for the standard model? Once one starts changing the rules this becomes unclear.

aspects can be notionally replaced by non-relativistically by lattice models

This confuses theory with computational approximations IMO but whatever. Unclear what your point is exactly.

 

[vanhees71]

One professor said you will spend your whole life trying to understand it beyond its formalism which everybody understands and almost certainly get nowhere. I certainly have tried and failed miserably so basically and frustratingly gave up. Interpretations are valuable for the reason I said - it elucidates the formalism better. And every now and again someone way beyond my class like Bell makes a breakthrough, but they are few and far between.

Thanks
Bill

QT is a physical theory, and if you understand its formalism and how to apply it to observations in the real world, you have understood all there is to understand. What philosophers do with it for whatever purpose (I've never understood which purpose, to be honest), is their problem but not one of physics and it cannot be solved within physics. The only incomprehensible thing with QT is thus what philosophers mean with their unprecisely defined words, not QT as a physical theory.

 

[UsableThought]

QT is a physical theory, and if you understand its formalism and how to apply it to observations in the real world, you have understood all there is to understand. What philosophers do with it for whatever purpose (I've never understood which purpose, to be honest), is their problem but not one of physics and it cannot be solved within physics. The only incomprehensible thing with QT is thus what philosophers mean with their unprecisely defined words, not QT as a physical theory.

I apologize if I am about to ask something that you have already answered many times in other threads; I don't recollect seeing a direct answer in the threads I've gone through, but it would be easy for me to have missed it.

Anyway - does the above quote mean you disagree with @Demystifier's conclusions in the paper he wrote on QT "myths" (that is, on interpretations not strictly proven)? Specifically when he finishes up his conclusion with the following:

To conclude, the claim that the fundamental principles of quantum theory are today completely understood, so that it only remains to apply these principles to various practical physical problems – is also a myth. Instead, quantum theory is a theory which is not yet completely understood at the most fundamental level and is open to further fundamental research. Through this paper, I have demonstrated this by discussing various fundamental myths in QM for which a true proof does not yet really exist. I have also demonstrated that all these myths are, in one way or another, related to the central myth in QM according to which objective unmeasured reality does not exist. I hope that this review will contribute to a better general conceptual understanding of quantum theory and make readers more cautious and critical before accepting various claims on QM as definite facts.

Another way of asking my question is, are there differences I am missing between what you're saying and what Demystifier is saying?

I should add that one reason I like this paper is that it is very careful to avoid deeming anyone interpretation of QT as "the truth"; rather, the author points out that although there are many plausible interpretations, as well as quite a few implausible interpretations, nonetheless an interpretation is an interpretation, even if we happen to agree with it.

 

[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.