# Physics and “reality”

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13 minutes ago, joigus said:

Forces do appear in simplified contexts, if you want to call them that.

If you define your force as the gradient of the potential,

-V'=F

then the time rate of change of the space-average momentum of the wave is the space-average of the 'force'. So they are connected. Only in the average.

As for classical systems the wave is sharply peaked around a central value, you get the familiar picture which you're trying to use to explain the more general picture.

You don't understand quantum mechanics. That's (part of) your problem.

Right at the beginning in your link it is said:

"The Ehrenfest theorem, named after Paul Ehrenfest, an Austrian theoretical physicist at Leiden University, relates the time derivative of the expectation values of the position and momentum operators x and p to the expectation value of the force �=−�′(�) on a massive particle moving in a scalar potential �(�),[1]"

Then it deals with particles. It deals with waves' functions but associated to the position and momentum of the particles. The associated Schrodinger's wave equation for instance, is related to the probability for a particle to be at some position at some time, it does not represent a particle made by waves but a wave mathematically associated to a particle. It's all about particles at the end.

Edited by martillo

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29 minutes ago, martillo said:

Right at the beginning in your link it is said:

"The Ehrenfest theorem, named after Paul Ehrenfest, an Austrian theoretical physicist at Leiden University, relates the time derivative of the expectation values of the position and momentum operators x and p to the expectation value of the force �=−�′(�) on a massive particle moving in a scalar potential �(�),[1]"

Then it deals with particles. It deals with waves' functions but associated to the position and momentum of the particles. The associated Schrodinger's wave equation for instance, is related to the probability for a particle to be at some position at some time, it does not represent a particle made by waves but a wave mathematically associated to a particle. It's all about particles at the end.

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33 minutes ago, joigus said:

I knew the conversation could lead us to the subject of wave-particle duality and here my participation reaches the end I think. I'm currently working on a model of particles that explains their wave-like behavior so solving the wave-particle problem for the particles' approach but I know this enter in the category of personal theories and I perfectly know I cannot go on with this here (@swansont remarked it to me several times). The wave-like behavior is explained with the concept of trains of particles which leads to a structure for the particles, a new model of the elementary particles surge and so on. Impossible to describe all this shortly. Too many areas of Physics affected. I appreciate very much all the time given to me by all of you in the forum. It is very important in my work to be able to discuss some things here but for my pain I'm not able to continue the conversation. Thanks a lot anyway.

Edited by martillo
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2 hours ago, martillo said:

I'm trying to get to your point but it is being rather difficult for me. I think what you are really asking is which of them, forces or energy, actually determines the kind of the reality of the universe.

No, we are discussing whether physics, specifically, represents things that exist in reality, or whether these are mathematical conveniences.

2 hours ago, martillo said:

I mean, Newtonian Physics seems to be force based -- everything made by the forces -- while Relativity Physics seems to be energy based -- everything made by energy.

There is no mainstream physics that says things are “made of” energy.

2 hours ago, martillo said:

If this is not what you are asking please let me know to be able to answer you properly.

I am asking which is the fundamental entity, in your view, and which is the emergent property.

2 hours ago, martillo said:

If that is actually the case then I would stay with forces because is what let me choose between a particles-based universe against a waves-based universe. Waves cannot explain forces. Only interference with addition or subtraction of their intensities is possible between waves, a wave cannot exert a force to another wave. For instance how to explain attraction or repulsion between things made of waves, how to explain collisions and bounces between them? All of them well verified as present in the reality we are. The universe becomes then particles-based then and not waves-based. Forces is then the determinant thing of the reality of our universe.

The question was whether forces represent reality.

But you’ve admitted here that your view is that none of QM is real.

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50 minutes ago, swansont said:

I am asking which is the fundamental entity, in your view, and which is the emergent property.

For me the fundamental entity is force F and the emergent property is Energy E defined as: E = ∫Fdx.

50 minutes ago, swansont said:

The question was whether forces represent reality.

Yes they do.

50 minutes ago, swansont said:

But you’ve admitted here that your view is that none of QM is real.

IMHO the "Wave Mechanics" part of QM is not real. The concept of the photon and its dynamics (E = hν, photoelectric effect, Compton effect, etc.) is real. The equation E = mc2 is real for the photons but considering photons with mass m such that λ = h/mc. It is that those formulas do work but the theories developed behind are wrong for me. They are valid but for different physical phenomena than the described by those theories or models.

Unfortunately I can't explain it more, entering in the category of personal theories I know...

Edited by martillo
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• 3 weeks later...

Better late than never, sorry for waiting so long.

On 3/6/2023 at 1:55 PM, Markus Hanke said:

(...) any perception, any measurement, any experiment we can perform always boils down to interactions, at the most fundamental level.

I fully agree. I would even take it one step further. 'Interactions', I would say, are causal relationships. The natural sciences look at nature through 'causal spectacles'. A phenomenon is explained, at least for the moment, if we have a causal explanation. Of course, it may turn out later, that the explanation is not correct, or not complete, when we get new experimental data, or more precise background theories.

If we (think we) know all possible causal relationships that an entity has, then we could say we know this entity. E.g. if we know all possible causal connections that an electron can have, then we could say we know what an electron is. To try to 'look behind the scenes' what an electron 'really' is, is a scientific empty question. It is at most an ontological question.

On 3/6/2023 at 6:50 PM, TheVat said:

The Kantian distinction between phenomenon and noumenon still seems to serve physics with a guiding principle.  Phenomena, those interactions that are accessible to our senses (or enhanced senses), do not provide a window to the noumenon or thing-in-itself, i.e. that which exists independently of human senses (our measurements).

Yeah, I think this distinction is still useful, especially to describe the limitations of quantum theory: we encounter there a limit where we have no causal explanation anymore. There is no one to one connection with a cause and its precise effect. So as I expressed elsewhere, the 'wave-function' is itself not measurable, it only allows for statistical predictions: it is the limit of what we can say about nature. The 'electron-as-a-thing-in-itself' disappears behind its statistical, causal behaviour. Scientifically we cannot say more.

On 3/5/2023 at 10:13 PM, Lorentz Jr said:

Okay, I take back the word "entire". I know the subject has been discussed by Peter Woit, Jim Baggott, Sabine Hossenfelder, Lee Smolin, and Roger Penrose. My understanding is that they're still in a fairly small minority though.

You confuse critics of the modern 'main stream physics', with people who study the fundamentals of physics. There are many people engaged in this topic. Just google 'philosophy of physics'. And it also seems you forgot, in your previous reaction, how much was discussed by the 'fathers of QM'.

I agree with both articles linked in this thread: the one of Katie Mack, with which Swansont started the thread, and the Mermin article ("What's bad about this habit").

Edited by Eise
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16 hours ago, Eise said:

If we (think we) know all possible causal relationships that an entity has, then we could say we know this entity. E.g. if we know all possible causal connections that an electron can have, then we could say we know what an electron is. To try to 'look behind the scenes' what an electron 'really' is, is a scientific empty question. It is at most an ontological question.

I completely agree. This is why I’m personally biased towards looking at the wave function not as a description of the system itself, but rather as a description of how it relates to other systems. Which is essentially Rovelli’s approach to the whole issue.

It’s a bit like a tree - it has many branches, but the bird can only land on one branch at a time. That doesn’t mean the act of it landing somehow makes all the other branches magically go away - it means only that for that particular bird, only that particular branch matters at that time, since this is where it interacts with the tree. Once it sits perched there, the other branches have become irrelevant, but not any less real; to the bird it just might look as if the tree has been reduced to that one branch it is sitting on. Prior to landing, there were many branches, each with a certain probability to become the landing spot; but the actual contact itself is always made with only one specific branch, which is determined by how the bird flies his final approach. This changes nothing about either the tree nor the bird, and requires no unknown mechanisms to work.

This is of course an imperfect analogy, but you might get my drift.

But I would even go a step further - I question the assertion that “a system exposes a causal interface to its environment; therefore, there must be something that possesses such an interface (ie the “real” system)”. I think this does not necessarily follow at all - I see no reason why the causal relationships cannot be the system. There doesn’t have to be anything “underlying” it - reality can just be a network of relationships, rather than “things”.

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1 hour ago, Markus Hanke said:

I completely agree. This is why I’m personally biased towards looking at the wave function not as a description of the system itself, but rather as a description of how it relates to other systems. Which is essentially Rovelli’s approach to the whole issue.

It’s a bit like a tree - it has many branches, but the bird can only land on one branch at a time. That doesn’t mean the act of it landing somehow makes all the other branches magically go away - it means only that for that particular bird, only that particular branch matters at that time, since this is where it interacts with the tree. Once it sits perched there, the other branches have become irrelevant, but not any less real; to the bird it just might look as if the tree has been reduced to that one branch it is sitting on. Prior to landing, there were many branches, each with a certain probability to become the landing spot; but the actual contact itself is always made with only one specific branch, which is determined by how the bird flies his final approach. This changes nothing about either the tree nor the bird, and requires no unknown mechanisms to work.

This is of course an imperfect analogy, but you might get my drift.

But I would even go a step further - I question the assertion that “a system exposes a causal interface to its environment; therefore, there must be something that possesses such an interface (ie the “real” system)”. I think this does not necessarily follow at all - I see no reason why the causal relationships cannot be the system. There doesn’t have to be anything “underlying” it - reality can just be a network of relationships, rather than “things”.

I'm tending towards interpreting a thing as a composite of 'behaviours', where maths describes quantitavely each parameter within a system, and how they interact to describe the system as a  discrete mental object. Am I way off?

Edited by StringJunky
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1 hour ago, StringJunky said:

I'm tending towards interpreting a thing as a composite of 'behaviours', where maths describes quantitavely each parameter within a system, and how they interact to describe the system as a  discrete mental object. Am I way off?

I think you aren’t too far off with that. The only thing I’d point out though is that ‘behaviours’ require interactions - so again, we arrive at the view that systems aren’t actually defined by stand-alone ‘things with properties’ that are real even in isolation from everything else, but rather by interactions and relationships with other systems. Thus, ‘reality’ might be contextual, and it becomes an essentially meaningless concept if you try to divorce it from relationships to other systems; something can be said to be real precisely to the extent to which it relates to its environment in specific ways.

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3 minutes ago, Markus Hanke said:

I think you aren’t too far off with that. The only thing I’d point out though is that ‘behaviours’ require interactions - so again, we arrive at the view that systems aren’t actually defined by stand-alone ‘things with properties’ that are real even in isolation from everything else, but rather by interactions and relationships with other systems. Thus, ‘reality’ might be contextual, and it becomes an essentially meaningless concept if you try to divorce it from relationships to other systems; something can be said to be real precisely to the extent to which it relates to its environment in specific ways.

Cheers. Thanks to this board, I've gradually weaned myself off the commonsense view of fundamental objects as physically material, like in our everday macro view of objects we can see unaided.

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Like so many classification schemes, phenomenological v noumenoligical is very limited and incomplete.

Yes I agree the idea is good and can serve a useful purpose, but I still consider that the plain old English concrete v abstract nouns covers more situations, which do not require the causal connection of ph v nou.

For instance I have just used a couple of abstact nouns (classification) schemes and ideas.

Is there a causal relationship between the idea and its realisation ?

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