Physics and “reality”

[exchemist]

20 hours ago, Markus Hanke said:

I’m not so sure about this, because it doesn’t seem clear to me at all that/why there should be ‘something’ that is ontologically distinct from an interaction. If there is, then we have never observed it directly - any perception, any measurement, any experiment we can perform always boils down to interactions, at the most fundamental level. Even if there is ‘something’ there, then all we can ever see is the interface it exposes to its environment - and this tends to be highly contextual, especially in the quantum realm. Based on human intuition we tacitly and naturally assume that if there’s an interaction, there needs to be ‘something’ there that interacts, but I’m not so sure.

But of course, these are just philosophical musings of mine (even if they do, as you correctly observe, gel well with Rovelli et al), so I might well be entirely wrong

All I mean is that the word interaction implies an event involving more than one entity. It is an action "inter", i.e. between, entities. What is interacting? There have to be somethings to interact, or it is wrong to describe the phenomenon as an interaction - it would just be an event.

Clearly something is there in between (which we may describe by a wave function for example), sufficient to render the next interaction predictable. If there were nothing, there would be no predictability about the next interaction. So it seems to me it is the nature of that something that is up for debate.     

[studiot]

26 minutes ago, exchemist said:

All I mean is that the word interaction implies an event involving more than one entity. It is an action "inter", i.e. between, entities. What is interacting? There have to be somethings to interact, or it is wrong to describe the phenomenon as an interaction - it would just be an event.

Clearly something is there in between (which we may describe by a wave function for example), sufficient to render the next interaction predictable. If there were nothing, there would be no predictability about the next interaction. So it seems to me it is the nature of that something that is up for debate.     

Do we not also recognise the notion of self-interaction or self-activation for some phenomena in Physics ?

 

[joigus]

1 hour ago, studiot said:

Do we not also recognise the notion of self-interaction or self-activation for some phenomena in Physics ?

 

Correct.

https://en.wikipedia.org/wiki/Self-energy

Is it just a manner of speaking due to electrons not being isolated 'things' in any meaningful sense?

[studiot]

Further to my last post, this topic makes me think of the mathematical idea of equivalence relations.

The idea has wider application than just maths; many physical interactions are relations, but not equivalence relations, in that one or more of reflexivity, symmetry or transitivity ar not satisfied.

 

https://en.wikipedia.org/wiki/Equivalence_relation

[Genady]

2 hours ago, studiot said:

many physical interactions are relations

I don't immediately see it. Could you elaborate?

[studiot]

34 minutes ago, Genady said:

I don't immediately see it. Could you elaborate?

How about the Lorenz transformations ?

They are equivalence relations.

 

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/152115/A_novel_equivalence_relation_in_relativity.pdf?sequence=1&isAllowed=y

Edited March 7, 2023 by studiot

[Genady]

3 minutes ago, studiot said:

How about the Lorenz transformations ?

They are equivalence relations.

 

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/152115/A_novel_equivalence_relation_in_relativity.pdf?sequence=1&isAllowed=y

Yes, they are.

But they are not interactions.

Quote

many physical interactions are relations

 

[studiot]

1 hour ago, Genady said:

Yes, they are.

But they are not interactions.

 

Why not ?

They have a relative velocity, isn't that a physical interaction between two distinct entities ?

[Genady]

3 minutes ago, studiot said:

They have a relative velocity, isn't that a physical interaction between two distinct entities ?

I don't think that having relative velocity constitutes a physical interaction. Maybe it does in some sense, but I am not familiar with such sense. In every meaning of physical interaction that I am familiar with, such a relation is excluded. E.g., interacting particles in QFT.

[Markus Hanke]

14 hours ago, studiot said:

Why not ?

They have a relative velocity, isn't that a physical interaction between two distinct entities ?

I would look at LTs as a self-consistent way to choose new labels for events in the same spacetime - it’s much like looking at the same physical situation from a different perspective. 

[joigus]

22 hours ago, studiot said:

Further to my last post, this topic makes me think of the mathematical idea of equivalence relations.

The idea has wider application than just maths; many physical interactions are relations, but not equivalence relations, in that one or more of reflexivity, symmetry or transitivity ar not satisfied.

 

https://en.wikipedia.org/wiki/Equivalence_relation

Equivalence relations are at the basis of categorical thinking, or Aristotelian categories. We're hardwired to think in terms of categorical thinking. When we can't place the category, when that category does not close in mathematical terms, it's loosely defined, we feel confused.

I think it was Wittgenstein that worried a lot about that problem.

[studiot]

Thank all you good folks for your thoughts.

I fear this is becoming a semantic or interpretive issue as to whether or not there are mathematically defined equivalence realtions is Physics, and this was not what I meant when I posted

23 hours ago, studiot said:

many physical interactions are relations, but not equivalence relations, in that one or more of reflexivity, symmetry or transitivity ar not satisfied.

My main point is that reflexivity, symmetry and transitivity are valuable notions that could have wider applications regardless of whether we are talking about interactions, relations or some other phenomenon.

I would also remind you that the zero interaction, relation, whaterever is acceptable in maths so should the zero interaction be acceptable in Physics ?

E.G. Gamma ray do not interact with electric fields ?

I am suprised that @swansont doesn't appear to have a view on this, as I would value hearing it.

[Sensei]

On 3/5/2023 at 7:07 PM, swansont said:

“Yes, everything in physics is completely made up – that’s the whole point”

Good to have the source code

Backup.

To restart.

 

9 minutes ago, studiot said:

E.G. Gamma ray do not interact with electric fields ?

The gamma ray is red-shifted in one reference system and blue-shifted in the other..

 

[Genady]

1 hour ago, joigus said:

when that category does not close in mathematical terms, it's loosely defined, we feel confused.

But we are fine with loosely defined categories in real life.

[studiot]

24 minutes ago, Sensei said:

The gamma ray is red-shifted in one reference system and blue-shifted in the other..

Thank you, I was referring to Rutherford's experiment, conducted in a single frame.

https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_(Zumdahl_and_Decoste)/02%3A_Atoms_Molecules_and_Ions/2.04_Early_Experiments_to_Characterize_the_Atom

Quote

Building on the Curies’ work, the British physicist Ernest Rutherford (1871–1937) performed decisive experiments that led to the modern view of the structure of the atom. While working in Thomson’s laboratory shortly after Thomson discovered the electron, Rutherford showed that compounds of uranium and other elements emitted at least two distinct types of radiation. One was readily absorbed by matter and seemed to consist of particles that had a positive charge and were massive compared to electrons. Because it was the first kind of radiation to be discovered, Rutherford called these substances α particles. Rutherford also showed that the particles in the second type of radiation, β particles, had the same charge and mass-to-charge ratio as Thomson’s electrons; they are now known to be high-speed electrons. A third type of radiation, γ rays, was discovered somewhat later and found to be similar to the lower-energy form of radiation called x-rays, now used to produce images of bones and teeth.

Figure [Math Processing Error]: Effect of an Electric Field on α Particles, β Particles, and γ Rays. A negative electrode deflects negatively charged β particles, whereas a positive electrode deflects positively charged α particles. Uncharged γ rays are unaffected by an electric field. (Relative deflections are not shown to scale.) Image used with Permission (CC BY-SA-NC). Schematic of a radioactive element in a lead container projected through slits to produce a narrow beam that impacts a photographic film. Two plates, one positive and one negative, deflect the beam depending on whether it is beta, gamma, or alpha. Beta particles deflect towards the positive plate and have a large deflection due to small mass. Alpha particles deflect towards the negative plate and have a small deflection due to high mass. Gamma rays do not deflect.

These three kinds of radiation—α particles, β particles, and γ rays—are readily distinguished by the way they are deflected by an electric field and by the degree to which they penetrate matter. As Figure [Math Processing Error] illustrates, α particles and β particles are deflected in opposite directions; α particles are deflected to a much lesser extent because of their higher mass-to-charge ratio. In contrast, γ rays have no charge, so they are not deflected by electric or magnetic fields. Figure [Math Processing Error] shows that α particles have the least penetrating power and are stopped by a sheet of paper, whereas β particles can pass through thin sheets of metal but are absorbed by lead foil or even thick glass. In contrast, γ-rays can readily penetrate matter; thick blocks of lead or concrete are needed to stop them.

 

[Genady]

1 hour ago, studiot said:

My main point is that reflexivity, symmetry and transitivity are valuable notions that could have wider applications regardless of whether we are talking about interactions, relations or some other phenomenon.

One example of all three is thermal equilibrium.

[joigus]

1 hour ago, Genady said:

But we are fine with loosely defined categories in real life.

It certainly doesn't cramp my style.  

[studiot]

52 minutes ago, Genady said:

One example of all three is thermal equilibrium.

Good one, thank you. +1

 

But remember that sometimes only one or two are satisfied for example Newton's third law.

Ths can be equally interesting, as in maths.

[NTuft]

On 3/6/2023 at 2:18 PM, MigL said:

Markus Hanke ""

I would have no problem taking that step also.
I only mention 'things' because the questions are always"But what is an electron, really ?" or "What is a photon ?" or possibly your favorite "But what is gravity, really ?".

TheVat ""

How would it make a difference ?
Everything we see ( contingent ) affects us through interactions.
That which is not contingent does not affect us through interactions.
IOW, whether it is there or not makes absolutely no difference to us, or the world around us.

Why is it needed in our models, and, by Occam, why is it needed at all ?
( argument applies to religion/mysticism as well )

I can see the utilitarian argument, but if there were some non-contingent, non-interacting "field" isn't it possible that our observations or reality is contingent in a way that couldn't necessarily be measured? I know that's a mushy, philosophical-religio-mystical question, but I don't see physics as "made up", rather that it's trying to develop a description.. To me, the explanatory power for theory is deficient if it's not encompassing reality, even if utility wouldn't require a complete understanding.

On 3/7/2023 at 8:44 AM, studiot said:

Why not ?

They have a relative velocity, isn't that a physical interaction between two distinct entities ?

On 3/7/2023 at 8:57 AM, Genady said:

I don't think that having relative velocity constitutes a physical interaction. Maybe it does in some sense, but I am not familiar with such sense. In every meaning of physical interaction that I am familiar with, such a relation is excluded. E.g., interacting particles in QFT.

Lorentz force, 

Quote

[...]For any charged particle q in more general situations moving in the presence of electric and magnetic fields the interaction is usually given by the Lorentz force:
   

  In general, field theory and Maxwell’s equations are a ‘macroscopic’ approach as they were developed from a continuous medium model (the ether). However, as we will see in the following section, Weber’s force is ‘microscopic’ in that sense as it describes the interaction between two charged particles in its standard form. For a better comparison between Maxwell’s and Weber’s theory, Assis shows the derived force between two point charges from field theory [24] up to second order in v/c based on the work of Liénard, Wiechert and Schwarzschild, which was first obtained by O’Rahilly [25] as



  In this formula q₁ is the test charge and q₂ is the source charge generating the fields and , where according to Assis time retardation, radiation and relativistic effects have been included. The constant c is the speed of light and denotes the acceleration of the point charge. It is apparent that the expression depends on the square of the source charge velocity and on its acceleration, whereas Weber’s force depends on the relative velocity and acceleration, as will be seen in Section 3.1.2.[...]
[...]Both the Schwarzschild force (24) and Lorentz force (23) have been criticised as violating conservation of linear and angular momentum. To restore conservation it is usually argued that the energy is lost or gained by the electromagnetic field generated by the charges or that self force needs to be taken into account [29,30]. However, a system of two point charges seems extremely difficult to test. The general applicability (or non-applicability) of Newton’s third law to the Lorentz force and generally in electrodynamics has been discussed in [31–33]. Cornille [32] also claims that if the electrodynamic force laws indeed violate Newton’s third law, then it inevitably leads to the conclusion that energy can be extracted from the ether, as the ether exerts a force that is responsible for the violation.

  It has further been criticised that the velocity in the Lorentz force formula (23) is not clearly defined, that is what it is defined with respect to, was not even given by Lorentz himself [6,34]. It thus remains ambiguous if the definition is w.r.t a coordinate system or a source charge, which might itself be moving, although there seems to be support to the idea that Lorentz viewed the velocity as relative to the ether [6,34]. However, in relativistic treatments this is usually resolved by a chosen inertial frame of reference and regarding the velocity relative to the measuring device or observer.

  In an interesting review about Maxwell’s equations and the field approach Tran [35] concludes that there are only few experiments supporting the Maxwell-Ampère and Maxwell-Faraday equation, at least not to the same degree of accuracy that the continuity equation and the magnetic law are supported. There is further discussion about conceptual problems in classic electromagnetism and modern particle-field theories in the literature [36,37]. This mainly focuses on the problem of point charges and their diverging self-energy, as the calculated energy of an electron with its own field tends to infinity based on classic electromagnetism. One solution is the renormalisation approach in the quantum theory of Dirac where the point charge is treated as a singularity and the infinite energy is subtracted as a constant from the problem to renormalise the energy content. The other solution is the extended particle model, where elementary charges are not treated as pointlike anymore and consequently the divergence in the singularity disappears. Pietsch [36] discusses both approaches and the associated cost of the proposed solutions, and for an interesting discussion of these approaches including a mathematical perspective, see [38], on which Pietsch bases their arguments. Pietsch then argues that both approaches are incompatible at a fundamental level and a better solution is needed, in which direct-action theories are proposed. Lazarovici [37] also discusses the self-energy problem and the Lorentz-Dirac as well as the extended particle solutions as unsatisfactory, but also involves free fields, among other philosophical, mathematical and physical arguments, and proposes the Wheeler-Feynman direct-action theory in particular as a solution to those problems. The renormalisation approach has also been criticised by other authors [39], including Feynman [40] and Dirac [41]. A similar argument has been made by Kastner about the Wheeler-Feynman direct-action theory, not only does it avoid self-energy problems, it is also not subject to Haag’s theorem and the consequent problems of free and interacting fields in quantum field theory (QFT) [42]. [...]
Foundations of Electromagnetism: A Review of Wilhelm Weber's Electrodynamic Force Law , pgs. 954-955, emphasis added.

 

Edited March 8, 2023 by NTuft
added first part with equations

[studiot]

55 minutes ago, NTuft said:

Lorentz force, 

Since I first mentioned Lorenz I should point out that I was talking about the Lorenz Transformation, not the Lorenz force , which is an entirely different phenomenon.

[swansont]

On 3/7/2023 at 10:44 AM, studiot said:

Why not ?

They have a relative velocity, isn't that a physical interaction between two distinct entities ?

Which one is it? EM, strong, weak, gravitational?

1 hour ago, NTuft said:

Lorentz force, 

That’s qE + qv X B

There’s only a force if there’s a charge. The interaction is electromagnetic, not the relative velocity.

1 hour ago, NTuft said:

I can see the utilitarian argument, but if there were some non-contingent, non-interacting "field" isn't it possible that our observations or reality is contingent in a way that couldn't necessarily be measured? I know that's a mushy, philosophical-religio-mystical question, but I don't see physics as "made up", rather that it's trying to develop a description.. To me, the explanatory power for theory is deficient if it's not encompassing reality, even if utility wouldn't require a complete understanding.

How could an aspect of physics be real if it can’t be measured?

[NTuft]

47 minutes ago, studiot said:

Since I first mentioned Lorenz I should point out that I was talking about the Lorenz Transformation, not the Lorenz force , which is an entirely different phenomenon.

They're not entirely unrelated, though. Searching the respective wiki articles for the other's terms, "transformation" or "Lorentz force", has details [Transformation of other quantities; Relativistic form of the Lorentz force]. The E and B fields defined by Lorentz force do not have a timelike quantity so I think you're correct to say they're different from Lorentz transformation including time.

8 minutes ago, swansont said:

[...]

That’s qE + qv X B

There’s only a force if there’s a charge. The interaction is electromagnetic, not the relative velocity.

Yes, the corrected distribution got in there with the edit. However, also from the wiki's, the Lorentz transformation can illustrate that what appears as a static electric charge and E field in a rest frame appears to be a moving charge with consequent current flow and induced B field from another frame in relative movement--it only becomes an electro-magnetic interaction with some relative velocity, either of the charge or the observer thereof. 

[swansont]

48 minutes ago, NTuft said:

Yes, the corrected distribution got in there with the edit. However, also from the wiki's, the Lorentz transformation can illustrate that what appears as a static electric charge and E field in a rest frame appears to be a moving charge with consequent current flow and induced B field from another frame in relative movement--it only becomes an electro-magnetic interaction with some relative velocity, either of the charge or the observer thereof. 

And? 

The relative motion doesn’t create the interaction. You could transform into a frame where v = 0. You would have an electrostatic interaction that accounted for everything.

[joigus]

1 hour ago, NTuft said:

The E and B fields defined by Lorentz force do not have a timelike quantity so I think you're correct to say they're different from Lorentz transformation including time.

The Lorentz force does have a time component, though. When you write down the complete --covariant-- form of the equation it gives,

\[ f^{\mu}=qu^{\nu}\left.F_{\nu}\right.^{\mu} \]

as a 4-vector equation. Where \( \left.F_{\nu}\right.^{\mu} \) produces all the components of \( \boldsymbol{E} \) and \( \boldsymbol{B} \). These equations decouple into,

\[ f^{0}=q\boldsymbol{v}\cdot\boldsymbol{E} \]

\[ f^{k}=q\left(\boldsymbol{E}+\boldsymbol{v}\times\boldsymbol{B}\right) \]

and where I think I may be missing a gamma factor. The 0-th Lorentz equation gives you the power gain or loss, and the spatial equation is the conventional Lorentz equation.

[NTuft]

2 hours ago, swansont said:

And? 

The relative motion doesn’t create the interaction. You could transform into a frame where v = 0. You would have an electrostatic interaction that accounted for everything.

There may be something brought to bear on this here, A novel equivalence relation in relativity (+1 @studiot),

Quote

[...] But standard special relativity cannot tell us directly that lightspeed objects do not exist in spacetime because it does not contain any concept of existence. Embedding it via the existence criterion makes this explicit and gives meaning to features of special relativity which could previously only be regarded as meaningless curiosities. Sometimes, paradigm changes happen precisely when seemingly meaningless curiosities in a model of reality are recognized to carry novel significance, and arguably, the birth of special relativity itself was due to such a development [2].
• The ontic equivalence relation establishes a novel classical geometric correspondence.
Because of dimensional reduction, lightspeed objects must by the ontic equivalence relation exist in a 2 + 1 dimensional spacetime. The mathematics of special relativity gives hints of this: As an object approaches the speed of light, its direction of motion and its time direction are both observed to approach the lightlike direction. In the limit of c, they both become lightlike [3]. But that means that in a lightspeed frame, our spacetime is a vector space with a linearly dependent set of vectors, which in turn implies that in a lightspeed frame, 3 + 1 spacetime has too many dimensions. Also, special relativity is clear that in such a frame there are only two independent spacelike directions.
  The existence of lightspeed objects in 2 + 1- dimensional spacetime can be interpreted in terms of a classical and a quantum picture.
  The classical picture is that as a lightspeed object traverses a null geodesic in spacetime, it defines a rest frame on a null-plane, so that what is in 2 + 1 dimensions the passage of proper time corresponds in 3 + 1 dimensions to motion in space. Since the rest frame in a null-plane has to be represented in 3 + 1 dimensions necessarily in an atemporal manner (due to the connection between existence in a spacetime and timelike proper time), it suggests a novel interpretation of the fact that the stabilizer subgroup of the Poincar´e group (‘Wigner’s little group’) for massless objects is isomorphic to E(2), the group of isometries in the Euclidean plane [4]. As the correspondence involves analogous quantities associated with spaces of different dimensionality, we will for clarity use left subscripts to indicate the total number of dimensions of the space with which the quantity is associated. Let 3d ∶ E 3 → [0,∞) be the distance function for three-dimensional Euclidean space, and 3τ∗ ∶ M3 → [0,∞) be the timelike plus zero (indicated by adding *) interval function [5] for three-dimensional Minkowski spacetime, then C ∶ 3τ∗ → 3d (3) will be called the classical τ ∗ −d duality. It reflects the fact that, unlike certain other relations such as set membership, existence in a spacetime is not inherited by a one-dimension higher embedding spacetime, an immediate consequence of the ontic equivalence relation.
  In [6], it was implicitly shown that classical electrodynamics obeys the classical τ ∗ −d duality, as the magnetic force field of an infinite line current can be reinterpreted as the line integral of a two dimensional Coulomb force field such that a spatial distance covered by the line integral corresponds to the worldline of a Coulomb source in a twodimensional leaf of a foliation of space normal to the direction of the current (i.e. really a worldline in 2 + 1 dimensions). This reconceptualization permits the recognition of geometric relationships between Maxwell’s equations not evident in the standard formulation.

 

[Ed.: Excuse bad formatting, see link]

1 hour ago, joigus said:

The Lorentz force does have a time component, though. When you write down the complete --covariant-- form of the equation it gives,

fμ=quνFνμ

as a 4-vector equation. Where Fνμ produces all the components of E and B . These equations decouple into,

f0=qv⋅E

fk=q(E+v×B)

and where I think I may be missing a gamma factor. The 0-th Lorentz equation gives you the power gain or loss, and the spatial equation is the conventional Lorentz equation.

So the f⁰ is the 0-th and f^k is the conventional. I don't have a handle on co-variant, contra-variant, vector indices or tensors here, I'd barely made a start on what I think is Einstein's vector convention. is the power gain/loss a boost? I ought to go through the sections I pointed at to get the details, but if you could explicate what this is saying I'd appreciate it; I don't even know what questions to ask.


Referring to the equivalence relation in relativity cite, does it make sense that the E and B fields are conceptually lightlike objects? I think it's such that they're thought of as the medium in which it propagates. What about the dimensionality? When swansont said that it could be reverted to a v=0 frame and electrostatics could describe it I was thinking that was like going from 3-D to 2-D spacelike dimensions, and then lo-and-behold the next section I read goes into classical electrodynamics... Which is not correct, as electrostatics can be 3-D, but as soon as it is, I think there is the additional degree of freedom for rotation, which again is a relative motion that can induce the B field.
And? I think that there was some back-and-forth about whether an interaction hinges on a relative motion, and I think magnetism does. I highly recommend the reading on equivalence relation in relativity, I don't have a good handle on relativity, and several readings of the initial pages are necessary.

5 hours ago, NTuft said:

I don't see physics as "made up"

"...everything in physics is made up to make the math work out.
...in the end, everything we do is to make the math work out."

Edited March 8, 2023 by NTuft
cleared spaces in quote, added last encouragement wrt Shirazi paper