Physics and “reality”

[martillo]

59 minutes ago, sethoflagos said:

How about Coulomb  force? It is so similar in form to Newtonian gravitational  force that one wonders whether it too is a fiction. Is spacetime possibly also configured to allow charge to propagate along some electromagetic geodesic as does momentum in a gravitational field? I'm sure this is an idiotic question in a sense, but  I'm prepared to endure the humiliation of an informed response.

Seems not. That's why the non classical approach is through "virtual photons". At Wikipedia (https://en.wikipedia.org/wiki/Virtual_particle) you can find the following:

"In quantum field theory, forces—such as the electromagnetic repulsion or attraction between two charges—can be thought of as due to the exchange of virtual photons between the charges. Virtual photons are the exchange particle for the electromagnetic interaction."

You must take into account what @swansont said:

On 3/10/2023 at 4:59 PM, swansont said:

The EM force, for example, is mediated by virtual photons. IOW, the model uses something that it blatantly acknowledges are not real. 

 

Edited March 12, 2023 by martillo

[Genady]

4 hours ago, sethoflagos said:

How about Coulomb  force? It is so similar in form to Newtonian gravitational  force that one wonders whether it too is a fiction. Is spacetime possibly also configured to allow charge to propagate along some electromagetic geodesic as does momentum in a gravitational field? I'm sure this is an idiotic question in a sense, but  I'm prepared to endure the humiliation of an informed response.

The attempts to make a geometric theory of electromagnetism started pretty soon after GR was formulated. See Kaluza–Klein theory - Wikipedia

The current attempts are rather to make GR like other fields. You know, “If the mountain will not come to Mohammed, Mohammed must go to the mountain.”  

The forces, in Newtonian sense, are absent in both ways. 

[martillo]

36 minutes ago, Genady said:

The forces, in Newtonian sense, are absent in both ways. 

Yes, everything discarding the concept of force. Why so much rejection to the concept of force? What is so bad with the concept of force to go on denying it? I don't get it...

[Genady]

11 minutes ago, martillo said:

Yes, everything discarding the concept of force. Why so much rejection to the concept of force? What is so bad with the concept of force to go on denying it? I don't get it...

See these two posts in another thread:

https://www.scienceforums.net/topic/128993-hijack-from-jumping-out-of-the-black-hole-what-about-the-event-horizon-from-nowhere-to-everywhere/?do=findComment&comment=1233020

https://www.scienceforums.net/topic/128993-hijack-from-jumping-out-of-the-black-hole-what-about-the-event-horizon-from-nowhere-to-everywhere/?do=findComment&comment=1233026

 

[martillo]

24 minutes ago, Genady said:

See these two posts in another thread:

https://www.scienceforums.net/topic/128993-hijack-from-jumping-out-of-the-black-hole-what-about-the-event-horizon-from-nowhere-to-everywhere/?do=findComment&comment=1233020

https://www.scienceforums.net/topic/128993-hijack-from-jumping-out-of-the-black-hole-what-about-the-event-horizon-from-nowhere-to-everywhere/?do=findComment&comment=1233026

 

Thanks. I have just posted a comment about the first:

https://www.scienceforums.net/topic/128993-hijack-from-jumping-out-of-the-black-hole-what-about-the-event-horizon-from-nowhere-to-everywhere/?do=findComment&comment=1233038

 

 

Edited March 12, 2023 by martillo

[martillo]

Now returning to @joigus and @MigLsubjects:

21 hours ago, joigus said:

Certainly not. But, as long as we're considering Newtonian physics, consider also this: To the extent that Newtonian physics is valid, inertial frames must exist within a reasonable degree of approximation. If they do, I can always go to an inertial frame where only those forces coming from fields and their identifiable sources are present. Now I go to a non-inertial frame of reference, and fictitious forces appear. That is, forces that in no manner can be identified with any physical sources by means of fields; forces that to all intents and purposes are kinematic in nature; ie, can be removed only with a reference re-labling. Now go to another non-inertial frame if you like. It's still incumbent upon you --the claimant that forces are real-- to explain why those forces are not present in an inertial frame, while they 'magically' seem to appear out of thin air in a non-inertial frame.

18 hours ago, MigL said:

Point I was trying to make Martillo, is that you can't have a force in one frame, and not in another, and call that force 'real', as all frames are equally valid.

I think the concept of fictitious forces complicates it all. To avoid it let us consider that between accelerated frames what exist is a transform o coordinates. If A is the acceleration of a frame in relation to a stationary frame then the transform of coordinates is given by:

a' = a - A

where a is the acceleration of an object in the stationary frame and a' is the resultant acceleration of the object in the accelerated frame.

Now Newton Law states: a = F/m and we get:

a' = F/m + a

where F is the (real) force acting on the object.

Please don't try now to multiply both sides by m and as the units will correspond to forces introduce the names of pseudo- forces in the equation. Please let us stay just with that equation as it is formulated.

Then what happens is that the resultant acceleration and so its relative motion changes. Particularly in a free fall, the acceleration of the accelerated frame is equal to the acceleration of the object and so the resultant acceleration of the object in the accelerated frame is zero:

If a = A then a' = 0

The acceleration of the object in the accelerated frame is zero. The motion of the object is null, no motion.

Now what about the force? The force is also zero. There's no force perceived in the accelerated frame. 

Both acceleration and force are frame dependent in accelerated frames.

The force F is real but is not perceived in the accelerated frame of the free fall.

What about Newton Law? Is not preserved. Newton Law is not valid in accelerated frames. It is valid in the classic inertial (Galilean) frames only.

All this is valid within Classical Physics and I don't have any problem with the concepts here.

I know you will say that The Force Law must be the same in all referential frames following the main principle of Relativity but what if it could be questioned? I mean many new theories are being developed with their own principles so why can't a new theory be developed just liberating from this constraining principle? Would it be counterintuitive or what to assume that some laws would be frame dependent? It is said Physics does not need to follow the common sense so why not to allow a theory without that principle? I do not pretend to discuss any new theory here. I'm just saying that may be it is possible to find a new model or theory with this feature.

[apprentus]

The quote from the article is correct in that physics is based on mathematical models and approximations. These models are not necessarily a reflection of an ultimate truth or reality, but rather are tools used to describe and predict the behavior of the physical world.

The concept of an electron, for example, is a useful construct within the framework of quantum mechanics, but it is not necessarily a representation of a physical object that exists independently of our observations and measurements. The wavefunction that describes the behavior of electrons is a mathematical construct that allows us to make predictions about their behavior, but it does not necessarily reflect an objective reality.

Ultimately, the goal of physics is not to uncover an ultimate truth or reality, but rather to create models that accurately describe the behavior of the physical world. As our observations and measurements become more precise, our models will continue to evolve and improve, but they will always be subject to refinement and revision.

[studiot]

16 minutes ago, apprentus said:

The quote from the article is correct in that physics is based on mathematical models and approximations. These models are not necessarily a reflection of an ultimate truth or reality, but rather are tools used to describe and predict the behavior of the physical world.

The concept of an electron, for example, is a useful construct within the framework of quantum mechanics, but it is not necessarily a representation of a physical object that exists independently of our observations and measurements. The wavefunction that describes the behavior of electrons is a mathematical construct that allows us to make predictions about their behavior, but it does not necessarily reflect an objective reality.

Ultimately, the goal of physics is not to uncover an ultimate truth or reality, but rather to create models that accurately describe the behavior of the physical world. As our observations and measurements become more precise, our models will continue to evolve and improve, but they will always be subject to refinement and revision.

 

I see that you have just joined SF and offered us a couple of good posts, so welcome.

Please note that you can only make a total of 5 posts in your first 24 hours as an anti spam measure.

After that you can post at will.

 

Don't you think that your view of Physics is a little narrow ?

Much of Physics is concerned with observation and measurement.

More is concerned with collating, cataloguing, classifying and correlating theory and observation.

And some lines of physical thought are certainly rational but they are not mathematical.

Go well in your membership.

 

[martillo]

I apologize for a mistake in my previous post:

2 hours ago, martillo said:

Now returning to @joigus and @MigLsubjects:

I think the concept of fictitious forces complicates it all. To avoid it let us consider that between accelerated frames what exist is a transform o coordinates. If A is the acceleration of a frame in relation to a stationary frame then the transform of coordinates is given by:

a' = a - A

where a is the acceleration of an object in the stationary frame and a' is the resultant acceleration of the object in the accelerated frame.

Now Newton Law states: a = F/m and we get:

a' = F/m + a

where F is the (real) force acting on the object.

Please don't try now to multiply both sides by m and as the units will correspond to forces introduce the names of pseudo- forces in the equation. Please let us stay just with that equation as it is formulated.

Then what happens is that the resultant acceleration and so its relative motion changes. Particularly in a free fall, the acceleration of the accelerated frame is equal to the acceleration of the object and so the resultant acceleration of the object in the accelerated frame is zero:

If a = A then a' = 0

The acceleration of the object in the accelerated frame is zero. The motion of the object is null, no motion.

Now what about the force? The force is also zero. There's no force perceived in the accelerated frame. 

Both acceleration and force are frame dependent in accelerated frames.

The force F is real but is not perceived in the accelerated frame of the free fall.

What about Newton Law? Is not preserved. Newton Law is not valid in accelerated frames. It is valid in the classic inertial (Galilean) frames only.

All this is valid within Classical Physics and I don't have any problem with the concepts here.

I know you will say that The Force Law must be the same in all referential frames following the main principle of Relativity but what if it could be questioned? I mean many new theories are being developed with their own principles so why can't a new theory be developed just liberating from this constraining principle? Would it be counterintuitive or what to assume that some laws would be frame dependent? It is said Physics does not need to follow the common sense so why not to allow a theory without that principle? I do not pretend to discuss any new theory here. I'm just saying that may be it is possible to find a new model or theory with this feature.

I should have written:

Now Newton Law states: a = F/m and we get:

a' = F/m - A

I had to went out in a hurry and couldn't verify and edit this at the time.

Edited March 12, 2023 by martillo

[swansont]

As someone mentioned in another thread, there are formulations of mechanics that do not use forces - Hamiltonian and Lagrangian mechanics.

[MigL]

Hamiltonian formulation is essentially an energy equation.
( except when co-ordinates are time dependent )
And sure enough, energy is also frame dependent.

Seems you just can't get away from this frame dependency thing, Martillo.

[martillo]

24 minutes ago, MigL said:

Hamiltonian formulation is essentially an energy equation.
( except when co-ordinates are time dependent )
And sure enough, energy is also frame dependent.

Seems you just can't get away from this frame dependency thing, Martillo.

I think you misunderstood something. I said for me there's no problem for acceleration, force, and even Newton Law to be frame dependent. Is Relativity Theory that makes a problem with its first principle stating that the laws of physics are the same and can be stated in their simplest form in all inertial frames of reference. For me is a too strong constraint imposed on the Physics Laws. For me some laws are frame dependent as Newton Second Law is. Consider for instance De Broglie Law λ =h/mv which depends on the velocity v. The question is, related to which referential is this velocity considered? For me the answer is a classical absolute frame at rest in the Universe. The velocity v is an absolute velocity. It is said this formula is invariant under the relativistic Lorentz Transform, fine, but the question remains: which velocity is considered? Velocity in relation to what? Only an absolute velocity relative to a frame at rest in the Universe makes sense to me.

1 hour ago, swansont said:

As someone mentioned in another thread, there are formulations of mechanics that do not use forces - Hamiltonian and Lagrangian mechanics.

There are some formulations that do not use forces, fine, but what's the problem to have a formulation that do use the concept of forces? Why to deny the very useful concept of force? I don't understand that.

[swansont]

1 hour ago, martillo said:

I think you misunderstood something. I said for me there's no problem for acceleration, force, and even Newton Law to be frame dependent. Is Relativity Theory that makes a problem with its first principle stating that the laws of physics are the same and can be stated in their simplest form in all inertial frames of reference. For me is a too strong constraint imposed on the Physics Laws. For me some laws are frame dependent as Newton Second Law is.

Not for inertial frames. Newton’s first law tells you when the second law works. And we already know you need fictitious forces (which sort of gives away the game) if the first law doesn’t apply.

1 hour ago, martillo said:

Consider for instance De Broglie Law λ =h/mv which depends on the velocity v. The question is, related to which referential is this velocity considered? For me the answer is a classical absolute frame at rest in the Universe.

You can’t have personal laws. There is no rest frame of the universe, and we can’t have a discussion about reality if you decide to have your own version of it.

 

1 hour ago, martillo said:

The velocity v is an absolute velocity. It is said this formula is invariant under the relativistic Lorentz Transform, fine, but the question remains: which velocity is considered? Velocity in relation to what? Only an absolute velocity relative to a frame at rest in the Universe makes sense to me.

Then you have some work to do, understanding physics.

1 hour ago, martillo said:

There are some formulations that do not use forces, fine, but what's the problem to have a formulation that do use the concept of forces? Why to deny the very useful concept of force? I don't understand that.

We’re talking about reality. If you concede that these are concepts, and not reality, then this particular discussion is over, right?

Which is the underlying reality, forces or energy? (or none of the above)

[MigL]

That deBroglie relation is observer dependent.
The velocity, as well as the wavelength, change depending on the relative velocity of the observer. Alternatively, the 'rest' wavelength is measured in the particle's rest frame, which, unlike photons, can be at rest.

Relativity is another thing you cannot simply wish away.

[StringJunky]

1 hour ago, martillo said:

 Only an absolute velocity relative to a frame at rest in the Universe makes sense to me.

If there is just you and a rock for company, in space, which you are sitting on with uniform velocity, and you see another object getting larger; who is moving, you or the other rock?   If you can't answer this small scenario, you can't have an answer for the complicated ones. Frames can only be arbitrary.

Edited March 12, 2023 by StringJunky

[martillo]

1 hour ago, swansont said:

Not for inertial frames. Newton’s first law tells you when the second law works. And we already know you need fictitious forces (which sort of gives away the game) if the first law doesn’t apply.

But right for non-inertial frames.

 

1 hour ago, swansont said:

Then you have some work to do, understanding physics.

In the line of understanding  Physics I'm asking which velocity it is currently considered as right to apply on the De Broglie Law λ =h/mv. I think the considered velocity in practice is that measured in physics' laboratories and so a "stationary" frame is considered but laboratories are on Earth, which rotates and move around the Sun, which at its time moves in a Galaxy, and so on. There's no preferred lab to give the standard to obtain the velocity. So I ask, which is the totally right velocity to be used in the formula? relative to what referential?

1 hour ago, swansont said:

We’re talking about reality. If you concede that these are concepts, and not reality, then this particular discussion is over, right?

Which is the underlying reality, forces or energy? (or none of the above)

Right, no problem. Both are real, forces and energy. Any law of physics is real although not visible including the forces laws and the energies laws. Only objects in the Universe are visible, not the laws that govern their behavior. Both are real, the objects always made by the elementary particles and the laws that govern them. It is just that the laws are not directly visible. You can see their effects, like the the leaves of a tree moving by the force and energy of the air, but the forces and the energies are not directly visible. Can we agree on this?

1 hour ago, MigL said:

That deBroglie relation is observer dependent.
The velocity, as well as the wavelength, change depending on the relative velocity of the observer. Alternatively, the 'rest' wavelength is measured in the particle's rest frame, which, unlike photons, can be at rest.

Relativity is another thing you cannot simply wish away.

You say it changes with the observer frame. I can think in different labs over Earth, the moon, in the space whatever looking at the same experiment like Davisson-Germer experiment somewhere. They all will measure different velocities and so obtain different results. Which would be the right one then?

1 hour ago, StringJunky said:

If there is just you and a rock for company, in space, which you are sitting on with uniform velocity, and you see another object getting larger; who is moving, you or the other rock?   If you can't answer this small scenario, you can't have an answer for the complicated ones. Frames can only be arbitrary.

That's a complicated problem to solve I agree. I would need some experiment to make on the rocks involving some frame dependent physics law. The results would be frame dependent and so it would be possible to decide but I would need that frame dependent law to test. I'm saying to @swansont and @MigLthat the De Broglie Law could be one but we are discussing about it right now...

Edited March 12, 2023 by martillo

[MigL]

The 'rest' frame of the particle is the one where the particle is at rest.

[martillo]

16 minutes ago, MigL said:

The 'rest' frame of the particle is the one where the particle is at rest.

But the 'rest' wavelength of a particle at rest is always infinite. λ =h/mv. 

[MigL]

That statement was for clarification.

My previous post indicated that the deBroglie wavelength is inversely proportional to the particle's momentum.
IOW, observer dependent.

[swansont]

1 hour ago, martillo said:

In the line of understanding  Physics I'm asking which velocity it is currently considered as right to apply on the De Broglie Law λ =h/mv. I think the considered velocity in practice is that measured in physics' laboratories and so a "stationary" frame is considered but laboratories are on Earth, which rotates and move around the Sun, which at its time moves in a Galaxy, and so on. There's no preferred lab to give the standard to obtain the velocity. So I ask, which is the totally right velocity to be used in the formula? relative to what referential?

To whichever reference you choose. It won’t matter.

 

1 hour ago, martillo said:

Right, no problem. Both are real, forces and energy.

You can’t have two realities.

1 hour ago, martillo said:

Any law of physics is real although not visible including the forces laws and the energies laws. Only objects in the Universe are visible, not the laws that govern their behavior. Both are real, the objects always made by the elementary particles and the laws that govern them. It is just that the laws are not directly visible. You can see their effects, like the the leaves of a tree moving by the force and energy of the air, but the forces and the energies are not directly visible. Can we agree on this?

I think you are diluting the notion of reality to the point where it’s meaningless.

 

1 hour ago, martillo said:

You say it changes with the observer frame. I can think in different labs over Earth, the moon, in the space whatever looking at the same experiment like Davisson-Germer experiment somewhere. They all will measure different velocities and so obtain different results. Which would be the right one then?

How would they measure different results? The velocity relative to the crystal is what matters.

They would only measure different velocities if there was a preferred frame, but there isn’t.

 

 

[martillo]

1 hour ago, swansont said:

You can’t have two realities.

Both, forces and energy are two things of the same reality. Why only one would be real and the other not? 

1 hour ago, swansont said:

How would they measure different results? The velocity relative to the crystal is what matters.

You are right.

1 hour ago, swansont said:

They would only measure different velocities if there was a preferred frame, but there isn’t.

Actually that experiment hasn't been tested for considerable different velocities in the labs so I cannot reach a valid conclusion. Only if different results would be obtained the existence of a preferred frame would be deduced. As for now you are right there's nothing that can demonstrate the existence of that frame. 

2 hours ago, MigL said:

That statement was for clarification.

My previous post indicated that the deBroglie wavelength is inversely proportional to the particle's momentum.
IOW, observer dependent.

@swansont is right in that what matters in that experiment is the velocity relative to the crystal target.

Edited March 13, 2023 by martillo

[swansont]

7 hours ago, martillo said:

 

You are right.

Actually that experiment hasn't been tested for considerable different velocities in the labs so I cannot reach a valid conclusion. Only if different results would be obtained the existence of a preferred frame would be deduced. As for now you are right there's nothing that can demonstrate the existence of that frame. 

@swansont is right in that what matters in that experiment is the velocity relative to the crystal target.

Either the relative velocity is the pertinent quantity, or some absolute velocity is. It can’t be both.

 

Quote

Both, forces and energy are two things of the same reality. Why only one would be real and the other not? 

They are mathematically related. One would have to be emergent from the other.

[joigus]

9 hours ago, martillo said:

Both, forces and energy are two things of the same reality. Why only one would be real and the other not? 

Energy only occurs in a theory that's invariant under time translations. This much we understood when Lagrangian and Hamiltonian mechanics became general enough, well-understood enough, that it became mathematically transparent why it should be so.

In classical physics (both Newtonian and Einstenian) you can always widen your outlook so as to see your physics as happening in a background that is everywhere the same, and at all times the same (in Newtonian theory, absolute space; in SR, space-time). If your system doesn't conserve energy, you can always understand it in terms of it being part of a bigger system that does conserve energy.

That's why energy is conserved in both theories.

In GR, on the other hand, and very importantly, energy is something of a bit schizoid dual* concept that has to be connected through Einstein's field equations. Energy must always be exactly zero when you consider the energy term on the LHS of the equations, and the RHS of them. You have a sort of geometric energy, and a material-content energy, plus a vacuum energy that's conventionally placed on the LHS of the equations. All the energy terms must be counterbalanced. In order to incorporate the caveat in its very name, we could call it 'energy-like balancing scalar invariant' or something. I don't think the term would stick. Unfortunately, we're stuck with just 'energy'.

In 'raw' quantum field theory (QFT, in flat space-time) you always have energy conservation for an isolated system, for reasons similar to those that make SR an energy-conserving theory.

When you try to combine both (GR & QFT) the desire to asign 'reality' to energy and momentum becomes, if anything, even more unclear. Especially if you want to include the Big Bang in the picture. There you have several models where the 'creative work' is done by the vacuum --inflationary models--, where energy and momentum appear because of features of particular geometric models --CPT-invariant universe, conformal, cyclic, you name it.

But, whatever the framework, energy and momentum's entering the scene must be accounted for, and it doesn't seem easy to do that by attaching to them any concept of 'hard reality'. By 'hard reality' meaning: They are something that is there, has always been there, and will always be there, 'from ever', forever, and for every observer or way of looking at it, or measuring it. Something has to give at certain critical points, and under certain symmetry demands.

* It's actually even worse than dual. It's a triad: We have matter-content energy, geometric energy, and this vacuum-energy term that we can place either on the RHS or the LHS of the equations if we will.

Edited March 13, 2023 by joigus
minor correction

[martillo]

57 minutes ago, swansont said:

They are mathematically related. One would have to be emergent from the other.

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

Edited March 13, 2023 by martillo

[joigus]

33 minutes 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.

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

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

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. 

Edited March 13, 2023 by joigus
minor correction