Four or Five fundamental forces

[Dmitry67]

I would say, there are 4 *fundametal interactions* and 5 *force sources*
Pauli ep is not an interaction but it behaives exactly like a force in some cases, for example, it is responsible for the stability of the white dwarfs and neutron star.

If you don't agress that Pauli e.p. is not a force, please fill the void in the following sentence:

In the while drarfs the gravitational force is compensated by ... that is why these objects do not collapse.

 

[tim_lou]

the so called 5th force is actually included in other forces already. The coulomb potential is in fact only an approximation. The actual physics comes from QED and when one goes beyond the first order approximation, one gets a spin dependent potential. So in fact, just by electromagnetism, the "coulomb" force is dependent on the spin of the two particles that are interacting.

Saying the Pauli exclusion principle is a force is wrong because if the QED interaction term is gone, then there will be no interactions. Two particles will never scattering/ or annihilate with one another. In fact, in this hypothetical world, there can never two particles having the same spin and momentum (the math just does not permit this from happening).

As for Dmitry67's sentence, if you really want to avoid using degeneracy pressure, you can say the gravitational force is compensated by spin dependent interactions from QED. You may complain that neutrons have zero net charge, however, there is still electromagnetic interaction (since the constituent quarks have charge).

 

[DaTario]

I would say, there are 4 *fundametal interactions* and 5 *force sources*
Pauli ep is not an interaction but it behaives exactly like a force in some cases, for example, it is responsible for the stability of the white dwarfs and neutron star.

If you don't agress that Pauli e.p. is not a force, please fill the void in the following sentence:

In the while drarfs the gravitational force is compensated by ... that is why these objects do not collapse.

It is easy not to get satisfied with your proposal of separating interactions from forces. These two concepts are entagled. Fundamental interaction and fundamental force seems to be the same thing.

Best wishes,

DaTario

 

[Dmitry67]

You may complain that neutrons have zero net charge, however, there is still electromagnetic interaction (since the constituent quarks have charge).

What about the neutrino?
They are fermions, right? So the pauli's principle is applicable to them too?
Should we also claim that "there is still electromagnetic interaction" between the neutrinos?
:)

 

[tim_lou]

The neutrinos interact via weak interaction. Similar "repulsion" effects will result if you take that into account. The reason why I mentioned QED only is because it is the one that I am familiar with. However, not knowing much about weak interaction, I do not know if the massive bound states (like neutron) can arise. If no bound state exists, the question of degeneracy pressure simply isn't valid.

The pauli exclusion principle essentially comes from the creation operator being anti-commuting, it is a feature of the free theory. This property is universal in any interaction (in the interaction picture) be it QCD, QED, or other things.

Ideas like pauli exclusion principle appear often in statistical mechanics. It is a general universal feature regardless of how complicated the interaction is. Similar to how a system tends toward maximum multiplicity. If the exclusion principle is a fundamental force, then I would say The tendency toward maximum entropy is another fundamental force, phase transitions would be another force... that just doesn't work, they are merely universal behaviors of more fundamental forces. A bound state of neutrons and/or a "hypothetical" bound state of neutrino all follow the pauli exclusion principle but fundamentally, they come from different interactions. Just because their behaviors look the same doesn't mean they come from the same interactions.

 

[Dmitry67]

It is easy not to get satisfied with your proposal of separating interactions from forces. These two concepts are entagled. Fundamental interaction and fundamental force seems to be the same thing.

Best wishes,

DaTario

If you did not knew that pauli e.p. was not an interaction, how would you describe a neuron star? You would say that for some reason neutrons inside interact with each other, they repel each other and create a force strong enough to stop the collapse.

I understand that the mathematics behind is absolutely different, but at least on the macrosopic level Pauli.e.p. manifests exactly like a force

 

[Phrak]

What's a force?

 

[DaTario]

I woud say that is a concept which has as inputs neigbohr quantifiable features of a given real scene and it gives us at the end, through the machinery of Newtonian mechanics, the way our particle moves.
DaTario

 

[alxm]

Exchange energy is not a force.

Exchange energy the difference in energy due to applying different boundary conditions (symmetric/anti-symmetric solutions) to the Schrödinger equation.

To take another example of boundary conditions, if you solve the particle-in-a-box problem, you'll find that the energy is dependent on the size of the box. That doesn't mean 'size' is a fundamental force of nature.

 

[Dmitry67]

What's a force?

Good question, as gravitation is also not a force.
And electromagnetism is unified with weak interaction
How many forces do we still have?