Is the 5th Fundamental Force Real?

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Discussion Overview

The discussion revolves around the concept of a potential fifth fundamental force in the context of atomic nuclei stability. Participants explore the roles of the strong force and electromagnetic force in maintaining the structure of atomic nuclei, questioning the mechanisms that prevent collapse and the nature of forces at play.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that the strong force holds protons and neutrons together in the nucleus, while the electromagnetic force prevents protons from repelling each other due to their positive charge.
  • There is a question about what prevents the nucleus from collapsing entirely, with some proposing that degeneracy pressure, related to the Pauli exclusion principle, plays a role.
  • One participant speculates that without the electromagnetic force, the strong force might only compress the nucleus into degenerate matter, raising questions about the conditions under which further collapse occurs.
  • Another participant mentions that neutrons are composed of quarks and have a strong interaction, countering a claim that neutrons do not have a strong interaction.
  • Some participants discuss the possibility of additional forces or gauge fields existing at high energies, suggesting that the four known fundamental forces may not be exhaustive.
  • There is a mention of the nuclear force becoming repulsive at very short distances, which complicates the understanding of nuclear stability.

Areas of Agreement / Disagreement

Participants express differing views on the nature of forces acting within the nucleus, particularly regarding the role of the strong force and the electromagnetic force. There is no consensus on whether a fifth fundamental force exists or how existing forces interact at small scales.

Contextual Notes

Some claims about the repulsive nature of the nuclear force at short distances and the implications of degeneracy pressure remain unresolved, with participants referencing external sources without reaching a definitive conclusion.

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I'm not sure if this is the right place to post this thread, so if there's a better place I'm all ears.

As I understand it the force that holds protons and neutrons together in the nucleus of an atom, is the strong force.
But what force is keeping the nucleus from collapsing altogether?

The article http://en.wikipedia.org/wiki/Degenerate_matter explains that the Pauli exclusion principle is responsible.
But pressure means force, and this force does not seem to be 1 of the 4 fundamental forces.

Is this then a 5th fundamental force?
 
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Well, you have the electromagnet force repelling them, and the strong force keeping them together.

I once wondered why the nucleus doesn't explode from all the electromagnetic repulsion (all the protons in the nucleus are positively charged) but the explanation is the strong force keeps them together.

So those two forces keep the nucleus stable.
 
Jonnyb42 said:
Well, you have the electromagnet force repelling them, and the strong force keeping them together.

I once wondered why the nucleus doesn't explode from all the electromagnetic repulsion (all the protons in the nucleus are positively charged) but the explanation is the strong force keeps them together.

So those two forces keep the nucleus stable.

Then why wouldn't a couple of neutrons implode?
 
I like Serena said:
Then why wouldn't a couple of neutrons implode?

What makes you think a neutron would implode?
 
Jonnyb42 said:
Well, you have the electromagnet force repelling them, and the strong force keeping them together.

I once wondered why the nucleus doesn't explode from all the electromagnetic repulsion (all the protons in the nucleus are positively charged) but the explanation is the strong force keeps them together.

So those two forces keep the nucleus stable.
+1

those are the only two forces I'm familiar with that keep an atomic nucleus in equilibrium (that is, keeping it from either collapsing or coming apart).

I like Serena said:
As I understand it the force that holds protons and neutrons together in the nucleus of an atom, is the strong force.
But what force is keeping the nucleus from collapsing altogether?
i'm wondering, what gave you the impression that an atomic nucleus would collapse in on itself if there were no force preventing it from happening? I'm not even sure that if the electromagnetic force were to suddenly cease to exist, the strong force would do much more than compress the nucleus until it became degenerate matter supported by degeneracy pressure. in other words, without the electromagnetic force to force protons in the nucleus apart, i don't know that the strong force is enough to turn atomic nuclei into anything more compact than neutron degenerate matter. consider that the Tolman–Oppenheimer–Volkoff limit (the mass limit at which neutron star degenerate matter can no longer support itself against gravity and collapses to a black hole) is FAR greater than the mass of an atomic nucleus. then consider that neutron stars approach atomic nuclei densities, and their constituent particles are therefore close enough together to be held together by the strong force (and not just gravity). and yet, the strong force does not overcome the neutron stars degeneracy pressure to cause any further collapse. only an increase in the neutron star's gravity (via an increase in mass to tip the scale past the Tolman–Oppenheimer–Volkoff limit) would cause further collapse. I'm no particle physicist, but i think a mass of nucleons would would have to be several orders of magnitude more massive than that of an atomic nucleus (as in 2 to 3 solar masses) in order to be on the verge of further collapse.
 
@OP:

What keeps the Earth from falling to the Sun?
 
I like Serena said:
Then why wouldn't a couple of neutrons implode?

[Neutrinos] are not composed of quarks and therefore don't have a strong interaction.

If you want to know why they don't collide due to gravity (lol) look https://www.physicsforums.com/showthread.php?t=406212".EDIT: I'M SORRY, I THOUGHT YOU SAID NEUTRINOS,

NEUTRONS are composed of quarks, but they are never found (as far as I know!) together without protons. But of course to fully answer your question I think you need quantum field theory. Since I don't know too much about that I won't try to act like I do.

Also, you are trying to think of these insanely small particle in terms of Newtonian physics, but unfortunately things behave differently at such small scales.
 
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Jonnyb42 said:
Neutrons are not composed of quarks.

This is wrong.
 
Jonnyb42 said:
Neutrons are not composed of quarks and therefore don't have a strong interaction.
If you want to know why they don't collide due to gravity (lol) look https://www.physicsforums.com/showthread.php?t=406212".

Neutrons are composed of quarks and do have a strong interaction
 
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  • #10
neutrons also have angular momentum
 
  • #11
Dickfore said:
@OP:

What keeps the Earth from falling to the Sun?

Speed of the Earth makes it orbit the Sun.
So are you saying that the neutrons orbit each other or something?
 
  • #12
It is generally believed that there must be many more forces (or more abstractly, gauge fields) than the usual four but they would only reveal themselves at very high energies (as I understand). Most of what we observe, including the atomic nucleus, can be explained by a balance of the 4 known forces.
 
  • #13
I like Serena said:
Speed of the Earth makes it orbit the Sun.
So are you saying that the neutrons orbit each other or something?

Probably what was meant was the analogy of two opposite forces being in equilibrium and cancelling out. Of course, in the case of neutrons the interplay between the electromagnetic and the strong force is much more complicated.
 
  • #14
Doesn't the nuclear force get repulsive at small distances.
 
  • #15
cragar said:
Doesn't the nuclear force get repulsive at small distances.

I've googled your remark and found for starters that there is another thread in PF that asked a similar question although the answers do not satisfy me. Here's https://www.physicsforums.com/showthread.php?t=113545".

Furthermore I found a reference at wikipedia: http://en.wikipedia.org/wiki/Nuclear_force saying:

"The nuclear force is only felt among hadrons. At much smaller separations between nucleons the force is very powerfully repulsive, which keeps the nucleons at a certain average separation. Beyond about 1.7 femtometer (fm) separation, the force drops to negligibly small values."

So apparently the strong force is responsible for neutrons not collapsing into each other.
However this is only a short sentence with no references.

And as yet, I haven't found other references that mention that the strong force repels.
 
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  • #16
raul_l said:
It is generally believed that there must be many more forces (or more abstractly, gauge fields) than the usual four but they would only reveal themselves at very high energies (as I understand). Most of what we observe, including the atomic nucleus, can be explained by a balance of the 4 known forces.
hmm...i was under the impression that the opposite happens at high energies. that is, as energy increases, the 4 fundamental forces begin to combine one by one, and by the time energy levels are high enough, the 4 fundamental forces will have combined into a single unified force. of course i got this impression from reading about the Big Bang and the brief moments succeeding it...and perhaps i misunderstood some things.

cragar said:
Doesn't the nuclear force get repulsive at small distances.
this is something i was unaware of regarding the strong force. if this is true, then i have to rethink my response to I Like Serena's question about what force keeps an atomic nucleus from collapsing in on itself. obviously the strong force only works over extremely short distances, but i had no idea that it could become repulsive between particles that got too close in proximity. but then we come back to the 2 main forces that keep the nucleus stable - the electromagnetic and strong forces. so is it that the electromagnetic force keeps protons in an atomic nucleus from collapsing in on each other, while the "repulsive" strong force keeps neutrons from doing the same? i mean obviously the electromagnetic force cannot be responsible for keeping neutrons in an atomic nucleus from collapsing in on each other b/c they carry no charge and therefore do not repulse each other in that way. initially i thought it might be neutron degeneracy pressure that keeps the strong force from collapsing the neutrons in an atomic nucleus (since the electromagnetic force can't achieve this with neutrons). but depending on the legitimacy of the strong force's sometimes "repulsive" characteristics, it may be the strong force that keeps neutrons in an atomic nucleus "together" AND keeps them "apart" so to speak.
 
  • #17
I like Serena said:
Speed of the Earth makes it orbit the Sun.
So are you saying that the neutrons orbit each other or something?

Neutrons and protons are fermions, which means the Pauli exclusion principle holds for them. If we want to squeeze them into a small volume in space, then they must obtain different momenta, specifically some of them get higher momenta than in the ground state (which is called a degenerate Fermi Sea). This increases the total kinetic energy of the system. An increase in the energy as you decrease the volume of the system is interpreted as pressure. This pressure is called degeneracy pressure.

This pressure opposes any attractive force between them until an equilibrium is establish. Nevertheless, its origin is in the increase in the kinetic energy of the system, just like in the case of the solar system.
 
  • #18
94JZA80 said:
i was under the impression that the opposite happens at high energies. that is, as energy increases, the 4 fundamental forces begin to combine

It was surprising to me too. I heard about it in a M. Gell-Mann lecture. See this http://www.youtube.com/watch?v=7qiJTNKTihk&feature=related at 01:15. As I understand what happens is that as the 4 known forces start to become one new forces begin to emerge.
 
  • #20
Borek said:
https://www.physicsforums.com/showthread.php?t=42989

https://www.physicsforums.com/showthread.php?t=230839

https://www.physicsforums.com/showthread.php?t=409034

https://www.physicsforums.com/showthread.php?t=181298

Especially check this post:

https://www.physicsforums.com/showpost.php?p=2755214&postcount=9

Thanx :cool:!

I see I'm not the first that had this thought!
There's lots of previous discussion.

And I was just thinking about how the Pauli's exclusion principle acts in every way as a force, when I got to your last link that basically states exactly that!
 
  • #21
I like Serena said:
And I was just thinking about how the Pauli's exclusion principle acts in every way as a force, when I got to your last link that basically states exactly that!

At the same time it explains that while it looks like a duck, it swims like a duck, it quacks like a duck - its a rabbit.
 
  • #22
Borek said:
At the same time it explains that while it looks like a duck, it swims like a duck, it quacks like a duck - its a rabbit.

I keep wondering, why can't it be a duck too?
Isn't that a matter of "relativity"?

Perhaps someday the other 4 forces will turn out to be rabbits as well!
 

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