Is the 5th Fundamental Force Real?

In summary, the strong force is responsible for holding protons and neutrons together in the nucleus of an atom, while the electromagnetic force counteracts the strong force's repulsion between positively charged protons. The Pauli exclusion principle also plays a role in preventing the nucleus from collapsing altogether. It is believed that there may be other fundamental forces at play at very high energies, but the four known forces can explain most observed phenomena. At small distances, the nuclear force can become repulsive, keeping nucleons at a certain average separation. The exact nature of the nuclear force is still not fully understood and requires further study.
  • #1
I like Serena
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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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  • #2
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.
 
  • #3
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?
 
  • #4
I like Serena said:
Then why wouldn't a couple of neutrons implode?

What makes you think a neutron would implode?
 
  • #5
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.
 
  • #6
@OP:

What keeps the Earth from falling to the Sun?
 
  • #7
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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  • #8
Jonnyb42 said:
Neutrons are not composed of quarks.

This is wrong.
 
  • #9
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!
 

1. Is there evidence for the existence of a 5th fundamental force?

As of now, there is no conclusive evidence for a 5th fundamental force. While there have been some anomalies and theories that suggest the possibility of a new force, further research and experimentation is needed to confirm its existence.

2. What is the 5th fundamental force supposed to be?

The 5th fundamental force, if it exists, is believed to be a force that cannot be explained by any of the four known fundamental forces (gravity, electromagnetism, strong nuclear force, and weak nuclear force). It could potentially help explain phenomena such as dark matter and dark energy, which are not fully understood by the current four forces.

3. How would the discovery of a 5th fundamental force impact our understanding of the universe?

If a 5th fundamental force is confirmed, it would greatly impact our understanding of the universe and the laws that govern it. It could potentially change our understanding of gravity and how it interacts with other forces, as well as provide new insights into the nature of dark matter and energy.

4. What are some ways scientists are trying to detect the 5th fundamental force?

Scientists are using various methods to try and detect the 5th fundamental force, such as studying the behavior of subatomic particles and their interactions, observing the effects of gravity on large scales, and conducting experiments with high-energy particle accelerators. Additionally, some scientists are exploring theories that propose the existence of a 5th fundamental force and are testing their predictions.

5. What are the potential implications of discovering a 5th fundamental force?

If a 5th fundamental force is discovered, it could have significant implications for our understanding of the universe and the technologies we use. It could potentially lead to new discoveries and advancements in fields such as astrophysics, particle physics, and cosmology. It could also have practical applications, such as improving our understanding of energy and developing new technologies based on the principles of the 5th force.

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