What is the source of gravitational repulsion in certain cases?

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In summary, the conversation discusses the concept of nuclear force and its role in preventing the collapse of nuclei. It is explained that the nuclear force has a repulsive core which counteracts the attractive electromagnetic force. This repulsive force is dependent on the spin orientation of quarks in the particles. However, it is noted that gravity is always attractive, except in certain cases where a negative pressure can cause a repulsive effect. This is exemplified by the concept of a vacuum domain wall in cosmology.
  • #1
juan avellaneda
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i was wondering this

if the nuclear force overcomes the electromagnetic force in the nucleus, then what prevents the nuclei for colapse itself

i read in somewhere this
" the nuclear force has a repulsive core which prevents the nuclei from collapsing in on themselves"

what is this "repulsive core"?
 
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  • #2
The potential energy between two nucleons obeys the Yukawa potential. At small separation distances the potential energy is positive, and there is a strong repulsive force between the two nucleons. At larger distances, the potential energy is negative, and there is an attractive force. You can search for Yukawa potential and find out everything you want to know.
 
  • #3
nuclei

many thanks for your reply, it seems that all forces are not always attractive or repulsive, but dependes of quarks spin orientation in the particles
thats what i understood in some lecture i attend
 
  • #4
Except gravity. As far as we can tell, gravity is always attractive.
 
  • #5
Originally posted by FZ+
Except gravity. As far as we can tell, gravity is always attractive.

In some cases gravity is replusive. This happens because pressure is also a source of gravity and because a non-zero cosmological constant gives gravitational repulsion.

When there is a negative pressure present in that source which is so large as to overcome the attractive source due to other sources like mass terms in Einstein's equations, then there can be a resulsive effect.

A vacuum domain wall is a well-known example from cosmology.
 

1. Why don't nuclei collapse under the strong nuclear force?

The nuclei of atoms are held together by the strong nuclear force, which is one of the four fundamental forces in nature. This force is incredibly powerful, but it only acts over very short distances (less than the diameter of a proton). This means that as nuclei get larger, the strong nuclear force becomes weaker compared to the repulsive force between protons. This balance between attractive and repulsive forces keeps the nucleus stable and prevents it from collapsing.

2. How do protons and neutrons stay together in the nucleus?

Protons and neutrons are held together in the nucleus by the strong nuclear force. This force is generated by gluons, which are particles that act as carriers of the force between quarks (the building blocks of protons and neutrons). The strong nuclear force is able to overcome the electrostatic repulsion between protons and hold the nucleus together.

3. What role does the Pauli exclusion principle play in preventing nuclei from collapsing?

The Pauli exclusion principle states that no two identical fermions (particles with half-integer spin) can occupy the same quantum state simultaneously. This means that in the nucleus, each proton and neutron must occupy a unique energy level, preventing them from getting too close together and causing the nucleus to collapse.

4. Can nuclei ever collapse under extreme conditions?

In certain extreme conditions, such as in the core of a massive star or during a nuclear explosion, the balance between attractive and repulsive forces in the nucleus can be disrupted. This can lead to the collapse of the nucleus and the release of large amounts of energy. However, these conditions are not common and do not occur in everyday situations.

5. What happens when nuclei do collapse?

When nuclei collapse, they release a tremendous amount of energy, which is the basis for nuclear power and nuclear weapons. The collapse can also result in the formation of new elements, as protons and neutrons may rearrange themselves into different configurations. However, this process is highly unstable and typically results in the emission of particles and radiation as the nucleus tries to achieve a more stable state.

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