There are two kinds of particles in the universe. One is Fermions and the other is Bosons. "Fermions having the same properties (like spin, energy, angular momentum) cannot occupy the same place. Remember, like poles repel. This is the Pauli's exclusion principle. Electrons, protons and neutrons are fermions.
Two electrons having same properties cannot co-exist. For example, in the first orbit of the atom, two electrons can occupy. But they should have opposite spin. Other electrons should go to higher orbits. It is like filling -up seats from the stage to the balcony in a theater. That is why there is lot of empty space in an atom. In spite of empty space, we cannot squeeze a solid materials. Because electrons offers resistance due to Pauli's exclusion principle. Hence we are not able to force our hands through the table and we are not falling thorough the earth. Solid remains solid. Also we can understand periodic table arises because of Pauli's exclusion principle.
Neutrons quantum properties allow little more tight packing. Hence they all live in the small space of nucleus.
WHITE DWARF, NEUTRON STAR, BLACK HOLE
At the end of a star's life, it stops burning. Then gravity comes into action. The gravity collapse the star into itself - an implosion. The star shrinks, and becomes white dwarf. Here all the electrons go and occupy the lowermost energy levels with out violating Pauli's principle.
When the star's mass is just greater than 1.4 times of our sun's mass (Chandrasekhar's limit), there is more gravity, more compaction. Now the protons and electrons merge and become neutrons. The star just becomes a ball of neutrons - called neutron star. Its size is nearly a size of a city (10 - 12 km). The great star is shrieked to such a size and the neutrons occupy a small space again without violating Pauli's principle. Still heavier star just become 'black hole'.
BOSONS
Small ice cubes can join, melt, freeze and become one big ice cube. Similarly bosons can mingle and co-exist as one unit. They do not obey Pauli's principle. One good example: Photons are bosons. Photons can join and become one solid beam of light . That is LASER.
In the electrical super conductor, electrons become bosons (explore how?). Here resistance becomes zero and conductance becomes infinity.
In the super fluid, liquid molecules becomes bosons. They flow without resistance (zero viscosity) in a steam lined way.
If we find easy way to make Bosons, future will arrive quickly.
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Dikeshit verma rool no1517996
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