Classical physics deals with non-extreme conditions where quantum mechanics (QM) and Einstein's theory of relativity (ER) are not needed. Modern physics incorporates elements of QM or ER, or both, and is needed when dealing with extreme conditions like very small distances, high velocities, or large distances. Key differences between classical and modern physics include: particles being distinguishable versus indistinguishable, the size of the phase space cell, restrictions on particles due to principles like Pauli Exclusion, and possible arrangements of particles in cells.

3. DIFFERENCE BETWEEN CLASSICAL AND MODERN
 Physics that incorporates elements of either QM or ER (or both) is said to be modern physics.
 Modern physics is often encountered when dealing with extreme conditions. Quantum mechanical effects tend to appear when
dealing with "lows" (low temperatures, small distances), while relativistic effects tend to appear when dealing with "highs" (high
velocities, large distances), the "middles" being classical behaviour.

4. PARAMETER
CLASSICAL OR M-B
STATISTICS
BOSE-EINSTEIN STATISTICS FERMI-DIRAC STATISTICS
Particles Particles are distinguishable Particles are indistinguishable Particles are indistinguishable
Size of phase space cell
The size of phase space cell can
be as small as we require
The size of the phase space cell
cannot be less than h3 The size cannot be less than h3
Number of cells
If ni be the number of particles
and gi the number of cells then
gi>>ni so ni/gi<<1. Thus,number
of cells can be made as large as
possible
The number of cells is less than or
comparable to the number of
particles gi < ni
ni/gi  1
The number of cells has to be
greater or equal to the number of
particles so ni /gi  1
Restriction on particles No restriction
No restriction Restriction due to Pauli Exclusion
Principle
Two particle distribution in two
cells The particles are distinguishable
and can be arranged in four ways
The particles are indistinguishable
and can be arranged in three ways
No two particles can occupy the
same cell. Hence, only one
arrangement

5. THEORY OF RELATIVITY

9. CLASSICAL ASTRONOMY

19. WHITE HOLE