Satyendra Nath Bose | Quantum Physics

Context (TH): This year marks 100 years of Satyendra Nath Bose’s discovery.
He was an Indian physicist specialising in mathematical physics.
He is best known for his work on quantum mechanics in the early 1920s, providing the foundation for Bose-Einstein statistics and the theory of the Bose-Einstein condensate.

Early life

Bose was born in Calcutta (now Kolkata) in 1894.
After completing his schooling, he joined Presidency College to study physics.
After a few years, he was appointed as a faculty in the newly founded Rajabazar Science College.
Later, he joined the Dhaka University as a lecturer.

Bose & Saha (his friend) published the first English translation of Einstein’s papers on general relativity.
- Saha was one of the first people to start finding applications of the developing quantum theory to molecular physics.
Developed the foundation for Bose-Einstein statistics:
- Bose read Planck’s papers on the distribution of energy in blackbody radiation to teach this material to his class.
- It was while teaching quantum theory in Dacca that he first noticed a logical problem in all known derivations of the Planck law of blackbody radiation.
- In 1924, Saha stayed with Bose in Dhaka and pointed out the 1923 papers of Wolfgang Pauli, Einstein and Paul Ehrenfest and their relation to Einstein’s 1917 paper.
- This led him to develop Bose statistics – a new method to count states of indistinguishable particles and applied it to his derivation of Planck’s radiation law.
- He discovered the correct set of equations to use to work out the behaviour of collections of photons (particles of light).
Bose Discoveries (along with Einstein)
- Define the two classes of subatomic particles: fermions and bosons.
- Discovered Bose-Einstein Condensate (BEC)

Planck’s law: It states that electromagnetic radiation from heated bodies is not emitted as a continuous flow but is made up of discrete units or quanta of energy.
- Planck’s law is about radiation. All hot objects, from a bowl of hot soup to the Sun, emit radiation in a range of frequencies.
Black bodies: objects that can emit light but cannot reflect it.

Formulated in 1915, it revolutionised our understanding of gravity.
Instead of viewing gravity as a force between masses, Einstein proposed that massive objects cause a curvature in the fabric of spacetime.
In other words, massive objects, like planets or stars, bend the space and time around them, creating what we perceive as gravity.
Einstein’s idea helped explain why Mercury moves a bit strangely in its orbit and why light from stars bends when it passes close to the Sun.

Bose–Einstein statistics, proposed by Satyendra Nath Bose and expanded by Albert Einstein.
It applies to particles known as bosons (e.g., certain types of atoms).
Unlike classical statistics, it treats these particles as indistinguishable, emphasising their quantum nature.
Classical statistics (like those of Maxwell-Boltzmann) treat particles (electrons, protons, and neutrons) as distinguishable – each has its own identity and energy state.
It introduces the idea that identical particles can occupy the same quantum state. This concept is crucial for understanding the behaviour of particles, especially at extremely low temperatures.

Imagine you have a collection of bosonic particles, like atoms, cooled down to near absolute zero. At such low temperatures, the principles of Bose–Einstein statistics come into play.
As you cool these particles, they start behaving less like individual entities and more like a single, collective quantum entity. They gather in the same lowest energy state, essentially becoming indistinguishable and behaving collectively.
The result is Bose–Einstein condensate – a unique state of matter where a large number of particles occupy the same quantum state, behaving as one superfluid entity.
Bose–Einstein statistics tell us how particles that follow quantum rules (like bosons) behave.
Bose–Einstein condensate is what happens when a bunch of these particles are cooled to super-low temperatures.

Bosons and fermions are fundamental particles that exhibit distinct characteristics in quantum physics.
Bosons have integer spins (0, 1, 2, …), and fermions possess half-integer spins (1/2, -1/2, …).
Bose-Einstein statistics governs bosons. Multiple bosons can occupy the same quantum state simultaneously. i.e. they disobey the Pauli exclusion principle.
In contrast, fermions, Subject to the exclusion principle, no two identical fermions can occupy the same quantum state simultaneously.
Bosons include Photon, Gluon, W and Z bosons, and Higgs bosons.
Fermions include Electrons, protons, and neutrons.

It is a branch of physics that explores the tiny building blocks of this world, particles like electrons and photons.

In 1898, J J Thompson discovered electrons using the properties of cathode rays.
In 1900, Max Planck sowed the seeds for quantum theory by stating that electromagnetic energy could only be emitted in quantized form. His quanta are now called photons by physicists.
- Energy Packets (Quanta): This means that energy comes in specific, well-defined amounts rather than as a continuous flow. Albert Einstein later embraced this idea.
In 1905, Einstein proved the photoelectric effect by suggesting that light is made up of packets of energy. With that, he proved that light exists in discrete packets of energy, giving the light a particle behaviour.

It suggests that particles, such as electrons and photons, can exhibit both wave-like and particle-like behaviours, depending on the circumstances.
- Double-slit experiment by Thomas Young in 1801. This experiment proved the wave nature of light, and this result was opposite to what Einstein proved with the photoelectric effect (particle nature).

If two particles become entangled, changing the state of one particle instantaneously affects the other, no matter how far apart they are.

Proposed by Werner Heisenberg. It says that you can’t know everything about a particle at the same time. If you precisely know a particle’s position, you’ll have less certainty about its speed, and vice versa.