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Modern Physics

Mechanics in the modern era is the study of fundamental aspects of the universe using post-Newtonian theories. Early in the twentieth century, various physicists and mathematicians made experimental findings that were not explainable by classical physics (which explains normal physical phenomena). These theories gradually gave rise to modern physics.

The two theories which laid the foundations of modern physics are the theory of relativity and the quantum theory. Physical phenomena are explained by quantum theory at a microscopic level, while large-scale physics involving particles closer to the speed of light needs the help of relativity theory. Physicists now use both theories to approximate the predictions of classical theory.

Father of Physics

Physics encompasses both the study of theoretical and experimental aspects of all-natural phenomena. The subject has developed through the efforts of many scientists. Three scientists have been awarded the title "Father of Physics" at different times, based on their most important contributions.

For his contributions to Astrophysics, Galileo Galilei is known as the Father of Observational Physics.
It was Sir Isaac Newton who established the laws of motion and gravity. His theory is the basis of classical physics. It works well on a small scale. Additionally, he came up with the calculus theory. The world of Physics considers Sir Issac Newton to be the Father of Classical Physics for his contributions to this field.

Modern physics owes its origins to Albert Einstein. A special relativity theory and a general relativity theory are his contributions. These theories govern high-speed objects and gravity. For his explanations of the photoelectric effect, he won the Nobel Prize.

The advent of Quantum Theory

During the development of classical physics, the physicists had problems explaining experimental results of black body radiation, photoelectric effect, electron interference, and the stability of atoms. The theories of classical physics consider waves and particles as different concepts. In 1900, Max Planck proposed the theory of light as a collection of packets of energy, known as photons. Each photon possesses energy.
E = hv

Assume that h is Planck's constant and v is the frequency of light. This hypothesis describes the black body radiation phenomenon despite contradicting the classical view that light is an electromagnetic wave. The photoelectric effect was explained by Einstein later in 1905 based on the idea that light is composed of many photons (energy units).

Conversely, the mathematics involved in the theory could consider electrons as waves only if they were interfering with one another and maintaining the stability of an atom. De Broglie proposed that particles behave like waves with wavelengths:
λ=hp
where,
p denotes its momentum.

We see objects with relatively short wavelengths in daily life, as classical theory dictates that every object's wavelength is minimal compared to its size. However, when we consider a subatomic particle such as electrons, the wavelength becomes comparable with their size.

Importance of Quantum Theory

Quantum theory is necessary for explaining physics at small scales (such as the atomic scale). For example, we can find the values associated with a bound system by measuring energy and angular momentum. The theory, which originated in mathematics, was developed by physicists including Heisenberg, Bohr, Schrödinger, and Dirac. Scientists like Steven Hawking and Richard Feynman contributed to the development of Quantum Field Theory during the late twentieth century.

A Brief History of the Theory of Relativity

Time and space are not separate concepts, according to Einstein. Space and time are relative to the frame of reference from which we make an observation. Newton's theory of time considers it a constant which has no relationship to the observer. There were no explanations for Mercury's precise positioning or time difference between its satellites in the classical theory. However, the relativity theory was able to explain them. The concept of "spacetime" was introduced by Einstein. Gravity results from the weight of something large entangling with spacetime. Einstein also recognized the simple relationship between mass and energy. For each mass m, E is equivalent to,

E=mc2

Here,
c denotes the speed of light in a vacuum.

Modern concepts of physics

Quantum theory finds its basis in the following concepts:

  • Dual Nature of Light: This theory introduces the concept of the dual nature of light. Light is present in the packets of energy known as photons, and they also exhibit wave characteristics.
  • Shrodinger's Uncertainty Principle: If an electron is moving in a region, then we cannot measure the momentum and position of that electron simultaneously.
  • Measurement Paradox: When you measure a system or observe it, you change its state.

Relativity consists of the following concepts:

  • Any massive object cannot have a faster speed than light. Therefore, physics laws never change no matter how many observers are present.
  • Spacetime curvatures result due to bodies with heavy mass.
  • Objects that approach the speed of light experience length contraction (length reduction). Similarly, time dilation occurs in a moving clock with velocities closer to the speed of light.
  • The laws still preserve the chronology of events or the causal structure (causality) of events.
  • There is no difference between a gravitational mass and an inertial mass.
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