What is Quantum Physics

Table of Contents

Quantum Physics Definition

People like to attach names to things, whether a pet, an item, or an abstract idea of the meaning of the universe. But when we dissect these ideas further, there is a different kind of world that isn’t visible to us in full: to understand the glass in our hands or the house we live in full, we hereby require a fundamental makeup or map at an atomic level, explaining these properties at the most basic level of levels. This is what we work with when we study Quantum Physics.

A subfield of physics, Quantum Physics governs matter in its most elementary form. It maintains that forms of matter (such as energy) can be broken down to a primal level, which studies the properties of subatomic particles, atoms, and electrons in depth.

Exhibiting specific behavior, the field of quantum mechanics can be broken down into the following postulates:

  • Particle-wave duality: All matter has properties that resemble waves (see Superimposition). It seems like diverting the reader. No hyperlinks found if the writer intends to add them.
  • Particle-wave: Waves can be explained using probabilistic models (see Uncertainty).
  • Properties: Properties may work together (see Entanglement). Examples: The Heisenberg Uncertainty principle.
  • Observance: Individual observance may alter the outcome (see Entanglement).

Central concepts of Quantum Physics

It was quantum physics that deciphered atoms into a nucleus (consisting of protons and neutrons) and electrons from its prior models, which had particles orbit the nucleus, much to how the earth orbits the sun as we know it today.

Photon energy

Atoms of light are stored in small packets, otherwise known as photons. A photon has the following properties:

  • Frequency v, nu
  • Wavelength λv=c
  • Speed c
  • Energy E=hv
  • Momentum p=hv/c
  • A higher frequency is linked to more energy required to oscillate, whereas a lower frequency is linked to less energy.
  • Max Planck value = h= constant = 6.63 x 10-34 J.s

Black body radiation

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If you ever, as a kid, played with glow sticks, you knew how exciting it was when you bent one and could see your surroundings for hours on end. Physicists explain that everything glows in some respect. Some glow more than others and depend on two factors: temperature and wavelength. When a property’s wavelength is shorter and has more heat, it will glow more than its converse: a property with a longer wavelength that is cooler will not glow as much.

A body of heat, a blackbody, is considered an ideal system that absorbs all radiation falling on it without reflecting any part. Its radiation is known as Blackbody radiation which is a fundamental pillar for understanding this area of deep physics.

Wien’s Displacement Law

A study on blackbody radiation, Wien’s displacement law, shows that the temperature has a direct influence on wavelength: As temperature increases, the wavelength gets shorter and more stacked together, and when temperature decreases, the wavelength expands and spreads.

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This phenomenon can be mathematically represented as follows:

\lambda (max) = \frac{b}{T}

where \lambda (max) is the peak wavelength at the maximum point, is the constant of proportionality, and is the absolute temperature of the object’s radiation. The result could be further reduced to the following:  \lambda (max)=\frac{2.89 \times 10^{-3} m.K}{T}


Planck’s constant

Based on wavelength and temperature’s influence on blackbody radiation, Max Plank developed the following equation, which can be used to determine the energy of an oscillator:

E=hf or E(n)=nhf if n\neq 1, where n is a quantum number, f is the oscillator’s frequency, and h is the Plank constant.

The three principles (superposition, uncertainty, and entanglement) guard the annals of quantum mechanics and are explained below in more detail:


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If we think of waves in quantum physics, they have ripples: high and low points. These points can add up to become bigger or smaller, spreading to the complexity of wave sizes and forms. This phenomenon is called superposition. One example of superposition is the double slit experiment (explained in the next section), where waveforms can break and behave as light or particles depending on the number of slits. Behaving like a wave in some experiments, light produces interference patterns (highs and lows). As with the wave example, the superposition principle has it that various solutions can contribute to the solution of one another. 


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One concept of uncertainty is the relationship between a dependent variable and an independent variable: We need to derive one from the other. Both cannot be derived simultaneously. Likewise, the better we estimate an uncertainty, the more proportional our result will be. As such, if we have a better approximation for one variable above, we will have a better estimate for the result in tandem. One such probabilistic model example is the wave equation which involves the likelihood that particles can be mapped with a probability distribution:


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The behavior of one object is symbiotic in behavior to another object. These objects are each thought of as distinct but also at the same time in unison – that is, they have matching behavior. This behavior makes prediction possible in the following manner: by stipulating behavior in one object, you can predict the second object’s course.

Behavior of particles in quantum physics

In describing quantum physics, researchers identified numerous paradoxes – such as the double slit experiment in physics – that have plagued them in discerning the physical world, leading them to contradict theories and complex results. We will explain some of these paradoxes below:

Double slit experiment

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The double slit experiment shows how matter and light – contradictory to what most physicists would claim as an either-or scenario – can behave not only as waves but also as particles. In other words, matter and light have specific properties that emanate as particles or waves depending on the course of view.

Imagine that you stand facing a wall with two slits as an experiment. Next, imagine a cart with endless balls where you take a ball and throw it at the wall in front of you. Chance has it that some of these balls will bounce off, whilst the rest (a minority thereof) will go through the slits.

Now, imagine that behind this wall is another solid wall without any slits. You still keep throwing balls at wall one with a twist: you now dip them in chocolate before throwing them. Consider what would happen if the balls passed through the slits from wall 1 to hit wall 2. Indeed, if you guessed that the balls passing through the slits at wall one would form chocolate stripes resembling the slits on wall 1, you would be correct.

Similarly, we can project a light (single colored) onto a similar background to wall 1. This experiment can be done with a simple flashlight and a piece of paper cut with one slit. For only one slit, the light collected at the end – as with the group of balls thrown through the slits – will match the pattern of the slit.

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However, for two slits, something interesting will appear when recording the pattern at the other end: The light will split into multiple separate light forms (an interference pattern), diffracting into constructive and destructive interference. This result shows us that although light behaves as a particle in experiment 1, much to the behavior of tennis balls, it acts – contrary to what is first believed – as a wave in experiment 2.

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Example Problems 

Given that a human body emits a temperature of 35°C, calculate the peak wavelength of the blackbody radiation using Wein’s displacement law.

1. Substitute the surface temperature in T in Kelvins

Temperature in Kelvins = 35 + 273 = 308 K

2. Find λ (max) value.

\lambda (max)= \frac{2.89 \times 10^{-3} m.K}{308} = 9.41 \times 10^{-6} m

Suppose we have the following system with the energy quantized: weight = 4 kg, force constant = 20 N/m, stretch distance = 0.200 m. Calculate the quantum number n for this system. 

1. The total energy, E, of the object is given as \frac{1}{2} k A^{2} = 0.5 (20)(0.400)^{2} = 1.6 J

2. The total frequency, f, of the object is given as \frac{1}{2\pi } \sqrt{\frac{20}{4}} = 3.51 Hz

3. Rearrange the Plank equation to get n alone: n = \frac{En}{hf} = \frac{1.6}{ 6.626 \times 10^{-34} (3.51)} = 6.8 \times 10^{32} (Note that the units cancel as n is unit less). 



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