Quantum Theory - A Theory Which Completely Changed Our Understanding

Quantum Theory – A Theory Which Completely Changed Our Understanding

Until the early 20th century, everyone thought that we have pretty clear laws of physics that govern everything around us, The classical physics and the equations we had till then predicted everything we say, be it a moving ball, be it ripples, be it planets. Classical physics explained things with great certainty and applied to all the objects we knew until then.

But then, there came some experiments and some results which literally shook the world. These evidences built up to something which is popularly called the Quantum Theory. Basically, it is a physical theory that describes the properties of nature on an atomic scale. Now, this theory was so counter-intuitive that even the greatest minds in physics could not digest it. Einstein himself spent years to prove this theory wrong (which he could not do). He believed that we were missing something there.

So, What is Quantum Theory? Why is it is so counter-intuitive? How did it all happen? Let us dive into the quantum world and understand things…

Introduction to Quantum Theory

Quantum theory (otherwise known as quantum physics or quantum mechanics) is one of the two main pillars of modern physics, along with general relativity. These two theories claim to explain virtually everything about the universe. General relativity gives us our picture of the very big (space-time and gravity), while quantum theory gives us our picture of the very small (atoms and their constituents).

This is the video version of this article

Technically, quantum theory is actually the theory of any objects isolated from their surroundings but, because it is very difficult to isolate large objects from their environments, it essentially becomes a theory of the microscopic world of atoms and sub-atomic particles.

Now, this theory is so weird, it is so ridiculous and it has so many counter-intuitive things that you can’t even imagine. So, don’t be afraid we are not gonna go into much depth and anyhow it is safe to say that no one understands quantum mechanics completely.

'I think I can safely say that nobody understands quantum mechanics' - Richard Feynman Click To Tweet

So, before seeing more about quantum theory lets first see the history wherein we will understand a few important things of quantum mechanics.

How did it all begin?

It all basically started with a quest to know more about the basic building blocks of matter, i.e the atoms. To understand the beginning of quantum leap, you need to know about a few events which are

  • 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.
  • In 1905, Einstein proved the photoelectric effect by suggesting that the 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 behavior.

So, around this time there were a lot of new experiments and a lot of new things including Einsteins’ Theory of Relativity. A lot of people were trying to explain atoms and atomic behavior as well. One such behavior was that atoms have a strange property wherein they emit extremely selective wavelengths when heated. (These lines are called an emission spectrum and it is unique for every atom)

Bohrs’ Atomic Model

This property was explained by Neils Bohr in 1913. He developed an atomic model named Bohrs Model wherein he said that electrons have fixed orbits and electrons can exist only in these orbits.

He explained that when heated, electrons get agitated and jump from lower state to a higher state called electron excitation. When these electrons get back to their original state, called de-excitation, they emit energy which is very definite. Now here is the catch, it is like electrons just jump from one state to another, they don’t travel the space between. It is like Mars switching its orbit into Jupiter’s orbit suddenly without traveling the space between.

Bohrs Atomic Model
Bohrs Atomic Model (Kurzon / CC BY-SA (Source))

Bohr now put together his model with the concepts of Max Planck and he explained that atoms and electrons have energy which is quantized i.e it has some minimum value and will only have the multiples of these values and this is why there are only specific discrete orbits where electrons exist.

Quickly, a lot of evidences came up proving Bohr correct. This was the beginning of the Quantum era.

The idea of electrons jumping their fixed orbits without traveling space in between itself is a weird sounding thing, right? But more and more weird things were yet to come which literally shook everyone and set a battle ground between some of the greatest physicists for the stakes of nature of the reality itself.

The next big thing was hidden in an experiment called Youngs Double Slit experiment.

Double Slit Experiment

Basically, this double-slit experiment was performed 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.

Scientists were not able to understand that how can light show one kind of behavior in some experiments and completely different behavior in some other experiments.

What is the Double Slit Experiment?
In this experiment, there is a barrier which has two slits and behind the barrier, there is a detector. Now, if it is a particle moving from the barrier, it would hit the detector only at two spots which are right behind the slits. But if it is a wave, the two slits would split the wave and then the waves would join and hit the detector at various points creating an interference pattern.

It was in the 1920s, there was another surprise when two physicists named Davisson and Germer performed the same Double Slit Experiment with electrons. It resulted in electrons showing wave nature. What??? Yes, that was the reaction of everyone. An electron that was considered a particle till then showed the properties of a wave.

Physicists argued that somehow while traveling electron spread up like waves. A lot of people could not digest it. But a physicist called Erwin Schrödinger came up with an equation called Schrödinger wave equation. This equation described these electron waves with pretty good accuracy.

Schrodinger wave equation
Schrödinger wave equation

Though we got an equation which described the wave, how can an electron be a wave? The answer came from another physicist named Max Born. Born suggested that this wave was not a normal wave rather it was a probability wave. Herein the probability of an electron existing at one place is dependant on the wave size. This again was ridiculous. This is when Einstein gave his famous quote…

'God does not play dice with the universe.' - Albert Einstein Click To Tweet

Einstein argued that there was something missing in it and he believed that we should be able to predict everything with certainty. But Bohr believed that it is all uncertain, a particle-like electron can be in any state and at any location until and unless observed. Quantum theory suggested that an electron can be a particle as well as a wave at same time. All this was and is still really confusing to any common person.

Heisenberg's Equation
Heisenberg’s Equation where x is the position, p is the momentum and h cross is the Plancks constant divided by 2*pi

Adding to all the uncertainty, Heisenberg stated his Uncertainty Principle. It said that its impossible to exactly measure the position and momentum of a particle at the same time.

Adding to these mysteries there came another ridiculous, mysterious, absurd and most crazy prediction the equations of Quantum mechanics made…

Quantum Entanglement

If you don’t know about this till now, be ready to hear something which will blow your mind.

Quantum Mechanics predict that two particles can be linked together when they are close enough and they become entangled and their properties get connected. Now, the weird thing here is that these particles will be connected even if we take them long away in opposite directions, without any physical connection, What??? Yes, that is true, we will see its possible applications later in the article.

John Stewart Bell
John Stewart Bell

This was first found by Schrodinger and was studied by Einstein. Einstein showed this bizarre prediction of Quantum mechanics to say that something is surely missing and particle cannot get connected just like that as if there was no space in between. Einstein called this as the particle getting connected by some spooky actions.

No one could understand whether the particle really get connected or it is decided beforehand only that these particles will have particular properties.

It was in 1967 when young astrophysicist John Clauser. He set up an experiment using the research of an Irish physicist John Bell and he proved that entanglement is real and the particle gets connected. Don’t ask how does it happen? or Why does it happen? As Professor Walter Lewin says “It is an illegal question and you are not supposed to ask that, it is supposedly how world ticks

After this, there were a lot of improvements in quantum theory. All of these gave rise to a field of physics called quantum mechanics. It was widely accepted and confirmed again and again by several experiments.

Quantum mechanics was accepted as a superior set of rules which govern everything around us. It was also explained how classical mechanics come from quantum mechanics only.

The current problem which is eating away all the physicists on the planet is to get a unified theory. A unified theory is a theory which can explain all the four fundamental forces of nature.

Though some theories like the M-theory (a theory in physics that unifies all consistent versions of superstring theory) and the loop quantum gravity gave some hope, they did not really prove that effective.

Simply, we need a theory which unifies two of the best theories of namely Quantum Mechanics and the General Relativity.

Let us wait for the grand unification. In the meantime, let us look at the other side of the world where these theories gave rise to a whole new segment of technology.

Applications of Quantum Theory

All these arguments, proofs, evidences were going on one side but on the other side the accepted things were used in technology advancement. Due to these quantum mechanics, the equations and all the theories, we understood electrons better and it paved a way to lot of new devices like the diode, the transistor and the integrated circuits.

Quantum mechanics is the base of all the modern-day electronic gadgets. So, besides that let us discuss some applications which are already being used and some applications which might become true in the future.

Quantum Cryptography

For the people who don’t know, cryptography is basically the encoding and decoding thing used to securely transfer data.

Classical cryptography basically has two keys that are used to encode and decode the information. Though this classical method is safe, there is always a risk of someone cracking the key and decoding the information.

Researchers used quantum properties to make something called quantum keys. Here the communicator sends information using the polarized photons. Quantum rules dictate that “reading” the polarized photons will always change their states, and any attempt at trying to read the data will alert the communicators to a security breach. This makes Quantum cryptography pretty secure.

Quantum Computers

Quantum computer developed using quantum theory
Quantum computer based on superconducting qubits developed by IBM Research.

We all know the modern-day computers works on binary code that is 0s and 1s. The bits in the current circuits basically have two states where it can be either 0 or 1. If you can have both 0 and 1 at the same time, you get something called as Quantum Bits or qubits.

Quantum bits are basically superconducting circuits that can run in two directions at once. The resulting computers would be so powerful that our brains can’t even imagine.

We are yet to build quantum computers which can be used anywhere like normal computers. The major problem we face is that these qubits work only at low temperatures as they use superconducting materials.

A lot of researches are going on and the operating temperature is slowly coming up. Here is one such recent research.

We don’t really feel a need for something so fast as our daily needs are not that much. But some scientific works are so heavy that they need too much power which can be only achieved by quantum computers.

For example, to do a simulation of two black holes merging together as shown in the post below, NASA has to spend 46 days on a 13.3 petaFLOPS computer called Blue waters. Believe me, it is too powerful and NASA could only do partial simulation and some parts of the model were neglected as the processing power was insufficient. It was just two black holes, imagine the power one would need to simulate a whole universe…

So, in such cases, we would need quantum computers and it would help us a lot in understanding the cosmos.


Teleportation has been one of the biggest dreams. It basically means that we should be able to send objects from one place to another without the object traveling the space in between.

You would ask, is it even possible? Yes, in theory, it is possible to teleport objects. By using the property of quantum entanglement, we can have a lot of entangled particle at two far places and we can make an object interact with one set of entangled particles and by this we can transfer the exact quantum states of the object to another set of entangled particles which would result in teleportation.

Now, this might sound like science fiction but this has been already done with photons and other elementary particles. Scientists have teleported these particles from one place to another without them traveling the space in between.

Probably, we might also be able to teleport humans as shown in star trek using this so-called spooky quantum entanglement.

Let us wait and see

In Conclusion

So, that was a brief about quantum theory, how it all happened and what is the importance. Quantum mechanics still have a lot of scope for development. Once we achieve a whole unified theory we would have a lot better understanding of the universe. But no one knows we might find something more and more mysterious in this grand journey.

Quantum Theory Infographic

Quantum Theory Infographic
Quantum Theory © AtomsTalk

2 thoughts on “Quantum Theory – A Theory Which Completely Changed Our Understanding”

  1. Sai teja bro i want to know the details of integrated mtech in university of hyderbad ,can u please share those details like campus placements ,study etc

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