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Introduction | Mysteries in QM | Double Slit Experiment | Superposition | Entanglement
What do you see swimming in the fluidity of your eyeballs in front of you at this very moment? Do you see words pouring, and filling the absolute length of your vision while you stare at this screen? Does the appearance of life reflect reality? Life as seen from the eyes of 6 billion humans. Low and behold, twelve billion eyes that deceive and lie to us all. When we delve deeper into the subatomic state of matter, we see that our eyes paint a false picture of what the fundamental nature of the universe really is.
When the world on a large scale, is reduced to a very small scale, we see that things are very different in reality from how they first appeared. On a large scale everything makes common sense and follows the laws of classical physics perfectly, but when we look deeper into it we find that our observations greatly contradict classical physics and it starts to act in a strange, peculiar way. This is where quantum mechanics come into the picture. It is a branch of physics that explains the behaviour of matter in the atomic level, where things start behaving very oddly.
A century in which man landed on the moon, Einstein discovered the theory of relativity, the internet captivated the world, as well as numerous advancements; quantum mechanics has been described as the crowning achievement of the 20th century.
Quantum mechanics deals with physics on the subatomic scale, as the laws of classical physics are not accurate enough on this scale. At school you would have been taught classical physics….those tedious laws and equations which made Days of our Lives seem interesting. Not anymore! Mysteries await you…catapult yourself into the wonderful world of quantum mechanics now.
The infamous double slit experiment is the grandfather of quantum mechanics. It formed the main cornerstone of the exploration of quantum mechanics. Scientists were baffled and it caused them to forever step into the mysterious and strange world of quantum physics. After the findings in the double slit experiment, a huge debate began, the question being: Is matter made up of particles or is it waves? That is the fundamental question and the basis of the quantum mechanics.
The experiment
Curious about what mysteriously happened in this experiment that baffled scientists? Ponder no more. The experiment is explained to you below, in easy-to-follow layman’s terms.
Step 1 | Step 2 | Step 3 | The twist
The first step in the double slit experiment was to fire balls of matter such as marbles or paintballs through two slits. What do you think happened? As expected it formed two bands on the screen behind the slits (see Screen 1).
Screen 1
Next, waves were pushed through two slits. When each wave got to the slits, they split and two waves emerged after the slits. The next waves then followed, and the tops (crests) of these waves clashed with the bottom (troughs) of the previous waves (see Motion 1). This clash resulted in constructive interference and deconstructive interference. On the screen behind the slits, an interference pattern was formed (see Screen 2).
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Motion 1 |
Screen 2 |
The bright bars in the interference pattern in Screen 2 represent constructive interference, which is where two crests or troughs of the wave meets. The darker bars are caused by destructive interference which is when a crest and a trough meet and cancel each other out.
In the previous 2 steps balls of matter or macroscopic particles were being used. In this step and the next; microscopic particles are being used in the experiment such as photons, electrons or atoms. In our explanations we are using electrons.
Now, what happens next, is that electrons are now fired through two slits. What do you think happens? Two bands formed on the screen? Schockingly, nothing like what we expect happens! Instead of forming two bands after going through the two slits like the marbles, the electrons form an intereference pattern(Screen 3 & 4) like waves! Welcome to the quantum world! Seemingly, the electrons have assumed a life of their own and defied all logic. Strange indeed that ‘particles’ act like waves, which brings us back to the question: Is matter a wave or particles? At this point you would say it is a wave, but wait…there is another twist.
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Screen 4 |
Screen 3 |
When an observer or measuring device(Motion 2) is placed at the exit of the slit, the electrons react to the device. As if the electrons somehow know that they are being watched! When being ‘observed’ the electrons now behave differently and act like how we first expected them to and form two bands behind the screen(Screen 5). It acts like a particle whereas before it acted like a wave, when it was merely being observed! The act of observing caused the electron to behave different! This is the eeriness of the quantum subatomic world. This is what has baffled the greatest minds for centuries. So, is matter made up of particles or waves or both? That is the question. You decide.
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Motion 2 |
Screen 5 |
Superposition is when something is existing simultaneously as more than one thing. Let’s take a simple practical example to demonstrate superposition. If we switched the light off and shot a bullet at a target, we do not know if the bullet hit the target or missed. In the darkness, we say the bullet is in a state of superposition, because it neither has hit the target nor missed. It has simultaneously hit and also missed the target. It is in no definite state, and will remain in this superposition until we switch on the light. When we switch on the light, we break the superposition and the bullet has either hit or missed the target. We have forced it to become one classical state whereas in the darkness (when it couldn’t be ‘measured’) it existed in a quantum superposition state. Superposition is imperative in the field of quantum computing.
Quantum entanglement is a well-known quantum mechanics phenomenon. Let us use the following simple hypothetical scenario to understand entanglement. You enter your lab and create two electrons that are exactly the same, formed at exactly the same time, and in the same place. Now, you take one these electrons to one end of the universe and the other electron to the opposite end of the universe. They are now billions of light years apart, but they are entangled. This means that whatever you do to one electron, the other electron will respond in exactly the same way. Even though space exists between them they still have some connection. This spooky connection is known as entanglement in quantum mechanics.
There are multiple applications for quantum mechanics, such as quantum computing. It is also important for understanding chemistry, and many technologies operate at a level where quantum mechanics become important such as nanotechnology and teleportation. Quantum mechanics is a field that is actively researched and new discoveries are being made every day. It is widely considered as the future and culmination of all modern physics. It will, eventually, be applied to every aspect in life as we know it.
Now that you have a good understanging of quantum mechanics, you are well prepared to enter the world of quantum computing.