things are usually straightforward and
logical. A car is either at rest or moving, the stereo is either on or off, a cat is either
dead or alive—one state or the other. There is no middle ground or a combination of states.
However, the same can't be said about the world on the most fundamental level—on the scale
of the most basic particle we’re made of. Onthat scale, a particle doesn't exist in one
state or the other, but in a number of states all at once. Like Schrodinger explained, a
cat (of the fundamental world) would not be either dead or alive. It would exist between
the two states, both dead and alive. This, he called superposition, where a particle
exists in a combination of states. Strange, right? But this is
the strange realm called the quantum world, ruled by quantum physics.
It has become quite a popular subject in recent years and the bulk of credit goes to science
fiction. The theories of alternate universes and time travel are certainly keeping us entertained,
but what exactly is this subject that is feeding the world of sci-fi with so much great content?
What is quantum physics? 'Quantum' is a Latin word that literally means
'how much,' but it is used for talking about the minimum amount of some physical entity.
Aptly, we use it to represent the most elementary particles that are the basics
or 'the minimum' of this very big world. So, quantum physics deals with the foundation
of our world – the electrons in an atom, the protons inside the nucleus, the quarks that
build those protons, and the photons that we perceive as light. These constitute everything
that we are made of, both matter and energy. That sounds pretty simple, right?
So how is it any different from regular physics? That 'regular' physics is the physics that
deals with Newton’s laws of motion and its related mechanics. This is more
formally called Classical Physics. This is the physics of our day-to-day lives—the
rolling of balls, the rotation of the earth, and the mechanics of engines.
However, if classical physics is so wide-ranging, why was it insufficient?
We must go back in time to the 1900s to witness the birth of Quantum Physics. This was a
time when scientists were still unable to understand the observations of the photoelectric
effect. Simply put, the photoelectric effect is a phenomenon in which light hits metal,
resulting in the knocking off of electrons. According to 'normal' physics, the
electrons should start escaping the metal when the brightness of the light
exceeds a sufficient limit. Yet, in reality, it was the color of light that determined
whether electrons would be emitted or not. This was when Albert Einstein turned
to Max Planck’s equation. Planck's equation stated that light waves carry
energy in small packets called ‘quanta’. This explained how each color of light
had a specific amount of energy associated with its wavelength. This energy, in turn, was
responsible for the electrons getting knocked off. Einstein used Planck's equation to propose
that light not only acts as a wave, but also a particle, a particle later named photon.
Since then, physicists realized that regular physics simply wasn't sufficient to
understand the microscopic world. They termed this 'regular' physics
Classical Physics, a physics of the past, and another branch of physics dealing with
the fundamental world as 'Quantum Physics'. This world is therefore now
called the 'quantum world'. Let's be honest, our brains are
made for this macroscopic world, where they can understand the running of a car
on a road or the mechanics of a pen, but they are unable to initially understand the quantum world.
For instance, imagine you are standing in front of a massive wall and want to reach the other side.
This wall is surrounded by deadly alligators, so your only options are either climbing
it or making a hole through it. However, if you don’t have enough energy to do either,
you won’t be able to reach the other side, right? Well, that is how the macroscopic world works.
But in the quantum world, a particle can still go through such an energy barrier without sufficient
energy. This ability is called quantum tunneling. This phenomenon is responsible for the nuclear
fusion that fuels the energy production of stars. As complicated as quantum physics may seem
to some, it gets special love from popular culture. You may often see the dramatization
of unusual quantum phenomena depicted in our macroscopic world through movies and TV shows.
Take for instance, the Marvel universe. Marvel movies are famous for their
heavy use of “quantum physics”, at least the words, if not the actual physics!
Even though most of it is fiction being labeled as quantum physics, there are some scenes that are
based on theoretical concepts. One of these is the 'multiple realities' of Doctor Strange.
First, let's understand the quantum physics on which it is based.
This subject deals with particles in terms of probabilities. For instance, while talking about
the position of an electron, a physicist might say, “The electron is most likely to exist in
this range of length, say between 1 to 3 units.” However, the same thing can be interpreted as
electrons existing in different realities at different positions in the possible range.
So, it can exist at 2 units in one reality, while at 3 in another reality or any other
possible number between its most probable range. In short, there are many realities
covering each possible position of the particle. See, mathematics and its implications again!
A massive magnification of this concept is what we see in Doctor Strange’s multiple
realities. Each possibility of a reality is a separate universe in itself there,
allowing there to be multiple universes. Another very famous use of this concept is in the
beloved movie, 'Endgame,' specifically its idea of time travel. The movie understands that if we
change the past, the future will also be changed. So, if they go back in time and kill Thanos, who
will bring about the apocalypse and why would someone travel back in time to kill him then?
This issue is called the Grandfather paradox. A solution to this paradox was given by David
Deutsch. Yes, that 'David Deutsch' mentioned by Tony Stark in the movie. Deutsch said that the
only way to remove this paradox is if we talk about the events in terms of probabilities in the
same way we talk about particles. In other words, changing the past only has a certain
probability of happening. That means that they might not even be able to kill Thanos
in the past, probabilistically speaking! To sidestep this paradox, the clever thing
they did was go back and bring all the Infinity Stones before they were destroyed.
Returning them to the same time would avoid any change due to the missing Stones. One
must admit that it was indeed a clever fix! Quantum physics has certainly fed a lot of fiction
to the general masses, but it has also become a necessary area of knowledge. It has assimilated
itself into other domains of science and is still expanding. For instance, quantum computers are
aimed at doing tasks that are too complex for a classical computer. There is heavy focus on
building a better communication system using quantum physics for better safety and privacy.
Energy production via a nuclear reactor was only possible due to the study of nuclear fission via
quantum physics. It is also deeply ingrained into the subject of astrophysics. After all, the best
way to answer the questions of the universe is if we understand its most basic building blocks.
Regardless of whether we fully understand this subject or not, it is certainly growing in
importance. With more talk of quantum physics to come, it is safe to say that it will
soon become an integral part of our lives.