[Both in English and Bengali]
OVERVIEW
It is a popular notation that the reality of nature is
so mysterious that it is virtually impossible for us to even imagine it, let
alone fully comprehend it. Since the birth of modern science through Sir Isaac
Newton, no theorem has been truer to that popular notion of incomprehension
than Quantum Physics. As weird as it may be, it is also the most successful
theory of the universe at a smaller scale with innumerable successful
applications. Even after a century of extensive studies the theory remains
shrouded in mystery and the fog of controversy. Quantum physics is not
intuitive to us. While taking a leisurely walk at midnight if you are told that
the moon only exists when you look at it, you are bound to be baffled, just as
Albert Einstein was. Perhaps you would also debunk the whole theory saying “God
does not play dice”. However, as Pascal Jordan put it,
“Observations not only disturb
what has to be measured, they produce it...we compel (the electron) to assume a
definite position...we ourselves produce the results of the measurements!”
The “Quantum century” essentially began with Max
Planck’s suggestion that radiation is quantized, meaning it comes in discrete
packets rather than a continuous distribution. About five years later an
unknown young man working as a clerk at the Swiss patent office in Bern by the
name of Albert Einstein used Planck’s idea to explain the “Photoelectric
effect”.
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In 1911, Ernest Rutherford explained the atomic structure with the
help of his famous Rutherford alpha ray scattering experiment. Two years later,
the first comprehensive model of the atomic structure based on quantum theory
was given by Niles Bohr. In the following two decades we would learn about the
wave-particle duality (De Broglie) , the exclusion principle (Pauli) stating
two Fermions cannot exist in the same quantum state simultaneously, the
mass-energy conservation, the famous wave mechanics which remains the very
first course on Quantum Physics offered to undergraduate students
(Schrodinger), the ingenious concept called “the uncertainty principle” which
says the more you know about energy/position of a particle the less you know
about its time of energy/momentum (Heisenberg). Paul Dirac in 19320 combined
the Special Theory of Relativity with Quantum Mechanics to describe the
electrons. The next few decades truly belonged to “Particle Physics”; from
mesons to pions and kaons, from cosmic ray particles to the invention of the
Bubble chamber.
Indeed, 1953 marked the beginning of “particle
explosion”, a true proliferation of particles. This great endeavor resulted in
an intricate theory known as the “Standard Model” finalized in the 70’s and the
most decisive confirmation arriving in 2013 in the form of the Higgs Boson, popularly
known as the “god particle” as it is believed to be the particle which gives
mass to any object.
“A handful of elementary
ingredients that act like bricks in a gigantic Lego set, and with which the
entire material reality surrounding us is constructed. The nature of these
particles, and the way they move, is described by Quantum mechanics. These
particles do not have a pebble-like reality but are rather the ‘quanta’ of
corresponding fields, just as photons are the ‘quanta’ of the electromagnetic
field. They are elementary excitation of a moving substratum similar to the
field of Faraday and Maxwell. Minuscule moving wavelets. They disappear and
reappear according to the strange laws of quantum mechanics, where everything
that exists is never stable, and is nothing but a jump from one interaction to
another!!”
-
Carlo Rovelli
THE BOTTLENECK
Although many successful experiments back the “Standard
Model” picture, it comes with its own set of peculiarities and obscurities.
Without dwelling into the technicalities, let me just say , the Standard model
is incredibly simple and powerful as long as we are in the low energy domain.
At higher energies made possible by modern day accelerators, all kinds of
problems start popping up. For those who have read some elementary special
theory of relativity and why the Newtonian mechanics is inadequate at light
speeds would find the ambiguities eerily familiar.
The “standard model” has never lived up to the billing
of being “the solution”. To this very day many physicists believe it to be
“incoherent”, “patched up” pieces of a puzzle lacking “order”. The uses of the
equations of the standard model is convoluted and often yields nonsensically
large values of measureable quantities and one needs to follow the arduous
process of renormalization to extract meaningful information. The great
scientist Paul Dirac, the author of the principle equations of the model
famously remarked “we have not yet solved the problem”.
The standard model also fails to explain what is
famously called dark matter- matter which we infer from their gravitational
signature alone.
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This dark matter constitutes almost 95% of our known universe.
What are they made of? Nobody knows. We can only say that they are not atoms,
electrons, protons etc.; they are nothing like we have ever explained. In fact
the model falls flat when encountered by the gravity problem, and gravity is
one of the four fundamental forces of nature. The relative weakness of the
gravitational force in comparison with other fundamental forces remains
inexplicable through standard model. All we can say that some alterations may
come into the picture as we discover new, never before seen particles.
THE DESPERATE ATTEMPT: SUPER-SYMMETRIC STRINGS
In an attempt to “unify” all four fundamental forces of
nature , physicists have resorted to a very complicated yet elegant theory call
the “superstring theory” often popularly called “the theory of everything”!!.
Let us try to get a feel for it before talking about its predictions and
limitations.
The atoms are made up of electrons, protons and
neutrons. What’s inside? What constitutes them? The known answer would be
quarks! Standard model tells us that, and these quarks have been found with
hadrons, and we have a decent estimate of their masses and properties like
spin, baryon number etc. What if we were to somehow go beyond? What if we would
look deeper into quarks? String theory says we would find little tiny loops
vibrating at different frequencies.
“We are talking about an
elemental umber form of matter. One object such that if it vibrates in a
different way, it can create all the things we see around us. Therefore,
instead of having the whole zoo of subatomic particles, you just have “the
string”!!!”
-
Michio
Kaku
Simple enough, right? So what’s the catch? The theory
only makes sense in ten dimensional hyperspace!! Frankly, it is beyond science
fiction. This is the cost of unification, it says “The mind of god is music
resonating through ten dimensional hyperspace!”
Let me ask you to close your eyes and visualize a one
dimensional object. Did you think of a line or a wire? If yes, then at a
fundamental level you agree with all the hocus pocus of the theory! To you and
me, a single, taut thread is indeed one dimensional! But ask an ant! It would
say your one dimensional thread is a perfect, bulky, thick cylinder with a
diameter which happens to be much smaller than its length!! For them it is a
three dimensional object, they can walk along its periphery! A dimension
nonexistent to us as we are too big to perceive it! So, all dimensions are not
similar, as weird as it may sound we perceive bigger and smaller dimensions in
some way. What if there are more dimensions than three that are simply
incomprehensible to us because they are too small?
Much smaller than any known particle, curled up and
embedded in the fabric of space itself. Seven more dimensions curled up into
our known three big dimensions. These unseen dimensions might hold a key to our
understanding of the universe at a fundamental level. The deepest question in
physics has been the existence of certain constants (Planck’s constant, mass of
electron etc.) whose values have been measured with incredible precision. If you
take any of the numbers and tweak it by a very small amount, the universe as we
know shall not exist, you would not be reading this! These constants are
therefore extremely important clues that we must attempt to decipher!!!
This is where the extra smaller dimensions come in. They
might be the key to understanding the vibrational constraints/geometry of the
superstrings telling us which vibrations are allowed. If we can extract the two
dozen or so constants from the strings and they match with our reality, then
bingo!! We shall have an idea of why the universe is how it is! In case you are
wandering why only ten and not more? As it turns out, any such universe will be
unstable and collapse to ten dimensions. At ten spatial and one time
dimensions, Einstein’s General Relativity emerges beautifully!
“Let’s say a beautiful crystal shatters and lands on a
tabletop, and there are little insect like flatlanders living on the tabletop
and they say “let us reassemble the crystal!!” They bring it together and then
they have a crystal called Quantum theory, another called Relativity: the
theory of space-time, but then they bring these two chunks together and they can’t!
No matter how much they try! Then one day, someone says let us go to the world
of up. Let us move one crystal up and fit it in the third dimension, and it
will create a beautiful unified crystal. That’s where we are we think!!”
- Michio Kaku
LOOP QUANTUM GRAVITY
“Here, in the vanguard, beyond
the borders of knowledge, science becomes even more beautiful- incandescent in
the forge of nascent ideas, of intuitions, of attempts, of roads taken and then
abandoned, of enthusiasms. In the effort to imagine what has not yet been
imagined.”
-
Carlo
Rovelli
Coming to this last section, I shall just present the
idea briefly and leave all technicalities aside. Loop Quantum Gravity is
another very popular theory that many scientists throughout the world see as
the future way to go. However, the predictions are as crazy as it can possibly
be! Are you ready for it? Then let’s begin. The GTR treats space not just as an
inert stage, but rather a dynamic quantity, a chief actor of the play. Matter
tells space how to curve, the curved space-time tells matter how to move around
it. Spread out a bed sheet tightly and hold onto it, drop a ball into it. The
weight of the ball causes curvature in the fabric! Just like the sun would do
to the fabric of space-time. Smaller objects placed around the ball would move
in an orbit around that curvature (planets).
On another hand, Quantum Physics says all these files
are essentially quantized, a finite, granular discrete structure. Loop Quantum
Gravity just adds them up and says, space itself is quantized, made up of
“atoms of space” if you like!
The constituents of space are a billion billion billion
times smaller than our known atoms. We are talking and entirely different realm
altogether!! In this reality the reality itself is unrealistic! Space is not
empty, it is like the shirt you are wearing right now, intricately weaved
structure of threads knotted into loops!!!! The fabric of space is just like
the fabric we wear! These loops are not in space, THEY ARE THE SPACE!!
And if that was not enough, the entire concept of time
as we know it goes out of the window! None of the mathematics, the equations
describing this realm contain what we explicitly call “time”!! Don’t get the
wrong idea, change is omnipresent. But everyday events that we assign a
timeline to does not exist that way. Each event time is exclusive and internal;
related to the quantum events of that particular reality. The
interaction/interplay of quanta of space and matter is the reality of this
domain.
The most controversial yet beautiful prediction of Loop
Quantum Gravity is about the origin of our universe. We are somewhat familiar
with the concept of the “Big bang”, where a whole universe simply exploded out
of an immensely dense infinitesimal point. As per Loop Quantum Gravity, such immensely
compressed universe would generate a unbelievably strong repulsive quantum
force. The “Big Bang” may very well have been the “Big Bounce!!” According to
Loop Quantum Gravity our universe has risen like the mythical phoenix, which
collapsed under its own weight and exploded brilliantly when the quantum
repulsion was too much. In this moment of bounce, there is no time, no space,
everything that we can see (our universe), our entire comprehension dissolved,
compressed, fused into the ethereal cloud of probability- the realm of “Quantum
Gravity”!!
US
We are at another unique moment of the evolution of science.
Two spectacular and successful theories seem incompatible.
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Such moments are
rare and have always preceded quantum leaps in our understanding of the
universe. This is exactly the phase when many often infer “Wow! The end of
science!” The sync of theories, the fitting of individual pieces of puzzles is truly
the moment to be excited about!! Kepler’s law and Galileo’s studies merged at
the hands of the greatest genius that even lived to give us the “Principia
Mathematica”, the single most important book ever published in the history of
our race. Electricity and Magnetism merged through Maxwell to give his famous
equations, building blocks of modern physics! When electromagnetism was in
apparent conflict with mechanics, Albert Einstein came up with relativity, and
the rest is history.
We now have a front row seat to witness the next big revelation,
the biggest so far!!
The Bengali Translation was published in Bibokshito 2018 Issue. Here given that piece of translated script. Thank You.
