DECODING NATURAL LAWS: SCIENTIFIC JOURNEY CONTINUES THROUGH THE CENTURIES

Why Imagination is the Currency of the 21st Century

At the age of 16, Einstein imagined chasing after a beam of light, and this thought experiment played a memorable role in his development of special theory of relativity. The theory says ‘motion of anything in this universe faster than the velocity of light is impossible’.
Einstein cherished what he called Gedankenexperimente, ideas that twirled around in his head rather than in a lab. Of course, your school teacher will call it daydreaming. If you are Einstein you get to call them Gedankenexperimente.

“I am enough of an artist to draw freely upon my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.”  Albert Einstein

Einstein's thought experiments should give an inner call for action to  teachers/educators to foster imagination. If we hope to inspire our kids to solve the challenging  problems of 'climate change', 'pandemic','energy crisis' we need to do more than drill them in math and memorize formulae. We should stimulate their minds’ eyes and encourage them to emerge as thinkers and visionaries.

Because, Einstein dared to culture a wandering mind, scientists of of the 21st century are making a living by expounding and writing papers on terms like big bang, black hole, gravitational waves, expanding universe and many others.

Again, quoting the genius, “A human being is a part of the whole called by us universe, a part limited in time and space. He experiences himself, his thoughts and feeling as something separated from the rest, a kind of optical delusion of his consciousness. This delusion is a kind of prison for us, restricting us to our personal desires and to affection for a few persons nearest to us. Our task must be to free ourselves from this prison by widening our circle of compassion to embrace all living creatures and the whole of nature in its beauty.”

Imagination leads to an experiential science. Science paves the path for technological invention

GPS (Global Positioning System), a multi-billion dollar growth industry with applications in airplane navigation, oil exploration, bridge construction, sailing etc. are experiential science in action. GPS is based on 24 artificial satellites that contain atomic clocks to provide very precise time data which is ultimately converted to the position data. It is a radio location technique for accurate position determination used by us even when driving a car. Because of relativistic gravitational potential (as the satellites are in orbits 20,000 km above the ground), the atomic clocks in satellites of GPS system get advanced by 38.2μs every day with respect to the identical clocks in the ground station. Thus the clocks in the satellites need relativistic correction of 38.2μs per day, otherwise position determination will be erroneous by several kilometres.

Einstein’s famous mass-energy equation: E = mc², where E is the energy equivalent of mass m of the body being multiplied by square of the velocity of light (c = 3 x 10^8 m/s), gave the clue to generate nuclear power with fission process. Planck-Einstein relation: E = hν, where h is Planck’s constant (6.626 x 10^-34 J-s) and ν is the frequency of oscillation of the radiation. This together with Einstein’s relativity theory  forms the basis of particle accelerators of high energy physics-that is capable of producing energy of the order of tera i.e. trillion electron-volt.

Einstein also established that light consist of particles called ‘photon’ through his photoelectric effect. He received Nobel Prize in Physics in 1921 primarily for this photon concept (that paved the way for the development of quantum mechanics) in addition to his theoretical works on relativity. The phenomenon of photoelectric effect has plethora of applications including those in solar cells, in sensors of digital camera and so on.

Imagination fuels the concept of Black Hole

In 1930s Indian born American scientist Subrahmanyan Chandrasekhar based on Einstein’s relativity theory and quantum mechanics came up with ‘Chandrasekhar Limit’—stars with 1.4 times the solar mass. It so happens, on a long sea voyage from India to England in 1930 at the age of 19, he worked it out. According to the science of quantum mechanics, there are forces that develops —known as ‘electron degeneracy pressure’— within the very atoms of the white dwarf star that counteract the force of gravity. Chandrasekhar determined that any star having 1.4 times solar mass after its death (i.e. when its nuclear fuel is exhausted) settles as a stable ‘white dwarf’.

It was established subsequently by other researchers that stars with 1.4 to 3 times the solar mass would settle after death as ‘neutron star’—some of which as observed from Earth are known as pulsar (pulsating star).

However, supermassive stars with 25 solar mass or more (after its ‘death’ i.e. when its nuclear fuel is exhausted) settles to a black hole. It was not possible at that time to prove the existence of black hole. Chandrasekhar got the recognition of his work with award of  Nobel Prize in Physics only in 1983 after the first black hole was experimentally observed in 1972.

Nothing, even light can ever escape from the pull of the monstrous gravity of  a black hole. Thus, the name coined by relativity expert, John Wheeler. The gravity’s stupendous grip is so inexorable for a black hole that it curves space and warps time to extreme extent according to Einstein’s general relativity. Anything and everything (planet, star and even a whole solar system or galaxy) that comes close to its ‘event horizon’, a point of no return, get swallowed by its inescapable gravitational attraction.

Inside a black hole there is only one thing—singularity—where all physical laws including relativity theory (from which the possibility of black hole was predicted) fails.

As imaged by the Event Horizon Telescope (EHT): The first direct visual evidence of a supermassive black hole and its shadow- M87* is a black hole at the centre of the massive galaxy M87, ~55 million light-years (one light year equals 9.46 trillion kilometres) from Earth. The black hole is 6.5 billion times more massive than our Sun.

Prior to 1971, all theoretical studies of black holes had been based on Einstein’s general relativistic laws, and those studies were unequivocal: It is a hole and cannot radiate. Black holes are now known to spin, and as it spins it creates a tornado-like swirling motion in the curved space-time around it when it radiates; not only gravitational waves, but also electromagnetic waves, and all other forms of radiation that can exist in nature.

The black holes were catalogued at the initial stage of their experimental studies only indirectly through their gravitational tugs on stars in their neighborhood and fireworks left behind by the superheated matter being sucked into it by its monstrous gravitational pull.

Like the Cheshire cat in Alice’s Wonderland, the black hole disappears from the view (in the optical sense), leaving only its “smile”—the signature of the distortion of space-time (based on the theory of general relativity) caused by super-intense gravitational field.

In 1972 radio astronomers identified the first black hole in distant space: Cygnus X1, 6000 light years from Earth, by studying the X-rays that are generated very close to the hole’s event horizon. In 1994, the Hubble telescope first discovered that the galaxy Messier 87  (55 million light years away from the Earth) contained a black hole M87*.

In 2019 EHT (Event Horizon Telescope) has imaged black hole M87* located at the heart of the supergiant elliptical galaxy Messier 87 in the constellation Virgo.

EHT—an Earth size virtual aperture radio telescope, sharpest astronomical instrument ever assembled on Earth,  consisted of eight radio telescopes, operating at millimeter-wave frequency: 230 GHz i.e. 1.3 mm wavelength spanning the Antarctic, Europe, Africa, North America, and South America.

The image of black hole obtained by EHT matches very well with the predictions worked out by theoretical physicists on the basis of general theory of relativity.

Wrapping up with Einstein's Gedankenexperimente

Years later, when his younger son, Eduard, asked why he was so famous, Einstein replied by using another simple thought experiment to describe his insight that gravity was the curving of the fabric of space-time. “When a blind beetle crawls over the surface of a curved branch, it doesn’t notice that the track it has covered is indeed curved,” he said. “I was lucky enough to notice what the beetle didn’t notice.”

In fact, Einstein did more than just notice what the blind beetle couldn’t see. He was able to imagine it by conjuring up thought experiments. That ability to visualize the unseen has always been the key to creative genius. As Einstein later put it, “Imagination is more important than knowledge.”


Subal Kar
Former Professor of Radio Physics and Electronics, Calcutta University
Author of a forthcoming book 'Knowledge about Universe-Down the Ages'