Advanced science, Astrophysics, International, Technical

Black Holes and the 2020 Nobel Prize in Physics

2020 Physics Nobel Prize winners

Three scientists have been awarded the 2020 Nobel Prize in Physics. They are the British mathematical physicist Roger Penrose, German astrophysicist Reinhard Genzel, and American astronomer Andrea Ghez.

Penrose, a professor at Oxford University, is recognised for his research on black holes carried out in the 1960s. According to the Royal Swedish Academy of Sciences, Penrose has been honoured “for the discovery that black hole formation is a robust prediction of [Albert Einstein’s] general theory of relativity.” Professors Genzel of Max Planck Institute and Ghez of the University of California in Los Angeles were awarded the prize “for the discovery of a supermassive compact object” in a region called Sagittarius A*, located at the centre of our galaxy, The Milky Way.

The criteria for awarding Nobel Prize in Physics are defined in specific terms. Alfred Nobel’s Will stipulates that the prize should be awarded “to the person who made the most important discovery or invention in the field of physics.” The crucial words in the Will are “discovery” and “invention.” It is arguable whether developing a theory can be considered a discovery per se, but it is certainly not an invention in the sense that we normally associate an invention with. That is why the prize is seldom given to theoretical physicists, unless their theory is testable or verifiable.

When theorists won the prize by themselves, for example John Bardeen, Leon Cooper and Robert Schrieffer for their theory of superconductivity, it was for a major theoretical formulation of an existing phenomenon, and thus can be considered as part of the “discovery” of that phenomenon. And theoretical physicists Peter Higgs and François Englert were awarded the Nobel Prize after the particle—Higgs Boson—predicted by their theory to complement the Standard Model of the Universe was experimentally detected.

While the awards to Genzel and Ghez are incontrovertible because they fit Nobel’s criteria quite nicely, Penrose is a rather unusual choice in that his award is not for a discovery. It is for using ingenious mathematical methods to reveal the implications of Einstein’s tour de force—the intimidatingly difficult-to-comprehend Theory of General Relativity.

However, long before Penrose’s prize-winning work on black holes, German physicist Karl Schwarzschild provided the proof of their existence just less than two months after Einstein published the general relativity equations in 1915. By solving the equations exactly, he identified a radius, known as the Schwarzschild radius that defines the horizon or boundary of a voracious gravitational sinkhole—a single point of zero volume and infinite density.

If a massive object could be compressed to fit within the Schwarzschild radius, which is three kilometres per solar mass, no known force could stop it from collapsing into the sinkhole. Today, we call this sinkhole a black hole. His work formed the basis for later studies of black holes, showing that the concentration of matter in a black hole is so great that no light could escape its staggering gravitational pulls, but rather follow a trajectory curving back towards the black hole, thereby making it unobservable.

Lest we forget, Einstein did not win the Nobel Prize for his revolutionary work on general relativity or special relativity. The Nobel Committee decided against them on grounds that the relativity theories were abstract and unproven, although observational proof of general relativity was provided in 1919 by the Cambridge astrophysicist Arthur Eddington. He famously measured the deflection of starlight passing near the Sun during a total solar eclipse. The deflection, known as gravitational lensing, resulted from warping of space, as predicted by general relativity. Instead, Einstein received the deferred 1921 prize in 1922 for his 1905 quantum interpretation of the photoelectric effect because it can be attributed to the discovery of the effect—emission of electrons from metal surfaces under certain illuminations—by the German physicist Heinrich Rudolph Hertz in 1887.

Despite his fame and impact on theoretical physics, Nobel Prize eluded the brilliant physicist, mathematician and cosmologist Stephen Hawking, even though there is a general consensus that he has done more than anyone else since Einstein to deepen our knowledge about the cosmos. As noted by Penrose, a Nobel Prize for Hawking would have been “well-deserved” yet was possibly held back by the committee’s desire to honour observable, rather than theoretical scientific studies that are difficult, or almost impossible, to verify experimentally. Penrose’s work, albeit monumental and worthy of the Nobel Prize, cannot also be experimentally verified because of the very nature of the topics. So why relax requirements for work which are mostly theorems, some hypothesised in collaboration with Hawking?

Penrose is not the first scientist to predict the existence of black holes. The idea of black holes dates back even before Schwarzschild, to 1783, when an English cleric and amateur scientist named John Michell and more than a decade later French mathematician Pierre-Simon Laplace used a thought experiment to explain that light would not leave the surface of a very massive star if the gravitation was sufficiently large. Michell called them “dark stars.”

In 1930, during a long voyage to London, 19-year-old Indian astrophysicist Subrahmanyan Chandrasekhar showed via calculations that when a massive star runs out of fuel, it would blow itself apart in a spectacularly violent explosion into a black hole. He received the Nobel Prize in 1983, not for his work on black holes, but for “studies of the physical processes of importance to the structure and evolution of the stars.”

For decades, the concept of black holes was no more than a mathematical aberration. They are well-nigh impossible to detect because light, one of our cosmic messengers, cannot escape from black holes. Hence, there is a total information blackout. How do we then infer about their existence? As the physics of black holes developed through the years, physicists realised that indirect routes were available. Consequently, our current understanding of black holes is built on inference drawn from data collected by X-ray, optical and radio telescopes.

Indeed, their existence was eventually confirmed in 1971 when astronomers detected a hint of radio wave emissions coming from an object in the constellation Cygnus. The emissions were later interpreted as the fingerprint of the black hole Cygnus X-1. Since then, numerous black holes, including supermassive ones, have been detected in our galaxy and elsewhere in the Universe.

Quamrul Haider is a Professor of Physics at Fordham University, New York.

Astrophysics, Disasters - natural and man-made, Economic, Environmental, International, Life as it is, Technical

Our frontier mentality and the Future of Earth

No one witnessed the birth of Earth. The Earth does not have a birth certificate to authenticate its age. But there is no doubt about Earth’s antiquity. It is 4.55 billion years old. In the context of the Universe which burst into existence 13.7 billion years ago, Earth is in its early middle age. It will live for another five billion years, when the Sun will become a Red Giant, swallowing the nearby planets and ending its luminous career by dwindling into a white dwarf.

Although Earth is very small—a mote of dust—in the vast cosmic arena, it is the only planet that is filled with exquisite beauty, a cornucopia of boisterous wildlife slithering, scampering, soaring and swimming all over the planet. It showcases timeless marvels—a panoply of wonders—sculpted by Nature over millions of years. It is home to towering mountains, alpine glaciers, lush green rainforests, subtropical wilderness and millennia-old humongous trees, gushing geysers, beautiful coral reefs, lofty waterfalls and pristine lakes. The Earth is also home to incredible sandstone arches, deep canyons, varicoloured petrified wood and multi-hued badlands, massive caves filled with imposing stalagmites and stalactites, sparsely vegetated and colourfully painted deserts, gigantic sand dunes, and hundreds of species of flora and fauna.

Evidence of life—bacteria and single-celled organisms—date to 3.85 billion years ago. Since then, life suffered wave after wave of cataclysmic extinctions. The dinosaurs are perhaps the most famous extinct creatures who roamed the Earth’s surface unchallenged during the Mesozoic Era. After surviving for nearly 165 million years, they became victims of the greatest mass deaths in the history of our planet 65 million years ago when a large asteroid hit the Earth.

About 25 million years ago, most of the present day species emerged. Now, fast forward to about two million years ago and we see the evolution of our ancestors—upright, biped, primate mammals. Evidence shows that modern humans originated in Africa within the past 200,000 years, yet there was no move toward high level civilisation. It was the Sumerians of Mesopotamia who developed the world’s first civilisation roughly 6,000 years ago.

We have had the planet to ourselves for a small fraction of time. During this short time interval, we outfoxed other species in the game of survival. Maybe they ran out of luck in evolution’s lottery, or perhaps sometime in the distant past, we became completely dissociated from the checks and balances between man and nature and became a super-predator.

Since the beginning of the Industrial Revolution circa 1760, we made a toxic mess of our natural environment, resulting in an ever-hotter climate, melting glaciers, rising sea levels, widespread droughts, frequent and much wilder storms, crop failures and tens of millions of climate refugees. Our unrestrained use of fossil fuels for more than a century had been slowly pushing the planet toward climatological catastrophe.

Today, we are fixated on enjoying the present and refusing to account for the consequences of our actions on tomorrow. Social scientists interpret this type of behaviour as frontier ethic, prevalent in Western culture as well as others. This ethic embraces a rather narrow view of humans in the environment and even a narrower view of nature. It is characterised by three tenets.

The first is that the Earth has an infinite supply of resources for exclusive human use. There is always more and it is all for us; humans are apart from nature and immune to natural laws; and human success derives from the control of nature.

This tenet no doubt evolved in the prehistoric time when human numbers were small and the Earth’s resources did indeed appear inexhaustible. Not anymore. The massive increase in economic activity and the upsurge in population growth in the last 200 years have brought us face-to-face with the planet’s limitations.

The second tenet sought to position humankind outside the realm of nature. Many people still continue to view human beings as separate from nature and persist in thinking we can do whatever we please without harming the planet. To the contrary, our independence is an illusion, engendered by our remoteness from a world we see through rose-coloured glasses and thermo-paned windows.

As for the third tenet, industrialised nations view nature as a force that must be conquered and subjugated. Hence, we manipulated wildlife, fisheries, land, rivers, oceans and forests like so many pieces in a board game, until the environment reached a dangerous point of disequilibrium.

Over the years, the frontier ethic permeated our lives so much that we became more remote from the natural world outside our artificial environments. It influences our personal goals and expectations without thinking about the effects on the long-term health of the planet.

It cannot be overemphasised that the fate of the planet, our home, and the millions of species that share it with us, as well as the fate of all future generations, lies in our hands. Do we realise that because of resource and ozone depletion, global warming and other problems, the human species will be wiped off the face of the planet if we do not change our lifestyles? At the least, things will deteriorate to the extent that we could lose centuries of technological and economic progress in the next few decades. Our wonderfully diverse biological world, the product of billions of years of evolution, could be eradicated in a fraction of the Earth’s history.

So, what should we do to keep the planet habitable for our future generations? Scientists have urged world leaders in vain to combat global-warming emissions, which have only continued to soar upward. Should we instead rely on a pandemic, such as the coronavirus that is shutting down countries across the globe, slowing down economic activities, halting industrial productions and travel, thereby causing a significant decline in air pollution and carbon/nitrogen emissions all over the world?

The coronavirus pandemic is a tragedy—a palpable human nightmare unfolding in overloaded hospitals with alarming speed, racing toward a horizon darkened by economic disaster and chock-full of signs showing more sufferings to come. This global crisis is also an eye-opener for the other global crisis, the slower one with even higher stakes—anthropogenic climate change.

The cure due to coronavirus is temporary and totally unacceptable, whereas the threat from the adverse effects of climate change will remain with us for years, unless we shape up pronto. Nevertheless, coronavirus should make us wonder if lessons learned from the pandemic might be the beginning of a meaningful shift from business-as-usual attitude.

On this International Mother Earth Day, let us pause for a moment and imagine what the Earth would look like when it will be bereft of mirth, when there will be no wilderness and wildlife, when lakes will be filled with sudsy waters, when coastlines will become unrecognisable and when the air will become a witch’s brew. Can our planet still be called Earth? The answer is no, because we do not have the insight to predict the consequences of our frontier mentality and exercise restraint where we must.

I end the piece with the following words of wisdom from the Native American Chief Seattle. “The Earth does not belong to man, man belongs to the Earth. All things are connected like the blood that unites us all. Man did not weave the web of life, he is merely a strand in it. Whatever he does to the web, he does to himself.”

Quamrul Haider is a Professor of Physics at Fordham University, New York.

Advanced science, Astrophysics, Life as it is, Religious, Technical

Everything from Nothing

Can everything we see on earth and the planets, the stars, galaxies, supernovae and so forth come from nothing, from absolute vacuum, from empty space and can even empty space prop up from nowhere? This sort of query, some might say, is an absurd baseless query; while others might say it is a profound scientific inquiry, beyond the pigeon-holed mode of thinking.   

Philosophers and theologians of all persuasions tried to convince us that everything we see in the universe is the divine creation. But we must set off with certain fundamental assumptions – we have to accept the existence of an all-powerful, omnipresent, omniscient entity called God or Yahweh or Allah and we cannot question his origin, his present whereabouts or his mode of creation etc. Based on these premises, the revelations, directives etc as stated in the ‘Book’ should be followed as ordered by the creator!   

But science is unwilling to accept this premise without any evidence or verification. That is why there is a conflict between science and religion. As Richard Dawkins, Emeritus Fellow of New College, Oxford and Evolutionary Biologist said, “I am against religion because it teaches us to be satisfied with but not understanding the world”.

Science had moved away from accepting the divine proclamation that human beings are at the centre of creation of the creator, Earth is at the centre of the universe and the Sun goes around the Earth! Scientific discoveries have proved many of these proclamations, if not all, are blatantly wrong.

Science explored material objects on Earth – day-to-day objects to their physical and chemical composition, physical objects to molecules to atoms and sub-atomic particles. On the smallest scale, quantum mechanics explored the origin of matter and anti-matter and on the mind-boggling expansive scale of the universe the general theory of relativity explored the stars, galaxies, black holes, warm holes, universe and even multi verse.

The theologians would burst out in fury if someone, be it scientist or a science writer, tries to give the scientific explanation of something or everything coming from nothing. They would throw out their anger, what is then the omnipresent omniscience divine power called God or Yahweh or Allah doing? Is He not the undisputed Creator of everything in this universe? For centuries the religions had been proclaiming and propagating this message relentlessly. Now any attempt to explain it otherwise, on the basis of scientific ideas and theories, would be branded as heretics and atheism.

Nonetheless science has progressed enough to give a rational explanation to the creation of everything from nothing. But, first, we must understand the scientific meaning of the term ‘nothing’. In everyday language, nothing means the absence of anything. If we consider a volume of space say, 20cm by 20cm by 20cm, in front of our eyes, we may say there is nothing in there as there is no book, no pencil, no string, no fruit or anything else in that small volume and so, we may consider, there is nothing. But then, we must recognise that there are millions of air particles of various types in that volume that we cannot see but we breath all the time. So, there are things where we perceive to have nothing.

Let us take an air-tight glass case where obviously there are air particles along with air pollutants, allergens etc. Now if we pump out these particles very carefully and make it an ultra-high vacuum, can we say that there is nothing in the glass case? No, we cannot say that there is nothing in the glass case and that is because the modern physics shows us otherwise.

Quantum fluctuations in an absolute vacuum

The two branches of modern physics – the general theory of relativity and quantum mechanics – give us a description of physical processes which are mind-boggling, counter-intuitive and occasionally plainly weird. Even Einstein, who singlehandedly produced the general theory of relativity and pioneered quantum physics, had extreme difficulty in absorbing the full implications and interplay of these two theories.

Einstein produced the mass-energy equivalence, which is: E=mc2; a very elegant and at the same time extremely important equation. What it means is that the mass of an object such as an atom or a molecule or a large number of molecules in a ball or an apple or a pencil and so forth has an equivalent energy and conversely an amount of energy has an equivalent mass. It is not theoretical physicists’ crazy idea, it had been found in practice in particle physics experiments, in radioactive decay and in nuclear reactors. A certain amount of energy suddenly disappears and a very small particle called electron and its anti-particle called the positron appear. The electron is what we use to generate electricity and is used to run a television, radio, mobile phone etc and in our everyday parlance, it is a matter. On the other hand, positron is an anti-matter. When this matter (electron) and anti-matter (positron) come in contact, they annihilate each other and an amount of energy is produced which is exactly equal to what disappeared in the first place to produce this electron and positron pair.

Alongside this mass-energy equivalence, one may consider quantum physics’ uncertainty principle produced by Werner Heisenberg. We must remember that quantum mechanics deals with very small particles such as electrons, positrons, atoms and sub-atomic particles. The basic tenet of this principle is that we cannot simultaneously measure certain pairs of observables such as energy and time or position and momentum of a particle with absolute accuracy. The degree of inaccuracy or uncertainty of the pair of observables (ΔE.Δt or Δp.Δx is always higher than a quantity called Planck constant (h/2π). In other words, if we measure the energy of a quantum particle very precisely, then there would be an inherent uncertainty in time at which the energy measurement had been made and the product of these two uncertainties is going to be higher than the Planck constant, h/2π. This uncertainty principle is the bedrock of quantum mechanics. It had been proven time and time again that this uncertainty principle is inviolable and holds true in all quantum events. Heisenberg received Nobel Prize in Physics in 1932 for his contribution to Quantum Mechanics.

In the sub-world of quantum mechanics, there may be a situation which is known as quantum fluctuation. In an otherwise complete vacuum (having nothing), a quantum fluctuation can produce an amount of energy and that energy can generate a virtual electron-positron pair in the system. Now that energy comes from the nature, as if the nature is lending that energy to the system. When the electron-positron pair comes in contact with each other and they do it in a flash, both of them disappear instantly, and an amount energy is produced (equal to the energy that produced the pair in the first place) and that energy is returned to the nature and everything is squared up.

This borrowing of energy from nature, electron-positron pair formation (or for that matter matter-antimatter formation) and annihilation and then returning the energy to the nature are taking place all the time everywhere, even in a vacuum where we consider there is absolutely nothing. These are the quantum fluctuations. These are not mad professor’s or mad scientist’s utter gibberish, these are actual physical phenomena which have been demonstrated in high-energy physics laboratories. If one measures the charge of an electron with high precision, one can find a sudden fluctuation in the charge of the electron or a slight wobble in the electron trajectory. This is due to interaction of the real electron and the momentary appearance of the electron-positron pair.  

Billions and trillions of matter-antimatter particles are being generated and annihilated all the time in space. Now a situation may arise when a small fraction of these particles is not annihilated instantaneously and these matter, anti-matter particles move away from each other. In fact, it had been estimated that approximately one in a billion of such pairs had escaped annihilation and moved away to lead separate lives at the time of Big Bang. Electrons and other matters (atoms) in our everyday world (called fermions) came out and formed our world or the present universe, and the positrons and other anti-matter particles formed the anti-matter world somewhere far away from matter world, or they may have formed a separate anti-matter universe.

Our matter universe and the anti-matter universe are blood enemies. Should they come in contact, they will kill each other instantly and an unimaginable release of energy will take place. However, this energy is what these matter universe and anti-matter universe owe to the nature, because this energy was borrowed at the time of forming matter and anti-matter particles in a gigantic scale. Whereas all the other particles returned their energies to the nature, these particles, statistically one in a billion particles, escaped repayment and formed the universe.

The Big Bang from quantum fluctuations

This is how the universe, as perceived now, came into existence. It is the formation of universe out of nothing and the likely disappearance of the universe to nothing. There is no need to invent a divine power and then lay everything at the feet of that invented divine power. In fact, such an invention, all within the confines of our minds, would create more insurmountable problems in explaining things as they stand – such as where is the divine power now, how did he create these things, did he create the universe on a whim or did he have an ultimate purpose etc?

Albert Einstein was deeply sceptical about the divine power. He expressed his thought quite bluntly in saying, “I want to know how God created this world, I am not interested in this or that phenomenon, in the spectrum of this or that element. I want to know His thoughts; the rest are details”.  

It must be stated that the present perception of creation of the universe is not a done deal. The debate about the universe, its progression, its ultimate fate etc are all raging in the scientific community. This is the credit for science – science never claims to have achieved the ultimate truth; anything that is held to be true now can be changed in the light of new evidence, new facts. This is in stark contrast with religion where everything is claimed to have come from God or Allah and hence not subject to any alteration or modification. This is what science rejects.

  • Dr A Rahman is an author and a columnist.

Advanced science, Astrophysics, Cultural, Environmental, Life as it is, Religious, Technical

Entropy and the arrow of time

Greek philosophers some millennia ago and since then many philosophers over the centuries round the world had been raising the deep-rooted perennial questions: what is life, where was its beginning and where is its end, what makes life continue and many more intractable questions like these. These are perennial questions of profound significance, which had so far been answered in many divergent ways – in pure incomprehensible philosophical terms, in supernatural religious terms and so forth.

However, scientifically inclined people, who used to be branded centuries ago as natural philosophers, would pose the same questions in somewhat different terms: how did life begin, when is the beginning of life, how did it evolve, what is the nature of time and what is the flow of time etc? Again, these questions are not easy to answer, but at least scientists have structured and sequenced the questions so that answers become easier.

Natural philosophy evolved from pure philosophical inquiry and inquisitiveness. Scientific disciplines were considered effectively the extension of wider philosophical queries. That is why even today the highest academic degrees, both scientific and non-scientific, are titled as Doctor of Philosophy (PhD). Physical sciences are the ones which describe physical processes of natural sciences in numerical and quantitative terms.  

Heat, temperature, enthalpy, entropy, energy etc are quantities within the subject matter of thermodynamics and statistical mechanics. These subject matters along with Newtonian physics, electricity and magnetism, optics etc were bundled together as the ‘classical physics’. This naming of ‘classical physics’ does not mean that these subjects have become ‘classical’ – sort of outdated and outmoded – and there is nothing more to learn from these subjects; far from it. It only means that these traditional subjects have been set aside in order to concentrate on newer disciplines (roughly from the beginning of 20th century) like the general theory of relativity, quantum mechanics, particle physics, cosmology etc. which are called the ‘modern physics.’

This traditional segregation of branches of physics into classical physics and modern physics is purely arbitrary. There is no boundary line, no demarcation either in terms of time or disciplines between classical and modern physics. Entropy, the parameter which was invented in the 19th century as a thermodynamic quantity, has profound implications in the concept of space-time continuum and the big-bang theory of modern physics!

Entropy measuring disorder and the arrow of time.

First of all, we need to understand what heat is before we can go to understanding entropy. In olden days – 17th century or earlier – people used to visualise heat as some sort of fluid called ‘caloric’. In fact, this caloric is composed of two parts – hot and cold parts. A body is hot because it has more hot fluid and less cold fluid. On the other hand, a body is cold because it has more cold fluid than hot fluid. When hot and cold bodies come in contact with each other, hot fluid moves from the hot to the cold body and thereby rendering the cold body somewhat hotter! Nonetheless, those scientists did manage to identify a very important parameter called ‘temperature’ that measures the body’s ‘hotness’ or ‘coldness’.  

In reality, heat is the thermal energy which arises due to vibration, oscillation or physical motion of atoms and molecules that make up the body. When a body at a higher temperature comes in contact with another body at lower temperature, the excess vibrational energies of the atoms and molecules are transferred to the body at lower energy. It is the temperature that dictates the direction of flow of heat.

Let us now consider what entropy is. Entropy is a thermodynamic quantity that is the ratio of amount of heat energy that flows from one body (hot) to another body (cold) at a certain (absolute) temperature. As the probability of energy flowing from higher energy to the lower energy is much higher than the other way around, it has always been found heat flows from a hotter body to a colder body and entropy is assigned to be positive in that situation. Should heat flow from a colder body to a hotter body – its probability being very low indeed -, entropy could theoretically be negative. But in nature heat never flows from colder to hotter body and entropy is never negative. The very nature of heat (arising from motions of atoms and molecules) being transferred from hot to cold bodies, entropy is a measure of disorder in the composite system. As disorder increases, so does entropy.

It may be pointed out that when heat is shared between the bodies, it does not matter the relative sizes of these bodies. For example, A hot tea spoon dipped in a bucket of water would have some amount of heat transferred from the spoon to the water, although the total energy of the bucket of water may be much higher than that of the spoon. As stated above, it is the temperature which dictates the flow of heat and thereby the increase in entropy.

This increase in entropy or the degree of disorder is intricately linked to the flow of time or in physics terminology, the arrow of time. As neither time nor entropy does flow in reverse, they are always moving in the forward direction. From our previous example, the heat from the spoon is transferred to the bucket of water as time passes and that is the arrow of time. A situation can hardly be visualised (although theoretically possible with infinitesimally low probability) when heat flows in reverse, that is, the dipped spoon would recover heat from the bucket and become hot again!

From the time of big-bang, the entropy had been going up i.e. the degree of disorder had been spreading. That is quite natural as heat flows from one hotter part of the universe to another colder part of the universe and that means entropy is always increasing.

With the advancement of biological sciences, it had been speculated that a time will come when human beings will live for a very long time and may even become immortal. Living longer with better medical care is already happening. People on the average now live almost double the age of what they used to live about a couple of centuries ago. But being immortal means humans will not age in time and that implies that the past, present and future will all merge into one – no change in age, no change in body functions or flow of nutrients from one part of the body to another! It is a continuation of the same thing over and over again. In other words, human beings will live in suspended animation – neither alive nor dead – as energy flow will stagnate to zero entropy and there is no arrow of time. If that is what is meant by immortality, then probably that can be achieved. But, in reality, human beings, or for that matter, any form of life can never be immortal in true sense of the term. A body can live for a long period of time and gradually decay, but can never last forever.

– Dr A Rahman is an author and a columnist

Advanced science, Astrophysics, Cultural, International, Technical

Mysterious dark matter and dark energy

Physics is traditionally viewed as a hard subject requiring a great deal of mathematical prowess, devotion and perseverance to muster the subject matter. To a large extent, it is definitely true. But it does also offer, in its turn, a great deal of satisfaction, excitement and sense of achievement.

The 21st century physics, spanning from quantum computing to super-thin layer material called graphene to ultra-efficient LED bulbs to efficient harnessing of renewable energies to black holes to dark matter and dark energy, the range of topics is endless and it will disappoint no one with its vast challenges and ensuing excitement.

In our day-to-day lives, we encounter matter comprising protons and neutrons bundled together at the centre, called nucleus, of an atom and electrons whizzing around the nucleus. Some decades ago, these protons, neutrons and electrons were thought to be the fundamental particles of all matter; but not anymore. Now, quarks (six types) are thought to be the fundamental matter particles, which are glued together by force particles to form protons and neutrons.

These atoms and molecules making up matter here on earth are what we are accustomed to. The laws of physics, or for that matter of natural sciences, were developed to explain the natural processes as we encounter in our lives.

The basic physical principles are like these: a body has a definite size comprising length, breadth and height; it has a mass and weight; it is visible when there is sufficient light. If we push a body, we impart momentum, which is the product of mass and velocity. As it has the mass, it has gravity, meaning it attracts every other body and every other body attracts this body. These are the basic properties of a body as described in classical physics.

But there is no reason to be dogmatic about these basic principles. These principles can change here on earth or in our galaxy or somewhere outside our galaxy. When they do change, we would feel that things have gone topsy-turvy.

We live on a very tiny planet, called Earth, which revolves round the star, called Sun. There are eight other planets, thousands of satellites, comets and asteroids, all held together by the gravity of the Sun. The Sun, though extremely bright and overwhelmingly powerful to us, is a small star in our galaxy, called the Milky Way. It is estimated that there are over a billion, yes, 1,000,000,000 stars, many of them are much bigger than the Sun, in our galaxy. Now our galaxy is by no means the biggest or dominant galaxy in the universe. Cosmologists estimate that there are around one billion galaxies in our universe! Some of these galaxies are hundreds or even thousands of times bigger or massive than our galaxy. There are massive black holes at the centres of most of the galaxies, exerting gravitational pull to keep the galaxy together. Some of these black holes are millions of times bigger than the Sun. Now we can have a feel of how big our universe is!

Physics, or more appropriately astrophysics, studies the processes of these vast expanse of celestial bodies. The Sun as well as our galaxy, the Milky Way having over a billion stars are not static. The stars are spinning, the galaxy is spiralling, and everything is in motion.

Strange glow from the centre of the Milky Way

It was estimated, purely on physical principles, that the stars at the edges of a galaxy should move slower than the central ones, as the force of gravity of the galaxy is weaker away from the centre. But astronomical observations show that stars orbit at more or less at the same speed regardless of their distance from the centre. That was a great surprise, indeed shock, to the astrophysicists. The way this puzzle was eventually tackled was by assuming that there are massive unseen matters that exert tremendous amount of gravitational pull to keep the outlying stars moving at nearly the same speed and that mysterious matter is called the dark matter.

There are other tell-tale signs that there is something amiss in the material accounting of the universe. A strange bright glow spread over the length of the Milky Way was thought to be due to ordinary pulsars (pulsating stars) along the length. But now it is thought that dark matter may be responsible for this glow! But how does it do that, physics does not know yet.

But is this dark matter a fudge to solve the apparent conflict of physical behaviour with observations? Not really, this is how science progresses. Well thought out ideas are advanced and those ideas are tested and cross-examined against observations and the idea or concept that passes the tests is taken as the valid scientific concept.

But how do we know dark matter is there, if we cannot see them. We cannot see them because dark matter does not interact with light or electromagnetic radiation such as visible light, infra-red, ultra violet, radio waves, gamma rays and so on. Light goes straight through the dark matter, as if it is not there.

It should, however, be pointed out that dark matter is not the same thing as black hole. A black hole is made up of everyday particles (matter particles and force particles) – electrons, protons, neutrons, atoms, molecules, photons etc. Its gravity has just become so strong (because of its mass and super-compacted size) that it pulls and crushes everything to its core and nothing can escape from its clutches, not even light! A beam of light coming close to a black hole is pulled right insight and that is the end of that light beam never to be seen again!

Dark energy expansion

Dark matter, although invisible, does exert gravitation pull and this gravitational pull that makes dark matter attractive to scientists. The Universe, although expanding, is not in danger of runaway expansion. There is something that is holding the whole thing together and that something may be the dark matter.

Immediately following the Big Bang, the then Universe expanded very rapidly, known as inflationary phase, for tens of millions of years followed by expansion for some billion years and then it stabilised for a few billion years and now it is again in the expansion phase. The present expansion is that the space itself is expanding and so every star and every galaxy is moving away from every other star or galaxy. What is giving these celestial bodies energy (repulsive in this case) to move away from each other? Scientists came up with the proposition that there must be some unknown, unseen energy, which is now called the dark energy.

On purely material and energy balance of the Universe, it is thought that our visible (and known) Universe accounts for only 4.9 percent of the total Universe, dark matter accounts for 26.8 percent and dark energy for 68.3 percent. So, we only know in the vast mind-boggling universe extending over 13.8 billion light years a meagre 5 percent and the remaining 95 percent is hidden or unknown to us!

Scientists all over the world are trying hard to find evidence of dark matter and dark energy. CERN’s Large Hadron Collider (LHC) is trying to find any remotest evidence of dark matter and energy. On theoretical basis, some scientists are proposing that dark energy may emanate from a fifth form of force, which is yet unknown. The four forces that we know are electromagnetic, weak nuclear, strong nuclear and gravitational forces. The fifth force may be a variant of gravitational force – a repulsive gravitational force – that comes into play in the vast intergalactic space.

When Einstein produced the general theory of relativity in 1915, he introduced, almost arbitrarily, a parameter, called the cosmological constant, into the theory to counter the effects of gravitational pull and make the Universe a static one. That cosmological constant effectively introduced the repulsive effects. It may be pointed out that the Universe was thought to be static at that time. But only a few years later when it was incontrovertibly shown that the Universe was, in fact, expanding, Einstein humbly admitted that it was his “biggest mistake”. Now, more than hundred years later, it is assumed that the cosmological constant may be considered to be the quantity to cater for the dark energy! Could Einstein’s “biggest mistake” be a blessing in disguise, it offers not only a correct presumption but also a saviour of modern cosmology?

  • Dr A Rahman is an author and a columnist