Written By: Dr. Gulfaraz Ahmed
Physics is essentially the science of matter, light and energy. It deals with the processes and phenomena of the physical nature in the universe. The modern day physics is organized into classical physics, quantum mechanics, particle physics, astrophysics and cosmology, etc. It aims at observing the patterns, behaviours and consequences of the physical phenomena. Physicists often use thought-experiments and mathematical models and develop hypotheses, which on confirmation through experimentation achieve the status of scientific theories. Theories are then used for understanding the present and predicting the future results and outcomes. Physics was established as a discipline of science in Archaic Greece about four centuries BC. Pioneering works of legendary philosophers and scientists like Archimedes, Socrates, Plato and Aristotle were treated as authority right till the beginning of the 17th century. Although in the intervening period Muslim scholars preserved, translated and in many important ways extended the Greek science, in essence it was a new wave of scientific revolution brought about by the liberation of mind from the religious dogmas in Europe during the course of Reformation and Renaissance preceding the 17th century that laid the base for modern physics and the 17th century came to be known as the Century of Science. Science has since then witnessed spectacular advances and has succeeded in rationally explaining many unknowns which in the past used to be attributed to supernatural phenomena.
Glossing over the recent history, physics got a boost by the pioneering work of hitherto unknown Einstein at the start of the 20th century. He published three important papers in 1905. One of these was on photoelectric effect for which he was awarded the Nobel Prize in physics in 1921. In this work he followed the idea of Max Planck that electromagnetic energy like light does not travel in the form of a continuous wave but in discreet packets of energy called quanta. He experimented with various metals using light of varying intensity as well as frequency (various colours of the spectrum) and produced varying streams of electrons. The second paper presented the Theory of Special Relativity which explained the relationship between space and time, and provided the mathematics for analyzing the relativistic motion close to or at the speed of light. As a precursor to Einstein's Special Relativity Theory Maxwell had, a century earlier, established that light was an interaction between moving electricity and moving magnet and was an electromagnetic wave. Einstein theorized that it would be a self-supporting wave only if it moved at a fixed speed in all reference frames. This distorted the previously held fundamentals of time and space. According to Special Relativity both time and space contract along the direction of motion i.e., the space contracts and time slows down. The moving observer himself sees no difference in his own frame of motion but another observer in a different inertial frame (frames moving with constant speed or zero acceleration) measures the relativistic changes. The magnitude of contraction was calculated using the equations already developed by Edwin Lorenz, George Fitzgerald and Henry Poincare. As an object approached the speed of light it would contract in the direction of motion to a singularity and become very heavy approaching infinity and it would be impossible to accelerate it further. No kind of matter is thus able to achieve the speed of light which serves as a fundamental limit on physical motion. Photon is a particle of light, which itself is not an object but an electromagnetic interaction, and it travels at the speed of light because it has no mass and moves at a constant speed of 3x10^8 metre/second. The speed of light is constant in all directions regardless of the fact that the light source is moving with constant speed or accelerating. Special Relativity is built on this edifice which has become a fundamental of modern physics. Having no mass, photons do not need a medium to propagate and light can travel through vacuum and that is why we see the galaxies in outer space. Einstein's ground breaking work on mass and energy equivalence by his epochal equation of E = MC2 together with Special Relativity provided another view of the impossibility of matter achieving the speed of light. As the mass approached infinity it would need infinite amount of energy to accelerate it to the speed of light. Time dilation postulated in the theory was later practically proved by sending two accurate atomic clocks on board scheduled flights eastward round the world twice and similarly placing two clocks on westward round the world flights twice and then comparing the time with an identical clock placed on the ground in USA in 1971. Time dilated and onboard clocks slowed down by a fraction of a second exactly as predicted by the Theory of Special Relativity. In his third paper published in 2005, Einstein proved the existence of atoms creating the foundation for the Standard Model.
In 1915 Einstein produced the General Theory of Relativity, which provided a theoretical model for predicting the motion of accelerating frames of motion like the galactic bodies. It provided mathematical basis to Newton’s model of calculating gravity presented a century earlier. Newton’s model gave accurate force of gravity for objects moving at ordinary speed and was not able to handle objects moving close to the speed of light. General Relativity works for relativistic motion near the speed of light and vindicates Newton's theory of gravity at slow speeds. Newton's mathematical model provided a method of calculating the force of gravity; it did not explain the origin of gravity. Einstein's General Relativity provides an understanding of the origin of gravity as a consequence of the time-space warp. Any massive body bends or warps the four dimensional (time and three space dimensions) grid giving rise to the force of gravity. The greater the mass or higher the speed, the greater is the warp and hence the force of gravity. For example, gravity on the surface of the Earth is six times that on the surface of the Moon. Gravity at the event horizon of the Black Hole at the centre of our galaxy Milky Way may be billions of times higher than at the Sun. When Einstein had originally developed the mathematical model of General Relativity, it predicted an unstable and expanding universe. Einstein, thinking that an unstable universe would be hard to believe, fudged it by adding a cosmological constant that made it unchanging. He later recanted and called it as his greatest mistake in 1929 when Edwin Hubble proved that the universe was actually expanding.
Physics witnessed a big surprise when it was discovered in 1998 that the universe was not only expanding but accelerating. The acceleration part cannot be explained by the known fundamental forces and new explanations are required posing major challenges to the physicists. Einstein's General Relativity Theory had predicted that light rays would bend as they passed by the massive bodies. This prediction was practically proved concurrently by a British team, led by astrophysicist Arthur Edington, and a German Team by observing light rays emanating from the stars behind the Sun, which normally cannot be seen, during a solar eclipse in the islands of South America in 1919. The light rays bent precisely by the amount predicted by the theory which catapulted Einstein into an unprecedented fame. From then onward this theory has passed every test and challenge. The toughest test it passed happened only recently in 2013. Einstein had predicted generation of gravitational waves in the universe from massive bodies moving at high speeds. He had predicted that a massive system of binary stars revolving around each other at very high speed would emit gravitational waves as the system dissipated its energy. He had further provided that as a result of the loss of energy and hence the mass from the generation of the gravitational waves, the time period of the revolution would keep reducing. The gravitational waves had, however, never been detected directly or indirectly till recently. A few years back scientists had identified a massive binary system only about 7500 light years away from the Earth. One of the two binary stars was a neutron star whose mass was over two times that of the Sun but it occupied a space only about 17 kilometre across. The other star was a white dwarf compressed to a small size with its mass close to that of the Sun, which is revolving around the massive twin nearly 300 times a second. Scientists thought that this massive system moving at such a high speed could provide an opportunity of putting the General Theory of Relativity to the toughest test so far by detecting the generation of gravitational waves indirectly through reduction of its time period. After painstaking observations and calculations it was established that the time period of the binary system was reducing by 8 millionth of a second every year which is exactly in line with the amount predicted by Einstein's theory. Very recently an American observatory directly detected the gravitational waves emanating from the collision of two black holes on February 10, 2016 proving Einstein right in the toughest test yet.
One of the most fascinating results of the theories of relativity is the theoretical possibility of travelling through time. Theoretically it is possible for someone to travel into the future of others left behind, by time travel. Similarly the Theory of General Relativity allows the manipulation of space-time for travelling into the past. Practically, however, it might not be possible to surmount the real challenges to time travel.
Theoretical physics is indifferent to the direction in which time flows and it is theoretically possible for the time to run backward. Maxwell's equation for the interaction between electricity and magnetism, which explained the nature of light, had a strange implication. It had two equally valid solutions: one produced 'retarded waves’, of the light, as we understand and the other 'advanced waves' which started from the destination and ran backward to the source. The latter made no sense and therefore the other solution was ignored. Over a century later American physicists John Wheeler and Richard Feynman were studying the behaviour of an atom as it emitted quanta of light or a photon. They observed that a photon is emitted by a single electron from an atom and that the atom experiences recoil as the photon leaves. They tried to explain the recoil by considering the forgotten advanced waves that travel backwards to the source. They think that two photons are involved in the self-interaction: one photon leaves the atom and is absorbed by another atom; the absorbing atom also releases another photon which reached the source atom in time to cause the recoil, through the quantum leap, by travelling back in time. This is still a speculative area of physics and could have more surprises in store!
Special and General Theories of Relativity provided classical mechanics the capacity to treat systems of motion of large galactic bodies moving at relativistic speeds. But a new branch of physics was developing at the onset of the last century which was to handle the physics of the very small, the quantum particles, which reveal the nature of matter and light. It had become quite evident to the physicists that classical physics that dealt with the certitude of motion of the heavier bodies, would not provide a handle on the probabilistic motion of the quantum particles. The probability function was presented by Schrodinger’s famous Wave Function, a bizarre possibility of all the particles could have equal probability of being everywhere at the same time. It was the act of observation or measurement that created the reality by fixing a particle. The Wave Function that gives the sum of all probabilities collapses to a definite state in the act of measurement. Known as Heisenberg's Principle of Uncertainty it requires that if you fix the position of a quantum particle you disturb its momentum which is needed to predict accurately its future position. Equally strange is the behaviour of the entangled particles which seemed to act like one entity even if separated over long distances. It appears that if a measurement is made on one of the entangled particles, the other knows this fact along with the outcome of the measurement instantly even though there appears no known means of communication between the two. Quantum Entanglement implies an interaction between two particles which while remaining separate act like one instantly. Nothing actually travels between the entangled particles; it is only the information that reaches there instantly. Einstein had referred to it as the spooky action at a distance. It was because of these bizarre possibilities that he had disagreed with the uncertainties of quantum mechanics saying that God does not play dice with the universe. He believed that there was a hidden reality in the quantum world that had yet to be discovered. Einstein spent his remaining life looking in vain for that hidden reality. Meanwhile, quantum mechanics, though bizarre looking, has met all experimental confirmations and has led to numerous technological breakthroughs.
With the help of classical physics and quantum mechanics, we could separately handle massive bodies as well as quantum particles moving close to or at the speed of light. All attempts to-date to integrate the mathematics of the large bodies and that of the quantum particles have broken down as there is no way yet of integrating the force of gravity with the other electromagnetic forces, weak and strong. A major conundrum is thus posed by some cosmological objects that are very large in mass but very small in size like a black hole. Classical and quantum physics together do not provide mathematics of the physics of a black hole that may have a mass of thousands of suns but the event horizon of only a few kilometres. The escape velocity from the event horizon of a black hole is so high that not even light can escape it. The time is therefore stationary at the event horizon. No information is available about what goes on inside black holes; that continues to remain a mystery to physics. It poses a new frontier for understanding the universe. Such problems cannot be solved until we achieve the unification of the gravity and non-gravity physics, which is what the so called, Theory of Everything (TOE) is loosely referred to.
Four fundamental forces (Electromagnetic, Weak, Strong and Gravity) acting through corresponding quantum particles known as gauge bosons (photon for electromagnetic, W and Z particles for weak force, gluon for strong force and yet to be discovered illusive graviton for the force of gravity) together are the cause of actions that shape and govern the universe. Electromagnetic and weak forces were unified at high energy level by Abdus Salam, Glashow and Weinberg in early 1970s and they were jointly awarded Nobel Prize for this work in 1979. The Strong and Electromagnetic interactions are unified in nature. Negative charge of an electron which forms part of electromagnetic interaction and positive charge of the three quarks of a proton which forms part of Strong interaction is perfectly balanced resulting in neutrality of the matter. However, all attempts to achieve the Grand Unification Theory (GUT) of Strong and Electro-weak interactions have remained elusive so far. Proving of GUT requires creating those particles that require very high energy levels which are not likely to be achieved in the HADRON in the near future. Meanwhile, scientists are looking beyond the unsuccessful GUT and ambitiously attempting to unite all the four forces including gravity into a Theory of Everything (TOE).
A novel concept of creating a single building block of all quantum particles hit the minds of the scientists. They visualized it like a vibrating quantum string which at different frequency and energy levels represented different quantum particles. String Theory will overcome the major limitations of quantum physics by eliminating the singularity and explaining the quantum interaction of gravity by its force carrying hyper-dimensional particle graviton when it is successfully finalized. It will be able to explain the interactions of all the four forces during the early moments of the universe before the splitting of the particles and forces. No one has seen the quantum string in any experiment but this conceptualization provides some interesting options of quantum representations. There had come about a number of String Theories which have been combined into one theory called M Theory. It postulates an 11 dimensional graviton: one of time, 3 of physical space and 7 additional curled up dimensions for quantum connection. It might be that after the Big Bang the energy level was such that the three space and time dimensions inflated, creating space and time but the other 7 dimensions remained curled up and compacted and are embedded in space and time everywhere. The string requires the seven curled up dimensions to create all the particles known to be part of the Standard Model through various patterns of vibration. Superstring Theory proposes the length of the curled up 7 dimensions to be in the order of 10-35m (close to the Planck Length) and this would require energy of particle collision in the order of 1019 GeV to detect the higher dimensions. This is about a million, billion orders of magnitude larger than can be achieved in the HADRON presently. If the extra dimensions are somehow discovered physics will change fundamentally and it will succeed in unifying gravity and non-gravity physics through the TOE that Stephen Hawking called a simple and elegant equation that will handle all interactions in the universe right from the earliest time. TOE would enable the scientists to go back in time right to the limit of know-ability at the Plank Time of 5.5x10-44 seconds after the Big Bang revealing the secrets of the early universe from presently known limit of 10-33 to the know-able limit of 5.5x10-44 seconds. The HADRON Collider has not yet been able to detect particles smaller than quarks which could explain the TOE.
Humanity has always been very curious to understand the universe, and at all times it had a leading model of some sort for its physical visualization. In 340 B.C. Aristotle gave a metaphysical model that the earth was stationary and in the centre and the sun, the moon, the planets, and the stars moved in circular orbits around it. A new model was presented by Copernicus in 1514 that the sun was stationary at the centre and the earth and the planets moved around it in circular orbits, which was further advanced by Galileo about a hundred years later. Newton in the 17th Century rejected the centrality or hierarchy of any heavenly body by rejecting metaphysics and gave a rational model of the universe where all heavenly bodies obeyed the same laws of physics without any distinction. This liberated the universe from the supernatural connections and brought it in the realm of science. Einstein, by his General Relativity Theory, presented a scientific view of the universe and explained the origin and action of gravity that played a key role in shaping the universe and presented the model of the expanding universe. This remained as a guiding model till it was challenged recently in 1998 when it was observed beyond doubt that the universe was not only expanding but is accelerating with increasing speed. This model is in line with the original model developed by Einstein before his fudging it by the insertion of the cosmological constant. If Einstein had not arbitrarily made the universe stationary by inserting the cosmological constant, we would have known in 1916 what was then discovered in 1998, saving nearly 80 years for advancing physics. The acceleration of the universe is an enigma that physics has yet to find new frontiers to unfold the unknown secrets.
A new model was presented by Copernicus in 1514 that the sun was stationary at the centre and the earth and the planets moved around it in circular orbits, which was further advanced by Galileo about a hundred years later. Newton in the 17th Century rejected the centrality or hierarchy of any heavenly body by rejecting metaphysics and gave a rational model of the universe where all heavenly bodies obeyed the same laws of physics without any distinction. This liberated the universe from the supernatural connections and brought it in the realm of science. Einstein, by his General Relativity Theory, presented a scientific view of the universe and explained the origin and action of gravity that played a key role in shaping the universe and presented the model of the expanding universe.
Since it was established by Edwin Hubble in 1929 that the universe was expanding, scientists had been observing that farther the galaxies they could see faster were they moving away from one another by analyzing the red shift of the light reaching the earth. It was logical to think that billions of years back the universe must have been much smaller and back at zero time it would be a singularity of zero size. It is to the credit of the living giant of a physicist Stephen Hawking that he postulated the beginning of the universe in his book on “the Beginning of Time”. Einstein’s General Relativity Theory also leads to the beginning of the universe from a singularity. As all mathematical laws including the General Theory of Relativity break down at a singularity, it is not possible to predict the nature of the universe that came out of it. Friedman had also described the universe right back to the Big Bang. The time that we measure every day, the space that we encounter and the matter that we see was not there before the Big Bang. The time is passing, space is expanding but it is not known whether the matter is also changing, increasing in some unknown form like dark matter or staying constant or decreasing.
Soon after the Big Bang the universe was very hot and as it expanded the matter or radiation in it cooled which would have played a major role in shaping it. In fact even the type of particles that would have existed in the early universe was linked with the temperature. One second after its birth it would have cooled to about ten thousand million degrees, which is about ten thousand times the temperature at the center of the sun. As the universe expanded with the speed of light, nearly 3x108 m/s, after the big bang it reached a size of 1.65x10-35meters in 5.5x10-44 seconds. This is the smallest distance that is at the limit of quantum determination and is called Planck Length. For distances smaller than this that correspond to the time earlier than 5.5x10-44 seconds there is quantum confusion as defined by Eisenberg Principle of Uncertainty. So our knowable universe starts at the Planck’s Time. At this time quantum particles had not yet started separating and there existed only one unified force. From 10-37 to 10-33 all quantum particles separated creating the four fundamental forces one by one. The first to separate at 10-37 second was the force of gravity. The next was the Strong Force that separated with its particle gluon at 10-35 second. Last to separate were electro-weak interactions through their corresponding photon, W and Z gauge bosons at 10-33 second. It is for this reason that unifying the force of gravity and the strong force with the electro-weak interactions is so challenging.
If we want to study the universe from 10-33 to the limit of know-ability i.e., up to the Planck Time (5.5x10-44 seconds), we need to unify all four fundamental forces into one mathematical model. That is what is behind the global quest for a TOE. But why are we so fixated to know the secrets of the early moments of the birth of the universe, it is because by looking into the past we would be in a position to better visualize the future of the universe. Unification aims at searching the particles that were released at very early time after the Big Bang. Such particles that separated at very high energy levels require equally high energy physics to separate them. The largest particle smasher Hadron is constantly being upgraded through more and more powerful super conducting magnets to achieve speed of racing protons close to that of light which on collision create very short lived particles of interest but it is still not able to that the required level of speed of collision.
There are other models of universe competing with the Big Bang concept like the universe being a sequence of contraction and expansion instead of a time and space singularity at the start of the Big Bang. Similarly, the concept of multiverses co-existing but not interfering with one another except at the time of some cataclysmic events is full of future surprises. Looking at the big surprises in physics that continue to be discovered every now and then provides a bizarre contrast with once held view that physics had all been fully discovered. It was a result of the ongoing endeavour that the hitherto illusive Higg’s boson was discovered in 2013 at the Hadron to complete the Standard Model of physics. Higg’s boson creates Higg’s field which is responsible for giving all matter its mass. This has been an epochal development. The standard model of the constituent parts of matter that started with Dalton's theory of indivisible atoms grew to the generation of the elementary particles of protons, neutrons and electrons and finally to the latest generation model of two broad categories of particles (fermions that include quarks, compound protons and electrons) and gauge bosons. Fermions constitute the matter in the universe and the gauge bosons carry various forces or interactions. The fermions carry spin in multiple of halves (1/2) and the gauge bosons have the spin as multiple of integers. To-date 17 particles have been discovered which include 12 kinds of fermions (6 quarks and six leptons or electrons) and five gauge bosons, including the latest discovery of Higgs Boson in 2013. The quantum theory predicts a total of 18 elementary particles and the remaining particle called graviton that provides the interaction of gravity is yet to be discovered. The Standard Model therefore describes only the interaction among three fundamental forces of electromagnetic, weak and strong to the exclusion of the fourth force of gravity. The discovery of graviton would lead to the unification of all four forces into a Theory of Everything. A key particle of this model that was predicted in 1964 by Edwin Higgs among others that later came to be called as the Higgs particle remained elusive till 2013, casting doubt on the robustness of the iron-cage Standard Model that had been successful in predicting many other particles that were later discovered but the non-ending quest for Higgs particle had posed a big conundrum. Its discovery after all has nearly completed the Standard Model. Even then the Standard Model with its known particles can explain structure of at the most 5% of the material universe. The rest defies our explanation; there may also be what is called dark matter, which is sensed only by the gravitational pull on astronomical objects like the visible galaxies and also on the rays of light. The unproven supersymmetry (SUSY) theories propose the possibility that there are massive electrically neutral dark particles of mass in the order of 1019 times that of a proton which might be stable enough to seed the dark matter. No evidence of the massive particles has however been detected so far. But there is more in the universe that is not known and that is the dark energy. While drawing an energy balance scientists estimate the universe is composed of 4% normal baryonic (protons and neutrons) matter, 23% dark non-baryonic matter and 73% illusive dark energy. Physics thus faces monumental challenges to explain the dark matter and the dark energy and it is far from being complete as was once thought. Dark matter gravitates and is an object in space but dark energy presents an enigma. It does behave like gravity and is something connected with the space itself. It acts against gravity and may be responsible for accelerating the expansion of the universe which was detected through the motion of farthest galaxies. The mysterious force that might be responsible for the observed acceleration in the expansion of the universe against expectation could be the dark energy.
Dark energy's origin is still elusive. It is associated with the vacuum of the free space and causes a negative pressure in regions devoid of gravity-attracting matter and causes the empty space to inflate unlike the positive pressure that causes deflation due to attraction. Dark energy might be a fifth fundamental force that has yet to be understood and explained. Physics cannot rest on its laurels; physicists have to explain the universe that has kept its mystery still to itself. It may be interesting to recall when Max Planck was attending university towards the end of the 19th Century and was considering pursuing a career in physics or music, his physics professor advised him to pick music as theories of physics were complete and there was little left to do in this field. Lucky that he still picked physics and was later to discover that the new surprises would blow apart everything his predecessors had assumed to be true. It perhaps is truer now than it was then. Physics has never been at a brink of completeness.
The largest particle collider Hadron restarted its operation on April 05, 2015 at twice the previous power to discover how the universe works, which may enable it to discover the dark matter and perhaps the extra quantum dimensions that may prove the TOE. Will the newly achieved speed of racing particles in the Collider lead to unfolding more of the hitherto held secrets of reality should be happening in the near future? Once thought to be complete, physics faces numerous conundrums and is set to meet many surprises!
The writer holds a PhD degree from Stanford University, California USA. He is a former Federal Secretary and has been CEO/Chairman of OGDCL and Chairman NEPRA.