Black Holes : The Recycle Bins of Universe

"A Black Hole is a region in spacetime where the Gravity is so strong that not even light can escape." This is the most standard definition of a Black Hole. The idea of a Black Hole was first proposed by an English clergyman - John Michell in 1784. However upon the discovery of wave nature of light, his idea was quite overlooked as it wasn't clear how a wave would be influenced by gravity. Some years ahead in time, Karl Schwarzschild discovered the first solution of the mathematical equations of Einstein's General Relativity which characterized a Black Hole. Physicist John Wheeler coined the term "Black Hole" - since they attract everything and almost nothing can escape from them. In this blog article, the formation of Black Hole, its anatomy and some strange consequences will be presented.

Image of Powehi captured by the Event Horizon Telescope.

              How is a Black Hole formed? It is definitely not easy to create an object that would basically attract everything that comes close enough to it. The density of such an object should be nearly infinite. A tremendously high amount of energy and work needs to be done to compress something into such a small space. The quantitative relation between any object's mass and the radius it needs to be compressed into to become a Black Hole was given by Schwarzschild. The radius is called as - "Schwarzschild Radius". This relation in itself is quite simple :

                                                         

                                                       R_g = 2GM/c².

              

                                                         

 Rg here is the Schwarzschild Radius, M is mass of the object, G is the Gravitational Constant and c is the speed of light. In the equation, 2, G, and c are just constant values. Hence, the radius is proportional to (depends on) mass of the object. Greater the mass, greater is the radius. If you were to convert Earth into a Black Hole then you must compress its entire mass into the size of a small marble. This really gives us an idea of how dense a Black Hole is. It is impossible at the present time and perhaps also in the future to artificially synthesize a Black Hole. But, this doesn't mean they don't exist at all. Even though the genius astrophysicist - Stephen Hawking disagreed with the notion of Black Holes at some point of time. We now have solid evidence of its existence. Black Holes do form naturally. However, as discussed before, the process is violent. They are typically formed when huge stars having a mass of almost 8-20 times greater than the mass of our Sun, die in an explosion called as - "Supernova". Doing a quick walkthrough of Stellar Physics - A star produces energy by means of nuclear fusion occurring at its core i.e. it fuses hydrogen and helium to produce new elements along with release of energy. The outer layers of a star tend to collapse onto its relatively denser core due to gravity. But, the radiation released from the nuclear fusion occurring at the core just balances this weight of the outer layer.

 With time, this fuel reservoir of hydrogen and helium in a star depletes and as a result it fuses heavier and heavier elements releasing lesser energy every time. Until a point is reached when no energy is released from this fusion and the weight of outer layers of stars is no longer balanced. They collapse onto the dense core of the star, which is now even denser because of the heavier elements fused and then rebound out causing a huge explosion - "The Supernova". When the mass of this star is great enough, the impact on the core due to this explosion is tremendous causing it to compress into a small volume. Thus, forming either a neutron star or a Stellar Black Hole. There also exists another class of Black Holes known as Supermassive Black Hole. It is believed that these black holes reside at the center (nucleus) of almost every galaxy in the Universe and that the stars in these galaxies revolve around this Black Hole in simple or complicated orbits. Our own Milky Way galaxy holds one at the center. and its named as Sagittarius A*. Supermassive black holes are far larger than stellar black holes and are believed to be formed either by the merging of smaller stellar black holes or by collision of multiple stars in compact star clusters. Astrophysicists have also hypothesized the existence of another class of Black Holes called Intermediate Black Holes, which are sort of midway between stellar black holes and supermassive black holes. Oddly enough, there are no firm observations which prove they exist. Another hypothetical class of black holes called Primordial Black Holes are believed to exist. These black holes might have formed in the early universe just after the Big Bang when the Universe was non-homogeneous and density irregularities caused matter in some regions to collapse into a Black Hole.

              Let us discuss the structure of a black hole now. Note, that by structure I mean those parts which could be observed by us using different means. What exactly happens inside a Black Hole is something of great mystery and something about which we know very little. Broadly speaking a black hole comprises of an accretion disk, the photon sphere, an event horizon and finally the singularity. An accretion disk consists of heated matter like gas, dust and plasma which orbits the Black Hole. Due to their high energy, they radiate X-rays and ultraviolet rays. The photon sphere as the name suggests is a sphere of photons (light rays) surrounding the Black Hole at a fixed distance. This sphere is made of photons which just manage to escape the Black Hole. However, due to its immense gravity their paths are bent forming a sphere around it. The next part of a Black Hole is crucial, because it is what marks the point of no return  - "The Event Horizon". Any object or creature unlucky enough to cross this point is doomed to fall into the black hole and stay there eternally. The event horizon  is the point beyond which one must travel faster than light to escape. Followed by event horizon is finally the "Singularity". A point in spacetime having infinite matter density. The density is so high that the spacetime around this point is highly warped giving rise to all sorts of strange effects.

Warped space and time around a Black Hole.

              

              But what exactly happens if one falls into a Black Hole? You must have heard numerous times that due to the strong gravitational effects the unlucky human would experience something called - "Spaghettification" meaning that since, the lower part of the human would be closer to black hole than the upper part. The gravitational pull on it would be immensely stronger than the upper part of the body. This will make the body stretched like a spaghetti. However, it is believed that this shouldn't be the case with supermassive black holes, where the tidal forces wont be that strong. What would happen in such circumstances? Due to the strong warping of spacetime around the singularity, any observer falling into it will experience "gravitational time dilation" i.e. the observer's time will slow down as compared to someone away from it. A second for the observer might be hundreds of years on Earth. Due to this, the observer would see the entire future unravel in front of him/her in just a matter of time. Since, the space around the Black Hole is warped too, the observer would notice strong distortions in the geometry of space. This is all we can speculate until the observer crosses the "event horizon". What happens after that? - Nobody knows at all. What happens at the singularity? Again, we don't have a firm theory for that. To answer those questions a Quantum Theory of Gravity needs to be summoned. In previous blog articles, I discussed about Quantum Mechanics - the theory of very small. Einstein's General Relativity which predicted the existence of Black Holes is apparently a large scale theory and fails to apply in the realm of Quantum Physics and vice versa. In normal situations this discrepancy can be ignored. But in bizarre scenarios like at the heart of Black Hole. there is so much matter condensed in such a tiny space that both relativistic and quantum effects ought to be considered. Thus, a marriage of the two theories will allow us to peek into the singularity and also not cross the event horizon.

             Numerous efforts are being made to obtain such a theory and many potential candidates had emerged with time (the famous String Theory being one of them). But each theory is incomplete in one aspect or the other. Inspite of that, it never stopped some great physicists from presenting elegant theories about the quantum effects which could possibly be accompanied with a black hole. Stephen Hawking's famous theory of "Hawking Radiation" is one of them. The work of physicists like Gerard 't Hooft, Jacob Bekenstein and Roger Penrose gave rise to the interesting subject of Black Hole Thermodynamics. I shall discuss their beautiful work in the next blog article. Until then, remember not to fall into a Black Hole unless, you want to be a spaghetti.

- Thank You.

              

                                                       

Theory and Experimentation in Physics: An Analysis on Examples from the Past

 

1.          Introduction

            Every branch of Science is categorized into theoretical and experimental parts. However, in the areas of Physics and Chemistry the distinction between the two becomes prominent. In this essay, I would like to discuss these two different aspects in Physics and their significance by isolating examples from historical discoveries.

            We have no knowledge about the exact origin of Science. One can say it originated through a series of simple experiments (both practical and theoretical) conducted by people when they started observing nature; through astronomical observations made by the Babylonians and the mathematical discoveries of Euclidean Geometry; through Archimedes Principle and the Pythagorean Theorem. There were advances in experimental as well as mathematical and theoretical sides of Science. At that stage, the concepts were too tender and could not be broken down into simpler statements. Almost all of them were empirical. Why the Pythagorean Theorem holds? – Nobody knows, of course one can derive it but those derivations themselves involved some fundamental axioms[1]. But philosophers and scientists of that time used these fundamental theorems to construct models which described reality along with some predictions. These predictions in turn could be verified by experiments, which transform them into “a law”. Prior to that, it is simply regarded as a theory. No matter how beautiful, elegant or intuitive it is, there exists no obligation to accept it as a law. With simple mathematical tools, philosophers of the past determined the radius and circumference of Earth, without even traversing the entire Earth. Their predictions were later verified through experiments. However, as time went by, there were significant developments both in theory and experiments. It was realized that Physics could be split into its theoretical and experimental parts. Thus arose two branches of Physics: Theoretical Physics and Experimental Physics. In the present day, people choose to specialize in one or the other. Despite, the distinction these two branches overlap inevitably and according to my belief the experimental part shall continue to hold an upper hand. After all, experiments distinguish reality from fantasy. The act of observation is what completes Physics as well as Science. Nevertheless, one should not deny the importance and potential possessed by Theoretical Physics. In the history of Physics, there are two great examples in which a discovery was made in one of the branches and later extended into the other. These examples are the two main pillars of Modern Physics : 1.) Einstein’s Theory of Relativity and 2.) Quantum Physics.

 

2.) Special and General Theory of Relativity

            Einstein’s Theory of relativity was a special modification of Galileo’s Theory of Relativity. In the early 20^th century, a series of experiments showed that electromagnetic radiations travelled through space at a constant velocity. These experiments also ruled out the concept of hypothetical luminiferous aether as a medium for the propagation of electromagnetic radiations[2]. Physicists were baffled when this constancy of velocity was not maintained in Galilean Relativity. Since, the existence of ether was disproved and repeated experiments confirmed the velocity of electromagnetic radiations to be unchanged, there was no option left but to reject or modify Galilean Relativity to accommodate the experimental observations. In the year 1905, which was also called as Annus mirabilis (miracle year) for Albert Einstein, he published four papers in the Annalen Der Physik scientific journal. The third paper titled – “On the Electrodynamics of Moving Bodies”[3] carried the idea of Special Theory of Relativity. The paper suggested brilliant modifications of the equations of Galilean Relativity so that the constancy of the velocity of electromagnetic radiations can be preserved. Even though, Albert Einstein was accredited for this genius theory. The equations involved in it are called as – “Lorentz Transformation Equations”, named after a Dutch physicist – Hendrik Lorentz, who originally derived those equations. But, Lorentz chose to adhere with the previous idea of hypothetical aether and interpreted his theory accordingly[4]. The genius of Einstein was to use these results by Lorentz to explain the constant velocity of light. This clearly points out the fact that even though Lorentz’s theory was correct, the way he interpreted it made a lot of difference about the perception of reality. The Special Theory of Relativity was for inertial frame of references (objects moving with constant velocity with respect to another object). A much more general theory was required for non-inertial (accelerating) reference frames. It took Einstein nearly ten years and a number of failed attempts to come up with a General Theory of Relativity. He borrowed the mathematics from Differential Geometry and Tensor Calculus to demonstrate how space and time is curved by mass and energy giving rise to Gravity. It is believed that when Einstein was working for a General Theory of Relativity. There was yet another German mathematician named David Hilbert who was also simultaneously working for it. He was thought to be closer to discovering it, but Einstein won the race[5]. General Relativity was later confirmed by a number of experiments and observations. In 1915, Einstein predicted the existence of Gravitational Waves using his theory – these are ripples in the fabric of spacetime. He believed that it would be impossible to detect these waves. However, nearly a century after its prediction, the LIGO (Laser Interferometer Gravitational – Wave Observatory) observed these waves and confirmed its existence. General Relativity also predicted the existence of Black Holes. In April 2017, the first image of a Black Hole was captured using the Event Horizon Telescope and Einstein’s Theory of Relativity passed another test.

            This long tale of the Theory of Relativity is a supreme example of how powerful a theory can be. If forged properly by considering all pre-existing laws, it can be a vital tool for understanding reality and even yielding testable predictions. The sheer power of mathematics and imagination allowed Physicists to predict something which had never been observed before. Yet, they were so precise that those assertions were verified in the same form as predicted, almost a century later.

 

3.) Quantum Physics

            On the contrary, there is another contender on the stage. A theory which arose from a set of observations conducted in the early and mid twentieth century – Quantum Physics. It is known for its unintuitive and chaotic character. Quantum Mechanics was discovered when Physicists started conducting experiments with small scale objects and the nature of radiations. They observed the laws of classical mechanics failed to explain the behavior of these objects and a new theory was necessary. The subject introduces an unavoidable element of uncertainty and randomness into the quantum realm. Unlike the Theory of Relativity, Quantum Physics is not theoretically rigid. It is associated with a number of different theories or “interpretations” for the same experimental observations. The most orthodox explanation is the – Statistical Interpretation[6] or the Copenhagen Interpretation because it was mostly formulated by Niels Bohr and Werner Heisenberg in Copenhagen, Denmark. Another well known interpretation was formulated by Louis De-Broglie and later used by David Bohm to present the Pilot Wave Theory or Bohmian Mechanics[7]. Of course, there are other interpretations like Hugh Everett’s Many Worlds Interpretation[8] or the Spontaneous Collapse Theories. All these different theoretical formulations of Quantum Physics debate on whether reality is deterministic or stochastic. Inspite of this, one should not forget that the core of these theories is the fundamental observations made through experiments. These interpretations are nothing but different models of the same reality and till date one has no reason to believe in one and disregard the other.

 

4.) Conclusions

            Why are there different theories associated with Quantum Physics but not with Relativity? I believe it boils down to the sequential manner of theory and experiment. Special and General Relativity was first predicted theoretically through a series of “thought experiments”. Hence, when actual experiments were conducted later, there was no ambiguity in the conclusions because they were conducted with the purpose of testifying Relativity. On the other hand, Quantum Physics was first hinted from experiments conducted with small scale objects. Owing to this, physicists had the experimental results in hand but the task of formulating a theoretical model for them got tedious. Each model had the potential to describe these results in their own manner whilst having their own imperfections. Had relativity not been discovered by Albert Einstein, then we would have certainly obtained hints of it. Perhaps from the errors in Global Positioning System satellites; and from the precession of perihelion of planet Mercury; and from the Gravitational Lensing observed near a galaxy or a black hole. However, the chances of formulating the Theory of Relativity in its exact form as we have today from these observations would have been less. The Theory of Relativity would then have been one amongst many other seemingly possible interpretations of those observations. This might demonstrate how sometimes psychological aspects decide how we view reality. To conclude, both theory and experiments are paramount in Physics. Although, practical experiments should be viewed as keys to unlocking the secrets of Universe, for they are depict reality. Our theories are merely viewpoints on this Universe and are doomed to change with time. With each experiment conducted with increasing precision, these theories would be discarded or refined to fit into reality. The inverse of this cannot be true.

5.) References

 

[1] C.G. Hempel, “Geometry and Empirical Science”, The American Mathematical Monthly, 2018, 52:7-17

 

[2] R.S. Shankland, “Michelson-Morley Experiment”, American Journal of Physics, 1964,32:16

 

[3] A. Einstein, “On the Electrodynamics of Moving Bodies”, Annalen Der Physik, 1905

 

[4] H.A. Lorentz, “Simplified Theory of Electrical and Optical Phenomena in Moving Systems”, Koninklijke Nederlandsche Akademie van Wetenschappen Proceedings, 1:427-442

 

[5]  Einstein and Hilbert's Race to Generalize Relativity

 

[6] M. Born, “Statistical Interpretation of Quantum Mechanics”, Science, 122:675-679

 

[7] D. Bohm, “A Suggested Interpretation of the Quantum Theory in Terms of “Hidden” Variables.I”, Physical Review,85:166

 

[8] H. Everett, “Relative State Formulation of Quantum Mechanics”, Reviews of Modern Physics, 29:454

 

 

           

Quantum Theory : The Physics of Very Small (Part 2)

In Part 1 of this blog article, we saw the foundations of Quantum Physics and how the results of several experiments were arranged upon each other to form a chaotic yet precise theory. At the end of that article, I gave a teaser of the Statistical Interpretation of Quantum Physics. In this part, I aim to provide a technical and concise explanation of the Statistical Interpretation of Quantum Physics and its loopholes. In the end, we shall discuss several other interpretations of Quantum Physics. But first - "What do we mean by interpretations of Quantum Physics?" - An interpretation of Quantum Physics is simply an explanation for the results and observations obtained from the experiments and theories. "Why is there an interpretation for the Quantum Theory?" - Short answer - Because the Quantum Theory we have today does not make any sense at all and Physicists are trying to make sense of it with "an interpretation" or "explanation".  Some interpretations however make things worse and totally shatters our intuitions. The best example of such interpretation is the one we are going to explore in this article.

              A quick recap from the last article - Objects in Quantum Physics behave both as particles and as waves. One cannot simultaneously know the position and the momentum of such objects and the outcomes of experiments cannot be predicted with certainty. Rather, one can calculate the probability for all possible outcomes. This is all that's needed to delve into the Statistical Interpretation of Quantum Mechanics which also has another name - "The Copenhagen Interpretation". According to this interpretation, you cannot completely know the state of a system in the "classical" sense. But in a "quantum" sense, you can know the state of a system with the help of a mathematical term - "the wavefunction" represented by the Greek letter psi - Ψ. This "wavefunction" is all that can be known about a quantum system. Its name is quite self-explanatory for its purpose. The wavefunction is a mathematical function responsible for the wave behavior of particles. For those of you who are unaware of what exactly a mathematical function is. A mathematical function is sort of a machine with an input and output. You plug in certain numbers (or variables) as input and you get a different or same output. There are functions of all kind in mathematics. Generally, the input of this wavefunction is a number representing the position of particle in space. So, what output does a wavefunction have for an input? It gives us a complex number called as - "Probability Amplitude" whose square (or multiplication by complex conjugate) gives the "Probability Density" for a particle to be present at a given position. I know, you might haven't understood some or all of what I just said. Let us break down the answer first. The output of this wave-function is a complex number. A complex number is a combination of a real number and an imaginary number. An imaginary number is, as the name suggests a number which does not exist. To avoid getting a pile up of unknown terms, I will not go into much depth. Why the output is a complex number will be answered later. So this complex number when multiplied with another complex number but with a reversed sign (also called as its Complex Conjugate) gives us the "probability" to find a particle at that input position. Simple as that.

             Where does the waviness come in all of this abstract mathematics? - It comes from that complex number output given by the wavefunction. This output is called as "probability amplitude". These complex amplitudes represent the mathematics of waves. They are periodic i.e. their value changes by a fixed amount in fixed interval of time. Just like a guitar string vibrates up and down, there exists a wave travelling on that string. The reason complex numbers are used is because they are a neat way to represent periodic functions i.e. the sine and cosine functions by a beautiful formula called as Euler's Formula.  However, these probability amplitudes are complex valued. They contain both real and imaginary numbers. Imaginary numbers as we know cant be real, thus these "probability amplitudes" alone cannot yield us the probability we need. But, by multiplying them with their complex conjugates, the imaginary part is cancelled or rather converted to real part. Thus, we square the probability amplitudes to obtain the actual probability to find a particle at a position. All of this is too technical, and for a layperson it would be convenient to only remember that the wave nature of particles is defined by their "wave-functions". But, let us just examine what all this mathematical machinery tells us about the actual physical observations. I said the wave nature of particles can be explained by their wave functions. They are complex valued functions and are harmonic (periodic i.e. repeating after fixed interval) in nature. But then for a specific input, they give out "probability amplitudes" which in turn give actual probability when squared. All this means that the particles in themselves are not wavy. Instead, it is the probability itself that is waving. Odd enough? - Welcome to the strange world of Quantum Physics. It can then be concluded that matter waves are nothing but waves of probability. Just like a light wave is a wave in the electromagnetic field. However, some quantum physicists believe that these matter waves are not at all physical, like the electromagnetic waves. These waves are quite abstract. They are in a different mathematical space called as the - "Hilbert's Space". Not the real space in which we live.

A graph of wavefunction against position

               This was the Statistical Interpretation of Quantum Physics in a nutshell. The theory on its outside may seem too fragile and impractical. But its only when you explore its mathematical construction, you realize how beautifully and flawlessly the theory describes quantum observations. However, like every scientific theory, it too has some imperfections and loopholes. The most bothering ones are the "Measurement Barrier" and the "Quantum Information Eraser Paradox". Let us understand the "Measurement Barrier" first. Remember, in part 1 of this article, we learnt the "Wave-Particle Duality". According to which, objects in the world behave both as particles and as waves depending on the circumstances. The circumstance I was talking about actually refers to "measurement"performed on that object. There exists this peculiar relationship between "measurement" performed on a system and its "state". This relationship is rather a hostile one. In the Classical World measurements performed on a system does affect its state by a very negligible amount. Thus, such measurements do not make significant changes in the system. But in the delicate Quantum World, no matter how careful one is, any measurement performed on a "system" is certain to change its "state" in an unpredictable manner. This unpredictable change of state upon measurement is called as - "Collapse of Wave-function". What it means is that prior to measurement the quantum object exists in a superposition of states. For example - a quantum object having a specific wavefunction does not really have a definite position in space. It exists everywhere at once in a superposition. It only has a certain probability to exist at any position. This behavior is just like waves, which do not have a fixed position. However, after measurement one knows the exact position of that particle. It stops behaving like wave and its wavefunction collapses to a single point. Thus, the probability of that particle to exist at that point becomes one. The graph of wavefunction contracts to a localized point. However, at which point will the particle turn out to be present is impossible to predict. The outcome is totally random. This unpredictable collapse to a random position after measurement is known as the collapse of wave-function. Physicists are unable to provide any mechanism for why such collapse occurs after measurement. Hence, the act of measurement disturbs the state of a system in an unpredictable and gives rise to the - "Measurement Barrier". The second paradox - "Quantum Information Eraser Paradox" or also known as "Delayed Choice Experiment" is a consequence of this "measurement barrier". It arises in the following way - The fact that particles behave as waves when not observed and then collapse to a localized point upon observation potentially suggests that information about the particle can be lost or destroyed.

              How? - Well, we would borrow an experiment which was originally used to demonstrate wave behavior of light - The Double Slit Experiment and use the electron version of it. The one which was described in part 1 of this article. We would have an electron gun, which would fire electrons at a constant rate, ahead of it would be a plate with two narrow slits in it and next to the plate is a screen (say a phosphor screen which would produce a scintillation (spark of light) when the electrons arrive at it). The electron gun fires electrons one by one at a steady rate. Initially, the electron is fired from the gun and is detected at the screen at a specific spot. However, as time passes one would observe a peculiar pattern of electron accumulation on the screen. This pattern closely resembles the interference pattern (shown in part 1) which is observed when light is used in the experiment instead of electrons. Hence, we conclude the electrons behave as waves. But let us take a deeper look into what exactly happens. If we consider the moment when a single electron is fired from the gun, it goes towards the plate with two narrow slits. Now, here comes the weird part. We do not know exactly which slit the electron goes through. There is no way to find it out without actually observing it. Let us neglect this part which is unknown to us. We do know, that after that, the electron would arrive at our phosphor screen and would be detected at a specific point. We do know this because we are actually observing the electron. Therefore, the only moment at which we know the exact position of the electron is when we observe it at the screen. The path in between is totally unknown and when something is unknown to us we assign it a "probability". Hence, we have a 50-50 % percent probability of the electron going either through the first slit or the second. Yet, we observe an interference pattern at the screen, which could only be produced by waves. Hence, it can be concluded that the electron actually travels as a wave when it is fired from the gun. Since its a wave, it can travel through both slits at the same time and interfere with itself. It then picks up a random spot on the screen, which we cannot determine but only predict with a probability and it gets detected there. Where is the paradox in all this? - Suppose for example, I want to know through which slit the electron went. I can do this by putting up an electron detector at both slits, which might be a light source that could scatter light off the electron whenever it went past it. This way, I would be able to tell whether the electron went through first slit or the second. When this experiment is performed, one notices no interference pattern at all on the screen. That is right : No wave-like behavior at all. These particles are too shy and deny to act like waves when one is observing them. Henceforth, the wavefunction which originally determined the wave behavior of electrons is of no use. The electrons travel like ordinary particles and produce a pattern as shown below.

              

              This means that observations performed on the electron at the slit not only forces it to behave like particles but it also destroys all the information that the electron's wavefunction carried. But, another principle of Quantum Physics states that quantum information can never be destroyed. This here is the Quantum Information Eraser Paradox, and it demands a solution to the "Measurement Barrier" to eradicate this paradox. There are many other theories out there which provide an alternative explanation for the quantum observations. Theories like - "Pilot Wave Theory", "Many World's Theory", "Hidden Variable Theories" etc. are some of the examples of different interpretations of Quantum Physics. I would not go into the detail of each. The Pilot Wave Theory explains that a particle has a "guiding wave" associated with it. The particle rides on this wave and thus behaves accordingly. Hence the name - "Pilot Wave Theory". 

(Above image is of a phenomenon in fluid mechanics called as Walking droplets. These are also identified as Hydrodynamic quantum analogs, because they are analogous to the main idea of Pilot Wave Theory. The droplet in the above image moves along with the ripple or wave below it. Same is the scenario in Pilot Wave Theory, where the particle like that droplet moves according to the guiding wave associated with it. This image is an excellent visual analogy of the theory. I suggest watching this amazing video by Veritasium explaining the phenomenon - Is This What Quantum Mechanics Looks Like? )

              Yet, another interpretation - "The Many World's Interpretation" by Hugh Everett suggests that the wavefunction of particles is real and it does not collapse at all. Instead all the possible alternatives happen in a different parallel universe or world. For example, if I toss a coin and get heads, it might have given the alternative result i.e. "tails" in a different Universe. There is another theory called as the "Hidden Variable Theory" which states that besides the position and momentum, a particle should have another hidden variable(s), which when known can give us the complete state of the particle without any ambiguity. Thus eliminating the uncertainty associated in Quantum Physics. As intuitive and logical these theories might sound, one can provide no subtle reason to disregard one and believe in the other. Even the "Statistical Interpretation" itself is subject to many imperfections and need to be rectified. Thus, the field of Quantum Physics is yet tender and shall definitely undergo much development in the future. Nevertheless, it still finds numerous applications in Quantum Computing, Integrated Circuits, Semiconductors, Electronics and much more. The subject in itself is a vast ocean and what I described in these two articles are only drops of such ocean. 

- Thank You

                                           

               

                                 

Quantum Theory : The Physics of Very Small (Part 1)

"Determinism" - This word means a lot to every Classical Physicist who ever lived or any other human living with a sound brain. Determinism is something which we humans are equipped with almost every time. A person driving a car immediately determines an impact if something suddenly appears in front of the car and reflexively applies brakes, a juggler can exactly determine where each ball will land due to the force with which he threw it upwards and hence positions his hands at that place before the ball comes down, etc. In Classical Physics, "Determinism" states that an experimenter is able to predict the exact results he/she would achieve in an experiment by knowing the present condition of his/her apparatus and using the Laws of Classical Physics to determine how it would evolve with time. These "laws" are basically "Newton's Three Laws of Motion" which almost everyone is familiar with. They predict how the "state" of a "system" would change with time. But, what does a "state" and a "system" mean firsthand? A system can be regarded as any object or a collection of objects which is under study and isolated from the experimenter. It can be a football lying on the ground, or a collection of billiard balls, or a gas in a container. The "state" of a system is then its initial set of conditions. For example, if you are a system then your state would be specified by your identity, physical traits, job, etc. In Classical Physics the state of a system is mostly defined by the "positions" and "momenta"(mass multiplied by velocity) of all the objects in that system. If these two quantities are known then one can easily calculate other quantities like Energy from these two. Newton's Laws of Motions can then be applied on this state to predict the future state with certainty. However in the 20th century, Physicist's started experimenting with small scale objects and phenomena, and realized that they behaved too strangely. Not only did the concept of "Determinism" broke down at those small scales but also some strange observations were made which defied our intuitions. These observations just not fitted in the scope of Classical Physics and demanded a separate branch - "Quantum Physics". In part 1 of this blog article, I shall discuss what truly defines the foundations of Quantum Physics with a little bit of historical background.

              First, let us see some history behind the birth of Quantum Physics. It is not born from a single experiment but is a result of accumulated observations from experiments performed to study small scale objects such as atoms, molecules, electrons as well as by studying the nature of electromagnetic radiations or light. I am not going into the detail of each experiment, but we would discuss the results of each one and how they connected in the end to form a Quantum Theory. In 1900, a German physicist Max Planck was studying the radiations absorbed by a black body. When he proceeded to formulate a mathematical theory for his observations, he encountered severe problems. His mathematical results gave infinities. Whenever an infinity pops up into Physics, its not good for the theory. Planck found only one way around the problem using a mathematical trick. The trick was to assume that radiant energy can only be absorbed and emitted in "chunks" or "packets" and not continuously. One such chunk of energy is called a "Quanta". Hence, the name - Quantum Physics. For example, if you have a garden in the quantum world where "water" has a quanta. Then you can only water your plants with packets of water and not continuously using a water pipe. Planck then proceeded to show that a single quanta of energy is directly proportional to the frequency of that radiation. He expressed it as -
                                                                                
                                                                           E=hv  

where v is the frequency of radiation and h is a constant called as the Planck's constant. Thus, one chunk of energy is equal to hv and any body can only absorb energy in whole number multiples of this "chunk" like 2hv, 5hv, etc. but not 0.5hv. Max Planck initially thought these results to be ridiculous and abandoned his theory. It took Albert Einstein, to experimentally prove that Planck was right by his Photoelectric Experiment for which Einstein was awarded the Nobel Prize. He demonstrated how light can only be absorbed in discrete chunks called as "photons" (the particle of light). A revolution was sparked and was about to shatter all physicists living in the comfort and warmth of Classical Physics. Soon after Einstein proved Max Planck's Theory the haze of confusion started spreading. The reason being everyone was aware of the fact that Light or Electromagnetic Radiations behave as waves. Maxwell's Equations and many other experiments such as Thomas Young's Double Slit Experiment proved that light propagated in the form of waves in the electric and magnetic field. Just like ripples on the surface of a pond. But then Einstein demonstrated it behaved as a particle too in the Photoelectric effect. The results were paradoxical. As we know, a wave does not have a definite position. It is spread out in space. It makes no sense to ask at what point a wave is located? - It is everywhere at once. However a particle has a definite position in space. How can then something behave both as a particle and as a wave at the same time? This gave rise to the Wave-Particle Duality in Quantum Physics. It was stated that light behaves both as a particle and as a wave depending on the circumstances. In Thomas Young's Double Slit Experiment, light behaves as waves and shows interference. Whereas, in Einstein's Photoelectric Experiment it behaves as particles. Problem solved? - Not yet. In 1924, Louis De-Broglie published his PhD thesis in which he reasoned that since light was initially thought to be waves but then turned out to also be like particles. Matter - which is thought to be like particles might also be waves in some circumstances. He called them - "Matter Waves". Mathematically, he postulated that the wavelength of these "Matter Waves" is inversely proportional to the momentum of body. Higher the momentum, lesser the wavelength and lesser is the wave behavior. Soon, experiments confirmed that matter indeed behaved like a wave sometimes.  However, this wave effect is seen on extremely small scales. Particles like electrons  show wave like behavior in certain circumstances. They diffract and show interference just like waves. Why large scale objects don't show wave behavior? - Because they carry large momentum, owing to their high mass. Since, De-Broglie's law stated that more the momentum, lesser the wavelength and lesser is the wave behavior. We don't see everyday objects acting like waves.

Interference Pattern of Light in Double Slit Experiment

             

Interference Pattern showed by accumulated electrons passing through Double Slit.

              This discovery came as something unexpected. The story didn't end here. We are yet to come to Heisenberg, Bohr and Schrodinger. The pioneers of early Quantum Physics. Soon, the results of Quantum Theory were used to explain stability of atoms. Neils Bohr put forth his atomic model which perfectly explained why electrons are able to revolve around the nucleus of atom in fixed energy levels without collapsing onto it. In 1925, a young physicist- Werner Heisenberg published a paper which carried the famous "Uncertainty Principle". Heisenberg discovered something in the strange quantum experiments which were coming up. With De-Broglie's idea of "Matter Waves", Heisenberg deduced that the idea imposes a limitation on how much we can know about the "state" of a "system" (more precisely a "quantum" system). Earlier, I explained the meaning of "state" and "system" in Physics. The "positions" and "momenta" of all objects in the system are known specify its "state". But, the limitation imposed by Heisenberg's Uncertainty Principle was rather a severe one. It stated that - "It is impossible to simultaneously have exact knowledge of the position and momentum of a quantum object." No matter how hard you try, you cannot know the position and momentum of a particle at the same time with certainty. If you know one then the other would be uncertain. The original way in which Heisenberg reached this conclusion was different than today's interpretation for the principle. Today's explanation for the reason behind this principle is linked with the "wave behavior" of matter predicted by De-Broglie. As stated before, the wavelength of the matter wave of an object depends on its momentum. When any object is carrying a lesser momentum it has a longer wavelength. This means that it shows more wave-like behavior and as I said before - a wave is not localized in space. It is spread out and does not have a well defined position. On the other hand, if a particle carries more momentum, it has a shorter wavelength and lesser wave behavior. It is then said to be localized in space at a point. Thus, it is easy to understand where the Uncertainty Principle came from. A quantum particle whose momentum is well known, possess a defined wavelength and shows wave behavior. Its position then becomes uncertain. Whereas, a particle whose momentum is not known, does not have a wavelength defined, and is localized at a position like a particle.

              The Uncertainty Principle now forms the heart of Quantum Physics. If it is disproved then the entirety of this subject would fall apart. But no one has ever been able to do so. There is just no  way around it. Uncertainty Principle is a fundamental limitation in the Quantum World. It is responsible for majority of the chaos associated in Quantum Physics. This principle then implied that it is impossible to have complete knowledge of the "state" of a "quantum system". As we saw before, that position and momentum are needed to completely specify the state of a system. But the Uncertainty Principle forbids simultaneous knowledge of these two variables. Thus, one can never specify the state of "quantum system". This is where the entire notion of "Determinism" collapses. If one is not able to specify the present state of a system without ambiguity, then it would not be possible to determine its future state with certainty. Here, the final piece of our Quantum Puzzle fits in - "Probability". The world on its tiniest scale is totally random and in-deterministic. In 1926, a physicist named - Max Born formulated the Statistical Interpretation of Quantum Mechanics. I am going to discuss this interpretation precisely in part 2 of this article. But for now, it introduced "Probability" in Quantum Mechanics. When we are unaware of certain events we assign a probability or "chance" or "odds" to it. Similarly, in Quantum Physics since it is impossible to predict the future state of a system with certainty, we can find out the probability of a system to end up in a specific state. Einstein was most against this view of Quantum Physics and stated - "God does not play dice".

              Summing it all up, Quantum Mechanics is chunky, random and unpredictable. Things in the quantum realm like Energy or Electric Charge do not have continuous values but only come in indivisible chunks of definite value. Also they act both as waves and as particles depending on the circumstance. In the quantum world, you cant predict the exact position and momentum of the particle at the same time. If you know one precisely, there is an ambiguity in the other. This means that you cant determine the outcome of an experiment with hundred percent certainty. Rather, you can say the probability that an outcome has in a given experiment. So this is it? - No. I would call this the story before interval. We are yet to see what happens when these observations of Quantum Mechanics contradicts our intuitions and are faced by many other explanations to make sense of it. All this along with "the climax" would be discussed in part 2 of this article.

- Thank You!


              

Solar Eclipses : What's harmful and What's not?

On 21st June 2020, after waiting for many long years, I witnessed a partial solar eclipse. You cant deny the fact of how beautiful the event is! A star which otherwise shines so brightly during daytime, gets obscured by a small celestial body, 400 times smaller than it. All a matter of perspective and positions. Once in a while, the Moon can pass between Sun and Earth causing a Solar Eclipse, whereas the Earth passing between Sun and Moon gives rise to a Lunar Eclipse. Solar Eclipses have proved significant in the development of Science. Greek astronomer Hipparchus used a solar eclipse to determine the distance of Earth from Moon. On 29 May 1919, Sir Arthur Eddington - A British astronomer provided the first ever confirmatory test of Einstein's General Theory of Relativity by observing the relative shift in positions of stars behind Sun, during a Solar Eclipse. But nowadays, there is a whole load of myths and fears about an eclipse - especially in the Indian culture. Of course, there are some threats that a solar eclipse pose to our eyes. But - "Is there anything more going on?", short answer is - No. In this blog article, I shall discuss the only potential harm a solar eclipse can cause and debunk some myths along with giving historical reasons for why they rose in the first place.

Annular Solar Eclipse

             
              You must have heard every time a solar eclipse is about to occur, people go around chanting - "Do not look at the eclipse with naked eyes! Use proper solar filters to gaze directly at the sun." People even forbid the use of goggles and X-Ray films which seem to be safe and give minimum strain on our eyes. However, it is not just about the strain on eyes. There is something more here. Our Sun, is a giant ball of plasma emitting all sorts of radiations in space. The Sunlight you can see is only a part of the spectrum of radiations emitted by Sun. It is called as - "Visible Light" (the name is quite self-sufficient in explaining them). But there are other radiations like - X-Rays, Ultraviolet Rays, Radio waves, Microwaves, Infrared rays etc. What is the difference in all these? - Well, the most notable difference is you cant see them with your naked eyes. Another difference is they all have different energies and wavelengths. X-Rays and Ultraviolet Rays have shorter wavelengths and are highly energetic. On the other hand, Microwaves and Radio waves have a long wavelength and are less energetic. The problem here is that X-Rays' and Ultraviolet Rays' high energy is not so good for us and can cause biological damage. As said before, the Sun emits all these different types of radiations which obviously reach Earth too. Good news, is that most of them are absorbed by a protective shield of Earth called as the - "Ozone Layer". But, some rays sneak their way into the Earth. Prolonged exposure to these radiations cause "sunburns" and in worst cases - "skin cancer". But how does all this relate to a solar eclipse? The rays are there all the time whether an eclipse occurs or not. Correct, now if I were to tell you to look at the Sun on a bright sunny day for 10 seconds straight. It would be near impossible. Your eyes would get half closed and your pupils will shrink, and you would be forced to look away. This is your body's natural defense for protecting your eyes from getting damaged by over-exposure. In this case, it protects you indirectly from letting all those harmful rays damage your eyes. But during an eclipse, a portion of  the Sun is covered by Moon. This reduces the intensity of sunlight reaching our eyes, thus deceiving both our eyes and brain. We can stare at the Sun for as long as we want, but what is not realized is that the harmful Ultraviolet rays are still being emitted from the uncovered portion of Sun. If one continues to look at the eclipse with unaided eyes, then these radiations are certain to cause damage. That's it, this is the only harm a solar eclipse can cause. Except, of course if you are too caught up in staring at the eclipse and your house is on fire. Though this is very unlikely.

              However, people believe there are many other threats that a solar eclipse poses to us. They avoid going out during an eclipse, conducting any good task, buying something new, etc. Some even go as far as abstaining from eating or drinking anything and bathing after the eclipse. The root of this behavior goes to historical circumstances, when most people lacked knowledge of the cause of a solar eclipse. Solar Eclipses have been viewed as omens in the old times and thought to bring death and destruction. In 585 BCE, a solar eclipse is said to have stopped a war between the Lydians and the Medes, who believed the dark skies as a sign to make peace with each other. During the Peloponnesian War between Athens and Sparta, a Lunar Eclipse occurred which made the superstitious Athenians believe that their enemies possessed some supernatural powers. They began to retreat. The Spartans saw an opportunity in this and charged in on the Athenians, making them lose the war. It had happened much often, when we humans are incapable of providing a logical explanation for any circumstance or event, we assign to it some divine intervention. I am quite sure this must have been the case for eclipses. In the present, advances in Science and Astronomy shed light on what exactly happens during an eclipse. Today, almost everyone is aware that eclipses are nothing but a wonderful play of positions and shadows. Yet, some people tend to remain on the safe side and hold belief in past superstitions. When such people are asked for the reasoning behind their belief, they fail to provide a plausible explanation. Some believe that light from the Sun is reflected from the outer edges of moon, thus altering their original nature and rendering them harmful. However, this should occur almost every ordinary night, when the Moon is up in the sky reflecting light from the Sun. As far as we know, the only harm an eclipse can do is if you stare at it with unprotected eyes that too in the case of a Solar Eclipse. To conclude, an eclipse is just a normal astronomical event in terms of its effect on our lives, but as Sir Arthur Eddington did, it can serve as a valuable event to testify a theory.

- Thank You!

The Nature of Time

If one day, someone were to approach you and ask - "What is time?" (in a qualitative sense). You would soon realize that the answer is not as easy as you thought. "Time is something that flows?" or "Time is an inevitable entity which keeps passing?" or "Perhaps the constant ticking of the second hand of your watch.". But, these answers seem abstract and possess no rigid meaning. All these answers might be described as characteristics of time but does not really define its meaning. It is as if you are trying to find out the identity of a person by saying - "He has green eyes. dark hair and muscular built." However, the main question of who the person actually is remains unanswered. For decades Physicists' views about the nature of Time has changed drastically. From old Newton's view of absolute time, to Einstein's view of relative time. till the present in which some theories actually disprove the existence of time. The aim of this fairly lengthy post is to summarize all these definitions (or characteristics) of time and finally present my views about what it might mean.

                Let us go back to the possible answers stated in first paragraph. We all experience passage of time. The rising of Sun in the east and then with time setting in the west, people getting older with time, the changing of years, etc. It is something that flows. But what are some of the physical aspects which truly define passage of time or the "arrow of time". The answer lies in one important branch of Physics - "Thermodynamics". This subject defines a physical quantity called as - "Entropy". It is a measure of disorder or randomness of physical system. There is a law in thermodynamics which states that the entropy of a system always increases and never decreases. For example - take a glass full of water and add a few drops of ink to it. With time, you will notice that the ink spreads into water and after sometime the water gets colored. Prior to adding ink to water, the ink was in a more ordered state. It was confined in the container and its particles (molecules) were close enough. But once it was added to the water, it spread out into the water and got less confined i.e. more disordered. There are loads of other examples where it can be shown that entropy always increase. How does this explain the nature of time? - Cosmologists have known since the early 20th century that our Universe is expanding. They concluded this when galaxies were observed to move away from each other by an astronomer - Edwin Hubble. It was then the famous astrophysicist - Stephen Hawking realized that as Universe is expanding with time, if one reverses the direction of time then it should contract. Until, one reaches an instant when all the matter of the Universe is contracted into an infinitesimal point -called "Singularity". This led to - "The Big Bang Theory", which said that the beginning of our Universe was from such infinitesimal point. All the concentrated matter then underwent a rapid phase of expansion and now it is still expanding. In other words, our Universe was in a ordered state at the time of Big Bang and as it started expanding, its disorder increased i.e. its Entropy increased. The Entropy of our Universe now is constantly increasing as it expands and that is what defines the Arrow of Time. In the future, there is a chance that this expansion will be stopped by the force of Gravity and everything will start contracting back into a Singularity. During this phase of contraction, the Universe will start going back into an ordered state, Entropy will decrease. This can mean that the Arrow of Time will get reversed. Since increasing Entropy provides us with our current "Arrow of Time", a decreasing entropy shall simply reverse its direction. The consequences will be far more bizarre. For example, in our present arrow of time associated with increasing entropy, a vase falling off the table will simply break. But during the contraction phase of our Universe, when the arrow can be reversed, a vase will be broken first and then re-arrange into a more ordered state on the table. In our current arrow of time, we can remember our past but cant remember the future. This may sound absurd now. but it can be a consequence of our current arrow of time. When this arrow is reversed, it might happen that we will remember the future and not the past. Hence, we have our answer. The flow of time is characterized physically by increasing Entropy of our Universe. When we experience the passage of time, we are actually experiencing an increase in entropy.

                But there are many other theories, which treat time much differently. After all the notion of "time" is an important part of many Scientific as well as Non-Scientific theories. The "time" variable is used in Science to calculate rate of change of specified quantities. "Speed" of an object, rate of population increase, measure of electric current, etc are some examples in which the concept of "time" is a basic necessity. How is time defined in such theories then? - Majority of these theories make use of a variable - t. For example - If someone wants to measure the rate of increase of population in a city, then the variable t would be used exclusively in the Mathematical model. This variable would be zero at the start of measurement and then its value would increase periodically. The person can then measure the population at each value of t and thus obtain the rate of increase of population. Many physicists along with Sir Issac Newton referred to time as being "absolute". This means that passage of "time" is same for every individual regardless of his/her state of motion. There is a "Universal Clock" and time passes the same for everyone in accordance with that clock. Of course, this notion is hard wired in the brains of most people. We really think that time passes the same for everyone. I am not referring here to the time as we measure using our clocks or calendars. That time is always different in different regions, giving rise to time zones. The time, I am talking about here is the variable - t, which I used just earlier. What this means is that if there were two people living in a city. One located in his apartment which somehow provides him the view of entire city, while another guy is cruising around in his car. Let us go back to our experiment where we saw how to measure rate of increase of population. They both start counting simultaneously, then according to Newton's view of "Absolute time", the rates they calculate should be the same. It would not make any difference, even if one of them was moving while other was stationary in his apartment. Time would pass the same for both of them.

                This view was neat and convenient. It comforted our intuitions about the nature of time and many Physicists remained in its favor. Until the game changer of Physics published four papers in 1905 that shattered this view of time. The game changer was no one but - "Albert Einstein". In his paper, he introduced - "The Special Theory of Relativity" which radically altered our views of space, time, mass and energy. The subject itself is vast and deserves another blog post. In brief, what this theory did was it proved that Space and Time are not absolute but are "relative". The idea of absolute time has no meaning in Special Relativity and that how one experiences time depends on his/her state of motion "relative" to another observer. Considering our previous example, the guy moving in car would get a different rate of growth of population than the guy located in apartment. This effect is called time dilation. In this effect, when one observer is moving relative to another one at rest, then on comparing his time with the stationary observer, he/she would find out that his/her time is actually running slower than the time of stationary observer. Initially, the theory was hard to digest. However, there was nothing that could be done to disprove it. Einstein further extended this idea to General Theory of Relativity, explaining the origin of gravity. In this theory, "Gravity" is an illusion. The presence of mass and energy bends space and time, and objects only follow this curved path through space and time. This theory treats time as a fourth dimension along with three dimension of space. We can move forward-backward, up-down, and left-right in our three dimensional space. However, we always move forward in the time dimension (We get older). This serves as a great idea for science fiction, where there might be some superior living beings able to control their motion through the time dimension as well. The General Theory of Relativity was elegantly represented by Einstein's Field Equations which used geometry of curved surfaces (Differential Geometry). The theory was proved to be consistent over and over. Even after 100 years of its proposal, we are still observing some of its consequences for the first time ever.

A Computerized representation of bending of 4-D Spacetime by Earth

             
              So, the Theory of Relativity turned the boring time variable into something dynamic. It can slow down, it can bend, stretch and warp. But, the story does not end here. Remember when I said, some new theories are aiming to disprove the existence of time. Why disprove something which is so dynamic and whose effects are noticed in everyday life? The answer lies in something much more deeper - The Theory of Everything. As the name suggests, Physicists are aiming to formulate a theory explaining our entire Universe in one single, elegant equation. Of course, we are way too far from achieving such theory. But everyday we are getting closer than before. The key in formulating such theory involves unifying all the forces of Universe i.e. Electromagnetic Force, Strong and Weak Nuclear Forces and ultimately Gravity. It turns out that the first three forces can be unified, but Gravity is the hardest to unify with other forces. One essential step required to do so, is to obtain a Quantum Theory of Gravity. Whenever the word Quantum pops up, you should know that things get tiny. Much, much tinier than your eye or even any artificial microscope can peer into. Whenever this word is put in front of any physical entity (field), then that entity is said to be "quantized". Put it in front of an electric field, it gets quantized and we get - "electrons" (particles of electric current). Put it in front of an electromagnetic field and we get - "photons" (particles of light). As one can guess, putting it in front of a gravitational field would yield us with "gravitons" (particles of gravity).The process of quantization can be thought of as using a "cheese grater". Here, the big cube of cheese is a field and on grating it or "quantizing" it, we get smaller chunks of cheese or the field We saw earlier that Gravity is nothing but curvature of space and time (more appropriately spacetime). In other words, space and time is the gravitational field. Thus, we need to quantize space and time. Modern physicists have came up with many brilliant ways to quantize space. The two leading theories are - the famous String Theory and Loop Quantum Gravity. Only problem facing the way is quantizing time. The mathematics for this process gets utterly complex. This is the reason why some physicists aim to completely eliminate time itself from the equations. I shall present one final argument here. In second paragraph, when I was describing the time variable - t, I described how this variable would take the value of 0 at the start of measurement and then increase periodically. The question arises - "How do we know that the value of this variable is increasing periodically?". We would need a reference object to make sure that the value of t is increasing periodically or uniformly. This reference object should be periodic itself, for e.g. the pendulum of wall clocks. But then we have no firm reason to believe that the pendulum itself is periodic. We would need another reference object to confirm its periodicity. It seems like we are caught in a loop here. This truly makes us take a step back and think about "time". It can then be said that "Time" is nothing but an interwoven connection of variables. The t variable, or the pendulum of clock, the rotation of Earth etc. But none of these variables have a separate meaning, as we would have no means to confirm that they are periodic. We can only refer to them in terms of connection with other variables. How can one then believe in Time? Something which possess no true meaning when viewed without connection to other. This is another reason to disprove its existence.

                Summing it all up, we have many theories viewing time in different ways. I believe that "Time" is our own construct. Something which we use to make things convenient. It would be absurd if I invited you to a party and gave you only the location of the place where it is held. When I supplement the invitation with appropriate time, then it will be convenient for you to find the "event" i.e. The Party. Nevertheless, it is completely appropriate to keep using it in its different form. Until, we reach a dead end only then we have to find a new way of expressing it or else completely abandon it.

- Thank You.



   

Are we alone (yet)?

Many times we look up at the night sky and wonder - "Are we alone in this vast Universe?". It is quite common that when I tell people I am an astronomy enthusiast, they end up asking me - "Do aliens exist?". Surprisingly this question is closely similar to the question - "Does God exist?" for we have no firm evidence to answer either of them. As much as you hate it, we can do nothing but have our own beliefs at this point. Some people believe Earth is the only place in this Universe to harbor life, others believe in some form of life existing outside our Earth. However, if we reconsider all the parameters one shall be obliged to think that the chances of extraterrestrial life existing are substantially high. In this article, I shall address all such parameters and end with possible reasons of why we haven't found any signs of extraterrestrial intelligent life yet.
             
                First and foremost reason to believe that life must exist outside Earth is the fact from a study that - "Almost every star in our Milky Way galaxy hosts at least one alien planet revolving around it." It is mind boggling to think of the billions of stars in our galaxy each hosting at least one planet and some even having planetary systems like our Solar System. One can even extrapolate this fact to a generalized conclusion for all galaxies. After all why our galaxy's stars should be the only one to host planets? The Universe as we know it contains hundreds of billions of galaxies, each holding billions of stars, which can possibly contain planetary systems. It then gets difficult to rule out the possibility of alien life existing in our Universe. It becomes even harder, after NASA's Kepler Space Telescope discovered thousands of planets revolving around host stars in our galaxy. Out of these discovered "Exoplanets" many of them were in the Habitable Zone of their host star. Planets located in this sweet spot called as - "The Goldilocks Zone" are neither too close nor too far from its star. Thus, having favorable conditions for life to flourish. In May 2016, NASA announced Kepler's discovery of 1284 new planets and 9 planets out of these were in the habitable zone of their host star. In rough terms, 9 out of every 1000 exoplanets lie in the habitable zone of a star. Combine this conclusion with our earlier assumption of almost every star having at least one alien planet and the probability of alien life existing shoots high.

Artist's depiction of Kepler-22b - An exoplanet detected by Kepler Space Telescope in the Habitable Zone

                 Another reason I shall present here is something which is not thought of very often. It is the assumption that every form of life requires the same elements for survival as are required by majority of species on Earth. The primary elements for survival on Earth are water, oxygen and a source of energy mainly glucose. Humans metabolize glucose using oxygen to produce energy to carry out bodily tasks essential for survival. It is a misconception that all organisms need water and oxygen for survival. For example - "Methanotrophs" are a type of organisms which utilize the compound - Methane as their only source of energy. Such organisms are found in areas where methane is produced. Any person with sufficient interest in astronomy would know a celestial body covered with lakes of methane and ethane i.e. Saturn's moon - "Titan". We dont even know yet, whether microbial life exists on Titan or not. Since, Earth is covered with water and majority of living organisms and animals on Earth need water for survival. There might exist other worlds, like Titan covered with Methane where organisms need Methane for survival, or some other planet with abundance of another element on which the living organisms depend on that abundant element for survival.

                All such factors point out that life must surely exist on a place other than Earth. If it does, "Why we have not found it yet?". "Why we have not obtained even the slightest clue of alien life existing?" There can be many possible reasons, some or all of which may be responsible for our inability to find signs of alien life. One obvious answer would be that the extraterrestrial life might not be advanced enough to mark its detectable presence. Since, any life existing outside our Earth can be called as aliens. It is not necessary that all aliens should be those green headed creatures invading Earth as depicted in movies. They can even be tiny microorganisms hidden in corners of a lonely planet. We only have to look closer to be able to find them. Such microorganisms can perhaps exist in our own Solar System too. In time, these organisms can then evolve to give rise to an intelligent species able to thrive and communicate with us. This brings us to another reason that life existing outside Earth might not be advanced enough to communicate with us. To the contrary, some people believe that the aliens existing outside are advanced enough but are choosing to remain silent for some reason. They are observing us and our actions, but still choose not to communicate. However, this scenario is a little vague and best be neglected. There is another scenario, in which intelligent alien civilizations developed in one or many places in the Universe underwent an apocalypse and the entire civilization might be wiped out. This reason seems plausible. If in the future, I surely not desire so but if the Earth is struck by a giant meteorite, or comes under the impact of a Supernova, or any other natural or artificial apocalyptic disaster, then the Human race along with all its developments would be wiped out. Only thing that would reach the aliens will be our electromagnetic signals as well as light from Earth. This brings us to a final possibility - We know that light or electromagnetic radiation travels at a finite speed of 299,792 kilometers per second. Einstein's theory of relativity predicts that this speed is the ultimate Cosmic Speed Limit. Nothing can travel faster than this speed. This implies that we always see the past. What we call as present is merely an illusion! Think about it, the time taken for the light from Sun to reach Earth is approximately 8 minutes 20 seconds. Therefore, the Sun as we see it in the sky is 8 minutes old. If it were to explode at this instant, we would see it after 8 minutes. This causes a delay in the time at some event happens and the time at which light from that event reaches our eyes. At small distances this difference is negligible but at large cosmic scales light takes sometimes tens, thousands or even millions of years to reach us from a specific place. The purpose of stating all this is that, even if there exists an advanced alien civilization sending out radio signals out in the Universe about their existence, it might not have reached us yet. It is still travelling, through the cosmic void at a constant speed. Perhaps, it will get deflected from a planet, star or even get devoured by a black hole before reaching us. Some of our first transmitted signals are now expanding into space as a radio bubble with a diameter of about 200 light years. This number seems insignificant in front of the 105,700 light years of diameter of our Milky Way galaxy. This means that it would take almost 105,500 years for our radio bubble to cover the entire Milky Way. To make things harder, there exists a property of electromagnetic radiation to loose their intensity the farther they travel. Thus, it gets more difficult to detect these faint, low-intensity radio waves. This is a problem both - for us and for the alien civilization (if they exist) trying to communicate with us by sending messages.

             

Extent of our radio bubble (depicted by the blue dot) in the Milky Way Galaxy

             
               This entire article was nothing but full of speculations and anticipations based on observations, logic and some assumptions. As I said before, there is nothing we can do but have our own beliefs until any solid evidence comes forth. However, time shall surely tell the answer to our questions. If the arguments I posed in previous paragraphs are valid, then we can rephrase our question and ask - "Are we alone, yet?"

- Thank You