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.