Time , a pretty familiar and a pretty much commonly UNDERSTANDABLE word isn't it or as we perceive it to be ? Time is generally a very important and highly took care of subject in the life of living beings , humans are as we all know are quite time bounded people , also all the wild animals and domestic animals can be seen being valuing time , plants as well do all their processes in the flap of time . While most of us percieve time as we see the clock tick, it isn't that straightforward in truth . As we shall see it is a vast and pretty debatable topic , with a range of unsolved questions like why does time even exist ? , what causes the Arrow of time ? and will try to uncover many of its mysteries .
Difference between Common perception and Physics :-
Well we can differentiate time in 2 categories Common Time and Scientific Time or Physics time . Well the common time is the time according to the perception of the common person, It is easily the time which can be ‘managed’, 'utilised' or even 'saved' . It is the usual sense and complexion of time we all use and make in our lives. To define it, it is the time that has the use in our daily life i.e. it is generated on the basis of common sense or it is generated due to human needs of having a factor which is comparable & can govern the course of human work.
The Scientific time or Physics time is the time which has a logical meaning and which is simply not generated or has nothing to do with common sense . This meaning of time is in sharp contrast to the common meaning of time in fact , in physics , time itself dies . It means that in physics there is nothing to distinguish between Past , present and future . It can be described as a frozen river which does not flows , has no ends or no beginnings . The laws of physics allow a glass which falls on the ground and is shattered , to also unshatter and form our neatly 'ordered' glass to start with. What I mean from the word 'Ordered 'is not what we simply perceive to be ordered .
How can we understand time :-
To understand the very nature of time , you need to know a thing or two , because as to make your own conclusions , your mind needs to be equipped with the adequate amount of information . The first one in our quest to understand time is Entropy
Entropy can be simply defined as the amount of disorder or randomness there is in the universe . To understand this take the example of our glass which we shattered in our example earlier . When a glass shatters all it's constituent pieces scatter around or just go away from each other . Or take the example of a book thrown in the air unbinded and its pages scatter away . In both examples it is shown that the particles always show a tendency to go away from each other or to just scatter way . But what set this cycle in motion ? I mean what was the first such example of particles showing their tendency to scatter away ? The first example , yeah you got it , it was the big bang . The big bang set all the matter in the universe in this cycle as that massive explosion resulted in all the matter go into disorder. But was the big bang a highly ordered state ? no , but was the big bang singularity before the big bang a highly ordered state ? Yes , of course . The big bang singularity is described where all the matter of the universe was before it's exlposion . But the concept of entropy leads us to a question , why does matter tend towards disorder ? The answer may lie in the Arrow of Time
Arrow of Time:-
First developed by the great Bristish Astronomer Arthur Eddington ,The arrow of time is the tendency of time to be seemingly always trying to move on or to always move forward in time , towards the future . We all commonly use the phrase ,” time stops for none “ and this concept is pretty similar if you want to understand the arrow of time . We all see that time always goes towards the future , hitting a football it goes where you strike it , it goes towards the future , it will not rewind and come back to your feet and you’ll not come back to your shooting stance , we’ve not seen anything like that have we ? It’s fairly easy to understand that time moves on but this is not like that according to the laws of physics. Equations of physics do not distinguish or differentiate between past and future. You can move forward in time and you can also move backward in time, there is nothing to distinguish .There are equations which move equally valid and consistent forward in time as they do backward in time . But then how can we unshatter our glass in the earlier example ? physics shows us that to do stuff like that just reverse the velocities of all the particles which broke away and you’ll have your neatly ordered glass now . But, we’ve not seen such happenings in nature so how can we be so wrong about a thing so familiar ? and that leads us to think is time influenced by anything ?
Time Dilation :-
In around the start of 20th century, physicist were struggling to deal with dynamics of bodies near the speed of light, and so there was the rise of Albert Einstein. In 1905, through a series of breakthrough papers on,” The Electrodynamics of Moving Bodies “Einstein beautifully showed what influence of speed on a body is and showed what changes took place in some major physical quantities of a body, those quantities which were thought to be fully understood by the help of Classical Mechanics, the collection of those papers is what is called today as,” The Special Theory of Relativity “. In this, Einstein showed that as you move through space, time slows down. To understand this, think about yourself going to your mother when she calls you for doing any work. As you move towards her , time has slowed down for you , if only a tiny bit but it has . On Earth we cannot feel this effect fully but if we move through outer space even at small speeds for some time according to ourselves, then time for us has slowed down as compared to a person on Earth .And Einstein also showed that as we move comparable to the speed of light and near to it, time drastically slows down for us and if move at the speed of light then time itself freezes for us. One of it’s greatest implicated theories is the twin’s paradox.
Twins Paradox :-
The twin’s paradox is one of the best explanation for the concept of time dilation. Consider there be 2 twins, Eden and Diego. Let’s say that Diego was born 2 minutes before Eden and as soon as Eden was born, some Alien spaceship came and took him with them and for the next 20 years in his perspective, took him on a travel across the vastness of the cosmos and when he felt homesick they felt great sympathy for him and took him back to his planet earth but it took them 20 years in his perspective to do so . When they finally reached Earth , Eden is 40 years old , by easy calculations , but when he would see how much the Earth has went forward in time from his arrival , he will come to notice that the Earth has gone a staggering 59000 years into the future from the time of his departure . Can you believe that? Well you have to. This is one of the most astonishing and beautiful concept of time dilation and is truly is beautiful, isn’t it? But, didn’t we come to see that Einstein had shown that motion influences time and isn’t there any other thing that does so other than motion? And can we only travel to the future as it is quite evident from the paradox, can’t we go to the past ? Well Einstein’s work exactly 10 years after his great discovery we’ve just discussed, showed a yes to the former question and led to a yes for the latter.
Time and Gravity :-
In 1915, 10 years after presenting some truths of nature through Special Relativity, Einstein showed another masterpiece in “ The General Theory of Relativity “ . In this , monumental theory Einstein showed how space & time and Gravity are inter related and showed the large scale structure of gravity and produced ten scintillating equations in the “ Einstein Field Equations “ . To the interest in our topic, he showed that Gravity has a great influence on time. He showed that the stronger the gravitational field is there around a body, the slower the time will be for the body. Einstein showed that heavy or massive bodies bend space-time around them and anything coming in their bent space-time revolves or experiences a force pulling it to the massive body and that force was gravity. Now, the more a body bends space-time , the more gravitational force it generates . The bending of Space & TIME clearly shows that the body is influencing time and so Einstein said and described that the body will slow the passage according to it’s bending of Space-time . We were puzzled earlier as to why we don’t feel time dilation much here on earth and now we got the answer that it’s because of Earth’s low bending of Space-Time responsible for this phenomenon. So where can we feel this effect the most ? Well near a black hole . If you could ever somehow travel near a black hole for 1-2 hoursin your perspective , for you then time has only passed a couple of hours but when you’ll return back to the Earth nearly a century would’ve past on our planet ! And to the question on how we can move to the past , A great solution from the equations of General Relativity shows that you can move backward in time through something we now call a “Wormhole”.
Godel Solution and The Wormhole :-
Many solutions of the equations of General Relativity have been shown over the years and has led to many a great discoveries like Black Holes , and one such solution was given by Kurt Gödel in 1949 . In this he described that an observer could travel into the past . Though the solution is quite complex, as Einstein remarked “ If you can’t explain it simply , you don’t understand it well enough.” In this , he proved the existence of something called closed time like curves or CTC’s . In physics, Closed time like curves are a world line which allows user to come to their starting point. So what’s a world line people ? a line stretching throughout the world, eh? no, not like that. A world line of an object is the path tracing the events of the body in it’s history at each instant of time. Think it of a line, at which one each of its point has a thing or two of your past . The Gödel Solution allowed the existence of closed time like curves and so allowed the backward time travel. While there are still questions about this solution and some of it’s features which do not seem to describe our universe it is still pretty feasible . And so of all the stuff , from what thing are we going to travel to the past ? There you have it , your much awaited wormholes . Wormholes are objects which are said to carry out the process of backward time travel. Quite like if I have access to a wormhole , I’ll jump into it and go to the me who was starting to write this article and say “ hello and keep going the past me !” But we don’t usually see people bumping out in our world and saying that they’re from the future and hey. And it could have striking consequences as well , like if someone goes to the past and meets Sir Isaac Newton under the apple tree and say’s to him , “ Hey , you’re stupid!” and Newton running behind that guy to beat him up and maybe never discovering gravity as we know he did ! , but still we don’t see it happening either . Einstein once remarked Space-Time as a piece of bread while explaining his General Theory of Relativity , so if we can make slices of Bread does the same goes for Space-Time ?
The Slices of Space-Time :-
Now if we take space-time as a bread , we’ll come to know about some peculiar , radical and highly thought arousing stuff , Now consider that you are sitting on your device reading this article and millions of light years away in a remote galaxy , an alien is sitting thinking about something . Now consider you both are sitting still, not moving in relation to one another , you both share the same now slice of space-time and so the passage of time in your slice is that felt by you guys . Now just think that the alien is invited to play a game of football, he runs opposite to the direction of Earth to his playground. Suddenly he remembers about a far way planet called Earth and wants to see it now . So , his great high tech telescope allows him to see Earth . But , just here , he turns back while running opposite to Earth’s direction and looks back and say he turns his head around 450 to see Earth . That may seem a small angle but now when we cut the slice 450 backwards , his telescope will now point towards the events in the past of Earth , simply because there is a vast distance of millions of light years between the alien and the Earth and that small angle cuts a gigantic slide on the space-time bread, and so it will see the part of slice already passed by Earth . Now he will see events we consider in our past and he may see, say, events around 400 years ago to our present time ( in accordance to the angle his slice is cut upon ) like Galileo presenting his ideas on the rotation of Earth around the sun . Now if we just consider for some reason , he runs in the direction of Earth and now looks from his telescope cutting at the same angle as earlier he will see events such as those we consider in our future which are likely to happen , like people teleporting from London to Delhi. Quite bizarre isn’t it? But that’s where the beauty and the beast of physics lies , it may seem awkward but at the same time it pleasures your heart.
So , what do we make of the nature of time ?
Albert Einstein (please don’t be annoyed at the times I’ve used his name in it, but I just have to) once remarked saying “Time is just an illusion.” And I and the whole of physics world couldn’t agree more. As we’ve seen from all the above theories and concepts we can say that it’s an illusion and merely something we perceive, as many others, about the Universe. But, new ideas and concepts are always welcomed and if some you reading this article may contribute to our knowledge in physics, that will be highly appreciated, I know I would and will surely give my best to do so.