INTRODUCTION
What exactly is time? You would say some hours and minutes like say, 10 AM. But just think about it more deeply. Is time just a measure of a period? Because if we go deep at the quantum level, time is a bit weird to understand. Can we define time? Time is defined as a period and a period is defined as time. Something is fishy. Time is not that easy to understand, especially back in the 19th century. As we saw in our Space-Time post, time is the 4th dimension according to Albert Einstein. In today's article, we are going to discuss what exactly is time according to Einstein's Theory Of Special Relativity and Stephen Hawking's Brief History Of Time.
HISTORY OF TIME: LIGHT
The history of time is very long. We started thinking about time only when we discovered the fastest thing in the world: light.
Let's see some properties of light:
1) Light is an electromagnetic wave which was explained by James Clerk Maxwell. Read More About Electromagnetic Waves Here:
2) Light is made up of massless photons. Read More About Photons Here:
3) Light travels at a constant Speed.
4) Light's speed is 3 x 10^8 meters per second.
According to Albert Einstein, Classical Relativity said that anything in the universe is not in absolute motion or absolute rest. Each and everything moves relative to each other.
Now let us understand this with an example. Let's say there are two boys Tim and Sam playing catch with a ball on a truck. The speed of the truck is 60kmph and the speed of the ball to be 15kmph. Now, when Tim throws the ball towards Sam, then the speed of the ball will be 15kmph and not 60+15=75kmph. Why? Because for them, they are at rest. They are not moving. The truck is moving. But if another person say John is standing on the road and watches them play, then the speed of the ball for him will be 60+15=75kmph. Why 75 here? Because although he is at rest, he is not on the truck. And therefore he watches the truck go away from him with the speed of 60kmph and then we added the extra 15kmph of the ball's speed as well. If you are confused, then just give it a thought. It makes a lot of sense. But now we know, John itself is not at rest. He itself is moving as the Earth is moving!
Everything is moving. Stars, solar system everything! Therefore, nothing in the universe is at absolute rest. Objects are moving relative to each other. But now a lot of questions will start arriving in your mind. Does relativity apply to each and every thing in the universe? Is speed for everything in the universe relative to each other? Is there nothing that has a constant speed irrespective of its source.
Here comes light into the picture. James Clerk Maxwell told that light is an electromagnetic wave and it has a constant speed no matter what source its coming from. But wait, that doesn't seem to be right when we are talking about relativity. And if everything moving in the universe is relative to something, then the speed of light is relative to what? This was a problem in the 19th century. Einstein accepted Maxwell's theory claiming it to be right and that light has a constant speed for all the observers i.e. 300000 km per second. He also said that light's speed was the fastest in the universe. Always!
In 1905, Einstein published the Special Theory Of Relativity in which he explained the laws of physics, constancy of light, time dilation, length contraction etc. in a very detailed manner. This was named the Special Relativity theory and the special element here was light!
TIME EXPLAINED
In order to prove that light had a constant speed, Einstein in his Special Theory Of Relativity said that as the speed increases time needs to slow down. Simply put, if any object hypothetically travels 90% speed of light, then time would slow down for it to maintain the constant speed of light. Einstein told this phenomena as "Time Dilation" which is the slowing down the passage of time for an object to maintain consistency for the speed of light.
The faster you get into the space dimension, the slower you get in the time dimension. And if you reach light speed, then time dimension would completely stop for you and you won't move in time dimension. Now, a very interesting thing here is, that photons, which make up light are massless. This means we can never reach the speed of light. But wait, why? We'll discuss briefly about this in our next post on Einstein's Theory Of Relativity where he gave the world a very famous equation: E=mc².
Now according to the theory, if we exceed the limit of light, somehow hypothetically, then time travelling to the past will be possible. However, there's a catch. This is just a theory. No one has ever actually tried to do it as we know we can not travel with the speed of light.
When time was created after the big bang, it's nature was to always keep on going. This can be seen in the Second Law of Thermodynamics where Entropy increases with Time. Which simply means that anything transforms from an orderly state of existence into disordered state of existence with time. This helps us understand that before the Big Bang, there had been very little entropy. And as time is moving forward, entropy is also increasing in the universe. The universe is transforming into a more disorderly state of existence. Now to know more about entropy, visit this article: Entropy.
So, Basically, if we see more clearly, then Time is an element in physics and according to Einstein it is interconnected to space and they are intertwined into a common fabric of the universe called spacetime. Time is not absolute but relative and it depends on the speed at which an object is moving. Objects travelling close to light speed will have their clocks tick slower because of Time dilation. And reaching light's speed will stop time itself. Imagine if this happens! And finally time got its property of moving forward from the big bang.
Albert Einstein in one of his lectures once said that the distinction between the past, present and the future is a stubborn illusion!
So, that's it. I hope you enjoyed and learnt something new from here. Please comment and share this article for more.
Thank you for reading.
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