THE ARROW OF TIME

I guess many of you all come with situation where you see a cup of tea falling off a table and breaking into pieces on the floor. Now any one of you if ever had filmed it anytime you would notice that, you can easily tell whether it is being run forward or backward. If you run it backward, you will see the pieces suddenly start gathering back themselves together off in their original form and then jump back in the table. Now anyone of you ever think why the thing backward is called backward not forward, I know it’s a very nonsense question, but as I say there is always an extraordinary sensible answer behind a nonsense question. It’s called backward because we don’t see this kind of behavior in our normal day to day life.

The explanation that is usually given as to why we don’t see broken cups jumping back onto the table is that it is forbidden by the second law of thermodynamics. This says that disorder or entropy always increases with time. An intact cup on the table is a state of high order, but broken cup on the floor is a disorder state. One can therefore go from the whole cup on the table in the past to the broken cup on the floor in the future, but not the other way around until and unless it’s your smartphone or camera.

The increase of disorder or entropy with time is one example of what is called an arrow of time, something that give a direction to time and distinguishes the past from the future. There are at least three different arrows of time. First there is the Thermodynamic arrow of time – the direction of time in which disorder or entropy increases. Second, there is the psychological arrow of time. This is the direction of time in which we feel time passes—the direction of time in which we remember the past, but not the future. Third there is the cosmological arrow of time. This is the direction of time in which the universe is expanding rather than contracting. 

One can argue that the psychological arrow is determined by the thermodynamic arrow and that these two arrows always point in the same direction. If one make the no boundary assumption for the universe, they are related to the cosmological arrow of time, though they may not point in the same direction.

Now some of you may ask this question: Why does disorder increases in the same direction of time as that in which the universe expands ?.... Or like The time goes forward is it because the universe is expanding ? Now what if the universe would have be contracting, would our so called future would be in past ?

What do you think guys ? ….. do comment ….
The detailed explanation of the three arrow of time would be in the next posts.

References

 Stephen Hawaking's "THE BRIEF HISTORY OF TIME" SIXTH LECTURE

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