Time:- Entropy and the Arrow
This article is part of a series of articles on time. This is article 3/5. Read the second article here!
In the last articles, we constructed upon the idea of the symmetry in time, according to classical physics concepts. But, to discover true meaning of time, to try and answer why things happen as they do, why spilt milk doesn’t un-spill or why splattered eggs do not un-splatter, we need to look at another concept. Towards the end of the article, we will see how does it deal with the issue of the universe, and why it has evolved in the way it has.
Entropy and Time
Though I have discussed Entropy elsewhere(here),I feel the urge to reintroduce the topic. Entropy is a derivative of statistical probability, which shows how organized a system is. This is necessary because, according to the second law of thermodynamics, most systems tend to go towards level of high entropy, or become highly unorganized. (again explaination in the article linked above) This is key. Consider a bottle of Coke, which has a bout 10²⁴ molecules of CO2 in it. When you open it, the molecules rush out, in one and only situation, do they rearrange themselves inside the bottle.
Similar things happen in our realm. When systems are given power to choose, they always will choose high entropy. Over time and temperature, entropy is bound to increase in the system. This is the reason why Splattered eggs don’t un-splatter, and why spoilt milk does not un-spoil(both splattered eggs and spoilt milk are unorganized). Entropy, although not completely related to time, does manage to give time a direction. It manages to somehow undo time’s symmetry. Or does it?
Entropy and Time’s Symmetry
So how does entropy treat time’s symmetry? Does it undo it? Surely not, as the laws that apply to entropy, although classical, are universal, and act on everyone, everywhere, all the time. So, entropy does not undo Symmetry laws, it actually follows it. But how? Lets get back to our example with coke, when 10²⁴ molecules of CO2 were released from the bottle. Let the “now” be the Y axis, with -3 as the “now”. The left hand side is the past, and the Right is the future, with the parabola being entropy of the system. This is shown in the graph below. But, why do we get identical parabolic curves, and not parabolas that are opposite? Thats because even though the entropy before you opened bottle was low, it in fact, could have been much lower. The molecules could have been beside each other, or arranged in an unique pattern for example. So, entropy does follow the laws of Symmetry, not because it some exception, but because the entropy could have been lower.
When Gravity comes in
Note that I have been ignoring a very important point in this discussion, Gravity, for we cannot talk about entropy without talking about gravity. After reading the previous section, you maybe wondering, if systems tend to alleviate to higher entropies, why is our universe so organised? Well, the answer is, that it isn’t. Why you may ask. That’s because of Gravity. Gravity is a universal force, and hence applies to the very particles that we are made up of. When particles of dust gained enough mass, they had enough gravity to bring in more particles of dust, forming clumps, eventually forming galaxies and stars and star systems that we see today. What you see as organised, is deep down, a unorganised mess of star-dust and atoms. Black Holes, are the epitome of entropy, since they have the biggest gravitational pull, and since entropy and gravity are interdependent, we can consider our universe a mess, since it has enormous gravitation.
Evolution of the Cosmos
The previous answer to the question why has our universe evolved the way it has, is partially correct, but there is a deeper reason behind it. And that also answers the question many of you may have in mind, why was the egg intact before it splattered, and why not already splattered, since our near 14 billion years old universe has lived enough to reach that stage? The answer is because of history. The egg came from a chicken, which came from another egg, and so on. It’s turtles all the way down. But, before the first egg or chicken came along, there were particles, atoms, of which they were formed. These were in turn formed by the Big bang, which in itself was highly organised. So, entropy has increased, but since the start of the universe was so organised, rate of change of entropy in current levels, keeps eggs intact, and the universe evolving the way it has.
Now that we have talked about time in the world around us, lets talk about quantum dimensions and time’s behavior in them .Next article:- Time and the Quantum.