Entropy

With a lot of focus being given towards thermodynamics, I wish to write about Entropy

In all, Entropy is a crucial link of 2nd law of thermodynamics which says that Entropy of a isolates system which is not in equilibrium will tend to increase over a period of time, approaching the maximum at equilibrium and the entropy chances dS of a system undergoing infinitesimal reversible process is given by δq / T, whereδq is the heat supplied to the system and T is the absolute temperature of the system

Entropy is nothing but a macroscopic measure of microscopic disorder within a system. To explain in common language its the measure of disorder. Few common examples of deck of cards, Air conditioners, Die can be given

A deck of cards is very organised as all the cards are arranged properly. But when the game is over, the cards are scattered here and there. Thus the disorder happens and we can say entropy increases. A die is used to play board games. Entropy also is the a form of multiplicity

In a two die game, the probability of getting no. above 7 is higher than getting two or three.

Thus the multiplicity of getting a 7-8 no on die is more than getting 2 or 3

Thus Entropy of getting higher nos is more than lower nos

If we consider the property-

Entropy of a system which is isolated and not in equilibrium will increase over a period of time approaching maximum at equilibrium.

Air conditioner or AC has a indoor unit and one outdoor unit. AC is used to cool the air temp. inside the room. But AC does this only when the temperature of the outdoor unit increases

In other language- Entropy of the system can decrease only when it increases the entropy of the other system. thus entropy of indoor unit decreases when it increases entropy of outdoor unit

In Astrophysics and astronomy entropy of the universe is an important concept

Entropy of universe will increase over a period of time . It also means that all the activities happening in universe increase its entropy

A simple example is of thermal radiation. For it we consider a black hole

A black hole though rotating or non rotating has singularity in form of ring or non ring pattern.

Singularity is nothing but the concentration of dense matter or mass in zero volumed region thus making the space time curvature infinite...

Singularity has low entropy as the matter is in a organised fashion. At the microscopic level, there is some particle and anti particle separation and collision happening as per quantum mechanics. Once of this particle falls in the event horizon as seen by external observer and he also sees that the other particle is emitted by black hole, A black hole thus follows a perfect black body principle which allows it to emit thermal radiation at certain temp.

Thus emission of matter will allow the entropy of Black hole to increase.

The question arises is that If the ENTROPY of Universe will increase and is increasing then how come universe has a low entropy or more organised fashion and what about the entropy at the Big bang..

Lets go back in time---

When the big bang happened, matter was scattered everywhere in the universe. Though planets, stars were not formed but there were intense hydrogen clouds..Gravitational energy was the dominant force at that time. And heat energy, light energy were just getting formed due to conversions due to compressions of hydrogen clouds... Thus we can conclude that gravity was the only persistent force and the Universe was hotter at that time..Since then the universe is expanding and becoming cold. If the universe is becoming cool from hot temperatures then it means the universe is releasing its heat in form of heat energy is some other system as as per Second law, a system can become cool only when some other system kept in its contact increases..

Thus the total entropy of universe is increasing as the heat energy is increasing

So when a equilibrium stage happens that is no available energy to do work, there will be only heat energy remaining in the universe...

This is popularly called as Heat Death Of Universe. On the contrary, as most of the energy and heat providers i.e suns will die after many years, the temperature of the universe is expected to go down thus there is a so called - Freeze death of universe concept