8.3 Time, Thermodynamics and Emergence

We walked through the laws of classical physics explaining the bigger things and the laws of quantum physics explaining the smaller things. If you look at most of the laws, they usually explain how the state of objects evolve from one time to another time. But neither of the theories explain clearly why time flows in one specific direction.

There is a poignant song named Return to Innocence that shows the life of a couple from the end to the beginning. When we watch it, we can clearly say that the video is in reverse. How?

Imagine you are watching a video that shows a broken egg coming together to form a whole egg. You will immediately tell that the video is running in reverse. But the physical laws we have seen so far do not outlaw a broken egg coming together. Still, we seem to have a clear sense of direction in which Time flows. What scientific theory explains this?

The explanation of the arrow of time comes in terms of the second law of thermodynamics. It says that the entropy of a system only increases with time in a closed system. A super-simplistic way to define entropy is using the word disorderliness. In our egg example, a broken egg is in a more disorderly state compared to a whole egg, thereby having higher entropy. How do we quantify this disorderliness? It is defined as the number of possible microscopic ways we can arrange a system to get its macroscopic appearance.

Imagine a set of playing cards which are ordered based on its numbers and type. This is its macroscopic appearance - cards arranged in an order. There are a very few ways to do this(ascending, descending orders of numbers and types). But imagine the macroscopic state that the cards are in random order. There are numerous ways to jumble the cards. The latter state is more disorderly and has high entropy. The second law of thermodynamics states that systems tend to move towards a high entropy state with time, i.e the cards in random order.

But we can always arrange a set of disorderly cards in a specific order, thereby moving the system from high entropy to low entropy state. Doesn’t that go against the second law of thermodynamics? Remember that the law states that entropy increases in a closed system. So you should not see the cards in isolation. If you add the human who arranged the cards into the system, that person burns food and spends energy to arrange the cards and this energy which is spent results in more disorderliness in the system by generating heat. Though you are making the cards orderly, the process of doing so creates more disorderliness in the system. Even if you create a machine that can put back a broken egg by bringing back all the atoms in place, the machine will end up spending a lot of energy and causing more disorderliness in the system.

The universe at its very beginning is said to have very low entropy and we are moving towards a state of high entropy. The second law of thermodynamics affects us in numerous ways. I personally believe that it is the cause of all our miseries.

Now, we will discuss the topic of emergence. The laws of classical and quantum physics work well in fundamental particles and simple objects. But how do we explain the behaviour of complex objects? We can easily predict how a perfect sphere would roll in the ground. But what if we have a sphere with lots of bumps. It gets difficult to do so. This doesn’t mean that the fundamental physical laws are weak. It is still theoretically possible to figure out the movement of the deformed sphere. But practically speaking, it would be insanely hard. We will have to combine multiple laws, apply them on each part of the deformed sphere and bring them all together.

One popular philosophical debate on emergence is weak emergence vs strong emergence. Weak Emergence says that the behaviour of bigger objects can be explained by the behaviour of its parts. So if we just start from the laws of quantum physics of sub-atomic particles like electrons, quarks and so on, we can explain the behaviour of an entire planet which is built of about 10^52 sub atomic particles. Strong Emergence says that there are certain properties of the bigger objects which cannot be explained by the behaviour of its smaller parts. As things stand, most scientists lean towards weak emergence. We are yet to find clear evidence for a property that is strongly emergent.

8.3 Time, Thermodynamics and Emergence

Further Reading