Natural Sciences

Understanding Natural Phenomena 5: Can You Unscramble an Egg?

Editor’s Note: This article is a part of the series Understanding Natural Phenomena.

In the previous four posts in this series, I have introduced rudiments of the Big Bang theory, and some elementary ideas from quantum mechanics. Another crucial notion for understanding the evolution of our universe, and of life on Earth, is that of ORDER vs. DISORDER.

Can you scramble an egg? Yes. Can you unscramble a scrambled egg? No way. The physics behind this common-sense fact has far-reaching consequences. It is so important that it is stated in the form of a law in science. It is called the second law of thermodynamics.

The law states that, in any system not interacting with the surroundings, things cannot become more ordered than they were to start with, but they can become more disordered. (Scrambling an egg amounts to creating a state of more disorder. A scrambled egg getting unscrambled would amount to the emergence of order out of disorder.)

If there is a second law, there must also be a first law of thermodynamics. Indeed there is. It states that, although energy can be transformed from one form to another, it cannot be created or destroyed. It is thus the law of conservation of energy.

Historically, the science of thermodynamics emerged in the 19th century when efforts were intensified for using heat energy for doing mechanical work. The steam engine was an embodiment of this effort. People tried to maximize the amount of mechanical work (locomotion) they could get from a given amount of fuel, or from a given amount of heat energy. They soon concluded that, no matter how efficient the design of an engine, there is a limit to the percentage of heat energy that can be converted to mechanical work. Why should there be a limit?

Let us denote heat energy by Q, mechanical work by W, and something called ‘internal energy‘ by U. Imagine a gas in a container at some temperature T1. Suppose you add some heat Q to this system. Naturally, its temperature would go to some higher value T2. This is because the atoms or molecules of the gas are moving around randomly, with an average speed of motion, and adding heat raises this average speed, and therefore the temperature.

The motion and internal vibration of the molecules of the gas implies the existence of energy; and internal energy U is a measure of that. The temperature increases from T1 to T2 because the internal energy has increased from, say, U1 to U2 when heat Q was supplied. What the first law of thermodynamics says is that, when heat Q is expended, some part of it goes into doing mechanical work (in this case thermal expansion and the consequent lifting of the piston in the figure below), and the rest goes into increasing the internal energy, or temperature. Thus

Q = W + (U2U1).

But why can we not have W = Q? That is, why can we not convert all heat to work? That would amount to having U2 = U1 in the energy-conservation equation above, which amounts to expecting that temperature would not rise (from T1 to T2) when heat Q is supplied to the system. This is impossible. What is needed for that to happen is that all the chaotically moving molecules in the container in the above diagram should move in a concerted or special way to move the piston by such a distance that W = Q. This is clearly impossible because there is no reason for the randomly moving molecules to move in that special way, even on an average. Therefore W < Q always.

When heat Q flows into the system, its temperature T1 must rise to a higher value T2. Similarly, if there are two systems (or two parts of the same system), one at temperature T1 and the other at a higher temperature T2, then heat must flow from the hotter part to the cooler part. This will happen spontaneously, and will go on till T1 = T2; i.e. till equilibrium has been reached.

What has happened here is that there was a temperature GRADIENT (T1T2), and Nature destroyed the gradient. In fact, a valid way of stating the second law of thermodynamics is to say that NATURE ABHORS GRADIENTS. We see this happening everywhere. Those who work with vacuum technology know how difficult it is to maintain vacuum in any system. Vacuum in a container means a pressure gradient w.r.t. its surroundings. The vacuum deteriorates with time, in keeping with the law that gradients must decrease spontaneously.

Similarly, concentration gradients tend to be annulled with time. The sugar poured into your cup of tea gets dissolved with time, even when you are not stirring it. The figure below illustrates this for the case of two gases (coloured red and blue for fun). If you remove the partition, the gases mix, rather like the scrambling of an egg.

But the gases will never unmix on their own, just as the egg will not unscramble on its own. Any isolated system always progresses towards a state of maximum disorder. That is what the second law says.

But we also see so much order around us:

  • We are able to grow highly ordered objects called crystals out of a highly disordered precursor, namely a solution or a melt.
  • At the moment of the Big Bang, there was no order or structure at all. Then how so much order has emerged in the universe?
  • Most important of all, how has life, which signifies a very high degree of order, emerged out of nonlife?
  • Why is anything alive at all? Why not a state of total equilibrium, namely death and complete decay? What stops this from happening?

About the author

Vinod Wadhawan

Dr. Vinod Wadhawan is a scientist, rationalist, author, and blogger. He has written books on ferroic materials, smart structures, complexity science, and symmetry. More information about him is available at his website. Since October 2011 he has been writing at The Vinod Wadhawan Blog, which celebrates the spirit of science and the scientific method.

6 Comments

  • I am reading “The fabric of the cosmos” by Brian Greene. In this book, he refers to the initial moments of the universe after the big bang as characterized by “extreme order and symmetry”. He says so because the physical forces (and particles) have not yet broken down into various particles. He says that there is a direct proportional relationship between “heat” (temperature) and symmetry. Increase of heat gives rise to an increase of symmetry.

    There seems to be a difference in the language you are using here. Doesn’t using the word “order” imply symmetry ? Shouldn’t the word “disorder” be used instead, to characterize the cooler moments of the universe much farther away from the big bang ? I don’t know which words convey the meaning in an easier way..

    • Kiran, some of the points you raise will get discussed in future posts in this series.

      Regarding order vs. disorder, which one is more symmetric, ice or liquid water? Ice has more order, but it is less symmetric than water. Ice crystals have only some specific axes of symmetry, and, what is more, none of these axes is infinite-fold symmetric. Water is more disordered and more symmetric: It looks the same from any direction. All directions are infinite-fold symmetry axes for it.

      • The state of maximum disorder corresponds to maximum symmetry. The Big Bang moment was such a state. After that a succession of symmetry-breaking transitions occurred, leading to more and more order and structure and self-organization. The emergence of the Higgs field was one such transition. Future posts will cover these things.

    • My sorts of answer to the questions raised above.

      For me symmetry is a sort of order.

      ‘unscrambling and scrambling’ of an eggs is neither order nor disorder OR equivalently is both order and disorder, the key being with respect to what a thing is viewed/defined from.

      There are only forces in the nature. Force which causes convenience is order and the one which causes inconvenience is disorder. And since convenience is simply relative and meaningless concept with respect to the absolute one (if possible/exists) the ‘order and disorder’ are simply relative and have never independent existence. This is the basis of ‘Maya’.

      I hope you may answer above raised questions in a more convincing way than this.

      • It is not good etiquette to preach your pet theory when the person whom you are responding to asked a physics question and not a metaphysical one.

      • In all such discussions where different parties seem to have in mind different definitions of the words being used, a useful exercise is to taboo your words and replace them with their extended meanings and see if it still makes sense. For scientific discourse to proceed and not be hijacked by postmodernists, revivalists and new-agers, it is a good idea to always perform the exercise recommended at the end of this article, whenever confronted with non-standard usages of scientific terminology.

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