**Book Name : **Einstein’s Fridge : How the difference between hot and cold explains the universe.

**Author: **Paul Sen

**Genre : **Non-Fiction/ General Science

**Book Post :** 31

**What is it about?:** Why does a cup of hot tea go cold but cold tea does not gain heat to become hot again? What are the limits of computing? Why must we eat and breathe? All these questions are answered by Thermodynamics, the branch of physics that deals with energy and entropy. In this book, the author Paul Sen traces the journey of how the ideas of Thermodynamics started. From the father of Thermodynamics, Sadi Carnot himself to James Joule, William Thomson, the tragic Ludwig Boltzmann, James Clerk Maxwell, Albert Einstein, Claude Shannon, Stephen Hawking and many more. All these incredibly talented thinkers have carried the torch of scientific enquiry into the phenomenon of heat and cold. In the book the laws of thermodynamics, various thought experiments, physical experiments, debates, arguments and thinking are discussed.

**How I came to read it : **In keeping in line with my recent reads on Thermodynamics I was looking for more books on the same subject and my google search threw up this title so I borrowed it from my local library network (Fraser Valley Regional Library).

**Did I like it? :** Loved it. It has easily gotten into my favorite books list. I would place it along my two other favorite science books ‘ A Brief History of Science’ by Stephen Hawking and ‘Quantum’ by Manjit Kumar. These three books in combination provide a superb explanation of physics from the atomic level to the cosmic level. Paul Sen does a good job of explaining many complex concepts in a simple easy to understand way. The best thing about this book is that it flows in the sequence of how the concepts unfolded in history. One chapter ends with a question posed by the current theory and then the next chapter answers it and it goes on. From Sadi Carnot’s initial question about the efficiency of a steam engine and to the nature of heat it moves logically from one question to another and in the final chapter we reach black holes in space. The journey is splendid. The final chapter was one of the best I have read in all my non fiction book reading so far.

**10 things I learned from this book (of the many):**

1. The study of thermodynamics started with the intention of improving the efficiency of the steam driven engines of the 1700s. This was the reason why Sadi Carnot started his study of these engines and eventually to heat and cold.

2. James Prescott Joule was the first person to try to determine the conversion between work and heat. William Thompson is the one who introduced the word ‘Thermodynamic’ to the scientific lexicon and he was also the first person to put forward the idea of heat death of the universe.

3. Ludwig Boltzmann, an Austrian physicist, developed statistical mechanics and used it to explain the second law of thermodynamics. He was the first person to try to explain this law at the molecular level. His 1872 paper was a scientific landmark.

4. The equation for entropy S=k ln W is one of the greatest equations mankind has come up with and is considered one of the foundational statements of physics. It means the entropy (s) of any system is the number of indistinguishable arrangements it can take. This equation is inscribed on the grave of Boltzmann in Vienna.

5. Contrary to what many people think Einstein did not receive his Nobel prize in physics for his theory of relativity. It was instead for his paper on the photoelectric effect. He published 4 papers in 1905. They were some of the most influential papers ever published in science (In fact they have a name called *Annus mirabilis papers*). The miracle year papers. The first was on Photoelectric effect, second one on Brownian motion, third on special relativity and the fourth was on mass-energy equivalence.

6. Einstein’s general theory of relativity was a response to a question about Newton’s equation of gravity. Newton said that the force of gravity is directly proportional to the product of the two masses involved and inversely proportional to the distance between the centers of the masses. And we also know that if you drop two objects from a distance both will fall at the same time irrespective of their individual masses. They both accelerate at the same rate towards the earth. Why is that? How does Earth know the mass of the object falling on it and vary its pull accordingly so that all masses accelerate at the same amount? This is something that was first pointed out by Newton himself. No other force in nature acts like gravity. A lighter object and a heavier object if placed beside a magnet will accelerate towards the magnet at different rates. But if those 2 objects fall on the earth from a distance they will both accelerate towards the earth at the same rate. Einstein said that Earth does not exert any pull at all instead mass of the earth curves the space around it and slows down the passage of time around it.

7. Emmy Noether was a German mathematician born in 1882. She is considered by many to be the most important woman in mathematics. She was one of the leading mathematician of her time and amongst many contributions she came up with what is called Noether’s first theorem which establishes the connection between symmetry and conservation of energy. She showed that for the laws of physics to be unvarying over time, energy must be conserved.

8. When we think of Einstein we tend to think of his theories about relativity and space. I had no idea he also worked on an everyday machine like a refrigerator. He, along with a friend, created a fridge called the Volks-Kuhlschrank or the people’s fridge which had methanol as its cooling medium. He also came up with a unique compressor design called the Einstein-Szilard compressor. The invention of Freon and later the start of the turmoil in 1930s ultimately destroyed Einstein’s inventions.

9. The minimum amount of heat dissipated when a bit of information is processed is called Landauer Limit. This is a fundamental limit set by the laws of physics. This value of this limit is 3000 billion-billionths of a joule. Real transistors dissipate 10 billion times as much heat.

10. Singularity, Stephen Hawking and Jacob Bekenstein.

Singularity is a word that is heard very often these days in sci fi movies. So what does it mean exactly? We know that the general theory of relativity states that objects with massive weights curves the space around them and slows down the passage of time. Now if there is an object in space who’s weight is extremely high and it is compressed to a high density then space and time around it would become infinitely curved. This would create a singularity. These are also called gravitational collapsed objects or Black holes.

Now what connection does black holes have with Thermodynamics? To understand this lets take a look at a few concepts. Every blackhole has a boundary around it after which nothing can escape not even light. For example if a box drifting in space crosses the event horizon of a black hole then it falls into the singularity at the center of black hole and never returns. Not even light escapes can escape this. This means that whatever objects falls into a black hole forever remains inside it. This means the mass of a blackhole always increases and can never decrease. If you notice by now there is only one other thing in the universe which always increases and can never decrease. That is entropy of the universe. Stephen Hawking who worked on this thought this to be a coincidence but later Jacob Bekenstein came up with the idea that this does indeed have a connection. Increasing the mass of a black hole also increases the power of its pull so the event horizon also becomes bigger. So if you add energy to a black hole its entropy increases, its mass increases and the event horizon becomes bigger. Looking at this from another view, entropy increases the energy content of a black hole increasing its mass and the size of its event horizon. This is the link between Thermodynamics and blackholes. The Second law still holds strong here.