That word “derivative” sounds interesting, and I sensed or wished that it would imply something deep.  Unfortunately after searching in his blog and pondering on this life-death topic for a long time, I figured it means nothing but his Chinese translation “乐观是向上的!”  I take this awkward Chinese to mean that being happy is to be optimistic.  That sounds a good grandpa advice, but way short of what I expect from this great Havard professor I admired so much.  For someone I dreamed to follow when I was a college student, I want much more.  Perhaps indeed there is a lot more in his mind, but he didn’t elaborate.

To me his definition is simply a rephrasing of happiness.  In a less arcane way, I think he just wants to say “happiness is a positive change in one's mood”! It does not say anything about what "happiness" is, or how to achieve happiness - you’re lucky if you are born optimistic and hopeless if you are born pessimistic.

In one sense “happiness” is very much like “entropy” – we understand entropy only through its change, a change in order/structure/meaning.  Thus I define “happiness is to reduce entropy”.  I think mine is better.  First, “entropy” sounds definitely more grandeur than “derivative”; second, “entropy” has a lot more substance to cover; and third, “reduce” is a verb, which tells you action is important, there is still hope if you’re not an optimistic person.

Entropy is the most wonderful thing in all things that I ever learned.  It gives a meaning to everything.  If the world is just matter and energy, it will be nothing for us.  Being is not meaningful.  But as soon as the entropy concept comes to human mind, we are different, to be or not to be is not debatable anymore, at least to me."Not to be" means striving for the maximum entropy, you do not need to know more about things, you become dirt.  But "to be" means to know, to put things in order, to give them structure, to clarify, to have meaning, it’s about the quality and not quantity, and to receive energy and reverse the direction dictated by the second law of thermodynamics.  All the effort of life is nothing but this, evolution and religion share the same thoughts in this sense.

Time thus has meaning, we can be sad or happy, we miss the old times, the ancient times, and look to the future.  

When do we feel happy? Not when we get something of brand names, not during a delicious dinner, or all those things you dream of, they are pleasures, illusions, not happiness.  You are happy only when you understand something, big or small.

How do we keep alive - get information, not just food.  By reading or talking/listening, we clarify things, that is why human being dominate other animals.

I thought Boltzmann did not know this, as he committed suicide in the end.  But he knows, he addressed to the Austrian Imperial Aceadmy of Sciences on May 29, 1886 as follows:

“Between sun and earth…energy is thus not at all distributed according to the law of probability… The general struggle for existence of animated being is therefore not a struggle for raw materials – these, for organisms, are air, water, and soil, all abundantly available – nor for energy which exists in plenty in any body in the form of heat (albeit unfortunately nor transformable), but a struggle for entropy, which becomes available through the transition of energy from the hot sun to the cold earth.  In order to exploit this transition as much as possible, plants spread their immense surface of leaves and force the sun’s energy, before it falls to the earth’s temperature, to perform…certain chemiscal syntheses…The products of this chemical kitech consititute the object of struggle of the animal world.”