I also found myself thinking hard about the statement that there are more ways for a system to become higher entropy than there are for it to become lower entropy. This may also be true, but a system cannot evolve in all the ways that are possible; the laws of physics must be followed. A few billiard balls bouncing off each other in space will not become higher entropy as a function of time. What is the boundary condition for complexity before a system must increase in entropy? What is inherently different in a complex system? The only thing I can think of proposing is the fact that the position and/or momentum of objects can be expressed as probability waves and only when that uncertainty can influence the evolution of the system does it matter that there are more ways a system can become higher entropy than lower entropy.

Chiming in at the end of the Chapter 2 week, I clearly prefer just one chapter per week.

Doesn’t that suggest that time itself , like space itself, actually has no direction?

Or maybe, more generally,does it serve any purpose to treat entropy and time as distinct concepts?

I am understanding the book quite well. Still, when I finish it, read some other related materials, wait for awhile then read it again, I will understand more.

My friends amazed that I can ask a question about the book, and get answer back from someone with such mind boggling education and knowledge.

They are impressed when I give the a sort of “word of the day”, which I try to put into some sentence, in a casual way. Words like dynamical, retrodiction etc. These are smart poeple, nurses mostly. Most have very little interest in science, and see learning about the universe etc. as too hard. But I have helped a few to be more interested.

Are there plans for a paperback ?

In 48., how does gravity causes a ‘small’, relatively-homogeneous, expanding, PRE-INFLATION, low-entropy universe to become “non-smooth”?

Entropy is sort of challenging to comprehend. I get those “ah-ha” moments and “wait, what?” moments on occasion. As we get further into the book, there may be times that you have to refer us back to the first few chapters or get all Entropy 101 up in here, in the club’s Q&A.

Defined. Now it makes sense to me. Thanks! I really found that to be the toughest concept in the whole book.

Susan– I think you’re on the right track. There is no universal choice of “open system” and “closed system”; a closed system is just one that is isolated from the outside world, so we can always turn a closed system into an open system by bringing it into contact with something else.

Tim– Let’s keep the Chapter 3 stuff for next week. And yes, the free will stuff is explained a bit more later, especially in Chapter 9. But the basic point is simple: according to the underlying laws of physics, the past and future are determined by the present. But we don’t know enough about the present to actually do a very precise prediction or retrodiction. For the past, however, we also have access to a low-entropy initial condition, which greatly restricts the space of possible things that could have happened. In the future there is no such boundary condition, so things are much more wide open; that’s what gives us the feeling that the past is settled while the future is still to be decided.

rww– It’s not that a smooth distribution is high-entropy in the late universe, it’s that a smooth distribution is high-entropy when gravity can be neglected. That’s certainly not the case in the early universe. Think of it this way: if a universe like ours were to contract rather than expand, we would not expect it to smooth out along the way. It would get lumpier as it contracted, entropy increasing all along the way. It’s only once we get to the very late universe, when everything has fallen into black holes which then begin to evaporate away, that the universe smooths out again.

As a poster said above, I won’t be offended to learn that I have missed the whole point. I’m once through the book (obviously too quickly) and look forward to reading it a second time in step with the blog.

Now to a question: Sean, you mention that the concept of free will is connected to the arrow of time. Right now I do not know how to make sense of that. Is it somehow connected to this line of thought: “I have a free will, this is not a contradictory to the existence of an omniscient entity. If you offer me different kinds of ice-cream, I have the free will to choose chocolat or vanilla. After I chose, you know my choice, because now it is in your past. That is not a contradiction to my ability to choose freely. If a beeing exists to whom everything in my future lies in it’s past, it would already know of all my choices, despite the fact that I am, was and will be free to choose.”
Is that somehow connected to what you have in mind? Is it explained in more detail in later chapters of your book?

I had some catching up to do as I just found your book over the weekend. I’m really enjoying it, thanks!

I found the idea that the early universe was extremely low in entropy especially interesting. Now I was a humanities guy, so my knowledge of this stuff comes only from books on popular science. I’ve not seen other books that highlight the low entropy as one of the early universe’s qualities. I’m not sure why, the idea seems on its face to be a deep and rich one!

Now I tend to associate low entropy with order and structure, and high entropy with disorder and randomness. So seeing that connection highlighted, the vision that comes to mind is of an early universe that displayed elaborate structure. Am I mistaken on that?

Best wishes!