Comments on: The Arrow of Time in Scientific American

By: Sean and Horacio « The Gauge Connection

Sean and Horacio « The Gauge Connection — Mon, 18 Aug 2008 17:50:59 +0000

[...] have been spent around the world. Sean has written an article on this on Scientific American (see here). Contrarily to some wisdom around this problem is really deep as there is no reason on Earth to [...]

By: eCID

eCID — Wed, 30 Jul 2008 15:20:56 +0000

P.S. Instead of the “Arrow of Time”, does Barbour suggest THE ARROW OF ENTROPY?

Following the motion picture projector analogy, the film spool that collects frames that have already passed the projection port are “expired QUANTUM EVENTS” (history?). The film spool that contains frames remaining to pass through the projection port are QUANTUM POSSIBILITIES. The sytem is reversible.

By: eCID

eCID — Wed, 30 Jul 2008 14:22:13 +0000

As a latecomer to these discussions, I wonder if the ideas of Julina Barbour (”The End of Time”) have come up?

Basically, he posits that there is no time–only NOW.

My analogy is that of film in a motion picture projector. As per Barbour (my interpretation), only the frame actually in the projector window is “reality”.

By: JCF

JCF — Tue, 29 Jul 2008 18:13:07 +0000

Re “I will be typing these exact words under my own free will again,” one question to ponder is whether the “I” typing those words will be the same “I” typing your post, although certainly in no case aware of prior “I”s. In Nietzsche’s inconclusive consideration of “perpetual recurrence” he thought the same “I” would experience the identical same life all over again but he found the idea “horrifying.”

By: Dane C. Sorensen

Dane C. Sorensen — Mon, 28 Jul 2008 16:57:30 +0000

So many messy problems with the idea of reversing time. First of all and most importantly you would reverse the second law of thermodynamics. This law is not reversible as all the other laws of physics are. The Universe would not start going backward in time if it did happen to start to contract – do you get younger when you drive in reverse? Peter Lynds has done a fine job of solving the problems of the Big Bang. Also, has Lynds points out, if the Universe was created in a big bang, why was there an infinite amount of time before it decided to do so? Seems absurd. Why now? The only rational solution to Kant’s thoughts is the Universe is cyclic. Gravity is a force that can cause the Universe to return to the primordial soup once again. Lynd’s theory that singularities are not allowed, along with the second law of thermodynmics forces the Universe to Bang yet again as it has forever.

And yes, a cylic Universe would imply that eventually in some distant cycle I will be typing these exact words under my own free will again. Cheers!

By: James G

James G — Sat, 26 Jul 2008 23:25:45 +0000

Excuse my ignorance, is entropy behaviour a classical or non classical result?

In a small particle system ( < 1000 newtonians simulated on a computer) it seems obvious that “chaos” is the “norm” without recourse to quantum mechanics.

At what number of particles does it become necessarry to “invoke” the existence of quantum microstates?

Sean’s article is just one of many which fails to even address this simple question.

By: Sean

Sean — Thu, 24 Jul 2008 15:27:59 +0000

James, there are certainly good questions to be asked about how we divide the many microstates of the world into a smaller number of macrostates. I believe that some ways of doing the division are naturally picked out by the laws of physics, but it’s still an open question.

However, it doesn’t really matter. In terms of what we now call “broken” and “unbroken” eggs, there are certainly many more ways to re-arrange the molecules within the set of broken eggs than within the set of unbroken eggs. That’s an objective fact about the world, so you can’t just choose to insist that broken eggs have a lower entropy. You could choose some very specific form of broken eggs to define a particular kind of macrostate, and if you do it carefully there will be very few microstates that correspond to that choice; but in that case, unbroken eggs will almost never evolve into that specific form, so it will still be true that entropy almost always increases.

By: James Wan

James Wan — Thu, 24 Jul 2008 07:03:31 +0000

Sean, I have one question:
I don’t understand why a social (or human) concept is involved in physics. What I’m wondering is the example of “broken egg”. They were given to prove that “broken egg” has higher entropy because there are countless forms of broken eggs but only one form of good egg. Here we inolves a concept that isolate “good egg” from “broken egg”, but this is from the point of view of human beings. If evaluate this from the view of nature, the “good egg” is just one of the countless forms of egg. It has not any speciall meaning to the nature than any form of “broken egg”. So when an egg is broken, why do we say that its entropy increased? For example, from the point of view of a bird, maybe the broken egg is more meaningful to him/her. So to the bird, when the egg is broken, he/she may thinks the entropy of the egg is decreased.

By: Words in the Clouds | Cosmic Variance

Words in the Clouds | Cosmic Variance — Tue, 22 Jul 2008 14:58:32 +0000

[...] I’m not so modest; this is my Scientific American article. [...]

By: What Do You Say? | Cosmic Variance

What Do You Say? | Cosmic Variance — Wed, 09 Jul 2008 16:31:31 +0000

[...] interview was spurred by the recent Scientific American article on the arrow of time, and most of the questions are pretty straightforward queries about entropy [...]