Comments on: From Eternity to Here: The Quest for the Ultimate Theory of Time http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/ Random samplings from a universe of ideas. Mon, 09 Nov 2009 05:46:49 -0600 http://wordpress.org/?v=2.8.4 hourly 1 By: Sili http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/comment-page-1/#comment-60419 Sili Tue, 20 Jan 2009 18:59:46 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/#comment-60419 If you do use scrambled eggs, then you do so at <a href="http://www.qwantz.com/archive/001049.html" your</a rel="nofollow"> <a href="http://www.qwantz.com/archive/001050.html" rel="nofollow">own</a> <a href="http://www.youtube.com/watch?v=6-qd9Ww45So" rel="nofollow">peril</a> (last link possibly NSFW - at least if you have your speakers on (but why would you have so at work?)). If you do use scrambled eggs, then you do so at own peril (last link possibly NSFW – at least if you have your speakers on (but why would you have so at work?)).

]]> By: Sandy http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/comment-page-1/#comment-60077 Sandy Sun, 18 Jan 2009 17:43:07 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/#comment-60077 That's great Sean, I love to read books about the arrow of time. I have 2 requests: Please don't use scrambled eggs or breaking tea cups as examples of entropy!! They are not examples of entropy and I wish physicists would stop using them (as such). I would really appreciate a good discussion that justifies using the Second Law of Thermodynamics outside of its specific parameters. That’s great Sean, I love to read books about the arrow of time. I have 2 requests:

Please don’t use scrambled eggs or breaking tea cups as examples of entropy!! They are not examples of entropy and I wish physicists would stop using them (as such).

I would really appreciate a good discussion that justifies using the Second Law of Thermodynamics outside of its specific parameters.

]]> By: Jean Paul B. http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/comment-page-1/#comment-60024 Jean Paul B. Sun, 18 Jan 2009 06:44:00 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/#comment-60024 Well, while Uwe Price made a lot of good thinking in his essay, I believe he ended, like most thinking on the arrow of time, by having it chasing its own tail. Resolving the question of the second law of thermodynamics by a very specific low entropy initial condition, seems to me just a tautology. It does not answer why entropy is growing with time, but how it could have been possible. So this kind of answer is about the cosmological non-contradiction of the second law, not its reason why. There are several alternative answers about the reason why. One is the now rather outdated Prigogine's notion that even at the microscopic level time is not reversible. Another is that time arrow is an illusion in a timeless universe driven by Hamiltonian constraints. Then to get back our perception of time you have to introduce something like the thermal hypothesis of Conne/Rovelli. My belief is that this last approach might be on the right way, while still wanting of more fundamental insights on how we build memory (and partial amnesia). What do you think? Well, while Uwe Price made a lot of good thinking in his essay, I believe he ended, like most thinking on the arrow of time, by having it chasing its own tail. Resolving the question of the second law of thermodynamics by a very specific low entropy initial condition, seems to me just a tautology. It does not answer why entropy is growing with time, but how it could have been possible. So this kind of answer is about the cosmological non-contradiction of the second law, not its reason why. There are several alternative answers about the reason why. One is the now rather outdated Prigogine’s notion that even at the microscopic level time is not reversible. Another is that time arrow is an illusion in a timeless universe driven by Hamiltonian constraints. Then to get back our perception of time you have to introduce something like the thermal hypothesis of Conne/Rovelli. My belief is that this last approach might be on the right way, while still wanting of more fundamental insights on how we build memory (and partial amnesia). What do you think?

]]> By: andy.s http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/comment-page-1/#comment-59999 andy.s Sun, 18 Jan 2009 01:18:04 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/#comment-59999 Well, that's a-whole-noether question, now isn't it? Well, that’s a-whole-noether question, now isn’t it?

]]> By: Neil B http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/comment-page-1/#comment-59980 Neil B Sat, 17 Jan 2009 22:56:49 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/#comment-59980 Andy, it is formally reversible but that has little chance of "just happening" so after decay, isn't there "more entropy" than before because it is effective disorder? Also, do you know the answer to my question about Noether? Andy, it is formally reversible but that has little chance of “just happening” so after decay, isn’t there “more entropy” than before because it is effective disorder?
Also, do you know the answer to my question about Noether?

]]> By: andy.s http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/comment-page-1/#comment-59977 andy.s Sat, 17 Jan 2009 22:37:36 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/#comment-59977 I look forward to it Sean. But I bet you'd sell more if you explained it all to your <a href=http://scienceblogs.com/principles/2009/01/pop-science_book_racing.php rel="nofollow">dog.</a> Also: re entropy. <blockquote> Consider a muon. Before it decays is structureless and just like a stable particle in terms of properties, but when it decays there is then more complexity in the universe than before etc - how can entropy be coherently defined for such entities </blockquote> Not sure if entropy would increase in this reaction. Muon decay goes like $latex \mu^- \to \nu_\mu + W^- \to \nu_\mu + e^- + \bar{\nu_e}$. That reaction should be reversible, and in chemistry, IIRC, a reversible reaction does not increase entropy. I don't know, maybe it's different with particles. I look forward to it Sean. But I bet you’d sell more if you explained it all to your dog.

Also: re entropy.

Consider a muon. Before it decays is structureless and just like a stable particle in terms of properties, but when it decays there is then more complexity in the universe than before etc – how can entropy be coherently defined for such entities

Not sure if entropy would increase in this reaction. Muon decay goes like \mu^- \to \nu_\mu + W^- \to \nu_\mu + e^- + \bar{\nu_e}. That reaction should be reversible, and in chemistry, IIRC, a reversible reaction does not increase entropy. I don’t know, maybe it’s different with particles.

]]> By: Neil B http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/comment-page-1/#comment-59929 Neil B Sat, 17 Jan 2009 18:25:06 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/#comment-59929 Does Noether's Theorem have something to say about the arrow of time, although it does not deal with entropy ? ... Yeah, NT is all about things being constant, but to make the point wouldn' t you need a progressing time frame to work it out in? And BTW does Noether's Theorem generalize to universes analogous to ours but with other number of space dimensions? It seems like it should, but I've seen various statements that action etc. has special properties in three-D space. Does Noether’s Theorem have something to say about the arrow of time, although it does not deal with entropy ? … Yeah, NT is all about things being constant, but to make the point wouldn’ t you need a progressing time frame to work it out in? And BTW does Noether’s Theorem generalize to universes analogous to ours but with other number of space dimensions? It seems like it should, but I’ve seen various statements that action etc. has special properties in three-D space.

]]> By: Sili http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/comment-page-1/#comment-59903 Sili Sat, 17 Jan 2009 16:02:43 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/#comment-59903 Speaking of books, didn't you promise signed copies of your opus one to people who gave to Donors Choose? Or did I imagine that? I might have, since I seem to recall your offering access to your Trophy Wife(tm) to particularly good givers. Speaking of books, didn’t you promise signed copies of your opus one to people who gave to Donors Choose? Or did I imagine that?

I might have, since I seem to recall your offering access to your Trophy Wife(tm) to particularly good givers.

]]> By: Sean http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/comment-page-1/#comment-59804 Sean Sat, 17 Jan 2009 05:39:53 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/#comment-59804 When we negotiate foreign rights, I'll try to insist that every copy of the Spanish version come with a coupon for free ice cream. When we negotiate foreign rights, I’ll try to insist that every copy of the Spanish version come with a coupon for free ice cream.

]]> By: P. C. http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/comment-page-1/#comment-59798 P. C. Sat, 17 Jan 2009 04:23:43 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/01/14/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time/#comment-59798 I want the book NOW. And translated to Spanish, please. And I want icecream. Thanks! I want the book NOW.
And translated to Spanish, please.
And I want icecream.
Thanks!

]]>