Comments on: Erasing Landauer’s principle, http://dabacon.org/pontiff/?p=977 Theoretical Musings Thu, 09 Sep 2010 14:06:56 +0000 hourly 1 http://wordpress.org/?v=3.0.1 By: Dave Bacon http://dabacon.org/pontiff/?p=977#comment-318478 Dave Bacon Wed, 25 Feb 2009 22:26:35 +0000 http://dabacon.org/pontiff/?p=977#comment-318478 Ooops. Thanks rarruec, fixed that. How did that get by everyone reading this post?!? Ooops. Thanks rarruec, fixed that. How did that get by everyone reading this post?!?

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]]> By: rarruec http://dabacon.org/pontiff/?p=977#comment-318476 rarruec Wed, 25 Feb 2009 21:36:24 +0000 http://dabacon.org/pontiff/?p=977#comment-318476 "disipates an amount of entropy equal to Bolztman’s constant times natural log of the number of bits erased" Actually it would be: Boltzman's constant times natural log of the number of possible states of the system. If we are talking of a bit, for example, the formula would be: klog(2^ 1 bit). If we have two bits, it would be klog4, and so. If I'm wrong please write to me rarruec@gmail.com, I'm very interested about this topic. “disipates an amount of entropy equal to Bolztman’s constant times natural log of the number of bits erased”

Actually it would be: Boltzman’s constant times natural log of the number of possible states of the system. If we are talking of a bit, for example, the formula would be: klog(2^ 1 bit). If we have two bits, it would be klog4, and so.

If I’m wrong please write to me rarruec@gmail.com, I’m very interested about this topic.

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]]> By: Dave Bacon http://dabacon.org/pontiff/?p=977#comment-35007 Dave Bacon Mon, 08 Aug 2005 16:48:52 +0000 http://dabacon.org/pontiff/?p=977#comment-35007 No, I don't think you're misssing anything! Certainly it's my ignorance on display here! I guess the question I have, and I think this is the question that goes to the heart of the discussion about Landaur's principle, is how to treat this long life time. If we take straightaway thermodynamics, then, of course, we just say, we haven't waited long enough for thermodynamic equilbrium to be reached. But in this setting what does "storing information" really mean? It seems that this is a concept "outside" of thermodynamics. But in such a setting, couldn't we just as well argue that thermodynamic equilbrium is a "bad" concept? And since hard drives are (well old ones (basically)..new ones have real cool things going on with them but the effective idea is the same.) Ising models, the question is, if we are going to take these devices, acting as storage devices, seriously, then it seems that thermodynamic reasoning breaks down. That is, if we put a long time cutoff, then certainly thermodynamics doesn't have anything to say about the two highly stable states. I certainly feel like making this critique is valid. It is not a critique of thermodynamcis, but more of the fact that for the purposes of talking about information storage in long lived states, thermodynamics isn't perhaps the full language we need. This is why I argue that thermodynamics is incomplete. But I should clarify and say that I think it is incomplete when discussing long lived macrostates. No, I don’t think you’re misssing anything! Certainly it’s my ignorance on display here!

I guess the question I have, and I think this is the question that goes to the heart of the discussion about Landaur’s principle, is how to treat this long life time. If we take straightaway thermodynamics, then, of course, we just say, we haven’t waited long enough for thermodynamic equilbrium to be reached. But in this setting what does “storing information” really mean? It seems that this is a concept “outside” of thermodynamics. But in such a setting, couldn’t we just as well argue that thermodynamic equilbrium is a “bad” concept? And since hard drives are (well old ones (basically)..new ones have real cool things going on with them but the effective idea is the same.) Ising models, the question is, if we are going to take these devices, acting as storage devices, seriously, then it seems that thermodynamic reasoning breaks down. That is, if we put a long time cutoff, then certainly thermodynamics doesn’t have anything to say about the two highly stable states. I certainly feel like making this critique is valid. It is not a critique of thermodynamcis, but more of the fact that for the purposes of talking about information storage in long lived states, thermodynamics isn’t perhaps the full language we need. This is why I argue that thermodynamics is incomplete. But I should clarify and say that I think it is incomplete when discussing long lived macrostates.

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]]> By: Wolfgang http://dabacon.org/pontiff/?p=977#comment-35006 Wolfgang Mon, 08 Aug 2005 16:35:05 +0000 http://dabacon.org/pontiff/?p=977#comment-35006 > This isn’t my understand of how a magnetic storage > device works. I do not know enough about real world hard disks to understand whether the Ising model is a good description. > This isn’t my understand of how a magnetic storage
> device works.
I do not know enough about real world hard disks to understand whether the Ising model is a good description.

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]]> By: Wolfgang http://dabacon.org/pontiff/?p=977#comment-35005 Wolfgang Mon, 08 Aug 2005 16:30:45 +0000 http://dabacon.org/pontiff/?p=977#comment-35005 > but the question is why does it retain this > information ??? You turn H > 0 on for a brief time, the spins flip accordingly and the lattice remains in this state for a long while (but not forever) if the temperatur is low enough (as you have pointed out) and external pertubations (e.g. H) are small. Nothing mysterious, or am I missing something? > but the question is why does it retain this
> information
???
You turn H > 0 on for a brief time, the spins
flip accordingly and the lattice remains in this
state for a long while (but not forever) if the
temperatur is low enough (as you have pointed out)
and external pertubations (e.g. H) are small.
Nothing mysterious, or am I missing something?

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]]> By: Dave Bacon http://dabacon.org/pontiff/?p=977#comment-35004 Dave Bacon Mon, 08 Aug 2005 16:13:01 +0000 http://dabacon.org/pontiff/?p=977#comment-35004 Uh, that I don't understand. If I can apply an external magnetic field to set the bit of information, but the question is why does it retain this information, even after the the field is shut off. This isn't my understand of how a magnetic storage device works. Uh, that I don’t understand. If I can apply an external magnetic field to set the bit of information, but the question is why does it retain this information, even after the the field is shut off. This isn’t my understand of how a magnetic storage device works.

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]]> By: Wolfgang http://dabacon.org/pontiff/?p=977#comment-35002 Wolfgang Mon, 08 Aug 2005 15:48:28 +0000 http://dabacon.org/pontiff/?p=977#comment-35002 > Especially when it comes to storing information? If you store information you will use an external field H and your problem disappears. > Especially when it comes to storing information?
If you store information you will use an external
field H and your problem disappears.

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]]> By: Dave Bacon http://dabacon.org/pontiff/?p=977#comment-35001 Dave Bacon Mon, 08 Aug 2005 15:08:59 +0000 http://dabacon.org/pontiff/?p=977#comment-35001 Wolfgang: Indeed. Should this trouble me? Both limits (ensemble average and time average) are to me, but approximations to what I'd do in the real world. But is there are good fundamental reason to worry more about ensemble averages? Especially when it comes to storing information? Wolfgang: Indeed. Should this trouble me?

Both limits (ensemble average and time average) are to me, but approximations to what I’d do in the real world. But is there are good fundamental reason to worry more about ensemble averages? Especially when it comes to storing information?

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]]> By: Wolfgang http://dabacon.org/pontiff/?p=977#comment-34999 Wolfgang Mon, 08 Aug 2005 13:37:36 +0000 http://dabacon.org/pontiff/?p=977#comment-34999 > the probability of flipping to the all spins align > in the other direction vanishes The way you state it, the problem is not with thermodynamics but with ergodicity; The time average does not equal the ensemble average. > the probability of flipping to the all spins align
> in the other direction vanishes
The way you state it, the problem is not with thermodynamics but with ergodicity; The time average does not equal the ensemble average.

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]]> By: Wolfgang http://dabacon.org/pontiff/?p=977#comment-34996 Wolfgang Mon, 08 Aug 2005 12:06:51 +0000 http://dabacon.org/pontiff/?p=977#comment-34996 > in the infinite size limit (below the critical > temperature) the probability of flipping to the > all spins align in the other direction vanishes The way you state it, the problem would be with ergodicity not thermodynamics; The ensemble average would not be the average over long times. > in the infinite size limit (below the critical
> temperature) the probability of flipping to the
> all spins align in the other direction vanishes
The way you state it, the problem would be with ergodicity not thermodynamics; The ensemble
average would not be the average over long times.

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