From: michael k teehan (miketeehan@worldnet.att.net)
Date: Sat Dec 20 1997 - 04:22:49 MST
----------
> From: michael k teehan <miketeehan@worldnet.att.net>
> To: extropians@extropy.com
> Subject: Re: the ultimate refrigerator
> Date: Friday, December 19, 1997 7:40 PM
>
>
>
> ----------
> > From: Wei Dai <weidai@eskimo.com>
> > To: extropians@extropy.com
> > Subject: Re: the ultimate refrigerator
> > Date: Friday, December 19, 1997 7:45 PM
> >
> > On Fri, Dec 19, 1997 at 11:57:33AM -0800, Robin Hanson wrote:
> > > In making my contribution to reversible computing
> > > (http://hanson.berkeley.edu/reverse.html) I learned enough say with
> great
> > > confidence that there is no particular advantage to erasing bits at
> lower
> > > temperatures. If it were otherwise you could make a perpetual motion
> machine:
> > > erase bits (= replace unknown bits with known bits) at low temps and
> then
> > > reverse the operation (replace known bits with unknown bits) at high
> temps.
> > > By the "costs less energy" intution this cycle would create available
> energy.
> >
> > Isn't that exactly what a heat engine does, when you think of it in
> > information theoretic terms? Of course it is not a perpetual motion
> > machine since when it erases bits, it raises the temperature of the low
> > temp heat sink, and when it randomizes bits, it lowers the temperature
of
> > the high temp heat source, so eventually the temperature difference
> > disappears. (Of course I'm excluding black holes here, since
> > when you "heat up" a black hole by dumping energy into it, it actually
> > gets cooler.)
> >
> > I don't see how you can say there is no advantage to erasing bits at
> lower
> > temperatures, since your free energy is limitied, and at lower
> > temperatures the same amount of free energy allows you to erase more
> bits.
> > The trick is to obtain a low temperature without spending energy on
> active
> > cooling, and that's what a black hole allows you to do. Perhaps what
> > you're saying is that it wouldn't help to cool your computer to 0.1K if
> > the best heat sink you have access to has a temperature of 3K. I
> certainly
> > agree with this.
> >
> > I think we're probably not really disagreeing, just emphasizing
different
> > aspects of the same idea.
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