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Art Matheny (matheny@usf.edu)
Wed, 11 Sep 1996 11:10:30 -0400 (EDT) 

Date: Wed, 11 Sep 1996 11:10:30 -0400 (EDT)
From: Art Matheny <matheny@usf.edu>
Subject: Re: [mSQL] capacity of msql 
Message-Id: <Pine.GSO.3.95.960911104331.13024C-100000@curiac>

On Tue, 10 Sep 1996, Kevin Kenny wrote:

> Gary Bickford <garyb@fxt.com> asks:
> >This has been a question in my mind for some years - how much does a bit
> >weigh (mass), anyway? This may be the key to quantum informatics.
>
> Wrong units. A bit is 9.5692e-24 Joule/Kelvin.
>
> A bit isn't a unit of mass, it's a unit of entropy. A system
> supporting N quantum states has an entropy of kT ln N, where T is the
> absolute temperature and k is Boltzmann's constant. Since a system
> with Q bits has 2**Q quantum states, its entropy is kTQ ln 2. The
> entropy of a single bit is then kT ln 2, making `bit' a fundamental
> constant. If you do thermal noise analysis of a communications channel,
> you find that the Nyquist limit for energy per bit is exactly this
> number -- it all works out!

I don't have a thermodynamics book handy, but haven't you computed the
thermodynamic free energy. (The entropy of a bit is simply k*ln(2), I
think.) Using the mass-energy relation, E=m*c**2, the mass of a bit at 300
degrees Kelvin is approximately 9.5692e-24 * 300 / 9e16 = 3.2e-38 Kg. 

-- 
 LLLL  LLLLL LLLLLL  Arthur Matheny       LIB 612
LL  LL LL  LL  LL    Academic Computing   University of South Florida
LLLLLL LLLLL   LL    matheny@usf.edu      Tampa, FL 33620
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