Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!cmcl2!rna!cubsvax!peters From: peters@cubsvax.UUCP (Peter S. Shenkin) Newsgroups: net.arch Subject: Re: electrons as a bound on memory size (was VLMM, crypt) Message-ID: <541@cubsvax.UUCP> Date: Mon, 22-Sep-86 11:15:07 EDT Article-I.D.: cubsvax.541 Posted: Mon Sep 22 11:15:07 1986 Date-Received: Mon, 22-Sep-86 21:12:55 EDT References: <15505@ucbvax.BERKELEY.EDU> <5100124@ccvaxa> <972@cit-vax.Caltech.Edu> <505@gvax.cs.cornell.edu> Reply-To: peters@cubsvax.UUCP (Peter S. Shenkin) Organization: Columbia Univ. Bio. CG Fac., NY Lines: 41 In article nather@ut-sally.UUCP (Ed Nather) writes: >In article <505@gvax.cs.cornell.edu>, jqj@gvax.cs.cornell.edu (J Q Johnson) > writes: >> ...why use matter to encode data at all? ...simply >> modulate an EM wave directed at a >> distant point (that destination might be a reflector of some kind if you >> know you will want to retrieve your data at the same location you generated >> it). Result: effectively infinite bulk storage at the cost of a finite >> and small number of electrons. > ...any EM >"wave" is made up of individual photons, which must appear in groups >(using current technology) of 5 or more to generate a detectable signal. >Even if you could get it down to 2 photons (1 == off, 2 == on, 100% detection >efficiency) the storage will be far from infinite -- it will be, in fact, >finite. (*gasp*). > >There is also an energy requirement... OK, let's try to quantify this a bit. The mass of the universe is felt to be ca. 1e37 kg; if all this were converted to radiant energy via Einstein's relationship (E=mc**2) this corresponds to 1e54 J. Now, a photon has energy given by Planck (E=hv, where v is the Greek "nu", freqency); but presumably one has to use photons of E >= ~kT (T the temp, k, Boltzmann's constant) lest the signal be lost in thermal noise. At the present epoch, T =~ 3K (the 3-degree-K cosmic background level), so that kT is about 4e-23 J. Let's say it takes 10 kT to encode a bit at an acceptable signal-to-noise level; then the number of bits one can encode is (1e54/4e-22)=~2e75; that is, (2 x 10^75). Note that as the universe cools down, it gets cheaper to convey a bit, so that the number of bits it is possible to store is continually going up! (I pass over any difference between storing and conveying information, because how could you use stored information if it weren't conveyed?) This would seem to imply (perhaps stretching things a bit, but what the hell -- you only live once!) that at the moment of the big bang there was no information present in the universe (since T was infinite, I believe). Peter S. Shenkin Columbia Univ. Biology Dept., NY, NY 10027 {philabs,rna}!cubsvax!peters cubsvax!peters@columbia.ARPA