Perhaps I wasn't clear. [Need more coffee...]
On Wed, 3 May 2000, Billy Brown wrote:
> Robert J. Bradbury wrote:
> > Some questions related to this would be:
> > (a) What are the (energy/entropy) costs of destroying information in
> > the real world vs. the virtual world? [Reversible computing is
> > going to produce the densest computing but it does so at the
> > expense of minimizing the erasing bits.]
>
> Uh, Robert, a bit is a bit. The storage and manipulation constraints are
> exactly the same no matter what the bit is used for.
The work by Bennett, Landauer, etc. say the "cost" in computing is
the cost of erasing information. For example, if I have a capacitor
storing some electrons, there is a heat produced in removing those
electrons to discharge the capacitor. They way you reduce this problem
is to allow the capacitor to charge and discharge very slowly (along the
ideas of reversible computing). However in a virtual world it isn't
clear to me that those constraints exist. If you have the freedom
to design the ecology, could there be a way that allows the
virtual erasure of some information to result in the virtual
creation of other information (along the lines of allowing
the electrons to cycle between two capacitors). You have
to design the system so that the transforms on the information
waste less energy than similar transforms using "real" atoms
or molecules. For example -- can I design a virtual system
where the energy cost of breaking a virtual C=C bond is cheaper
than the energy cost of breaking a real C=C bond (~1.19 aJ)?
>
> > (b) Is the real world less expensive than the virtual world for
> > "storing" an arbitrary amount of information? [It seems to
> > me that a virtual world based on storage in photons should
> > be cheaper than a real world based on storage in atoms.]
>
> You can't store information in a virtual world at all. Any information that
> appears to be stored there must actually be represented in some physical
> memory device in the real world. Which means you always come back to the
> constraints of physical-layer devices.
Ah, but there are many examples, say from mathematics, where a simple
formula can represent a huge amount of information. Moravec's article
points out how optimizing compilers can transform one representation
of a process into a much more efficient representation. The Transmeta
efforts show how you can design a machine that can refine processes
into increasingly efficient operations.
I agree there always has to be a physical representation. But almost
all "information" in the current "real" world is represented in atoms,
atomic bonds, electric charges in specific locations, etc. I'm thinking
along the lines of a "virtual" computer where the information is
represented by photons at specific positions in space. It seems
likely that a computer of that type (i.e. no matter, other than that
required to produce the photons), could potentially have a much higher
information density than "matter" based computers or Moravec's
Higgsinium or Monopolium (that are still based on "atomic" models).
Robert
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