
Von Neumann-Landauer limit - dedalus
https://en.wikipedia.org/wiki/Landauer%27s_principle
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philipkglass
The usual extropian retort to this limit has been "reversible computing," but
as far as I can tell there has been little work on reversible computing
hardware -- far less than quantum computing. It looks like the University of
Florida made some hardware in the early 2000s. Can anyone offer insights about
why hardware research is so scarce here? Are there reasons to think it's a
dead end prior to fabricating anything?

[https://en.wikipedia.org/wiki/Reversible_computing](https://en.wikipedia.org/wiki/Reversible_computing)

EDIT: searching Google Scholar, it looks like only ~50 papers/books mention
reversible computing in the past year, compared to 1000+ for quantum
computing.

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tgb
Oh it's worth noting that quantum computing research _is_ reversible computing
research. Quantum operations are unitary operators which necessarily have
inverses. Famous quantum computing results like the "no cloning" theorem are
basically just consequences of the reversibility of QC.

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akvadrako
I suspect any non-trivial reversible computer will be a quantum computer.
Quantum gates can perform almost any reversible operation and losing
information (by not being reversible) might be physically equivalent to
decoherence.

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md224
I picked up _The Information_ by James Gleick when I was visiting the Living
Computers Museum + Labs in Seattle[1]. Really interesting book... talks about
the development of language, the birth of computing, the concept of
randomness, the physics of information, etc. A fascinating and comprehensive
overview of the topic.

[1] This place is awesome and you should check it out if you're in the area:
[http://www.livingcomputers.org](http://www.livingcomputers.org)

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emmelaich
I remember reading Feynman's thought experiment and him deciding that it
doesn't require _any_ energy to flip a bit.[1]

How does that square with Landauer's limit?

[1] Apologies for the lack of reference. I'll try and find it.

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abecedarius
Basically, it costs free energy to _forget_ a bit. If you flip a bit, that
doesn't mean you forget it, as long as you remember you'll have to flip it
back (or reinterpret it).

("Basically" because there are whole books on the subtleties of physics and
information. I haven't mastered them.)

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akvadrako
This is the correct answer. If you don't overwrite a bit, but instead move the
old value to an auxiliary bit known to be zero, that can be theoretically done
for free.

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guskel
I believe there is some breakthrough yet to be found in the intersection of
entropic gravity and computational limits.

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Synaesthesia
I’d be curious to hear more about that idea but thank you for introducing me
to this theory of entropic gravity.

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malux85
Me too - any links or articles for the best material much appreciated

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Synaesthesia
Having read some more about this entropic gravity theory it does have quite a
few pretty strong criticisms, detailed on the the wiki page.

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deepnotderp
As interesting as it is to think about the limit, it's so pointless from a
practical point of view since the cost of computation is dwarfed by the cost
of data movement in modern machines.

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agumonkey
As inspiring as thought provoking.

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_nalply
Yes. I imagine the last probe doing its last bit flip in the heat death of the
universe. Then nothing can be computed anymore and all what will happen is the
decay of the matter of the probe. So sad.

~~~
digi_owl
I get the feel that something like that was the plot of a short story i read
ages ago.

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a_t48
The Last Question -
[http://multivax.com/last_question.html](http://multivax.com/last_question.html)
?

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shpx
Related discussion

[https://news.ycombinator.com/item?id=14002160](https://news.ycombinator.com/item?id=14002160)

[https://news.ycombinator.com/item?id=14146677](https://news.ycombinator.com/item?id=14146677)

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davidivadavid
Recently mentioned in Venkat Rao's Breaking Smart newsletter.

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bandrami
So you're telling me ignorance can combat global warming?

