
Optical solutions to NP-Complete problems - adamnemecek
http://www.cs.ubbcluj.ro/~moltean/optical/
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benten10
For those who may not be aware -- As always in these situations: Scott Aronson
said it first!

For reference, here's the highly amusing and interesting paper he's written on
this:

"NP-complete Problems and Physical Reality"
[http://www.scottaaronson.com/papers/npcomplete.pdf](http://www.scottaaronson.com/papers/npcomplete.pdf)

Abstract:

"Can NP-complete problems be solved efficiently in the physical universe? I
survey proposals including soap bubbles, protein folding, quantum computing,
quantum advice, quantum adiabatic algorithms, quantum-mechanical
nonlinearities, hidden variables, relativistic time dilation, analog
computing, Malament-Hogarth spacetimes, quantum gravity, closed timelike
curves, and “anthropic computing.” The section on soap bubbles even includes
some “experimental” results. While I do not believe that any of the proposals
will let us solve NP-complete problems efficiently, I argue that by studying
them, we can learn something not only about computation but also about
physics."

~~~
dogecoinbase
A favorite example of mine, using photons to solve Traveling Salesman in
quadratic time:
[https://www.osapublishing.org/oe/abstract.cfm?id=140598](https://www.osapublishing.org/oe/abstract.cfm?id=140598)

Spoiler: the number of photons required scales up so quickly that the
phenomenon cannot be observed for sufficiently high N.

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echelon
Using physical space and particle interactions for solving computational
problems seems like such an elegant hack. Proteins fold and chemistry just
works in 3D space, yet we have problem computing these things. I wonder why we
don't do more computing on the physical fabric of the universe itself. It
seems like an optimally efficient tool for problem solving.

Are there any other approaches along this same vein? It's incredibly
fascinating.

~~~
taneq
Well, there's spaghetti sort:
[https://en.wikipedia.org/wiki/Spaghetti_sort](https://en.wikipedia.org/wiki/Spaghetti_sort)

Also things like using slime mold to solve the traveling salesman problem:
[http://phys.org/news/2013-03-blob-
salesman.html](http://phys.org/news/2013-03-blob-salesman.html)

And if you want to go simpler, there's always mechanical analog computers:
[https://youtu.be/s1i-dnAH9Y4](https://youtu.be/s1i-dnAH9Y4) (it's long but
well worth a watch IMO)

Oh, and obviously anything involving a scale model, especially for fluid
dynamics (so wind tunnels, wave tanks etc), is doing the same thing in spirit.

~~~
hackcasual
Slime molds aren't guaranteed to find optimal solutions

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zdkl
You'll have to break out "Moldy Carlo" simulations for that!

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dekhn
Amusingly, physics people were doing fourier transforms using optical
techniques (lenses) well over a hundred years ago.

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dharma1
interesting - got a link?

~~~
4ad
[https://en.wikipedia.org/wiki/Fourier_optics](https://en.wikipedia.org/wiki/Fourier_optics)

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SilasX
As I understand it, it's exploiting how light signals move very fast and thus
you can sweep through many solutions. But, as they seem to note in
"weaknesses", you're effectively offloading an exponential amount of work to
the light, and so haven't done anything for the big-O behavior; you're just
making a (potentially) less scarce resource applicable to the problem, no
different (economically) from finding cheaper ways to build computers.

~~~
hammock
You could say the same about fiber optics vs copper wire. Increasing bandwidth
can drive revolutionary change.

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dkarapetyan
This is like sleep sort:
[https://rosettacode.org/wiki/Sorting_algorithms/Sleep_sort](https://rosettacode.org/wiki/Sorting_algorithms/Sleep_sort).
Same principles apply. Time delays are used to achieve the result.

I thought this would have used the quantum/wavelike properties of light but I
was wrong.

~~~
zitterbewegung
Optical quantum computers do exist
[https://en.m.wikipedia.org/wiki/Linear_optical_quantum_compu...](https://en.m.wikipedia.org/wiki/Linear_optical_quantum_computing)

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dharma1
Love this. This is interesting too - optical computing for machine learning

[http://www.lighton.io/](http://www.lighton.io/)

I think we'll see much more physical computing in the future for specific
things

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adrianratnapala
What do they do for the nonlinear parts? I.e. the gates.

Is it all like Fourier transform where all the work is linear; or do they have
to convert it to electricity and then back to light?

If they do that, then do they gain anything over purely electronic solutions?

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partycoder
Reminds me of the infamous "sleep sort".

