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The most interesting thing in this article is the reference to "Ultimate physical limits to computation." It's something I never thought about before and hones

• dschobel 16y ago
  Agreed. Unfortunately the Nature article is behind a paywall but the original paper is available on arxiv: http://arxiv.org/abs/quant-ph/9908043 http://arxiv.org/abs/quant-ph/9908043
  • foco1234 16y ago
    I've read the intro. of the paper, but I'm not a physicist, so this question might seem dumb, but here goes: The paper describes the "ultimate laptop" as being a computer that can use one atom to store 1 bit of information. Why is an atom the smallest unit of matter a computer can store a bit in?
    • gwern 16y ago
      Does Lloyd actually say that? IIRC, he simply reuses the Bekenstein bound: https://secure.wikimedia.org/wikipedia/en/wiki/Bekenstein_bound https://secure.wikimedia.org/wikipedia/en/wiki/Bekenstein_bo... Which is more than 1 bit per atom. (It does seem implausible for 1 bit per atom to be right. I mean, atoms themselves vary in hundreds of ways - # of protons, # of electrons, etc. Just using each element to represent a byte would seem to get you more than 1 bit per atom.)
      • mbreese 16y ago
        But they also vary in size significantly, so it wouldn't be practical to store 8 different types of atoms. I think adjusting the spin state of one atom for one bit might be the limit.
        • jerf 16y ago
          This is a discussion of the theoretical limits. They may be substantially higher than the actual engineering limits we can attain with real configuration of real atoms. (Or relevant other building blocks as appropriate.) However, the theoretical limits turn out not be entirely useless even if we can never attain them in practice; they offer some insight about the nature of the universe, and it may yet be some thoughts on how the universe can process information that cracks open the problem of what happens in black holes, rather than what you might think of as conventional physics. There's been a lot of interesting work done in that area; for instance, read http://en.wikipedia.org/wiki/Holographic_principle http://en.wikipedia.org/wiki/Holographic_principle and observe how many times the word "information" comes up.
• sammcd 16y ago
  A proffessor once told me never to believe the physical limits. He mentioned how a wavelength of light was the smallest we could etch silicon. He then mentioned that today (at the time of the class) we were etching with 1/20th the wavelength of light. He then said that he could not explain how the new 1/20th of of a wavelength drawing works because new physics had been learned, and it had not been in his physics book.
  • wcoenen 16y ago
    Well, for practical purposes the wavelength of light doesn't really have a lower limit. If the wavelength of visible light isn't small enough, you use ultraviolet. If you need smaller wavelengths still, you could use gamma lasers - though so far these are only possible in theory. There is some speculation that positron annihilation could be used to drive such a laser. edit: looks I was wrong - while ultraviolet lasers exist, the currently available ones still don't have a small enough wavelength for say a 45 nm process. Other tricks like multiple patterning and immersion are used.
  • jessriedel 16y ago
    Your sentiment is healthy, but you should distinguish between "we don't know of a way to do X" and "X is impossible under the current laws of physics". The former is like etching sub-wavelength silicon. The latter is like moving faster than the speed of light. > new physics had been learned, and it had not been in his physics book. Again, there is a difference between learning new techniques and phenomena running on top of known physical law, and learning new fundamental laws. When engineers say "new physics", they refer to the former, but when physicists say "new physics", they refer to the latter. And there hasn't been any new physics, more or less, since the 60's. The computational limits are thought to be encoded in the fundamental laws, in a way very analogous to the limiting speed c.
    • suraj 16y ago
      My brain is probably addled by reading a lot of science fiction. But here are my thoughts on the matter. We know of two ways in which energy is manifested in stable form. The matter particles and the force carrying particles. Recent astronomical observations point to a third form i.e. dark matter. So hopefully in future we may uncover (or device) yet another form of energy which would find 128bits on a low side.
• jodrellblank 16y ago
  See also: http://en.wikipedia.org/wiki/Computronium http://en.wikipedia.org/wiki/Computronium
• anon114 16y ago
  I'll just leave this here: http://en.wikipedia.org/wiki/Matrioshka_brain http://en.wikipedia.org/wiki/Matrioshka_brain
  • runjake 16y ago
    Reddit memes usually aren't kosher around here.
    • Dn_Ab 16y ago
      I dont read reddit much so that concept has a much more positive association for me since it brings to mind Accelerado and the crazy economics 2.0 with its sentient corporations using humans as currency and crazy intelligent 419 scams.
      • natep 16y ago
        You're talking about the content of anon114's link, but what was reddit-like about his comment was the formulaic "I'll just leave this here: <link>" which doesn't contribute as much to the discussion as the comments that do get upvoted.
• Dylan16807 16y ago
  The problem is that it's a poor reference for storage. It's focused on maximum computation in a certain chunk of matter, which is a massive waste of energy. One of the comments on the blog talks about charging individual electrons at five orders of magnitude less energy, at the cost of much more mass. It might be possible to optimize this down to a lake-sized level of storage mass and boiling energy.