6 ms·

Mind expanding on this a bit more? What is that that limit and how does it relate to the clock speed?

the8472 6y ago
https://en.wikipedia.org/wiki/Landauer%27s_principle https://en.wikipedia.org/wiki/Landauer%27s_principle Note that the gates themselves used here are reversible, so the limit shouldn't apply to them. But the circuits built from them them aren't reversible as far as I can see in the paper, so it would still apply to the overall computation.
Enginerrrd 6y ago
It's not about clock speed per se. It's about the lowest possible energy expenditure to erase one bit of information (or irreversibly destroy it by performing a logical operation). The principle comes about from reasoning about entropy loss in said situations. There's a hypothesized fundamental connection between information and entropy manifest in physical law. The idea is that if you destroy one possible state of a system, you have reduced the entropy of that system, so the 2nd law of thermodynamics implies that you must increase the entropy of the universe somewhere else by at least that amount. This can be used to say how much energy the process must take as soon as you choose a particular temperature. This applies to any irreversible computation. IMO, The fact that it's only 38x the minimum is MIND BLOWING.
- jcims 6y ago
  Is there an idea of entropic potential energy/gradient/pressure? Could you differentiate encrypted data from noise by testing how much energy it requires to flip a bit?
  - kmeisthax 6y ago
    Only if you were measuring a system with access to the key material and doing something with the plaintext, in which case this would be a side-channel attack (and an already-studied one). The whole point of encryption is that the data output is indistinguishable from noise without knowing the key.
  - Raidion 6y ago
    No, because the energy of the system isn't related to the order of the underlying data, it's related to the changes that happen to the underlying data. If you have 5 bits and flip 3, it takes the same energy regardless of if the 5 bits have meaning or not. This is speaking in terms of physics. There obviously could be some sort of practical side channel attack based on error checking times if this was an actual processor.
- ajuc 6y ago
  > IMO, The fact that it's only 38x the minimum is MIND BLOWING. It's like if someone made a car that drives at 1/38th the light speed.
  - yazaddaruvala 6y ago
    For anyone too lazy to math, its a car that can go: 28.4 million km per hour (i.e. 17.6 million miles per hour) I wonder how much that speeding ticket would cost. Disclaimer: Assuming the one-way speed of light is 300k km/s
    - TheRealNGenius 6y ago
      No need to assume when we can define ;p
      - bananabreakfast 6y ago
        I think they were alluding to the fact that it is impossible to measure the one-way speed of light, and even the definition is an assumption based on the two-way speed
        6nf 6y ago
        Since the one-way speed is impossible to measure can we just define it to be half of the two-way speed? There's no way to tell if that's correct or not but it makes no difference in any measurements you could make. So maybe for convenience we can just choose the one-way speed to be half the two way speed to simplify the calculations.
        triclops200 6y ago
        That's exactly what's done most of the time, but it should be noted that it's convention and assumption.
    - faeyanpiraat 6y ago
- centimeter 6y ago
  > The fact that it's only 38x the minimum is MIND BLOWING. It doesn't run at room temp. The difference is much larger than 38x. It's closer to 1000x.
  - the8472 6y ago
    The landauer limit is temperature-dependent. The difference was calculated for the system's operating temperature.
    - centimeter 6y ago
      > The landauer limit is temperature-dependent. No it's not. It's linearly dependent on temperature. The figure commonly stated is arbitrarily chosen to be at room temperature.
beefok 6y ago
This book goes into some great detail about this. :) https://www.amazon.com/dp/B004ZLS3TU/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1 https://www.amazon.com/dp/B004ZLS3TU/ref=dp-kindle-redirect?... I will always recommend it!

https://en.wikipedia.org/wiki/Landauer%27s_principle https://en.wikipedia.org/wiki/Landauer%27s_principle Note that the gates themselves used here are reversible, so the limit shouldn't apply to them. But the circuits built from them them aren't reversible as far as I can see in the paper, so it would still apply to the overall computation.

Enginerrrd 6y ago

It's not about clock speed per se. It's about the lowest possible energy expenditure to erase one bit of information (or irreversibly destroy it by performing a logical operation). The principle comes about from reasoning about entropy loss in said situations. There's a hypothesized fundamental connection between information and entropy manifest in physical law. The idea is that if you destroy one possible state of a system, you have reduced the entropy of that system, so the 2nd law of thermodynamics implies that you must increase the entropy of the universe somewhere else by at least that amount. This can be used to say how much energy the process must take as soon as you choose a particular temperature. This applies to any irreversible computation. IMO, The fact that it's only 38x the minimum is MIND BLOWING.

jcims 6y ago
Is there an idea of entropic potential energy/gradient/pressure? Could you differentiate encrypted data from noise by testing how much energy it requires to flip a bit?
- kmeisthax 6y ago
  Only if you were measuring a system with access to the key material and doing something with the plaintext, in which case this would be a side-channel attack (and an already-studied one). The whole point of encryption is that the data output is indistinguishable from noise without knowing the key.
- Raidion 6y ago
  No, because the energy of the system isn't related to the order of the underlying data, it's related to the changes that happen to the underlying data. If you have 5 bits and flip 3, it takes the same energy regardless of if the 5 bits have meaning or not. This is speaking in terms of physics. There obviously could be some sort of practical side channel attack based on error checking times if this was an actual processor.
ajuc 6y ago
> IMO, The fact that it's only 38x the minimum is MIND BLOWING. It's like if someone made a car that drives at 1/38th the light speed.
- yazaddaruvala 6y ago
  For anyone too lazy to math, its a car that can go: 28.4 million km per hour (i.e. 17.6 million miles per hour) I wonder how much that speeding ticket would cost. Disclaimer: Assuming the one-way speed of light is 300k km/s
  - TheRealNGenius 6y ago
    No need to assume when we can define ;p
    - bananabreakfast 6y ago
      I think they were alluding to the fact that it is impossible to measure the one-way speed of light, and even the definition is an assumption based on the two-way speed
      - 6nf 6y ago
        Since the one-way speed is impossible to measure can we just define it to be half of the two-way speed? There's no way to tell if that's correct or not but it makes no difference in any measurements you could make. So maybe for convenience we can just choose the one-way speed to be half the two way speed to simplify the calculations.
        triclops200 6y ago
        That's exactly what's done most of the time, but it should be noted that it's convention and assumption.
  - faeyanpiraat 6y ago
centimeter 6y ago
> The fact that it's only 38x the minimum is MIND BLOWING. It doesn't run at room temp. The difference is much larger than 38x. It's closer to 1000x.
- the8472 6y ago
  The landauer limit is temperature-dependent. The difference was calculated for the system's operating temperature.
  - centimeter 6y ago
    > The landauer limit is temperature-dependent. No it's not. It's linearly dependent on temperature. The figure commonly stated is arbitrarily chosen to be at room temperature.

beefok 6y ago

This book goes into some great detail about this. :) https://www.amazon.com/dp/B004ZLS3TU/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1 https://www.amazon.com/dp/B004ZLS3TU/ref=dp-kindle-redirect?... I will always recommend it!