4 ms·

Not a physicist so I'm probably getting different concepts mixed up, but maybe someone could explain: > in principle, energy is not gained or lost from the sys

Not a physicist so I'm probably getting different concepts mixed up, but maybe someone could explain: > in principle, energy is not gained or lost from the system during the computing process Landauer's principle (from Wikipedia): > any logically irreversible manipulation of information, such as the erasure of a bit or the merging of two computation paths, must be accompanied by a corresponding entropy increase in non-information-bearing degrees of freedom of the information-processing apparatus or its environment Where is this information going, inside of the processor, if it's not turned into heat?

abdullahkhalids 6y ago
If your computational gates are reversible [1], then in principle, energy is not converted to heat during the computational process, only interconverted between other forms. So, in principle, when you reverse the computation, you recover the entire energy you input into the system. However, in order to read out the output of computation, or to clear your register to prepare for new computation, you do generate heat energy and that is Landauer's principle. In other words, you can run a reversible computer back and forth and do as many computations as you want (imagine a perfect ball bouncing in a frictionless environment), as long as you don't read out the results of your computation. [1] NOT gate is reversible, and you can create reversible versions of AND and OR by adding some wires to store the input.
aqme28 6y ago
I was curious about this too. This chip is using adiabatic computing, which means your computations are reversible and therefore don't necessarily generate heat. I'm having trouble interpreting what exactly that means though.
- patagurbon 6y ago
  But you have to save lots of undesirable info in order to maintain the reversibility right? Once you delete that don't you lose the efficiency gains?
  - jlokier 6y ago
    You don't need to delete the extra info. After reading the output, you run the entire computation backwards (it's reversible after all) until the only state in the system is the original input and initial state. Then you can change the input to do another calculation. If implemented "perfectly", heat is produced when changing the input and to read the output. Reading the output will disturb it so the computation won't perfectly reverse in practice, however if the disturbance is small, most of the energy temporarily held in circuit is supposed to bounce back to the initial state, which can then be reset properly at an appropriately small cost. Quantum computation is very similar to all of this. It too is reversible, and costs energy to set inputs, read outputs and clear accumulated noise/errors. The connection between reversible computation and quantum computation is quite deep.
ladberg 6y ago
It's still getting turned into heat, just much less of it. The theoretical entropy increase required to run a computer is WAY less than current computers (and probably even the one in the article) generate so there is a lot of room to improve.

abdullahkhalids 6y ago

If your computational gates are reversible [1], then in principle, energy is not converted to heat during the computational process, only interconverted between other forms. So, in principle, when you reverse the computation, you recover the entire energy you input into the system. However, in order to read out the output of computation, or to clear your register to prepare for new computation, you do generate heat energy and that is Landauer's principle. In other words, you can run a reversible computer back and forth and do as many computations as you want (imagine a perfect ball bouncing in a frictionless environment), as long as you don't read out the results of your computation. [1] NOT gate is reversible, and you can create reversible versions of AND and OR by adding some wires to store the input.

aqme28 6y ago

I was curious about this too. This chip is using adiabatic computing, which means your computations are reversible and therefore don't necessarily generate heat. I'm having trouble interpreting what exactly that means though.

patagurbon 6y ago
But you have to save lots of undesirable info in order to maintain the reversibility right? Once you delete that don't you lose the efficiency gains?
- jlokier 6y ago
  You don't need to delete the extra info. After reading the output, you run the entire computation backwards (it's reversible after all) until the only state in the system is the original input and initial state. Then you can change the input to do another calculation. If implemented "perfectly", heat is produced when changing the input and to read the output. Reading the output will disturb it so the computation won't perfectly reverse in practice, however if the disturbance is small, most of the energy temporarily held in circuit is supposed to bounce back to the initial state, which can then be reset properly at an appropriately small cost. Quantum computation is very similar to all of this. It too is reversible, and costs energy to set inputs, read outputs and clear accumulated noise/errors. The connection between reversible computation and quantum computation is quite deep.

ladberg 6y ago

It's still getting turned into heat, just much less of it. The theoretical entropy increase required to run a computer is WAY less than current computers (and probably even the one in the article) generate so there is a lot of room to improve.