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Comment by pc86 | Hacker News Reader

> it takes k T log 2 joules to erase one bit of information...and our brain uses around 20 Watts of power

Yet another time when my Political Science education fails me. What should I take away from this?

The brain has a fixed amount of energy it can use per second, and it takes a fixed amount of energy to erase one bit of information (which you can think of as performing a computation). This means that there are a limited number of computations that the brain can do in one second.

(I'll add that there's no need to make this argument from thermodynamic principles. Your brain has a finite number of neurons, and each neuron can only fire a few times a second, so that limits the number of computations that your brain can do per second as well. And that limit is a lot tighter than the thermodynamic limit.)

> What should I take away from this?

Just that you should not omit with "..." the most important part of the statement for you. You haven't studied physics. Then you see the formula and the textual name of it with the most probable entry in Wikipedia and then you throw the most useful bit for you away and ask what the formula without the name means, even though the name would give you an explanation.

pc86's quote:

> it takes k T log 2 joules to erase one bit of information...and our brain uses around 20 Watts of power

Original:

> it takes k T log 2 joules to erase one bit of information (Landauer's principle), and our brain uses around 20 Watts of power.

The explanation:

https://en.wikipedia.org/wiki/Landauer's_principle

I assumed there was some relation between k T log 2 joules and 20 Watts, probably giving some sort of context to how easily or not easily information in our brains could be lost. The theoretical principles behind the amount of energy required to erase one bit, while interesting, doesn't necessary matter for that relationship, does it?

Landauer's principle would come into effect if you had a theoretical "Computorium" material that could perfectly turn energy into computation. Then the computation you could produce per volume of space would be limited by it.

Our brains are (very) far from being the perfect computing material (so are our chips).

The theoretical minimum is only useful here to show that our brains cannot do free work. (Irreversible) computation always has a cost.

The 20 Watts are the important number. Our brains have a certain energy budget and have to perform within that constrain.

the log 2 comes from Shannon coding, because information (tm) encoding is modeled on a bit string of discrete energetic states (something quantum, too, I guess). And there is a transformation to the frequency domain (ie via discrete fourier transform). Entropy is always messured in Watt, doesn't. make sense to equate psychologic information content with physiologic enthropic consumption.

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