6 ms·

Maybe something along the lines of "our brains would overheat" - there's a small temperature window in which proteins won't denature, it takes k T log 2 joules

by pizza 10y ago

Maybe something along the lines of "our brains would overheat" - there's a small temperature window in which proteins won't denature, 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. Maybe tin foil hats make good heatsinks.. Interestingly enough there is some evidence that the Gibbs free energy of ketone metabolism is more thermodynamically efficient than glucose in the brain (c.f. Dr. Richard Veech's work). You can measure a lower temperature gradient between the tongue temperature and the brain's. *edit: s/Beech/Veech..

midgetjones 10y ago
I was not expecting such a useful and interesting answer. Thanks!
taneq 10y ago
That's interesting indeed - is there any chance there's a connection between ketone metabolism being more efficient and 'hungry intelligence'? http://www.nytimes.com/2006/12/10/magazine/10section1C.t-1.html http://www.nytimes.com/2006/12/10/magazine/10section1C.t-1.h...
- Nomentatus 10y ago
  Note too that digestion is an extremely energy-intensive process, so that means less glucose to the brain (etc.) So much so that humans actually lose energy digesting raw meat.
pc86 10y ago
> 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?
- acqq 10y ago
  > 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 https://en.wikipedia.org/wiki/Landauer's_principle
  - pc86 10y ago
    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?
    - acqq 10y ago
      There is a relation but it is not too important in practice, which you'd find if you'd attempt to read what you avoided... twice. The theoretical information change limits are theoretical, in practice, there's always significantly more energy used, so 'pizza didn't even have to mention that limit in this case (although knowing that the limits exists is also important in considering what is possible and what simply is not). The wikipedia article you ignored shows that in the formula T is temperature in Kelvins, i.e. 310 K for a body temperature, and k is of order 1-e28. You get some small energy, log 2 is not relevant for the order of magnitude. Then you need to use time to get just the power in Watts, and which time should you use? Even looking at extreme processes: does killing somebody "erase" all the memory at once? Certainly not, as the processes in the brain are much more complex.... but the destruction of just a pieces of a brain makes it not functioning at all, like all complex systems, etc. And it the end it would be still not much relevant to hang to the formula for any known system, either developed by evolution or by humans. Also once you google the name of the limit you get a lot of articles, not just the one in Wikipedia. Ditto for the brain power usage.
- antognini 10y ago
  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.)
Xophmeister 10y ago
Doesn't that imply that people who live in hotter climates have...how can I put this politely?...a disadvantage when it comes to the stability of their brains? I would assume that the brain has a certain amount of redundancy, but has this ever been researched: How hot can it get before people start getting noticeably "stupider"?
- pavel_lishin 10y ago
  Our bodies can cool themselves decently well by sweating. I think that if the climate was affecting you to the point where your brain was getting cooked, the symptom would probably be less "slightly dumber" and more "seizures and organ failure". But I'm not a doctor or a scientist, so I could be completely wrong. Hopefully someone more informed will weigh in.
  - monocasa 10y ago
    It'd make sense that there would be a mechanism for graceful degradation, no?
    - pavel_lishin 10y ago
      I think that sweating profusely and feeling thirsty is the graceful degradation. I don't think there's a way to gracefully degrade from "my brain is a burger patty now".
  - kalendae 10y ago
    When diving to 90ft+ you get 'stupider' (nitrogen narcosis). Our instructor had us do simple math problems on a board underwater and timed us. We were doing them very very slowly but you don't feel that it is slower. It was an interesting experience meant to warn you that you won't realize that you are affected by nitrogen narcosis.
    - nojvek 10y ago
      I've been there. It feels so good, you forget things and get unfocused
adrianN 10y ago
Blood seems to be a pretty decent cooling agent. Our muscles can generate a lot more waste heat and we manage to get rid of it.
- cr0sh 10y ago
  It's probably not so much the blood as a whole, but rather the water in it (in fact, I would expect the other parts in blood would make the water less efficient for heat carrying capacity - but they also may have other advantages to that end).
  - lotyrin 10y ago
    Interesting to imagine this difference as a species which has evolved distinct specialized circulatory systems for cooling and for oxygenating tissues.
ajkjk 10y ago
That hardly seems relevant. kT log 2 joules is something like 10^-7 times the energy of an electron. I seriously doubt that that is anything but negligible compared to the other operations brains are performing.
- mickronome 10y ago
  Did an estimate a couple of years ago that the brains estimated information processinh and the cost of 'erasing' the same amount of information under the assumption that all processed information is lost, it seemed to imply that the cost of forgetting is somewhere in the range 1/1000 of the amount of energy the actual information processing is thought to consume ( approx 8W ) It seems crazy that it can be that close given the miniscule energy information carries, to me those ~8mW is completely mind boggling big. The most reasonable explanation is that my calculation was wrong, but at the time it did not appear to be the case, although it probablys is anyway :)

by pizza 10y ago

midgetjones 10y ago

I was not expecting such a useful and interesting answer. Thanks!

taneq 10y ago

That's interesting indeed - is there any chance there's a connection between ketone metabolism being more efficient and 'hungry intelligence'? http://www.nytimes.com/2006/12/10/magazine/10section1C.t-1.html http://www.nytimes.com/2006/12/10/magazine/10section1C.t-1.h...

Nomentatus 10y ago
Note too that digestion is an extremely energy-intensive process, so that means less glucose to the brain (etc.) So much so that humans actually lose energy digesting raw meat.

pc86 10y ago

> 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?

acqq 10y ago
> 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 https://en.wikipedia.org/wiki/Landauer's_principle
- pc86 10y ago
  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?
  - acqq 10y ago
    There is a relation but it is not too important in practice, which you'd find if you'd attempt to read what you avoided... twice. The theoretical information change limits are theoretical, in practice, there's always significantly more energy used, so 'pizza didn't even have to mention that limit in this case (although knowing that the limits exists is also important in considering what is possible and what simply is not). The wikipedia article you ignored shows that in the formula T is temperature in Kelvins, i.e. 310 K for a body temperature, and k is of order 1-e28. You get some small energy, log 2 is not relevant for the order of magnitude. Then you need to use time to get just the power in Watts, and which time should you use? Even looking at extreme processes: does killing somebody "erase" all the memory at once? Certainly not, as the processes in the brain are much more complex.... but the destruction of just a pieces of a brain makes it not functioning at all, like all complex systems, etc. And it the end it would be still not much relevant to hang to the formula for any known system, either developed by evolution or by humans. Also once you google the name of the limit you get a lot of articles, not just the one in Wikipedia. Ditto for the brain power usage.
antognini 10y ago
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.)

Xophmeister 10y ago

Doesn't that imply that people who live in hotter climates have...how can I put this politely?...a disadvantage when it comes to the stability of their brains? I would assume that the brain has a certain amount of redundancy, but has this ever been researched: How hot can it get before people start getting noticeably "stupider"?

pavel_lishin 10y ago
Our bodies can cool themselves decently well by sweating. I think that if the climate was affecting you to the point where your brain was getting cooked, the symptom would probably be less "slightly dumber" and more "seizures and organ failure". But I'm not a doctor or a scientist, so I could be completely wrong. Hopefully someone more informed will weigh in.
- monocasa 10y ago
  It'd make sense that there would be a mechanism for graceful degradation, no?
  - pavel_lishin 10y ago
    I think that sweating profusely and feeling thirsty is the graceful degradation. I don't think there's a way to gracefully degrade from "my brain is a burger patty now".
- kalendae 10y ago
  When diving to 90ft+ you get 'stupider' (nitrogen narcosis). Our instructor had us do simple math problems on a board underwater and timed us. We were doing them very very slowly but you don't feel that it is slower. It was an interesting experience meant to warn you that you won't realize that you are affected by nitrogen narcosis.
  - nojvek 10y ago
    I've been there. It feels so good, you forget things and get unfocused

adrianN 10y ago

Blood seems to be a pretty decent cooling agent. Our muscles can generate a lot more waste heat and we manage to get rid of it.

cr0sh 10y ago
It's probably not so much the blood as a whole, but rather the water in it (in fact, I would expect the other parts in blood would make the water less efficient for heat carrying capacity - but they also may have other advantages to that end).
- lotyrin 10y ago
  Interesting to imagine this difference as a species which has evolved distinct specialized circulatory systems for cooling and for oxygenating tissues.

ajkjk 10y ago

That hardly seems relevant. kT log 2 joules is something like 10^-7 times the energy of an electron. I seriously doubt that that is anything but negligible compared to the other operations brains are performing.

mickronome 10y ago
Did an estimate a couple of years ago that the brains estimated information processinh and the cost of 'erasing' the same amount of information under the assumption that all processed information is lost, it seemed to imply that the cost of forgetting is somewhere in the range 1/1000 of the amount of energy the actual information processing is thought to consume ( approx 8W ) It seems crazy that it can be that close given the miniscule energy information carries, to me those ~8mW is completely mind boggling big. The most reasonable explanation is that my calculation was wrong, but at the time it did not appear to be the case, although it probablys is anyway :)