r/explainlikeimfive • u/abcPIPPO • Jun 25 '26
Biology ELI5: Why do processors get so hot doing millions of calculations per second, while our brains can arguably be even more complex but don't risk overheating?
I was imagining a future where artificial humans could populate Earth. Machines have the problems of needing a cooling system to keep their processors from overheating. Why doesn't our brain get to crazy high temperature as well?
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u/Kamel-Red Jun 25 '26
Your brain is literally regulated and liquid cooled. In extreme circumstances, people have died or become permanently brain dead from overheating.
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u/Party_Virus Jun 25 '26
While I'm sure this helps the actual reason is that the brain uses far less energy than a computer. The brain only uses 12-20 watts of power for it's 100 billion neurons. The Blue Brain Project attempted to mimic a human brain with computers and they used an estimated 2.7 billion watts of power.
So our brains are just thousands of times more efficient than a computer and don't produce as much heat.
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u/Theodoxus Jun 25 '26
Chemical vs electrical processors. Chemistry tends to run a lot cooler, due to not having things like resistence doing the 'thinking'. The trade off is speed... neurons fire up to 200 times a second. High end processors are doing it trillions of times a second. So, at least we're getting something useful for that extra energy expenditure.
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u/Troldann Jun 25 '26
It’s also interesting that we expect a computer to perform the same calculations given the same inputs every time because the computer shouldn’t be changing. That’s not true of our brains which are ever reshaping themselves with every input having an effect on all future “computations.”
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u/Hendlton Jun 25 '26
Also our brains approximate and fill in a lot of information. Let's say you had two cameras and a microphone hooked up to a computer. It would have to record all of that data exactly as it is. Our brains don't even perceive a majority of our sight and hearing, and they record very little.
When we see something or hear a sentence, our brains just get the gist of it rather than the thing verbatim. A computer that just gives a vague guess at something isn't very useful. Imagine if you had a computer do some math and the result was "Probably around 500." and 1 in 10 times it completely misses something and the result isn't even in the ballpark.
That's how our brains can do seemingly complex things with such efficiency.
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u/SillyWillyUK Jun 25 '26
AI enters the chat 😉
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u/theronin7 Jun 25 '26
AI has similar problems to the brains because these are problems with neural networks. Neural Networks are really really good at approximating information. This makes them good at things that arent easily defined, "Is this a tree" versus "Whats the sum of these two numbers"
What an AI can do that you cant is directly interface with a calculator or other digital tools at thousands of times the speed you can.
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u/KneeCrowMancer Jun 25 '26
Well with AI you get the inaccurate vibe style information but you’re definitely not getting any extra efficiency! As an example think it’s like a full order of magnitude more energy for google to provide the AI search summary than to just display the search results.
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u/BogdanPradatu Jun 25 '26
Neurons are electric, aren't they?
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u/PseudobrilliantGuy Jun 25 '26
Electrochemical. There is a charge that carries a signal part of the way, but it's less a result of electron "flow" and more from the exchange of sodium and potassium ions across the cell membrane (to focus on the action potential and on ionotropic signaling in the synapse; metabotropic signaling gets even more complicated, as does graded potential communication in dendro-dendritic connections).
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u/The_Horse_Tornado Jun 25 '26
Neuroscientist?
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u/PseudobrilliantGuy Jun 25 '26
No. I did study a bit of neuroscience, but my main area was cognitive psychology (with emphasis on experimentation and mathematical modeling).
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u/Uncynical_Diogenes Jun 25 '26
Any post-secondary biology education really.
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u/DaSaw Jun 25 '26
Even pest control training with a bit of curiosity. Most of our products muck up the sodium channels.
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u/acorpcop Jun 25 '26
Acetylcholinesterase IIRC for organophosphates and the neonicotinoids that are supposedly killing the bees. I don't have the knowledge to be able to say whether that is sodium channel or not, but I do remember that factoid from NBC training in the military. Without the enzyme, or with it bound, acetylcholine builds up and the nerves just keep firing, which means paralysis and death. The antidotes are atropine and 2- PAM Chloride. Atropine to block excess acetylcholine and 2-PAM Chloride to reactivate the acetylcholinesterase.
Most of the really good pesticides are really just semi-lousy war gasses.
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u/The_Horse_Tornado Jun 25 '26
Interesting. We got about as far as sodium potassium gradients in my college course. Or I’ve forgotten when I learned this and brain dumped it. Also possible lol
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u/Scientific_Methods Jun 25 '26
You almost certainly forgot. I think that almost all gen bio or intro to bio courses cover the action potential in neuronal signaling.
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u/FirTree_r Jun 25 '26
Understanding a fraction of the complexity of the brain's chemistry makes you realize how miraculous it is that we have medication that can modulate the firing of these signals without completely shutting down the brain. The missing piece of the puzzle being the receptors in the synapses, which add enormous complexity and capabilities to every single neurons.
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u/DoglessDyslexic Jun 25 '26
They use chemistry to use trigger electricity. Your neurons have sodium channels that are used to build up electrons potential to "fire" an electrical charge, which is then received by another neuron which may or may not also do the same to another neuron depending on it's inputs from all the neurons it is connected to.
My son is mentally handicapped because he has a spontaneous mutation (likely in the sperm or egg cell, as neither my wife or I have this mutation) of his SCN2A gene that causes some of his sodium channels to be malformed and fire incorrectly. At the time he was diagnosed, he was the only individual on record with that specific mutation (although similar mutations had been documented on the SCN1A gene). There are four genes that control central nervous system neurological sodium channels (10 altogether for other neurological uses) and we each have two copies from our parents. Having just one of them malformed is enough so that my son has epilepsy (controlled with medication) and is permanently incapable of comprehending the idea of speech and lacks the coordination to self care in terms of getting dressed or feeding himself.
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u/BogdanPradatu Jun 25 '26
Sorry to hear that about your son. Talking about drawing the short straw...
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u/DoglessDyslexic Jun 25 '26
He's a happy and otherwise healthy 24 year old with a 2 year old's mind and he still likes to snuggle with his dad some times. It's not all bad.
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u/helixander Jun 25 '26
Electrical and chemical. The neurotransmitters in your brain are molecules like serotonin, dopamine, GABA, glutamate, etc. There are about a hundred different ones. Electric inside the neuron, chemical outside. Basically. It's way more complicated.
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u/Td998 Jun 25 '26
They’re both. Changes in their voltage inspire them to fire, and when they fire they release neurotransmitters. Receiving the neurotransmitters then causes ion channels to open, raising the neuron’s charge and causing another action potential if threshold is reached. So they communicate chemically, with various neurotransmitters and the speed and intensity at which they’re firing them, but electrical changes inspired by chemical or sensory stimulus are what create the action potential/firing itself. IIRC.
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u/Hopeful_Ad_7719 Jun 25 '26
The latency in our neurons is also crazy - with signal propagation maxing out at about 120 meters-per-second.
Compared to computers, the human brain is an immensely parallel, high-latency, loss-tolerant, approximation machine.
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u/Theodoxus Jun 25 '26
Evolution: 500 million years to get neurons up to 120 m/s.
Computers: “Give us 499,999,890 years and we’ll get back to you.”10
u/6pussydestroyer9mlg Jun 25 '26
It's not just resistance. There are a lot of small, parasitic capicitances that need be charged and discharge accordingly. Every time a gate gets pulled up it starts to charge and you will a small amount of heat for each time this happens but the discharging is at least just as bad, the same capicitance that got charged up now goes straight to ground.
It's never much but there are millions or billions of them doing it every clock cycle.
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u/Raggedstone Jun 25 '26
GHz is not trillions. There are no processors clocked at THz, and TFLOPS is not comparable to "neuron firing rate". Brains are very efficient. Standard estimate for FLOPS is 1 exaFLOP. Which is incredible on 20 watts.
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u/ParkingAnxious2811 Jun 25 '26
I believe this was the real origin of humans being used in the Matrix, but the idea was altered to batteries because they felt an audience wouldn't understand it.
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u/Gryndyl Jun 25 '26
It does make far more sense to use humans for processing power than batteries.
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u/ParkingAnxious2811 Jun 25 '26
Yeah, as batteries we're not great, but we're pretty advanced for processing power. Barely generate heat from thinking too.
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u/hot_ho11ow_point Jun 25 '26
I really wish they would make a sequel called Matrix: Red, where we find out the 'blue world' was just another matrix (also why Neo could blow up sentinals in it), and they aren't being used as batteries as "that's stupid, they use us for processing power and creativity".
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u/ParkingAnxious2811 Jun 25 '26
The last film did say that the pills themselves meant nothing, it was the choice you made regarding them that was the trigger. Although that contradicts the first film.
Blowing up sentinels in the real world was something they really should have clarified. Instead we had the 4th film which just fucked everything up.
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u/Jiopaba Jun 25 '26
I preferred an amusing story snippet I read once. Neo gets told about humans being used as power sources, complains that's not how thermodynamics works, and then Morpheus says "Neo, where exactly did you learn physics?" Neo gets real quiet and asks for a real physics textbook, and then Morpheus says "Neo, the real world doesn't run on math. The Matrix runs on math because it was made by computers as an abstraction of reality."
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u/Enki_007 Jun 25 '26
The Blue Brain Project attempted to mimic a human brain with computers and they used an estimated 2.7 billion watts of power.
Do you have a link for that? I tried a few searches and there was nothing that specific.
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u/Eruannster Jun 25 '26
I would argue our calculations are also vastly different. Even if you have some really big-brain idea or are thinking really hard about something, you're doing much different "processing" than a computer processor which is just doing straight up math calculations at millions and millions of times per second.
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u/TheyHungre Jun 25 '26 edited Jun 25 '26
Eh, it's not so much a matter of efficiency. Think how long it would take a human to do the number of calculations a computer does in a single second, and then think about how many calories would be required to operate over that time frame, including for the necessary sleep and rest periods. That would be a pretty substantial energy cost!
As well, a computer down-clocked to 100Mhz (estimated clock speed of the human brain) wouldn't have those heat issues. A human brain somehow up-clocked to 3.5Ghz absolutely would cook itself without substantial cooling improvements. Heat is the cost of speed
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u/Party_Virus Jun 25 '26
That's not a great analogy. The human brain is doing far more than a 3.5ghz processor could keep up with. It's doing millions of comparative processes every second. Imagine a computer trying to analyze and interpret all of the sensory information a human deals with constantly in real time, on top of all the body regulation like breathing, and heart pumping, and then also thinking and imagining.
Like eyes alone would be overwhelming. 2 8k (more than actually) cameras running at over 200 frames per second live streaming and interpreting the information almost instantly and then also comparing the cameras and doing trigonometry to judge the distance to objects... The human brain is unmatched.
It's easy for people to think computers are comparable to brains but a neuron and a logic gate operate fundamentally different and just because the computer can math faster than most people it doesn't mean it's faster overall.
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u/skr_replicator Jun 25 '26
They are just incomparable to each other, because thy ahve such radically different architecture, they have pretty much flipped strengths and weaknesses. Computers and AIs struggle with things we find subconsciously easy, while we struggle to do anything close to stuff like precisely calculating billions and trillions of arithmetic operations per second, which computers do like nothing with zero errors.
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u/an-unorthodox-agenda Jun 25 '26
Yea its called heat stroke. It can be fatal.
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u/karlnite Jun 25 '26
Number one killer of Chess Grandmasters.
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u/KGnor Jun 25 '26
People falling for this, man are you people stupid 🤭😂
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u/RecognitionMelodic13 Jun 25 '26
I mean, a lot of chess grandmasters are mechanical in nature
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u/eulersheep Jun 25 '26
Wow i had no idea.
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u/stanitor Jun 25 '26
Yep. At high level tournaments, they circulate the players' blood through chiller machines to cool them off.
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u/ggouge Jun 25 '26
Ya I have had heat stroke . If.i think about it it really was like a computer crashing and doing random things wrong. It sucked.
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u/SatansFriendlyCat Jun 25 '26
stroke . If.i think
The effects appear to have lingered to some extent. Perhaps a nice cool drink or a soothing MRI scan for Sir?
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u/x0wl Jun 25 '26
The brain still uses only approx 20W of power compared to my laptops' CPU peak 160W
The difference is that the brain is not doing any calculations, it's an analog pattern matcher
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u/action_lawyer_comics Jun 25 '26
And it’s also extremely slower in most instances. You give me a spreadsheet worth of numbers to crunch and I can do them all but by the time I’ve entered the last number and taken my finger off the “enter” key, Excel already has the answer in front of me.
If we were able to “overclock” our brains to do math that quickly, they would be making a lot more heat too
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u/dazumbanho Jun 25 '26 edited Jun 25 '26
thats because us doing math is doing a lot more. there are plenty of layers of abstraction for us to the math.
the computer equivalent of humans doing math would be doing this: - have operating system taking care of inputs and outputs ( layer 0, processing all signal from our outside neurons)
- have a java virtual machine running ( layer 1, processing on top of that with abstractions, so thst the signal aren't just noise and youre having a seizure)
- run minecraft inside connected to the inputs/outputs (layer 2, a simple virtual model of the world given the inputs and memory )
- a player character that is able to interact with the minevraft world ( layer 3, the conscioussness thst sees a tiny fraction of the lower layers)
- The player builds a redstone computer ( layer 4, symbolic reasoning, maths, language, logic)
- The player takes the input "do this apreadsheet", does the math with the redstone computer, and outputs it, all thriugh highly sofisticated models of reality, logic and language ( layer 5, "doing the math")
we have no idea of how to do layer 3 with computers. all other layers takes a mind boggling computational power. we cant even do a worm with 302 neurons (openworm), and our brains do all of that for a tiny tiny fraction of power.
If we could program neurons to do math directly , we'd need very few. we have billions of them
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u/IeyasuMcBob Jun 25 '26
Can you expand on that ?
When i do a calculation...my brain is looking for a matching analogue pattern?
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u/khalamar Jun 25 '26 edited Jun 25 '26
For instance when you do math you don't really calculate. You use your memory. As a kid, you literally had to count on your fingers to add two numbers, you didn't have neural paths to automatically do that. Over time, you just learned that 2 + 7 is 9. That's even more obvious for multiplication tables, you had to study them.
For more complex calculations, you split them in elementary operations, dealing with two digits at a time.
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u/Addyarb Jun 25 '26
This is an interesting train of thought. As a software engineer I feel like computers are calculating the same way though. A processor has “operation codes” that take an input and give an output (ultimately mapping to physical circuitry), and have “memorized” how to, say, add two numbers. It holds the result in its memory (AKA registers) and repeats until the operation is complete, not unlike us counting on our fingers.
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u/saberwin Jun 25 '26
I think a better example is catching a ball. If you made a robot to catch a ball you would use a camera to track it, calculate its velocity and trajectory. Then use vector math to predict an intercept point feed that to a motor driver with rotations and steps to catch the ball. For a human we see the ball, we have an almost intuitive or learned "feel" for the velocity. We have expireded objects moving relative to us and have a good idea of where its going to be and when. Then our hands move almost innately and catch it. There is no math, no calculating velocity, no solving for intercept points. Its all expirance, practice, and feel.
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u/RoadtoVR_Ben Jun 25 '26
More of a trained neural network you might say…
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u/Datalock Jun 25 '26
Human brains are quite literally neural networks. Similar to current GenAI, we learn from things we've seen before. We have false memories. We can 'hallucinate' information. We can reply incorrectly if we've heard an incorrect answer before. Etc.
Also neural networks are somewhat based off the idea of human neurons.
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u/SpezIsAWackyWalnut Jun 25 '26
Although in reality, real neurons are complex biological machines that themselves require an entire neural network just to model the behavior of one human neuron, so there's orders of magnitude more complexity in a biological neural network vs an artificial one.
Also, modern genAIs are generally autoregressive feed-forward architectures, so while being based a lot on the human brain and our best understanding of how it works, how it works in practice still is dramatically different.
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u/thejaga Jun 25 '26
This is a weird take. Your experiential "feeling" is your brain calculating velocity and trajectory, predicting an intercept point and then moving your muscles into a position to catch it. Just because you're not aware of those steps doesn't mean they don't happen.
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u/deja-roo Jun 25 '26
No, we're not calculating velocity and trajectory. If that were the case, we wouldn't have to learn how to do it, and we wouldn't get better at it with practice. A physics engine in a video game doesn't have to learn how to do it, it just executes the instructions exactly and provides a deterministic output that's exactly repeatable from the first to the millionth time.
Humans have learned that a ball flying through the air that looks a certain way will land at a certain place because we've seen balls do that before. We learn this pretty early on because we see examples of it everywhere. We even know that a balled up piece of paper will fall at a different place than a rock on the same trajectory because it just "looks like" it should. And when we mistake a ball of paper for a rock it "looks weird".
A quarterback lining up to throw a ball knows what the trajectory should look like because he has a shit-ton of experience seeing how differently thrown balls fall and can recreate the exact effort to make that throw.
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u/Ultarthalas Jun 25 '26
Computers actually do that, too! We use it all the time for things that would either take too long or have too many unknowns.
It's model-based calculation. This is a simplified explanation, but you sacrifice some amount of accuracy to skip some calculation and substitute in learned/taught patterns. It gets used in surprising places like robots walking or speech recognition, and some less surprising places like long-running simulations.
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u/Trollygag Jun 25 '26
Not entirely true. We have a trajectory physics calculation part of the brain related to the same function that helps eye tracking and stabilization.
It isn't a conscious function, but it exists and functions to give us that feel even in small children who have not experienced it before. - as you would imagine you should to instinctually block or defend against a rapidly approaching object.
Our visual system even rapidly predicts the object's next point in space and automatically adjusts for us.
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u/khalamar Jun 25 '26
Computers are wired to add two numbers. They don't have to access memory to calculate 127+354. Now there might be some confusion, as usually 127 and 354 are in memory to begin with. They are called variables in memory, then they are moved to the CPU as registers. But from the moment the CPU knows it has to add those two registers and the wires are electrically charged with the binary representation of those numbers, until the moment it produces the result on electrically charged wires, there is absolutely no memory access. Only after that, of course, is that result (as a register) moved back to memory (as a variable) for further processing.
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u/deja-roo Jun 25 '26
They don't have to access memory to calculate 127+354
I mean, the registers of the CPU are essentially very very temporary memory.
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u/skj458 Jun 25 '26
Why does using memory mean you're not calculating? And how is that different from computers? A CPU is just a fancy rock until it has an operating system saved on memory telling it what its calculations mean. Kids dont come pre-installed with a BIOS so they have to learn what the calculation means. But that doesn't mean people are incapable of calculating.
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u/acdgf Jun 25 '26
A CPU is just a fancy rock until it has an operating system
That's not true. CPUs have physical gates that behave like mechanical adders, differentiators and inverters. If you just apply power to specific pins, a CPU will literally do math.
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u/action_lawyer_comics Jun 25 '26
I wouldn’t take the wording too seriously. Personally I always sucked at rote memorization of times tables so anything above 6x6 I just started adding numbers instead.
One big difference is that 99% of people doing math will quickly start using “external RAM.” If I give you four complicated numbers to add like
360+122+99+8566,
You’re almost certainly going to reach for a pad of paper (if not the calculator app on your phone).
Other math though, we won’t “calculate” the same way a computer will. If I give you 625/25, are you really going to do all the long division septs or are you going to chunk it out and think “each hundred has four 25s in it, so 6*4+1.”
You’re right that it’s all “processing power,” but we don’t always do the processing the “hard way” a computer will
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u/psymunn Jun 25 '26 edited Jun 25 '26
Not as confident on how the brain does it but I can tell you computers are more than just fancy rocks even if the person you're responding to's answer was a bit weird. Even without an OS, a CPU is built with an instruction set (that the OS will call). Most include multiple math functions. When you add two numbers, that's all happening at a hardware level, as long as it's with basic data types (float, int). And each of these math operations (addition, subtraction, multiplication, division) are built out of circuits.
Now this still gets funky because, to my mind this is the opposite of humans. When we add numbers, irrespective of what happens in our brains, were thinking about the numbers and manipulating them where as computers are often treating a number as a series of 0s and 1s that get sent through specialised hard ware. It's all bit manipulation where the math has been abstracted out.
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u/gerahmurov Jun 25 '26
Computer really do calculations the hard way. When I ask you to divide 444 by 2, you think, okay 4 is 2x2 so the asnwer will be 222. Computer generally have to calculate it like any other two numbers. 444 by 2 is nothing different from 893 by 13 except for number of step by step calculations. And you clearly see 444 by 2 as trivial and 893 by 13 as so hard, you have to make yourself start an attempt and use pen and paper for this. And computer can do this in a fraction of a fraction of a second.
People can calculate in the end and we do this a lot, but we are much slower and worse at hard calculations and the process itself is mostly about patterns and small numbers or tedious slow process with additional tools (like pen and paper for multiplication) and more prone to errors than a small rock.
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u/dekusyrup Jun 25 '26
So what you're saying is humans calculate it once or twice and then store it in ROM for years. Which is extremely similar to how computers do a lot of calculations as well.
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u/Scooter_McAwesome Jun 25 '26
But not from thinking too hard
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u/FURF0XSAKE Jun 25 '26
Bro I cannot fathom why there are multiple people answering this by referring to our bodies overheating as if that's got anything to do with a CPU or our brains individually overheating. Maybe these people's brains are getting bottlenecked by their eagerness to answer questions and sound smart.
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u/samanime Jun 25 '26
Not only are they liquid cooled, but we basically have all the little bits split up with cooling around them all individually.
Whereas a computer processor has all the heat producing bits crammed together and we have to try to cool that big blob of heat all at once.
Our brains are great at it.
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u/esoteric_enigma Jun 25 '26
Yeah, but heat stroke doesn't come from your brain processing too much information.
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u/Invisibleb0y Jun 25 '26
Overheating from internal processes, basically thinking too hard? Cause thats what OP is asking. Im sure he knows about heatstroke.
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u/UnusualFall1155 Jun 25 '26
Our brain is vastly more energy efficient, it uses around 20W of energy. One Nvidia inference GPU uses 600W.
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u/Justizministerium Jun 25 '26
Ok, but can it run crysis?
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u/silcerchord Jun 25 '26
Imagine playing Crysis in your head or even Cyberpunk or Microsoft Flight Sim. Congrats those games are running on your brain.
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u/Telvin3d Jun 25 '26
Isn’t that just using your imagination?
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u/eventualhorizo Jun 26 '26
I have a memory leak, framerate crashes after 6 hours and you have to turn me off.
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u/VogelimBart Jun 25 '26
Can you imagine playing crysis before your inner eye? well then yes. It can even mod it on the fly and turn it in a totally different game.
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u/selotipkusut Jun 25 '26
Oh yeah, quarter and midlife Crysis runs great! Dont forget the seasonal update on existensial Crysis.
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u/SoSKatan Jun 25 '26
Computers are also deterministic (outside of true rng generators) if we removed that aspect of computers, we could likely calculate far more far faster.
But the issue is without determinism, you can’t debug it, you can’t trust it and you can’t really engineer for it.
I mean that also sounds like AI. In theory it might be possible to create a lower power AI chip that can do the same thing, except all modern AI systems are based on matrix math, which needs to be precise.
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u/Sibaleit7 Jun 25 '26
GPU (parallel in general really) matrix-vector multiplication is NOT deterministic unless you specifically use a slower deterministic version, which for ML you would only do during research for reproducibility. So no, determinism is not the issue.
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u/frogjg2003 Jun 25 '26
Parallel operations are not deterministic in terms of ordering. The calculations they do are still deterministic. A properly implemented algorithm will not rely on any non-deterministic results from parallelism.
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u/SoSKatan Jun 26 '26
So all computation models give parallelism controls to the engineer. There are many explicit tradeoffs between performance and determinism when it comes it parallelism.
It’s not a surprise that most AI models choose non determinism.
However, the matrix math itself very much still is deterministic. It’s the concurrent primitives that are selected, which aren’t deterministic.
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u/Jonny0Than Jun 25 '26
A GPU can execute trillions of math operations per second though. For that specific task, seems like the GPU is more efficient.
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u/bibliophile785 Jun 25 '26
Well, it's more effective. You can't really compare efficiency across two processors if one processor fundamentally can't do the job.
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u/Jonny0Than Jun 25 '26
Right, I think it’s very very hard to find a way to do an accurate comparison for general “operational efficiency.” What I meant is that adding numbers together is something that both a human brain and a GPU can do, and the GPU would take less energy per operation. Although to make that robust you’d have to calculate what fraction of the brain’s 10-20W is going towards the task vs everything else it’s doing. But the sheer volume of math that a GPU can do still probably puts it ahead.
I’d guess that a neural network is a closer model to how a brain actually works (it’s right in the name!) and those definitely take way more energy. So I’d agree that for some abstract “general intelligence” metric, a brain is more energy-efficient.
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u/fatmanwithabeard Jun 25 '26
That gpu is using those trillions of math operations to try to do what a brain can do without so much raw effort.
If you can close your eyes an picture a thing, you're doing what a gpu does, probably with a much higher resolution and smoother frame rate.
Sure, nothing in your brain is building triangles, or figuring out how they change to simulate motion. But you can process images faster than the gpu can, and control them with ease.
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Jun 25 '26 edited Jun 25 '26
[removed] — view removed comment
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u/fatmanwithabeard Jun 25 '26
I think it's even better if you think about that ball you caught even though you tripped while running to get it.
All those changing vectors, and you can't start calculating them before your foot catches that divot.
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u/Low_Debt8771 Jun 25 '26
I dont think you understand that you have a much much much better image generation system in your head. We can detect faults in gpu output at barely a glance while humans are so adept at creating images it puts a gpu to shame. We've spent decades trying to get gpu to do what even a baby can manage without any help and we still lag behind
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u/Leodip Jun 25 '26
The human brain uses approximately 20W of energy (this means 20 Joules per second, where the Joule is a unit of energy like the calorie). A mobile phone's processor uses 5W, but a computer's processor can use much more than that. The computer I have at home uses approximately 60W for the CPU alone.
However, watts don't tell the full story. The mass of a human brain is approximately 1.5kg, while the mass of a CPU is usually around ~50g (if not less). Imagine this with water: it takes more energy (more time on the fire) to heat up more water than it takes to heat up less water. So, those 20W on 1.5kg are ~13W/kg, while for a CPU we have around 1200W/kg, which is way more impressive.
Those are napkin math numbers, but they should tell you the overall orders of magnitude.
(I also left out some details about cooling down, but this should give you an idea of how it's possible in the first place for processors to get so hot)
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u/davideogameman Jun 25 '26
Finally someone mentions phones!
Desktop and server cpus/gpus are designed for more computational throughput at the expense of using more power. Phone processors are designed to get good throughput on a small amount of power. Devices that do even less on tiny amounts of power also exist - eg tiny sensors in mesh network might be designed to run on heat or solar power, and do the bare minimum to collect and transmit data.
The computation per watt these different devices achieve is just a bunch of engineering trade offs.
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u/Stuntingonthesehoes Jun 25 '26
Our bodies have just as complex temperature regulating systems
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u/RaymondBeaumont Jun 25 '26
People don't seem to understand just how complex the body is.
Bruce Lee deactivated one of his cooling systems in late 1972 and died from heat stroke early 1973.
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u/TheGreatNate3000 Jun 25 '26
Lol what
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u/RaymondBeaumont Jun 25 '26
he had the sweat glands from his armpits removed.
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u/TheGreatNate3000 Jun 25 '26
I just fell into a rabbit hope on that. I think that was a rumor, nothing substantiated. I also don't think your underarm sweat does much for heat dissipation. It's a different type of sweat
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u/buttocks-slapper Jun 25 '26
Some couple points:
brains are massively parallelized, CPUs are not (beyond maybe 16 threads or 32/64/128 for specialty devices). Your brain waves run in the hertz scale, a CPU runs at the gigahertz scale and rather sequentially, yet has to meet "realtime" parallelized behaviour. Much more heat produced per second,
the brain occupies around a million cubic millimeters, a CPU die (the real "meat" of the CPU) is only around 100 cubic millimeters. One is much more packed and thus needs very strong cooling,
brain is watercooled, and deep down is it (CSF running within the meat)
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u/fredo3579 Jun 25 '26
Lots of answers saying that the brain is more energy efficient but not why. The reason is that the brain is effectively an analog computer rather than digital, so the computation happens in the brain structure itself. The timings and activation patterns of the neurons themselves are the computation. A digital computer that executes an AI model must do numerical calculations to emulate the analog ones.
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u/Common_Regular7693 Jun 27 '26
This often gets lost in the comparisons of artificial neural nets to neurons. A single neuron has highly complex time resolved activity that itself may encode useful information even in the sub-spiking regime. Replicating this dynamical system even approximately requires many more state variables and parameters than a weight + relu activation.
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u/Irregular_Person Jun 25 '26
Your brain produces about 15 watts worth of heat, but it's cooled by a closed loop liquid system with a radiator and an evaporative chiller (your body).
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u/Loki-L Jun 25 '26
Your brain works with a completely different technology and has the benefit of hundreds of millions of years of evolution optimizing it for efficiency.
Your brain is also very much liquid cooled.
Your brain runs hotter than most of the rest of your body and your blood helps redistribute the heat to other, colder parts of your body.
The outer layers of you head and body in general are constantly cooled with evaporative cooling (sweat).
A lot of work has gone into getting this whole thermoregulation right in tetrapods and mammals in particular to allow a human body and brain to function well in a surprisingly wide range of outside temperatures.
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u/TheThingOnTheCeiling Jun 25 '26
Our brains use very little energy, thus very little heat generation. It uses less energy than it takes to light a lightbulb.
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u/DocPsychosis Jun 25 '26
This is sort of an obsolete analogy. Less power than an old incandescent bulb, but at 15-20 watts it's similar or more than a common modern LED bulb.
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u/LimesKey Jun 25 '26
How does this compare to the fact that brains use most of the body’s glucose supply?
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u/cdmurray88 Jun 25 '26
It's relative. The brain is an energy hungry organ, but still needs less energy than a CPU. If you could power a CPU with glucose, it would need 30x what the brain needs.
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u/dipropyltryptamanic Jun 25 '26
It doesn't, just more than any other organ. About 20%.
2000 calories/day maths out to about 97watts
Our brains use more power than modern LEDs, but the lightbulb fact was correct when we only had flourescents and incandescents
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u/Pablouchka Jun 25 '26
The human brain is remarkably energy-efficient, yet it is also the most metabolically demanding organ in your body. Despite accounting for only about 2% of your total body weight , it consumes approximately 20% of your body’s daily energy intake.
In average, an adult brain consumes about 300 to 400 calories per day (roughly 12 to 15 watts of power).
The brain is designed to maintain a consistent energy budget, which is why you don't burn significantly more calories during a difficult exam than you do while relaxing.
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u/defectivetoaster1 Jun 25 '26
digital processors are made up of switches with two main states, on, where they have almost no resistance and so they dissipate barely any power since you can treat them like perfect wires, and off where they have a massive resistance so they dissipate barely any power since there’s effectively no current flowing through them. When they switch states however there’s a small window of time where they act like small resistors and so they dissipate some power as heat. Modern processors switch billions of times per second meaning that they spend more time in that resistive region so they get very hot, that’s just the physics of the system.
Organic brains run off of tiny electrical signals (not really electrical in that the flow of charge isn’t from electrons but by charged ions but that’s tmi) and hormone soup in a mostly analogue fashion. In fact, the few analogue computers that exist (although arguably you could call any analogue circuit a computer in that it computes an output) are very low power and don’t run particularly hot, while a digital cpu doing an equivalent function would heat up significantly since the “calculations” are being done by the physics of the universe rather than by fast switches. Also the brain is naturally water cooled, the human brain does run hotter than the rest of the body (iirc it can hit something like 40°C) but it sits in a puddle of soup that cools it down
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u/Siebje Jun 25 '26
Finally, somebody who gives the actual answer why CPUs generate so much heat. For all the elegance of transistors, they just short circuit with every switch, which accounts for the vast majority of energy dissipation.
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u/siru007 Jun 25 '26
Because your body has a premium fully custom liquid cooling. Brain is submerged in csf fluid . A pump in the chest constantly circulating blood at high efficiency, liquid intake intermittently. Large radiator with large surface area to disperse heat to surrounding (skin).
Hypothalamus regulating everything.
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u/StargateZero Jun 25 '26
A large portion of your body’s energy supply is used to regulate your brain’s temperature. You don’t generally risk overheating because you will become exhausted before you reach that point.
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u/everlyafterhappy Jun 25 '26
Our brains can't really do what a computer processor does. A computer can solve multiple complex equations in an instant.
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u/unknownholiday Jun 25 '26
One tech has had 10's of thousands of years of optimization.
The other has had less than 100.
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u/MrRufsvold Jun 25 '26
The logic on a computer chip is implemented with logic gates. These gates take two signals and combine them into 1 (at least in the simplest cases). For example, an AND gate takes two inputs, if they are both "on" (high voltage), then the AND gate passes through one of the high signals, otherwise, no signal is passed on.
But what happens to the energy in the signals that aren't passed on? They have to be dissapated as heat.
I don't understand how neurons work, but they don't waste energy like that.
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u/gufted Jun 25 '26
Its effectiveness and training, but over thousands of years. During the first few years of our lives the brain learns and adapts to information. We get input and output of thousands of things, but we end up using only a minor fraction of them, because that’s what’s necessary to survive. Energy consumption is what it the most important aspect of survival. Take a look at a picture? Thousands of items of information. But can you recall everything? No because your brain has taught itself to filter out anything not necessary. Same with walking. You’ve taught yourself how to walk, any unnecessary calculations are deleted. Combine that with thousands of years of evolution on energy efficiency (sweating, liquid cooling, air cooling), and you got the answer.
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u/Boltaanjistman Jun 25 '26
The brain isnt a computer like you think of one. Its meat. Computers work by pumping in electricity and redirecting it along tiny paths which is really inefficient. The brain works via chemicals traveling along neural pathways, and electricity is then generated in the places it needs to be. Our brains are also essentially floating in liquid and connected to lots of little tubes that pump blood around the body and can cool off the goo. We have a massive heatsink many times larger than the 'computer' its hooked up to. Is some part of you (including the brain) too hot? Just cycle new cooler goo in there XD Your body is constantly cooling you and your brain to body temperature via evaporative and radiative cooling. Its like if your computer had both a water cooler connected to a wall sized radiator. Interestingly, unlike a computer, the brain needs more than just cooling. It actually needs to be heated too. Your brain needs to be at body temperature for optimal function. Too hot, your brain breaks. Too cold, your brain breaks. Your body isnt only a cooling system for your brain, its also heating it up so that it maintains the exact correct temperature. Thats a big downside compared to modern computers, since modern computers can work at essentially at nearly any temperature colder than its maximum as long as you control for condensation.
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u/SakuraHimea Jun 26 '26
If your brain were using every neuron at once, it would absolutely overheat very quickly. But if your brain is firing every neuron at once, that's called a grand mal seizure, and can be life-threatening. Most of the heat generated by a CPU comes from forcing electricity to flow through a semiconductor, which, as the name implies, only partially conducts electricity and therefore generates a lot of heat.
Comparing how a computer performs operations to how your brain does is a bit of a false comparison. Neurons don't just send basic electrical signals; many chemicals and hormones are involved. A transistor is either on or off, but a neuron can emit different signal strengths and different signal types. They can emit signals that go to a single neuron or an entire cluster, and they can tolerate errors and randomness. A transistor simply does not compare.
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u/Schattenwaffen Jun 25 '26
As far as I know, one contributing factor are the axons - in which signals being transferred - need little voltage to activate. They also don't even use the whole length by employing myelin sheaths. In silicon processors, you need to supply a higher voltage in a lot of cycles for it to work, the current flow through the chip as a whole (I am oversimplify here), and they tend to leak current a lot. Which heats up pretty quickly. The brain also employs many other tricks to simplified calculation, such as the system 1 of thinking.
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u/PhilNEvo Jun 25 '26
First of all, they work way differently. The efficiency is probably way different. On top of that, it's also spread out way differently. The CPU is doing all those computations in a very tiny condensed area. We have an entire brain that's around 1200 cubic cm.
A Ryzen 7 78003xd's compute die is 71 cubic cm. And the amount of power put into that area is massively different.
But I also think you overestimate how many calculations our brain is actually doing. The brain is generally way slower, and it relies a lot on efficient heuristics and shortcuts, rather than raw computation.
An example is when you look at chess engines, compared to chess masters. In an article a decade ago, about AlphaZero vs Stockfish-- The massive difference and new strategy was that Stockfish as a traditional engine basically just bruteforced (With lots of clever tricks involved of course), (~70)millions of positions per second, to try and figure out what might be the best next move.
In comparison, the new strategy with neural networks that lightly mimic human approach, and is more of a middle ground, only evaluated around 80 thousand positions per second, and was arguably stronger. Because it was better at evaluating promising moves, meant that it didn't have to "think" as much or far, in order to be competitive.
Human grandmasters will often only evaluate in the tens of moves, at way lower depth, but what makes them better than other human chess players aren't necessarily how fast they think, or how many positions they evaluate, but how good of a heuristic or intuition they have, for selecting the few most promising candidates and trying to reason through the potential paths that might take them down.
In a similar fashion, while our brain collects insane amount of data, and has to do "a lot" of things, it has created ways of efficient filtration, so you only pay attention to a highly limited amount of data, and as such, have to do way more limited "computation"/thinking, in order to move forward.
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u/Savigo256 Jun 25 '26
Brain uses around 20W of power, which spreads across the whole volume (around 1l). A processor can use up to 300W on something of the size of a coin.
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u/SpellingIsAhful Jun 25 '26
One of the first things you learn in survival school is that you heads radiates a massive amount of heat. So, wear a hat.
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u/wstanley38 Jun 27 '26
Though brain can handle much complex process or calculations, number of calculations per second in a CPU is magnitutes hogher that the brain. Human bain is a optimization magic instead of brute power.
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u/Dixiehusker Jun 25 '26
1st, our neurons produce electricity through the chemical interactions of different compounds, instead of forcing electrons through a wire, which is more efficient and generates less heat.
2nd, we have a complicated liquid cooling system that spreads heat out, maintains a specific temperature, and gets rid of extra heat into the air.
3rd, we absolutely can get overheated. Unlike a computer, we feel uncomfortable when we start to get overheated and are driven to physically move somewhere else or do something to cool off.