I feel like this is dramatically missing the point. It is trivial to come up with a communication system where signals travel at the speed of light. In fact, anything visual meets this criteria: sign language, semaphores, clicking your flashlight on and off. Radio waves travel at the speed of light. All of humanity became a giant "lightspeed-intelligent" brain when radio was first invented.
It really does matter what you're doing with those signals, how much information each contains, how many you're sending, how much power it takes to send and receive them, how they're encoded, etc. Focusing on the fact that they travel at the speed of light is silly.
> The advantage of this over biological computation is clear: Biological computation happens at max 100m/s, 6 orders of magnitude less than the speed of light
You are trying to compare computation power by measuring distances. You are basically saying "one biological computation" is a million times slower than "one silicon computation" because of how fast signals travel, completely ignoring what is actually happening in those extremely different computations. It's still not clear that brains can be compared to computers at all, but if you try to simplify it down to FLOPS (a much better measure of computation speed than "how fast do some signals go"), our best estimates are that one brain has the computational equivalent of somewhere between 1,000 and 100,000 modern GPUs.
That is a good example of another very very probable pattern. If an alien civilization at the other end of this universe exists, it is very, very probable that they also have communication networks that operate close or near the speed of light.
> It really does matter what you're doing with those signals, how much information each contains, how many you're sending, how much power it takes to send and receive them, how they're encoded, etc. Focusing on the fact that they travel at the speed of light is silly.
You're correct that the speed of the signals isn't the only aspect that is important. It is however not silly to focus on it, because it represents a fundamental, physical, upper bound on a key aspect of the maximum 'performance' of signals/information transfer. The amount of information that can be encoded in electromagnetic radiation would be another.
> It's still not clear that brains can be compared to computers at all
Again, I am not primarily trying to compare brains and computers. Lightspeed intelligence could technically be biological. I am also not saying that current artificial neural networks do as much with their signals as our brains. The fundamental point was and is that an intelligence with signals that propagate at the speed of light will emerge and become dominant.
There are a bunch of secondary points that can be made as to why biology has a much harder time than brains in developing lightspeed intelligence (evolving something like glass fiber, the limitations of brain size, cooling issues, etc.), but those are not as important as the fundamental point.
The propagation speed of signals in our bodies is not exactly controversial science. Just see Wikipedia for this [0].
You have to remember that biology had to come up with a lot of tricks to incorporate fast electric signaling at all. Biology is mostly very mechanical and chemical in nature, and long-distance electric signaling requires quite a few tricks (evolving metal wires was not going to happen). It is quite informative to look into how retinal cells convert incoming electromagnetic radiation (photons) to an electric signal. The visual cycle of retinals [1] is particularly interesting, imho.
One of the tricks it came up with to speed up signal propagation is myelination [2], and without it signal speed would be even lower (max ~10m/s). At such speeds, a two-metre signal path alone would take around 200ms. Imagine controlling your feet with 200ms ping.
> It's definitely more than a bunch of neurons messaging each other. Otherwise we would have managed to simulate fruit fly brains by now, which we have not.
The latter says nothing fundamental. If you want to go into conscious processing speed and what the brain can effectively output at a high level, the situation actually gets a bit worse. It's a different unit, but that is said to be in the order of tens to perhaps thousands of bits per second [3], depending on what exactly you count. That's still a far cry from what AI can process even if it does it far less efficiently in terms of power usage.
[0] https://en.wikipedia.org/wiki/Nerve_conduction_velocity
[1] https://en.wikipedia.org/wiki/Visual_cycle
[2] https://www.sciencedirect.com/science/article/abs/pii/S00068...
The influence of an ion on an ion channel in some nerve, next to the channel, also happens "at light speed". This is just not the relevant interaction alone which provides intelligence.