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Comment by cletus | Hacker News Reader

One big issue with communicating with aliens is sensory differences with humans. Humans perceive a sound range, the so-called visibl spectrum and certain limited smells (compared to man animals). Even here there are animals that perceive different spectra and the magnetic field.

What's more human communication relies on a basic common wiring (e.g. Paus s between words seem to be basically universal regardless of language and culture).

So if an alien landed here what if they didn't perceive sound at all and saw only in the ultraviolet range? I find this subject fascinating and it's certainly rich fodder for sci-fi.

Anyway the article asks how the interviewee would handle this situation without touching on this far more pressing problem.

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Later in the article when describing a practical protocol for a first-contact scenario, they explain this problem as discovering the 'modality' of communication.

That is certainly an interesting problem, one I first saw in a Hackaday post from a few years ago [1]. Personally, I've always wondered how any aliens would interpret the Arecibo message - if they could even decode it, that is.

[1] http://hackaday.com/2015/10/06/electronics-for-aliens/

I always thought aliens would think the marks on the golden disk are as meaningful as the defects on the semiconductor chips. I can't imagine why they would wonder if it's a message.

We get radio bursts from dying stars and try to interpret them as messages. Intelligence as we know it is pretty obsessed with trying to extract information from its environment, even where none may exist at all.

Thanks, that's my article! I'm glad you remember it after all this time.

This makes me wonder: is there a specific advantage in us being able to see the specific wavelengths we see or is it just a random thing and we would be fine if we could see only other wavelengths like UV or infrared?

Visible is pretty smack dab in the middle of the Sun's peak spectrum: http://plantphys.info/plant_physiology/images/solarlight.gif

And there are other constraints, too. UV is blocked by water (and our lens material) and can induce chemical changes (read: damage) easier than visible light. Damaging sensitive retina. Not that this is an unsolvable problem (bees see UV), but it is a biochemical constraint. Infrared, especially far infrared, doesn't work too well without a cooled sensor. And the energy per quanta is less, which reduces your options for good, high-sensitivity biomolecules that can detect them, kind of the opposite problem of UV.

So yeah, there are a few reasons why visible light is visible light and why we can't see UV or infrared. It's not entirely arbitrary or random. But "seeing" with sound is also a viable evolutionary approach, but less effective in a low-density medium like air and more effective (even than light) in a medium like water.

> Visible is pretty smack dab in the middle of the Sun's peak spectrum...

Does this mean that our vision system evolved to pick up the most energetic part of the Sun's spectrum that ends up at the surface? Did it evolve this way so our vision systems' cellular agglomerate don't have to expend as much energy gathering that part of the spectrum as opposed to other parts of the spectrum?

If so, then is there any linkage via evolutionary theory that imply our vision system might be among the first vision systems to evolve on the planet, because it filled the most-favored evolutionary niche associated with the lowest energy expenditure to gain a evolutionarily competitive advantage over other pre-human species?

I would point out that the crystal field splitting energies happen to correspond to the region around visible light, which means that being able to finely distinguish gradations of visible light would lead you to be able to visually distinguish between many different organometallic ions. I suspect that matters more than the flux of visible light in the solar spectrum.

> UV is blocked by water (and our lens material) and can induce chemical changes (read: damage) easier than visible light. Damaging sensitive retina.

Perhaps in an environment where UV provides the best illumination (due to the star being hotter, etc) creatures would evolve disposable eyes.

It's not entirely "random", but it is contingent. I.e., yes, we would be fine if we could see other wavelengths. Indeed, there are creatures than can see other wavelengths. Lots of insects and birds can see UV, and lots of snakes (specifically pit vipers) can see IR.

Seeing IR difficult because it is blocked by water and our own bodies radiate it, so it would be useless for our retinas to be able to detect it. You need completely different kinds of eyes (hence pit vipers' eponymous pit organs).

IR aside, the visual spectrum is centered where it is because that's where the sunlight that can make it through our atmosphere is brightest. We're adapted to see the light that's actually there, in nature. The range of light that's available actually does include some UV, and the ancestral tetrapod presumably could see that, which is why birds still can; mammals, however, went through a period in our evolution where our primarily-nocturnal ancestors had no need for four-color vision (because there wasn't enough light to support it) and not much UV was available to them, so we lost the UV sensitivity entirely and went down to only 2 kinds of receptors. This is why, e.g., dogs (and most other mammals) are colorblind. Apes eventually independently re-evolved a third color receptor because that was advantageous in things like identifying edible fruit which were important to their lifestyle, but there was never a strong evolutionary pressure to regain UV sensitivity.

The atmosphere and water are both reasonably transparent to visible light but a lot less transparent to other parts of the spectrum.

We don't actually pause between words as we speak, and there are many languages which don't have spaces either.

>So if an alien landed here what if they didn't perceive sound at all and saw only in the ultraviolet range?

If they were capable of interstellar travel this would be a trivial problem to solve in comparison so yeah highly implausible plots.

Well this is the somewhat depressing part: interstellar distances just seem so vast one has to wonder if it's ever going to be feasible. This is worsened by the timescales just being hopelessly long for how long we live. It seems far more likely that AIs are more viable to send than living organisms.

We will not live in meat forever. Once strong AI happens, or maybe even before, human consciousness will be transcribable into more resilient matter. That type of consciousness could be hibernated for millennia in transit. Or play endless games in transit. Its a bit silly to imply "living organisms" a being somehow better, especially when the vast majority of future humanity will live their potential endless lives in smart-matter panels orbiting this and other suns.

With time dilation the distances are not that vast. But even without, it is plausible to send biological matter in some form of hibernation across the galaxy in a space ship at ~0.3c. The energy requirements are pretty big, but you could use something like black hole star ships to efficiently convert matter into speed.

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