# How would our eyes have to be different to see outside the "visible spectrum"? **URL:** \ **Category:** Factual Questions\ **Created:** [June 24, 2003, 9:45pm UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144 "2003-06-24T21:45:21Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![BrainGlutton](https://avatars.discourse-cdn.com/v4/letter/b/82dd89/32.png) [@BrainGlutton](https://boards.straightdope.com/u/BrainGlutton)\ **Post date:** [June 24, 2003, 9:45pm UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/1 "2003-06-24T21:45:21Z")
What we call the “visible spectrum” is only a tiny slice of the whole spectrum of elecromagnetic radiation wavelengths. Sometimes in a science-fiction story there is an alien race who can see into the infrared and/or the ultraviolet. How would that work? How would our eyes have to be constructed differently to see the infrared and ultraviolet? Is it something to do with the size of the receptor cells? I believe a radio antenna has to be at least as long as the maximum wavelenght it is meant to receive. It seems to me being able to see into the infrared would have an obvious evolutionary survival advantage: The bulk of “black body” radiation is in the infrared for most objects slightly warmer than room temperature – so an animal that could see that radiation would be able, for instance, to see other animals glowing in the dark from their body heat. Yet so far as I know, no animal can see in that range. Is it because animal eyes that perceive infrared are physiologically impossible? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 24, 2003, 9:58pm UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/2 "2003-06-24T21:58:13Z")
Some snakes are able to perceive body heat, even to the extent of ‘imaging’ it - they have pits on their faces that are lined with cells sensitive to changes in radiated heat; the pit acts a bit like a crude pinhole camera - so it could be considered a type of eye (almost) ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [June 24, 2003, 11:19pm UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/3 "2003-06-24T23:19:21Z")
If you are interested in this I suggest you find some of the work of George Wald. The man did a lot of work in precisely this field. Basically he came to the conclusion that all carbon/water based life will probably use the same slice of the spectrum. Longer wavelengths like microwaves and radio waves can’t be used because they get absorbed by water. This makes them useless for an organism that evolved in water. It also makes it very hard to evolve an eye, since it would need to evolve in cells without an aqueous cytoplasm, which is highly unlikely. The other problem is that any atmosphere in which carbon/water based light evolves will be pretty similar t ours. This means it will absorb these longer wavelengths very fast making them an unlikely choice to evolve receptor pigments for. The shorter wavelengths like gamma and X-rays are far too energetic to be safe for carbon based life. They have a nasty habit of shaking pigment molecules to bits, not to mention DNA and proteins. As a result organisms will evolve pigments specifically designed to stop these wavelengths entering the cell. No real way to evolve a receptor pigment for something that never reaches the cell interior. These short wavelengths also have a problem with focussing, since they need very dense material to produce much of a refractive effect. These are the biggest problems to overcome in evolving an eye to see past the visible spectrum. Obviously the closer you get to the visible spectrum the less of a problem this is, and many invertebrates can see into the near UV for example. Evolving eyes to see IR isn’t very effective. As you say, it enables an animal to see black body radiation, but the range for IR is short in humid air and almost nothing underwater. Producing a true eye would also require producing a lens and ground materials with high IR transparency, which isn’t easy for water based life. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [June 24, 2003, 11:19pm UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/4 "2003-06-24T23:19:33Z")
IIRC, it’s the cornea which is impervious to UV light at “normal” levels, and the retina is able to resolve it. Hence people who have had cataracts removed are able to see slightly into the UV portion of the spectrum (which registers as violet, apparently). ---
**Author:** ![BlueMit11](https://avatars.discourse-cdn.com/v4/letter/b/7feea3/32.png) [@BlueMit11](https://boards.straightdope.com/u/BlueMit11)\ **Post date:** [June 25, 2003, 3:05am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/5 "2003-06-25T03:05:11Z")
According to a show about predators and their devices that I remember seeing on the Discovery Channel, Hawks can see UV light. They use this to somehow track rabbits-I forget exactly how. They reason they can and we can’t is because the receptors of their eye regenerate more rapidly than ours, counteracting the damage done by viewing the UV. ---
**Author:** ![MLS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MLS](https://boards.straightdope.com/u/MLS)\ **Post date:** [June 25, 2003, 3:25am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/6 "2003-06-25T03:25:22Z")
I’ve also seen depictions of how insects see flowers deeper into the spectrum, often revealing a “target” around the center of the flower where the pollen and nectar are. ---
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [June 25, 2003, 4:15am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/7 "2003-06-25T04:15:20Z")
The visible spectrum is visible becaue the pigments in the retina react to it. This is a physical property. Extending the range would require a different pigment. Given such a pigment, the necessary structural changes, if any, are trivial. As others have already pointed out, other creatures have evolved structures transparent to IR and UV. Very long and very short EM waves, as **Blake** has pointed out, are impractical for our biochemistry, but could exist if one stipulates the exotic biochemistry necessary. ---
**Author:** ![Sock\_Munkey](https://avatars.discourse-cdn.com/v4/letter/s/aeb1de/32.png) [@Sock\_Munkey](https://boards.straightdope.com/u/Sock_Munkey)\ **Post date:** [June 25, 2003, 4:20am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/8 "2003-06-25T04:20:44Z")
Rodent and rabbit urine reflects a lot of UV light, this is how seeing it helps hawks. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [June 25, 2003, 5:20am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/9 "2003-06-25T05:20:10Z")
Is there any reason animals can’t develop radio receivers and transmitters? Animals already use electrical impulses to send singlas within the body, and some animals can generate high voltages. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [June 25, 2003, 5:47am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/10 "2003-06-25T05:47:21Z")
> [@](#): > > Rodent and rabbit urine reflects a lot of UV light, this is how seeing it helps hawks. AFAIK it doesn’t reflect much more than almost any other biological compound, including rabbit and rodent fur or plain dirt. It does fluoresce under UV, but that’s not particularly useful to an organism without a UV lamp. > [@](#): > > Is there any reason animals can’t develop radio receivers and transmitters? That’s what this entire thread has been about. Radio waves are just extremely long wavelegth light, with all the associated problems. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [June 25, 2003, 6:13am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/11 "2003-06-25T06:13:08Z")
I don’t see any reason why organisms should not be able to develop radio communication- some biological equivaent of the ‘cat’s whisker’ radio might allow communication between members of a flock of birds, for example. This was imagined many years ago by Olaf Stapleton in _Star Maker_, one of the first essays into speculative xenobiology. But to see detailed images using radio waves would need a reciever many times larger than the wavelength- to see a radio galaxy you would need eyes the size of Jodrell bank. As far as seeing Ultraviolet goes, Claude Monet might have been capable of this; [(Quote from this link)](http://education.guardian.co.uk/higher/medicalscience/story/0,9837,724257,00.html) An illustration of how ultraviolet appears is provided by the Impressionist painter Claude Monet. Following cataract surgery in 1923, his colour palette changed significantly; after the operation he painted water lilies with more blue than before. This may be because after lens removal he could see ultraviolet light, which would have given a blue cast to the world. (/quote) * * * SF worldbuilding at [http://www.orionsarm.com/main.html](http://www.orionsarm.com/main.html) ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [June 25, 2003, 6:15am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/12 "2003-06-25T06:15:35Z")
> [@](#): > > \*Originally posted by Blake \* > \*\*Radio waves are just extremely long wavelegth light, with all the associated problems. \*\* OK, so I missed the bit you talked about it, but all you said is: > [@](#): > > onger wavelengths like microwaves and radio waves can’t be used because they get absorbed by water. This makes them useless for an organism that evolved in water. But I have to disagree here. I think a directional radio antenna can be constructed with water-based organic material. It certainly doesn’t require substances which are transparent to radio waves. And if you do need a substance like that, I think bones and exoskeletons meet the criteria. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [June 25, 2003, 6:56am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/13 "2003-06-25T06:56:07Z")
Yes you could rig up an antenna outside the cell, and hence out of water. This is highly improbable though, since it would require constructing the antenna simultaneously with the reciever. An irreducable complexity problem. WIth no antenna the cell can’t receive the signal. WIth no reciever in the cell the antenna is just wasted material. This can only be circumvented by having both evolve form pre-existing structures and then meshing later. The trouble is that I can’t see how this could happen. If you can then the problem could be surmountable, but still highly unlikely. Constructing a radio antenna with water based carbon compounds may well be possible, but there is again the irreducable complexity problem. Why evolve within a cell an antenna with nowhere for the signal to go, or a reciever with no antenna to recieve it. The reason why one needs transparent materials is that at some point the signal has to enter the cell. You may have gotten around ths by putting the antenna outside the cell, but this just takes us back to the first problem in this post. Then if one organism does manage to crack radio reception, so what? It doesn’t provide any advantage and only wastes energy. The first organism to evolve an eye had plenty of incoming information. Ditto with the ear. The first organism to evolve a radio receiever will have no information at all. The point here is that nothing is theoretically impossible using evolutionary proceses, but some things are so highly improbable and of such limited use that they probbaly won’t happen. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [June 25, 2003, 6:57am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/14 "2003-06-25T06:57:56Z")
Bah. “Why evolve within a cell an antenna with nowhere for the signal to go, or a reciever with no antenna to provide the signal?” ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 25, 2003, 7:32am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/15 "2003-06-25T07:32:03Z")
I seem to remember reading somewhere that the feathered [antennae](http://www.kendall-bioresearch.co.uk/MICROANTEN3.gif) of moths functioned something like a Yagi antenna. I’m not sure what wavelength they were talking about, but presumably it would be possible to calculate it by measuring the spacing etc. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [June 25, 2003, 7:40am UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/16 "2003-06-25T07:40:34Z")
Aren’t moth antennae primarily smell receptors? ---
**Author:** ![The\_Chao\_Goes\_Mu](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_chao_goes_mu/32/3191_2.png) [@The\_Chao\_Goes\_Mu](https://boards.straightdope.com/u/The_Chao_Goes_Mu)\ **Post date:** [June 25, 2003, 6:03pm UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/17 "2003-06-25T18:03:15Z")
* * * I’ve also seen depictions of how insects see flowers deeper into the spectrum, often revealing a “target” around the center of the flower where the pollen and nectar are. * * * I thought these insects (such as honeybees) did, in fact, see in ultraviolet. Their eyes actually lack the filtering capabilities to see color. ---
**Author:** ![The\_Chao\_Goes\_Mu](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_chao_goes_mu/32/3191_2.png) [@The\_Chao\_Goes\_Mu](https://boards.straightdope.com/u/The_Chao_Goes_Mu)\ **Post date:** [June 25, 2003, 6:13pm UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/18 "2003-06-25T18:13:27Z")
* * * **I’ve also seen depictions of how insects see flowers deeper into the spectrum, often revealing a “target” around the center of the flower where the pollen and nectar are.** * * * I thought these insects (such as honeybees) did, in fact, see in ultraviolet. Their eyes actually lack the filtering capabilities to see color. ---
**Author:** ![The\_Chao\_Goes\_Mu](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_chao_goes_mu/32/3191_2.png) [@The\_Chao\_Goes\_Mu](https://boards.straightdope.com/u/The_Chao_Goes_Mu)\ **Post date:** [June 25, 2003, 6:19pm UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/19 "2003-06-25T18:19:14Z")
Sorry about the double post. As all of you may have guessed, I’m new here. ---
**Author:** ![Rocketeer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rocketeer/32/4437_2.png) [@Rocketeer](https://boards.straightdope.com/u/Rocketeer)\ **Post date:** [June 25, 2003, 7:14pm UTC](https://boards.straightdope.com/t/how-would-our-eyes-have-to-be-different-to-see-outside-the-visible-spectrum/184144/20 "2003-06-25T19:14:57Z")
Some fish (sharks) can sense electric fields. I suppose it’s not really seeing, though, because there doesn’t seem to ba any focussing mechanism. More like an additional “touch” sense.