organisms living outside our normal parameters?

are there any organisms out there that have been discovered that do not live within the visible spectrum? Is this even possible?

I know this sounds like a really stupid question, (and it REALLY sounds stupid when you type it out), but animals can communicate outside the normal range of human hearing. it would seem to me that it could be possible that an animal could be invisible to us because it didn’t reflect light within the visible spectrum. As counter-intuitive as this sounds, does one actually exist?

Can it?

And if it can’t, why not?

If it did, I can’t imagine the size of a creature being large.

Please, give me the answer gently. I’d blame the question on my five year old. But I don’t have a five year old.

ETA: I’m not referring to something microscopic, invisible to the naked eye. And I doubt the answer is “Yes, they are all around us, you just haven’t bumped into them yet.” Sort of like the ball players in the movie “Field of Dreams”.

No, I am NOT drunk, or under the influence of anything that I am aware of. :wink:

if it didn’t reflect any light in the visible spectrum it would appear to be black as it would be absorbing all the visible light that fell onto it.

To be invisible your creature has to be transparent with transparent organs as well, or change colors to mimic the environment. See Jellyfish and Squid.

Well, the orgqns were what almost stopped me from even posting this. obviously, everything about the animal would have to follow thw same rules, or youd see the heart, stomach, whatever. And even if they followed those rules, one vitemamd youd see a chunck of food just floating along, inside the animals invisible innards.

This was a reasonably common theme in golden era SF- an entity that was ‘:)a colour we can’t see’ - but as **coremelt ** rightly notes, thats just another way to say black.

There are nearly transparent fish. Not totally transparent though. The totally invisible ones would have to remain that way after death until they decomposed sufficiently to be undetectable.

There are a few transparent organisms but like glass, they still refract light, so they aren’t invisible.

To be invisible, something would not only have to be perfectly transparent, its refractive index would have to match that of the medium - air, water, whatever - in which it lived.

I don’t think you are going to find any, but jellyfish (and similar things like comb jellies) are about the closest.

As coremelt said, something that did not reflect light wold be black, and (in daylight anyway) black things are usually relatively conspicuous.

what about in an extreme environment, like an underground cave, where light cannot reach?

If there’s no light a creature can be bright florescent green and it’s still going to be “invisible” to any creature that can’t generate light somehow. Most cave adapted creatures seem to be white, since there’s no evolutionary advantage to having any pigmentation any more.

Everything is invisible where there’s no light.

If you don’t limit yourself to organisms but just try to find substances that fullfil your criteria you’ll find the world sorely lacking in solids and liquids that both match your criteria and are sufficient to build a living organism.

I see the (also common in SF) theme of “a being composed of pure energy” marching in the direction of this conversation, so…

Aside from the fact that matter can be regarded as energy, the notion of a ‘being composed of pure energy’ isn’t really viable - electromagnetic energy is generally trying to go somewhere, fast - and an organism won’t remain organised if its organs want to disorganise themselves in every which direction at the speed of light.

Let’s put it this way: we haven’t seen any yet.

Pink unicorns are generally held to be invisible.

This was the premise of the invisibility of the creature in Ambrose Beirce’s 1893 short story The Damned Thing.

http://en.wikipedia.org/wiki/The_Damned_Thing_(Short_Story)

The problem with the idea is that your hypothetical thing of an infrared color (or whatever) still has to do something with the visible light that hits it. If it doesn’t let it pass through unchanged, then the object will be visible.
Getting the light to pass through unchanged is the hard part. Not only must your thing be transparent, it must have the same refractive index as the medium it’s in – that’s why you can see diamonds and glass and other transparent objects. (and it’s impossible for a solid or liquid to have as low a refractive index as gases. So it’s easier to be invisible underwater). Even if you could manage to match the refractive index at one wavelength, if you don’t match it at all visible wavelengths you’ll still be visible (that’s the basis of Christiansen filters).
Aside from tyhis, there are only three ways to be truly invisible (as opposed to camouflaged):

1.) Bend the rays around you, or in some way present the same image/wavefront on one side of you that hits you on the other side.

2.) make sure that you and your background have the same high temperature, so that you and your bavckground are blackbodies em,itting light with the same emittance at al wavelengths, and are overwhelming any other light sources. This will result ion your being vaporized for visible light. You have to decide if it’;s worth it. Might be viable if your opposition only has long wave infrared vision.

3.) Turn out all the lights. In the dark everything is invisible. As long as it can’t see your blackbody emission in the infrared. (like pit vipers and Alien Predators. And covering yourself up with mud won’t help(Predator). Nor will standing in a refrigerator, as in Hardware . You have vto cover yourself with cold stuff (Tremors 2).)

I think an organism could be so large that we could not recognize any form to it, a single cell being larger than our universe for instance.

There’s a definitional problem in that idea. But the large size thing isn’t totally ridiculous. The Gaia theory treats the whole earth as something like an organism. It’s not that we don’t see the earth, but until modern times we were something like blind men feeling up an elephant.

So how do we know that they’re pink?

They’re pink unicorns. What other color would they be?

You have to take that on faith.