Why haven't we created a material that is completely invisible to the human eye?

Question

Why haven&#039;t we created a material that is completely invisible to the human eye?

Jazmyn Bean · Accepted Answer

Light allows us to see an object in several ways. You've named some but not others.
If the photons are absorbed, then we can't see the object. You got that right. But suppose they aren't absorbed, then what?
Suppose the photons travel straight through the object unaffected. Then we wouldn't see it either. For example, a clean sheet of glass and ordinary air can both be hard to see because visible light photons mostly travel unaffected through them. Refraction lets us see a sheet of glass when it "shimmers", and waves in the air when it's very hot, because refraction affects their path just enough that we can see the change and the inconsistency at the edges or ripples.
Similarly a material placed in another material of similar absorptive and refractive properties would be hard to see because both affect light similarly, there wouldn't be an easy edge or change to observe - and that's how we detect an object once our eyes receive the photons.
Essentially as you can see, there are only a few basic ways to make something inherently invisible (as opposed to hiding it from view using some other object or effect). We need to not let our eyes see a change where the object should be - that could be no edges, or no changes that suggest an object in front of the background.
So there is also an aspect that it's not a binary (yes/no), it is a continuum (how readily can it be detected with visible light). Meaning, how invisible is the object, how hard is it to detect with light. Also the effect causing this may be very sensitive to the situation - it might be that it only happens in certain conditions, or the observer in certain places relative to it.
That means that we can anticipate achieving invisibility by fooling the eye (camouflage and other effects where we do see, but cannot discern an object), by light being unaffected by the object compared to if the object was absent (hard in air as refraction and other optical effects only need to be slightly present to give away the objects presence), by light being absorbed (only if the absence doesn't suggest an object by hiding the background), or by light being bent around the object or recreating the background (high tech "invisibility").

Why haven't we created a material that is completely invisible to the human eye?

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