Real x-ray vision, the ability to (at least) detect X-rays as a 'visible' light (or any other detection system) seems it would be very problematic. X-Rays are a high energy form of electromagnetic radiation and are very damaging to living tissue (at least on Earth).

So developing a sensor to detect it would suggest that the evolutionary process felt the need to detect them, maybe as a way to avoid them?

So what would cause a species to be able to detect x-rays and still live in a viable environment that wouldn't cook them to death?

Or might they have developed (like Superman) an X-ray transmitter for communication? Or a natural biological weapon?

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    $\begingroup$ Are you suggesting xray vision for superman is like normal vision in that superman is seeing the existing xrays (like we see light) or more like sonar where superman is generating the xrays and bouncing them off targets to see what returns (the latter being the reason all the women in superman's life develop extremely aggressive breast cancer)? I don't think background xray radiation is enough to see, nor am I aware of a biological process capable of generating xrays $\endgroup$
    – Twelfth
    Nov 10, 2014 at 18:43
  • $\begingroup$ No, I'm pretty sure Superman's vision is more like a radar system. Though I think just being able to detect EM outside of 'visible light' would be more reasonable that his 'laser beams'. $\endgroup$
    – bowlturner
    Nov 10, 2014 at 18:57
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    $\begingroup$ Mantis shrimp make Superman's super powered visual perceptions look like black and white TV. Since mantis shrimp actually exist, I'm pretty sure that x-ray vision is biologically possible. Heat vision is another story though ... $\endgroup$ Nov 11, 2014 at 6:15
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    $\begingroup$ @RBarryYoung Being able to distinguish many different frequencies within a fairly narrow band doesn't have anything to do with being able to detect frequencies way outside that band. $\endgroup$
    – smithkm
    Nov 11, 2014 at 20:41
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    $\begingroup$ I don't think it is correct to say "it would suggest that the evolutionary process felt the need to detect them, maybe as a way to avoid them?". The evolutionary process begins with random mutations. Only those mutations that offer an advantage to the host will survive in the long run. However, there may be many generations of hosts before a unhelpful mutation dies out. $\endgroup$
    – abcdefg
    Jun 22, 2015 at 0:37

5 Answers 5


X-Rays are not death rays.

Yes, they are (or at least can be) high-energy radiation, but at low levels they can still be detectable without "cooking" anyone or anything. In fact, at this very moment (unless you're sitting your lead-lined radiation shelter), you are being bathed in X-Rays that are the result of the background cosmic radiation interacting with our atmosphere and generating a slew of secondary radiation. It's of course heavier in the upper layers of the atmosphere; so much so, in fact, that it's actually a concern for airline crews and very frequent travelers -- though that's mostly from the other types generated rather than the X-Rays per se.

Back to the point: Why would any creature evolve the ability to detect X-Rays? Putting aside that evolution isn't some intelligent entity that sits on a mountain pondering, "What should I evolve next?", as anyone who has been to the dentist or broken (or suspected they broke) a bone, X-Rays are good at passing through things. So one advantage a creature with "X-Ray vision" would have could be the ability to better see other creatures (or hazards) hiding in foliage, for example; they'd be able to see a skeleton behind that cluster of leaves over there.

Another advantage -- though of more utility to an intelligent creature -- would be to be able to see and diagnose skeletal problems, such as broken bones, without the need for complex machinery. This could allow a herd to more readily identify and care for an injured individual, or a predator to more easily spot the weakling in the herd and go for them. (Consider e.g. a hairline fracture, which you could walk on with not much more than a limp just fine; suddenly have to start running and zig-zagging to avoid a predator, however, and your own evasions could snap the bone the rest of the way, crippling you at the worst possible moment!)

And, of course, it would give any creature that could see them a big bright practically-neon warning sign to stay away from any very high-level sources that could be dangerous to even be in the general vicinity of.

That said, however, the background radiation isn't strong enough to get photographic quality images of bones. Not in our environment, at least. There could still be some of the same benefits, but far from the dramatic representations of Superman's power (which, more often than not, is "see-through vision", not really "X-Ray vision" /soapbox). There are, however, other types of radiation, other particles, that could have similar results for a creature capable of detecting them, yet don't pose a health hazard by simply being present at the necessary levels to be useful.

On the other hand, a creature in an environment where X-Rays per se are present at a high enough level to be truly useful would no doubt have evolved in a way to be resistant to, if not immune to, the negative effects X-Rays have on our biology; they most likely, in fact, have a completely different biology altogether that isn't affected by X-Rays. It's even possible that "X-Ray vision" would be the de facto form of vision, instead of seeing what we describe as the "visible spectrum".

A third possibility is that a creature has evolved the ability to project short bursts of X-Rays somehow, and combined with this sensory organ that can see them can use it as a sort of echolocation. Evolutionarily this would probably evolve as the eyes developing a third addition to the rods and cones that can "see" X-Rays, and then the creature developing a unique form of bioluminescence that emits X-Rays; it would probably require a massive expenditure of energy, so it wouldn't be something like the angler fish that just lets the thing glow all the time, but it would be useful to a predator on the prowl or a herd animal concerned for the health of a herd mate. Honestly, though, without a stronger description of how something biological could generate and project X-Rays, I doubt I'd find this plausible.

  • $\begingroup$ Many of those things went through my head when I was asking the question, but you've organized them well. $\endgroup$
    – bowlturner
    Nov 10, 2014 at 17:22
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    $\begingroup$ X Rays are good at giving a view of the crystalline structure of matter that they pass through. The evolutionary value of this 'sight' seems minimal. $\endgroup$
    – Oldcat
    Nov 11, 2014 at 1:33

Kromey's answer is much more thorough...I'm sticking to biology instead of evolution

There are x-ray sensitive cells apparently (google planarian X-ray-sensitive stem cells for a bunch of barely readable research papers on the topic). Wasn't aware of this until your question prompted the search. From this standpoint, it does seem biologically possible to have 'eyes' that can actively detect x-ray radiation and translate what it receives into an image in the brain. However if this detection method can co-exist in our current eye isn't known, and I suspect highly unlikely as they are vastly varying cells. So off chance that an eye designed purely around detecting xray's is biologically possible, highly doubtful that it would be found in the same eye that detects our visible spectrum.

Xray creation is a bit different...our medical version is firing high speed electrons into tungsten (or tungsten alloys). The impact knocks out lower energy electrons, which are replaced by high energy eletrons that emit the extra energy in the form of xrays as they replace the lower level ones. This is a high energy process occurring in a vacuum. If there is a biological process that replicates this, 'exploding eye syndrome' (EES?) is likely a medical term for their doctors. I can't find any information on a more 'natural' process for xray generation that doesn't require this high energy setup.


  • Yes, it's possible in the right conditions an 'xray' eye could evolve, but would require different conditions than earth (all they would see here is grey outlines)

  • No, it is very unlikely to outright impossible that an xray 'eye beam' could ever develop like sonar has


X-rays, unlike light, are ionizing radiation, meaning x-ray photons have enough energy to knock electrons out of an atom completely. Molecules can be engineered to respond to particular wavelengths of light, which is how our retinas (and other things) work, but all organic molecules respond to x-rays the same way, by being smashed. So color x-ray vision would be out.

Also, x-ray optics are very different to light optics. The wavelength is much smaller, so lenses and apertures must be very small (below microscopic scale); and all matter (certainly organic matter) is very nearly transparent to x-rays, making it hard to construct a retina or a light-tight enclosure, both of which are needed for directional light detection.

I can imagine scenarios where aliens have x-ray detectors, but those organs definitely wouldn't look anything like our eyes. They'd probably be very large, perhaps surrounded by a mineral or metallic shell, with nothing like a visible pupil or iris.

If you were a gasbag creature living in a Jupiter-like planet, with a pulsar a couple of light years away, you might be able to see a lot by detecting x-rays, and there probably wouldn't be enough visible light to be useful. You'd get a lot of cell damage, but there are ways round that, like having robust error-correction built into your DNA coding.


Superheros which Superman has shown the capacity to "meet or beat" in regard to their superpowers - such as The Flash - make the claim that they can perceive events which span the course of an attosecond or less. Superman's perception of events would necessarily need to be on a similar level; while not necessarily as acute as The Flash, one has to cede that the ability to successfully maneuver at high percentages of c means an enhanced perception of events.

Processing that intake is another story, but Superman is often shown to filter out the noise of the entire planet Earth and hear a single cry for help, or focus his visual acuity down to microscopic levels. He can direct his sensory perception with incredible focus.

If Superman's yellow-sun-charged intellect and perception allow him to perceive the world around him as well as correctly process the information, it is possible that his so-called "x-ray vision" works in a manner similar to femto photography. Femto photography, as demonstrated during this widely-shared TED Talk, can not only catch light in the act of movement but can extrapolate the position of objects that are beyond line-of-sight; purportedly, the technology has been used to image objects around corners, and could potentially be used to view the internal organs of an individual without the use of x-rays.

Now, Superman's sight is commonly attributed as "x-ray vision" which produces a strong association to the actual use of x-rays, and whether or not it is directly tied to his ability to fire heat rays from his eyes is a matter not easily solved (nor specifically asked in this question). However, I simply submit that if one is already willing to accept the premise of Superman's powers under a yellow sun, and then compare it to those feats which he has shown proclivity in achieving, the act of simply perceiving events with such fidelity and having a super-intelligent brain that can correctly interpret the data collected in such a short span of time just becomes a matter of inference.

  • $\begingroup$ This answer wasn't even in the ball park for what I was looking for, but it was excellent none-the-less! +1 btw. $\endgroup$
    – bowlturner
    Nov 11, 2014 at 21:01
  • $\begingroup$ Ohhhh, I got hung up on the Superman aspect of it. Blimey $\endgroup$
    – Stick
    Nov 11, 2014 at 23:02

Supermans X-ray Vision may not actually be X-ray. There are two ways how vision might work

  1. When any electromagnetic wave passes through any material some amount energy in the wavelength corresponding to the characteristics of the material will be absorbed (this how spectrometer works) so when multiple materials of different types are arranged in layers they absorb some wavelength corresponding to their matrial and the resulting waves will interfere with each other and are diffracted or reflected thus masking the signal of the inner layer thus making it opaque. When humans see we only see the visible spectrum thus we see colors corresponding to the material wavelength. So if supermans vision has more range in the elctromagnetic vision than us and if he is able to some how able to filter the noise and form image with these wide signals he might be actually be able to see through objects of some thickness.

  2. Supermans eyes may have cells that can vibrate at different frequencies simultaneously.For example when superman sees through metal inside wood the cells in his eyes may vibrate at resonance frequency of the metal thus some how detecting it and giving him ability to see through wood (some what like metal detector). This also explains how his heat vision works.But to have this superman must have really big eyes or somehow his biology has to find a way to put many cells in very small area.

In evolutionary point predators hunting for prey might develop such vision to hunt for prey that hides among solids.


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