I watched Kyle's Because Science video on The Predator and 1 thing he talked about was IR vision. Here was his argument:

If you can see nothing but infrared light, you can only see the ambient temperature and thus you couldn't see anything.

I would argue strongly against that simply because not all things react to heat in the same way or to the same extent.

1 simple way to disprove his argument would be to have a set of materials that each react differently to heat such as these:

Metal: conductor

Glass: Traps heat

Body of human or animal: Emits heat

Water: High heat capacity

Plastic: Insulator

Make sure they are at exactly the same temperature and then see them in infrared. You would clearly see differences in what appears to be temperature.

The metal would appear to at least be several hundred degrees if not thousands of degrees. The glass would also appear very hot but not as hot as metal. The body would appear to be at the temperature it actually is at. The water would appear to be significantly colder(it might look as cold as ice even if it isn't that cold). The plastic would appear to be only slightly colder than the body. You wouldn't be seeing the temperature but rather the reaction to heat.

Another easy way to test would be to look at the body of a human or a creature at its starting position, and then continue looking at that same position as the creature or human moves while at the same time not sensing movement with any other senses. You would see a faint heat signature that dissipates within milliseconds and the colder it is, the faster the heat signature dissipates. In other words, even if you couldn't tell the exact shape of the creature or human, you could still tell that it moved by seeing a faint heat signature.

Thus I do believe that Kyle is wrong.

You could sense the movement of an object or how it reacts to heat, not just the ambient temperature. Yes, you could tell just from looking outside whether it is 40 degrees or 80 degrees. But you could also tell how an object reacts to a change in temperature or if an object has moved. Nothing would get past you since there is no object that doesn't emit heat. Even black holes emit a small amount of heat. Yes, even cold blooded creatures like lizards that would blend into their environment as far as temperature, you could still see.

In other words, unless your eyes were injured, got cataracts, or are effected by genetics, you would never go blind until you die. You wouldn't even be night blind. Even in a jungle at night during a new moon, you could still see everything around you. You would even be able to see your own abdominal and chest organs. You could see if you are pregnant or gravid long before you actually look bigger. You could see if something was inflamed and what it is before you get any symptoms.

But am I right that you could see anything with infrared vision including black holes and cold blooded creatures and that night blindness would simply be impossible without something directly effecting your eyes?

closed as off-topic by Mołot, M i ech, nzaman, Renan, nullpointer Nov 23 at 1:55

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about worldbuilding, within the scope defined in the help center." – Mołot, nzaman, Renan
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 4
    I miss the worldbuilding here. It's a plain physics question. – L.Dutch Nov 22 at 6:22
  • 2
    I'm voting to close this question as off-topic because it should be moved to Physics Stack (after several edits). – M i ech Nov 22 at 11:41

This is only (maybe, sort of) true for vision in the far IR, say greater than 3 microns wavelength. By contrast, visible light is 0.4 to 0.7 microns. And even then it is demonstrably untrue.

Sunlight has appreciable energy out to about 3 microns, so at wavelengths less than 3 microns you get differences in reflected light which would allow "normal" vision.

Beyond about 3 microns, all you see is emitted thermal radiation, which peaks at about 10 microns for room temperature black bodies. If all objects were at the same internal temperature and all objects were black bodies, Kyle would be correct. However, since most objects, especially living creatures, are not at ambient and they have varying emissivities, long-wave IR vision is perfectly possible. It's called thermal vision when you shop for a unit which does it.

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So, assuming you are not seeing a blank image, I wouldn't pay much attention to whatever some dumb script writer thought he knew.

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