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Heiiii my first question here!

Right so I'm writing my story and I was going to make the spirit beings just turn invisible (just classic spirit stuff you know) But after reading in this website a fair bit, I prefer it if they just shifted from our visible spectrum to outside of it, and that would be much better because then if they turned completely invisible they wouldn't also be able to see (They can't see you, you can't see them - rule).

Now I dont know much about the history of "ghost hunting" and the equipments+method they've been using so I would preferably make my ghosts in the range of electromagnetic spectrum that famous ghost hunting equipments are able to see.

Also I want a viable way for them from being in our visible light spectrum to outside of it.

So basically I have two questions :

  • where would my spirits shift themselves in the electromagnetic spectrum to be invisible in our eyes but is visible to famous ghost hunting equipments

  • how can my spirits achieve this?

Handwaviums can be used a fair bit!

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    $\begingroup$ Hi, there's an issue with your question as stated : we don't know what "famous ghost hunting equipments" there are in your world, so we can't know which frequency band they can detect. Indeed, remember It's your world, so you can choose whichever equipment (IR camera, mirrors, dogs/cats...) ghost hunters use. Until more details are added, it is more of a brainstorming question. And, well, Stack-Exchange isn't good at all asking for ideas 🐶. $\endgroup$
    – Tortliena
    Jul 24 at 15:30
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    $\begingroup$ Just a note, for clarity: an object which does not emit any visible light appears black, not "invisible". $\endgroup$
    – AlexP
    Jul 24 at 15:35
  • $\begingroup$ AlexP oh my bad, thank you! $\endgroup$ Jul 24 at 16:56
  • $\begingroup$ @AlexP Transparent materials, perhaps with antireflection coatings? Emit in the IR, but not in the visible if at room temperature $\endgroup$
    – UVphoton
    Jul 24 at 16:56
  • $\begingroup$ @UVphoton: Transparent and with the same index of refraction as the environment. For example, glass is pretty much invisible in water; but in air, not so much. $\endgroup$
    – AlexP
    Jul 24 at 17:49

2 Answers 2

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Infrared

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Ghosts are cloudlike creatures. Visible light goes right through them. They cannot be seen with the naked eye.

They are perceptible to humans as a clammy sensation because they are warmer than the surrounding air. This is because the large distance between the ghost molecules interacts with the long wavelengths of infrared light. Ghosts are visible on infrared cameras.

Some Ghost Hunters have eye cells that detect infrared light. Unfortunately but there is no room in their visual field to represent this light the normal way. They internalize the presence as a ghost as a strong intuition that something is there.

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Your spirits are themselves made of electrical fields.

Because otherwise you could throw flour on them and see them. Not that there is anything wrong with that. Breading! But no- your spirits are intangible and consist of coherent energy fields which coalesce and move about according to ghost rules. They perceive the world (in a way) because external electromagnetic fields affect their own fields.

They cannot be seen because they do not emit electromagnetic radiation and do not block or affect extrinsic radiation of any wavelength. They can be detected by devices which detect electromagnetic fields, and possibly visualized using charged particles, which they do affect. So maybe the flour, but a cloud of static charged flour particles.

And they can be heard. Under certain circumstances, spirits generate infrasound.

Naturally occurring phenomena allowing for hallucinations or "visions"

from http://nerdist.com/spooky-science-the-ghost-frequency/

So what’s going on here? It turns out that the infrasonic frequency “can affect humans and animals in several ways, causing discomfort, dizziness, blurred vision (by vibrating your eyeballs), hyperventilation and fear, possibly leading to panic attacks.” If you want to try it for yourself, you can listen to an 18.98 Hz recording on YouTube, but your mileage may vary. You might experience ghostly visions, or maybe even a sense of paralyzing fear similar to that of a tiger’s prey that hears the predator’s low-frequency roar just before it pounces. Or you might not experience anything at all, but better safe than sorry.

Humans cannot hear infrasound but we might be able to feel it. Moving electromagnetic fields can affect our bodies as well. Ghosthunting equipment can definitely detect both the moving fields and the infrasound. Could we speed up the infrasound to frequencies we can hear? Yes. Be careful with that, though. Do you want to hear?

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