Is it theoretically possible to become invisible and if so how?
In: Physics
Theoretically yes, piratically no, at least not for common understanding of the word.
You might try to argue semantics and try to convince people that stuff like darkness, fog, smoke or even a blanket thrown over somebodies head count as invisibility because they prevent you from being seen, but for most people invisibility has a very fixed meaning:
It means that people will look at you and instead of seeing you they will see something that looks like what is behind you as if you weren’t there.
Most of the ‘stealth’ stuff we have for planes and boats, does not satisfy that requirement. These stealth vehicles simply are built to reflect radar as little as possible.
Camouflage as used by the military might be closer to it, but it mostly relies on dressing people in something that sort of looks like the background and our eyes not being very good at telling the difference.
Active camouflage that changes coloration and texture pattern to matches the background would be even closer, but we aren’t there yet. Octopuses can do that (and also change their shape), but technology can’t reproduce it yet and even if we could it wouldn’t be true invisibility.
For true invisibility we would need to reproduce the background exactly, which gets hard when people look at you from more than one direction.
There are some people who think that new materials may help with that but so far it is al science fiction.
One big problem with depictions of invisibility in fiction is that if all light passes either through you or around you somehow magically, you would be effectively blind. (If not blind you would appear as a pair of eyes floating in the air.)
Another problem often ignore in fiction is how far into the electromagnetic spectrum invisibility should extend. You could just cover the frequencies that human can actually see, but that would leave you visible to all sorts of animals and detection equipment.
Even worse humans don’t just reflect incoming light they also give off some infra-red light of their own. There is nothing we can do to stop that. Warm stuff giving of light is a fundamental part of how the world works. Cooling a human down to prevent them from giving of infra-red light, would actually make them more visible (and uncomfortably cold). Any attempt to magically capture all outgoing infra-red light inside an invisibility field would sooner or later cook the human if left on for too long.
This is also why any notion of ‘stealth’ in space is nonsense. You can’t hide the heat you give off.
So in conclusion, we may invent all sorts of technology to hide ourselves better an become less easily visible, but true invisibility would require magic or technology sufficiently advance to be indistinguishable from it and also leave you blind, and hot and still easily detectable by anyone really looking/listening/smelling after you.
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