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I reasoned with myself one day that we as humans cannot really 'see' the universe with our simple naked eye, and only when we discovered the existance of things such as ultra-violet rays and the like could we make instruments to 'see' them...and so couldn't it be possible that the universe is much more 'full' then we currently think, as we can't actually 'see' what's there with our limited perceptions, and simply haven't the instruments to view or sense them for us, as we are obviously ignorant of their existance in the first place?
Let's say, for instance, there could be anything between here and the moon, only we have not the capabilities nor the knowledge of its existance to sense, view or detect it in any way.
It sounds like you're talking about more than just light but I want to start with that. The sun's emissions peak in the visible region (i.e. it's brightest in those wavelengths) of the spectrum, which is why our eyes evolved to see visible light in the first place. Aside from stars, however, the emissions of most things
don't peak in the visible part of the spectrum--since the wavelength things emit at is temperature dependent--and yet we still see most things. What I mean by that is that almost everything around you, including you, is emitting radiation in the infrared portion of the spectrum. It's true that in a pitch black room you can't see much without the help of special goggles designed to pick up infrared light but when a source of visible light (the sun or perhaps a lamp) is around then things become visible, simply because they'll reflect visible light, even if they're not emitting it.
As things heat up, they emit light of shorter wavelengths (higher frequencies) so something at room temperature that just keeps getting hotter and hotter will go from glowing red to blue to white. However, the amount of visible light it emits will keep increasing, even as its temperature gets so hot that its peak wavelengths move into the ultraviolet or even beyond that. What that means is that we can never heat something to the point that it becomes invisible because even if its emitting most of its radiation in a low wavelength that we can't see, it still leaves a long tail through other wavelengths--that is, it emits lots of visible light that we can see, too. So its really only the cooler bodies that don't put out enough visible light for us to see but as long as the sun shines on them they'll at least reflect enough light for them to be visible to us.
I guess your broader point, though, is that maybe there are things analogous to wavelengths of light that can't be seen. Dark matter has been mentioned in this thread and that might be a decent example of what you're thinking about. Only particles that are charged will interact with light (of any wavelength); if it's not charged, it won't emit electromagnetic radiation and we won't see it (even with the fanciest detectors that can see at almost any wavelength).
As far as we understand, there are only four ways that something can interact with the rest of the universe. One is electromagnetically (i.e. through light) but as I just said, only charged particles can participate in this way. Another is through what's called the weak nuclear force. Instead of trading photons, particles interacting this way trade what're called W and Z particles. Light can travel over great distances but W and Z particles can travel only over extraordinarily tiny distances so the weak force is a very short range force. The same is true of the third method of interaction, the strong nuclear force. They're called "nuclear forces," incidentally, because they only work over the scale of atomic nuclei. The fourth way to interact is gravitationally and that, of course, does work over large distances. So you can have something that contains charged particles (and thus emits light) and also interacts gravitationally. A good example is the sun--it's bright but also we can feel its gravitational pull. You could also have something with no charge (i.e. doesn't emit any light) but does emit gravitation. We wouldn't see something like that but we'd see its pull on other objects. It would literally be dark matter.
In order for there to be another way things interact that we can't see and don't know about there would need to be some fifth force, which is possible. There is, however, another possibility which you might find interesting. In this suggestion, the same forces (interacting through photons, W's, Z's, etc) are at work but they're still invisible to us because they are a sort of mirror image of the photons, W's, and Z's we're familiar with. It takes a little while to explain but ultimately it suggests there really could be anything between here and the moon and we wouldn't be able to detect it (except through its gravity).
Check it out in this thread:
Mirror matter.
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What if there is some type of dark matter that dosent even affect gravity?
As we understand the universe, all energy couples to gravity. Meaning that if it exists, it interacts with other things through gravity. You can't avoid it.