Hello, Is everything in the universe invisible in its natural state? This question sounds strange, and maybe it's a bit hard to see what I mean, but I'll try to be as clear as possible. Imagine yourself outside of the universe, and that there are no other living beings in it. Since the light isn't reaching your eyes, you can't see the universe. The light inside the universe doesn't mean anything to you, it's just energy. Now, if you have, let's say, a room with nobody inside, being outside of the room would be the same as being outside of the universe when it comes to the meaning of light in the room. Yes, I understand, you can't see an object if your eyes are not exposed to the light reflected off an object, but what if there is no living being to interpret the reflected light? So, maybe a better question is what does light mean to a human if there is nobody around to form an image from the light? Thank you very much.

Two replies: 1. I'd caution against equating natural with non-human , let alone with non-living . Many living beings are in their natural state despite being alive, and many (if not all) human beings are in their natural state despite being human. A hermit crab in its borrowed shell is in its natural state, and so is a human being fully clothed inside his/her house. We human beings naturally clothe and shelter ourselves. 2. Your question seems a bit like the old chestnut 'If a tree falls in the forest, and nothing is around to hear it, does it make a sound?' If a given object reflects light in the visible spectrum, but nothing is around to detect that reflected light, is the object visible? Both questions turn on how we define terms, in particular 'sound' and 'visible'. If sound is simply vibrations that would be detected by a sound-sensor were one present, then surely the falling tree makes a sound. Likewise, if 'visible' means ' would be seen by a normal human observer looking...

Does the fact that our perceptions can be represented geometrically and that geometry consists of eternal truths independent of the mind prove that an external reality underlies our perceptions?

I don't think that such an argument would rationally compel external-world skeptics (who say that no one can know that there's an external world) to abandon their view. External-world skeptics think that no one can know that solipsism is false, where solipsism is the claim that nothing external to oneself and one's mind exists. The solipsist won't grant that geometry consists of truths that are independent of his own mind, because he thinks nothing is. The solipsist could admit that his perceptions have a geometric character to them without having to attribute that character to something external. So I don't think solipsism can be disproven in the way you suggest. All of this assumes that solipsism is otherwise intelligible. But one might argue that solipsism is unintelligible because it relies on the incoherent idea of a 'private language', an idea explored in detail in this SEP article .