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Originally Posted by freeztar
I found the use of the word "touch" philosophically profound. Photons "touch" our eyes. When I look at Mars, I'm not experiencing Mars directly, I'm "touching" the photons reflected off of it and into my vision. It then goes into my perception and is interpreted from there. Mars is tangible to me only by interfacing my optic nerves with the reflected photons off its surface. All other senses can be thought of in the same manner.
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You've got a good point. Also, if gravity is an interaction of gravitons then it would be equally tangible.
Quote:
Originally Posted by freeztar
So, is time tangible?
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Certainly not - at least, I would think not. Time seems no more tangible than space (distance). I intuitively think of both time and space as descriptions of the universe rather than anything in the universe. Properties of the universe should apply to things in it, but not in a tangible way.
For example, describing the universe, I would say there are three dimensions (not counting time). That property of the universe applies to everything in it, but doesn't make "3 dimensional" a tangible thing that can be touched. It's just the way things most fundamentally are - 3 dimensional. The universe has this property time, and that property applies to everything in it. But, that doesn't make time something you can touch.
The way I think these fundamental properties of the universe can be identified is recognizing the "things" or "concepts" that apply to every situation and every thing. They are the things that have to be present to fully describe anything. If a photon hits an atom and ejects an electron and you want to fully describe what just happened then time and distance absolutely have to be in the description or you can't describe it. You could not simulate it on a computer without those variables. If a moon is orbiting a planet then you need space and time in the description. I can think of no real situation that is possible in our universe where space and time are not a property of what is happening.
Interestingly, it is possible to describe different universes by changing these properties. What if time went the other direction? Well, entropy would decrease over time. The broken plate on the floor would come before the unbroken plate on the table. That's not our universe, but it logically would work for such a universe to exist. What if there were 4 spatial dimensions? We can describe that mathematically and investigate what a universe like that would be like - but it's not our universe.
EDIT:
So, perhaps it all depends on how you look at it. If you define tangible to mean "the ability for two things to interact" and you don't put any constraints on those two "things" then you could logically conclude that 'time' is interacting with 'matter' and therefore a tangible interaction is happening. If, on the other hand, you define tangible in the more traditional sense as "the ability for mass to interact" then there is no tangible interaction happening.
It is, however, important to stress how real these non-tangible processes are. For example, if a photon is emitted in a distant galaxy and lands here on earth then something made the photon change on its way here. Its wavelength got longer and it lost energy. Did something tangible happen to the photon? Not really, but something real certainly happened to it.
On a side note, it seems incredibly difficult to use human definitions and human concepts to describe these things. They come with a lot of baggage. Describing the universe with math is so much more definite and applicable than with words like tangible and time.
