DAMN YOU YAZ!!!! I'M T N S, NOT TIME!!!! Time is the subject matter, not the poster
You say length and time is a constant, but speed effects how we perceive things. Speed is Distance/Time, so surely one of them is not a constant.
Little interesting thing to think about is that light itself is suprisingly travelling at the speed of light. Those stars you see, might not even exist anymore, but according to the light travelling across the universe, it's still burning merrily away. That is kind of what Yaz meant by seeing things differently in different times.
Perception creates difference. We see stars and planets far away doing things that happened ages in the past. Distance creates that difference that makes time vary. If everything were to exist in one point, then there'd be no such thing as distance. So I'm guessing distance is the variable, as obvious as that may have seemed to begin with.
So I'm not even seeing the cursor flashing in this text at the time it's actually flashing. So every single point in the universe exists in a unique time. So that might be what is meant by the fourth dimension. Everywhere is measured by length, width and height, but each point exists in unique time.
Actually that's even more interesting. Think of light like a piece of clay. You put your hand in it and it keeps the shape, but eventually degrades. Light is a lot like that. The moment light is emitted from an object, it's like freezing mass in time. The energy remains unchanged, unless it degrades, so the image seen remains unchanged for however long the light is moving. So I guess time is unique to matter, whereas energy is isolated out of time, until it interacts with matter.
Now that's interesting!
But light is affected by time as well, because light isn't everywhere at every moment. It travels also at a set speed from point A to B, which are dictated by matter. But that is because light energy is, as Yaz said, photons, which are very small masses. Light comes from an object that is excited, which is how a plasma works. Interestingly I think badash's link mentioned stuff about plasmas. So it is perfectly believable that light, having been created by the excitation of particles, is accountable for all of the missing energy in the universe. You can only see light if you're standing in it's path, otherwise it can't be seen.
Just try standing in a dark room with a small window and see if you can see the light entering the room, the only reason you can see it is because of a) Diffraction and b) Dust particles reflecting some of the light. From the side of a light wave, if we imagine it as a piece of string, it can't be seen. Perfect example is fibre optics. Look at the end and there's light, look at the side and there's nothing, although that's due to the critical angle of the fibre.
So there could be light EVERYWHERE, but unless we're standing directly in it's path, we can't see it. Which is why the universe appears dark.
Just a thought.
Açieeed! style by