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Time, Space and Light-Cones
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Simultaneous is not simultaneous. Space and Time do not exist. These, and other strange and wonderful things, are the hallmarks of Einsteins' Theory of Relativity. Something can’t move through Space without moving through Time as well (note: simultaneously!). The Theory of Relativity dispenses with Time and Space, and instead describes a new thing called Spacetime.
Imagine a train moving in a straight line Eastward. We can map its movement through Space, Time or, best of all, Spacetime! With a simple Spacetime graph, we map Space horizontally and Time vertically. In the real World, there are three Dimensions of Space – length, width and height. Thankfully, theere is only one Dimension of Time, and it runs from the Past to the Future (unless you’re looking backwards.) To graph something using all four dimensions is hard, so instead we just take two Dimensions of Space and make a horizontal plane, then map Time vertically.
Now imagine a flash of light. Say you were standing on a hill on a moonless night and turned on a torch for a second. The light would spread out in every direction, lighting first the bushes near by, then later the trees in the distance. If we think about it in just 2 dimensions we can draw it like an expanding circular wave in a pond, maybe caused by a rock we threw inside it. We all did something like that in our life! Now, to get to our case in point, we have to map this "Event" (I call it "splash" because it is easier to imagine than a flash in the night, even though the principle behing them - the Events - are absolutely the same).
Now, if we map Time vertically, and stack the sequential (and increasing in size) "waves", which pile-up one on top of the other, we get a cone whose Summit looks down. The flat area is "our Present" Time (see the upper portion of the imaged picture). Now, let's go back to the Light. A Light Cone is a flash of light moving through Spacetime. Usually people draw it as two Cones: the bottom one is Light collapsing into a single Event, and the top one is it exploding out again. (watch the imaged picture again and very well)
Did you get it?
But "why all this"? Is it really useful to do that? Well, I do not know. Some people think that, in this way, we can better imagine the World. It shows how the Past can influence the Present and the Future. When the Light Cones overlap, it means that two Objects - or Events ! - interact/ed with each other. Every Event in the Universe has an associated Light Cone, so this is a (kind of) mathematical way to represent the Universe, and the basis for lots of complex Physics (such as curved Spacetime, and why simultaneous Events are relative to the observer.)
The Theory of Relativity replaced the absoluteness of Space and Time with the absoluteness of the Speed of Light. However, all that given, I do believe that this "speculation" is very inspirational, but I also - and very humbly - think that something "BIG" is still missing here.
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(Dettagli)
