Quote: Originally Posted by nilank
The concept of time as a 4th dimension has been confusing me since I was born, lol.
Time as the fourth dimension perhaps an old concept, almost 100 years old concept of time is spacetime. According to it, space and time are not two distinct ideas, but they are interrelated and interdependent.
Space is the vacuum between two objects, and a space has its own geometry. Not just teh same as the Eucledian geometry that we all know, but somehow different, as our daily Eucledian geometry is not perfectly applicable for an infinite graph paper.
In this space's geometry, when matter comes, time generates. Other than the existence of matter, spacetime is like a flat rubber sheet having infinite elasticity. When matter comes, it makes a crunch on that sheet. The heavy the matter is, the deep the crunch is. So different matters create different depths of crunch there.
At teh same time, matters are not of fixed (zero) velocity in that spacetime geometry. Otherwise they have only one option to follow, that is to move at a constant speed in a single direction. If they do so, the time is shorter for them, depending on their pace, velocity. As the pace is tending to the speed of light, the clock moves slower and slower for them. Lights speed is the limiting value here.
Then why time exists as we find it? It exists in this way for those matters having lesser speed, and for that lesser speed they are captured in the crunch of the spacetime of a heavier object. As earth is captured in the crunch of sun. As per newtons law, earth is moving in equal speed, and even in a single direction. It's earths bad luck that the single direction is elliptical due to the shape of the srunch, and it is being forced to move around the sun. Simple, that the net force on the object earth is the crunch of sun. And this very thing generates the concept of time for us. Day = the time earth takes to complete a spin on its axis. Year = the time earth takes to complete a full round around sun.
If earth's speed was different, and it could generate a speed more than the escape velocity from its path, the calculation time must have been different for us.
Time stops, too. Where there is no motion. Even where light cannot move. Blackholes .... where the concentration of matter is infinite, and so it creates a crunch of infinite depth in spacetime. The necessary escape velocity form a black hole is more than the speed of light, so there is no outward movement (apparently
). And that is why time ends there.
Theoretically there is a start of time too, an opposite singularity of black hole, that is big bang.
Practically, there are objects like quasar which makes us think that there was time even before big bang.
And, there are some other important questions about time that which is the shape of time ... is there any shortcut (wormhole) in the time's shape etc.
If you become a scientist, and search the answer to those questions, it will be a great