Existing comment:
INFINITE SPACE? INFINITE TIME?
Infinity is not just very, very, big - infinity is forever! Does space go on forever - or is it finite? If it is finite, does it have an edge, a boundary? And does time go on forever, or is it finite? If finite, does it have a beginning and an end? Einstein and Minkowski unified space and time in a four- dimensional theater, so what is true for one may be true for the other.
The Earth is approximately a sphere in three-dimensional space - forget about mountains, valleys and ocean depths. Its surface is two-dimensional, forget about up & down. It is finite in area, but there is no edge, no boundary. Set off in any direction, travel as straight as you can, and you end up where you started.
Can you imagine the whole of three-dimensional space being like that - finite in volume, with no edge? Set off in any direction, travel as straight as you can (like a ray of light), and end up where you started. That is a "closed space." It is mathematically possible and is difficult, but not impossible, to imagine.
The whole Universe is expanding now, we believe from a volume much smaller than an atom 13.7 billion years ago, the Big Bang. The expansion seems to be accelerating due to dark energy. Most physicists think the Universe will continue expanding forever. But they cannot be sure, and forever is not just a very, very, long time. But maybe - pure speculation - in the far future it will start collapsing down to end in a tiny "Big Crunch." Perhaps time began and will end with those singular events. Or perhaps time, like space, is finite with no beginning and no end, but is a closed loop. The Big Bang and the Big Crunch would then be the same thing! The Universe could be a fluctuation in some even vaster Totality, with gazillions of other completely disconnected universes: The Multiverse! |