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Euler

Euler

7/30/2013 1:36:58 PM
So I've seen many people, myself included who struggle to come to grips that the universe may be infinite in size when it originated from a single point and is construed to be expanding at a finite speed over a finite time period. The following Physics FAQ cleared this up for me and i thought it was pretty interesting (albeit very old): [quote]There is no centre of the universe! According to the standard theories of cosmology, the universe started with a "Big Bang" about 14 thousand million years ago and has been expanding ever since. Yet there is no centre to the expansion; it is the same everywhere. The Big Bang should not be visualised as an ordinary explosion. The universe is not expanding out from a centre into space; rather, the whole universe is expanding and it is doing so equally at all places, as far as we can tell. In a conventional explosion, material expands out from a central point. A short moment after the explosion starts, the centre will be the hottest point. Later there will be a spherical shell of material expanding away from the centre until gravity brings it back down to Earth. The Big Bang—as far as we understand it—was not an explosion like that at all. It was an explosion of space, not an explosion in space. According to the standard models there was no space and time before the Big Bang. There was not even a "before" to speak of. So, the Big Bang was very different from any explosion we are accustomed to and it does not need to have a central point. If the Big Bang were an ordinary explosion in an already existing space, we would be able to look out and see the expanding edge of the explosion with empty space beyond. Instead, we see back towards the Big Bang itself and detect a faint background glow from the hot primordial gases of the early universe. This "cosmic microwave background radiation" is uniform in all directions. This tells us that it is not matter that is expanding outwards from a point, but rather it is space itself that expands evenly. It is important to stress that other observations support the view that there is no centre to the universe, at least insofar as observations can reach. The fact that the universe is expanding uniformly would not rule out the possibility that there is some denser, hotter place that might be called the centre, but careful studies of the distribution and motion of galaxies confirm that it is homogeneous on the largest scales we can see, with no sign of a special point to call the centre.[/quote] [url=http://math.ucr.edu/home/baez/physics/Relativity/GR/centre.html]Linky to the FAQ, for those interested.[/url]

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