Re: Big Bang

mathieson.dave@xxxxxxxxx wrote:
On Apr 6, 7:21 pm, Guido <NOguyhillS...@xxxxxxxxxxxxxxx> wrote:
Terry wrote:
Shouldn't we be able to see the center of the universe? Shouldn't it
be empty and the empty growing larger?
According to Hubble's law, all objects in the universe move away from
us, and the farther away an object is, the faster it recedes. At some
point stuff will recede from us with the speed of light, determining the
extent of the observable universe. The distance at which this happens is
independent of the direction you are looking in, so the observable
universe is a sphere with you in the center.

Therefore: yes, we are able to see the center of the universe, and no,
it is definitely not empty.

One thing I've never fully understood about Hubble's law - at what
scale does it apply? I know that things like stars and galaxies are
all moving away from each other, and the best explanation that's
usually given is that 'the space itself between them is expanding'.
But does this also apply to space at much smaller scales, e.g. the
space within us? I realise that the effect would be miniscule at these
scales, but is it happening at all, or is there some aspect to this
expansion that means that it only happens at larger scales?

As a rule of thumb, Hubble's law holds true only on scales comparable to the distance between galaxies. High-density regions do not in fact expand (note that I do not mean earth-like densities, but merely densities much higher than average in the universe) because they are kept together by their own gravity. So our solar system does not expand, nor does our milky way. OK, there might be some residual effect, but it will be very very tiny.

Of course, other forces are also at work. As others stated human beings are kept together by electromagnetic forces, but on a planetary scale and higher everything is electrically neutral (because the EM force is so large compared to gravity) so gravity is the dominant force.

.

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