singular point

[reloaded]

uhmmmmm , call me stupid if you like , but if there was a single big bang , how come the universe expands in all ways equally and not from the starting point ? surely this cant be !

[dafyd]

it does expand from a starting point... somewhere in the middle of the universe is a point that isn't moving, where the universe started.

[NetSquirrel]

The idea that the Universe is isotropic (I think I have the right word there) is old and dates back to...well I forget...someone will know.  The analogy we were given in AS Cosmolgy was to think of the expanding Universe as a balloon with more and more air being blown into it.  The skin of the balloon represents the main bulk of the matter in the Universe (the galaxies and so on).  This analogy doesn't sound perfectly accurate, but is quite close I'm told.  Obviously, there is some matter closer to the "centre" of the Big Bang and some further away than the main group, so the skin of the balloon would have to be quite fuzzy.

[bernardo]

It is perfectly possible for the Universe to expand from a starting point, and in all directions equally.  There is no contradiction.  WVNBIVDB

[GuavaHalf]

Think of cake mixture with currants in. The currants are galaxies and the mixture is the space between them. As the mixture is heated up the mixture expands in all directions and the currants get further apart.

[reloaded]

uhmmmmmmm , call me even more stupid if you like , but i kinda understand the balloon and currant bun theories , except neither of the two start from a single point .surely any bang , explosion or expansion starting from a single point of reference must expand radially from that point .the balloons surface is a good example of how the universe expands now , but when did it lose its outward direction from its starting point ? can we ever follow the expansion in reverse to find the point of the big bang ? ps thankyou for all your answers : ) 

[anthomson]

You are assuming that the point has a medium in which to expand out. But the singularity IS the universe and the big bang is completely self contained.  Better to think of it as a rapid expansion rather than as an explosion. The universe is isotropic (no centre) and homogenious (the same through out). In the expansion every point within the universe is moving away from every other point. You could therefore consider any and each point within the usniverse as the centre since the rest of the universe will be moving away from it.

[reloaded]

uhmmmmmmm , thats what my brother said , i still dont get it tho , even gases must expand from a point outwards . so ok then , what would happen if the universe started to contract back on itself , it has no reference point to end up back as a single point .

[Yinzer]

Ouch, my brain...

[NetSquirrel]

It's one of those things people tend to just get taught and remember all the fancy terms, as opposed to actually understanding what the terms mean.

[ajmmac]

if u have an explosion in a building large enuf then all parts of the building will be projected outwards in 3 dimensions--in this case a sphere with eachpart moving away from each other part hence the building will expand into the surrounding atmosphere in the form of a sphere--in theory--but some parts will be blocked by obstructions and have their path diverted--like into the earth but u would still get a crater of some kind--an eplosion i a stationary object at high altitude would act in the way the big bang does until gravity took over and all the bits fell to earth

[reloaded]

uhmmmm well i kinda see how ajmmac explanation is , but thats my point , if it explodes or expands in a sphere style , then radial expansion of stars will be shorter than stars expanding on the circumferences bit like an onion . i just dont get it

 

[ajmmac]

ur correct reloaded--the expansion of matter on the circumference of the sphere has now got slower than matter near the centre--hence the belief that the universe must eventually start to contract again due to gravity and will ultimately contract back to its point of origin and probably collapse to a black hole

[reloaded]

so that means the universe doesnt expand uniformly in all directions !!!!!!!!