Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Garry Reynolds on 02/08/2010 12:30:02
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Garry Reynolds asked the Naked Scientists:
Hi,
I have been questioning mainstream reasoning for a while, albeit only to myself.
My problem is that the "Big Bang" would, if it happened, have been in a particular spot in "space".
The resulting explosion would have sent matter in all directions, presumably, somewhat evenly.
Why, then, can't this spot be located? Why isn't there a huge void where it all began?
The galaxies have been moving away from this for billions of years at a speed much slower than that of light, yet we can supposedly detect light, which travels much faster and originated well before we were set on our way-how can we be in front of it???
I can't put it much better and I hope you understand my puzzlement.
Thanks
From the desk of Garry Reynolds
Adelaide, South Australia.
What do you think?
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The normal answer given by cosmologists is that everything is getting further apart not by moving through space, but the space is expanding. A 2d model of this can be made if you draw some galaxies on the surface of a balloon and blow it up, everything gets further apart without moving across the balloon
So the big bang happened everywhere.
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Another analogy is the "raisins in the cake", see http://www.pnas.org/site/misc/classics2.shtml. The universe is like a cake mix, and the galaxies are like the raisins. As the cake cooks it gets bigger, and the raisins get further apart. My favourite however is a stress ball, like you have in an office:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fthumb%2F6%2F66%2FStress_ball_manipulation.jpg%2F220px-Stress_ball_manipulation.jpg&hash=429ce0d2055da7dbca553066d97bfc1d)
Squeeze it down in your fist, then let go. Think of the expansion of the universe as something like this. The big bang is when space started expanding. It wasn't an explosion of matter through space.
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...My problem is that the "Big Bang" would, if it happened, have been in a particular spot in "space"...
...Why, then, can't this spot be located?
It sort of depends...
If the Big Bang originated from a zero-sized geometrical point, then when it transitioned to having a non-zero size there could have been nothing in the initial point state to result in non-uniformity in the later state.
Both space-time and energy emerged from the BB, but while energy can interact with itself, space-time does not; rather than being a 'something' space-time appears to be a 'somewhere' within which 'something' can exist. As space-time does not appear to interact with itself, then apart from reacting to energy, it is essentially as uniform as the point from which it originated, and just like the originating point, it cannot be said to have a center unless you regard all of it as being the center.
Conversely, some think that the BB did not originate from a geometrical singularity but a quantum sized one. A quantum sized singularity would have non-zero size, and would thus have the potential for difference within the initial state, which could then be propagated as the BB progressed. However, although a quantum sized singularity might be non-zero in size, you cannot precisely say where any of it is at any particular point within that non-zero sized region: like the geometric singularity, its initial state is essentially uniform too, because any differences within it are also everywhere within it. Once again, you end up with space-time being the same everywhere, which means no center.
However, while the universe is generally considered to have no spatial center, it appears to have a temporal origin i.e at least one 'end' - a starting point in time, being a bit under 14 billion years ago. Having one 'end', time would logically seem to require another 'end'. Now, the length of the time line between the two ends could be either finite or infinite, but furthermore it could also be static or dynamic.
If the universe's time axis were to be finite and static, then if it had a length of a bit under 28 billion years we could say that we were roughly near the 'center' of the temporal universe. Alternatively, the length of the time could be infinite, but otherwise static, in which case the future will already be predetermined, but unknowable until we get there. However, although we could say that we were ~14 billion years from one end of the time line the idea of a center becomes meaningless because both the center of an infinitely long line and its further end are both infinitely far away.
In a finite but dynamic universe, we are located right on the far end of the time line from the origin but the line is getting continuously longer, carrying us along with it, further away from the origin and the past. Being finite though, at some point it'll reach its maximum extent and who knows what would happen then? In an infinite and dynamic universe we're still right at the end of the extending time line, but it has no limit and just continues to get ever longer.
I think the most widely held view is that the universe is both infinite and dynamic.
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