bangstrom » October 12th, 2019, 3:50 am wrote:How am I misinterpreting your quote below about an infinite universe and an expanding visible part?
BurtJordaan » October 11th, 2019, 11:49 pm wrote: Another thing that you have wrong is that the universe started out as a tiny thing - it is only the observable universe that started out tiny, simply because light could only have moved a short distance in the first nanosecond after the BB. As far as we can establish, the universe itself started out infinitely large and obviously then still is...
.
I think your misinterpretation of what he said lies in the fact that there is more than one observable universe. In fact, in a spatially infinite universe, there are an infinite number of observable universes, because there are an infinite number of locations — and the key point is, that
all the observable universes, not just ours, are undergoing expansion. IOW, the entire universe, even if infinite, is expanding, which is another way of saying, very simply, that the distances between galaxies are growing larger over time.
Imagine that you take a flat sheet of paper, a square. Draw a bunch of dots on it. These dots represent galaxies.
Say you have one hundred or so dots on the paper, arranged in rows and columns.
Now, find a dot at the very center of the page, and designate it to be the Milky Way.
This flat paper is a 2d representation of a 3d spatial universe. Now you must imagine that this paper is actually infinite in size — that it goes on forever in all its 2d directions.
The finite square section of the paper is the
observable universe, but only as seen from the center dot — the Milky Way.
However, because the paper is actually infinite, there could be observers at
any dot, and they will have their
own observable universe, and, as for us, it will seem that they are at the center of the whole shebang, and all the galaxies are moving away from them.
For example, if the Milky Way is the center dot, take a dot on the left edge of the paper, and suppose it has sentient observers. It should be evident that, since the paper is infinite in all its directions, these observers will see a
different observable universe than we see — their observable universe, and ours, will only
partly overlap. They will see parts of the universe that we cannot see, and we will see parts that they cannot see.
But both will see the same
phenomenon — that their observable universes are expanding; i.e., the spaces between that galaxies that each set of observers are able to see is growing greater over time. And both will imagine themselves to be at the center of it all, even though there is no actual center.
This means you could redraw the sheet of paper (observable universe) from the vantage point of the left-edge dot, and now THAT dot would be at the center of the page.
Now take two more sheets of paper of the same size. Suppose, again, that the initial sheet of paper had one hundred dots on it, with the Milky Way dot arbitrarily assigned to the center of the page. One paper (the Milky Way observable universe) will no longer have one hundred dots on it, but instead, say, fifty dots. This a snapshot of the future, in which the distances between the galaxies have grown so large that from the Milky Way vantage point, only half as many galaxies will be in the MW’s observable universe, compared with the paper representing the earlier time.
On the next sheet of paper, you could arbitrarily draw as many dots on it as you want — a billion, and trillion — with the Milky Way again arbitrarily at the center of the paper. (The left edge dot I mentioned earlier would, then, be at the center of its
own paper.) This would be a snapshot of the universe, from our vantage point, much
earlier in time, compared with the initial sheet with one hundred dots. So now there are many more objects in our observable universe — just as there would also be in the left-edge dot’s observable universe.
But again, there are an infinite number of observable universes, which is the same thing as saying there are an infinite number of different locations. So ALL these locations will see the same phenomenon — their observable universe expanding over time; earlier in time, the dots will all be closer together. And each set of observers will imagine themselves to be at the center of it all. Note further that if the universe is spatially infinite, as it seems to be, the vast, vast majority of observable universes
do not overlap at all — but each observer will see the same phenomenon, expansion.
The upshot, again, being that in an infinite universe, there are an infinite number of observable universes, and all of them are expanding.
I should add, as a fascinating side note, that in a spatially infinite universe, we should expect there to be an infinite number of sentient observers, including observers with their own telescopes, internets, etc.; and this is true no matter how rare life is — even if we, ourselves, are the only sentient observers in the Milky Way, or indeed in our (own) observable universe. This is because in an infinite space, any event with a non-zero chance of happening should be expected to happen infinitely many times. Clearly, life and intelligence happened at least once, and so … do the math.
The philosopher Brad Monton gave the example of a really bad dart thrower named Fred. Fred hits the bull’s eye (sentience, in the analogy) only once every one billion throws. But what if Fred throws his dart infinitely many times? He gets an infinite number of bull’s eyes.