(February 23, 2018 at 6:45 pm)Jehanne Wrote:(February 23, 2018 at 6:02 pm)SteveII Wrote: It seems that the fabric of space is expanding--like a loaf of raisin bread being cooked. Raisins are the galaxies and the space between them expands while it is being baked. Raisins move in the dough even as the dough is expanding. Everything is getting further apart but not from a center.
Expanding means the volume is increasing so I don't understand your last sentence.
Professional astronomers don't have a problem with space being an actual infinite:
Quote:The long explanation is below. However, if you just want a short answer, I'll say this: if the universe is infinitely big, then the answer is simply that it isn't expanding into anything; instead, what is happening is that every region of the universe, every distance between every pair of galaxies, is being "stretched", but the overall size of the universe was infinitely big to begin with and continues to remain infinitely big as time goes on, so the universe's size doesn't change, and therefore it doesn't expand into anything. If, on the other hand, the universe has a finite size, then it may be legitimate to claim that there is something "outside of the universe" that the universe is expanding into. However, because we are, by definition, stuck within the space that makes up our universe and have no way to observe anything outside of it, this ceases to be a question that can be answered scientifically. So the answer in that case is that we really don't know what, if anything, the universe is expanding into.
What is the universe expanding into? (Intermediate)
I just wanted your perspective on this question.
From a University of Cambridge conference series on the Philosophy of Cosmology, on the topic of "Do Infinities Exist in Nature" we get the conclusion at the end of the article:
Quote:And opinions are indeed divided. Both Barrow and Aguirre are happy with mathematical infinities and don't shut the door on physical ones either. "I think it's certainly true that we can develop theories that have infinity in them that can be perfectly useful," says Aguirre. "It's certainly true that as finite beings we can only experience a finite part of [the Universe], but I can't see any reason to place limits on whether the Universe can be finite or infinite in principle."
Ellis, on the other hand, does not believe that physical infinities exist and points to potential problems with using infinity in mathematical arguments pertaining to physics. He refers to a famous thought experiment due to the mathematician David Hilbert. Suppose you have a hotel with an infinite number of rooms, and suppose that the hotel is full. The paradox is that you can still fit a new person in; you simply move every person in the hotel one room along, so the person from room 1 goes into room 2, the person in room 2 goes into room 3, and so on. Since there isn't a largest number, you can do this without making anyone homeless and then you can fit the new person into room one.
Because of paradoxes like this one, Ellis thinks that you have to be very careful when you use infinities in a physical context. "I'll make a distinction; there are some times when people talk about infinity when all they really mean is a very large number, and they're just using infinity as a code word for a large number. In that case, I think it's more informative to make a guess what that large number is and to talk about that large number, not infinity. There are some cases where people use infinity in its deep sense; in the paradoxical sense. The paradoxical sense is, for instance, Hilbert's hotel. In my opinion, if a physics argument or any other argument depends on those paradoxical arguments, then this is a false argument and it should be replaced by something else."
In summary there is as yet no consensus as to whether infinities exist in the physical world. In the absence of concrete scientific answers it makes sense to turn to philosophers. "I think it's very important to get physicists and philosophers together," says Aguirre. "I think there's a reaction that a lot of my physics colleagues have about philosophers which is that they don't know any physics. They're just saying things about physics and they don't really know what they're talking about, and criticising physics but they don't really understand it. I think there may once have been some truth to that and I'm sure that there is now, but the philosophers that I talk to all know lots of physics. I see them as being specialists in thinking about the intellectual foundations of those questions, looking at them from a slightly bigger and different point of view than a more empirically or pragmatically engaged physicist would. I think that's incredibly valuable."
Emphasis added
The whole article is very interesting. Also distinguishes early on between actual infinities and potential infinities.