I have mentioned in previous posts, that some UFO researchers suggest that the origins of the UFO phenomenon lie in the concept of a 'multiverse.' This is the idea that there is more than one universe in existence.
I came across an article by George F R Ellis in the August 2011 issue of Scientific American (pages 18-23), put it aside to read later, and have only just come across it again.
Ellis argues that there are in fact two types of multiverse being discussed, which he calls level 1 and level 2.
Level 1. "The most straightforward assumption is that our volume of space is a representative sample of the whole. Distant alien beings see different volumes, but all of these look basically alike, apart from random variations in the distribution of matter. Together, these regions, seen and unseen, form the basic type of multiverse."
Level 2. "Many cosmologists go further and speculate that, sufficiently far away, things look quite different from what we see. Our environs may be one of many bubbles floating in an otherwise empty background. The laws of physics would differ from bubble to bubble leading to an almost inconceivable variety of outcomes. These other bubbles may be impossible to observe even in principle. The author and other sceptics feel dubious about this type of multiverse."
Ellis provides examples of a range of multiverse thinking.
1. "They may be sitting in regions of space far beyond our own." (Guth, Linde and others.) The chaotic inflation model.
2. "They might exist at different epochs of time." (Steinhardt and Turok.)
3. "They might exist in the same space as we do but in a different branch of the quantum wave function." (Deutsch.)
4. "They might not have a location, being completely disconnected from our spacetime." (Tegmark and Sciama.)
"For a cosmologist, the basic problems with all multiverse proposals is the presence of a cosmic visual horizon. The horizon is the limit to how far away we can see, because signals travelling toward us at the speed of light (which is finite) have not had time since the beginning of the universe to reach us from further out."
"All the parallel universes lie outside our horizon and remain beyond our capacity to see...That is why none of the claims made by multiverse enthusiasts can be directly substantiated."
Ellis concludes that "All in all, the case for the multiverse is inconclusive. The basic reason is the extreme flexibility of the proposal..."
"As skeptical as I am, I think the contemplation of the multiverse is an excellent opportunity to reflect on the nature of science and on the ultimate nature of existence: why we are here."