Quantum theory implies that vast numbers of other experiences of mine, including the experience of drinking coffee at this moment, are also taking place.

I am a dummy about quantum theory so although I was interested I hesitated to respond to the link to this review lest I appear ridiculous - I know you lot. Still, Jackie took the trouble to post it, so…pretentious random thoughts they may be...

The author under review (and the reviewer for that matter) says that the existence of the multiverse as a reality is what leads to those aspects of quantum mechanics that can be perceived and measured (we’re back to that darn cat again, I note). This is something I can only accept by suspending my disbelief. I do this in order to watch something like Babylon 5 or to read an early Keith Laumer novel, but to accept this metaphysical concept as a reality, as the author does, is far more difficult. It really seems to be opening up the possibility of wormholes and time travel. I don’t say this in order to ridicule, but to demonstrate the amazing nature of things being said here – almost as though if you can imagine it then it exists even if it’s impossible. That is all wonderful and may be a hope for the future. People like to query the value of pure research, but in truth it opens up almost limitless possibilities.

All of this started me hunting for more information on theories of the universe and I found a great deal, some of which I may just have understood, but most that I didn’t and some just weird. As etaoin said - there's a lot of stuff on-line, isn't there? I found some work by Devin Harris, a new name to me. As with Stephen Hawking’s ‘A Brief History of Time’ I was given a feeling of concepts that were almost within my grasp, tantalizing glimpses rather like a dream that seems quite logical while you are dreaming, but on waking drifts away and no longer quite makes sense.

The big bang process for development of the universe is a simple enough image, but it seems to me to indicate that the universe cannot (at least yet) be infinite because the fact of expansion predicates the existence of an expanding outer boundary, for matter anyway, and of a finite amount of matter within it. Apparently the universe may grow indefinitely or not, depending on its curvature which in turn is governed by its density, but I am not clear whether that means that it would include an infinite number of all types of object or a finite number spread infinitely far apart. If there are, or will be, an infinite number of objects, then it would seem that every alternative that is possible within the known and unknown laws of physics must occur (an infinite number of times?). Because those alternative realities would then already exist in this universe it appears to me that there would be no need for alternative universes peeling off from ours every nanosecond and then themselves splitting and re-splitting as the choices multiplied infinitely. Or is that actually the mechanism by which infinity works? Or is it just an analogue?

I am not sure I can suspend my disbelief to the degree required! I thought I understood the concept of infinity; that was a conceit, now I know I don't – or at least I don’t think I believe in it except as a mathematical convenience.