On Tue, Jan 21, 2014 at 02:41:46PM +1300, LizR wrote: > On 21 January 2014 14:18, Pierz <[email protected]> wrote: > > > > > > I have been thinking about this and it occurs to me that firstly, the > > single history is only partially true. Since quantum interference patterns > > occur in MWI due to interference between universes, which can only occur if > > universes can merge again after splitting, then at least at this level, the > > past is not well defined. If a universe merges back with another from which > > it had temporarily diverged, then an observer within that universe cannot > > say which path he followed to get there. She followed all possible paths. > > Of course those divergent universes were only trivially different, or else > > decoherence would have made the merging impossible. But of course in any > > real universe, there will be a vast number of such "nanohistories", because > > of the immense number of quantum interactions where merging occurs. So at > > this very short time/space scale level at least, it is impossible to define > > a single history. Correct? > > > > Imho, that is correct. The reason universes tend to diverge more than they > merge would be that the multiverse is far from thermodynamic equilibrium > this close to the Big Bang. > > > > > However at a macroscopic scale, it appears difficult for history to be > > intrinsically ambiguous. In other words the network of "nodes" of the > > multiverse is like a tree not a net. There may be tiny branches that rejoin > > one another at the smallest scale, but the limbs of the tree cannot merge > > back together. I can always define a single route back to the trunk, though > > if I go further up the tree, I will be forced to decide repeatedly which > > way to go. This branching is defined by time, so doesn't this effectively > > give an "arrow of time"? Yet the laws of physics are not supposed to be > > directional in time except through aggregation of effects as entropy. Are > > these two "arrows" related? How? > > > > See above. I didn't realise I was answering your later question when I > wrote that! To expand slightly... > > My opinion is that branching exceeds merging for the same reason that there > is a thermodynamic arrow of time. To see this, imagine a universe at > thermodynamic equilibrium. All processes can play out equally in either > time direction in such a universe (every googolplex years a Boltzman brain > pops up for a split second - but its time sense could go either way along > the time axis, they're now equally (un)likely). There is no reason why the > quantum processes involved in the MWI would not be similarly balanced once > there was no thermodynamic arrow of time. >
In my "Many Minds" interpretation, splitting corresponds with learning some fact about the world, and merging corresponds with forgetting it. This is also roughly the view Saibal Mitra has been arguing for too. Throughout most of our lives, we tend to remember more than we forget, which leads to the above imbalance, although once alzheimers sets in, I guess the imbalance will run the other way. Another example I have put to this list (but didn't mention in my book, AFAICR) is to say that we exist in a superposition of worlds where T. Rexes are blue and T. Rexes are green. There is always a possibility of a measurement that actually decides the issue (perhaps they were actually brown), in which case the universe differentiates, but contra the Deutsch interpretation, its is not a matter of fact, albeit unknown, what colour a T. Rex is. Finally, to Liz, yes - it is the same thermodynamic arrow of time as the second law. Cheers -- ---------------------------------------------------------------------------- Prof Russell Standish Phone 0425 253119 (mobile) Principal, High Performance Coders Visiting Professor of Mathematics [email protected] University of New South Wales http://www.hpcoders.com.au ---------------------------------------------------------------------------- -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
