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Author Topic:   Julian Barbour and quantum cosmology
randman 
Suspended Member (Idle past 4899 days)
Posts: 6367
Joined: 05-26-2005


Message 1 of 1 (374952)
01-06-2007 2:11 PM


One of the more frustrating aspects of the evos here is their constant denial of quantum mechanics. Over and over again, people post what physicists grappling with QM have to say, and what those experiments are, and the evos here, even at least one physicist or former physicist, simply deny the basic facts of both the experiments themselves and what the experimenters have stated about QM.
So from time to time, I may add comments from physicists working to resolve QM with what we see and experience on a macro-level just to illustrate the truth about what QM does say about the material world.
JULIAN BARBOUR: The question I'm always asking myself is, what is the universe and how does it work? I come at it from the point of view of fundamental physics, basic questions of quantum mechanics and its relationship to classical mechanics. Quantum mechanics was discovered in 1925 ” 1926, and it gave a completely new picture of physics which was extraordinarily surprising, and it's still very difficult to understand. It suggests the world is not at all like we see it. That has remained a really big problem, and it's getting more and more discussion, more and more interest from people. This is what I'm really thinking about; how to reconcile the fact that the world seems to be classical, we seem to have unique past, things seem to be in definite positions, and have a definite future ” that's what it seems to be like, but quantum mechanics tells us that it is different ” not like that at all. The aim is to try and find a description of the entire universe that is quantum mechanical and understand how it nevertheless it can look like the classical world that we actually see and experience.
I hope some at least will have a place in the new picture of the universe for which so many physicists are groping, one that is completely quantum ” mechanical and not half quantum and half classical. What my Italian collaborator Bruno Bertotti and I managed to show is that the world is strongly relational according to the physics as we know it now, but this hasn't been properly recognized. The people like Leibniz and Ernst Mach who criticized Newton really were right. Einstein somehow or other put this into his theory without anyone, including Einstein himself, properly appreciating it. The world is relational. It is about how real things relate to real things. This is potentially important for how we try to picture the quantum universe.
But you can see where the idea of a timeless universe will come from if you consider the way quantum wave mechanics was discovered by Schrodinger in 1926. In classical Newtonian physics, if you have three particles they will always be at definite positions at definite times. They will form some triangle, and the center of mass of the triangle will be somewhere and it will have some orientation. Now what quantum mechanics says is that, until observations are made, for all these quantities, there are no definite values, but only probabilities, all of which change in time.
When you've got to the top you can understand what you could see lower down, but you couldn't understand it properly when you were lower down. I see the progress of science being like that, that suddenly completely new vistas are opened up, and you find new ways to think about it. I do think we are discovering the world, not inventing it. But John Wheeler sometimes seems to suggest that we create the universe. He thinks
that by insisting on finding a consistent description of it we conjure it up by a kind of conspiracy. He illustrates the idea by a variation of the game of twenty questions in which there is no object at the start of the questioning. Instead, each answer that is given must be consistent with all those already given. Eventually, there emerges some object that matches the answers.
The people who will not like me are the people who don't want to take the many ” worlds interpretation of quantum mechanics seriously, and who are trying to modify quantum mechanics so as to banish that specter. I don't think Roger Penrose would take it very seriously, because he doesn't like any form of the many ” worlds interpretation of quantum mechanics. Stephen Hawking might be quite sympathetic, because he's been basically working along those lines for many years now. Other people who I would not expect to be sympathetic are Murray Gell ” Mann, Jim Hartle, and several others who have developed the so ” called consistent histories approach to the interpretation of quantum mechanics. They start out by taking a complete history as being a fundamental concept, whereas for me the Now is the starting point. They start with a string of Nows.
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