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PostPosted: Mon Sep 28, 2009 8:24 am 
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SpaceTime wrote:
Mike A

Can I politely disagree with you concerning the issue of non-locality.

Absolutely. I'm a layman with no physics qualifications beyond A-level. You are of course right that QM and relativity disagree about action at a distance (sort of - the interesting thing about entangled pairs is that, though they seem to communicate spin states, they cannot - as far as anyone can work out - be used to transmit readable information faster than light. No ansibles yet!).

Another curious thing with QM is that (if I recall correctly) a photon cannot be emitted unless it is going to be absorbed in the future. This kind of "foresight" appears to violate relativity; however, if you apply the Lorentz transform for a single photon, thus getting a "photon's eye view" of the universe, the whole of time and space along the photon's path is compressed into one point - so in a sense, for a photon the whole of time happens simultaneously. Weird!

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PostPosted: Mon Sep 28, 2009 9:01 am 
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Hallo Mike A---I think your second paragraph isn't correct. The idea you mention (about foresight), was first thought of by the American chemist G. N. Lewis, before 27. A more modern version was the 'Absorber Theory of Radiation' developed by J.A. Wheeler and R. Feynman.
These ideas are consistent with special and general relativity but do not follow from these theories. So your statement cannot be wholly accurate. I learned about Lewis' idea from Bertrand Russell's The Analysis of Matter, published in 1927. According to Russell, Lewis' ideas could support a worldview in which the chief real entity is Minkowski space-time, wherein (Russel claimed) no distinction between past and future exists, only a relation of temporal priority


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PostPosted: Mon Sep 28, 2009 9:06 am 
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p.s. I must add that no law of physics requires that photons behave as Lewis said they do. The notion's optional and depends on your philosophy of physics, not physics itself.


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PostPosted: Mon Sep 28, 2009 9:58 am 
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Yes, sorry, I'm very rusty on all this - absorption is only a requirement if you want physics to be time-symmetric, which a lot of physicists intuitively/aesthetically prefer - not that that necessarily means they're correct of course!

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PostPosted: Mon Sep 28, 2009 1:28 pm 
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I used to prefer a time-symmetric universe, since I thought that change was an illusion. Now I do not know what to believe. I'm a philosopher who knows a bit of physics, but nothing helps. I'll never reject the appearance of change, but it's at least as difficult to describe physical, real change clearly as it is to describe a time-symmetric universe. I should know, since two of my academic papers tried to take some first steps towards a time-symmetric account. It worked for the maths of Minkowski space-time, but the attempt to describe its world verbally failed at the very beginning.
My grandteacher Wilfrid Sellars put it neatly: 'If you start with change you can get stasis [lazy changes], but if you start with stasis you'll never get change.' Nobody knows the truth. Indeed, Augustine thought about this and said, roughly, 'If you don't ask me what time is then I know all about it, but if you ask me what it is, I know zilch.' That's in Book XI of his Confessions, written in 300 or 400something C.E. We have not gotten much further.


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PostPosted: Tue Sep 29, 2009 6:04 pm 
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And finally from cutting edge science to Science Fiction!

The Quantum Entanglement Portal - Parked in Earth's orbit sending information instantaneously back to an alien race, the other side of the galaxy, who are bent on invading Earth.

SpaceTime


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PostPosted: Tue Sep 29, 2009 7:57 pm 
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now I'm confused


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PostPosted: Tue Sep 29, 2009 9:58 pm 
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It's from the book, Roy.


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