On Wednesday, September 4, 2002, at 07:47  AM, Stephen Paul King wrote:

> Dear Tim and scerir,
>     I am VERY interested in this discussion! ;-) It seems to me that 
> fact
> that the amplitudes of observables in QM are complex valued and thus 
> do not
> obey trichotomy may be at the root of the difficulty. When we attempt 
> to
> make sense of situations such as those we obtain in EPR we have to be 
> very
> careful that we take into account the configuration of the experiment
> itself. This implies that the lattice of relations or poset aspect of
> causality is a posteriori and not a priori to the specifics of the
> experiment. This implies, at least to me, that it is a mistake to 
> assume the
> a priori existence of a space-time (with a unique light cone 
> structure).

I agree that imposing a space-time structure for quantum events is a 
problem. In fact, this is one of the motivations of quantum gravity 
work, to get rid of the "events on a background of space and time" 
which most QM has been using.

However, assuming a space-time and with local light cones seems very 
reasonable to me. We have no particular evidence that the light cone 
formalism isn't still applicable to quantum kinds of events (whatever 
EPR "spooky action at a distance" may be, there is certainly no 
evidence that faster than light travel of particles or photons is 
involved, so there's no reason to throw out the speed of light as a 
maximum speed).

You may be interested in Smolin's "Three Roads to Quantum Gravity." He 
argues for the _relational_ view of space-time as being more suitable 
than the absolute space-time coordinates in Newtonian and (ironically) 
most quantum theories. Relativity of course uses the less absolute 

However--and this is very important!--there are no theories given 
experimental support today which show real violations of causality. (We 
could debate for a few days whether delayed-choice experiments, 
Aharonov-Bohm experiments, etc. show violations of causality. While 
entangled states show behaviors not found in the macroscopic, 
classical, human-scale world, they don't violate causality.)

This argues for the emphasis placed on causal sets and causal 
relations. And hence on posets and lattices. (In my opinion, following 
the lead of the several authors I've mentioned a few times here.)

>     One possible solution is to consider space-times strictly from an a
> posteriori point of view. You had mentioned Greg Egan's novels and the 
> "All
> Topologies model" (for instance in the novel Distress) in previous 
> posts. Do
> you think that the ideas of the character Mosala could be used to "make
> sense" of this?

Well, I try not to get too many of my theories out of science fiction!

Not to sound flip or dismissive, but Egan's novels and short stories 
are best seen as romps through a landscape of strange and stimulating 
ideas. I like his stuff a lot because he's one of the few writers today 
able to (or interested in) keep up with modern physics and modern math. 
There was a time when SF writers were engineers or scientists (Asimov, 
Heinlein, Clarke, Hal Clement, even Larry Niven, who was at Caltech for 
a while). Their editors were also science-oriented people, like Hugo 
Gernsback and John Campbell, who wanted hard science in the science 
ficiton they bought.

In their day, these authors wrote stories and novels involving the 
then-weird ideas of hypercubes, Mobius bands, planets with extremely 
high gravity, time travel, neutron stars, and black holes. (Larry Niven 
was the Greg Egan of his day. Niven still writes, but his recent novels 
are less compelling and certainly no longer are exploring cutting-edge 

As SF spread in popularity to the Baby Boom generation, more and more 
non-scientists and non-engineers started writing. So we got more 
"sociological" SF (some of it very good, like Ursula LeGuin's stuff). 
And more of the "palace intrigue" kind of novels ("The planet Cthwox 
has been ruled by the Klanring for 2000 years. A spaceship from the 
Vegan Federation has arrived..."). And then there is fantasy...dragons, 
magic, etc.

A few writers have stuck to hard science themes. Vernor Vinge is a good 
example. And some of the "cyberpunk" themes have been more or less 
based on plausible science, including Gibson, Walter Jon Williams, 
Bruce Sterling, Dan Simmons, etc. (I also like a less popular author, 
David Zindell, and his quartet of novels set on the planet "Neverness." 
Mathematics plays an unusual role.)

Steven Baxter also writes Stapletonian novels about the distant future 
and the end of time, though his themes are often depressing (to me at 

Greg Egan is one of the few writers today actually _using_ the latest 
developments in physics and even math to explore ideas about the nature 
of our reality, the anthropic principle, and the colonization of 

It also turns out that Egan has been doing some Java and Mathematica 
programming for some of the spin foam papers by Baez and others. This 
doesn't mean that any particular idea he explores, whether in 
"Distress" or "Diaspora" or "Schild's Ladder," is "right," just that 
Egan is obvious technically competent to write about these ideas.

What fired me up about "Distress" in particular was the several-page 
synopsis of the "All Topologies Model." For some reason, this got my 
juices flowing. (The rest of the novel just sort of plodded along to a 
fairly predictable conclusion.)

I hope this explains why I don't look to Egan's fictional character for 
actual theories, just stimulation.

--Tim May

Reply via email to