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http://math.ucr.edu/home/baez/quantum_spacetime/
Hilb is the core category of Quantum Mechanics
nCob is the core category of Gen Rel
JB is saying that these two categories are LIKE each other in a distinctive way that SUGGESTS they might each be different facets of the same thing
quantum mechanics might be seen to arise from the structure of spacetime, if we only understood the latter better----yeah sure, I know quite a few people have speculated about that but what he is describing is a PARTICULAR TAKE on the idea that QM can be better understood if we see it as part of the spacetime machine.
there are links to Baez HDA:QS webpage in this thread and he gives the definitions of Hilb and nCob, but we can remark in passing that Hilb is the category of hilbertspaces with linear maps from one space to the other as the morphisms.
And nCob is where orientable (n-1)-dimensional manifolds are the objects and the morphisms are n-dimensional manifolds JOINING them.
Usual Gen Rel is about 4Cob, which is where the objects are (orientable) 3D spaces and the morphisms are 4D spacetimes connecting them. So a 4D spacetime is something that morphs you smoothly from one version of 3D space to another.
======================
I look at HDA:QS as having a goal of PERSUADING the listener to be interested in twocategories (and higher groups, higher gauge theory, essetially in doing geometry with higher algebra)
and the message of slides #1-14 is one of comfortableness and RESOLUTION OF PUZZLES
This gets the listener ready to venture into the higher algebra realm of twocategories, because he sees that just a LITTLE ordinary category theory can help a lot to resolve puzzles.
So we need to study slides #1-14 carefully.
They say that Hilb is very analogous to nCob, and if you look at some things that puzzled you about QM they will turn out to have ANALOGS in spacetime, i.e. in nCob, that are TOTALLY OBVIOUS. So what may seem peculiar and paradoxical in Quantum Mechanics becomes VERY INTUITIVE if you go over to the analogous thing in Spacetime.
things like the "clone-taboo" and "teleportation" turn into obvious stuff with wet spaghetti when you look at them in nCob.
This, IMO, makes slides 1-14 worth the price of admission EVEN IF YOU DON'T BUY TWOCATEGORIES.
But remember that the speaker is also hoping that we will get interested in twocategories as well, so I should devote a post to slides #15-23 also.
===================
these sets of slides could also be helpful
http://math.ucr.edu/home/baez/barrett/
they are for three talks given at Knoxville 29 April-1 May at a workshop on Geometric Topology
(the Barrett Lectures)
sometimes they give more pictures, and spell things out in more detail, than was possible in the
single Perimeter talk given 31 May-----what I am abbreviating "HDA:QS" for Higher-Dimensional Algebra: a Langauge for Quantum Spacetime.
http://math.ucr.edu/home/baez/quantum_spacetime/
Hilb is the core category of Quantum Mechanics
nCob is the core category of Gen Rel
JB is saying that these two categories are LIKE each other in a distinctive way that SUGGESTS they might each be different facets of the same thing
quantum mechanics might be seen to arise from the structure of spacetime, if we only understood the latter better----yeah sure, I know quite a few people have speculated about that but what he is describing is a PARTICULAR TAKE on the idea that QM can be better understood if we see it as part of the spacetime machine.
there are links to Baez HDA:QS webpage in this thread and he gives the definitions of Hilb and nCob, but we can remark in passing that Hilb is the category of hilbertspaces with linear maps from one space to the other as the morphisms.
And nCob is where orientable (n-1)-dimensional manifolds are the objects and the morphisms are n-dimensional manifolds JOINING them.
Usual Gen Rel is about 4Cob, which is where the objects are (orientable) 3D spaces and the morphisms are 4D spacetimes connecting them. So a 4D spacetime is something that morphs you smoothly from one version of 3D space to another.
======================
I look at HDA:QS as having a goal of PERSUADING the listener to be interested in twocategories (and higher groups, higher gauge theory, essetially in doing geometry with higher algebra)
and the message of slides #1-14 is one of comfortableness and RESOLUTION OF PUZZLES
This gets the listener ready to venture into the higher algebra realm of twocategories, because he sees that just a LITTLE ordinary category theory can help a lot to resolve puzzles.
So we need to study slides #1-14 carefully.
They say that Hilb is very analogous to nCob, and if you look at some things that puzzled you about QM they will turn out to have ANALOGS in spacetime, i.e. in nCob, that are TOTALLY OBVIOUS. So what may seem peculiar and paradoxical in Quantum Mechanics becomes VERY INTUITIVE if you go over to the analogous thing in Spacetime.
things like the "clone-taboo" and "teleportation" turn into obvious stuff with wet spaghetti when you look at them in nCob.
This, IMO, makes slides 1-14 worth the price of admission EVEN IF YOU DON'T BUY TWOCATEGORIES.
But remember that the speaker is also hoping that we will get interested in twocategories as well, so I should devote a post to slides #15-23 also.
===================
these sets of slides could also be helpful
http://math.ucr.edu/home/baez/barrett/
they are for three talks given at Knoxville 29 April-1 May at a workshop on Geometric Topology
(the Barrett Lectures)
sometimes they give more pictures, and spell things out in more detail, than was possible in the
single Perimeter talk given 31 May-----what I am abbreviating "HDA:QS" for Higher-Dimensional Algebra: a Langauge for Quantum Spacetime.
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