Exploring Matter in Loop Quantum Gravity

[wolram]

I think in LQG matter has only been tentatively considered, but if matter is
reduced to a," field", or wave function, could one transform into the other?

 

[marcus]

I think in LQG matter has only been tentatively considered, but if matter is
reduced to a," field", or wave function, could one transform into the other?

could space and matter transform into each other
or (it is a very general question and could be worded various different ways)
could geometry and matter turn out to be different facets of the same thing?

when you ask "could this be?" then, if it can't be ruled out on logical or experimental grounds, the other person has to say "yes"

then you get to ask "HOW" could this be? and the other person can probably not say

maybe i will try to venture an opinion about this, wolram, or someone else might. it is definitely venturing

 

[marcus]

the "Triangulations" people have put some kind of matter in their 2D models to see what happens---there are some papers about this

but only just now are they putting matter in their 4D models, and nothing is published yet

they are the QG leading edge right now. we will have to see how they put matter into their triangulated geometries picture-----indeed maybe when we see how they represent matter we will see that it DOES have some kind of interconvertibility with very small scale geometric features. but I don't know how they are representing matter, so can't tell.

the Loops 05 conference website has this "artist's impression" picture of the world seen from Triangulations perspective, you can see dim large shapes emerging in the distance. up close you get the microscopic triangulated view. it is not science, just imagery. but sometimes imagery can help get one started:

http://loops05.aei.mpg.de/index_files/Home.html

 

[wolram]

One of my two disconnected brains tell me that gravity must be the "mother",
of all things, if so then it must have the capability, to give "birth", to matter,
or that they are one and the same in different guises.

 

[wolram]

A picture worth a thousand words, i see Fay Dowker mentioned, not a name
that comes up often, but i think she has some clout.

 

[marcus]

i see Fay Dowker mentioned, not a name
that comes up often...

"causal sets"

causal is a key word, they are probably going to come out of the conference with a causal coalition of approaches to QG

where the model of spacetime is not a blank continuum, but has a kind of causal "grain" in it or an inherent direction of time

this is very explicit in the CDT "Triangulations" approach which has become prominent in the past year, but it is also present in the "causal sets" approach of Fay Dowker and Rafael Sorkin and other. Fotini M has thought about that too (she was apparently a post-doc of Renate Loll at some time, I see from Loll website)

so a coalition of approaches will come out that will in a sense "share results" in that they will try to carry results over from one to the other

oops I have to go, back later

 

[marcus]

... to give "birth", to matter,
or that they are one and the same in different guises.

the issue with any model is how you represent matter in it and how well that works.

I can try to second guess and venture to imagine how it could look with triangulations.

the matter can express itself through the ("action, lagrangian" ignore the technical verbiage) function that determines weightings and PROBABILITIES of certain montecarlo moves during the SIMULATION

there are these local modifications of the triangulation where the computer inserts more buliding blocks, or takes blocks away, and thus changes the curvature----or where it just REARRANGES the blocks in ways that might change the curvature

and the probability that the computer is going to do or not do one of these local tamperings with the blocks can be made to depend (thru the "action" function but forget the technical terms) on whether MATTER is supposed to be present

so the presence of matter along some spacetime worldline can be reflected or felt in a tendency to favor more or less or different-arranged buildingblocks, and this tendency might be able to PROPAGATE, and in any case it does the right thing in the sense of causing the spacetime to CURVE the way Einstein said it curves when matter is there.

so the presence of a matter particle might be seen in a sort of flickering tendency for there to be more microscopic triangular building block busy-ness, or wrinkliness in the geometry of certain place, instead of less

so in that way the model might represent, or depict, matter, and that depiction might work, who knows? at present CDT is proving very lucky so maybe its winning streak will extend and maybe that part will work out too.

meanwhile the other approaches have to try to catch up or converge with CDT.

of course we can't really look ahead, I am just "venturing a guess", we can only watch what is in progress now

it is an entertaining time to be watching

I have to take care of something else, back later

 

[wolram]

By Marcus
so the presence of a matter particle might be seen in a sort of flickering tendency for there to be more microscopic triangular building block busy-ness, or wrinkliness in the geometry of certain place, instead of less

Is this a light at the end of the tunnel, maybe LQG is about to be weened,
i like this description ,it may only be an analogy of some deep mathematics
but if it can be formed as so, it can only be a step forward.

 

[Mike2]

I think in LQG matter has only been tentatively considered, but if matter is
reduced to a," field", or wave function, could one transform into the other?

If matter develops from the only available material which is spacetime itself, then matter would have to consist of distortions of spacetime that do not dissipate away. A smooth curve would dissipate as every point seeks the lowest energy state of flatness. But other structures do not dissipate such as boundary holes or homology holes. And I suppose that a singularity would not dissipate either since it would then take an infinite time for infinite point to fall back into a flat state. So the question is whether CDT can create boundaries, genus holes, or singularities. I have to wonder if you can construct a singularity of finite triangles. But certainly you can construct boundaries and genus holes.

 

[marcus]

... But certainly you can construct boundaries and genus holes.

was just reading related discussion around page 33 of their most recent paper "Reconstructing the Universe", in particular footnote 11

 

[wolram]

Mike 2


If matter develops from the only available material which is spacetime itself, then matter would have to consist of distortions of spacetime that do not dissipate away. A smooth curve would dissipate as every point seeks the lowest energy state of flatness. But other structures do not dissipate such as boundary holes or homology holes. And I suppose that a singularity would not dissipate either since it would then take an infinite time for infinite point to fall back into a flat state. So the question is whether CDT can create boundaries, genus holes, or singularities. I have to wonder if you can construct a singularity of finite triangles. But certainly you can construct boundaries and genus holes.

I think it would be nice if a theory of gravity worked in every way, but
without the singularity, i have a feeling that in time the singularity will
be falsified, so if a theory works with it I am sure it will be wrong, this
is just hand waving on my part, but i hope i am right.

 

[wolram]

An interesting page i have just come across.

http://www.scienceforums.net/forums/archive/index.php/t-5730.html

includes QG without singularity.