
#1
Jul2610, 09:12 AM

P: 1,929

How a field request capacity of a channel? 



#2
Jul2610, 11:16 AM

Astronomy
Sci Advisor
PF Gold
P: 22,809

You can see if my intuition is helpful, use it or don't use it as you wish. Maybe it will work for you, maybe not. Here is something to try, if you want: Start by picturing a LQG black holethe area of the BH horizon is given by the network links which pass through it. Each link has a label that tells two things: 1. the area that the link contributes to the total horizon area 2. the dimension of a finite dimensional Hilbert associated with the link. These two things are the SAME thingmy intuition is that at some deep level area and information are identical because they are told by a single spin network label. A finite dimensional Hilbert space is a way of representing informationa range of choice. How much information is represented by picking one state vector out of the whole range of possibilities. (Read about Shannon information theory, codes, channelsit is just something to give intuition about the physics, it is not the physics itself ) This is how I personally understand that in the LQG discussion of black hole entropy, the entropy turns out to be related to dimension of a Hilbert space associated with the BH horizon. And of course that Hilbert space is also connected to the area. BTW I don't know what you meant by "fields control". In my comment in the other thread I did not say anything about "fields" or about "controlling" capacity. Channel capacity is a Shannon info theory concept which I was borrowing from a distant cousin of quantum theory just to be a help to intuition. 



#3
Jul2610, 01:26 PM

P: 1,929





#4
Jul2610, 01:52 PM

Astronomy
Sci Advisor
PF Gold
P: 22,809

How fields control the capacity of the spin network channels?The illusion or mirage of a field of force is something that appears to us largescale animals who observe the overall statistical collective effect of more basic micro business. 



#5
Jul2610, 02:05 PM

P: 1,929

And that's what I am adressing. Certainly there is something that makes distance decrease, even if with neutral charges. More labels shrinks the paths.
Now, using this point of view, it doesn't make sense in "coupling" matter with "gravity", but how bigger the representations the greater the paths are shrunk. 



#6
Jul2610, 02:22 PM

Astronomy
Sci Advisor
PF Gold
P: 22,809

That is represented either by the class of the GR metric, or at a quantum level by the spin network itself. Field = geometry = spin network. There is no question of needing some other exotic entity called "MTd2 field" to control anything about the spin network. The network is it. It is the dynamically evolving control, if you think of geometry in those terms. (Assuming, as I said, that you mean something more general than some kind of force or particle field.) 



#7
Jul2610, 02:27 PM

P: 1,929

No, I didn't mean that.
How a field, like the strong field, weak field, request capacity of a channel? 



#8
Jul2610, 04:01 PM

P: 1,929

Does spacetime exist without matter fields?
Does gravity exist without matter fields? 



#9
Jul2610, 05:11 PM

Astronomy
Sci Advisor
PF Gold
P: 22,809

That will be, I suppose, a whole new chapter in the dynamics. Both the spin network and the spinfoam model will have to be expanded to include matter labels. Spin networks consist of nodes and links, and the links could carry, for example, lines of flux. Some type of flux lines passing through the area represented by the link. Including matter by further labeling of the links and nodes was already discussed in Rovelli's talk at the Strings 2008 conference. That goes beyond where I can speculate. I suppose it would mean defining a new, more complicated, spinfoam vertex. A new more complicated Hamiltonian constraint for canonical Lqg. 



#10
Jul2610, 07:33 PM

P: 1,929





#11
Jul2610, 11:50 PM

P: 1,929

On second thought, marcus, it is very reasonable to think that all labels are due matter fields, if you keep in mind Erik`s prescription that there is no gravity. If there were any label not due a matter field, entropy would have a contribution from pure gravity, which is pure geometry in the point of view of spin networks, even if there wasn`t a graviton in the theory.
So, gravity is about the entropy of the matter fields, but such entropy happen as if they were caused by pure gravity, without matter fields. It fits your sugestion: "Spin networks consist of nodes and links, and the links could carry, for example, lines of flux. Some type of flux lines passing through the area represented by the link." Lines of flux whose hilbert space has the size of the link. It also has the weird sugestion that it doesn`t make sense to talk about emergence of gravity or even as gravity as a force. It seems that gravity is a property suficient and necessary for interaction, and that`s why it appears in spin network scattering calculations, even without matter fields assumed. I speculate that natter field is assumed somehow, if Erik is right. 



#12
Jul2710, 05:28 AM

P: 2,799

Mtd2, can you elaborate what your suggestion is? I don't think I understand what you mean except it's something about the relation between matter and gravity and how it emerges.
/Fredrik 



#13
Jul2710, 05:59 AM

P: 2,799

If the spinnetwork represents the the quantum state of the gravitational field, then the question is  from the point of view of which observer? And if we are looking at an observer invariant notion of information state, then what does that even mean? Two simple questions, less easy to answer, but that appear to be avoided. IMO  I associate the observer to matter; just like it should be clear, that it makes no sense to talke about measurement theory that is observer independent, it then by association makes no sense to talk about quantum states without matter, just like there is no sense in talking about an information state without a context that serves as a storage device. If this had nothign to do with your question then just ignore it. /Fredrik 



#14
Jul2710, 06:09 AM

P: 2,799

This point can even be used to reanalyse Einstiens hole argument. The original conclusion (reformulated in more abstract information theoretic form):
1) Either the laws of physics are not observer invariant or 2) it makes no sense to talk about physically distinguishable events There is a problem here becauase if we reject (2) then we also reject in deept sense a prerequisite for measurement hteorhy. This was not a problem for Einstein since he was working with deterministic views. If we reanalyse this argument today... there are more subtle things here that no longer makes sense to me at least. I think the correct conclusion is that 1) there are no inferrable _objective_ eternal fixed laws AND 2) there are no _objective_ notion of events; rather each observer has their own "real" but subjective events. And that the only way for two observers to level anything is by means of interaction. So, IMO, in the light of today I would reject the notion of objective manifold, BUT I would also reject the notion of objectivce timeless laws of physics because no real observer, can be processing information from real measurement reach a 100% confident deduction about that state of hte eternal laws of the entire universe, as the inference processes are taking place in time. And I think this is more than a practical curiosity. It must havec implicuiations also for how we understand the laws of physics. /Fredrik 



#15
Jul2710, 07:42 AM

P: 1,929

2.:I don't understand. 3.:Yes, that's what I mean. An observer is the measurement of a node at its links and the node in an instant of time. 4.:Yes. And they are static. I am only talking here about a state of system, a snapshot. Given that an observer is the measurement of a node at its links and the node in an instant of time, it will only exist while the states measured by a node and the node itself are not decoherenced. 



#16
Jul2710, 07:54 AM

P: 1,929

2.Yes, I agree about this. 



#17
Jul2910, 05:25 AM

P: 2,799

I'm not sure I fully understnad your suggest but thanks for your coments.
/Fredrik 



#18
Jul2910, 05:33 AM

P: 2,799

This means also that it's RATIONAL to argue like you do. Ie. the possibility is vanishingly small, therefore we ignore it. This is in line with rational action. I just suggest that this should be formalized and taken seriously. The conclusion is that the laws of physics have to evolve, as seen by any observer. Locally effectively static laws are simply a local equilibrium, due to local negotiation. The best analogy is with emergence of social laws. Edit: Humans often act AS IF, "rare events" NEVER happens. This is rational, because the information processing agent has limited resources, and it's simply not rational(from a gambling point of view) to occupy resources for such rare events, as you can use the resources more intelligently. The action of a given observer, could follow from a rational aciton principle, (in an entropic sense) from it's subjective view of the laws of physics. These evolving laws are possible also a key to unification. So I do not think the points I raised are just conceptual only. I think there are constructive points that could be used to find a better framework. /Fredrik 


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