Role of in-house concept analysis done by the QG scientists themselves

[Fra]

So what about the core principles of QM?

In this second article note how Rovelli presents the lesson of QM as "any dynamical entity is subject to Heisenberg's uncertainty at small scale" which is different from the "all dynamical fields are quantized of his earlier Quantum Gravity book's introductory chapter."

I personally think this is too fast to see the steps.

I'd like to propose that the core principles, is the content of Bohrs mantra that essentially says that the laws of physics doesn't encode what nature is or does, it encodes what we can say about nature and how it behaves. This summarizes almost the essence of science, namely that we infer/abduct from experiment (OBSERVATION) what nature SEEMS to be and how it SEEMS to behave.

Thus we arrive at an effective undertanding in a good scientific spirit, and all we have is our rational scientific expectations. There just IS no such thing as "real reality". It serves no purpose in the scientific process.

But as with the GR, there seems even here multiple ways to understand and extrapolate this.

I read it in a more explicit way so that the laws of physics encode the the observers expectation of nature as a function of their state of knowledge.

It seems like Rovelli's conclusion is that since he considers the equivalence class of observers as the physical core, he thinks that QM says that the laws of "quantized" physics, encodes expectations of equivalence classes of observations. In this view, he doesn't consider the quantum laws themselves subject to Bohrs mantra. It apparently enters as a realist element.

The alternative, quite similar to GR, is to think that combining this with the "observer democracy" rather suggest that physical law itself - including "quantum laws" are rather intrinsically observer dependent and that instead the problem becomes how to understand how the effective objectivity that we de facto see is a result of a democratic process (which of course would be purely physical to its nature).

/Fredrik

 

[inflector]

If we would start where you suggest (with e.g. the idea of "quanta of space")

(snip)

Area and volume are quantized as part of how nature responds to measurement. It is like what Niels Bohr said. "Physics is not about what Nature IS, but rather what we can SAY about Nature." So it is about information---initial and final information about an experiment, transition amplitudes. Or so I think.

Returning to the idea of quantization itself...

It seems clear to me that taking GR and quantizing it is a strategy that makes a decision.

We know that measurement is quantized through large quantities of actual experiment. But it seems to me that this quantization could come from two places:

1) That geometry itself is quantized

2) That there is an interaction in the process of measurement between the device doing the measuring and the object being measured that results in a quantization

All of the quantization of GR approaches seem to be deciding that 1) is more likely than 2). Is there some reason? Has this issue been specifically addressed?

For example, let's go back to the first concrete quantum weirdness experiment (at least that I know of), Stern-Gerlach. In that experiment, some of the silver ions were diverted up and some were diverted down and the classically expected smooth distribution did not occur. But it may be that the process of measurement is what does the quantization, right? Depending on your favorite interpretation of QM you might look at this in various ways but it comes down to the process of measuring resulting in two distinct values, up and down.

We also know through various experiments with http://en.wikipedia.org/wiki/Stern–Gerlach_experiment#Sequential_experiments" and light polarization that the measuring apparatus also changes the state of the objects being tested, whether ions or photons. So clearly there is a significant interaction between the measurement device and the object being measured.

So what says that it is not the process of measuring that results in the quantization rather than that geometry itself is quantized? Strategies that quantize the geometry seem—to me anyway—to assume that it is not the measurement that causes the quantization. They seem to assume that the objects exist in a state that is probabilistically quantized because the geometry itself is probabilistically quantized.

On the other hand, experimental quantum theory itself seems agnostic on this issue. Some interpretations refer to collapses of the wave function during measurement, but quantum theory itself doesn't say why the collapsing happens only that the measurements end up being quantized.

Am I missing something? Or is it fair to say that my points 1) and 2) above characterize two equally valid points of view, but that LQG and other quantize-GR theories assume 1) and NOT 2).

 

[friend]

So what says that it is not the process of measuring that results in the quantization rather than that geometry itself is quantized? Strategies that quantize the geometry seem—to me anyway—to assume that it is not the measurement that causes the quantization. They seem to assume that the objects exist in a state that is probabilistically quantized because the geometry itself is probabilistically quantized.

To add to this question, since it will take particles to measure the quantization of space, how would we know it is not just a further quantization of particles that we are measuring?

Also, aren't there quantum variables that can be measured in a continuous spectrum? For example, position and momentum of free particles can be measured anywhere, right? How would spacetime be in a bound state so that its has a discrete spectrum? What is the boundary of spacetime? Maybe it's the particles used to measure space that form the boundary of space, making it have a discrete spectrum.

 

[Fra]

I for one think that it's quite established that the issues of exactly what quantization means is NOT sufficiently addressed by Rovelli. He doesn't even try very hard.

Somehow that settles the issue. But he has also declared that this isn't his ambition.

To me the CORE essence of quantization, in despite of the name has nothing to do with wether something ends up literally quantized (in chunks), it's more the constraint that is applied be requireing "observability" or "inferrability". This I picture achieved by requiring the the predictions to be cast in terms of "expectations", computer from initial information that must originate from prior measurements.

So I think you are right to not ignore these things.

Strategies that quantize the geometry seem—to me anyway—to assume that it is not the measurement that causes the quantization. They seem to assume that the objects exist in a state that is probabilistically quantized because the geometry itself is probabilistically quantized.

I'm not sure I would agree with your two options. But I do agree that this is generally under-analysed.

Expectations of course exist in classical logic as well, and clasical probability. I think that what "causes" the quantum logic (or cause quantization as you phrase it) is that if we take seriously how information is encoded by the observer, and consider fitness of this code as an interacting one, then it seems a plausible conjecture that non-commutative structure in the code would have higher fitness and that the evolutionary selection of these "non-commutative histories" is the original of quantization.

I'd claim that an expectation (genereally inductive, probabilistic) is the essence of QM.

Classically we don't have expectations, we have laws that given initial conditions DEDUCES what WILL happen, in an objective sense.

QM expectations is in the form of deductive probability, QM DEDUCES what the probabilities are that certain things will happen. Thus the expectations encodes, in line woth Bohrs mantra, not what WILL happen, but what we can SAY about what will happen; ie what we EXPECT to happen.

So I see construction of the expectations as a key construct. So, we need to construct geometrical notions interms of expectations. Here Rovelli is possibly missing a point becase geometry is defined be relations between observations, and observers. So it may mean that geometry in the GR sense is not observable in the sense of QM, beucase it takes a collection of interacting observerations to observe it. (The democratic view).

Rovelli sometimes seems to assume that geometry exists, and doesn't even try to reconstruct it in terms of realistic measuremnts from the point of view of a single observer. So I basically question his choice of what's observable and what's not. Clearly IMHO at least, observer invariants are not what should be subjecto "quantization" for me that is a likely abuse of QM.

/Fredrik

 

[Fra]

What is the boundary of spacetime? Maybe it's the particles used to measure space that form the boundary of space

Mathematically we can picture an empty space without boundaries, but physically and in particular when constrained by the observability criterion that QM teaches us, the boundary of spacetime is obviously matter.

Anything else is just something that lacks physical basis IMO.

So I think your on the right track. For me, I've always associated matter with the observer. Gravity without matter is like a quantum theory without observers. Also in all experiments on "empty space" such as casimir effects, the boundary is critical. You can't observer an empty space without inserting a boundary.

To take it a step further, I think there has to be a theory living on the boundary (or more exactly, encoded in them matter) that somehow interacts and mirrors whatever is going on on in the extenral bulk. It's a vauge form of holography.But it's not necessarily exact, the holographic conection is more likely IMO to correspond to an equilibrium point. This is why maybe we need further understanding og this. because it may not be right to use an equilibrium condition as constraint, we may be missing out on physics.

Edit: I insinuated in another thread, but I think that this holographic connection (to be understood) can also be seen dual to the problem of understanding the more general theory mapping. If you consider a generalisation of RG, where you consider the theory space to include a larger set of observers, not just observational scales that you arrive at by changing energy scale, but observers with completely different topology and complexity, then it seems that the holographic duality is like a connection between two different points in theory space with are communicating. It seems to me that the RG space itself must evolve, as this itself should also be subject to observabiltiy constraints.

So it seems like QM + GR must be something like an evolving theory space at where at each "instant" the state of the space (I don't thikn it's a continuous manifold) it defines "connections" between expectations... like the "quantum version" of a GR connection which is not the same as a quantized connection. It seems to be something hairy where certainly the EH action itself is emergent, rather than put in by hand.

So the QG replacement of the GR state space must be something far more hairy, something like a theory space. And here, matter (or what corresponds to it) must be included from constructing principles. It wouldn't make sense otherwise.

/Fredrik

 

[cutbait]

IMO the first place to look would be the Dirac Sea. Electron and positrons that disappear and then can magically reappear from absolutely nothing. I have issues with any theory that claims to be based on math, but is really based on magic. What if the electrons and positrons did not annihilate, but are instead sitting at an immeasurable zero spin state. In addition, when energy is added they would spilt apart, and then come back into our measurable existence. Bosons are then not required to satisfy the math requirement for a zero spin state.

An electron's probability orbit around an atom could be nothing more then measurement error. Similar to how moths and bugs appear as "flying rods", to cameras that are not able to capture or measure at a fast enough rate. It is a shame we do not have something smaller then an electron or positron in which to measure with, but it would then be the same problem just the particle would have a different name.

Time is nothing more then the rate at which processes run at or complete in. If matter uses electrons and positrons to measure time with how do electrons and positrons measure time? Could energy and matter not experience time at a different rate? How could we measure the time that energy experiences? We cannot.

Quantization is due to having to measure things with matter. All current sensors and measurement devices are composed of matter. We are limited in measuring to what is happening at the transmitter and what is happening at the receiver or sensor. We cannot take a CRT and label an electron as it leaves the gun. To prove that it was the electron that actually hit the screen, and knocked an electron in the screen matter to a higher energy state.