Origin of universe...

quoting from the link above "Second, the string theorists think of themselves as physicists rather than mathematicians. They believe that their theory describes something real in the physical world. And third, there is not yet any proof that the theory is relevant to physics. The theory is not yet testable by experiment. The theory remains in a world of its own, detached from the rest of physics. String theorists make strenuous efforts to deduce consequences of the theory that might be testable in the real world, so far without success."

To be testable is fundamental to Physics, and this subject can not be avoided.
We can have a bad model, or a not so bad one, or a good one, and thay must be conform to observations to some degree. The good model is more accurate than the others, and possibly some predictions are derived from first principles. The good one as a strong possibility of beeing the simpler.

The String Theory(s) are out of the domain of testability, by its nature, and so are out of the reaml of Physics.

"what's the alternative" ? you ask.
In my opinion the effort must be done in the wave description of matter, the fields they originate and the properties of the space. The actual availability to large particle colliders has leading us to the particle nature of matter, and inhibited the pursue on the wave nature of matter.

In the 1st equation the assumed gravitacional energy say nothing about fields. Is this ok? I think not. Each particle sets field(s) that evolve in the space. Any work to be done on other particles is to be done by the field.
A mathematician may say that the equations are ok. But physically the reasoning had a bad start.

quoting from the link above "Second, the string theorists think of themselves as physicists rather than mathematicians. They believe that their theory describes something real in the physical world. And third, there is not yet any proof that the theory is relevant to physics. The theory is not yet testable by experiment. The theory remains in a world of its own, detached from the rest of physics. String theorists make strenuous efforts to deduce consequences of the theory that might be testable in the real world, so far without success."

To be testable is fundamental to Physics, and this subject can not be avoided.
We can have a bad model, or a not so bad one, or a good one, and thay must be conform to observations to some degree. The good model is more accurate than the others, and possibly some predictions are derived from first principles. The good one as a strong possibility of beeing the simpler.

The String Theory(s) are out of the domain of testability, by its nature, and so are out of the reaml of Physics.

Until now we describe the events in this Universe (the one that is testable) only with simple 3D+time. At least I dont know of any single example that does not fit.

I'm not a specialist in String Theory, and cannot contend about its contents. To remain out of ST is enough that not even its sponsors and specialists can think of a test or prediction.

"what's the alternative" ? you ask.
In my opinion the effort must be done in the wave description of matter, the fields they originate and the properties of the space. The actual availability to large particle colliders has leading us to the particle nature of matter, and inhibited the pursue on the wave nature of matter.

As an example of the consequences you can see the post #7 by hellfire and #30 of this thread:
In the 1st equation the assumed gravitacional energy say nothing about fields. Is this ok? I think not. Each particle sets field(s) that evolve in the space. Any work to be done on other particles is to be done by the field.
A mathematician may say that the equations are ok. But physically the reasoning had a bad start.

I do not agree with the formula as of #30 but I agree with the contents that is expressed in bold, and the equation can be reformulated in a more sustainable way.

Another example: in the Particle Physics Forum I put a conceptual problem about 'particle creation and annihilation and the remaining fields problem' and, because I mention Fields (without mention to any intervenient particle), I noticed a difficulty by others on the perception of the problem.

Well, suppose I am as you say. I have lots of phone calls to make and receive, lot of coordination on my collaborators, prepare the next conference, the anual meeting on special subject XPTO, control if the quantity of papers that my nucleus is producing are enough to guarantee the next annual budget to the department. A colaborator had some idea that I'am afraid of pursue or estimulate because it is non mainstream and I'm an inconfessable fear of become out, to be in is more confortable and pays my check.
Some students are waiting for guidance. And I have a full agenda. I am a specialist of XPTO.
Also I have XXX pappers published, (peer reviewed of course), written Y books about the 'N cagagésimo' of the untestable theory that nobody understands. Everyone applauds and I am a sucess. And I have free access to papers.



-- Now the way I like. My monthly pay check comes regularly and it is ok.
I love physics but I'm unconfortable with the panorama.
I am an amateur in the proper sense of the word (amateur = lover) and I read everything that I can. I am not an specialist, but a generalist and even the non-mainstream theories I' read about (The net as a lot of crackpot). I've not an agenda, and have time to talk to many intelligent guys that I know. I have the net, and access to all papers (that I could not reach because they are paid). May be that way I could find something interesting.
Study Einstein again (not Minkovsky - this is the mathematician), rethink and doubt systematically.

The best time to human thinking was in the classic antiquity (greek time). Lazy times.
To be uncommited to the production is fundamental to reach anything new. Do it for fun, not as an obligation.

Trying to quantize GR ? Why ?

We have to be patient with the pursue of any TOE.

If we dont know how to explain (AFAIK) the Titius -Bode law how can we aspire to know the ultimate goal of mankind?

quoting Chalnot "String theory is one attempt to reconcile quantum mechanics and gravity. Loop quantum gravity is another. We don't yet know which, if either, is accurate."

Trying to quantize GR ? Why ?
Photons are quantized not by themselves but because the emiters and receptors are ressonators. In the gravity problem I dont see ressonators.
May be the unification is not possible at all. I wouldnt be chocked.

As I said, you end up with unreconcilable contradictions otherwise. The primary problem is that it would mean that an extremely accurate gravitational measurement would allow you to get around the uncertainty principle. So at the very least it must be possible for General Relativity to be such that it can be represented as a superposition of states, so as to accord with the superpositions of states we see in quantum mechanics.

To attempt to illustrate this, imagine that I have a quantum particle (say, a hydrogen atom), prepared in the following state:

|psi> = |0> + |1>

...where |0> is the ground state of the hydrogen atom, and |1> is the first excited state. A hydrogen atom prepared in this superposition of states has no definite energy, and therefore no definite mass.

So what is its gravitational field?

D'accord!

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I'm not sure what this has to do with cosmology ...

In any case, it's already likely reasonably well understood (an example), and when planetary systems around a large sample of other stars are well characterised, today's theories will have some new data to sink their teeth into.

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Do you now understand why lots of people try to quantise GR?

This is a difficult problem. When we can not have a 'definite mass' is different issue as saying that it has no energetic content (mass/energy). Consider a surface apart surrounding your atom. The total energetic content before and after the excitation and any intervenient photon will be in balance and a definite one, nor 0 nor infinite.
In classic mechanics when we have a rope with more than one oscilation in presence we do not desesperate.
When we have to characterize the temperature (say gravity) of a glass of warmed water we will describe it in macroscopical way, not describing the states of all and each particle of water in the glass.
We are seeking the gravity within the 'particle' but perhaps we could find it (or only think of it) only in the space around it as an imprint of some vibration inside the matter.
But I dont feel the need to quantize. Who knows if it is a continual (opposed to quantic) interaction between the space and matter.

Thanks for the link, but I didnt find there an explanation. In another post we can talk about the origin of the Solar System and some difficulties that I have with the accepted model.

I think you are suggesting that the quantity of persons involved and expecting to solve the quantization of GR is proportional to the difficulties (or impossibility I think). As we dont know the answer the effort must be done.

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However, the experimental validation of QM is astonishing in its breadth and accuracy!
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...naive intuitions are a remarkably unreliable guide, and in the Land of Physics (and Cosmology), Experiment (and Observation) Rules, OK?