I'm going to address the title of this thread.

For 30 years or more everyone has known we have SR, and QM. As a triumph of unification QED - the most precisely tested theory ever - combines SR and QM.

But then we have GR and gravity. Combining that with QM has proven really really difficult.

I'd like to draw attention to a story that begain 10 years ago and that points very strongly to a new unification in which GR emerges out of QM. It was originally viewed as crackpot.

This is still early stage work, but it has been going on for 10 years and what makes me believe this is truly the new thing is the way that different apparently unrelated ideas in physics join up in this new area. I (and I guess many others) have long had the idea that spacetime ought to come from something else more fundamental, that the truly nonlocal nature of entanglement hints strongly that somehown QM is related to spacetime, and this is that.

The basic idea came from a paper to Journal of High Energy Physics from Raamsdonk in 2009, and it was rejected as of no merit (implying Raamsdonk is a crackpot) in 2010. Raamsdonk was not deterred, he submitted for General Relativity and Gravitation and was still rejected, but with a suggested major rewrite to make the material publishable.

Raamsdonk entered a shorter version of his work into a prestigious annual essay context run by the Gravity Research Foundation, won first prize, and, ironically, was thereby guaranteed express publication in General Relativity and Gravitation.

That is actually a very fast acceptance for any truly revolutionary theory: his ideas did even at that early stage exactly hit the sweet spot for what a lot of people dissatisfied with theoretical physics as currently understood felt was a promising direction.

And some here will remember that I've been every now and again saying stuff about his work, which comes under the heading of "deriving spacetime from QM" although it does not yet seem to have an accepted name.

The key idea: use quantum entanglement as the basic mechanism from which Lorentzian metric curved spacetime is derived: with gravity naturally falling out from the curvature is on GR. Einstein had it right that everything is geometry - but wrong in that the geometry is created by an inherently nonlocal highly spooky quantum phenomenon.

Why is this stuff so weird? We are used to seeing position and time as fundamental things in terms of which we express other theories. Foundations of QM have made it pretty clear for more than 40 years that this does not quite work: but here we have a realistic way to express physical theories in terms of something quite different from space and time, in such a way that the space and time we experience is an emergent phenomenon.

2015 summary in Nature (good place to start, but not uptodate)

It from Qubit research collaboration

Various parts of the puzzle (from Quanta magazine - a great semi-technical resource with links to the research itself)

https://www.quantamagazine.org…correcting-code-20190103/

https://www.quantamagazine.org…nd-entanglement-20150428/

https://www.quantamagazine.org…nus-dark-matter-20161129/ (a puzzle piece not yet well integrated!)

https://www.quantamagazine.org…irewall-paradox-20150424/

https://www.quantamagazine.org…ys-time-problem-20161201/

https://www.quantamagazine.org…particle-physics-20130917

https://www.quantamagazine.org…superconductors-20181119/

https://www.quantamagazine.org…tion-in-physics-20130524/

For many here the idea that theoretical physics could end up as a sub-branch of computer science will be sort of interesting - and while information complexity seems a very key concept in all this new stuff, the math required to calculate usefully with it goes quite a long way beyond what computer scientists usually handle!

For those disliking QFT.

Look at the Amplituhedron. A geometrical idea that allows the same calculations to be performed as given by Feynman diagrams, and that allow experimental results to be predicted, but is 1000s of times simpler (in terms of complexity and work).

When you find this sort of simplification - generating the same results - you know you have hit some deeper understanding. So even though the Amplituhedron is still not much understood - it works - and it is vastly significant.

What does that mean for standard model etc? It looks as though the theoretical underpinning (QFT) is correct but wrong in that it is grossly over-complicated. It is just that we need to abandon a few more preconceptions properly to understand the underlying structure.

What does this mean for new physics? I'm sure it will come but any theory that does this must first of all (in approximation) replicate the standard model.

I'm not including Higgs boson as part of standard model since gravity clearly needs something new and therefore it seems likely that while Higgs exists phenomenonically (experimentally as observed in LHC, and theoretically as a prediction) it will end up being seen as an emergent phenomena of some deeper structure.

Once that has been dealt with may be we will find that all the rest of the Standard Model emerges in the same way?

THH

Going from spacetime (as fundamental) to quantum mechanics as in the John Wallace ppt is evocative of many things - many relationships exist - but pretty definitely the wrong way round. Once you accept all the experimental results we now have for entanglement, and their Bell's Theorem like correlates, you become pretty clear that spacetime is not fundamental - an unification going in the other direction is a better bet.

What makes it difficult for me to evaluate the ppt is the compete lack of specific detailed references, or critiqued by others research conclusions. Where tantalising correspondences are shown there is no quick way to know whether in fact they fall out as natural from the other direction, or are just expected tautologies. Such "bubble research" is often fun to read but unlikely to be correct. It is also at the level of a broad historical summary - which is fine in motivating a research direction but not in justifying specific research as having value. You can see from my posts here that while I am in favour of deriving one of QM, GR from the other, I have strong reasons to prefer QM as fundamental, and therefore disagree with Wallace.

And, yay, it looks as though the Raamsdonk et al stuff is coming together and will do exactly this, in a very satisfying way, within my lifetime.

THH

Einstein could be easily correct and wrong at the same moment. I think that people just lack a bit of imagination for to realize it in full depth. In dense aether model the 2D water surface represents an analogy of 3D foamy space-time, which we are living in. If we would live at the water surface and used its surface ripples as the only source/mean of observations we would experience pretty much the same things, which we can observe with empty space by now.

First of all, this water surface would get unobservable for us. Simply because for waves of every environment this environment remains unobservable by its very definition of "environment" concept. If they could somehow interact with it, it would be an obstacle - not an environment anymore. Such an obstacles can indeed exist both at the water surface, both in cosmic space - but we call them a particles, not space anymore.

At second, this surface would looks inhomogeneous and blurry for us at both small, both large scales. This is because the water surface exhibits thermally induced inhomogeneities - so called Brownian noise - which are much smaller than the surface ripples, so that they can be observed with them neither. But these inhomogeneities would blur all images mediated by surface ripples at small distance scales for us. The Brownian noise of water surface therefore serves as a material analogy of quantum uncertainty for objects observed through layer of undulating vacuum filled by quantum noise.

Similarly to blue haze of atmosphere induced by thermal fluctuations of it, both Brownian noise of water surface, both the quantum noise of vaccum would introduce observable macroscopic net effects for us. For example, if we would introduce splash at the water surface, then the surface would get deformed. We couldn't observe this deform directly, because surface ripples could spread across this deform freely - nevertheless the deformed surface is expanded (it has larger specific area) so that it would delay and slow down the spreading of surface ripples a bit. This trivial effect immediately introduces both quantum mechanics, both general relativity theories into description of water surface loaded with energy density.

In general relativity the deformed space-time also exhibits lensing and it has its energy density assigned by Einstein's field equations. The delay of light propagation across deformed water surface would manifest itself by lensing phenomena in similar way, like for deformed space-time in general relativity. The curved undulating water surface would behave like lens for surface ripples passing through it and it would deform it even more.

At small distance scales the energy introduced into surface would also manifest itself by lensing, but in this case the lensing would be observed by surface ripples from outside like effect, which increases probability of occurrence of objects observed there. This is essentially what the Schrodinger equation of quantum mechanics tells for us: the introduction of energy into space increases the probability function of massive objects residing there. It's essentially description of the same lensing effect - just from perspective of massive objects propagation instead of light propagation, because at the case of quantum lensing the size of lensing is much smaller than wavelength of ripples which would observe it.

The behavior of vacuum thus doesn't differ from behavior of water surface at all, once we would observe this behavior strictly and consequentially by its surface ripples only.

Here is a good recent review of the "spacetime is generated by quantum entanglement" stuff.

It is a very exciting time now for theoretical physicists.

Spacetime from Entanglement

Brian Swingle

Annual Review of Condensed Matter Physics

Vol. 9:345-358 (Volume publication date March 2018)

First published as a Review in Advance on December 20, 2017

https://doi.org/10.1146/annurev-conmatphys-033117-054219

This is an idiosyncratic colloquium-style review of the idea that spacetime and gravity can emerge from entanglement. Drawing inspiration from the conjectured duality between quantum gravity in anti de Sitter space and certain conformal field theories, we argue that tensor networks can be used to define a discrete geometry that encodes entanglement geometrically. With the additional assumption that a continuum limit can be taken, the resulting geometry necessarily obeys Einstein’s equations. The discussion takes the point of view that the emergence of spacetime and gravity is a mysterious phenomenon of quantum many-body physics that we would like to understand. We also briefly discuss possible experiments to detect emergent gravity in highly entangled quantum systems.

Also relevant: Anti de-Sitter spacetime has a constant positive curvature and is maximally symmetric: that allows correspondence between quantum gravity and QFT via the holographic principle.

De Sitter spacetime (constant negative curvature) does not have the same symmetry group. But this is our spacetime and how to do the same thing with it is a key question.

https://arxiv.org/pdf/hep-th/0110007.pdf

Why has there been significant progress in understanding black hole entropy,
but almost no progress in understanding the entropy of de Sitter space? One
reason is that one of the principal tools we’ve used for understanding black hole
entropy is supersymmetry. Black holes can be supersymmetric, and indeed the
first black holes whose entropy was counted microscopically were supersymmetric.

Since then we’ve managed to creep away from the supersymmetric limit a
little bit, but not very far, and certainly we never managed to get all the way to
Schwarzschild black holes. So supersymmetry is a crutch that we will need to
throw away before we can do anything about de Sitter space. Indeed there is a
very simple observation [6] that de Sitter space is inconsistent with supersymmetry

in the sense that there is no supergroup that includes the isometries of
de Sitter space and has unitary representations.1 A second, related, obstacle to
progress in understanding de Sitter space is that so far we have not been able
to embed it in a fully satisfactory manner into string theory.
While the importance of understanding de Sitter quantum gravity has been
evident for decades, it has recently been receiving more attention [7–42]. One
reason for this is the recent astronomical observations which indicate that the
cosmological constant in our universe is positive [43–46]. A second reason is that
recent progress in string theory and black holes provides new tools and suggests
potentially fruitful new angles. So perhaps de Sitter quantum gravity is a nut
ready to be cracked. These lectures are mostly an elementary discussion of the
background material relevant to the problem of de Sitter quantum gravity

Quote

use quantum entanglement as the basic mechanism from which Lorentzian metric curved spacetime is derived: with gravity naturally falling out from the curvature is on GR

Quantum entanglement occurs within space - it cannot be used for explanation of space, after then. In addition, entanglement is low-distance quantum effect, gravity exactly the opposite one. Entanglement occurs between photons, which are massless, etc.

Quote from Zephir_AWT

[...]

Entanglement occurs between photons, which are massless, etc.

Quantenverschränkung auf den Kopf gestellt

Quantum entanglement turned upside down

https://www.uibk.ac.at/public-…/presse/archiv/2018/1002/

University of Insbruck (22.5.2018)

"Die Verschränkung einzelner Teilchen - seien es Photonen, Atome oder Moleküle - gehört heute im Labor zum Alltag."

"The entanglement of individual particles - be they photons, atoms or molecules - is part of everyday life in the laboratory today."

Ein Photon mit einer Billionen Atome verschränkt

A photon with a trillion atoms crossed

https://www.scinexx.de/news/te…ionen-atome-verschraenkt/

University of Warschau (03.03.2017)

"Forscher haben erstmals ein Photon mit einem makroskopischen Objekt verschränkt – einem Klumpen aus einer Billion Atome."

"Researchers have for the first time entangled a photon with a macroscopic object - a lump of one billion atoms"

Quote from RobertBryant

John Wallace has some problems with status quo QM.

Wallace was in Asti. He makes like many others (e.g. Bernard Schaeffer) simple classic experiments that directly refute the QM based SM.

The SM space is 3D,t X "permutation space".

There will never ever be any physics that explains our world based on this simplified view of the world. The biggest problem of the SM mathematical space is its lack of symmetry, what makes me always laugh, when I read an SM paper and see the term symmetry violation... If you like true comedy reading SM papers is an endless source of entertainment. It's a pity how much time and brainpower the best physicists/ mathematicians waste in finding a path out of the self chosen labyrinth!

One recent task (covered by many papers) was to explain that QM is more fundamental than all other models used for SM... This is what happens when mathematicians take over physics. They have absolutely no clue what fundamental means and needs - to be truly fundamental.

As said elsewhere: Precision is the prime key. If you can exactly calculate e.g., then "proton property" mass out of its magnetic moment. SM is a complete fail. They have absolutely no clue how to link basic properties to an integral picture and cannot make such calculations. Experiments count!!

In SO(4) all 4 forces are unified and can mathematically be derived and explained from hard measurements with absolute precision. SO(4) has a very high degree symmetry and nice features to describe connections. And of course we can calculate the proton mass from its magnetic moment.

Finally: Einstein knew that he was not right! He devoted his whole live to find a better model. And may be if he had had excel and a strong person computer we would already have it. Nevertheless he was a genius of his time and he was key for progress of the field!

Wallace was in Asti. He makes like many others (e.g. Bernard Schaeffer) simple classic experiments that directly refute the QM based SM.

I did not see that.

Can you reference the write-up of the experiment that "refutes QM"?

Quote from Zephir_AWT

Quantum entanglement occurs within space - it cannot be used for explanation of space, after then. In addition, entanglement is low-distance quantum effect, gravity exactly the opposite one. Entanglement occurs between photons, which are massless, etc.

No, that is untrue. Have you read the literature on this?

it does not help to make such arguments before having read how space & time can emerge from QM entanglement.

Quote

how space & time can emerge from QM entanglement

I'm not even required to read about it, because I can immediately spot a circular reasoning: quantum entanglement cannot establish itself without time and space.

Quote from THHuxleynew

it does not help to make such arguments before having read how space & time can emerge from QM entanglement.

It would be nice if you once could give us a paper that proves that QM (QED/QCD)) is (are) a basic/fundamental model(s) that allow(s) to exactly reproduce experimental quantities like the proton radius given other exactly known experimental values.

If you use a non fundamental model (e.g. QM) to prove something fundamental = given by an experiment then any logical derivation is wrong = a complete fail.

This is the arrogance of the current physics priests, that they believe and make people claim that QM (QED/QCD)) are fundamental! As soon as you use the inexact Coulomb gauge you are dead = no longer fundamental! The classic Coulomb gauge gives you 5 out of 10 digits for Hydrogen and far less for all other nuclei...

The only point where QM (QED/QCD)) have some merits are derivations from the permutation space that explain a part of the structure (not the ,masses!!) of the particle zoo.

As the newest experiments show: Entanglement is space like and not time bound! This also proves that the dimension of space can (must!!) be much greater than 4 what is the number the people use in your paper to explain space-time....

Quote from Zephir_AWT

I'm not even required to read about it, because I can immediately spot a circular reasoning: quantum entanglement cannot establish itself without time and space.

Zephir: I'm sorry but it is not good enough to say that unless you have read the papers that define quantum entanglement independently of spacetime and derive spacetime from that.

Now, perhaps you are an expert on quantum entanglement (I have my doubts). Even so, that will be QE as defined conventionally in terms of spacetime. You are not therefore an expert on what is the underlying geometric structure that might give rise to spacetime from considerations only of quantum entanglement. What entanglement does is to show that interactions at separated points in spacetime are connected. The derivation of spacetime works the other way round, given a set of QE-like connections, how can that be used to uniquely determine points in spacetime?

How about you read my links above on how this stuff works before dismissing it out of hand? It seems only fair.

If you say - well, none of this stiff has yet been proven for Anti De Sitter spacetime then I'd agree with you. But the methodology works for De Sitter spacetime and that is a very exciting achievement - it does seem likley that ADS spacetime can also be generated.