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Nickyv2423

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Are there any linear quantum gravity theories out there with respect to the wave function?

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In summary: Casual Fermion System.In summary, all mainstream quantum gravity theories are linear with respect to the wave function.

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Nickyv2423

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Are there any linear quantum gravity theories out there with respect to the wave function?

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All mainstream quantum gravity theories (string theory, Wheeler-DeWitt, loop quantum gravity, perturbative quantization of spin-2 field in a classical background, etc.)Nickyv2423 said:Are there any linear quantum gravity theories out there with respect to the wave function?

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haushofer

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Maybe you're confusing fields with wave functions ?

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Who are you referring to? The OP stated that he is talking about linearity with respect to wave functions. I assumed that by "wave functions" he means quantum states and not the gravitational fields. Dextercioby assumed the opposite.haushofer said:Maybe you're confusing fields with wave functions ?

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haushofer

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I meant the OP. If so, the question seems to make more sense to me.

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Nickyv2423

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What about asymptotic safety in quantum gravity?Demystifier said:All mainstream quantum gravity theories (string theory, Wheeler-DeWitt, loop quantum gravity, perturbative quantization of spin-2 field in a classical background, etc.)are linearwith respect to the wave function. Linearity (or superposition principle) is one of the basics axioms of quantum theory.

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It's also linear.Nickyv2423 said:What about asymptotic safety in quantum gravity?

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Nickyv2423

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How do you know? Not all quantum gravity theories are linear. Casual fermion systems is non linear and so is casual dynamical triangulation.Demystifier said:It's also linear.

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Can you support it by a reference?Nickyv2423 said:Casual fermion systems is non linear and so is casual dynamical triangulation.

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Nickyv2423

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I just emailed researchers in the field and they told me.Demystifier said:Can you support it by a reference?

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Can you copy/paste the exact question you asked and their exact answer?Nickyv2423 said:I just emailed researchers in the field and they told me.

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Nickyv2423

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Me -Demystifier said:Can you copy/paste the exact question you asked and their exact answer?

Hello, I know this is random but I just have a simple question concerning Casual Fermion System (CFS) as a theory of quantum gravity...

Is CFS a local or non local theory of Quantum Field Theory? If it is local, then it cannot be correct. Also, is CFS linear with respect to the wave function?

Felix Finster -

Dear Nick,

Thanks for your question! I am sorry for not writing back earlier.

The causal action principle (which gives rise to the physical equations in a causal fermion system) is non-linear and non-local. But of course, the resulting Euler-Lagrange equations are linear in certain limiting cases, in particular giving rise to a linear dynamics on Fock spaces.

For more information you could have a look at the survey paper

https://arxiv.org/abs/1502.03587

or the first chapter of the book

https://arxiv.org/abs/1605.04742

The connection to quantum geometry (which should also be the framework for describing quantum gravity) is worked out in

https://arxiv.org/abs/1107.2026

Just let me know if you have any further questions.

Felix

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Nickyv2423

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I don't have the reply from the CDT researcher I deleted itDemystifier said:Can you copy/paste the exact question you asked and their exact answer?

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You are right, this is really a non-linear theory with respect to the quantum state (which you call wave function). The theory has something to do with the so-called wave-function collapse. However, this is a very exotic theory, very very far away from the mainstream.Nickyv2423 said:For more information you could have a look at the survey paper

https://arxiv.org/abs/1502.03587

Asymptotic safety, however, is quite mainstream. As I said, all mainstream theories of quantum gravity are linear.

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Physics4Funn

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It's not the best place to start reading Finster's work as he has papers going back about 15 years.

I know Finster's approach is different, but considering how many smart people have looked at QG and UFT and made such limited progress, I consider even the nut cases worthy of a look.

So far I have found many new and useful ideas in Finster's CFS papers.

The basic concepts are appealing.

I have not found any errors so I am still studying it.

I posted a preprint using Finster's model looking for connections to dark matter.

In another thread about the Dirac sea, the only slightly more specific reply was that Finster's Dirac sea extension has many objections.

If you have specific objections, I will eagerly read them.

I'll post in the other thread next.

Thank you for any help as I have been looking for anyone has any comments about it.

Linear quantum gravity is a theoretical framework that attempts to combine the principles of quantum mechanics and general relativity in a linear manner. It postulates that gravity is a quantum field that operates on a linear space-time, as opposed to the non-linear space-time described by general relativity.

The current theories of quantum mechanics and general relativity are incompatible with each other, and do not provide a complete understanding of the universe. Linear quantum gravity theories aim to bridge this gap and provide a unified framework that can explain the behavior of both subatomic particles and large-scale gravitational phenomena.

As of now, there is no direct experimental evidence for linear quantum gravity. This is because the energy scales required to observe the effects of quantum gravity are currently beyond our technological capabilities. However, there have been theoretical predictions and indirect evidence that support the existence of linear quantum gravity.

Some examples of linear quantum gravity theories include loop quantum gravity, string theory, and causal dynamical triangulation. These theories differ in their approach and mathematical formalism, but all attempt to reconcile quantum mechanics and general relativity in a linear manner.

Developing a linear quantum gravity theory is a major challenge in modern physics. Some of the main challenges include the difficulty in experimentally testing these theories, the complex mathematical formalism involved, and the need for a consistent and unified framework that can explain all fundamental forces in the universe.

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