[ExI] Quantum gravity

John Clark johnkclark at gmail.com
Thu Sep 17 12:35:09 UTC 2020


On Wed, Sep 16, 2020 at 9:18 PM Stuart LaForge via extropy-chat <
extropy-chat at lists.extropy.org> wrote:

General Relativity and Quantum Mechanics are not compatible theories,
>> although both work very well within their realm of applicability,
>> General Relativity works great for gravity but can say nothing about the
>> nuclear forces, quantum mechanics can say a lot about the nuclear forces
>> but can't say anything about gravity.
>
>
> * > Dirac managed to combine Special Relativity and Quantum Mechanics and
> the math correctly predicted antimatter*


Yes and Dirac was brilliant, but the Dirac Equation says nothing about
gravity because Special Relativity says nothing about gravity or about
objects that are accelerating, that's why it's called special, it only
works in special circumstances. It took another 10 years of backbreaking
work for Einstein to figure out General Relativity which could deal with
general situations like those with gravity and acceleration.


> > *There might be some clever hack that allows GR and QM to similarly
> mesh.*
>

Maybe, but that has been the Holy Grail of Physics for a century and a lot
of geniuses have tried to find it including Einstein and Dirac and they all
ended up with nothing, so I believe it'll take more than just a simple
hack, it will probably take a change in the way we think about things as
profound is the quantum revolution of 1900. I just wish I knew what it was.


*> **I don't think it is a lack of theories of quantum gravity that is
> the problem. There are several theories already in circulation including
> several versions of string theory. The problem is none can make testable
> predictions.*


If it can't make testable predictions then it's not a theory it's
philosophical musings, even string theory fans say it's a theory on how to
someday get a theory about gravity. But even then I don't know how they'd
test it.

* > How do you go about deciding the validity of a theory that makes
> predictions about things in a physical regime that cannot be observed in
> nature or reproduced in a laboratory?*


Nobody knows and that's the problem.


>
> *> We need  more progress in the experimental side of things I think.*


Yes but easier said than done. We could quickly make progress if we had a
particle accelerator that was powerful enough to probe the Planck scale,
but with current technology such a machine would have to be at least as big
as the solar system, and it would be difficult to get congressional funding
for that. In my opinion the second best way would be to build machines to
more closely examine the behavior of neutrinos because they do seem to show
some small cracks in the standard model of physics, such experiments are
not cheap, nothing in big physics is, but they're not so expensive as to be
ridiculous. Also, just a few days ago there was a report that a pseudo-atom
consisting of an electron and a antielectron admitted microwaves that very
slightly deviated from the predictions of the most accurately tested theory
in all of science, Quantum Electrodynamics. If this is confirmed it could
really be important, it could give us a clue.

>>  no physicist has ever seen a mathematical hypotenuse, however they have
>> seen lines that connect diagonal corners on cardboard squares.
>
>
>
> * > As an approximation perhaps, but not as a scientific experiment
> to look for granularity in space. Why would you use something made of atoms
> which are known to be discrete to test the existence of the  continuum of
> real numbers?*


Because matter is the only thing we know how to make scientific instruments
or a machine of any sort out of, and like it or not matter is made of
atoms.


>
> *>The Pythagorean theorem is a property of  Euclidean space and not
> particles. That's why I suggested my  interferometry experiment. *


To conduct a interferometry experiment you need a interferometer, and they
are made of matter. And so are Gamma Ray orbiting telescopes. Quantum
mechanics predicts that if space-time really is discrete and not continuous
then high energy high frequency electromagnetic waves will travel at a
slightly slower speed than lower frequency lower energy waves. But a few
years back a 2.1 second long Gamma Ray burst occurred 7.3 Billion light
years away, and satellites were able to determine that 2 photons coming
from that burst had the same speed to one part in 100 Million Billion even
though one of the photons had 1 million times more energy than the other.
So Einstein won again, as usual. It's just not looking good for a discrete
space time.

>> Mathematics is the language of physics but mathematics is not physics. English
>> is a language too but the English word "*cow*" cannot give milk.
>
>
>
> * > But a virtual cow can give virtual milk and a virtual man could drink
> *


Agreed, but the very fact that they serve in different realms means that a
virtual cow is not identical to a physical cow, and the virtual cow
couldn't exist without physics. That's why I think physics is more
fundamental than mathematics.

* > it and they would all three be made out of math and information.*


It's not turtles all the way down, eventually you get down to matter. To
make a virtual cow you have to process information, and to process
information you need to make a Turing Machine, and Turing Machines
are made of matter. And matter is made of atoms.

John K Clark
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