[ExI] Quantum gravity

[Stuart LaForge]

Quoting John Clark:

>
> No, Einstein demonstrated it was unnecessary, but as I have said 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 before physicists had any  
inkling it could exist as an observable particle. Moreover  
relativistic mass-energy equivalence predicted nuclear forces account  
for the majority of the mass of an atom thereby enabling nuclear  
energy. There might be some clever hack that allows GR and QM to  
similarly mesh.

> One theory works for things that are large and
> massive and the other theory works for things that are small and light, the
> problem is that there are places where things are both small and massive,
> and in those places physics has no idea what's going on.  Resolving the
> contradiction between these two very good theories is probably the main
> goal of modern physics, and it's not going to happen until somebody
> develops a quantum theory of gravity.

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

>
> Your number is a 5 followed by 165 zeros, a googolplex is 10^(10^100),
> that's a 1 followed by 10^100 zeros. Saying that one number is
> astronomically larger than the other would be a vast understatement, but
> that's about the strongest word the English language provides. Compared to
> a googolplex 5*10^165 is zero to a wonderfully good approximation.
>

Yeah, I know. I noticed the -plex after I hit send, much to my  
chagrin. But if those atoms were radioactive, there would be about  
SQRT(2*pi*10^83) * 10^(83*10^83)/e^(10^83) possible orders in which  
the atoms could decay. That is still not a googolplex but it is much  
closer . . . only off by about 15 orders of magnitude or so. ;-P


>> * > Mistake? Plato could have been right. Why would you use something
>> so crude as a cardboard square to test something so precise?*
>
>
> Because 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? The Pythagorean theorem is a property of  
Euclidean space and not particles. That's why I suggested my  
interferometry experiment. If you can split a laser beam and have one  
beam traverse the two sides around one corner of a square and make it  
so that you can set the other beam to either go around the other two  
sides and corner of the square or across the diagonal, no matter how  
big or small you make the square, you should always get a sharper  
interference pattern if the two beams are going around opposite  
corners than if one of the beams are going across the diagonal. You  
should never get 100% constructive or destructive interference across  
the diagonal, if real numbers exist, because if a whole number of  
wavelengths of light fit along the sides of a square, then you should  
not be able to fit a whole number of wavelengths along the diagonal of  
that same square.

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

Stuart LaForge