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kye
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You will notice we focus a lot on Loop Quantum Gravity here and String theory out there. Are there other alternatives to these two in case they are found to be false years from now? What are they?
kye said:You will notice we focus a lot on Loop Quantum Gravity here and String theory out there. Are there other alternatives to these two in case they are found to be false years from now? What are they?
marcus said:Loop gravity is not a finalized theory. It is a general way of constructing a quantum theory of geometry and of cosmology.
Several loop gravity theories have ALREADY been found to be wrong, and the loop community has modified and come up with improved versions. It is a general technique and theoretical language.
The original loop cosmology model was shown to be wrong (around 2005) and replaced with "improved dynamics" loop cosmology in 2006. The original spinfoam quantum geometry was shown to be wrong by Rovelli in around 2007-2008, and replace by the EPRL spinfoam.
There are currently several versions being worked on either in the full theory or in the application to cosmology. I could probably list half a dozen versions. A lot of researchers like loop and are working on it.
Also ways of TESTING the loop cosmology models by observation (e.g. of the CMB) have been proposed and more are being worked on.
Besides loop and string there are other approaches being pursued (causal sets, energetic causal sets, causal dynamical triangulations, non-commutative geometry, asymptotic safety gravity, Horava gravity, Jacobson's Einstein Aether, Krasnov's approach, Shape Dynamics, group field theory, Rivasseau's "tensor track"...).
the total number of people working on all these (non-loop, non-string) alternatives is comparatively limited and some are in DECLINE, as interest runs out, or steady (confined to a handful of researchers and not attracting young postdocs). But if loop, say, stops gaining interested young researchers and progress stalls, you can be sure that there will be SOME alternative approach that springs up to take its place. It might not be any of the CURRENT alternatives, since the list of alternatives keeps changing as interest in some wanes and others (e.g. Shape) are invented.
tom.stoer said:In my pointing in is not correct to talk about "alternatives to LQG and ST" simply b/c LQG is not an alternative to ST.
LQG is an incomplete framework to quantize classical theories describing gravity - with GR as the simplest example - w/o unifying other interactions. ST is - in my opinion - an incomplete framework to derive or construct low-energy theories incorporating gauge, SUSY, gravity in a unifying manner (the high-energy completion is the highly speculative M-theory for which no mathematical formulation is known)
kye said:As far as Planck scale is concern.. what is the argument or theorem that something can even exist inside the Planck scale (it's so small).. the search for theory of quantum gravity is how to describe events inside the Planck scale where QM and GR break down. But the Planck is so very small.. maybe it just ceases to exist in principle? If so, there is no need to unify QM and GR? Or is there other reasons like we don't even how quantum particles interact with spacetime or how particles are coupled to spacetime and this is why they have to be unified independent of Planck scale breakdown of QM and GR?
kye said:You will notice we focus a lot on Loop Quantum Gravity here and String theory out there. Are there other alternatives to these two in case they are found to be false years from now? What are they?
Some alternatives to LQG and ST include Quantum Field Theory, Causal Dynamical Triangulations, and Emergent models.
These alternatives differ in their approach to understanding the fundamental laws of the universe. LQG and ST both attempt to reconcile general relativity and quantum mechanics, while other theories such as Quantum Field Theory focus solely on quantum mechanics.
Currently, there is no direct experimental evidence for any of these alternatives. However, some predictions of Quantum Field Theory and Causal Dynamical Triangulations have been observed in experiments, giving them some support.
One of the main challenges is the lack of a unified theory that can explain all aspects of the universe. Another challenge is the difficulty in testing these theories through experiments, as they often involve scales that are beyond our current technological capabilities.
It is possible that one of these alternatives could eventually become the dominant theory in theoretical physics. However, it is also possible that a new, yet undiscovered theory may emerge that could potentially unify all current theories.