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So I too love the idea that we don't need dark matter to explain all the gravitational effects we observe in the universe. However, is it just me or does the f

by cshreve 10y ago

So I too love the idea that we don't need dark matter to explain all the gravitational effects we observe in the universe. However, is it just me or does the falsification of this seem a bit sketchy: if we find a dark matter particle...then my theory is false. That's a bit like saying...oh yeah if we find a different way to unify general relativity and quantum mechanics...then String Theory is false. It seems like there should be a 'smaller' way to falsify it.

jcoffland 10y ago
I think you will find all the models are false to a degree. A model is only an approximation of the real thing. Quantum mechanics and General relatively cannot both be right. The obvious answer is that they are both wrong.
- duaneb 10y ago
  Isn't that just relativistic quantum field theory?
  - baq 10y ago
    that's the thing, gravity from GR doesn't quantize well, or actually at all.
    - raattgift 10y ago
      Einstein gravity quantizes remarkably well in the weak field limit; it's called perturbative quantum gravity, and is considered (with good reason) a sound effective field theory (in the Kenneth G Wilson sense of "effective"). One of the results of perturbative quantization is the discovery of the non-renormalization -- by power-set counting -- of gravity and why (very roughly and simply, it's because gravity is a long-range and self-interacting force). However, this only matters in systems where you would need to use Feynman diagrams involving multiple loops of gravitons, which essentially defines strong gravity, and you'll only find that well inside the event horizons of black holes, or in the extremely early big bang universe. Outside the strong gravity limit, perturbative quantization of Einstein gravity exactly corresponds with General Relativity, as indeed any theory seeking to extend or replace General Relativity pretty well must (since GR accords with so much observational and experimental evidence). There is also little reason to expect that we will never arrive at methods other than power-set counting to deal with the explosion of variables in many-loop systems, although that in itself should not preclude investment in other quantum gravity programmes that are very different.
- zamalek 10y ago
  A thought experiment of mine. Assume that all possible hypothesis or theories (explanations in general) form part of an "explanation space." Some explanations are good (theories), some have no evidence (hypothesis) and some are false (we are riding a giant turtle). Given the number of false explanations, the overall space is infinite. Hypothesis spaces would be islands within the false explanation space, theories islands within hypothesis and the truth as a single point within one of those theory spaces. The question is, does that mean that the theory space is infinite? If so, that would mean that it would be impossible to know that we've found the truth (as a single point within this infinite space) - we'd only ever be able to conclude that we've found a closer approximation. Scientists may never run out of work.
  - eli_gottlieb 10y ago
    >The question is, does that mean that the theory space is infinite? If so, that would mean that it would be impossible to know that we've found the truth (as a single point within this infinite space) - we'd only ever be able to conclude that we've found a closer approximation. Scientists may never run out of work. The theory space is definitely infinite, in either the interesting sense of something like "the space of all possible programs, treated as causal or directed-generative models" or in the trivial sense that you can take any simple, well-supported theory and come up with mathematical elaborations that don't change any of the pre-existing empirical predictions. In a certain sense, "the truth" may constitute an infinitely small point in a space that's more continuous than discrete.
  - ci5er 10y ago
    Your "explanation space" is almost certainly infinite and mostly empty. The closer any model approaches reality, the more it is indistinguishable from the object being described. Like any map, it becomes unwieldy with increased accuracy. The model becomes the size of the universe. So, a universe-sized model inside of an infinite explanation space?
maikb 10y ago
Remember that these people use a language that might sound similar to common english, but words have different meaning and it is much more precise. No reading between the lines. He gave an example of what would falsify his theory, that is all.
npgatech 10y ago
> "So I too love the idea that we don't need dark matter to explain all the gravitational effects we observe in the universe." It is an attempt to explain. Just like an attempt to explain (prediction) of Higgs Boson. It was only true once we observed it via experimentation. Falsification makes sense if the theory has been experimentally validated. You can't falsify something that has not been proven. There is no one claiming String theory or the theory discussed here is true - no experimental evidence has been produced.

by cshreve 10y ago

jcoffland 10y ago

I think you will find all the models are false to a degree. A model is only an approximation of the real thing. Quantum mechanics and General relatively cannot both be right. The obvious answer is that they are both wrong.

duaneb 10y ago
Isn't that just relativistic quantum field theory?
- baq 10y ago
  that's the thing, gravity from GR doesn't quantize well, or actually at all.
  - raattgift 10y ago
    Einstein gravity quantizes remarkably well in the weak field limit; it's called perturbative quantum gravity, and is considered (with good reason) a sound effective field theory (in the Kenneth G Wilson sense of "effective"). One of the results of perturbative quantization is the discovery of the non-renormalization -- by power-set counting -- of gravity and why (very roughly and simply, it's because gravity is a long-range and self-interacting force). However, this only matters in systems where you would need to use Feynman diagrams involving multiple loops of gravitons, which essentially defines strong gravity, and you'll only find that well inside the event horizons of black holes, or in the extremely early big bang universe. Outside the strong gravity limit, perturbative quantization of Einstein gravity exactly corresponds with General Relativity, as indeed any theory seeking to extend or replace General Relativity pretty well must (since GR accords with so much observational and experimental evidence). There is also little reason to expect that we will never arrive at methods other than power-set counting to deal with the explosion of variables in many-loop systems, although that in itself should not preclude investment in other quantum gravity programmes that are very different.
zamalek 10y ago
A thought experiment of mine. Assume that all possible hypothesis or theories (explanations in general) form part of an "explanation space." Some explanations are good (theories), some have no evidence (hypothesis) and some are false (we are riding a giant turtle). Given the number of false explanations, the overall space is infinite. Hypothesis spaces would be islands within the false explanation space, theories islands within hypothesis and the truth as a single point within one of those theory spaces. The question is, does that mean that the theory space is infinite? If so, that would mean that it would be impossible to know that we've found the truth (as a single point within this infinite space) - we'd only ever be able to conclude that we've found a closer approximation. Scientists may never run out of work.
- eli_gottlieb 10y ago
  >The question is, does that mean that the theory space is infinite? If so, that would mean that it would be impossible to know that we've found the truth (as a single point within this infinite space) - we'd only ever be able to conclude that we've found a closer approximation. Scientists may never run out of work. The theory space is definitely infinite, in either the interesting sense of something like "the space of all possible programs, treated as causal or directed-generative models" or in the trivial sense that you can take any simple, well-supported theory and come up with mathematical elaborations that don't change any of the pre-existing empirical predictions. In a certain sense, "the truth" may constitute an infinitely small point in a space that's more continuous than discrete.
- ci5er 10y ago
  Your "explanation space" is almost certainly infinite and mostly empty. The closer any model approaches reality, the more it is indistinguishable from the object being described. Like any map, it becomes unwieldy with increased accuracy. The model becomes the size of the universe. So, a universe-sized model inside of an infinite explanation space?

maikb 10y ago

Remember that these people use a language that might sound similar to common english, but words have different meaning and it is much more precise. No reading between the lines. He gave an example of what would falsify his theory, that is all.

npgatech 10y ago

> "So I too love the idea that we don't need dark matter to explain all the gravitational effects we observe in the universe." It is an attempt to explain. Just like an attempt to explain (prediction) of Higgs Boson. It was only true once we observed it via experimentation. Falsification makes sense if the theory has been experimentally validated. You can't falsify something that has not been proven. There is no one claiming String theory or the theory discussed here is true - no experimental evidence has been produced.