3 ms·

Okay, so this is another attempt to unify quantum field theory and gravity. By using gravity to get quantum fields, rather than by trying to quantize gravity.

pdonis 1y ago
I don't think so. The paper doesn't talk about gravity at all. It talks about electromagnetism.
- philipov 1y ago
  If the paper is attempting to express electromagnetism in terms of the metric tensor, then it is putting it into a form that makes it potentially compatible with gravity, which is also a metric tensor. Quantum theories use a completely different type of math, and trying to express gravity in that way (quantizing gravity) results in a bunch of broken equations. If both systems can be described using differential geometry, that is a step in the direction of unifying the theories, even if it's not a hole-in-one.
  - pdonis 1y ago
    > If the paper is attempting to express electromagnetism in terms of the metric tensor, then it is putting it into a form that makes it potentially compatible with gravity, which is also a metric tensor. But the metric tensor of spacetime, in General Relativity, which is our best current classical theory of gravity, only explains gravity. Gravity, by itself, uses up all of the degrees of freedom in the metric tensor. There aren't any left for electromagnetism or anything else. To get classical electromagnetism, you need to add another, different tensor to your model--a stress-energy tensor with the appropriate properties to describe an electromagnetic field. Of course doing this in standard GR is straightforward and is discussed in GR textbooks; but it does not involve somehow extracting electromagnetism from the metric tensor. It involves describing electromagnetism with the stress-energy tensor, i.e., with different degrees of freedom from the ones that describe gravity.(And if you want to describe the sources of the field, you need to add even more degrees of freedom to the stress-energy tensor to describe charged matter.) The paper does not, as far as I can see, address this issue; the authors don't even appear to be aware that it is an issue. Which makes me extremely skeptical of the paper's entire approach.
  - Iwan-Zotow 1y ago
    Metric tensor has 10 components, minus 4 for diffeomorfisms. How do you fit EM into that?

pdonis 1y ago

I don't think so. The paper doesn't talk about gravity at all. It talks about electromagnetism.

philipov 1y ago
If the paper is attempting to express electromagnetism in terms of the metric tensor, then it is putting it into a form that makes it potentially compatible with gravity, which is also a metric tensor. Quantum theories use a completely different type of math, and trying to express gravity in that way (quantizing gravity) results in a bunch of broken equations. If both systems can be described using differential geometry, that is a step in the direction of unifying the theories, even if it's not a hole-in-one.
- pdonis 1y ago
  > If the paper is attempting to express electromagnetism in terms of the metric tensor, then it is putting it into a form that makes it potentially compatible with gravity, which is also a metric tensor. But the metric tensor of spacetime, in General Relativity, which is our best current classical theory of gravity, only explains gravity. Gravity, by itself, uses up all of the degrees of freedom in the metric tensor. There aren't any left for electromagnetism or anything else. To get classical electromagnetism, you need to add another, different tensor to your model--a stress-energy tensor with the appropriate properties to describe an electromagnetic field. Of course doing this in standard GR is straightforward and is discussed in GR textbooks; but it does not involve somehow extracting electromagnetism from the metric tensor. It involves describing electromagnetism with the stress-energy tensor, i.e., with different degrees of freedom from the ones that describe gravity.(And if you want to describe the sources of the field, you need to add even more degrees of freedom to the stress-energy tensor to describe charged matter.) The paper does not, as far as I can see, address this issue; the authors don't even appear to be aware that it is an issue. Which makes me extremely skeptical of the paper's entire approach.
- Iwan-Zotow 1y ago
  Metric tensor has 10 components, minus 4 for diffeomorfisms. How do you fit EM into that?