I Distinguishing Einstein Cartan from GR: Experiments

[Dale]

Are there any experiments either already performed or even simply proposed that could be used to distinguish Einstein Cartan gravity from GR?

My current understanding is that they are the same in vacuum, and only differ in matter. In matter the Einstein Cartan metric can have torsion, unlike the GR metric, but in vacuum they agree. Because of the way spin is related to torsion in Einstein Cartan and how important spin is in QM, it seems like that might be a viable candidate for GR violations.

 

[vanhees71]

I'm not aware of any observation of torsion yet. It's difficult, because all our tests of GR vs. alternative theories of gravitation rely on huge (astronomical) macroscopic objects. So spin doesn't play a role but only macroscopic descriptions of matter (aka hydrodynamics) and the electromagnetic field, which in the gauge approach to gravity a la Kibble lead to standard GR.

 

[Vanadium 50]

The University of Washington gravity guys tried to build a high angular momentum source/target. It was a mix of two materials magnetized in opposite directions, but one had more spin than the other. This would allow them to test spin-dependent gravity. I don't know how far they got with this.

Even so, this device was many tens of orders of magnitude less sensitive than they would need to distinguish GR from Einstein-Cartan.

 

[andresB]

I'm not aware of any observation of torsion yet. It's difficult, because all our tests of GR vs. alternative theories of gravitation rely on huge (astronomical) macroscopic objects. So spin doesn't play a role but only macroscopic descriptions of matter (aka hydrodynamics) and the electromagnetic field, which in the gauge approach to gravity a la Kibble lead to standard GR.

In neutron stars the spins align resulting in a total big spin. That should result in some modification in the state/equilibrium equation of the star, I think.

 

[pervect]

Poplawski writes a lot about Einstein-Cartan theory. https://www.sciencedirect.com/science/article/pii/S0370269310011561 has a high citation count, it may or not be helpful. Unfortunately, I think Poplawski focuses on the aspect of the theory that predicts that BH collapse "bounces" in Einstein-Cartan theory, which may not be the sort of experimentally testable prediction you're looking for.

 

[andresB]

My Ph.D advisor also have some work on Einstein-Cartan cosmologies.

https://arxiv.org/abs/1812.04589