https://www.superphysics.org/tags/gravity/ Recent content in Gravity on Superphysics Hugo en Thu, 12 May 2022 00:00:00 +0000 https://www.superphysics.org/material/solutions/10-problems/ Thu, 12 May 2022 00:00:00 +0000 https://www.superphysics.org/material/solutions/10-problems/ <p>Modern Physics is currently stuck with <a href="https://backreaction.blogspot.com/2019/01/good-problems-in-foundations-of-physics.html">10 problems</a>, which we classify below and solve with Superphysics:</p> <!-- https://www.diva-portal.org/smash/get/diva2:996740/FULLTEXT01.pdf --> <!-- Grand Unification Sabine Hossenfelder A lot of physicists would rather have one unified force in the standard model rather than three different ones. There is, however, nothing wrong with the three different forces. I am undecided as to whether the almost-prediction of the Weinberg-angle from breaking a large symmetry group does or does not require an explanation. Quantum Gravity Quantum gravity removes an inconsistency and hence a solution to a good problem. However, I must add that there may be other ways to resolve the problem besides quantizing gravity. Black Hole Information Loss A good problem in principle. Unfortunately, there are many different ways to fix the problem and no way to experimentally distinguish between them. So while it’s a good problem, I don’t consider it a promising research direction. Particle Masses It would be nice to have a way to derive the masses of the particles in the standard model from a theory with fewer parameters, but there is nothing wrong with these masses just being what they are. Thus, not a good problem. Quantum Field Theory There are various problems with quantum field theories where we lack a good understanding of how the theory works and that require a solution. The UV Landau pole in the standard model is one of them. It must be resolved somehow, but just exactly how is not clear. We also do not have a good understanding of the non-perturbative formulation of the theory and the infrared behavior turns out to be not as well understood as we thought only years ago (see eg here). The Measurement Problem The measurement problem in quantum mechanics is typically thought of as a problem of interpretation and then left to philosophers to discuss. I think that’s a mistake; it is an actual inconsistency. The inconsistency comes from the need to postulate the behavior of macroscopic objects when that behavior should instead follow from the theory of the constituents. The measurement postulate, hence, is inconsistent with reductionism. The Flatness Problem Is an argument from finetuning and not well-defined without a probability distribution. There is nothing wrong with the (initial value of) the curvature density just being what it is. Thus, not a good problem. The Monopole Problem That’s the question why we haven’t seen magnetic monopoles. It is quite plausibly solved by them not existing. Also not a good problem. Baryon Asymmetry and The Horizon Problem These are both finetuning problems that rely on the choice of an initial condition, which is considered to be likely. However, there is no way to quantify how likely the initial condition is, so the problem is not well-defined. The Strong CP Problem Is a naturalness problem, like the Hierarchy problem, and not a problem of inconsistency. --> <h2 id="gravity-problems">Gravity Problems</h2> <p><strong>1. Quantum Gravity: How can gravity and quantum mechanics coexist within the same theory?</strong></p>