To chime in as a person with grad-level training in the subject matter: there is a glaring tension between Quantum Field Theory and General Relativity in the low-energy macroscopic-size limit, which is very bad. How bad? Imagine “proving” that 1=2 in Peano arithmetic, something like that. The issue is the black hole: firewall or horizon? question. GR says that there is nothing locally special about crossing the event horizon (and must be applicable, since GR has been tested in this low-curvature regime), while QFT says that, after a while, the horizon becomes a high-energy incinerator (and must be applicable, since quantum entanglement has been tested in this low-energy regime). The best physics minds on the planet are at a loss to explain the problem. Last time something like that happened in physics, a completely new and unexpected theory eventually resulted. Odds are, we are in for a similar paradigm shift some day, hopefully soon.
To chime in as a person with grad-level training in the subject matter: there is a glaring tension between Quantum Field Theory and General Relativity in the low-energy macroscopic-size limit, which is very bad. How bad? Imagine “proving” that 1=2 in Peano arithmetic, something like that. The issue is the black hole: firewall or horizon? question. GR says that there is nothing locally special about crossing the event horizon (and must be applicable, since GR has been tested in this low-curvature regime), while QFT says that, after a while, the horizon becomes a high-energy incinerator (and must be applicable, since quantum entanglement has been tested in this low-energy regime). The best physics minds on the planet are at a loss to explain the problem. Last time something like that happened in physics, a completely new and unexpected theory eventually resulted. Odds are, we are in for a similar paradigm shift some day, hopefully soon.