This question already has an answer here:
I am currently reading though Peskin and Schroeder and have recently encountered the UV cutoff. Basically, when we encounter an infinity in QFT which is caused by integration over momentum or energy, we can disregard this by limiting our integral as we know our formula is not exact and it is absurd to think that it should work at arbitrary energy.
This got me thinking about singularities. Basically knowing that GR is a not quantum theory and that surely at such high energy density and small volumes as found in black holes, QM effects will become very important, why is it that we are fine saying everything collapses into a singularity rather then saying we don't know and that the formula is invalid at such ranges?