Eli5: Why 10-43 (1 planck time) after the big bang? How did they calculate that number as the point of reference as to what we can know?

Question

Eli5: Why 10-43 (1 planck time) after the big bang? How did they calculate that number as the point of reference as to what we can know?

In: Physics

Answer 1

We know that some important thories, quantum theory and general relativity, are incompatible – they can’t both be perfectly true without leading to contradictions.

The planck units are units that define several fundamental physical constants, specifically the speed of light, the gravitational constant, the reduced Planck constant and the Boltzmann constant as 1 and derive all other units from that.

It just so happens that some planck units such as time or length are rough indicators for where we know quantum theory and general relativity to conflict with each other, meaning we know that our theories are inaccurate at those scales.