One non-math explanation - which you can find on quite a few webpages, in various forms (including those with some math) is the following*:
Quote:
Quantum mechanics and gravity (whether Newton's theory of gravity or Einstein's theory of General Relativity) do not fit so neatly together. The problem can be put in several different ways, but I favour this one. From [a] discussion of virtual particles [...], we [see] that virtual particles could be larger (i.e. more massive) if their lifetime and range were smaller.
Now both Newton's and Einstein's gravity predict that enough mass in a small enough space can produce a black hole: a region with a gravitational field so strong that its escape velocity is c. When we put the two ideas together, we find that there is a scale small enough for virtual black holes to exist. This is the Planck scale. On this scale, all of the weird, singular behaviour associated with black holes asserts itself. Space and time as continuous entities cease to have meanings when discussing distances of 10-35 metres and times of 10-44 seconds. So relativity, a theory of space and time based on a continuum, must run into serious difficulties.
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IOW, all the usual terms we feel we have an intuitive feel for - energy, in particular - require a 'something' in which to make sense. Whether that something is Newtonian or Einsteinian, it is continuous, at least wrt 'space' and 'time'. In the Planck regime (at the Planck scale), 'space' and 'time' can't be continuous ... if we apply one of the key results from quantum mechanics.
Ergo, not only does either GR or QM (or both) 'break down' at this scale (in this regime), but so do all the other things we intuitively feel are 'universal'.
It's not very satisfying; has anyone come across any better (non-math) explanation?
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