(February 24, 2016 at 9:20 am)Mathilda Wrote: Bloody hell I didn't know that at all. Hence the reason I suppose that calculations of black holes require the use of infinity. Does anyone have any ideas as to why this is a feature of gravity?
"Why" questions are always a difficult concept in physics. The mathematical reason is that (for example as opposed to Maxwell's equations) Einstein's field equations are not linear, i.e. twice the energy does not simply give you twice the effect. If we wanted to know why they have this structure, we'd need a deeper principle from which they are derived that we can point to, otherwise, physics and nature just are what they are.
In the case of gravity, one can start from a graviton field with spin-2 and try to make it linear such that like newton's gravity, twice the mass simply makes twice the gravity. People, notably Deser, have shown that in order to have the resulting theory fulfil certain conditions such as the local conservation of Energy, one is forces to include all the nonlinear parts as they are present in Einstein's full field equations.
Of course, one can math all one wants, in the end nature decides what's correct and what is not, and it looks like the weird nonlinear Einstein equations are correct. The gravitational wave signal from LIGO tells us once more that this complex structure with gravity making gravity is really there in nature, otherwise such a collapse would not look like this.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition
