After such scientific elaboration was Einstein stating that he created a pie in the Sky?

Question

Why did he say that?

Answer 1

The pie in the sky reference was probably about his efforts to achieve a grand unified field theory. The task was so difficult that he compared it to a "pie in the sky".

BTW, I have a possible explanation for the 8π that appears in Einstein's Field Equations. Basically, the stress-energy tensor is calculated over the surface of a 4-dimensional sphere, not a 3-dimensional sphere. So instead of 4π, you get 8π. The extra factor of 2 comes from the fact that the surface area of a unit 4-sphere is 2π, where as the surface area of a unit 3-sphere is just π.