For me they normally happen, these career crises, often, actually, on a Sunday evening, just as the sun is starting to set, and the gap between my hopes for myself and the reality of my life starts to diverge so painfully that I normally end up weeping into a pillow.
The power of a computational model is not just in its ability to compute, but in its ability to generalize from specific instances.
And I urge you to please notice when you are happy, and exclaim or murmur or think at some point, 'If this isn't nice, I don't know what is.'
量子引力问题不仅是物理学的问题，也是科学哲学的问题。