Bull markets don’t die of old age. They must be killed.
They’re not immortal though. Nor do they live a long time. If we ignore the March-April dip, this one is around 12 years old, and that’s a very long-lived bull market.
The thing about lobsters is, they don’t die of direct biological old age, but they do die, they die of biological factors, and they can be killed. Infection, molting, predators can all kill a ‘biologically immortal’ lobster.
 As a physicist it makes me so angry that the biologists have all the best names: Sonic the Hedgehog gene. Biological immortality. Goats.
What have we got? Big G and orthonormalized eigenfunctions.