A theologian, a psychiatrist and an astrophysicist walked into a bar...

...a theologian, a psychiatrist and an astrophysicist walked into a bar late one night...they argued about everything and anything under the sun, the origin of life, God, the uncaused cause, the big bang, evolution, dark matter and energy, multiverse, the grand unifying theory, the primal id, virtuous superego and the pragmatic ego, homeopathy, religion and hypocrisy, war, technology, greed and capitalism, meaning of life, placebo effect, utilitarianism, socialism, communism, neo-Platonic forms, postmodernism, gay marriages, consciousness, free will, altruism, love, faith, hope.

...and then all three realized that they had forgotten to bring their wallet and the bar only accepts cash.

Panic, and with a reputation to protect (because they were award-winning celebrities, highly respected, and renowned leaders in their respective fields), they pleaded for the bartender's understanding and trust. They asked for a phone call and gave references to back up their credentials. But no one picked up their calls and the references were alien names to the bartender. In desperation, they even went around asking the other half-drunk patrons whether they have read about their great exploits and inventions or seen them on tv. But none of them knew. Not even a soul in the bar.

So, the pissed-off bartender dialed for the police and all three prominent figures - half drunk themselves - were arrested and spent a night in a dinghy cell held in remand pending bail. In the cell, they continued where they had left off in the bar...they argued about everything and anything under the sun.

If you are looking for the punch-line, it is somewhere between knowing everything and not having anything (to pay for the drinks).

...sometimes in life, people don't care how much you know until they know how much you care; and in this case, to settle the bill. Cheerz.