22 karma · joined July 14, 2008
A bubble is when you're paying for something based purely on speculation about the future value of that thing, rather than on a rational analysis of the expected future return.
I would wager that Google does not have an internal projection of the value of any engineer showing them to be worth $3.5m over four years; rather, I'd bet that comp decision was made based on an irrational fear of yet another defection from Google to Facebook.
When people see a valuation in the marketplace (eg, a talent acquisition that makes everyone extremely wealthy) and assume they can achieve the same kind of returns with minimal effort, that is the hallmark of a bubble. The same thing happened with day traders and real estate speculation.