I think that in the fullness of time, it will be seen that today’s high asset prices were directly and unambiguously a consequence of extremely low interest rates and the creation of money by central banks and nothing more than that. When returns on lending are low, investors have to switch to riskier asset classes in order to generate the returns that they need to service their future cash flow requirements. For example, pension funds have to generate a certain amount of cash flow to cover their future pension liabilities, which are fixed and unchangeable. When central banks make money cheaper by lowering interest rates, pension funds have to shift to classes of assets that generate higher cash flow, even if that means taking on more risk. They don’t really have a choice in the matter.
There is a positive feedback loop here. Low interest rates cause large investors like pension funds to shift to riskier assets. This stimulates the risk appetite of retail investors, who pile in when they see the trend of increasing prices in these riskier assets, such as stocks and houses. The increase in asset prices reduces the effective returns on those assets, forcing pension funds another large investors to shift to even riskier things, like venture capital. Rinse and repeat.
I suppose nobody can say for sure that there hasn’t been some kind of long-term shift in global economic growth because of changes in technology, but it sure seems to me like cheap money is a more reasonable explanation for all of the craziness we have been seeing in the past year or two.