Want to buy shares of American companies? At the current level of the Standard & Poor’s 500 index, every dollar invested in stocks buys you about 5.5 cents of corporate earnings, down from 7.4 cents two years ago — and lower than just before the global financial crisis in 2007-8.

Prefer a more solid asset? The price of office and apartment building has risen similarly; office space in central business districts nationwide costs $300 per square foot on average, up from $147 in early 2010, according to Real Capital Analytics. In Manhattan, an investor in an office building can expect rent payments after expenses to add up to only a 4.4 percent return, known as the capitalization rate, lower than even in 2007, the top of the last boom.

What about overseas investments? Spain and other Southern European countries that were the nexus of the European debt crisis are not the only places where bond rates have plummeted (even Greece was able to issue bonds at favorable rates earlier this year). Emerging markets, which generally have higher interest rates because of higher inflation and less political stability, are offering record low interest rates as well. Bonds issued by the governments of Brazil and Malaysia, for example, are currently yielding only around 4 percent.

The high valuations now aren’t as extreme as those of stocks in 2000 or houses in 2006; rather, what is new is that it applies to such a breadth of assets. In 2000, when the stock market was, with hindsight, a speculative bubble, other assets like bonds, emerging market investments and real estate looked reasonable.

The Everything Boom brings obvious economic risks. In the most pleasant outcome, global economic growth would pick up, causing today’s expensive assets to begin looking more reasonably priced. But other outcomes are also possible, including busts in one or more markets that could create a new wave of economic ripples in a world economy still not fully recovered from the last crisis.

There are two principal reasons behind this low-return environment, though people might dispute which is the cause and which is the effect.