Is the S&P 500 now in a boom-bust cycle?

Question

This question was originally posted at money.stackexchange but was moved here per a commentor's suggestion after the question was put on hold for being opinion-based. The original question was:

When I google "SP500" I get the following chart:

Isn't this a boom-bust cycle, that's overdue for a "correction" that drops everything back down to below the 1,000 level like in 2002 and 2009? What are the arguments against such a prediction?

The first comment someone posted argued against a drop but was confusing because it claims drops can happen from "causal forces" other than cycles. That actually sounds like an additional reason for a drop (causal forces, not just cycles) although I wouldn't understand how a cycle would be established or maintained without causal forces in the first place.

It also claims "you would only expect it to come back down on schedule if you believe that it goes up and down on schedule". That sounds like "if there's a cycle, it will go up and down", but doesn't make it clear how you determine if a cycle is happening.

The second comment says "markets always move in cycles" although the first half of the graph doesn't seem to back that up.

The third comment says "in the long term the markets have exponential growth" although it then cherrypicks the portions of the graph that reflect that (in effect replacing a "long term" argument with "short term" examples). And exponential growth can't happen forever, right?

The final comment suggest a log graph, though none is offered. My first search result for a log graph led to this page, which actually seems to make the case the market is always cyclic, although it throws so many numbers around in such a complicated fashion I'm not left with a sense of real understanding. (I also find it odd to compute things like annualized growth rate over 140 years, when any individual's investing career probably rarely exceeds 60 years, and most investors probably average much less.)

Returning to the original question, is there any argument the market is not cyclic, and not overdue for a substantial drop? Also, is there any measurement indicating whether investors believe that, and are exiting index funds?

Answer 1

Here's the Efficient Market Hypothesis (EMH) explanation for why one cannot say that a correction is overdue:

Suppose that it were widely known that, by looking at the above figure, one could ascertain that the market was "due for a drop" one week from now. Financial analysts and investors would look at the graph and come to this conclusion. How would people respond to this knowledge? They would go and sell their stocks before those stocks loose a substantial portion of their value. However, this flurry of selling activity would cause the price of the stocks (and hence the stock index) to fall today—one week earlier than forecast.

This example is obviously a highly simplified and stylised exposition of how markets function, but it should serve to make clear the basic point: any hypothesised means by which one can look at a chart like this and forecast the future movement of prices is automatically self-defeating and any information about the future of the market is instantly built in to the current price of securities. The drop you think might be due will come, says the EMH, if and only if new information about the economy becomes available that suggests the economic outlook is less promising that people had thought.