How Low Can The Market Go? Henry Blodget | Mar. 2, 2009 /snip There were four massive stock bubbles in the 20th Century: 1901, 1929, 1966, and 2000. During each of these bubble peaks, the S&P 500 neared or exceeded 25X on professor Robert Shiller's cyclically adjusted P/E ratio.* After the first three of these peaks, the S&P 500 PE did not bottom until it hit 5X-8X. We're still in the middle of the last one. The most recent bubble peak, 2000, was by far the most extreme we have ever experienced. In 2000, the S&P 500 by prof. Shiller's...