美股三大股指全线收跌，多个估值指标亮“红灯”

Group 1 - The U.S. stock market experienced a significant decline, with the Dow Jones falling by 0.84% to 46,912.3 points, the S&P 500 down 1.12% to 6,720.32 points, and the Nasdaq dropping 1.9% to 23,053.99 points [1] - Valuation indicators for U.S. stocks are showing alarming signs, with the Buffett Indicator indicating that the market capitalization exceeds GDP by more than two times, reaching a historical high [1] - The proportion of speculative stocks has reached 11%, a level previously seen only during the 1999 internet bubble and the 2021 meme stock frenzy, according to Barclays [1] Group 2 - The current AI boom is accompanied by warnings of a speculative bubble, with many observers drawing parallels to the late 1990s internet bubble that ended in a market crash [4] - Major tech companies are investing billions in advanced chips and data centers to support the surge in usage of AI technologies like ChatGPT, Gemini, and Claude, indicating a shift in economic activity from humans to machines [4] - Research from MIT found that 95% of institutional investments in AI projects yield zero returns, while Harvard and Stanford studies indicate that AI-generated content often results in significant productivity losses due to its superficial quality [4]