Shares of Alphabet and Tesla fell on Thursday after both companies signaled increased AI spending, unnerving investors worried about the mounting costs of the artificial intelligence boom. Tesla stock closed 14.5% lower while Alphabet lost 7.1%. Elon Musk's EV maker posted its worst day since March 2025.Tesla lost about $200 billion in market cap on Thursday, while the Google parent saw about $300 billion wiped out.Both companies reported negative free cash flow for the second quarter on Wednesd...