Elon Musk’s next move could be a SpaceX-Tesla merger big enough to challenge Nvidia Corp. for the title of most valuable company on Earth. Just three sessions into its IPO, SpaceX has already surged nearly 50% to roughly $2.6 trillion, leaving Tesla Inc. and its $1.5 trillion behind. The wider that gap runs, the cheaper Tesla gets to absorb, and the more control Musk keeps over whatever emerges. The Math On A $5 Trillion Giant The case for a merger, laid out this week by Bloomberg columnist Liam