Can democracy survive the existence of trillionaires?French economist Gabriel Zucman, one of the world's foremost experts on wealth taxation, raised that question last week. He said anyone celebrating Elon Musk's US$1 trillion fortune needed to understand the fundamental tension between extreme wealth and the very possibility of democracy."The explosion of billionaire wealth has been one of the defining features of our time," he wrote."It is impossible to understand today's world if one ignores this upheaval. "For with the explosion of the wealth of the super-rich has come an explosion of their power The less tax you pay, the easier it is to accumulate wealth."And he warns that this spiral risks causing irreparable damage to our democratic ideals."Of course, it is hard to know where the tipping point is past which democracy becomes oligarchy," he writes."Is it when the wealth of the ultra-rich exceeds 50 per cent of GDP? One hundred per cent? Two hundred per cent? When they own not 80 per cent of privately held media, but 100 per cent? Or perhaps when they finally get their hands on our public media?"Nobody knows the exact concentration of wealth at which the kinds of plutocratic collapse we have seen in history becomes inevitable