In a post on the social media platform he owns, Elon Musk recently lamented: “Whoever said ‘money can’t buy happiness’ really knew what they were talking about.”Now the world’s richest person can put that maxim to an even bigger test as he adds a new title: world’s first trillionaire.SpaceX shares opened at US$150 each, 11 per cent above their offering price after they began trading in New York on Friday, valuing the rocket and AI-company Musk founded at roughly US$2 trillion.His fortune now...