Hyperloop could conceivably be a scam, but SpaceX, Tesla and SolarCity are much too real to be ponzi schemes.
A Ponzi scheme is essentially a investment that promises you a too good to be true return (ex:10% per month). It is actually paid by late investors, unless you "reinvest" it. It is typically backed by promises : shares of a company that doesn't produce anything yet, land that will supposedly become extremely valuable, etc...
The companies you cited have nothing in common with Ponzi schemes. While profitability is debatable, they have real customers and produce real goods and services. They also don't promise you anything in term of ROI. Of course, Elon Musk will tell you his companies are the best, but that's just standard advertising.
A Ponzi scheme is essentially a investment that promises you a too good to be true return (ex:10% per month). It is actually paid by late investors, unless you "reinvest" it. It is typically backed by promises : shares of a company that doesn't produce anything yet, land that will supposedly become extremely valuable, etc...
The companies you cited have nothing in common with Ponzi schemes. While profitability is debatable, they have real customers and produce real goods and services. They also don't promise you anything in term of ROI. Of course, Elon Musk will tell you his companies are the best, but that's just standard advertising.