What set of conditions (technical or socio-economic) can crash blockchain or bitcoin to zero USD? Is this notion of bitcoin crashing inconceivable at this point 10 years into its existence (so long as there is electricity and the internet)? My corollary question is: Can bitcoin be obsoleted by another cryptocurrency? What would that path of obsoletion look like for bitcoin? For example, I hear about other crypto currencies like Etherium or Lightcoin or Bitcash or Altcoin or Bitgold. What would be signs to look for that would make it prudent to cash out of Bitcoin to buy Etherium, for example.