Forbes technology blogger Alex Knapp in an article expressing a bit of skepticism towards Kurzweil’s vision of singularity writes:

“But all technology is, ultimately, going to be limited by the laws of nature. And those laws are going to place fundamental constraints on not only what’s possible, but what’s economically feasible”

This is completely accurate.  But the reason why I think a singularity is likely is because we know that nature allows for the existence of John von Neumann’s brain – a general intelligence device built using relatively cheap materials.  And it’s extremely unlikely that in coding for von Neumann the random forces of evolution came anywhere close to building the smartest possible machine that could be assembled consistent with (1) not violating the laws of nature, and (2) using stuff that could only be bought today for less than, say, $1 billion.