[rfrey]

"Any of the big companies -- Google, Facebook, and Amazon come to mind -- do tons of things that even 10 years ago would have been considered cutting-edge computer science research."

Absolutely true, but is it possible to work in those places without a PhD?

One path I can imagine would be to devote 2-3 years to independent study, attend appropriate conferences and get to know the researchers on a professional and personal level. Build some respect on your own dime before trying to move to professional work.

No idea if that would work, though - whether there are avenues for an amateur-but-devoted scientist to contribute to research, or whether that research would break down any barriers.

[versteegen]

I know someone who was doing a PhD on neural networks, and interned at Google during it (a research group involving NNs). He was told by that research team that they wouldn't hire him without his completed phd. He cut his phd short to a masters and got a job at Google anyway, but unfortunately I can't remember whether it was on that research team, or a generic software-engineer position (either way, the internship was the foot in the door).

You can certainly do good independent work, and write and publish papers if you want. If you can prove your conpetence, why shouldn't you be hired? At least, not every employer is going to have a major bias against those without PhDs.