[alex504]

A 100% salary boost is pretty large.

If they are doubling your salary at the start up your compensation at your previous role is probably at about the bottom or even below the bottom of what you would make on the market if the startup goes bust.

If the economy gets so bad that you get laid off from the startup and (seems unlikely at this point) that you would be unable to get any job at your current low salary, there is a decent chance you would have been laid off at the first job regardless.

I would say go for it, completely ignoring all quality of life variables like work life balance, getting along with your team, doing interesting work, and so forth. These things matter a lot as well so it's worth thinking about those. In terms of money it seems like a no brainer to me.