Totally different stages of business and incomparable. Google revenue is growing steadily, since $30B p.a for a single revenue stream is about as big as you can get.
If you want a proper comparison, Google's PE ratio was 150 at IPO (and 300 at the high range of estimates, and it eventually reached that)
A lot of smart people thought that was a bad buy at the time, as well:
and Twitter has revenue of $150M and is probably 2 years away from an IPO. Just because it hasn't made a profit each year, like Google, doesn't mean that you can compare its current 50x PE to Google's current 6x
I would suggest that Twitter are likely waiting to book an entire year of profits and 3-4 years of revenue growth before they file
If you want a proper comparison, Google's PE ratio was 150 at IPO (and 300 at the high range of estimates, and it eventually reached that)
A lot of smart people thought that was a bad buy at the time, as well:
http://nikcub.appspot.com/the-google-ipo-skeptics