Why do scientific things usually have an "X" in them?

[Eirik]

The military used to (maybe they still do) designate experimental aircraft with an "X" designator, much like they designate bombers with "B" and fighters with "F".

I think that's how "X" got the mystique of being something bold and exciting and at the limits of our scientific understanding.

[Mr. Hockstatter]

Horrible flashbacks of Dr. Zee from Galactica 1980.

[Mr. Hockstatter]

And all the X-Treme sports.  And Tech TV has a show called X-Play.  And wasn't Vin Diesel in something called XXX?

Hollywood's come a long way.