Convergence is the seventh episode of the second season. It was released on 11 November 2005.
This is a scientific term describing a meeting point or assimilation of seemingly diverse forms or forces. As well as the Eppes example, there is here a sense of the alignment of universal forces - that life knows what it is doing, bringing Charlie and Marshall back together.
When Charlie is speaking to Larry Fleinhart (roughly eight minutes into the episode) about his relationship with Marshall Penfield, he walks by a chalkboard with a number of equations written on it. Several of these can be clearly seen 8 minutes and 21 seconds into the episode. The lowermost equation, unlike the others, appears to have been included as a joke, as it reads: 1+1=2. Everything else on the chalkboard involves notational formalism related to more complicated mathematics, and this simple arithmetic equation is clearly unrelated.
Colin Hanks and Diane Farr previously starred in the tv show "Roswell." Diane Farr played the mother of Colin Hanks's character's friend.
Charlie mispronounces "Fourier" as "furrier." Any mathematician of Charlie's status would know it's pronounced (more approximately) as "Fouri-ay."
Agent Sinclair says there are only two variables for the bullet, muzzle velocity and angle of gun. In fact there are many more variables, wind velocity, air density, temperature, and mass of projectile to name a few.
When Charlie talks about GPS, he says the satellites are in geosynchronous orbit. GPS satellites are in orbit approximately 12,600 miles above Earth. Geosynchronous orbit is approximately 22,250 miles.
[This appears on the beginning of the episode] 7 Home Invasions 2 Murders $3.6 Million-Stolen 2 Antique Lamps