I remember getting a request for a cluster that was proposed to be split between a midwest USA site and London. Conversation was something like this (not exact numbers, but I did do the math at the time):
PHB: We need less than 50ms latency.
Me: Can't be done. We're at around 120ms right now with 10ms jitter using VPN.
PHB: What about MPLS?
Me: That might get us to 115ms with 5ms jitter.
PHB: Well, we have to come up with a solution. What else can we do?
Me: Slap Einstein? This is a physics problem, not an IT problem.
PHB: This is OUR problem to solve.
Me: Ok, if we buy our own glass, lay it in a straight line between us and London, which also includes some sort of housing for it that I don't know exists that would prevent issues with freezing/melting/icebergs, we'd end up with 72 ms.
PHB: So there really isn't anything we can do...*starts walking away*
Me: Hold on! I have another idea! We can tunnel through the earth, and skip the water issue if we can come up with a new type of shielding that can withstand tectonic forces and heat. That will allow us to get to 55 ms since we're not dealing with the curvature of the earth! Will that work?