Before we get into the nitty gritty, a little digression. You'll see the relevance shortly.

Imagine being offered a suitcase full of money if you manage to meet up with a complete stranger that day in #NewYork city. You don't know where. You don't know when. And you know nothing about the stranger other than that they have been made the same offer as you.

Somehow you need to #cooperate to win, but you can't #communicate because you don't know who to communicate with.

What do you do? (2/n)

This is a famous problem posed by #ThomasSchelling, a #Nobel prize winning #economist and a founding father of #GameTheory. He's also credited with the #ColdWar doctrine of #MutuallyAssuredDestruction, but that's another story.

This is an example of a game of cooperation between two non-communicating participants. And Schelling argued that there is a strategy that maximises the chance of success. (3/n)

The idea is that both need to consider likely meeting points. Natural choices would be famous landmarks or meeting spots. Outside the #EmpireStateBuilding? The lobby of #GrandCentralStation? There's maybe a few dozen spots people might go for. But that's a lot less than the number of buildings in #NewYork.

And a meeting time? Maybe noon, or 6pm. Maybe not 2.27 or 4.38. There seem to be preferred choices. #Schelling called these #FocalPoints. Today they're often called #SchellingPoints. (4/n)

So where do #aliens come into this? The Search for #ExtraterrestrialIntelligence, or #SETI, is a two player game involving us and them. Whoever they are.

We are basically playing an #interstellar version of the strangers meeting in #NewYork. But the incentive in this case isn't a suitcase full of money. It's the opportunity to establish contact.

Both parties must want to do so of course. But it'd be amazing if intelligent life is common yet we're the only ones wanting to say hello (5/n)

Even if one side is far more advanced, for the chances of #FirstContact to be maximised there needs to be #cooperative game play. This means both need to choose a #signal the other side may know about, even if they aren't as advanced.

A pretty simple signal is the #transit signal that occurs when a #planet passes directly in front of its #HostStar as seen by a distant observer. The #NASA #Kepker mission found thousands of #exoplanets this way (9/n)

@eamonn_kerins The problem as I see it though - is let's say that we happen to be the advanced civilisation (yeah I know - imagine...)

Let's say the other planet is roughly where we were around the 14th century. There is a significant chance that any signal we send could arrive before they are advanced enough to spot it.

And the same in the other direction, surely the signal they send would have to be at least 300+ years ago for it to arrive when we started looking.