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)

The #transit signal allows us to know the size of an #exoplanet. It can also tell us whether the #planet is at the right temperature to allow liquid #water. We can also probe the #atmospheres of transiting planets, and potentially look for #chemical #signatures suggestive of #life. That's a lot of info from a very simple signal.

So, what if both sides live on planets that are visible as transiting planets to each other? That's a situation of #MutualDetectability. Both sides know it. (10/n)

They both know they can see each other. They could both know that each other's #planet is potentially #habitable. They can even figure out who sees the stronger transit signal. The one with the clearer signal may feel the onus of responsibility to transmit a #signal whilst the other listens out for one.

It turns out that most stars in our #Galaxy are fainter than the #Sun so have weaker transit signals. And we already know that these are relatively rich in potentially habitable planets. (11/n)

So, i #proposed in a paper that we should conduct a #survey for potential habitable transiting planets around low mass stars that are located close to the #ecliptic plane. Previous studies had already noted that #star systems near the ecliptic, the plane of #Earth's orbit of the #Sun, would be able to view the Earth in #transit.

Such a survey would give a short list of mutually detectable targets. We can then listen or look out for signals from them. (12/n)
https://iopscience.iop.org/article/10.3847/1538-3881/abcc5f

The upcoming #NASA #Roman mission could do such s survey, perhaps focusing on a small area of the #ecliptic close to the #Galactic Centre where's there's a lot of stars. Such a survey would harvest a lot of exciting exoplanet science in itself, quite apart from the #SETI objective.

It'll be interesting to see if we find evidence for anyone out there. If they're game theorists, our chance of success may be better than we think.

End of thread.