SETI Sessions at RAS NAM 2013

A quick advertisement for the interested – the UK SETI community has a chance to meet over 3 sessions at the Royal Astronomical Society’s National Astronomy Meeting (RAS NAM), to be held July 1st to 5th at the University of St Andrews.

The list of talks looks very interesting (even without my contribution!). The deadline for abstracts is now April 1st, so if you’re keen to submit a talk or poster to the session, you still can.

SETI in the UK is in a transitional phase, edging toward the mainstream as astrobiology becomes more and more commonplace in UK research institutes. NAM 2013 is going to be a great opportunity for the UK SETI community to meet – there hasn’t been sessions on this scale for several years. Also, for any UK astronomers out there who have been thinking about how their research might apply to SETI, then here’s a golden chance to find out what SETI science looks like, and what you can do to be involved. If you can’t make it to the sessions, you can check out the Facebook page setinam2013 and the Twitter hashtag #setinam2013. See you there!

Starcraft as a Citizen Science Tool

In a similar vein to last week’s post, I’m proud to show you results from an outreach project I’ve been working on with Tom Targett at the ROE for the last few months.  As the result of a rather long-winded discussion of interstellar colonisation at coffee time, we got to thinking about how rigorously we could simulate conflict between competing civilisations.

Of course, we don’t have any evidence that other civilisations even exist, let alone fight each other for resources.  All we know is that conflict has been an important part of human history since time immemorial, and that we can see the origins of our penchant for tribalism and warfare in our primate cousins.

The D Day landings. Via ww2incolor.com

As it would be churlish from a scientific standpoint to assume that our aggressive behaviour is unique amongst intelligent species, Tom and I felt it was safe to assume in our current ignorance that intelligent species are completely capable of conducting interstellar wars, and would do so to secure resources.

This still left us with a bit of a problem – how can you model interstellar conflict when you know nothing about the combatants? It was then that we hit on the idea of calibrating our simulations by using ‘real’ data on how alien species fight.  StarCraft 2, a real time strategy game played throughout the world, has several races of belligerents, who fight each other frequently in the domain of Massively Multiplayer Online gaming.  In a classic example of citizen science, we found that the general public had generated a vast dataset of (admittedly fictional) alien behaviour, which we could use to drive our simulations.

So, we created a population of stars similar to the local Solar neighbourhood, and seeded it with six different races, each representing one of the three civilisations (the Terrans, the insectoid Zerg and the advanced, telepathic Protoss), carrying out one of two strategies.

The “macro” strategy refers to species which build up large amounts of resources before moving against an opponent in an attempt to overwhelm them; the “micro” strategy encourages rapid motion of a smaller military force to quickly eliminate a fledgling opponent. This gives 30 possible combinations of combatants.  As we had access to user data showing the outcome of each combination rehearsed many times in StarCraft 2 games played online, we could soon develop a probability that Race 1 defeats Race 2, and so on and so forth.

This allowed us to do two things: i) we could see if there was a preferred strategy for StarCraft 2 users to adopt, and ii) How does the balance of power change when these alien races are placed in a Galactic context?

We looked at i) by searching for a Nash Equilibrium.  This is a set of strategies (in this case for two players), that if both players agree to adopt, then there is no better solution to be found by changing tack.  When we did the analysis, we found that the best possible solution for both players is to randomly select from the six races.  This is a consequence of the Starcraft developers keeping the six races evenly matched, so that the game would remain interesting to the players.

A snapshot of the simulation. The colours represent the space colonised by each race

But is this still true if you place the species in interstellar space?  Almost: as the species are all quite evenly matched, the sector ends up in an equilibrium where each species has approximately 1/6th of the available resources (you can see a movie of the simulation, and download the paper at the link above).  But statistically, when watching this sector being colonised many times over, the Terrans have a slight advantage when using the “micro” strategy.  If we make the simulation more “realistic” by allowing the micro strategists to move faster in interstellar space, the micro strategy utterly dominates.  Even if we balance this by allowing the defenders of a star system to have a “defender’s advantage” (we calculated this by looking at how Starcraft 2 gamers fared when they selected the map to battle on), the three species that choose a micro strategy rule the sector (and presumably, the Galaxy).

As I said, this is fairly arbitrary – we don’t intend to claim the Zerg and Protoss are real! We were interested in seeing how the video games industry can help scientists understand difficult topics like life in the Galaxy, where actual data is so thin on the ground.

But thankfully, it does seem like Earth has a slight edge when it comes to interstellar dominion…

Not a snapshot from the simulation…

Galactic Grand Tours, and strengthening Fermi’s Paradox

It’s been a long time since I wrote about my research, as I once said (rather haughtily) everyone should do, so I’ll get back into the saddle.

Like all good science, this work started as a rather rambling lunch-time conversation about how humans should physically explore the Galaxy.  We took our inspiration from humankind’s exploration of the Solar System:

The paths taken by the Voyager spacecraft as they explored and left our Solar System

The Voyager spacecraft were launched with the primary function of exploring the outer Solar System planets and their environment, but have also travelled to far greater distances from the Sun.   Voyager 1 remains a scientifically viable instrument, despite being over 11 billion miles from its launch site – signals from the spacecraft take over a day to arrive at Earth despite travelling at the speed of light!

How the Voyagers managed to accelerate themselves sufficiently to travel so far from the deep gravitational well of the Solar System is a neat example of the conservation of energy.  The planets possess an enormous amount of energy stored in their orbital motion, and this energy source can be tapped using a gravitational slingshot maneouvre.  The probe slings around the planet, using the planet’s gravitational field to change its trajectory and fling it in a different direction.

How the slingshot looks like from (top) an observer on a planet surface and (bottom) an observer moving relative to the planet (via Wikipedia)

An observer standing on the planet’s surface will measure the speed of the probe to be the same before and after the slingshot (see diagram), but the planet itself is moving.  An observer floating at rest will measure the speed of the probe as it leaves to be different from the speed it possessed when it arrived at the planet.  If the planet and the probe are moving towards each other during the slingshot, then the probe’s speed will be boosted.  Alternatively, if the planet is moving away from the probe as the probe begins the maneouvre, then the probe’s speed will be decreased (this can be used to capture satellites in orbit).

The probe and the planet are exchanging momentum during the interaction.  If the probe speed is boosted, the probe is depleting the planet of orbital energy!  Luckily, the amount of energy it extracts is minimal in comparison to the total available energy, so Jupiter and Saturn aren’t going to be crashing into the inner Solar System any time soon.

This brings us back to our lunch-time conversation.  Gravitational slingshots need a massive body that orbits around some central object.  This is obviously true for the Solar System, but this is also true for the Galaxy.  The Galaxy has a centre, occupied by a supermassive black hole.  While the Sun is not gravitationally bound to it, it does orbit around it at approximately 200 km/s.  In other words, there’s plenty of orbital energy out there for interstellar probes to use!

We calculated that if a probe carries out a series of slingshots as it tours the Galaxy, the probe can be accelerated to approximately 1% of the speed of light without shipping enormous amounts of fuel (bear in mind Voyager 1 is travelling at 0.003% of lightspeed).  This got us thinking about Fermi’s Paradox.

Fermi’s Paradox simply wonders, given the large length of time that the Galaxy has existed, and the relatively small length of time it would take to travel from end to end at a small fraction of lightspeed, why aliens haven’t shown their own presence.  This Paradox gets stronger if we consider aliens sending probes that are self-replicating, making copies using material they find along the way.  Surely, this rapid spread of probes across the stars, growing their population exponentially like bacteria, would be so pervasive that we would have spotted one by now?

In the past, when SETI scientists simulate this type of exploration, simple trajectories for the probes are used, and they all travel at a relatively high fixed speed.  We wanted to see what adding gravitational slingshots to these simulations would do.  Our hunch was that this would make Fermi’s Paradox even stronger.  The result - it does.  Adding gravitational slingshots to the probe trajectory allows even spacecraft as slow as Voyager to explore a patch of the Milky Way around 100 times faster at vanishing energy cost!

So, even if ET is somewhat frugal with its resources – one reason often proposed as a solution to the Fermi Paradox – gravitational slingshots show that’s no reason not to explore the Milky Way…