The Fermi Paradox is about why there are no aliens on Earth today. “Where is Everybody?” Enrico Fermi asked his lunchmates one day in 1950, pondering that it must be that alien spacecraft—at almost any speed, really—have had plenty of time to get here by now, since the Galaxy is so very old.
The story’s been told lots of times, and Bob Gray has a nice paper about the real history of the term (it’s neither Fermi’s, nor a paradox!). The term is also sometimes used to refer to things like why SETI hasn’t found anything yet, but of course that’s not what Fermi meant (after all, when Fermi asked his question, the first modern SETI program wouldn’t even start for another 9 years!)
But is it true that a species would fill the Galaxy, given the capabilities? Working with Jonathan Carroll-Nellenback, a team I was part of tried to simulate things, and found that, sure enough even slow ships would fill the galaxy pretty swiftly. What we didn’t do, though, was make a nice movie showing how it happens.
Well now we’ve fixed that!
In this movie, Jonathan carefully tuned the parameters so that the maximum range of ships is about 3 parsecs, or within range of a couple dozen stars for Earth. The way exponential growth works, if the local density of stars is such that you always have plenty of targets within range, you’ll grow, but if that happens rarely, you won’t. And because stars move, you’ll always have fresh stars nearby to settle, if you wait long enough.
The whole movie spans about 1 billion years. The expansion front takes so long because we don’t let any settlement launch a new ship to settle a new star more frequently than once every 100,000 years. As the front expands, the parts moving inwards will encounter higher stellar densities and the expansion wave will accelerate. The parts moving vertically or outwards quickly run out of stars and stall.
What’s neat is that in this simulation, because the ship range is small and ships are sent out infrequently, the wave goes slowly enough that it is actually the motions of the stars that do most of the work, and you can see how they take what might have created a bubble of inhabited stars and smear it out, like jam getting mixed into oatmeal or cream getting stirred into coffee.
Eventually, the front reaches the middle part of the galaxy where the stars are typically closer together than in the outer parts, and then the expansion proceeds very quickly, but the outer reaches of the Galaxy never get inhabited.
Now, this is just an illustration—in truth if something like this happened the ships wouldn’t have a hard limit of 3 parsecs for their motions, and who knows how often new settlements would happen. We’re working on a new paper now that explores these things.
You can find a fuller description of the movie in our new Research Note of the AAS here.
Enjoy!
And on the second day of Summer, Solaris gave to me…a golden babble from her apple tree.
A New Type of Planetary Swarm know as Golden Skies.
But first….
Satellites and Global Warming
There are a lot of satellites orbiting the Earth.
Have there been any studies on how much beneficial radiation along with harmful radition, is reflected between the satellites orbiting Earth?
How much harmful radiation that is reflected back into space then reflects off of satellites and back to Earth where the radiation continues to reflect back and forth instead of escaping into space.
Would the radiation being reflected in the manner above, cause the upper most layers of clouds to heat up causing global warming?
Can satellites in orbit around Mars, be used to reflect harmful radiation away from Mars upper atmosphere to help re-populate the upper atmosphere with clouds?
Golden Skies would entail using very large sails similar to the panels of the Light Sail.
The panels would reflect harmful radiation away from a planet, while the underside of the panel would reflect beneficial radiation back and forth between the panel and the surface of the planet.
If Golden Skies was used in orbit around Enceladus, could harmful radiation be kept out while beneficial radiation was used to increase the surface temp of Enceladus that would then create clouds?
Would the clouds rain water and slowly uncover rocky surfaces underneath the ice of Enceledus?
Does Enceladus have enough gravity to keep the rain clouds from evaporating away into space?
Could advanced space faring species already be using Golden Skies which might cause the planet to be discovered from its very low dim light curve as a result of harmful radiation being reflected into space that might create a sun like radiance effect? An effect that would also hide the planet from probing eyes not able to get past the discovery as being nothing more than a star?