In the previous post on colonizing the Oort cloud, I pointed out that with sufficiently cheap transportation technology any place within range will be inhabited to some extent by recreational-touristic populations or populations that deliberately seek out isolation. This outermost part of the solar system is unlikely to be economically or demographically important at any point in the remotely near future, but there is a possibility for jump-starting development in the region that went unmentioned and will be elaborated on here: gravitational lensing. Specifically, the use of the sun as a gravitational lens for observation of and even communication with other solar systems.
A mass situated between an observer and a light source bends the light as it passes toward the observer through the force of gravity. This bending is similar to a lens, hence the term “gravitational lens” for such masses. The most famous cases of this phenomenon tend to be galaxy clusters that bend the light of other galaxy clusters behind them (as seen from Earth) so that the clusters are magnified. This is scientifically important because it enables our telescopes to observe distant galaxies at a resolution that would otherwise be impossible.
This is usually accomplished through so-called “strong lensing”, where the distortion is strong enough to render the object behind the mass as a ring or series of arc segments. This was the first type to be observed, starting in 1979 with the discovery of the “Twin Quasar”. “Weak lensing” is where the image is distorted but not to the point of forming a ring or arc segment, which is much less useful for magnifying distant objects but has recently been used to map dark matter concentrations across wide swaths of the universe. Gravitational lensing is particularly helpful in this case since, as the name suggests, dark matter does not emit enough light to be observed and can only be detected through gravitational effects.
Where this has implications for space colonization is the fact that every object that has mass bends light around it through its gravity, not just massive galaxy clusters. This effect is too small to be significant around, say, asteroids, but stars have more than enough gravity to act like magnifying glasses. “Microlensing” is a third class of gravitational lensing we observe that is generated by stars passing in front of (relatively massive) objects; because stars are far smaller than galaxy clusters the images produced are too small to be resolved by our telescopes, but a great increase in light can be observed as the star passes in front of a large object. This light can provide clues as to the nature of the object. Perhaps most prominently, a significant number of extrasolar planets have been discovered through microlensing.
Breakthroughs with Gravitational Lensing
On Earth we are at the mercy of chance alignments of stars and other objects to gain the benefits of microlensing, but the sun is a star itself and has more than enough gravity to act as a lens. If you could position the sun between you and a distant object the sun’s gravity would magnify the image and enable far greater resolution to be obtained than would otherwise be possible. If you move yourself so that the sun is directly in front of an object you wish to magnify, the light from the object that the sun bends comes into focus starting at around 542 AU away from the sun.
542 AU is where you will start to see a ring, arc, or other sort of image (depending on your exact position) of the background object around the sun, greatly magnified. Interestingly, there is no focal point in gravitational lensing; it continues to work no matter what the distance is, as long as it is beyond the minimum distance. This is rather convenient, since as some people (most recently Geoff Landis) pointed out the solar corona will interfere with the lensed image until you’re significantly further away (shrinking the apparent size of the corona). Of course, for observations it may be possible to adjust for such interference and keep one’s telescope at cl