Perception is a hot topic in philosophy. Do we directly perceive objects in the world, or only the images of objects on our retinas? Does the answer change when we see something reflected by a mirror or refracted through a lens? As anyone who needs glasses knows, sometimes putting something between your eye and an object can help you to see it better. Surprisingly, sometimes the most useful ‘lens’ is made of solid matter.
Solid matter can help us see distant objects by bending spacetime. It may sound far-fetched, but physicists routinely rely on this effect to see distant stars and galaxies that would otherwise be unobservable. Imagine a galaxy between the earth and the object we want to observe. Some of the light from the distant object will bend around the galaxy and converge at our telescopes on earth. From our point of view, it looks like there are two identical objects on either side of the galaxy, but really it is just light from one object, taking two different paths. Of course, depending on the exact arrangement, light can be bent around a galaxy in more than two ways (sometimes resulting in a halo of light surrounding the intermediate galaxy on all sides).
This effect of gravitational lensing has been known since Einstein, but just last week astronomers used it to generate an incredibly accurate image of a quasar surrounding a black hole. As the black hole consumes matter, it stretches, compresses and super-heats the matter, giving off an enormous amount of energy in the visible spectrum. This light bends around a galaxy on its way to earth, allowing David Floyd and colleagues at the University of Melbourne to construct an image of the process in a few weeks (rather than the usual decades). This precise image of something so tiny and so far away has allowed the first direct imaging of matter falling into a black hole, a truly remarkable advance.
By Lex Newman , University of Utah
(Vol. 3, December 2008)
By Casey O’Callaghan , Rice University
(Vol. 3, May 2008)