LMR-088 · Gravity & Time
Lensing
Mass bends light. Galaxies turn into natural telescopes.
§ A first look
§ Depths
Six ways into the same idea — from bedtime story to chalkboard. No order required.
L1 · Crayon
Told like a bedtime story.
For a curious 10-year-old. No jargon. Just a picture in your head.
Look at a straw in a glass of water. The straw looks bent where it enters the water, because the water bends the light coming from it. Big heavy things in space, like whole galaxies, bend light in a similar way. When light from a faraway galaxy passes close to another heavy galaxy on its way to us, the heavy galaxy in the middle bends and stretches the faraway one's light — sometimes smearing it into rings or arcs in our pictures. This bending of light by heavy things is called gravitational lensing. The universe occasionally lends us extra telescope.
§ Strange but true
- 01Galaxies bend light around themselves like funhouse mirrors — sometimes showing you the same distant object four times.
- 02We use it to weigh dark matter we can't see. The bend tells us the mass.
- 03Einstein predicted it in 1936 but said it would never be observed. He was wrong; we use it weekly.
§ From the field journal
Lensing
"Mass bends light. Galaxies turn into natural telescopes."
— observed, sketched, not yet fully understood.
§ Nearby