Olbers' Paradox applet written by Joseph V. Benik, Jr., Dr. Melissa Hayes-Gehrke, and Dr. Alberto Bolatto, and converted to Javascript by Jesse Averbukh. We acknowledge support from a CAREER award by the National Science Foundation, grant AST-0955836, and from a Cottrell Scholar award by the Research Corporation for Science Advancement, grant 19968. We also thank NASA for the galaxy images, available at nasaimages.org

Using the applet
  1. Move the slider from left to right to increase the amount of light coming to you from distant galaxies
  2. Toggle between drawing galaxy images or stars with the Draw Stars/Draw Galaxies button
  3. Troubleshooting
Frequently Asked Questions
  1. What is Olbers' Paradox?
  2. Olbers' paradox is the assertion that an infinite size universe which is infinitely old with a uniform distribution of stars should have a night sky which is completely bright instead of dark.


  3. Was Olber imagining stars or galaxies filling the sky?
  4. Olbers' paradox makes reference specifically to stars but he would have actually been looking at galaxies instead of stars. At the time Olber didn't know of the existence of separate galaxies beyond the Milky Way, he only knew of the existence of stars.


  5. Could the sky ever be completely filled with galaxies?
  6. If the sky was actually filled with stars or galaxies the surface temperature of the Earth would be the same as the surface temperature of a star like the Sun. This is the nature of the paradox since we know the Earth isn't that temperature.


  7. How does the expansion of the universe affect Olbers' Paradox?
  8. Since the universe is expanding the distances between our galaxy and other galaxies are getting larger so the light has more distance to travel. This applet doesn't show the expansion of the universe.


  9. What is the solution to Olbers' Paradox?
  10. Olbers' paradox has proved that the universe is not actually infinite in age. The light from distant galaxies has not yet had the time to reach us.