120 FAQs about General Cosmology (The Astronomy Cafe)

 

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 Back to the Astronomy Cafe - 365 of the most popular questions since 1996. Over 1 million page requests!

Beginner:

  1. Will better images than the Hubble Deep Field ever show the edge of the universe?
  2. What fraction of the universe is permanently hidden behind the Milky Way in the sky?
  3. How big is the universe?
  4. What is the temperature of space?
  5. When the Big Bang exploded, why wasn't a large empty region created?
  6. Do any other theories explain the cosmological redshift as well as Big Bang theory does?
  7. If distant observers looked at the Milky Way, what would they see?
  8. How far back in time can you see with a telescope?
  9. If I tell you how the universe works, how can I be sure I get credit for my theory?
  10. What exists beyond the current universe into which the universe is expanding?
  11. Hubble's original value for the expansion rate was 500 km/s/mpc. Why is this now considered wrong?
  12. Are the spaces between galaxies filled with stars or gas?
  13. If the universe is finite, what's outside?
  14. What did people think of the universe in 1850?

 

Intermediate:

  1. What is the universe a part of?
  2. If space increased faster than light moments after the Big Bang, why do we see anything near us in space at all?
  3. Why do galaxies ever collide if they were all ejected from a point at constant speed?
  4. Where can I get more information about the Cosmic Microwave Background Radiation?
  5. What does 50 kilometers/second/megaparsecs mean?
  6. If the Big Bang happened instantaneously, why are all the fragments at different distances and velocities?
  7. How much of the galactic redshift is due to cosmology and to ordinary Doppler effects?
  8. Did space really expand faster than light?
  9. Where does space end?
  10. What is the cosmological redshift?
  11. Why is the Andromeda galaxy approaching us if the universe is supposed to be expanding?
  12. Am I being stretched along with the expansion of the universe?
  13. Could the interaction between photons and intergalactic matter cause the cosmological redshift?
  14. If the space in between photons is empty, why can't some parts of the universe be colder than 2.7K?
  15. Could the universe be collapsing without our knowing about it?
  16. Is there a center to the universe?
  17. Is it possible the Milky Way really is the center of the Big Bang?
  18. There must be space reserved for the expansion of the universe, so where does it come from?
  19. Wouldn't the expansion of space show up inside the solar system in the predicted positions of the planets?
  20. Were does the concept of infinity fit into physics and cosmology?
  21. Why has the temperature of the cosmic background fallen since the Big Bang?
  22. If we are not seeing evidence for rapid expansion near us, could this mean that the universe is no longer expanding?
  23. What happens to a light beam when it reaches the edge of the universe?
  24. Stars convert some of their mass to light. Does this explain the 'missing mass' in the universe?
  25. Do galaxies move at the speed of light at great distances?
  26. What is the actual evidence that space expands and galaxies stay put?
  27. What percent of the universe is not visible yet?
  28. Do atomic orbitals expand as the universe expands?
  29. Does the blue shift of the Andromeda Galaxy contradict Big Bang cosmology?
  30. What is Olber's Paradox and how does modern cosmology resolve it?
  31. Will there ever be an end to the universe?
  32. Why don't the distances between stars also 'expand' with the universe?
  33. How can we still be seeing light from galaxies billions of light years away?
  34. How is the age of the universe determined?
  35. If gravity causes objects to rotate, wouldn't the universe be rotating?
  36. When the universe collapses will the night sky turn bright?
  37. What is the current best value for the cosmic background temperature?
  38. Can you list 10 or more observational facts supporting Big Bang Theory?
  39. Do you agree with the idea that the visible universe was once smaller than an atom?
  40. If the universe is finite, what's outside?
  41. Why do scientist's keep hammering on the Big Bang. It's only a theory, not divine truth. So why not give it up and try a new idea?
  42. Is the cosmological redshift real, or just an optical illusion caused by dust?
  43. What is out past the farthest reaches of where the universe has expanded into?
  44. Could our universe be a quark in another, bigger universe?
  45. Why can't we see infinitely far into space?
  46. Is there 'dark matter' that is really not matter in the universe?
  47. Is the Big Bang expansion really accelerating?
  48. Will our universe expand and bump into other universes?
  49. Will the expansion of the universe ever slow down to zero?
  50. When you look into space, what is the black stuff you see between the stars?
  51. Is it just a curiosity that the rate at which the moon is receding from the earth is nearly the same as the Hubble Constant?
  52. What is on the other side of the expanding universe?
  53. Why are galaxies colliding if the universe is expanding?
  54. What word is used to describe everything outside our universe?
  55. If the universe is infinite, how can there be other universes outside it?
  56. Is there nothingness outside of our visible universe?
  57. What would an observer outside our visible universe see if they looked in the direction of the Milky Way?
  58. If the universe is open and infinite, what is it expanding into?
  59. Could the universe be rotating, and if so, with respect to what?

 

Advanced:

  1. Could the fundamental constants in nature be changing to give us the illusion that the universe is expanding?
  2. Why does it make a difference is a neutrino has a rest mass if it carries energy anyway?
  3. Why isn't an oscillating universe very likely?
  4. How much of the galactic redshift is due to cosmology and to ordinary Doppler effects?
  5. What did the COBE satellite tell us about cosmology?
  6. What is the cosmological redshift?
  7. Why doesn't 'tired light' explain cosmological red shifts?
  8. What is the formula that relates redshift to distance in cosmology?
  9. I was taught the universe was infinite. How can an infinite universe expand?
  10. Why doesn't the actual location of galaxies right now make any difference?
  11. What would the contraction of the universe look like?
  12. What is space, itself, made of?
  13. How can an infinite universe have had a finite beginning in time?
  14. How can space have a temperature if atoms are so far apart?
  15. If our universe is a balloon with galaxies on the surface, what is inside the balloon?
  16. How do astronomers know that the cosmological redshift is NOT caused by a galaxy's gravitational field?
  17. What is the difference between a 'metric' distance and light travel distance in the universe?
  18. Why is the night sky dark?
  19. How could inflation have expanded the universe faster than light without violating relativity theory?
  20. What would an outer boundary to space in the universe look like?
  21. How is the value of the Hubble constant used to determine the age of the universe?
  22. If energy cannot be created or destroyed, and it takes an infinite energy for the universe to expand infinitely, where did the energy come from?
  23. Have there been many major paradigm shifts in cosmology?
  24. How can you tell the universe is expanding from measurements made inside it?
  25. How much expansion did the universe go through during 'Inflation'?
  26. If we see an object where it was 14 billion years ago, where is it now?
  27. How do quasars get to be so far away unless they travel faster than light?
  28. How was the distance to the quasar HS1700+64 determined?
  29. If the cosmic background is so smooth, why is matter in galaxies so clumpy?
  30. What does the recent announcement of their being 5 times more galaxies than previously known, do for the missing mass problem?
  31. Does infinity mean that space goes on forever?
  32. Why is the temperature of the universe 2.7 K and not absolute zero?
  33. If the universe is closed now, was it also closed before the Big Bang?
  34. What does it mean for a closed, finite universe to be a part of an undefinable, mysterious embedding space that is beyond observation?
  35. What is the cosmological significance of neutrinos having a small, but non-zero, mass?
  36. What existed in space before the Big Bang?
  37. Is there a connection between the laws of the microcosm and the structure of the universe?
  38. Where does the energy to accelerate the expansion of the universe come from?
  39. If the universe is expanding into nothingness, isn't 'Nothingness' something?
  40. How can an infinite universe expand?
  41. Could some of the 'missing mass' in the universe be in the cosmic background radiation itself?
  42. Is there a fifth force causing the universe to expand more rapidly?
  43. What is on the other side of the expanding universe?
  44. How close to the Milky Way were the Hubble Deep Field proto-galaxies when the Milky Way was born?
  45. If the ultimate fate of our universe is so bleak, what then is its purpose?
  46. Would Dark matter go away if Newton's Law of Gravity were incorrect at intergalactic distances?
  47. How do we really know that we are missing 90 percent of the matter in the universe?
  48. If the Big Bang happened in an infinite nothingness, the universe must have an expanding edge, right?
  49. Stephen Hawking says the universe has no boundary, so what is it that is expanding?
  50. If the universe is expanding, it has a boundary, so what is at the boundary?

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