220 FAQs about General Cosmology (The Astronomy Cafe)

1. What are the pros and cons for an infinite or a finite universe?
2. Could the 'missing mass' exist as a wire-like material that permeates space?
3. Could the fundamental constants in nature be changing to give us the illusion that the universe is expanding?
4. Will better images than the Hubble Deep Field ever show the edge of the universe?
5. Why does it make a difference is a neutrino has a rest mass if it carries energy anyway?
6. What are the speculations about the future of the universe?
7. Is the expansion of the universe slowing down right now?
8. Will astronomers need the cosmological constant to reconcile the ages of old stars and the universe?
9. How is it possible for the energy in the cosmic background radiation to remain constant as the universe expands?
10. Why isn't an oscillating universe very likely?
11. What is the universe a part of?
12. Is the total energy of the universe decreasing because of the redshift?
13. If space increased faster than light moments after the Big Bang, why do we see anything near us in space at all?
14. Why do galaxies ever collide if they were all ejected from a point at constant speed?
15. In Einstein's "The Meaning of Relativity" he says that the Hubble Shift must be a Doppler Shift". Does this mean all modern cosmology is wrong because it says that space stretches?
16. Why is the average density of the universe so important to know?
17. What exactly is the 'heat death'?
18. Where can I get more information about the Cosmic Microwave Background Radiation?
19. If the universe expanded 12 billion light years yesterday, wouldn't we see the same redshifts, so how is it redshift is related to age?
20. What does 50 kilometers/second/megaparsecs mean?
21. If the Big Bang happened instantaneously, why are all the fragments at different distances and velocities?
22. The age of the universe has changed again .What does it all mean?
23. If we seem to be at the center of the universe where the force of gravity must be exactly zero, what causes the universe to decelerate?
24. What fraction of the universe is permanently hidden behind the Milky Way in the sky?
25. How can space be a gravitational field and expand faster than light at the same time?
26. How much of the galactic redshift is due to cosmology and to ordinary Doppler effects?
27. Did space really expand faster than light?
28. How can some stars in the universe be older than the universe?
29. Does the speed of light place any limit on the size of the universe?
30. Where does space end?
31. How could galaxies 90 degrees apart in the sky come from the same Big Bang when their ancient light seen now, shows them billions of light years apart?
32. Why is the center of some universes ultra-bright?
33. What did the COBE satellite tell us about cosmology?
34. At what redshift is the cosmic horizon?
35. What is the cosmological redshift?
36. Where would the universe appear to collapse in a closed universe?
37. Why doesn't 'tired light' explain cosmological red shifts?
38. Why is the Andromeda galaxy approaching us if the universe is supposed to be expanding?
39. Why doesn't the distance derived from a galaxy's apparent magnitude equal its distance from us today?
40. What is the formula that relates redshift to distance in cosmology?
41. What is the shape of the universe?
42. I was taught the universe was infinite. How can an infinite universe expand?
43. Was the Big Bang purely dilation of space, or was some kind of conventional explosion involved?
44. How big is the universe?
45. Why isn't gravity redshifted in the universe the way light is?
46. Am I being stretched along with the expansion of the universe?
47. What is the most reliable way to determine Omega?
48. Why doesn't the actual location of galaxies right now make any difference?
49. Will the universe come to an end with all the black holes merging into a Big Crunch?
50. Will we ever 'see' our own creation by looking into space?
51. How can the dilation of space occur outside a bound system ( cluster of galaxies) when the universe itself is a bound system?
52. What would the contraction of the universe look like?
53. What is space, itself, made of?
54. How can an infinite universe have had a finite beginning in time?
55. How can space have a temperature if atoms are so far apart?
56. Why do galaxy redshifts appear to be quantized?
57. Would the sky be as dark as it is today if the universe were infinite and had an infinite number of stars?
58. Could the interaction between photons and intergalactic matter cause the cosmological redshift?
59. Isn't the geocentric theory of the universe the correct one for someone living on the Earth?
60. If the space in between photons is empty, why can't some parts of the universe be colder than 2.7K?
61. If our universe is a balloon with galaxies on the surface, what is inside the balloon?
62. I do not understand how to visualize a closed universe, can you help?
63. Why doesn't the universe look like a torus in space rather than an expanding sphere?
64. What is the mass of the universe halting from expanding since space is empty?
65. Does the expansion of the universe affect time?
66. Are 'collapse' and 'heat death' the only destinies for the universe?
67. How do astronomers know that the cosmological redshift is NOT caused by a galaxy's gravitational field?
68. If we are actually not at the center of the universe, why are there no blue-shifted galaxies?
69. Could the missing mass have been destroyed in the Big Bang?
70. What is the temperature of space?
71. How do you convert from cosmological redshift to recession velocity without assuming an age for the universe?
72. Why is the age of the universe sometimes stated as 1/(Hubble's constant)?
73. Why do some astronomers insist on using the special relativity Doppler formula for the cosmological redshift?
74. Does the red shift tell us the universe was once expanding and not that it still is?
75. Are there questions that astronomers can't answer because most of what they see only shows the way things were millions or billions of years ago?
76. When the Big Bang exploded, why wasn't a large empty region created?
77. How could Hawking and Freedman have made such obvious errors in calculating the age of the universe as not allowing for where the galaxies are right now?
78. Could the fact that everything is imploding explain why the universe looks like it is expanding?
79. What is the difference between a 'metric' distance and light travel distance in the universe?
80. Could the universe be collapsing without our knowing about it?
81. Is there a center to the universe?
82. Is it possible the Milky Way really is the center of the Big Bang?
83. Why is the night sky dark?
84. Do any other theories explain the cosmological redshift as well as Big Bang theory does?
85. How could inflation have expanded the universe faster than light without violating relativity theory?
86. There must be space reserved for the expansion of the universe, so where does it come from?
87. Wouldn't the expansion of space show up inside the solar system in the predicted positions of the planets?
88. Can a student in electrical engineering build a working radio telescope?
89. Has the Hubble Space Telescope discovered a star older than the universe?
90. Were does the concept of infinity fit into physics and cosmology?
91. If the cosmic background radiation is passing us now, why do we have to look far into space to detect it?
92. How can we still be seeing the birth of our universe in the cosmic background radiation when light travels faster than the expansion of the universe?
93. How do astronomers know that the universe is 'smooth' and 'flat' today?
94. Why has the temperature of the cosmic background fallen since the Big Bang?
95. Why is there an 18 microKelvin quadrupole anisotropy in the cosmic background radiation?
96. When light is redshifted by the expansion, where does its energy go?
97. Why is it that by NOT adding the cosmological constant, Einstein would have been the father of the expanding universe and not the contracting universe?
98. If we are not seeing evidence for rapid expansion near us, could this mean that the universe is no longer expanding?
99. What would an outer boundary to space in the universe look like?
100. In the balloon analogy to the expanding universe, what is inside and outside the surface of the balloon?
101. How is the value of the Hubble constant used to determine the age of the universe?
102. Does the cooling of the cosmic background to 3 K have to do with the scattering of photons?
103. Is gravity diluted in strength by the expansion of the universe?
104. How did galaxies now at 11 billion light years seen by the Hubble get there in less than 2 billion years?
105. Would the planets around all the stars in the universe account for the 'missing mass'?
106. If space is expanding, why do we see redshifts if galaxies are not moving through space?
107. If a galaxy is measured to be 5 billion light years away today, how far away is it in actuality?
108. What happens to a light beam when it reaches the edge of the universe?
109. What do you think the real value of the Hubble COnstant is?
110. Is the gravity we feel stronger than expected given the current locations of the galaxies due to cosmic expansion?
111. In a contracting universe, will entropy increase or decrease?
112. Would a sufficiently massive object hault or reverse the expansion of the universe?
113. Stars convert some of their mass to light. Does this explain the 'missing mass' in the universe?
114. How can astronomers estimate the age of the universe if it used to be expanding near the speed of light?
115. Do galaxies move at the speed of light at great distances?
116. If distant observers looked at the Milky Way, what would they see?
117. What is the actual evidence that space expands and galaxies stay put?
118. 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?
119. Could the cosmological redshift be due to the strong gravitational fields of nearby galaxies instead?
120. How significant is 'Omega Point Theory' to cosmology?
121. If the universe expanded from the size of a grapefruit to the size of the solar system by 10^-10 seconds after the Big BAng, was matter traveling faster than light?
122. What percent of the universe is not visible yet?
123. Big Bang theory says that all observers in the universe will see themselves at the center of the expansion. Do we know this to be true for very distant galaxies?
124. How can we still be seeing light from galaxies 15 billion light years away when the galaxy was only a billion years old.hasn't this light already passed us by?
125. Are galaxies far away actually seen to be crowded together as expected from Big Bang theory?
126. Do atomic orbitals expand as the universe expands?
127. Could the redshift be due to photons loosing energy to the cosmic background radiation 'fireball' field?
128. How can the images of distant galaxies be further away than the size of the universe at the time they were made?
129. Is the evidence that stars are older than the universe evidence that some stars survived the Big Bang from a previous cycle of our universe?
130. Does the blue shift of the Andromeda Galaxy contradict Big Bang cosmology?
131. If billions of supermassive black holes existed within the first billion years after the Big Bang, would this have altered the expansion of the universe?
132. What is Olber's Paradox and how does modern cosmology resolve it?
133. What determines whether our information horizon will eventually encompass the entire universe or not?
134. Have there been many major paradigm shifts in cosmology?
135. How can you tell the universe is expanding from measurements made inside it?
136. Will there ever be an end to the universe?
137. How much expansion did the universe go through during 'Inflation'?
138. If the universe were not expanding, would we still see a redshift from the gravitating matter in the universe?
139. Why are all of the quasars located so far away, and not distributed evenly in space near us?
140. Do all observers in the universe agree that the Big Bang happened about 15 billion years ago?
141. Have astronomers measured the hydrogen in the universe and found that it has an edge to it?
142. Could the gravitational fields of quasars cause their red shifts instead of the expansion of the universe?
143. Why is the motion of galaxies directly away from us and not mostly across our line of sight?
144. If an observer were at the center of an explosion, the fragments would be fewer in number as he looked outwards. Why do the Hubble photographs show lots and lots of distant galaxies?
145. Why is the Hubble Constant not a constant?
146. Why don't the distances between stars also 'expand' with the universe?
147. In an expanding universe, do the star distances also 'expand'?
148. Could the universe actually have an infinite age?
149. Do galaxies travel faster than light?
150. How can we still be seeing light from galaxies billions of light years away?
151. How far back in time can you see with a telescope?
152. How can cosmic expansion be slowing when distant galaxies are receding faster and faster with distance?
153. Are we really near the center of the expansion, or are we off to one side?
154. Can we tell where the Big Bang happened in space by measuring galaxy motions and directions in space?
155. If I tell you how the universe works, how can I be sure I get credit for my theory?
156. What exists beyond the current universe into which the universe is expanding?
157. How can we see light from objects 10 billion years ago when this light should have long ago passed us and the Earth is only 5 billion years old?
158. If we see an object where it was 14 billion years ago, where is it now?
159. What is the maximum distance light can travel in a closed universe?
160. What is the farthest object known in the universe?
161. If the universe is uniform and infinite what would cause it to collapse?
162. In the expansion age for the universe, where does the 2/3 factor come from?
163. What is meant by the term 'radius of the universe'?
164. How is the age of the universe determined?
165. What are all of the rungs in the cosmological distance ladder?
166. Is there a formula for the expansion speed of the universe?
167. What is the Great Attractor?
168. How do you calculate the age of the universe in year when the Earth was not even around to define a year then?
169. What is the diameter of the universe?
170. If gravity causes objects to rotate, wouldn't the universe be rotating?
171. When the universe collapses will the night sky turn bright?
172. How many light years is it to the edge of the universe?
173. Where in the universe is the Milky Way located relative to its edge?
174. If the light from the Big Bang has only now reached us, does this mean that the matter around us has been traveling at the speed of light or faster to get to where we are now?
175. Is the universe expanding?
176. If space is expanding everywhere, how do we measure this when our rulers are also changing?
177. Do astronomers allow for time delay when giving the ages of stars and galaxies?
178. I sometimes see Hubble diagrams with expansion rates near 128 km/s/mpc. Are they right or wrong?
179. Hubble's original value for the expansion rate was 500 km/s/mpc. Why is this now considered wrong?
180. How do quasars get to be so far away unless they travel faster than light?
181. How was the distance to the quasar HS1700+64 determined?
182. Does space curvature cause the images of distant galaxies to overlap?
183. If the cosmic background is so smooth, why is matter in galaxies so clumpy?
184. What does the recent announcement of their being 5 times more galaxies than previously known, do for the missing mass problem?
185. What is the current best value for the cosmic background temperature?
186. Does infinity mean that space goes on forever?
187. Can you list 10 or more observational facts supporting Big Bang Theory?
188. Do you agree with the idea that the visible universe was once smaller than an atom?
189. Do the different estimates for the age of the universe imply that the speed of light may have changed?
190. Why is the temperature of the universe 2.7 K and not absolute zero?
191. If the universe is closed now, was it also closed before the Big Bang?
192. Are the spaces between galaxies filled with stars or gas?
193. Are there any places in the universe where the temperature is lower than 2.7 K?
194. Is the amount by which light is bent important in cosmology?
195. How old is the Universe?
196. What the ding dang is a quasar?
197. How is it that, according to general relativity, space can be curved?
198. Is it your view that the universe is finite or infinite?
199. If the universe is finite, what's outside?
200. How can the density of a cosmological scalar field decrease less than the matter density as the universe expands?
201. 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?
202. In the expanding universe, space is said to be expanding while at the same time galaxies are not moving. Isn't this a contradiction?
203. What does it mean for a closed, finite universe to be a part of an undefinable, mysterious embedding space that is beyond observation?
204. Is the cosmological redshift real, or just an optical illusion caused by dust?
205. How long ago did the Big Bang take place?
206. What is the cosmological significance of neutrinos having a small, but non-zero, mass?
207. Does the term Big Bang only refer to what is inside our universe?
208. What existed in space before the Big Bang?
209. What is out past the farthest reaches of where the universe has expanded into?
210. Is there a connection between the laws of the microcosm and the structure of the universe?
211. How long did it take an object now 10 billion light years away to get there since the Big Bang?
212. If the universe is infinite, then its total mass should be zero. Does this mean there is negative mass to cancel out the positive mass found in stars and galaxies?
213. If stars come in clusters, and galaxies come in clusters too, could our universe come in clusters with other universes?
214. If a galaxy is 10 billion light years away, with the expansion, did it take light 10 billion years to get here?
215. Why is the night sky dark instead of bright?
216. Could our universe be a quark in another, bigger universe?
217. Is the amount by which light bends important in cosmology?
218. How can our universe have Third generation stars if it is only 10-15 billion years old?
219. Is it difficult to know what is happening now if it takes light time to get here?
220. Why can't we see infinitely far into space?

For more information about cosmology, go to my Cosmology Essays area.

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