204 FAQs about Astrophysics (The Astronomy Cafe)

1. Do anti-particles produce anti-gravity?
2. What is the speed of gravity?
3. What is energy?
4. How does the photoelectric effect support the idea that light is a particle?
5. Does the physical vacuum produce a pressure that can be measured?
6. How much of a charge excess would be needed in the universe to produce detectable non-gravitational motions?
7. Who are the people working on the Theory of Everything, and are they close to finding it?
8. Is there only one kind of atom with 106 protons?
9. Is it true that the barycenter is not affected by the masses of the system?
10. Are all particles and fields just vibrations in an energy field?
11. Have scientists confirmed the spontaneous creation of matter from the vacuum?
12. What is Jeans mass, Horizon mass and Damping mass?
13. Where can I learn more about anti-matter?
14. Was the resonant pendulum used by Galileo?
15. How do we know that Newton's LAws apply outside the solar system?
16. What are the chemical constituents to light?
17. When two laser beams interfere with each other, what happens to the energy?
18. Do we really know how gravity and magnetism operate?
19. Is there such a particle as the Chronon?
20. What is the substance of gravity?
21. Does everything in the universe consist of energy?
22. If the force of gravity were reduced 50 percent, how would this change stars and the universe?
23. Does time stop at Absolute Zero?
24. Why is the circle such a common shape in nature?
25. If no signal travels faster than light, what explains the EPR Paradox?
26. What is the difference between degrees Centigrade and Kelvin?
27. What do absolute space and time mean?
28. Why do bodies have gravitational fields?
29. Are the distances between atoms in my finger greater than that between Earth and Pluto, relatively speaking?
30. What is the Sagnac Effect?
31. What si the difference between inertial and gravitational mass?
32. How is it possible for the Sun to affect distant objects like Hale-Bopp?
33. What is the minimum mass of a cloud that can gravitationally collapse?
34. Are the rotation axis of bodies randomly determined?
35. If the Earth is head in place by gravity as it spins, does the galaxy also spin?
36. Why do some bodies have different gravities than others?
37. How do you get free energy from fission or fusion?
38. If I point my laser pointer at the Moon, why don't I see a spot?
39. How does it feel to be weightless?
40. What exactly is the Pauli Principle?
41. If liquid helium can flow forever, isn't this perpetual motion?
42. Where can I get more information about Element 115?
43. Why do electron-positron collisions produce energy, but not electron-proton collisions?
44. How does the size of a crater depend on the size of the meteorite?
45. Why don't I loose gravity when I step off the surface of a rotating cylinder?
46. Why does prefect knowledge of one parameter mean that the other parameter is infinitely spread out among other possibilities in the Heisenberg Effect?
47. When light travels, don't its electric and magnetic fields vanish during some part of the cycle, and where does its energy go then?
48. When we calculate the masses and orbits of planets, does it matter where they are right now?
49. Would space be totally empty and non-existent without virtual particles?
50. Why does the exchange of virtual photons cause attraction?
51. Does light have anything to do with the 5th dimension?
52. Does gravity produce gravity?
53. How do tidal forces differ from gravitational ones?
54. What is the Roche Limit and who discovered it?
55. If more dimensions exist at smaller scales, could they also exist at speeds greater than light?
56. Can matter waves be changed to a different 'color' the way light waves can?
57. Will it ever be possible to decide exactly how quantum mechanics actually works?
58. Why do gravitationally bound objects rotate counter-clockwise?
59. How do sound waves travel through outer space?
60. Can gravity be shielded?
61. CAn electromagnetic fields cause spacetime to bend?
62. What is the role of time in the so-called Theory of Everything?
63. Where on the Internet can I get information about superstring theory?
64. Do astronauts feel acceleration in space without gravity?
65. What is the relationship between electromagnetic fields, gravitational fields and space-time?
66. Could you give a technical explanation of the 'Slingshot' maneuver?
67. Do the fission products of a nucleus exist prior to the fission being complete?
68. Do other dimensions exist?
69. What happens to matter at Absolute Zero?
70. What is a cosmic string?
71. Are W and Z particles quarks or leptons?
72. If you drop a feather into the atmosphere from orbit, will it burn up or fall to the ground?
73. What causes the gravitational force to increase as a star collapses?
74. How is it really possible for there to be gravitational forces between distant galaxies?
75. Would a Bose-Einstein condensate with a Planck mass tell us anything about quantum gravity at low energy?
76. How are tachyons supposed to work?
77. What is a boson?
78. What would a macroscopic Bose-Einstein condensate look like, and 'do'?
79. What is the difference between the vacuum in interplanetary space, and the vacuum in intergalactic space?
80. Could a marshmallow traveling at the speed of light knock the Earth out of orbit?
81. Is visible light qualitatively different than other types of electromagnetic radiation?
82. Since the electromagnetic force is 10^42 times stronger than gravity, why doesn't a single cosmic ray pull the Earth out of orbit?
83. Where does the energy come from that produces virtual particles?
84. Why is there no Coulomb barrier for fission if there is one for fusion?
85. Can elementary particles be split?
86. Will Bose-Einstein condensates be helpful in understanding physics at the Planck Scale?
87. How faast is the force of gravity?
88. How does the gravitational 'slingshot' maneuver work?
89. Can events be truly random if cause and effect holds for all physical phenomena?
90. What is precession?
91. Can the structure we see in the physical world be simply a projection of how our brains work?
92. Why do things rotate?
93. Are the topologies of a sphere and a hypertorus the same?
94. Can sub-atomic particles be infinitely compressed?
95. Is the empty space inside particles the same kind as there is inside atoms?
96. What is infinity?
97. Would an Earth compass point to the north pole on other planets?
98. What is the difference between pulsars and quasars?
99. Since the field around a planet is constant, why does the 'slingshot' effect work?
100. Can 'binding energy' exist without a host?
101. Why is it you are never considered upside down anywhere on the Earth?
102. What does the term 'bulk properties' mean in astronomy?
103. How long can a person survive at 95 and 105 degrees F?
104. Do quantum worm holes produce a connectivity to space so that the non-locality problems in quantum mechanics never arise?
105. Where do the neutrinos go that are made by humans?
106. Could you try to resolve some conceptual problems I have with how gravity works?
107. What was the ultraviolet catastrophy, and how did quantum theory avoid it?
108. What exactly is a sub-atomic particles structure like?
109. So, is Schroedinger's cat alive or dead?
110. If there were no other objects in the universe, would you still have centrifugal forces?
111. How is Zeno's Paradox resolved in physics?
112. On which asteroids could you jump into orbit?
113. What are the Trojan and the Lagrange Points?
114. Is the photon that reaches your eye from a distant galaxy the very same one that started its journey across intergalactic space?
115. If two objects of different mass rolled down a hill, which would get to the bottom first?
116. What would the predicted properties of Element 115 be?
117. At what distance from the Earth do astronauts experience weightlessness?
118. How do you verify Newton's Law of Gravity?
119. Are there tornadoes in space?
120. Are quarks really considered fundamental particles?
121. Would a person tan or burn more quickly at high altitude than at sea level?
122. How does energy flow in those other dimensions to space-time outside the standard four?
123. Are quantum uncertainty and the existence of compact dimensions to space-time related?
124. Is the gravitational pull of a planet influenced more by its mass or its rotation?
125. how does a magnetic field differ from a gravitational field?
126. What is Grand Unification Theory?
127. What does it mean to travel to another dimension?
128. Does anti-matter fall faster than normal matter?
129. Have either amino acids or nucleic acids been detected in interstellar space?
130. If we developed better instruments, could we see Heisenberg's Uncertainty Principle in action?
131. How can strings be used for time travel?
132. Is there a 'smallest possible size' to space beyond which it cannot be further divided?
133. Are quarks really the smallest particles next to electrons?
134. Is there any evidence that the Laws of Nature change over time, or in different regions of the universe?
135. Could a very energetic gamma ray turn the sun into a nova?
136. Is anti-gravity possible?
137. What is the Everett-Wheeler Theory of quantum mechanics?
138. If there are an infinite number of points in a line, how is it that it doesn't take eternity to cross the street?
139. How pervasive is the role of chaos in astrophysics?
140. What is the escape velocity from the earth's surface including atmospheric drag?
141. If light were shone into a perfectly reflective cavity, what would happen?
142. Is there an Absolute Highest Temperature opposite to Absolute Zero?
143. Are the northern lights seen in the southern hemisphere simultaneously?
144. Why is accretion of matter onto a black hole more efficient in producing energy that thermonuclear fusion?
145. What is the difference between a newtonian and a relativistic treatment of planetary motion?
146. Why does a stationary gas cloud suddenly start spinning as it collapses to form a star?
147. Can you see Northern Lights from Minnesota?
148. Does data ever become obsolete before it can be properly interpreted?
149. How close can the moon come to the earth before disrupting?
150. How do you calculate centrifugal forces in a rotating space station?
151. Can radioactive decay be influenced by exposure to oscillating electromagnetic fields?
152. Can gravity be simulated using electromagnetic forces?
153. How the ding dang was the Astronomical Unit determined?
154. What is a nebula?
155. Does there exist a dark force in the universe?
156. What is 21 centimeter radiation?
157. What is the difference between a gamma-ray and a cosmic ray?
158. What is the most energetic form of light that astronomers have ever seen?
159. If a chemical in a candle flame produces different colors, why not stars?
160. How can stars pull together if there is no gravity in space?
161. Is time intelligent?
162. How can astronomers predict with such accuracy that a comet will collide with a planet millions of miles away?
163. If photons from matter and anti-matter look the same, how can astronomers say there is no anti-matter in stars or galaxies?
164. Can astronomers tell whether stars and galaxies are made of anti-matter?
165. Are there any particles smaller than quarks inside quarks?
166. Will the laws of physics change in the future?
167. What does albedo mean?
168. How can astronomers infer the distances to objects from where they once were, and aren't there too many interdependent variables to solve this exactly?
169. If you took a vacuum cleaner into space, what would happen?
170. Why is physics so complicated?
171. How do you reconcile Zeno's paradox with modern physics?
172. How many more senses do you think humans need to truly understand the universe?
173. Is human perception of statistics flawed?
174. Can electrons really be in two places at once?
175. How did 'hidden variables' theory get put to rest in quantum mechanics?
176. Why is the sky blue?
177. Is the blue color of a flame caused by continuum or line emission?
178. What are the different types of electromagnetic radiation?
179. Faint objects emit few photons. How is the quantum nature of the observation process reconciled with classical physics?
180. How do astronomers use incoming light rays to measure distances in the universe?
181. Are there any areas in astronomy or physics where it is unhelpful to think analytically?
182. How do you handle paradoxes?
183. Can things be infinitely small?
184. What is the latest on the nature and existence of 'dark matter'?
185. What happens to matter at Absolute Zero?
186. Why was there a slight imbalance between matter and antimatter just after the Big Bang?
187. If proton decay occurs, does this prove that a state of maximum entropy is the natural state of the universe?
188. Could you tell me what the arrows of time are in relation to cosmology?
189. Can virtual particles still be created in a vacuum where the temperature is absolute zero?
190. What is the cosmological significance of neutrinos having a small, but non-zero, mass?
191. What existed in space before the Big Bang?
192. Is there a connection between the laws of the microcosm and the structure of the universe?
193. 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?
194. Could our universe be a quark in another, bigger universe?
195. Is the amount by which light bends important in cosmology?
196. Are gamma rays and radio waves the ends of the electromagnetic spectrum, or is there something beyond them?
197. Does chaos really occur or exist in nature?
198. What is a parsec?
199. Do magnetic fields exist throughout space?
200. Since energy is quantized, does that mean that light is also quantized?
201. How far is a light year?
202. Can you explain how astronomers use the Doppler shift to measure speed?
203. How is a stellar parallax used to determine the distance to stars?
204. Do all elementary particles have spin, and where does it come from?

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