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Feb
22
revised How do we know Dark Matter isn't simply Neutrinos?
improved the answer
Feb
21
comment Do intergalactic magnetic fields imply an Open Universe?
Did you read the paper? They report other people who have measured significant intergalactic fields that are not part of any galaxy. Please read the paper before you criticize it.
Feb
21
revised How do we know Dark Matter isn't simply Neutrinos?
corrections
Feb
21
comment How do we know Dark Matter isn't simply Neutrinos?
@RobJeffries - thanks for the education. I will correct my answer...
Feb
20
comment How do we know Dark Matter isn't simply Neutrinos?
@RobJeffries - Further, even if all the neutrinos today are non-relativistic, they could still have been relativistic in the early universe when cold dark matter was needed to cause the growth of structures.
Feb
20
comment How do we know Dark Matter isn't simply Neutrinos?
@RobJeffries - Do you have a reference that states this? I do not believe that we know this for a fact. You could be right if all neutrino masses are heavy enough, but we have no constraints on the mass of the lightest neutrino. So that neutrino could still be extremely relativistic.
Feb
14
revised How do we know Dark Matter isn't simply Neutrinos?
fixed grammar
Feb
14
awarded  Good Answer
Feb
14
comment How do we know Dark Matter isn't simply Neutrinos?
@quuxman - I removed the broken link and added what I remember was the argument of what the link would have said.
Feb
14
revised How do we know Dark Matter isn't simply Neutrinos?
replaced broken link with what the link would have said...
Feb
12
answered What was the frequency of the gravitational wave recently detected, and why?
Jan
12
answered 3D glasses giving the opposite effect to that expected
Dec
6
comment Does the universe emit Hawking radiation?
@JohnRennie, There is nothing magic about a time like 100 Byr that will suddenly change our current universe into an exactly de Sitter universe. Because of the accelerated expansion caused by dark energy, the ordinary and dark matter content will continuously approach zero but will never magically become zero, so if there will eventually be a horizon, why isn't there already a horizon?
Nov
21
awarded  Popular Question
Nov
17
comment The Sun as a gravitational lens
@tomh - According to wolframalpha.com/input/… it would take 3 days 4 hours 14 minutes 12.63 seconds :-) But note that this is the time from when the radio waves just graze the Sun to when they are received at the radio telescope. So that number doesn't mean much. The waves have been travelling in space for many many years (depending on the distance in light years of the source).
Nov
1
awarded  Generalist
Nov
1
comment How do we know Dark Matter isn't simply Neutrinos?
@HarryMacpherson - There are nine general classes of evidence for DM: 1. Galaxy rotation curves, 2. Velocity dispersions of galaxies, 3. Galaxy clusters and gravitational lensing, 4. Cosmic microwave background, 5. Sky surveys and baryon acoustic oscillations, 6. Type Ia supernovae distance measurements, 7. Lyman-alpha forest, 8. Structure formation, 9. Bullet Cluster. Each of these classes includes MANY individual measurements. If that is NOT overwhelming evidence for DM then I don't know what could possibly convince you. I give up. You can get the last word in. I quit.
Oct
19
comment How do we know Dark Matter isn't simply Neutrinos?
@HarryMacpherson : The exact particle that is the DM particle is unknown and is being searched for and it's properties have not been determined. However, it is known that the DM must exist and that is must be particles. That is what there is a huge amount of evidence for.
Oct
19
comment Are we increasing the gravity of Earth with our population?
@LightnessRacesinOrbit - Today I cannot find the source on the web for the 10 tons per day of meteors, but I did find a source for 5 tons: onlinelibrary.wiley.com/doi/10.1029/2000GL012621/full - the number per year gives about 5 ton per day. Also, the 250 tons of atmosphere loss per day is from Wikipedia: en.wikipedia.org/wiki/Atmospheric_escape - 3kg/sec of hydrogen gives 250 tons per day.
Oct
18
comment Are we increasing the gravity of Earth with our population?
@trichoplax - I see you already have answers to the question Chris White added for you. To those answers, I would just add that the products of photosynthesis will increase the mass of the output products compared to the inputs since some of the Sun's energy goes into the bonds - in other words it is enothermic reaction - the question Chris White added for you is about exothermic reactions. The effect will be unmeasureable, but it must exist.