All Questions
21
questions
0
votes
3
answers
108
views
Is Dark Energy Taking Over?
First question, trying to keep it simple 😃
Because it's constant it grows in magnitude as the universe expands, whereas normal matter does not? Is this accurate as far as we know?
- 11
0
votes
0
answers
31
views
Why can't Dark matter be made up mostly of Neutrinos? [duplicate]
It's said that Neutirnos can only make up a tiny fraciton of dark matter.
So why can't Dark matter be mostly made up of Neutrinos?
Why can't there just be a huge number of them?
I suspect myself that ...
- 2,908
3
votes
1
answer
75
views
How did neutrinos eliminated from dark matter? [duplicate]
I am reading "Dark Matter and Dark Energy" by Brian Clegg.
In Chapter 3 it's discussing about cosmic microwave background radiation and the elliptical shape
of early universe obtained from ...
0
votes
0
answers
19
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Dark matter and un-smoothness in spacetime [duplicate]
Since dark matter currently is only observable with its gravitational effects and nothing else can we theorize that dark matter is only non-smoothness in spacetime that has been there from the Big ...
2
votes
3
answers
662
views
Why is the ratio of dark matter to normal matter larger in galaxies than the cosmic average?
There seems to be a discrepancy between the ratio of dark matter to normal matter in the Universe (about 5 to 1 according to $\Lambda$-CDM) and the ratio of the average dark matter halo mass to the ...
- 185
0
votes
0
answers
35
views
What is the dark energy & dark matter? [duplicate]
Can anyone explain to me simply what is the dark energy or what is the dark matter. I have been trying to understand it deeply. but I somehow failed.
-3
votes
1
answer
99
views
From which dark matter made of? [closed]
Observations indicate that about 90 percent of the matter itself in the
universe is made up of dark matter. Exactly what kind of things dark matter made of?
- 547
0
votes
1
answer
76
views
What if dark matter occupied three other dimensions and it could only interact with our three dimensions through gravity and time? [closed]
I recently thought about dark matter existing in three other dimensions similar to ours but wasn't sure if it was logical. It would be of great help if someone would give me a clear insight into this ...
- 23
1
vote
1
answer
192
views
Dark matter in the time window between freeze-out and kinetic decoupling
Background
After the freeze-out, when all annihilations have stopped, the abundance ($Y=\frac{n}{s}$) of thermal dark matter species no longer changes with time. However, it is still kept in kinetic ...
- 26.8k
8
votes
2
answers
377
views
Why does nobody ever consider the possibility that the universe is not smooth?
Disclaimer: I'm not an astronomer, physicist, mathematician, etc. so this is a question from a complete newbie.
One of the greatest mysteries of our age is "where is the dark matter?" The universe ...
- 3,101
2
votes
1
answer
2k
views
How do they know the numbers of the energy pie chart of the universe?
They say that the total energy of the universe consists of 4.9\% ordinary matter, 26.8\% dark matter and 68.3\% dark energy. I hear this pie part in virtually every lecture in cosmology. How do we ...
- 11.8k
2
votes
1
answer
143
views
Dark matter should be nonrelativistic at $1$ KeV or earlier. Why?
If the dark matter (DM) is non-relativistic at freeze-out and if the kinetic decoupling occurs much later than freeze-out, it is called cold dark matter. More precisely, it is stated that if the DM ...
- 26.8k
1
vote
1
answer
888
views
Why is the heat death, rather than a Big Crunch, the most accepted theory of the ultimate fate of the Universe?
The Heat Death is accepted by most as the end of the Universe, but how can that be? Wouldn't the Big Crunch make a lot more sense? I mean, even if everything in the Universe is spread out uniformly ...
- 41
8
votes
1
answer
2k
views
Why do physicists think that the dark matter is cold?
Most of the dark matter in the Universe is cold or nonrelativistic which rules out neutrinos as dark matter candidate as they are hot or relativistic. But why do physicists think that the dark matter ...
- 26.8k
2
votes
1
answer
526
views
Fall of the number density $n$ with the scale factor $a(t)$ for a relativistic particle species in equilibrium?
Consider the thermal dark matter (DM) scenario. Before the dark matter got frozen out, it was both in chemical and thermal equilibrium with the other particles in the early universe. At this point of ...
- 26.8k