All Questions
Tagged with cosmology estimation
42
questions
1
vote
1
answer
231
views
Estimation of the entropy of the universe
I heard the following way to estimate the entropy of the universe:
using that the entropy is dominated by photons, in particular the cosmic microwave background radiation, which has a wavelength ...
- 9,304
2
votes
2
answers
36k
views
More atoms in a grain of sand than stars in the observable universe?
in this video https://www.youtube.com/watch?v=AbgcITHmXBI the guys in the end says that there are more atoms in a grain of sand than stars in the (observable) universe.
My estimation with this:
100 ...
- 305
-2
votes
1
answer
300
views
How many Planck times would there be from the Big Bang to the Big Rip?
How many Planck times would there be from the Big Bang to the Big Rip? (approx.) Does this number have any numerical significance to mathematics?
If you had a CPU clock which had a timer counting ...
user84158
0
votes
1
answer
69
views
When did the universe become lighter than water at 1 g/cm3 [closed]
Did the universe become lighter than water before light could travel through it?
What temperature was it at the time where matter was roughly 1g/cm3?
- 33
5
votes
3
answers
344
views
How would we estimate, ahead of time, "the chances" of LIGO spotting black holes colliding in the period that it has been operating? [duplicate]
Can anyone summarize calculations that have been done about the theoretical probability of a detectable black hole collision happening in the observable universe within the time that LIGO has been ...
- 1,272
6
votes
2
answers
13k
views
How many electrons are there in the universe?
Someone on io9 estimated there were about 10^80 electrons in the universe, but I want to ask the Stack Exchange physics community.
- 377
8
votes
3
answers
1k
views
What was the density of the universe when it was only the size of our solar system?
What was the density of the universe when it was only the size of our solar system? Did it approach neutron star density? Is it physically correct to even ask such a question?
- 1,662
0
votes
1
answer
663
views
Does the Casimir effect give the correct value for Dark Energy?
My understanding is that the Casimir Effect is caused by vacuum energy. Quantum mechanics (QED) predicts vacuum energy, but gets the value grossly wrong, by a factor of $10^{120}$. On the other hand, ...
- 11.1k
21
votes
4
answers
21k
views
How far apart are galaxies on average? If galaxies were the size of peas, how many would be in a cubic meter?
The actual number:
How far apart are galaxies on average?
An attempt to visualize such a thing:
If galaxies were the size of peas, how many would be in a cubic meter?
- 2,283
47
votes
2
answers
41k
views
Dumbed-down explanation how scientists know the number of atoms in the universe?
It is often quoted that the number of atoms in the universe is 10$^{70}$ or 10$^{80}$.
How do scientists determine this number?
And how accurate is it (how strong is the supporting evidences for it)...
- 893
4
votes
4
answers
3k
views
How long does it take for expanding space to double in size?
I have been reading about Hubble's constant and trying to make 'sense' of the theory of the expanding Universe. Is is possible that space in the universe expands uniformly? If so, absent of other ...
- 229
16
votes
3
answers
8k
views
How many bytes can the observable universe store?
Is the number of states in the Universe countable?
What framework could be used to answer the question in the title?
- 588