All Questions
12
questions
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What is the expansion of space of one megaparsec in one year?
suppose we know Hubble's constant. In a hypothetical scenario an astronomer finds and confirms Hubble's law for a galaxy 1 mega parsec away.
Next year, how much distance will the hypothetical ...
1
vote
0
answers
91
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If all the black holes in the Universe were combined into one supermassive black hole, what would its diameter be?
I am curious to know if anyone has ever sat down and calculated what the diameter of a black hole would be, in kilometers, if it were to contain all the mass of all the black holes that are currently ...
- 478
3
votes
1
answer
619
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How fast is the edge of the observable universe expanding from the Earth?
If the universe is expanding at 73 kilometers per second per megaparsec, what is the fastest expansion speed that we can observe from Earth? I'm assuming that's the edge of the observable universe ...
- 51
1
vote
2
answers
655
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Calculating the size of the universe
I read the numerous threads here for example:
Lower limit of the size of the Universe? (WMAP)
Determining the size of the universe to calculate its age
Size of the universe
But I would like to try a ...
- 1,721
18
votes
2
answers
4k
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How long ago was the Universe small enough for interstellar travel?
Currently, even the nearest stars are lightyears away, and impossible to reach in our lifetimes. If space is always expanding, and was once infinitely smaller, then at what point in the past was space ...
- 719
6
votes
1
answer
171
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At any given point in the universe, are there a huge number of photons crossing paths?
If you're standing in a dark night-time place on the Earth and look up at the sky, you see stars. (About 6000, if you're in a sufficiently dark place). You're seeing photons that have passed though ...
- 161
2
votes
0
answers
234
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How to derive number of nucleons in Universe?
I understand that there are roughly $N=10^{79}$ nucleons in the visible Universe. This number comes from adding up the nucleons of $100$ billion stars in $100$ billion galaxies in the visible Universe ...
- 5,925
4
votes
2
answers
1k
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What paper can I cite for the estimated number of atoms in the observable universe to be lower than $10^{82}$?
The title contains the whole question. I am a logician in theoretical computer science and want to use the estimated number of atoms in the observable universe to show what a ridiculous amount of ...
1
vote
1
answer
231
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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
6
votes
2
answers
13k
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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
47
votes
2
answers
41k
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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)...
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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?
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