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Results tagged with universe
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user 1241
The universe refers to the cosmos; all of space-time and that which exists as part of it. Alternatively, it can refer to the observable universe, which only contains the part we can see. Questions tagged with this should ask about physics at scales the size of the universe or specific properties of the universe
6
votes
Alternative theories to the big bang?
There is virtually complete consensus among astrophysicists that the Universe is expanding, that it used to be much hotter and denser, and that various observed effects such as the microwave background … We think that we know quite a bit about what the Universe was doing over a wide range of times "after $t=0$," but we have absolutely no idea what happened "at $t=0$." …
- 20.1k
9
votes
What happend with the light from all the galaxies visibles from an earth telescope?
If the Universe is uniform, the number of such sources is proportional to $R^2\,dR$. … The Universe has a finite age, which means we can see out only to a finite distance. …
- 20.1k
4
votes
Have CMB photons "cooled" or been "stretched"?
I think the best way to think about it is that the sentence "the photons have cooled" is simply describing a fact, not explaining that fact. At early times, the photons at any given location had a the …
- 20.1k
19
votes
How can a quasar be 29 billion light-years away from Earth if Big Bang happened only 13.8 bi...
In the expanding universe, you have to be a bit careful to define exactly what you mean by distance. … So pretty much by definition, there can't be any contradiction between that distance and the age of the universe. …
- 20.1k
36
votes
Accepted
What has been proved about the big bang, and what has not?
The redshift (actually $1+z$) is just the factor by which the Universe has expanded in linear scale since the time in question, so nucleosynthesis occurred when the Universe was about a billion times smaller … The age of the Universe (according to the standard model) at that time was about one minute. …
- 20.1k
8
votes
Is spacetime simply connected?
To take a simple example, imagine that the universe is geometrically flat but has the geometry of a 3-torus. … The result is negative: we don't live in a multiply-connected universe with a sufficiently short length scale to be observable. …
- 20.1k
21
votes
Accepted
Shape of the universe?
This means that, if we do live in a 3-sphere Universe, the radius of the sphere is very large, and the distance you'd have to travel is much larger than the size of the observable Universe. … Even if that weren't true, the fact that the Universe is expanding would make it hard or impossible to circumnavigate the Universe in practice: no matter how fast you went (short of the speed of light) …
- 20.1k