All Questions
Tagged with space-expansion observable-universe
87
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2
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281
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Negative Horizon distance
Consider a flat universe, here, proper distance can be given by R-W Metric:
$$d_p (t_0) = c\int_{t_e}^{t_0}\frac{dt}{a(t)},$$ $t_e$ is the time when a photon is emitted from a distant galaxy, $t_0$ is ...
- 411
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64
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Horizon problem, what if our observable universe is roughly equal to the whole universe, especially in early times?
How do we know that at a time of 380.000 years, when CMB got free, the observable universe was not equal to the actual universe? Maybe they were roughly the same and couldn't that explain the horizon ...
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4
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3
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If the observable universe had only one galaxy, how would people know the expansion of the universe?
Hubble measured high redshifted galaxies to discover the cosmic expansion. In a hypothetical universe where only one galaxy exists, would there still be observational evidence for the Big Bang theory? ...
- 195
2
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2
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Why can't we see past the observable universe?
Why can't we see light from beyond the observable universe?
I've done a lot of research on this and all I've found is unsatisfactory answers and straight up nonsense.
Some claim that the universe &...
- 131
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What was the size of the observable universe at the matter-dominated era and its mass density?
For instance, at the scale factor $a=0.5$ and matter dominated era, what was the size of the observable universe and matter density?
- 476
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Does expanding universe length units also expand? [duplicate]
Information
I have read an explanation about the expanding universe which represents our universe as a metal plate that tends to expand simultaneously in all directions while being heated. One can ...
- 73
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1
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77
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How a star can move out from visible universe? [duplicate]
We see only stars whose light is not older than the age of universe. This is understood. If a star is too far away that currently we don't see it then possibly we will see it later, then the age of ...
- 362
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Hubble expansion across time dimension?
The expansion of the universe, as described by the Hubble's law, refers to the expansion of space itself. This expansion is observed in the three spatial dimensions (length, width, and height), rather ...
- 101
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55
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Big Bang and where do we stand relative to it? [duplicate]
Maybe dumb question, not sure, but I would need some help here to understand.
https://theglobestalk.com/james-webb-telescope-see-back-in-time/
So according to physics we can look back in time ...
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Can we infer the size of the whole universe from its expansion rate? [closed]
If the universe inflated to 100 billion km in its first second, that suggests only 1/160,000 of it was observable from any point at that moment. The expansion rate slowed after that, of course, but ...
- 384
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25
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Does only the space region movement due universe expansion affect the possibility of viewing a star?
My question is maybe simple and easy to answer because the intrinsic speed of the star affects only the final frequency of observed light but are there any tricks about the combination of object ...
- 467
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55
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Light emitted at $t = 0$
So solving for the scale factor from the Friedmann equation we can then use it to calculate proper distance via
$$d_p(t_o) = c \int_{t_e}^{t_o} \frac{dt}{a(t)}$$
For a particular universe $a(t)$ is ...
- 161
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138
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When will the particle horizon reach its limit of 63 billion light years?
In the far future, the particle horizon will reach 63 Gly，so when will that time? Just like today's universe time is 13.82 Gyr and the particle horizon is 46.5 Gly, how many years will the particle ...
-4
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1
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Cosmos at minimum 250x bigger than our observable Universe, so why then the need for a Big Bang?
Please correct me If I'm wrong but does not the BB only refers to our light speed limited observable Universe (OU) from our home position?
Also it is estimated that the Cosmos is minimum 250 times the ...
- 4,170
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663
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Why don't we see the big bang?
excuse my understanding, my brain is melting.
So I understand that pictures of far away objects is like viewing the past.
and I think I pretty much get that the big bang was in every direction since ...
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