Astronomy Stack Exchange
Astronomy Stack Exchange

Questions tagged [cosmology]

Questions about the origin, history, evolution and fate of the Universe.

548 questions
26
votes
7 answers

How do we know the laws of physics are the same throughout the universe?

How do we know the laws of physics are the same throughout the universe? Intuitively I would say they would vary in two natural ways: the constants in the equations may vary or the math in the equations may vary. As a guess they could change over a…
qwerty10
  • 395
  • 3
  • 8
11
votes
2 answers

How long would it take for a rogue planet to evaporate in the late stages of the Universe?

I've read once a popular science book, in which the author calculated how long would it take for the most massive black holes to evaporate because of Hawking radiation. He claimed that after that time the Universe will be the soup filled only with…
Danubian Sailor
  • 1,538
  • 10
  • 22
9
votes
4 answers

Does the universe have a celestial north?

You are away from the Earth in one part of the universe and looking at a galaxy in another part of the universe, then which way is up? Does the universe (or near universe) have a celestial north? If you took a picture of that galaxy, then is there…
John Canon
  • 670
  • 4
  • 13
8
votes
2 answers

Is everything quantum entangled?

So, I am learning about quantum entanglement in my quantum course and had a thought. If the Big Bang is the creation of everything - time included, and this came from a single "source". Would it not follow that all particles in the universe are…
sci-guy
  • 321
  • 3
  • 6
6
votes
1 answer

To what extent are structure formations unexplained?

I hear conflicting claims about our understanding of the structure formation in our universe. I heard that ΛCDM explaines well the large scale structure of the universe i.e. Comparison of the model with observations is very successful on large …
Jani Kovacs
  • 163
  • 3
6
votes
2 answers

what is a Friedmann model?

Can you explain what is a Friedmann model to a layman? And also give some examples of Friedmann models, specially I would like to know if the lambda-CDM model is considered a Friedmann model.
set5
  • 559
  • 1
  • 5
  • 13
5
votes
2 answers

What is the furthest object in the observable universe?

My question is about furthest object in the observable universe except Сosmic microwave background.
bellicose
  • 61
  • 2
5
votes
3 answers

If the Universe is infinite, why isn't it of infinite density?

If we make the assumption that the Universe is infinite, and has an infinite number of hydrogen atoms, then why is it not of infinite density - because, under Schrodinger's wave equation the probability of an electron being at any given point is…
adrianmcmenamin
  • 2,681
  • 15
  • 29
5
votes
1 answer

Minimum size of closed universe that satisfies ΩK < 0.005

According to this Wikipedia article: https://en.wikipedia.org/wiki/Shape_of_the_universe Results of the Planck mission released in 2015 show the cosmological curvature parameter, ΩK, to be 0.000±0.005, consistent with a flat universe. If we assume…
JeffB
  • 53
  • 3
4
votes
2 answers

What happens if there were only ordinary matter in the universe? Would the universe expand constantly? or will it decelerate?

This question hit me when I was watching 'Cosmos by Neil deGrasse Tyson' explaining how the universe is expanding and how it accelerates because of dark energy and dark matter, then I asked myself what if there were only ordinary matter in the…
Why am I here
  • 41
  • 1
4
votes
1 answer

Puzzle about proper distance

So I tried deriving the radial co-moving coordinate formula to an observable galaxy for which the light observed at time $t_o$ was emitted at time $t_{em}$. i.e $r_0=\int_{t_{em}}^{to} c/a_{(t)} dt$ I tried deriving it without thinking about the…
CosminA
  • 63
  • 2
4
votes
1 answer

Critical density of the universe (no, not that one)?

I seem to recall reading something that said if the density of the universe was off by as little as one atom per cubic meter, the universe, as we know it, would not exist; one less and there wouldn't have been enough gravity to form galaxies and…
BillDOe
  • 1,371
  • 7
  • 16
4
votes
1 answer

Missing Terms in Weinberg's treatment of perturbations on Newtonian Cosmology

I was reading Appendix F of Steven Weingberg's book "Cosmology". In this Appendix he works out the perturbations to a cosmological fluid described by non-relativistic hydrodynamics and Newtonian gravity. It turns out that the first order…
Spencer
  • 41
  • 6
4
votes
1 answer

Assumptions necessary for the strong form of Olber's Paradox

From Wikipedia, here's Lord Kelvin's statement of Olbers' Paradox: Were the succession of stars endless, then the background of the sky would present us a uniform luminosity, like that displayed by the Galaxy – since there could be absolutely no…
kuzzooroo
  • 369
  • 1
  • 4
3
votes
1 answer

Why is WR124 not brighter?

Wikipedia says the Wolf-Rayet star WR124 is 44,700 degrees, and is 562,000 times brighter than our sun. But the Stefan-Boltzmann Law says luminosity per sq meter is proportional to the temperature $T^4$. It's about 8 times hotter than Sol, so the…
Jack
  • 47
  • 2
1
2 3 4