Questions tagged [universe]
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
83
questions
1
vote
1
answer
34
views
Question about light and distance
If we see into the past with light and distance travelling so we can’t see things how they are currently, only how they were in the past; and James Webb took a photo from the beginning of the universe ...
- 11
2
votes
0
answers
76
views
An unusual calculation of our universe's age? [closed]
Does the following make sense? And has anyone else come
across this odd ~’cosmological coincidence’ before?…
…If we posit that our total universe mass is:
(1) $$M_{U}=\frac{{M_{pl}}^4}{{M_{p}}^...
- 149
1
vote
0
answers
71
views
How big was the universe after inflation? [duplicate]
If we assume the universe is a closed 3-sphere, how big was the universe after inflation, compared to nowadays? Was, relatively, most space already there? If we envision the universe as a 2-sphere, a ...
- 450
0
votes
0
answers
100
views
Movement of galaxies vs expansion of space
I can readily accept the theory that the universe is expanding as a mathematical model to explain the fact that all galaxies are moving away from each other, but I have difficulty understanding ...
- 1
2
votes
5
answers
503
views
What is the branch of physics that asks the question 'what was before the Big Bang'?
What is the branch of physics that asks the question 'what was before the Big Bang', assuming the Big Bang is truly what happened at the beginning of the universe? If there could be a better model ...
- 421
0
votes
0
answers
39
views
Planck time - what would I see? [duplicate]
Impossibly hypothetical, but to communicate the question: when the universe "ticks" a plank second, what does a particle do? I'd imagine the natural conception that it moves from position a ...
- 149
0
votes
0
answers
30
views
Complete Old Figure of Friedmann Universe Models
I have found this quite old figure (R. D'Inverno, Introducing Einstein's Relativity. Clarendon Press, 1992) that I want to modernize for a course using TikZ/LaTeX.
My questions are:
Do you know if ...
- 181
0
votes
0
answers
84
views
Numerical solution for the Mukhanov-Sasaki equation with Bunch-Davies vacuum state
I have the Mukhanov-Sasaki equation in terms of $u_k$
\begin{align*}
u''_k(\tau)+\left(k^2-\frac{a''(\tau)}{a(\tau)}+f(\tau)\right)u_k(\tau)=0
\end{align*}
and also the initial condition from Bunch-...
10
votes
6
answers
4k
views
Why do we say that temperature of Universe is around 2.7 K?
I am little confused, so please correct me if I am wrong.
Temperature of Universe is calculated using cosmic microwave background and it is around 2.7 K.
The cosmic microwave background is the relic ...
0
votes
0
answers
48
views
Big Bang as stretching space time?
I am still new to researching the big bang so please be patient. I am having trouble envisioning the expansion. As I understand under current theory it is not to be thought of as a singularity ...
- 101
1
vote
0
answers
44
views
Asymptotic development of the black-hole metric
In the Kruskal-Szekeres extension of the Schwarzschild metric parallel universes appear. In a couple of questions on this site, for instance: Where does the parallel universe in the Penrose diagram ...
- 9,778
-3
votes
3
answers
194
views
David Deutsch says "number of atoms in universe is finite", but then says "number of programs of all finite lengths is infinite". Contradiction? [closed]
From book "Fabric of reality" by David Deutsch (page 127 chapter 6 "universality and limits of computation").
We know from quantum theory that all such variables are quantized, ...
- 129
2
votes
2
answers
477
views
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
1
vote
0
answers
60
views
Is the universe closed or flat?
Apparently there is a tension in the measuring of the curvature of the universe (https://arxiv.org/abs/2307.07475) as apparently in 2018 the Planck collaboration got a series of results consistent ...
- 2,462
-2
votes
2
answers
95
views
Since the instant of the big bang, has the progression of the universe been entirely determined?
[Note I am asking up to, but not including, consciousness as this bleeds into philosophy and is a much messier question]
Assuming that the laws of physics have remained constant across space & ...
- 460