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4

It isn't the oldest thing we can see. Most of the hydrogen, helium and deuterium nuclei that are around in the universe now, were created in the time period between a few seconds and about 15 minutes after the big bang. The abundances of these nuclei in the universe is a direct probe of the physical conditions, and time evolution of those conditions, at ...


3

Interesting question! Let me see if I can shed some light with an analogy. Btw, I shall be referring to John's answer at points. Studying or researching in astronomy is very much like criminal investigation. You have the crime, you search for clues which are used to reconstruct the events of the crime. Here, we have a crime, the construction of the universe,...


18

You are quite correct that we can't see what happened before the CMB (this time is known as recombination) but this is not unusual in Physics. For example we can't see what happens at collisions in the Large Hadron Collider. All we can see is the debris that comes flying out of the collisions. But we understand the physics involved so by measuring the ...


-1

So , according to Sir Stephen William Hawking , NOTHING existed before Big Bang , as many of you may have seen in the interview of Sir Stephen Hawking (if not I had put a link below , just check it) . But if we think deeply for a while, if our universe has started witha Singularity (Big Bang),according to Big Bang Theory , and is going to end at a ...


3

As I said there's a mathematical laws behind this approximation. We use the Friedmann equations and EFE : $$\begin{cases} 3\frac{\dot{a}^2}{a^2}+3\frac{kc^2}{a^2}-\Lambda c^2=\frac{8\pi G}{c^2}\rho \qquad(1) \\[2ex] -2\frac{\ddot{a}}{a}-\frac{\dot{a}^2}{a^2}-\frac{kc^2}{a^2}+\Lambda c^2=\frac{8\pi G}{c^2}p \qquad(2)\\[2ex] R_{ij}-\frac{1}{2}Rg_{ij}=\frac{...


1

Of course it is approximation, as any almost any measurement beyond simple counting involves approximation, but there is quite a bit of evidence based on observation fitted to known laws. The main evidence springs from fitting observations of cosmological parameters, Hubble's constant $H_0$, density $\Omega$, curvature $\Omega_k$, and dark energy $\Omega_\...


0

To add to some other answers, it is possible for a surface to be intrinsically flat but also to be closed. A ball has positive curvature, but a ring like a donut or a life preserver has zero overall curvature, with the locally negative bits exactly cancelling the locally positive ones; you can even divide it up into a neat checkerboard. If you imagine a ...


2

The current hydrogen density in the universe is approximately $0.04 \times 6$ atoms per cubic metre. If we wind the clock back, this number goes up as $(1+z)^3$, where $z$ is the redshift. The CMB formed at $z \sim 1100$, thus the number density of electrons in the universe just prior to this was $n_e \sim (1+1100)^3 \times 0.04 \times 6 = 3.2\times 10^{8}$ ...


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