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6

I though I would discuss the transition from radiation to matter dominated phases and from there to the dark energy phase. A fair amount of this can be discussed with just Newtonian mechanics. General relativity changes this by some subtle means, but as a coarse grained view, to borrow a stat mechanics term, Newtonian mechanics captures a lot of this. We ...


16

The title and the text actually ask two different questions. While Kyle Oman and Thriveth answer the title excellently, I'll address the question in the text which asks "Why did the Universe expand in the first place, before dark energy (DE) started to dominate". The answer to this is inflation (we think). The first fraction of a second after the creation ...


9

The short version: The amount of matter in the Universe is fixed, so as the Universe expands, matter density will drop because the same amount of matter will be spread out on more space. Dark Energy, on the other hand, is (by definition) constant or almost constant in density. This means that no matter how dilute the Dark Energy is, if it waits long enough, ...


19

Let's start partway through the expansion of the Universe in the matter dominated epoch. At this time the energy density is dominated by matter, but the dark energy and radiation components are still present, just relatively small. The Universe is expanding, but the expansion is gradually slowing down. As the Universe expands, the density of matter scales ...


8

The most distant object that light we emit today can reach in the distant future is at the event horizon $$eH(t) = a(t)\cdot \int_{t}^{t_{max}} \frac{c\cdot \text{d}t'}{a(t')}$$ which is now approximately 17 billion lightyears away, see the future light cone in comoving coordinates which converges to this distance: If the light was emitted at the big ...


1

The metric for the de Sitter spacetime, which approximates the observable universe in stationary coordinates is $$ ds^2~=~-\left(1~-~\frac{r^2\Lambda}{3}\right)dt^2~+~\left(1~-~\frac{r^2\Lambda}{3}\right)^{-1}dr^2~+~r^2d\Omega^2 $$ The important term is $$ \left(1~-~\frac{r^2\Lambda}{3}\right), $$ that looks a bit like the Schwarzschild factor. This ...


0

Well first of all, Considering dark energy and other factors, what is the most distant object light could reach? If you are talking about an OBJECT like stars, galaxies etc... the farthest object we can "see" is located 13.39 bilions light-years (Galaxy GNz-11, you can search that) The 11 on the name indicates its redshift z=11. ...


-3

Just an idea I'm playing with, There is no dark energy/dark matter. The universe is not expanding into “infinite nothing”, but instead reducing into the amount of space it occupied at inception. Matter is reducing in scale because there is nothing in the universe requiring it to maintain a static size at the subatomic level. The gravitational effect of ...


-1

It changes. In fact, after 3000 billion years, the constants will have changed so much that all the current structures in the universe will be destroyed, including quarks and electrons.


1

Welcome here. From your profile I see that you are at the beginning stages of learning physics. This is an arduous process that needs a lot of elbow grease in solving problems and/or doing experiments in order to get a basic intuition for the subject. Here is a simplified answer to your questions: Why do most theories about what Dark energy and Dark ...


7

We want the Newtonian limit of the Einstein Field equations for nonzero vacuum energy(=cosmological constant). As $\rho_\mathrm{vac}=\Lambda/4\pi G$ is a mass(=energy) density, Poisson equation is $$ \Delta\Phi=4\pi G\rho(\boldsymbol r)-\Lambda \tag{1} $$ If we assume spherical symmetry, and point-like source $\rho\sim\delta(\boldsymbol r)$, the ...


3

You get an extra term that increases with r: $$a = -\frac{G\cdot M}{r^2} + j\cdot r$$ with j as the repulsive component.


9

The Big Bang Theory is a much more general and less specific description of our theory about the origin of the Universe than the $\Lambda{\rm CDM}$ model (by the way, I don't think that the hyphen is written in that acronym). The Big Bang Theory says that the Universe was expanding and the distances between two places where galaxies sit today used to be ...



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