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While cnosam's answer is completely correct, I don't know if it really solves your confusion. The key point is that, when a photon is emitted, it knows nothing about the current size of the Universe. It is emitted at a very specific wavelength given by quantum mechanics, not by cosmology. Traveling through expanding space subsequently increases its ...


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When calculating redshifts, we usually look for signature features in astronomical spectra, usually emission or absorption lines. For example, the universe contains lots of hydrogen. From quantum mechanics, we know that hydrogen has many different energy states which are fixed. This means it can only emit photons with a particular set of wavelengths (these ...


1

Firstly, you must know that there are many models for inflation which give different results to your a) and b) questions, and we still don't know which is the right one. I'll try to answer regarding the most accepted and simple models. a) During the period of inflation the distance between two separated points in the Universe increased at least ...


2

If cosmological expansion applies on the scale of the earth moon system, then in some short period of time $\delta t$ the distance between the earth and moon increases from $r$ to $r+\delta r$. So the force of gravity between the bodies changes to: $F+\delta F=\frac{GMm}{(r+\delta r)^2}\approx\frac{GMm}{r^2}\left(1+\frac{\delta ...


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No, we will always be able to see farther than the Hubble sphere (in theory). This spacetime diagram — taken from Pulsar's rendering of Davis & Lineweaver (2003)'s Figure 1, in this excellent answer — can help visualize it: Coordinates In this figure, time increases upward, we're the vertical line in the middle, Big Bang is the bottom line, and our ...


0

The initial energy to effectively fuel this expansion came from the Big Bang. Energy is not then continuously required to fuel further expansion. The temperature of the universe may decrease due to expansion, but the rate of expansion is accelerating due to currently unobserved dark energy, according to common theory. If the repulsive forces from the dark ...


4

The cosmological redshift of a galaxy is not interpreted as being due to the velocity of that galaxy away from us (the special relativistic interpretation), but rather as being being due the effect of the expanding space on the traveling photon (the general-relativistic interpretation).$^\dagger$ This expansion in turn makes the galaxies recede from us at a ...


0

You say right as Hubble's law state that farthest the galaxy is faster it is receding from us. $v=Hl$. H is Hubble constant. $H(t)=\frac{\dot{a(t)}}{a(t)}$, a(t) is scale factor. Experimentally it is confirmed by observing the radiation from distant object. Due to Doppler's effect observed frequency of light will be different from emitted one and it depends ...


1

What is a simple explanation to the fact that the universe is expanding? Show them a star map and point out the galaxies and the fact that it is a projection of three dimensional space to an image. Astronomers and astrophysicists have spent a lot of effort measuring the behavior of the galaxies, their motions relative to each other and to the solar ...


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The redshift of very distant galaxies is mainly due to the expansion of space whilst the light has been travelling towards us. The basic relationship (at non-relativistic speeds) is that $v = H_0 d$ where $v$ is the velocity implied by the redshift and $d$ is the distance. The constant of proportionality $H_{0} \sim 70$ km/s per Mpc. That is, a Galaxy ...


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Doppler shift distance measurements are only useful if the expansion velocity is much greater than the peculiar velocity of the galaxy, so that the latter can be neglected. As the expansion velocity is proportional to distance, we can only use Doppler shift if the measured redshift is high, that is, the galaxy is very far (as an estimate, I've seen $D\ge ...


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This paper explains the importance of physical mechanisms existing which can function as clocks at various eras. Your question is not simple Abstract We provide a discussion of some main ideas in our project about the physical foundation of the time concept in cosmology. It is standard to point to the Planck scale (located at ∼ 10−43 seconds after ...


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Well, the observations of the acceleration of the universe's expansion is perhaps the strongest argument against the Big Crunch argument. Nonetheless though, it is by no means a disproven theory- we cannot very accurately predict the future until we understand the 95% of the universe that isn't baryonic matter, the 95% that current theories have as the ...


2

Until dark energy (and dark matter) are properly understood, it is impossible to be certain of the future fate of the universe. The concordance $\Lambda$CDM model, deduced from observations of distant supernovae, from the cosmic microwave background and from baryon acoustic oscillations suggest that the expansion of the universe is accelerating and that ...


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I am not an expert to give the most proper answer but according to Hubble's law , the most distant galaxies are moving away from us faster than the speed of light, due to space expansion. This fact makes me think that also the gravitational effect of these galaxies is lost forever, and this looks to be the future of our universe. Even if a 'big crunch' ...


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Let's analyse the evolution of the curvature in the $\Lambda\text{CDM}$ model. If $\rho_R$, $\rho_M$, and $\rho_\Lambda$ are the densities of radiation, matter and dark energy, and $$ \rho_c = \frac{3H^2}{8\pi G} $$ is the critical density, then we can define $$ \Omega_{R} = \frac{\rho_{R}}{\rho_{c}},\quad \Omega_{M} = \frac{\rho_{M}}{\rho_{c}},\quad ...



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