# Tag Info

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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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One of ideas associated with string theory is the ekpyrotic universe. This starts with brane cosmology i.e. the idea that our universe is a four dimensional brane floating around in the ten dimensional string theory spacetime. There will be many such brane worlds and the ekpyrotic idea is that a collision between two branes would appear just like the Big ...

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Conformal space is nice because in it, photons have straight world-lines, so we can easily see what we must do to achieve causal contact between two points in the CMB, after the physical time $t_i=0$ of the initial singularity, but before the physical time $t_{\text{CMB}}$ of decoupling. Since we have $$d\tau=\frac{dt}{a(t)},$$ ...

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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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The statement that at the beginning of the universe energy/mass was concentrated in a single region under conditions of extreme temperature and density is usually extrapolated from experimental data on the energy/mass content of the universe and its expansion, which is then analyzed through the classical (i.e. non-quantum) theories of general relativity and ...

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In general relativity, the field equation relates the metric (through the associated curvature tensor) to the stress energy tensor $T^{\mu\nu}$. This can be interpreted as a flux of energy and momentum in spacetime (i.e. integrating $T^{\mu\nu}$ over a spacetime hypersurface, like a three dimensional hypersurface of constant time, tells you the rate at which ...

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EDIT: if i got it right , the answer to my question has to do with space-expansion , but to be honest i can't understand why. In an hypothetical situation that universe stops expanding and starts shrinking, we won't be able to detect such radiations anymore? One has to think of our three dimensions we live in and the effect of expansion or ...

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