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4

The Big Bang was originally defined as the zero time limit of the FLRW metric, so it's a mathematical construct and not primarily something physical. We have chosen to apply it to the zero time limit of the universe because we thought the FLRW metric was a good description of the universe, but then inflation gatecrashed the party and spoiled the fun. So if ...


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In my opinion it all hinges on whether one includes quantization of gravity or not. The classical Big Bang just uses General Relativity and solutions of its equations. A singularity has a well defined meaning in the classical approach. As physicists are convinced that the underlying framework of nature is quantum mechanical it is expected that gravity ...


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Galaxies would appear stretched along the line of sight, not jumbled. Let's say a galaxy is ten million light years away and, as you proposed, is 100,000 light years across and we see it nearly edge on. The front of the galaxy will appear to us as it did ten million years ago and the back of the galaxy as it did 10,100,000 years ago. Thus, if the galaxy ...


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I think the very short answer is: galaxies are very small, indeed tiny, compared to how far away they are, and secondly, compared to the size of the universe. The answer to the spirit of your question, is that simple! "Galaxies are tiny." You're used to hearing "galaxies are 100,000 light years across!" but that's a piffle compared to either the size of ...


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I suspect that the nice rotational formations of galaxies we see come from galaxies that are oriented in parallel with our solar plane so that the light arrives almost synchronously. Considering we are talking of gravitational forces the "almost" could cover a large window, the distortions not being too great to lose track of the shape. A galaxy whose ...


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Galaxy rotation happens at a very slow rate (compared to the speed of light). Let's suppose you are observing a galaxy edge-on that the delay from the farthest point is $\Delta t = d/c$, where $d$ is the galaxy diameter. If we take the lag from one extreme point to the other as D: $D = vt = \frac{v}{c}t$ (where $v$ is the rotational speed). You can see ...


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Well, i would say no. Why? Because an absolute center of mass would require a uniform covering (coordinate system) over the whole manifold, which, even if it exists, will probably not be on the manifold itself. An analogy would be the center of mass of a spherical surface/manifold. It would be exactly on the center of the sphere (i.e not on the sphere ...


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CPT does exchange particles with their antiparticles, so if there were a time direction associated with particles then it might make sense to say that, by CPT, the antiparticles would have to have the opposite time direction. But there's no time direction associated with particles. It doesn't even make sense to say that something is "going forward in time"; ...


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Yes, CPT is compatible with the idea that matter and antimatter are created at equal amounts. CPT is a basic theorem of quantum field theories, QFT:s. QED i a QFT and thus obeys CPT. The original QED is a theory of electrons, positrons and photons. In QCD, when a positron is produced an electron is produced at the same time (pair production). Likewise, when ...


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The most common explanation for the "matter-antimatter asymmetry of the Universe" is $\rm CP$ violation in interactions involving leptons. This scenario is usually called leptogenesis because it generates a net excess of leptons compared to anti-leptons. This $\rm CP$ violation is currently unconfirmed by experiment (though there is also not yet any evidence ...


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It's certainly possible, though on current evidence it looks unlikely. The past bound isn't really a bound in the usual sense of the word, but instead it's a singularity. If we solve Einstein's equations for the universe with a few apparently plausible assumptions we find that the universe is described by a scale factor, normally written as $a(t)$, and as ...


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I will reply to Why isn't the CMB at the edges of the universe? Why is it flying around in the middle? The occurrence of space time and matter after the Big Bang happened to all points in our universe. The expansion of space happened at the same rate outwards for all points of the universe. All points of the universe 380.000 years ago had ...


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At a basic level: The universe, in the beginning was very hot. So hot in fact that there were no atoms, only electrons and protons and neutrons and photons flying around. The photons were scatting off of the electrons and protons, as they interacted strongly because the electrons and protons are charged. The universe was much like the plasma you find in ...


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There are two immediate problems with this idea. First, the acceleration due to the dark energy appears to be the same in all directions. In general relativity (and Newtonian gravity for that matter) the influence of distant matter can only cause a tidal acceleration that expands matter in some directions and compresses it in others. A uniform expansion has ...


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We do not know if the universe is closed or open, so space could very well be infinite. However, that does not mean that there is an infinite amount of space in anything. Such a conclusion does not quite make much sense in terms of a logical,mathematical (or even philosophical) argument. Take Zeno's paradox for instance: The paradox states(in summary) that ...


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Yes, but it should be stated that the cosmic neutrino background is expected to be very cold and very difficult to see. Also, note that when temperatures approach the electroweak unification scale, the electroweak force will treat electrons and neutrinos identically, and the universe will become opaque to neutrinos.


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Scientists calculated this knowing that in the time between the Big Bang and the Era of Recombination there was a large 'soup' of superheated particles, which cooled down as the universe was expanding. Atoms could not form because every time an electron tried to 'orbit' a proton it was knocked out of orbit by a high energy photon. These high energy photons ...


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The calculation is described in detail in the Wikipedia article on recombination. If you consider the ionisation of hydrogen as a reaction: $$ p + e \rightarrow H + \gamma $$ Then you can write down an expression for the equilibrium constant as a function of temperature using the Saha equation: $$ \frac{n_pn_e}{n_H} = \left( \frac{m_ek_BT}{2\pi\hbar^2} ...


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Your question is really tricky. I am going to try to discuss two of the issues in the first two paragraphs. The rest of the paragraphs will speak only purely formally about how "old" classical cosmological equations would work in the case you describe and what a physically intuitive interpretation of the singularity could be. First, without quantum ...


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The question is very speculative :-) Physics is based on models out of our experience of a world extended in space and time together with mass and energy. One example: The concept of point is already a Euclidean idealisation. It lives in the world of mathematics - not of Physics (otherwise, you fall into Democritus and QM) Indeed, in Maths, we still struggle ...



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