# Tag Info

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For relativistic time dilation to pull 13.8 billion years down to 6500 years, the object would have to have a Lorentz factor of $\gamma = 2 \times 10^6$, or be traveling at 0.9999999999998891 of lightspeed. At this speed, a collision with an interstellar hydrogen atom would yield about a PeV, or 100x the energy released per collision at the LHC. It would ...

3

Pure states are a convenient abstraction for studying tiny, specially-prepared quantum systems. States of complicated systems are never pure. One makes (very small) systems pure by careful preparation. For example, a simple spin by means of a Stern-Gerlach magnet and a screen where only the up particles can pass. More complex systems need more complex ...

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The primordial helium was not created as neutral atoms. It was created only as atomic nuclei when the baryonic matter was still ionized. Only much later the electrons started to recombine with the atomic nuclei (hydrogen and helium) and only at that point the neutral hydrogen and helium are born. But the nuclei were there earlier.

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The rate of formation is much higher in the presence of dust. There needs to be a mechanism for the energy of formation of the hydrogen molecule to be dissipated. Dissipating energy via a photon involves a forbidden transition. Instead, the energy can be transferred to the vibrational lattice of a dust particle. See The Interstellar Abundance of the ...

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I read this question but I didn't understand the physics equations used in the answer. Let me offer a simplified explanation. The origional Big Bang cosmology asserts that the universe is expanding, which if true means that the proper distance $D$ between any 2 points is increasing. Since you can think of this expansion as "space itself expanding," then ...

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The size of the universe is given by a scale factor, normally written as $a(t)$, that is a function of time and is calculated by solving Einstein's equation for an isotropic homogeneous universe. Once we've calculated $a(t)$ we can differentiate it wrt time to get $\dot{a}(t)$ and use this to calculate the recession velocities. The scale factor is a ...

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Just because space is curved, it does not mean it is a subspace of a higher dimension. All space is curved, even euclidean space. Flatness is a relation between a curvature of some subspace and the space it is part of. There is the wonderful image of space expanding equally as one might blow up a balloon, but this image might be as easily explained by ...

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We don't know how the relationship between gravity and dark energy changes over time as gravity decreases (from the rest of the universe), because one cancels out the other to a degree we don't know. It is not reasonable to assume that as the universe expands more strings of dark energy magically appear to keep the density constant. Einstein originally ...

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The dividing line meets at $(\Omega_m,\Omega_\Lambda)=(0,1)$. From the Friedmann equations, it follows that the scale factor $a(t)$ satisfies the relation $$\frac{\dot{a}^2}{H_0^2} = \Omega_m a^{-1} + (1 - \Omega_m - \Omega_\Lambda) + \Omega_\Lambda a^2.$$ The universe has no big bang singularity if the above expression is negative (or zero) for some ...

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There's a difference between curvature of spacetime and curvature of space. Extrapolating from what we can see around us and assuming the cosmological constant lives up to its name, spacetime will eventually approach curved de Sitter geometry, in contrast to flat Minkowski geometry or anti-de Sitter geometry of opposite curvature. This is something of an ...

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I think this is an example,universe is rotating about its own central axis.if this is the case,take a curve beaker and a flat plate with some water in them.First shake clockwise the curved beaker and then flat plate.In which,beaker or plate did the circular motion was seen about its center?I guess curved one.So,our universe is curved.

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There is a central point, the point that is the opposite to the expansion of the sphere. We can't see it, but I would assume that in a similar way to how when large stars go supernova they leave behind a black hole, and how there are black holes in the middle of galaxies, there would probably be a black hole in the centre. We would never see it, because ...

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What muddies the waters a bit are that when I tried to search for the borde-guth thing, the first result was a Christian site, and of course when it was discovered that the universe was expanding, the big bang was taken by many Christian scientists as the creation of the universe by God, and that is still the most likely explanation for why the universe ...

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This is similar to the idea that if the universe was infinite in size and infinitely old, the sky would be as bright as the sun, since every point in the sky would end on a star, somewhere in the infinite universe. Since this is not the case, it led people to conclude that the universe is either finite in size or age. Similarly, even if the universe was ...

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It is only in the absence of dark energy that the correspondence between geometrical curvature and the ultimate fate of the universe is as straightforward as you describe. Measurements (primarily of the cosmic microwave background) indicate that our universe is flat or very nearly so, which should be interpreted geometrically (i.e. in terms of the sum of ...

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The Milky Way is receding from the members of the Hydra-Centaurus Supercluster. The Hydra cluster has a red shift of 0.0548. The Centaurus cluster has a red shift of 0.0114. The Norma cluster has a red shift of 0.0157. The local group is and will continue moving away from the Hydra-Centaurus Supercluster.

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Space itself was once concentrated in an infinitesimally small point. During the Bang of the Big Bang all distances between points got bigger. If you try to measure the expansion of the universe from any point you will draw the conclusion that the expansion started from that point. It seems that the expansion happened everywhere, and nowhere at the same ...

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Remember, the Big Bang theory is just that- a theory. I predict astrophysicists will soon discover galaxies 15,20,25, billion years old. Then what?

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Other than noting that galaxies are moving away from us, we have no frame of reference in order to state how the universe is expanding. We would need to be out side the universe in order to get a description.

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One cannot simply observe edge of universe without taking in consideration of the big bang being a silent inflation rather than a large explosive inflation. As when universe was created the temperature was too hot for matter to exist thus the photons being pure energy rather than a bright explosion. Next, if the big bang happened in presence of matter ...

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You are thinking that the big bang happened in a particular point in space and then expanded outwards from that point. This is not true. The big bang happened at all points in space. This is because space itself expanded in the actual bang. Therefore each point in space has its own "horizon" of 13.7 billion light years across. This edge is due to light ...

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I think you are missing that the source is actually referring to he observable universe explicitly - just somewhat indirect: It is not obvious as it is talking about "visible/observable universe", but about "total mass of the visible matter" and "mass density of visible matter". As far as I can see, any references to mass etc in the universe are covered by ...

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Besides the comments, stars have formed well after the Big Bang. Depending on where they are in the universe, it will take a while for us to see them.

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