# Tag Info

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Even though the fabric of space is expanding throughout the universe, our solar system is not. Our atoms remain the same size. So do the planets, moons, and stars, as well as the distances separating them. Even the galaxies in our Local Group aren't expanding away from one another. The math tells about the possible solutions, but it is necessary to look to ...

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Membrane theory with string theory, quarks are actually made up of vibrating strings of energy. Each vibrate at a certain pitch. Each vibration corresponds to a certain particle, a proton, an electron, etc. They also account for the four natural forces of the universe: gravity, electromagnetism, and the stronger and weaker nuclear forces. To figure out ...

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tl;dr Because space doesn't contract inside our Solar System. Wavelength increase is proportional to space expansion The prediction of general relativity — one of the most thoroughly tested and succesful theories — is that the wavelength of observed light changes in proportion to the factor by which space expands (Lemaître 1927). If space expands by a ...

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The density of material in the interstellar medium is inferred from (i) the electromagnetic radiation it emits; (ii) its effect on electromagnetic radiation passing through it. Often these approaches are combined to learn about different "phases" of the interstellar medium - e.g. hot, cold, high, or low density, ionised or not. For example, we can ...

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The old Physics FAQ has an article on this. The interesting parts (emphasis mine): This cancellation may seem less strange if one notes that a similar effect occurs in electromagnetism. If a charged particle is moving at a constant velocity, it exerts a force that points toward its present position, not its retarded position, even though electromagnetic ...

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It is not true that GR describes changes in a scalar gravitational potential as propagating with no delay. It's actually not even true that GR describes gravity as arising from a scalar gravitational potential. Most spacetimes in GR cannot be described by a scalar gravitational potential. The thing that Newtonian gravity describes as a scalar gravitational ...

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The peaks in the temperature and polarization spectra determine the angular size of the sound horizon at the time of recombination fairly accurately: $$\theta = \frac{r}{D(z)}$$ The sound horizon, which is represented by r, is the comoving distance a sound wave could travel from the beginning of the universe to recombination and is a standard ruler is any ...

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First, some definitions. The limits of observability in our Universe are actually set by cosmological horizons, of which the "observable Universe" is just one type. These depend on not only whether can we detect the thing from Earth, but also on when was the signal produced? There are various types of cosmic horizons: The particle horizon sets a ...

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I'm not sure how universal rotation is supposed to produce dark-energy-like effects in your scenario, but if there was a rotational effect, it would operate perpendicular to the axis of rotation but not parallel to it. This would produce a clear anisotropy in the expansion of the universe, which we simply don't see. In fact, Stephen Hawking pointed out back ...

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Any and all movement is with respect to something else. If you were the only thing in the Universe, you would not know if you’re moving or not, because you would not have any reference point to define this movement from. The same holds for the Universe itself. It is expanding, that we know by looking at galaxies and seeing that most of them have a redshift. ...

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An old conundrum was why do rotating galaxies and galaxy clusters not fly apart due to centrifugal (or -petal as you prefer) force, as the gravity due to their observable mass is too small to prevent this. The advent of dark matter (and energy) helped to explain this. If the universe is rotating, their gravitational force may prevent rotation adding to its ...

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Formally, black holes are a prediction of Einstein's theory of gravity. They have been observationally confirmed. Regarding theory: The field equations of Einsteinian gravity, the Einstein Field Equations, admit solutions. The first closed form solution of these equations was found in 1916 by Karl Schwarzschild which is the massive non-rotating, uncharged ...

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The answer is reasonably simple: (nearly) all matter consists of protons, neutrons and electrons, thus of either positively, or negatively charged particles or those with no charge. The next step you need to make is to assume that for some reason whatsoever a black hole accretes more protons than electrons (or vice versa). Such process might be envisionable, ...

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$\epsilon_\Lambda={\rm constant}$ is the definition of a cosmological constant. $\Omega_\Lambda$ is not constant. In our flat, or nearly flat, universe, the energy densities of matter and radiation scale as the size of the universe cubed and to the power of 4 respectively. That means that $\Omega_m$ and $\Omega_r$ were bigger in the past, yet the sum of \$\...

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