Questions tagged [cosmology]
The study of the large-scale structure, history, and future of the universe. Cosmology is about asking and answering questions about the "big picture" - the extent, origin, and fate of everything we know.
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What if the size of the Universe doubled?
My question has a silly formulation, but I want to know if there is some sensible physical question buried in it:
Suppose an exact copy of our Universe is made, but where spatial distances and sizes ...
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spacetime expansion and universe expansion?
First of all, does the expansion of spacetime solely cause the expansion of universe?
Secondly, if spacetime is the sole cause, do objects(matter with mass) themselves expand?
Thirdly, by spacetime ...
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Does the number density of photons $n_\gamma\approx 10^8 \:\mathrm m^{-3}$ refer to CMB photons only?
When we talk about the present-day number density of photons ($n_\gamma\approx 10^8 \:\mathrm m^{-3}$) in the universe do we mean the number density of CMB photons? I mean there are other sources of ...
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How does the formation of a solar system not break the second law of thermodynamics?
Please forgive: I am a layman when it comes to physics and cosmology, and have tried finding an answer to this that I can understand, with no luck.
As I understand it, the solar system evolved from a ...
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Is it possible that galaxies' redshift is caused by something else than the expansion of space?
I was thinking that maybe photons loss energy naturally when they travel great distances.
Or maybe the mass of all matter is increasing over time and therefore photons emitted in the past are ...
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How is the expansion of space distinguishable from objects moving away?
Suppose you are standing 5 feet (1.5 m) away from me. Then I move 10 feet (3.0 m) further away. Now you are at 15 feet (4.5 m) distance from me.
You say I moved. I say no; the space between us has ...
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Why are neutrinos ruled out as a major (or even sole) component of dark matter?
A number of times I have encountered in text-books and articles that neutrinos might contribute only a small fraction to dark matter. The reason has to do with the fact that if all of the dark matter ...
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According to Hubble's Law, how can the expansion of the Universe be accelerating?
Scientists today think the expansion of the universe is accelerating.
According to Hubble's law, objects further away are moving faster than objects closer to us. The further away an object is, the ...
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Will the night sky eventually be bright?
I have read that the night sky should have been bright because every spot should end up pointing to a star in the infinite universe but this is not the case because the universe is expanding. I am ...
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How is dark energy consistent with conservation of mass and energy?
I initially thought that dark energy must in some way violate conservation of mass and energy since the component of the energy density of space that comes from dark energy is constant, and space is ...
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Is the Fine Stucture constant constant?
I have read that the fine structure constant may well not be a constant. Now, if this were to be true, what would be the effect of a higher or lower value? (and why?)
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How is Doppler redshift of distant galaxies established?
Doppler redshift of distant galaxies gave first hint that the universe is expanding. I am curious to know how this redshift is actually measured and interpreted from observation. Suppose I observe ...
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Dumbed-down explanation how scientists know the number of atoms in the universe?
It is often quoted that the number of atoms in the universe is 10$^{70}$ or 10$^{80}$.
How do scientists determine this number?
And how accurate is it (how strong is the supporting evidences for it)...
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Hubble's law and conservation of energy
If all distances are constantly increasing, as Hubble's law say, then lots of potential energies of form ~$\frac{1}{r}$ changes, so how is the total energy of the Universe conserved with Hubble's ...
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How Are Galaxies Receding Faster Than Light Visible To Observers?
We know that some galaxies are moving away from us faster than the speed of light and we know it by measuring the redshift, but how's that possible? If they're moving away say at $2c$, how would the ...
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