All Questions
Tagged with cosmology reference-frames
97
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8
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429
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Are the mass, diameter and age of the Universe frame dependent?
Mass of the observable Universe is known to be $1.50×10^{53}$ kg. Age is approximately known to be 13.7 billion years.The observable Universe is a sphere with diameter of roughly $8.8\times10^{26}$ m.
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Is the size/age of the universe dependent on your velocity? [duplicate]
As Photons do not experience time or space, then according to my thought experiment, all photons must occupy some kind of singularity as well as what WE observe from earth.
I was also thinking that ...
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Clocks at different redshift: does calculating luminosity distance shift the frame of reference?
Luminosity is energy per time.
When we calculate a luminosity distance, using angular diameter distance times $(1+z)^2$, I think we are correcting the energy (from redshifted photons) by $(1+z)$ and ...
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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 ...
user371657
3
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3
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Trying to confirm that the trace of the energy-momentum tensor divided by the energy density is NOT invariant
I am analyzing this question in the FRW universe with a perfect fluid.
The trace of the energy momentum tensor $$T^{\mu \nu} g_{\mu \nu} = \rho - 3p $$ is of course an invariant quantity. It does, ...
- 57
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What would happen if we did a Newton's bucket experiment in the closest accessible approximation to "empty space?"
I will get right to the question; for readers unfamiliar with its genesis, I append a background section below.
I want to know how testable the prediction is that the water in a rotating bucket would ...
- 81
1
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4
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431
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Is there anything truly "stationary" in the universe? [closed]
Ok, so I read this question and it got me thinking about something. Is there anything genuinely stationary in our universe? What does it mean to be stationary or devoid of any motion? If there isn't ...
- 119
3
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CMB dipole anisotropy maping to earth visualization
I do not see how this dipole anisotropy is due to the motion of the earth (and thus a doppler effect). Does anyone have a visualization of how this maps onto the earth and the motion of the earth such ...
- 460
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Peculiar velocities, density gradients and geodesic motion [closed]
I am studying cosmology and I have learnt that the galaxies in the universe can be represented by a pressureless fluid. Therefore, they have a geodesic motion (the so called matter frame). When ...
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Why Space is non-uniform and anisotropic with respect to non-inertial references frames?
Why is space non-uniform and anisotropic with respect to non-inertial reference frames? Please explain with suitable examples.
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Wouldn't the cosmic background radiation (CMB) produce drag and thus create a preferential inertial frame?
Because the CMB is everywhere and is isotropic, if an object would have a certain velocity, it could have a pressure differential produced by the CMB which would produce drag till it would stop with ...
- 2,035
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If the universe expands uniformly in all directions, wouldn't that make the basis for an universal and absolute "now" and reference frame? [duplicate]
Let's consider a universe with constant expansion for simplicity's sake. In such a universe, the Hubble Parameter drops to half its value after double the time. If it happens to be 70 km/s/Mpc today, ...
- 139
-1
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3
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How "accurately" does the CMB tell the age of the universe?
Just to clarify, I am not asking about clock accuracy per se at all. The reason I am asking this question stems from the fact that on this site, most questions about the age of the universe answer ...
- 29k
2
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5
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The location of the exact center of the observable universe
If simultaneously in every direction, I were to precisely measure the distance to the edge of the observable universe (not: the physical universe), then would I find myself exactly in the center with ...
- 137
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Why is the CMB's frame not rotating?
I have read this question:
The existence of a CMB frame asserts that there exists a global frame in which the universe is (approximately) space-translationally and rotationally invariant (though not ...
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