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1 vote

If we consider the universe to be four-dimensional, does the Big Bang lie in its center?

Some other answers say the universe isn't embedded in a background space, but I think that misses the point; the universe doesn't have to be embedded in anything for this idea to make sense. If the ...
benrg's user avatar
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2 votes
Accepted

If we consider the universe to be four-dimensional, does the Big Bang lie in its center?

There are two important points in here. The first was raised in a previous answer (and I'll comment on it also), but there is another nuance. The Big Bang is not a point in spacetime Yeah, that's ...
Níckolas Alves's user avatar
0 votes

If we consider the universe to be four-dimensional, does the Big Bang lie in its center?

Differential topology allows us to describe a 4 dimensional (3spatial+1temporal) space expanding without needing to embed it in a higher dimensional space. The balloon is a common metaphor for an ...
Cort Ammon's user avatar
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2 votes

Are there any observations from the beginning of the universe until the CMB?

In astronomy there are broadly 4 ways you can "observe" or collect information about the universe (which is what I assume you mean by "observational evidence"). By receiving ...
ProfRob's user avatar
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1 vote

Does the Schwarszchild solution require the cosmological constant to stop it from expanding?

The original published version of the GR field equation in 1915 didn't contain a cosmological constant (Λ) term. Schwarzschild found his solution in 1916. Einstein proposed adding the Λ term in 1917. ...
benrg's user avatar
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-1 votes

Does the Schwarszchild solution require the cosmological constant to stop it from expanding?

When Einstein used GR with the Hubble constant, he found the age of the universe to be about 1.5e9 years, which at the time they thought was about the age of the Earth (Einstein, "The Meaning of ...
Ric's user avatar
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4 votes

Does the Schwarszchild solution require the cosmological constant to stop it from expanding?

The Schwarzschild solution sets the cosmological constant to zero. The expanding universe is a feature of when you model a universe with a homogenous and isotropic matter content. The Schwarzschild ...
Níckolas Alves's user avatar
-4 votes

Is the light from the stars within our Galaxy redshifted?

I believe that all nearby galaxies are blue-shifted. I believe that the galaxies that are just beyond them are blue-shifted also, just not observable so yet. I believe that all galaxies currently ...
Bobby's user avatar
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1 vote

Conformal Flatness in FLRW cosmology and interpretation of Stress Energy Tensor

In the FLRW model, you assume isometry and homogeneity of spacetime. Imposing these conditions on the stress tensor forces you to consider a perfect fluid stress tensor. You can show this rigorously ...
Níckolas Alves's user avatar
2 votes
Accepted

Does dark energy work on the principle of anti-gravity, i.e. repulsive gravity?

There is a sense in which you could say that the acceleration of the Universe's expansion is a kind of anti-gravity, in that the Universe is behaving effectively like there is a repulsive force ...
Andrew's user avatar
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0 votes

Solutions for nonrelativistic-matter perturbations

Deep in radiation domination ($y\ll 1$), the two solutions are $\delta=1$ and $\delta=\ln a$. Physically, these solutions describe the effects of particle drift in the complete absence of peculiar ...
Sten's user avatar
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0 votes

Solving Olbers' paradox with the expanding universe

As it seems, the problem is in geometric progression. We apply the sum of geometric series formula. With $\omega_0$ being initial parameter and r being blocking factor which already seems to be less ...
aki Ybhandary's user avatar
18 votes

Redshift of the CMB

It is the latter. The redshift at which electrons combine with photons is deduced from a calculated temperature at which that (re)combination occurs and the temperature of the microwave background now ...
ProfRob's user avatar
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5 votes

Redshift of the CMB

The redshift is measured from the shift in the peak of the blackbody spectrum of the CMB as a function of expansion factor (I think that the original reference for this is Tolman 1934). Indeed the ...
Kyle Oman's user avatar
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2 votes
Accepted

Cosmological redshift and distance calculus

One important point to clarify is that the idea that "z could be so high that the velocity would be relativistic" doesn't really make sense from a physical perspective. Making a comparison ...
Benjamin Horowitz's user avatar
0 votes

Can the age of the universe actually be calculated through Hubble's constant?

That's not even true for the Hubble parameter $\rm H(a)$, let alone the Hubble constant $\rm H_0$. The age of the universe is $$\rm t(a)=\int_0^a \frac{d \bar{a}}{\bar{a} \ H(\bar{a})}$$ where $$\rm H(...
Yukterez's user avatar
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2 votes

Can the age of the universe actually be calculated through Hubble's constant?

If we plot a graph of the distance between say two galaxies in the universe versus time, then the gradient of that graph is the speed, given by Hubble's law. If I have a point on that curve now, with ...
ProfRob's user avatar
  • 132k
1 vote

Does the zero-point energy get less dense as space expands?

The zero point energy is defined as the minimal energy a system may have. In vacuum, it "should" be 0 according to classical physics. In quantum mechanics, it is still a controversial ...
Joshua's user avatar
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2 votes

Horizon problem, what if our observable universe is roughly equal to the whole universe, especially in early times?

It is possible in principle that the observable Universe is the entirety of the cosmic mass distribution. This would be really surprising, since it would place us right at the center of the Universe --...
Sten's user avatar
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