# Tag Info

18

This seems to be a common misconception about the big bang. At present our theories can only suggest what happened AFTER the "bang". We cannot formulate what occurred AT the singularity with our current knowledge of physics. At a small neighborhood around a spacetime singularity quantum gravity becomes important and we simply have no clue at present how ...

12

As far as theory goes, the Cosmic Neutrino Background (CvB) was created within the first second after the Big Bang, when neutrinos decoupled from other matter. Nevertheless, while the universe was still hot neutrinos stayed in thermal equilibrium with photons. Neutrinos and photons shared a common temperature until the universe cooled down to a point where ...

8

I thought about this a little more since I prompted your question and there are a couple of other complications worth noting. This may be more like a comment than an answer, but it's too long for a comment. First, and directly addressing your question: the cosmic neutrino background is already present before the gravitational well of the star forms. If ...

8

It requires that they lose energy somehow (to drop hyperbolic orbits into periodic ones). There are two basic mechanisms available: gravitational scattering and weak scattering. In both cases we expect the interaction to be elastic, but that doesn't mean the neutrino has as much kinetic energy in the star's frame afterward the interaction as before: it ...

7

I just want to add something to the answers above, because I did not understand this initially. As far as clustering goes, the crucial point is how slow the neutrinos are travelling with respect to the characteristic escape velocities of galaxies (600 km/s) and clusters (2000 km/s). If you assume a rest mass of 0.1 eV, use the 1.95K temperature and the ...

6

Your post reminds me of this paper by Wigmans (also via arXiv) which I learned about during a colloquium in the distant past. Wigmans points out a narrow and interesting region in the parameter space for neutrinos in the mass region 0.1-1 eV. A longer paper (arXiv) by the same author; you'll enjoy mining citations. Such neutrinos, redshifted to the CνB ...

5

We know some physics that occurred with the early universe up to periods of time close to the big bang. The actual moment of the big bang is not known at least empirically. That moment did not occur at point, but was a process where the spacetime of the observable universe emerged. This was probably a bubble nucleation event similar to that proposed by ...

4

Because when we look around, we see that things are, on large scales, the same in all directions. This would be true in such a model only if we were at the centre of this system. That seems ludicrously unlikely: what are the chances that we are lucky enough to be at the one place in the universe where everything looks the same in all directions? So ...

3

As explained in this paper, the dominant effect is due to gravitational interactions, which can yield overdensities up to a factor of $10^3$ for neutrino masses of the order of 1 eV. The clustering of relic neutrinos can be modeled well using the collision free Boltzmann equation (Vlasov equation) where the densities evolve under the influence of the ...

3

Is there any other scientific theory that proves that big bang is the origin of time ? Here is a gross misunderstanding of what a scientific theory is. A scientific theory can never be proven. It is successful if it fits data and observations, then one says it is validated, and if its predictions are always validated. An invalid prediction requires drastic ...

3

How can we look into the past? Light has a fixed velocity of almost 300.000 meters per second. Sunlight takes about 8 minutes to reach us. So we see the sun always 8 minutes ago. As the other answer says, stars are much further away and it takes light that much longer to reach us. How do we know how far away the stars are? There are various methods that ...

2

Stars are very far away. So light takes a while to get from stars to you. The light arriving now shows you what the stars looked like when the light left. It is like getting a letter from a far away friend. The letter took a few days to arrive. It has news from a few days ago.

1

Our universe looks not only isotropic (the same in all directions) but also homogeneous (the same at each x, y, z at any one time). The fact that our position is not unique is not a principle, it is determined to be so from astrophysical and cosmological observations. Of course, the meaning is that these are so for cosmological distances, i.e., in the large, ...

1

See the lookback time to redshift relation in https://en.m.wikipedia.org/wiki/Redshift You can ignore inflation if you get redshifts, temperatures and universe size (radius, scale) ratios between now and times in the past after inflation. For recombination the relations of 1+z to the scale ratios and temperature ratios are linear and direct . So for T(then)/...

1

No one knows. One other thing ... the big bang hypothesis does not explain the origin of the universe (although I recognize that you used the word "formation", not "origin", but I'm not sure what exactly you meant by "formation"). It explains what happens after a certain epoch in our universe's history. What happens before that is completely unknown. ...

1

First off, let's start with the more common misunderstanding. The Big Bang was not an explosion of any kind. Popular science likes to depict it as an explosion because of the name "Big Bang" and also because it's more visually appealing than what the Big Bang actually was. The actual definition of the Big Bang is a little complicated, but suffice to say it ...

1

As a completely speculative answer, I would say: 1) According to our current theories OUR time did start with the bigbang. I say our time, because it is plausible to think of other parallel universes with their own laws and times. Not even so, but no law forbids that other universes have more than one time dimension. 2) You have two possible answers, ...

1

The thing that appeals to me about this idea is , if there is some theoretical way the virtual pair can be kept apart, then we might assume an identical anti-universe was created. This would neatly explain why we don't observe equal quantities of matter and anti- matter in our universe. All the anti-matter is in the other universe outside of our observable ...

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