56
votes
Is the Big Bang a theory or a model?
Back in the good old days, we used words like theory, model, hypothesis, law and so on, and their meanings arose from how the words were used, and dictionaries organised these senses - just like other ...
- 116k
48
votes
Accepted
Could liquid water have existed in open space 15 million years after the Big Bang?
Let's interpret your question to be about whether the conditions would permit blobs of water to remain liquid, whether or not water existed yet. And the answer is No, because the pressure was by then ...
- 3,691
38
votes
Accepted
Why didn't the Big Bang produce heavier elements?
I think that your thought process is flawed in that you assume that by drastically increasing the temperature you are guaranteed to get heavy elements. As odd as this may sound, this isn't the case (...
- 15k
38
votes
Why do galaxies collide?
The universe is expanding on a large scale. But locally things are always messy.
Locally, galaxies are not set in stone, they move relative to each other, and the directions are random. If they're ...
- 18.1k
37
votes
Accepted
At the Big Bang, when everything was close together, why did it not "collide", violating Planck length or Pauli Exclusion Principle?
The Pauli Exclusion Principle forbids two indistinguishable fermions occupying the same quantum state. It does not prevent them getting arbitrarily close together so long as they have very different ...
- 146k
28
votes
Accepted
Why was the Cosmic Microwave Background (CMB) released at a blackbody temperature of 3000K rather than 30,000K?
The CMB is produced as the ionisation fraction of hydrogen falls from a high value to a very small value. Contrary to what is written in the Quora answer you may have been misled by, this happens at a ...
- 146k
27
votes
Could the Methuselah star be evidence that there was a universe before this one?
First, if the Big Bang did originate with the collapse of a cyclic universe, the collapse reached densities and temperatures sufficient to not only ionize matter from the previous cycle, but to ...
- 1,158
23
votes
Is the Big Bang a theory or a model?
My understanding is that the "big bang" (which I am taking to be a synonym for $\Lambda$CDM cosmology) is a model. It sets out a (relatively) simple framework, starting from a set of ...
- 146k
21
votes
Could liquid water have existed in open space 15 million years after the Big Bang?
As others have mentioned in the comments, there wouldn't have been any oxygen to form water. Soon after the Big Bang, the protons were hot or dense enough to fuse up to helium and some lithium but ...
- 2,827
21
votes
Why isn't the CMB blurred by the blackbodies emitted in the time after atoms first formed?
It is. They're called galaxies and stars and we see them against the cosmic microwave background. However, they aren't (all) cooling because of the energy sources they contain.
But perhaps that isn't ...
- 146k
15
votes
Why do cosmologists assume that inflation began shortly after the Big Bang, rather than at the exact start?
The universe cannot have begun in an inflationary phase. Note that it is not necessarily the case that there was a phase that preceded inflation. However, if there was no phase preceding inflation, ...
- 4,260
13
votes
Accepted
What created the big bang's singularity?
No one knows what came before the Big Bang if, indeed, anything did. Theories include:
The Ekpyrotic universe theory where the BB was the result of the
collision of branes.
Various oscillating ...
- 7,580
13
votes
What parameters of the Big Bang model will have to be adjusted to account for JWST's observations of highly redshifted galaxies?
The big-bang model does not have much to say about the redshift-dependence of the galaxy mass function (NB It is really the luminosity function that is being probed), other than that at some high ...
- 146k
11
votes
What is in the center of the universe?
The universe doesn't expand away from any centre perse. All the distances are expanding uniformly throughout the universe. This causes such an effect that for each individual observer, it looks as if ...
- 266
10
votes
Accepted
BIg Bang Happened everywhere
Okay, I think I know what Max Tegmark is talking about in the video. He is referring to the fact that, when you observe the cosmic microwave background radiation (CMB) — i.e. the radiation that was "...
- 37.1k
10
votes
How do we know so many details about Big Bang, but we do not know if Universe is finite/infinite?
By observing the observable universe we can gather a lot of data about the constituents of the universe now and in previous epochs, right back to the cosmic microwave background. This data places ...
- 657
10
votes
Accepted
Why is the Cosmic Microwave Background evidence of a hotter, denser early Universe?
By request:
Beyond the fact that the cosmic microwave background (CMB) is a direct prediction of the big bang model, there is the question of how you would produce it in any other way. It is ...
- 146k
9
votes
Accepted
What made cooler temperatures suitable for atom formation?
The temperature of a gas is a measure of the kinetic energy of the particles. For molecules you can have rotational and vibrational energy, while for single atoms you just have translational energy, ...
- 37.1k
9
votes
Amount of energy of the Big Bang
Let's start by making some points clear:
1. We don't know what the Big Bang was.
Rather, we know that the Universe is expanding. If you extrapolate backwards, you'd expect the Universe to be denser ...
- 8,119
9
votes
Why do galaxies collide?
The galaxies don't really get "off track" - it's not impossible, but that kind of thing probably doesn't happen anymore (as space continues to expand). What actually happens is that galaxies form ...
- 498
9
votes
Why do galaxies collide?
I'm not sure that anyone has answered the question asked. The root cause is indeed that gravitationally bound structures with freefall timescales that are much shorter than the age of the universe are ...
- 146k
9
votes
Are there only a set number of atoms in the whole universe?
There are several processes at work:
Fission (of unstable elements) increases the number of atoms.
Fusion (occurs in stars and supernovae) decreases the number of atoms.
you could claim the formation ...
- 3,024
9
votes
Did Einstein supported Big Bang Theory cosmological model?
Einstein's opinions were not static, and he lived at a time when there were several competing theories and not much observational evidence.
Einstein introduced a cosmological constant $\Lambda$ into ...
- 116k
9
votes
Accepted
What is meant by "vastness of space, which now filled a volume of a hundred million light years"?
I think this is at best a weird typo, but more likely a confusion by the authors (who are not cosmologists or astronomers, but a biologist and a geologist).
The book is 10 years old, but our view of ...
- 37.1k
8
votes
What was "space" like before big bang?
This is a common question that comes up - one I've (at least tried to) answer a few times.
Let's try to understand what the Big Bang is. The Big Bang Theory is a model, and scientists came up with it ...
- 509
8
votes
Accepted
Why can't we point the centre of the universe from inflation graph we see?
That diagram does not depict the entire universe. At most, it depicts the history of what is now our observable universe (specifically, a 2D slice through it), with us at the center only because we're ...
- 1,158
7
votes
Accepted
Is it possible to get a glimpse of the Big Bang through gravitation waves?
Gravitational waves from the big bang may be "heard" but not by LIGO. The waves emitted at or around the inflationary epoch of the big bang are expected to be at much lower frequencies (milli-Hz or ...
- 146k
7
votes
How could universe inflate itself out of the very dense and curved early spacetime? Could it happen in a black hole too?
Great question! Sorry for this huge response, and it might not be a satisfying answer, but it'll address your questions.
Sadly, as with most of astronomy, the Big Bang is surrounded in mystery. It is ...
- 8,119
7
votes
Collision of Galaxies
The expansion of space is something that happens on the largest scales. At small scales, such as distances between nearby galaxies, other forces, such as gravity, dominate. Galaxy clusters are held ...
- 3,156
7
votes
Was the whole Universe close to Big Bang very small, or just very dense?
I am sorry this question is probably silly for professional astronomers, of which I am not one.
This question is by no means silly. Your question is a common one about cosmology (the study of where ...
- 8,119
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