Questions tagged [big-bang]

According to the current cosmological theories, it's the model that explains the early life of the universe, starting from a rapid expansion of hot and dense matter.

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101 views

Are these Stephen Hawking's statements legitimate? [on hold]

I am reading 'Brief Answers to the Big Questions' by Stephen Hawking and it seems to me that some of his statements are just hypotheses, but they are written in such a way that they 'sound' like they ...
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Any theory/author using the white hole model to explain the birth of the universe?

The maximally extended Schwarzschild solution (Kruskal diagram) envisages a white hole, which is the time-reverse of a black hole, i.e. a part of spacetime from which things can escape to us, while we ...
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Would Wheeler's oscillatory universe model create absolutely different universes in each cycle?

According to physicist John Wheeler, the universe is part of a sequence of cycles of Big Bangs and Big Crunches, called cyclic or oscillatory universe model: https://en.m.wikipedia.org/wiki/Multiverse ...
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What is the relation between $X_e$ and $n_e$?

I'm trying to compute the Damping Tail of the CMB. A critical parameter to this calculation is the mean free path of the photons in the plasma:$$\lambda_C=\dot\tau^{-1}$$Where$$\dot\tau=n_e\sigma_Ta$$...
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Big-Bang theory / Lambda CDM model [duplicate]

Is there any evidence that the 'big-bang' was indeed the 'beginning'? or, is it basically an assumption, based on the fact that we have 'discovered' nothing else that fits the bill?
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Does the age of the universe depend on the way it is defined?

I was reading some earlier posts on this question in stack exchange. These posts give me the impression that the age of the universe is defined in a certain way following prescriptions such as that: ...
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If energy exists today, wouldn't it have had to be created somewhere? [duplicate]

Energy exists today in different forms, and the 1st law of thermodynamics states that energy cannot be created or destroyed, only changed into different forms. However, since there is energy today, ...
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Flat yet finite Universe

I would like to ask you this question: Let's assume that the universe is perfectly flat and big bang happened as described by our theories some 14 billion years ago. Shouldn´t, therefore, the radius ...
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How can I compute the scale factor for an open universe?

I'm struggling in obtaining an analytical expression for an open-universe $a(t)$. I know it is usually calculated from the second Friedmann equation, and with respect to the image I know how to ...
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Thermodynamics of early universe - proton and neutron ratio [duplicate]

So, I have been reading about connection of particle physics and thermodynamics of early universe. Like after big bang, and quark - gluon plasma etc.. Anyway, after 1 second after big bang, the ratio ...
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Inflation v.s. Big Bang

It is said that that transition or certain quantum rotor field, and “rolling” down into the valley (of some quantum potential), is what causes inflation to come to an end, and create the hot Big Bang. ...
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Could the matter for a Big Bang come from the Hawking radiation of a super fast expanding universe?

If I understand it right, the universe will at some point in time expand so fast, that from any particular point in space, an observer will see an event horizon around himself. This event horizon ...
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Possible Beginnings of New Universes? [duplicate]

Black holes pull anything and everything that enters past the event horizon into the singularity. What if the current unknown output where all of this infinitely condensed matter goes to is the ...
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Isn't Big Bang theory a violation of law of conservation of linear momentum?

What Big Bang theory assumed in the formation of universe? Answer:-At its simplest, it says the universe as we know it started with a small singularity, then inflated over the next 13.8 billion ...
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What exactly is the problem that Inflation solves?

There's copious documents about how Inflation solves the problem that General Relativity predicts a lumpy CMB. That influation 'smooths' out the curvature fluctuations and, so, predicts a CMB at ...
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How is observable universe so big if the universe is so young? [duplicate]

The diameter of observable universe is 93 billion light years but the age of universe is only estimated to be 14 billion years. So how does light have 46.5 billion years to travel from the boundary of ...
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149 views

How inflation creates a universe from nothing?

I have a basic, mostly purely conceptual understanding of Quantum Field Theory, and after lots of Youtube (thanks PBS Spacetime!) I have an idea of how inflation works to turn the vacuum into a ...
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How can an inflaton field let spacetime expand?

Whatever the Nature of an inflaton-field, how did it make spacetime grow at an incredible rate? A little speck of spacetime was inflated to the entire observable Universe and everything beyond in very ...
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Earliest existence of particles and forces

I'm trying to understand the relation between particles and forces during the very early universe--the Planck epoch and subsequent stages as the fundamental forces separated. At what point did the ...
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Is a vacuum the same as 'outer space'?

Is a vacuum the same as 'outer space'? When The Big Bang is described the terminology used is that 'space (itself) is expanding'. If that's true what happens when the volume of a container, '...
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Where does the 379,000 year recombination prediction of the Big Bang theory come from?

The Big Bang theory postulates that recombination happened 379,000 years after the Big Bang. However, I have never seen a single statement as to how this number came about. I don't imagine they ...
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On the death and rebirth of universe in a black hole

Suppose in the end there will remain only one very large black hole, others have died. Now this black hole had absorbed all the matter and energy of the universe due to conservation principle. ...
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Why is momentum divergence from energy release not considered in Big Bang models?

From the formation of subatomic particles to the formation of atoms to the nuclear fusion in stars to the explosions of supernovae, the process of conversion of rest-mass energy from fields into ...
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How does the ratio of hydrogen to helium help prove the big bang theory?

From what I have read one of the key pieces of evidence for the big bang theory is the ratio of hydrogen to helium in the universe. I have not seen any explanation as to how the big bang theory ...
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Does an expanding universe assume a space within which the expansion is happening? [duplicate]

When I read about the expanding universe and inflation I often see pictures like this: (Source: https://en.wikipedia.org/wiki/Inflation_(cosmology)) or explanation like this: For getting an idea ...
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why do quantum fields exist? [closed]

Why did the big bang give rise to the quantum fields it did, could the big bang have created the universe any other way? and why not more elementary particles?
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Speed of at expansion at the start of the big bang [duplicate]

If I understand the basics of the big bang correctly it starts with a very small dense point. At the moment of the big bang, less then microseconds after, the universe is already the size of our solar ...
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What is the relationship between the Cosmological Constant and the Cosmological Principle?

I believe I've misunderstood a relationship between the cosmological constant and the cosmological principle having read: Einstein introduces his cosmological constant which attributes, in the ...
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How bright was the universe after Big Bang during photon epoch?

After 10 seconds of Big Bang, most of the leptons and antileptons annihilate each other leading to an outburst of photons. The universe was said to be dominated by photons resembling a glowing fog. ...
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Contractions between big bang and gravitational law [duplicate]

If big bang happened then the centre of the universe must be place of big bang. Let the mass of whole universe be $M$ and mass of small planet or any Astro object be $m$. Then the Gravitational ...
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Why don't we see galaxies going back in time?

Galaxies 4,200 megaparsecs away will travel faster than the speed of light away from each other, so why don't we see those galaxies as Going back in time up to the moment of the big bang?
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Why can’t you see at the start of the Big Bang?

I’m quite confused with regards to photon emission throughout the creation of the universe. From what I’ve heard, there was no light (of any frequency) in the universe until 300,000 years after the ...
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Is space itself expanding or is it just momentum from the Big Bang carrying things apart? [duplicate]

So, we observe that galaxies are moving apart (on average) and the further away from us they are the faster they are moving away from us. If space was expanding that would explain this. However, I ...
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What actually is the flatness problem?

One of the Friedman equations is given by $$ H^2\equiv\Big(\frac{\dot{a}}{a}\Big)^2=\frac{8\pi G}{3}\rho-\frac{k}{a^2},\tag{1} $$ which fixes the evolution of $a$ (with given $\rho(t)$) if values for $...
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Do we really need a new physics? [closed]

I have heard many times in news that a new discovery has taken place, and we need a new physics. It has recently been announced in scientific news that the world is apparently expanding faster. And ...
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Is there a relationship between Black Holes and the Big Bang?

As the question mentions, is there a relationship between the Big Bang and Black Holes? It appears the Big Bang is a ‘tacked on’ theory that doesn’t align with current theories (since we don’t know or ...
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Was Helium hydride really the first molecule?

This press release by NASA: https://www.nasa.gov/feature/the-universe-s-first-type-of-molecule-is-found-at-last/ When the universe was still very young, only a few kinds of atoms existed. ...
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Does the same hawking radiation mechanism of a black hole apply to all other event horizons, like the hubble horizon?

From my understanding of black hole evaporation, a pair of virtual particles manages to avoid annihilating itself when one of the particles in the pair passes the event horizon and the other escapes ...
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Do we need dark matter and dark energy, if the behaviour of the universe in its initial stages was similar to that of the Sun? [closed]

According to CMBR the universe was a cloud of plasma and was a perfect black body, $380,\!000$ years after big bang. But the Sun in our solar system also is in the state of plasma, thus making it a ...
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How can the big bang be “observed”?

The Big Bang Observer is a proposed spacecraft to study gravitational waves. Especially the one that are thought to originate from the Big Bang. Question. How can we observe waves that has an origin ...
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Does the expansion of the universe explain why the universe doesn't collapse?

Notes: 1. I'm in 8th grade so i don't have in-depth schooling on this. Lengthier explanations with more extra information that would improve understanding would be much appreciated. 2. I asked a ...
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Did the observable universe come from nothing?

Does the big bang theory hold that there is a possibility that the whole of the observable universe came out from NOTHING? I mean if all of this universe was occupying an extremely small size of a ...
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Does time stop inside a black hole? How about at it's singularity?

I'm a layperson who just read Brief Answers to Big Question and in the book, Hawking proposes that: A typical black hole is a star so massive that it has collapsed in on itself. It’s so massive ...
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Is there a contradiction between isotropy and the Big Bang? [duplicate]

Disclaimer: I'm not asking whether the Big Bang happened at a point. I'm asking whether the fact that the universe is isotropic and that the Big Bang happened contradict each other. To be honest I am ...
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Questions regarding photons and distance contraction

I've got a few question regarding photons and lorentz contraction. they may be really stupid questions (I am not a physicist). But they have been bothering me for a while. 1. Is Lorentz distance ...
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Neutrino energy density vs photon energy density

So I'm currently following a course in Cosmology and we're covering the densities of different species in the universe right now. Starting from the photon density $\rho_{\gamma}$ we need to derive the ...
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1answer
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Experimental status of the Big Bang theory

Take the most successful version of the Big Bang theory I'm aware that the Big Bang theory have unanswered questions related to the very first moments of the Big Bang. I also know that for our ...
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Imaginary time concept in S.Hawking's No Boundary proposal, extra-time dimensions and the Big Bang

In this post I will be refering to S.Hawking's lecture: http://www.hawking.org.uk/the-beginning-of-time.html I have a couple of questions regarding the Imaginary time and the Big Bang. In the ...
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Does the Universe itself move to any direction on top of expansion?

So the universe expands right, but does this expansion move to any direction in hyperspace as an expanding cluster of matter somewhere? It's like if you would explode a bucket of paint under the. ...
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$W$, $Z$ bozons and fermions gained their masses WHEN?

I have read these questions: How does the Higgs mechanism work? How does the Higgs boson give mass to other elementary particles like electrons? What is the difference between the Higgs Boson ...