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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How can we be sure if Universe has exploded with big bang? Can't it be implosion? [duplicate]

Why do we say the universe has exploded in the event of big bang? When we talk about big bang there was no concept of outside with the absence of space, so should’t the universe be imploded into the ...
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Does the Cosmic microwave background also lies in radio frequency spectrum?

I heard the CMB is the electromagnetic radiation from the big bang. It is 13.7 b years old but isnt it only in the microwave range of the spectrum (300MHz - 300GHz) . Can a FM radio receiver (87-...
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How can the universe expand faster than the speed of light? [duplicate]

In Neil deGrasse Tyson's Astrophysics for People in a Hurry, he writes: By now, one second of time has passed. * The universe has grown to a few light-years across... If nothing can move ...
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If Time and Space are intrinsically linked and space is ever expanding then surely time is slowing down [duplicate]

When we try to imagine the initial expansion after the big bang we see with the CMB that the universe went from initially smaller than a hydrogen atom to what we see today. However, when we try to ...
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Seeing the Big Bang [duplicate]

The Big Bang happened almost 14 Billion years ago. Theoretically speaking , if we could teleport (Instant teleportation) to somewhere that’s 20 Billion light years away from the Earth , if we looked ...
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What caused neutrinos to decouple at $t=1$ second?

Was it simply that the density and/or kinetic energy got too low, because of expansion? Or was it something about the weak force itself (which I thought gelled around $10^{-10}$s? For the CMB, ...
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Big Crunch vs Big Rip vs Heat Death vs Conformal Cyclic Cosmology… What's the Most Common View? [closed]

I just saw that Penrose recently published a paper on Conformal Cyclic Cosmology and it made me wonder, what exactly is the consensus view these days? I first heard of Penrose in connection with Orch-...
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Mass and Expanding Space

1) space is expanding at an increasing rate, therefore things are getting farther from each other and therefore increasing in velocity. 2) the faster an object moves relative to another, the more ...
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Does Big Bang predict the size of the fluctuations in the CMB? [duplicate]

From this Ethan Siegel’s article The temperature fluctuations in the CMB are only 1-part-in-30,000, thousands of times smaller than a singular Big Bang predicts. Does big bang predict the size ...
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Was the universe already expanding before inflation occured?

Was the universe already expanding before inflation occured or did inflation cause the universe to start off expanding? By “cause it to start off expanding” , I mean the cause of the initial ...
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Would eternal inflation be really eternal since quantum fluctuations are usually very rare and very small?

I’ve read somewhere that quantum fluctuations in the inflaton field are usually very rare and very small. If the effect of quantum fluctuations pushing the potential uphill is too rare and too small ...
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Is there any way to tell if the Big Bang happened everywhere or just in some regions of the entire universe?

On large scales, matter seems to spread uniformly in our observable universe so we think the Big Bang happened everywhere in the observable universe. Is there any way to tell if the Big Bang happened ...
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177 views

Heat death in eternal inflation

Heat death is the predicted fate of the universe. Eternal inflation theory states that new hydrogen atoms are created in each pocket universe so that means new hydrogen atoms are still being created ...
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Does object from which the universe is created still exist in its original form? [closed]

If time is passing more slowly near objects with bigger gravitational mass, could it be that the time at the object from which the universe is created has not started yet (or very little of time has ...
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How do we know the universe is expanding and wasn't already infinite?

From what I know, the decision that the universe was expanding came from the discovery of the redshift and that other celestial objects, such as galaxies, were moving away from us; the farther they ...
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In what sense the scale factor $a(t)\to 0$ lead to the big bang singularity?

How do we understand that the limit $a(t)\to 0$ (where $a(t)$ is the scale factor) lead to a spacetime singularity? Is it by substituting $a(t)$ in the FRW metric and concluding that space makes no ...
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How was it possible for the big bang to occur?

I think the person who asked this Phys.SE question meant a different thing than any of the people who wrote an answer thought so I'm asking what I'm guessing the author probably really meant. If there ...
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The surface of the last scattering and pictures of deep field

Maybe this question (in fact I have a few of them) is naive but nevertheless, let me try to ask it: it is concerning the furthest regions of our universe. Is the Hubble telescope capable to ...
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How is the primordial abundance of Lithium measured?

I was reading about the "Lithium problem" and I came across this Physics SE post: Discrepancy problem in lithium? The answer mentioned On the other hand, measurements of the $\rm Li$ abundance ...
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Alexander Vilenkin - The Universe probably had a beginning [duplicate]

Is it true that the Universe can not have an eternal past? It seems like Alexander Vilenkin tries to argue this? Does this imply that the Universe had a beginning? Link to his publication regarding ...
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How far back in cosmology is there observational evidence?

It seems "the first three minutes" are well established... back to the first second? 10 seconds? What about the "hadron epoch" going back to the first microsecond? Or before that? I know there are ...
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Could matter in the universe come from some process other than the decay of inflaton field?

Could matter in the universe come from some process other than the decay of inflaton field? Do we have any theoretical reasons that support the idea that matter was created from the decay of ...
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Did negative pressure cause the universe to start off expanding at the big bang?

What caused the universe to start off expanding in the first place. Was it negative pressure that drove the initial expansion or was it just something else?
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Why do we think that the energy density of false vacuum/scalar field doesn’t dilute with the expansion?

I have a question about inflation theory. Why do we think that the energy density of false vacuum/scalar field doesn’t dilute with the expansion? Could it be that the energy density does dilute with ...
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How do you explain cosmological red shifting in terms of gravitons?

We know that the photons from the big bang are continually being red shifted and losing more and more energy. In terms of the graviton view, how would you explain that? Where is the energy going? Are ...
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If the LHC test energy levels present just after the Big Bang, is it possible to test higher energies? [closed]

And, if so, would that be relevant to anything in this universe?
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Apparent contradiction between First and Second Laws of Thermodynamics

How is the Second Law of Thermodynamics not either false or incompatible with the First Law of Thermodynamics? In practice, the Second Law entails that, given an infinite amount of time, there should ...
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Was the big bang a black hole that collapsed [duplicate]

I know this might be a silly question and maybe a bit off topic, but I wonder, could the big bang have been the collapse of a gigantic black hole in which all off its contents was pushed out? I have ...
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Matter generation during cosmic inflation (Hawking radiation like…)

Is there any estimation of how much of the matter in the observable universe was not created during the big bang, but later during cosmic inflation? My thought is as follows: Suppose we are in the ...
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Is it sensible to talk about protons at the time when the universe was a quark-gluon plasma?

I'm currently studying from "Particle Astrophysics" by Perkins. On page 132 it says: After $kT$ fell below the strong quantum chromodynamics (QCD) scale parameter ∼ $200$ MeV, the remaining ...
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During big bang, everything expands same rate, homogenous, isotropic, nothing pulled towards each other. Did quantum randomness form stars, galaxies? [duplicate]

During big bang, space expands separating everything at the same rate, homogenous and isotropic, nothing is pulled towards each others. Did quantum randomness form stars and galaxies? If there is no ...
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Would the universe be significantly different if neutrinos were massless?

As far as I know, neutrino oscillation experiments have fairly conclusively demonstrated that neutrino states have mass. However, neutrinos are so frequently taken to be massless in cosmology that I ...
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How far are we from the “edge” of the universe? [duplicate]

According the the Big Bang theory, the universe started as a 0-dimensional point of infinite density. Shortly thereafter, it underwent inflation and grew to some measurable size, and continues growing ...
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Temperature after the big bang

I was just wondering about possible extreme temperatures. It came to my mind that shortly after the supposed big bang the universe was probably at its hottest in its entire Lifetime. But does it even ...
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How to explain curvature of spacetime at the time of big bang [duplicate]

According to Einstein mass causes curvature of spacetime ,so he basically defined mass using space i.e (mass is something which causes curvature of spacetime).Now at the time of bigbang there was no ...
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Why did CMB decouple when neutral atoms formed?

Atoms can absorb and emit photons. But it is said that when the neutral atoms were first formed the photons got decoupled. If the atom-photon interaction is allowed how can we say that photons were ...
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Does the big bang model describe a first momment in time for the entire universe or just the observable universe

The big bang model describes the universe as contracting as we wind time backwards. Since the observable universe is of a finite size this ultimately sets the first moment of time at around 13.8 ...
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Can we have bubbles of the tenth dimension in our universe?

If the gap between the branes in the Big Bounce theory is the 10th dimension, and branes have wrinkles as they collide, can our universe have 'bubbles' in the 10th dimension? This is in reference to ...
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What is energy debt?

What exactly is energy debt and why does not having energy debt mean that particles and antiparticles don't instantly annihilate each other. I'm struggling to understand why this happens (quote from ...
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Does the fact that energy is not conserved in cosmology open the possibility of new matter/atoms being created in the universe?

Does it open the possibility of new baryonic matter/atoms being created in the universe and avoiding the Heat Death of the universe?
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Size of the Universe at end of recombination (~477000 years)?

What was the size of the Universe at start of recombination (377000 years) when the Universe started to become transparent and release of trapped photons into what we now know as the CMB and till end ...
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Is it the same time, does time pass at the same pace everywhere in the universe? [duplicate]

According to big bang cosmology, the universe has a beginning, a definite age. Does this mean that it is the same time, that time passes at the same pace everywhere?
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Pauli principle before big bang [closed]

i understand that the Pauli exclusion principle states that two fermions cannot occupy the same quantum state. This question is not about a black hole. It is more about the singularity at moment of ...
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Why abundance of matter requires fundamental asymmetry - cannot be statistical symmetry breaking?

There are rather no doubts that there is more matter than antimatter in our Universe, it is usually assumed that it was created during short baryogenesis (violating baryon number conservation) period ...
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How likely are Primordial Black Holes to form in the early universe?

In the very early universe, tiny fluctuations created slight over- and under-densities in mass/energy. As far as I understand, if a region becomes sufficiently over-dense, a primordial black hole (PBH)...
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If the observable universe after inflation was all there was, would this form a black hole?

There have been other similar questions, but none of the answers address this point. Inflation ends after the first 10^-32 seconds. Our observable universe was the size of a grain of sand that ...
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How are the temperature, density, and size of the Universe calculated during the first few minutes after the Big Bang?

I'd like to know the assumptions cosmologist use when they give a timeline of temperature, density, and size of the universe from $T=0$ to $T=$ a few minutes later, as Steven Weinberg did in his book, ...
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Can matter/antimatter “annihilation” produce “dark matter”?

I was thinking about the following reasoning: If a matter and antimatter reaction produces energy, this energy would have particles itself. I found out (reading...) that one (the main?) product are ...
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What is the difference between a quantum fluctuation and a singularity in the beginning universe?

I am sure this is a naive question that shows my lack of sophistication in physics but I keep reading "the early universe was a "singularity", on the other hand ..... I also see quantum fluctuation ...
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TV snow and Big Bang

How come the white and black snow we see sometimes on TV is a result of the Big Bang? (the cosmic radiation) I meant the random dot pixel pattern of static in TVs, when there is no signal.