Questions tagged [universe]

The universe refers to the cosmos; all of space-time and that which exists as part of it. Alternatively, it can refer to the observable universe, which only contains the part we can see. Questions tagged with this should ask about physics at scales the size of the universe or specific properties of the universe

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How would quarks behave in the event of 'The Big Rip'?

I have always heard that you can't get a quark by itself because "the energy required to split them apart is enough to create another." But, in the case of The Big Rip, the idea is that ...
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What is matter really made up of?

We know matter is made up atoms, and atoms are made up of protons, neutrons, and electrons. And we know that protons and neutrons are made up of smaller particles known as quarks. Would probing deeper ...
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How to calculate $ |\Omega_{tot} - 1| $ at inflation time?

Suppose that we live in a universe that has the following properties: $$ |\Omega_{tot,0} - 1| = 0.001 $$ How can I calculate the value of $$|\Omega_{tot} - 1|$$ at some other time as, for example, the ...
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Is there any way to prove that contrarly to a flat 3D space, a curved 3D space can only be constructed in a 4D manifold?

This question is a result of me trying to understand how this universe can be possibly infinite if it isn't infinitely old. So to compare with an area that is flat it can be constructed both in 2D and ...
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In an infinite Universe, would we necessarily see multiple “Earths”?

With my memory issues I can't be certain it was Sean Carroll, though I believe it was a video of him that explained that in an infinite Universe, we would inevitably see large scale patterns repeated, ...
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How did a large amount of concentrated energy come in the first place? [closed]

If the universe wants to reach a state of entropy, how did it come to have such a large amount of concentrated energy in the first place?
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Angular size of the largest region in causal contact at the moment of recombination

I want to calculate the angular size of the largest region in causal contact at the moment of recombination (z = 1100) to our universe, so we have: $H_0 = 68$ (km/s)/Mpc, $\Omega_{m,0} = 0.31$, $\...
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Could our universe be expanding due to loss of mass from light waves, gravitational waves and other radiation that left our universe? [closed]

so I know that current evidence points to the universe expanding faster and faster, i.e. red-shift in the stars getting more and more the further they are. I know the current theory is that "dark ...
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Will the entropy of the universe be every real number (greater than whatever it currently is)?

Since the universe's entropy is going to increase indefinitely and it is going to be a continuous, does this mean that it will be equal to some power of pi or e or any other transcendental number?
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Can the universe ever contract?

I am currently going through this answer related to the Big Bang and from there a question arose in my mind: Can the universe ever contract? Can it ever come back to singularity? (Although I am aware ...
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Does the Big Bang imply a finite quantity of matter in the universe, and that the universe is spatially finite (if boundaryless)?

If all matter was created in the Big Bang (not counting spontaneous generation of particle-antiparticle pairs), wouldn't that imply that a finite (if very large) amount of matter exists in the ...
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Are there other theories than gravitational attraction taken into account as a reason for the extreme accumulation of matter in the universe?

This question is about how small the interstellar density is (less than 1 atom per cubic centimeter). But although the interstellar density is very low, matter tends to extremely aggregate in certain ...
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Does the FLRW metric account for the decrease in density for an expanding universe?

In other words, is it assumed that the fluid density is constant after expansion and through the time development of an expanding universe?
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What does Dr. Krauss mean by a universe from “nothing.” [duplicate]

I have read for a couple weeks now about a universe from nothing. I understand that the gluon field supports quarks in a proton. I understand that the universe has zero total energy. I'm confused ...
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Is total Universe “total” Energy relative?

I have read a lot about (what is the total energy of universe? And Is it zero?) here, such as, Is the total energy of the universe zero? and other sources. I thought decades about a question, not ...
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1answer
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Universe and Anti-Universe pair [closed]

Two years ago Latham Boyle, Kieran Finn and Neil Turok, in their work CPT-Symmetric Universe, proposed that the pre and post bang eras constitute a universe/anti-universe pair. For Anti-universe in ...
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Does the Hubble constant measured for huge distances mean it is not the actual Hubble constant but a very old one?

I am citing Wikipedia about Hubble constant.... "Hubble constant is most frequently quoted in (km/s)/Mpc, thus giving the speed in km/s of a galaxy 1 megaparsec (3.09×1019 km) away, and its value ...
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What does a universe with a boundary look like?

Physically, what would it look like if we lived in a universe with a boundary at finite distance?
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Tegmark's level 1 universe: how many universes?

In "Our Mathematical Universe" Tegmark claims that inflation theory implies the existence of an infinite set of universes. My simple question is: what kind of infinity, and why that kind ? I ...
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1answer
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Why was the universe initially opaque after the Big Bang?

It is theorized that till about 380,000 years after the Big Bang, the universe was opaque. Why did the particles present before the formation of atoms make the universe opaque? Why did the universe ...
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1answer
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Randomness in parallel universes [closed]

Suppose we have two completely identical universes (for instance in Tegmark's type III multiverse). In both of them, two identical men are sitting behind identical random number generators (RAN1 and ...
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Does Chew's bootstrap idea accept the possibility that there may be infinitely many possible laws of physics?

Physicist Geoffrey Chew proposed the concept of bootstrap (related to S-matrix theory) where he denied that fundamental laws of nature existed at all, as it is indicated in a writing in his memory ...
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If the Universe is already infinite and is expanding, how could it be expanding to more than infinity?

There are arguers that say the Universe is streching about every its point but also tell it is infinite. How it can possibly be?Maybe we should reinterprete what infinity means.
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Is it possible that a black hole has a universe in itself? [duplicate]

Every black hole has a singularity. But the singularity is covered by a thing called 'Event horizon'or ' Schwarzchild Radius'. Our universe is originated from a naked singularity. By naked singularity,...
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Child Universes

I was watching a program on the future of the Universe and it got into the eventual heat death resulting from Hawking Radiation as the last hurdle till nothingness (assuming the unproven theory of ...
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Suspecting that the universe is even more bigger

Is it plausible that a possible extraterestrial scientist from a galaxy 13 bilion light years from us sees this part of the universe nothing else than just background cosmic radiation... and even more ...
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Distinction between different points at Big Bang Singularity

As per the Big Bang model of Cosmology roughly 13.8 billion years ago a singularity exploded exponentially to eventually become the present universe. At the present time (basically current time-slice) ...
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2answers
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Is the universe some sort of inflating bubble?

Let say we are measuring the Hubble parameter (HP) observing two galaxies:one 5 billion light years from us and the second one, 10 billion light years from us. We should get two different numbers of ...
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Why quarks have limited mass?

I wanna ask why were the mass of first quarks not something like a very large number (because a lot of energy was present in that expanding universe) or much more than what we know from calculations ? ...
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1answer
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It seems like the many-world hypothesis would explain the Fermi paradox?

The fermi paradox asks why we don't see more complex life in the universe if we exist? Essentially, it seems either would naturally develop in our universe, in which case it would be plentiful, or it ...
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Is this formula for the time-temperature relation in this universe correct, or is there a more appropriate one?

I'm trying to simplify an equation into a form that uses the ratio of the number density of sterile to active neutrinos. For this, I need a relation between the time and temperature of the universe, ...
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When Matter condensed — the condenser

Did gluons, quarks, and electrons first appear at the same age of the universe or was one first?
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What is the closest anyone got to a proper description of a Galilean universe?

So assuming Einsteinian relativity is a bust, did any physicist thought through properly how a Galilean/Newtonian universe would work? Of course there are infinite ways of how it could, but one is ...
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What does CMBR has to do with quantum fluctuations during rapid inflation?

I know the almost homogeneous of cosmic microwave background radiation is claimed to be caused by the rapid expansion of quantum fluctuations in the early universe, but what does density of photons ...
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2answers
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How were quarks made?

I recently read about the early universe and found that first quarks were made $10^{-12}$ seconds after the inflation or the beginning. But what was the cause of this minute delay, since inflation ...
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Does the increasing rate of expansion of the universe have any implication on or alter the curvature of the universe?

I'm not really knowledgeable on physics but was curious about this and couldn't find any good answers related to it.
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Friedmann Equation with imaginary values

Consider the Friedmann equation with no radiation: $$ \frac{H(t)^2}{H_0^2} = \Omega_{m,0} a^{-3} + \Omega_{k,0} a^{-2} + \Omega_{\Lambda,0} $$ We can have values for $a(t)$ and the density parameters ...
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Do all measurements of the Hubble Constant have to be made at low redshift values?

As far as I can tell, groups that measure the Hubble Constant usually measure galaxy recession speeds $v$ and galaxy distances $d$. Then they plot one versus the other and the best-fit slope is the ...
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1answer
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Scaling of distance versus time in an expanding universe

As the universe expands, the (not co-moving) distance between any two points, say the distance between galaxy A and galaxy B, increases. Assume the universe behaves the same way in all directions. $D(...
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Can Hubble law be explained by galaxies moving away from one point at random constant speeds?

Let’s put a lot of material points at coordinates (0,0). Let’s give them completely random velocities. Let’s evolve this system for some time ...
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How do the laws of physics work in quantum system? [duplicate]

If I throw a stone in the air,how does earth know that it(stone) needs to be pulled. My point is are the rules of physics contained inside every single particle? Or is there a central body checking ...
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Why am I at the center of the universe? [closed]

In highschool they taught me that I'm not at the center of the universe, but when I look at all the maps of the Universe, I'm right in the center. The CMB source, particle horizon, Hubble horizon, ...
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Why isn't the 'Crisis in Cosmology' or 'Hubble Tension' explained by the Accelerating Universe?

The value of the Hubble parameter determined locally from the Type Ia supernovae is found to be greater than that determined from the Cosmic Microwave Background (CMB) radiation. This is known as the '...
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Does Universe have an overall Entropy? [duplicate]

I am just curious to know whether Physicists have given any measurable Entropy to the Universe? If yes then please tell me whether its value is increasing or decreasing overall?
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1answer
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Can we think of relativity as a measure to determine the finiteness of universe? [closed]

Let’s consider a hypothetical situation wherein an observer is in the standpoint of a light ray. The observer faces infinite time dilation. Thus time stops for the observer and it'd have transversed ...
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Origin of the universe [closed]

Does Big Bang Theory imply the creation of matter before that of radiation? Thus an original mass of a giant atom decays to produce radiation leading to the creation of matter in an expanding universe ...
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Scattering at the boundary of universe

Suppose that we have a particle moving at $0.8 c$ (or even a photon) and it is just, say $2 \times 10^{5} m$ away from the boundary of the universe (whatever that boundary be). Since the expansion ...
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Dimensions of Physical objects doesn't make sense [closed]

Can you show me a pure 1D or 2D object? A line and a plane have a thickness. A pure 1 D line is one with no width. But if its width is zero, it doesn't exist. Similarly, a 2D plane is perfectly ...
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How to determine current expansion rate of universe from observing past objects?

How to determine the current expansion rate of the universe from observing past objects? When we look into the light from objects far away, it not only very very far away in the distance it is also ...
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Does light return to its starting point in a closed universe?

I was reading about the possibility that our universe could be a closed sphere. from Sean Carroll “in a closed universe, one that wraps around on itself to form a compact geometry, like a three ...

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