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Questions tagged [universe]

Questions regarding all of time and space and its contents.

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-1 votes
1 answer
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Is the total energy of the Universe not invariant?

Consider a Universe which has only one object (bigger particle). The object exploded (somehow) into two smaller particles (with some release of energy). Consider the two particles to have masses M and ...
KeShAw's user avatar
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0 votes
2 answers
77 views

How can $\Omega_m<1$ indicate an infinitely expanding universe?

I was reading up about the cosmological density parameters $\Omega_m. \Omega_{rel}, \Omega_{\Lambda}$ corresponding to total matter(baryonic+dark), relativistic particle matter and dark energy. I ...
Ambica Govind's user avatar
0 votes
2 answers
997 views

Why does Helix Nebula look like an eye?

The infrared lights, the material clumps that radiate and the whole view resembling a celestial firework or giant eye
Helix Nebula's user avatar
1 vote
0 answers
74 views

What is Helix Nebula made up of?

The Helix is a planetary nebula, the glowing gaseous envelope expelled by a dying, sun-like star. Helix nebula consists of two gaseous disks, how they are formed or which material is present in it.
Helix Nebula's user avatar
1 vote
0 answers
58 views

Is there a granted minimum known size of the whole universe? (including the non observable part)

This Forbes article How Much Of The Unobservable Universe Will We Someday Be Able To See? claims The unobservable Universe, on the other hand, must be at least 23 trillion light years in diameter Is ...
Pablo's user avatar
  • 1,113
0 votes
0 answers
21 views

Luminosity distance in a FRW Universe

In the following presentation: https://www.slac.stanford.edu/econf/C0307282/lec_notes/pinto/pinto.pdf we have the relation for the luminosity distance in a FRW universe: \begin{aligned} D_L & =\...
Vincent ISOZ's user avatar
5 votes
3 answers
2k views

Is the gravitational constant really constant over our Universe?

For instance, if objects are travelling at relatively high speed around 'c', is G the same value for them as for us on earth? I believe a lot of matter is travelling fast away from other matter, so is ...
Bryan Major's user avatar
2 votes
0 answers
149 views

What happens at the edge of a finite and "bounded" universe?

So far, we know only about two types of universes: Infinite and finite universes (Unbounded edition). In an infinite universe, there is no edge. Because well, an infinite space doesn't have an edge. ...
Alastor's user avatar
  • 2,668
0 votes
2 answers
135 views

Light/Dark energy/Dark matter

So I have been working on my comic book project that takes place on another planet. But in my story, there will be warp gates and there will be other civs that can travel between stars. I am ...
Kul Tigin's user avatar
2 votes
3 answers
319 views

Is there evidence against a Universe Black Hole?

As far as I know, the critical density of our observable universe coincides with the density of a huge black hole of the same radius. It could be a BH expanding at the speed of light and growing in ...
Juan Casado's user avatar
4 votes
2 answers
345 views

Was the Big Bang an event within a preexisting Universe, or did it mark the beginning of the entire Universe, beyond just the observable Universe?

Could it be that the Universe is truly infinite, and the Big Bang was merely a singular, specific event that resulted in the birth of a 'bubble,' i.e. what we perceive as 'the observable universe'? ...
impact's user avatar
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13 votes
2 answers
3k views

If the universe has no true center, could it have antipodes?

Some time ago, I wondered where the center of the universe could be, and the answers I found were pretty much in agreement that there was no center of the universe, as paradoxical as that might seem. ...
J-L's user avatar
  • 259
1 vote
1 answer
99 views

Amount of black holes over time

Hello the number of black holes is much bigger than the number of black holes in the past right?Let $b$ be the number of black holes in the universe.Obviously $\frac{db}{dt}>0$ but what about $\...
Root's user avatar
  • 21
9 votes
3 answers
2k views

Are there some (simple) mathematical models which can simulate the cellular/web structure of the universe?

To visualize the structure of a solar system we have some simple mathematical model: Planets orbiting around a Star in circular motion. If we want to be more precise the circle becomes a ellipse, the ...
J. Doe's user avatar
  • 245
8 votes
2 answers
1k views

Size of the Unobservable Universe

If you search that question on Google, the answers will be "250 times the size of the observable universe" or "more than 15.000.000 the size of the observable universe". Both of ...
jack_O'Dim's user avatar
4 votes
1 answer
2k views

If the universe were infinite, how would it look through a telescope?

I assume there is some limit to how far our telescopes could actually see, and that this distance would be about the same in all directions. So, as a layman, I would assume that an infinite universe ...
hermancain's user avatar
6 votes
1 answer
151 views

What natural astronomical object is rare on a Hubble volume scale?

There are some milestone objects on different scales of the universe. The star is a notable feature on a solar system scale The supermassive black hole is a feature on a scale of a galaxy ?? The ...
FrogOfJuly's user avatar
2 votes
0 answers
89 views

Could entropy be reversed eventually in the far future?

In the far future there will be most likely a point where a maximal state of entropy will be reached in the universe and after the last black hole evaporates there could be no more structures and no ...
vengaq's user avatar
  • 1,017
4 votes
2 answers
5k views

Why speed of light is considered to be the fastest?

According to Hubble's law, as things move further and further away from one another, there might come a point when their speed gets faster than the speed of light. So, why is it that the speed of ...
Ed_Gravy's user avatar
  • 317
1 vote
0 answers
74 views

What Parts of the Observable Universe have we Observed?

Everyone talks about how big the observable universe is, all of the complexity, etc... But what parts of the observable universe have we actually seen? What Parts are hidden in relative shadows? Is ...
skout's user avatar
  • 309
1 vote
2 answers
452 views

Does space expand?

I know this has been asked and here are the links of at least two. The first link below is what I thought was the standard description. What does it mean for space to expand? Now by accident while ...
Sedumjoy's user avatar
  • 1,201
-4 votes
1 answer
145 views

How accurate are the calculations of the age of the Universe?

One major difference between a hypothesis and a theory is the amount of conjecture. A hypothesis is a sketch. A theory is a complete model. Today's standard narrative would have us believe that the ...
Ricky's user avatar
  • 1,345
0 votes
2 answers
122 views

the sun - relationship between gravity and temperature

In the sun's core, we know it's very hot. I was curious to research why it was exactly and I think 99% of answers are not fully correct. They say that it's because of nuclear fusions. I'd not agree as ...
Giorgi Lagidze's user avatar
0 votes
0 answers
38 views

sun - do gamma rays reach radiative zone

So in the sun's core, gamma rays are produced and right away, in the few milimetters, compton scattering happens. As I understand the compton effect, gamma ray will first collide with free electron, ...
Giorgi Lagidze's user avatar
1 vote
2 answers
203 views

sun's core - how much x-rays get emitted

We know from the sun, we receive x-rays, gamma-rays but at a very small number of photons. Question 1: why not much ? is it because most of the x-rays are absorbed in a process of ionization of the ...
Giorgi Lagidze's user avatar
0 votes
1 answer
104 views

Emitting light from the Sun [closed]

I might be asking too many questions here, but they all seem related to each other and knowing them simultaneously is the only way to understand this subject as I have tried my best googling already. ...
Giorgi Lagidze's user avatar
1 vote
3 answers
899 views

why does earth have speed?

I understand that Earth has a quite big speed such as it ends up around the orbit. The sun can't really attract it till the end due to Earth's speed and earth really can't escape due to gravity, hence,...
Matt's user avatar
  • 203
1 vote
0 answers
26 views

do we observe emission spectrum? [duplicate]

When light generated by the fusion in the sun goes through the layers of the sun and finally reaches outer layers and in the end atmosphere of the sun, we know it goes through hydrogen for example. ...
Matt's user avatar
  • 203
5 votes
3 answers
3k views

How can redshifted light be detected?

I've been reading about redshifts and it got me really curious. Basically, I want to figure out how we know light is redshifted and what's the original emitted light. I found the following question ...
Matt's user avatar
  • 203
2 votes
0 answers
69 views

Cosmic background radiation - what frequency tells us?

I understand that cosmic microwave background radiation is remnant of the universe after 380,000y of the origin. To me, this radiation is still a wave which has a microwave frequency and I also ...
Giorgi Lagidze's user avatar
4 votes
1 answer
78 views

How does carbon end up in the remnants

We know that one way carbon ends up in the interstellar medium which by the way is one or the heavy elements that help form the planet. But we also know that in the core, carbons fuse with another ...
Giorgi Lagidze's user avatar
4 votes
0 answers
68 views

What does it exactly mean for spacetime to have no global symmetries?

Are there spacetimes or metrics with no global symmetries? Spacetimes/metrics with no global Poincaré, Lorentz, diffeomorphism, CPT, translational and gauge invariances? And if there are, what does it ...
vengaq's user avatar
  • 1,017
1 vote
1 answer
247 views

Critical density of universe with intrinsic spatial curvature

$H^2 = \frac{8 \pi G}{3}\rho-\frac{kc^2}{a^2}$ Shown above is the first Friedmann equation. I understand that the curvature parameter, k, represents the spatial curvature of the universe which is ...
Scott's user avatar
  • 23
1 vote
2 answers
215 views

How do I find out when sidereal time was 13:30 on a certain date and location?

I live in Lehi, Utah, USA and I want to know what time of day it was on sidereal time on February 25th, 2023. Someone said it was 3:32 AM and I wanted to check and see if that was true.
Lorin Bishop's user avatar
2 votes
1 answer
99 views

How much of the variance of matter is due to scales

Imagine a Universe in which the matter power spectrum behaves as $$\mathcal{P}\sim k^{0.8}$$ How much of the variance (not variance squared!) of matter is due to scales around $k=k_1=10^{2.9}\mathrm{...
Alba's user avatar
  • 21
1 vote
1 answer
77 views

Could inhomogeneities or topological defects break the fundamental symmetries of the Universe?

I have heard that some types of inhomogeneities and topological defects in cosmology have been proposed to be able to break fundamental symmetries of nature such as the Poincaré, Lorentz, ...
vengaq's user avatar
  • 1,017
2 votes
2 answers
178 views

Will the Milky Way galaxy revolve around the Andromeda galaxy or vice versa?

As all of you know, in the Milky Way galaxy, the Solar System revolves around the Milky Way to complete the Galactic year (because we have the supper massive black hole in our Milky Way galaxy) then ...
Pash0002's user avatar
3 votes
1 answer
260 views

Conditions in the Early Universe

I am interested in how the large-scale properties of the Universe change over time. Does anyone know a trusted website which gives the temperature, density and radius (distance to the particle horizon)...
John Davies's user avatar
21 votes
2 answers
4k views

What equation tells you how far in space you can go from a point and return?

We know that hubble expansion increases the distance between points in space, and that the cosmological event horizon represents the distance from the observer at which objects are receding faster ...
user52978's user avatar
  • 313
5 votes
2 answers
339 views

Size of the whole universe if it were spherical

Suppose the universe is spherical and its density ratio is $\Omega \leq 1.00125$ $\Omega = 1.00125$ is approximately the maximum possible value of the density ratio according to the Planck Mission ...
Albert's user avatar
  • 2,182
15 votes
9 answers
6k views

How do we know we're not getting bigger?

Alright so I've been thinking a lot about how the universe expands and I've always wondered if we're getting bigger as well. Since everything would be getting larger at an equal rate (tools of ...
Landon's user avatar
  • 169
2 votes
1 answer
115 views

When did the first cold dark matter halos begin to originate?

I know that these dark matter halos should have been created in an early universe because during the formation of galaxies, the baryonic matter was too hot to form gravitationally self-bound objects ...
user9867's user avatar
  • 147
3 votes
1 answer
234 views

Mass Content of the Hubble Sphere

How does the mass encased within the Hubble sphere/volume (both proper and comoving) change with time?
Kontrola Faktů's user avatar
2 votes
1 answer
296 views

Why is time not a spatial dimension? [closed]

I am a little confused about dimensions. People say we have three spatial dimensions and one temporal dimension but I don't know how this is possible. How can there be different "types" of ...
Many_Questions's user avatar
-2 votes
1 answer
113 views

Shape of the Universe [closed]

When an explosion takes place, the contents get scattered in every direction. So how is it, that after the "Big Bang", everything only went in one direction, to form a flat Universe?
Peter U's user avatar
  • 1,619
1 vote
1 answer
110 views

What is the evolutionary leap in the great filter? [closed]

This might be very unclear, but in pictures explaining the great filter, there is an evolutionary leap that the civilisation is most likely not to be able to pass through. But what is that leap? Is it ...
schrodingerscat's user avatar
5 votes
1 answer
280 views

What is the elemental composition of the universe?

What is the current distribution of elements in the observable universe? Wikipedia lists the composition of the Milky Way, but I'm not sure how the values would change if intergalactic medium were ...
WaveInPlace's user avatar
0 votes
1 answer
117 views

Time and space travel as applied to expanding space and the ratio of/between time and distance

If a place is 500 light years away, then I set out to this place, then is it true to say that, the place which I set out from, will be 750 light years away from my destination, once I have reached it? ...
Lux Magi's user avatar
6 votes
2 answers
887 views

Why would galaxies (and galaxy clusters) be unaffected by the expansion of space?

"Gravity holds galaxies and cluster of galaxies together, and they get farther away from each other--without themselves changing in size--as the universe expands." Quoted from the OpenStax ...
GulbenkianD's user avatar
2 votes
1 answer
369 views

Will the stars dim in the future because of the expansion of the universe?

We know that the universe is expanding, and that means everything is spreading apart. So does that mean in the future all the stars will dim and eventually disappear in our night sky because of the ...
Prince Pugs's user avatar

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