Questions tagged [universe]
Questions regarding all of time and space and its contents.
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Is time finite or infinite? [closed]
I am not a scientist nor do I have a degree in Astrophysics, but I do like to learn new things by asking questions. With that being said, I have read that time is relative to space which began after ...
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Why can we trust Hubble Time if the rate of expansion is not constant?
The age of the Universe can be estimated from taking the inverse of the Hubble constant: $t_\text{universe} = 1/H_0 =d/v.$
It seems to me this method assumes that any given galaxy has been receding ...
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Why does it make sense to say the universe has no centre?
If we suppose we and everything in the universe is perfectly flat. That is, we have width and depth, but no height. And we are situated on the surface of a balloon blowing up with air and expanding "...
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Location of the big bang [duplicate]
If the big bang happened everywhere (as I always read when searching for an answer to "where is the universe expanding from") then we would see galaxies moving not just in an expanding ...
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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 $\...
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How can 'HD 140283' be older than the universe?
Scientists have known about the star HD 140283, informally nicknamed the Methuselah star, for more than 100 years, since it cruises across the sky at a relatively rapid clip. The star moves at about ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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If objects don't move when the universe expands, how can the expansion result in redshift?
I am approaching this topic from a layman's perspective and view this as a logic puzzle, but when someone tries to get me to accept the logic, I'm never convinced by their arguments.
According to ...
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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 ...
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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 ...
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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 ...
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Evidence of CMB redshift
Are there any known spectral lines shifted by ~1100? If not, then how certain is mainstream that the CMB has a redshift of ~1100? All I see is a blackbody radiation curve void of spectral lines.
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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.
...
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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, ...
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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 ...
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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,...
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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 ...
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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. ...
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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 ...
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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 ...
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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 ...
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The energy density of phantom dark energy increases with time. Does it violate the concept of accelerating universe?
Dark energy with equation of state parameter $\omega<-1$ is called phantom dark energy. Its energy density increases with time.
My question is whether this model violates the concept of ...
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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.
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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 ...
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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 ...
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What is in the center of the universe?
If the universe has formed & originated by a Big Bang Explosion, then there must be empty space left in the center of the explosion site, as all the matter is travelling at tremendous speeds away ...
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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, ...
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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{...
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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)...
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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 ...
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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 ...
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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 ...
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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 ...
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How did we measure the mass of the universe?
In an wiki article, observable universe, it was mentioned that,
Mass (ordinary matter) 1.5×10^53 kg
I wonder how did we measure the mass of our observable universe?
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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 ...
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Interpretation of Hubble constant in SI units
The standard interpretation of Hubble constant $\approx 70~\text{km/s/Mpc}$ means that each mega-parsec of distance adds $70~\text{km/s}$ to a galaxy recession velocity from us (or to a space ...
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Solar System formation, considering its and the universe's age
It is known that the Sun is 4.6 billion years old, and the complete Solar System is of a similar age. The class of stars to which the Sun belongs seems to be quite common. Stars of its class can live ...
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Mass Content of the Hubble Sphere
How does the mass encased within the Hubble sphere/volume (both proper and comoving) change with time?
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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 ...
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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?
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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 ...
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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?
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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 ...
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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 ...
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