Questions tagged [expansion]
Questions about the increase with time of distance between two distant points in the Universe.
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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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where are we in the universe as compared to the observable universe? [duplicate]
For distant galaxies to be accelerating away at equal speed in every direction, Earth would have to be at the centre of the universe. Since it is not, some region of the distant galaxies should appear ...
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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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Can the expansion of the universe cool my beer?
So the expansion of the universe stretches the light traveling through the void, as demonstrated by the cosmic microwave background radiation. These photons are lower energy than when they are ...
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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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Does the expansion of space stretch the space-time fabric?
This question appeared to me when I was thinking about General Relativity. During the expansion of space, the space in which particles reside is expanded. Now, general relativity states gravity is the ...
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Can the curvature of a closed universe be measured?
Suppose we were in a closed universe likened with a spherical surface such as that of the Earth's surface.
Assume also that the limits, represented by the limits of the observable universe, ...
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Coasting universe Hubble parameter behaviour
I’ve recently been trying to wrap my head around the potential behaviours of the Hubble parameter over time for various cosmological models but I’ve run into a little snag when it comes to a coasting ...
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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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Gas heating due to high viscosity?
Has there been any observation where a gas or a fluid expands following the Hubble flow (the expansion of the universe) and gets heated because it has a large viscosity (transforming its kinetic ...
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Expansion-Collapse cycle in cosmological structures?
Concerning cosmological structures (like galaxies, clusters of galaxies, gas bodies, superclusters...etc) if the elements that make them are close enough they will be attracted towards each other by ...
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Kinetic energy in cosmology?
Spacetime expands at an accelerated rate due to the Hubble flow. In many papers that I've read, objects coupled to the Hubble flow are treated as if they have some velocity and kinetic energy ...
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Can objects join the Hubble flow for a given amount of time and then somehow abandon it?
When two objects (e.g. two galaxies) are sufficiently far apart, they join the Hubble flow and they get further away from each other. Normally, this would last "forever" (until, from the ...
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Critical density and Hubble parameter
Is it possible for the Hubble parameter of an /expanding/ universe made of radiation, matter and cosmological constant to be increasing with time? I'm trying to figure out if any form of scale factor $...
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Farthest distance two objects are "gravitationally bounded", considering expansion of the Universe
The narrative is: "on greater scales the expansion of the Universe dominates, but on smaller scales gravitationally bounded objects still stay bounded". But how small is meant by "...
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Limits of the universe
I am considering the limit in the expanding universe where the expansion matches the speed of light.
If we consider that the expansion is accelerating, how will the situation be after the next 14 ...
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Does gravitational lensing disprove the cosmic expansion theory [closed]
Recently there was a picture from the JWST that showed a galaxy that was 12.5 billion light years away. Its light had been lensed by a galaxy that was 5 billion light years away. In a static universe ...
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Would an observer standing at the edge of the "observable universe" perceive the expansion of space-time?
I got this bizarre idea in my mind, after reading SCP-3321
There, as a person gets teleported through a wormhole, ends up at the edge of the Observable Universe, 46 billion light-years away from Earth....
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Deviations of conservation laws in the context of cosmological evolution?
If energy is "not conserved" in General Relativity (or at least, it is difficult to define it) in the context of an accelerating expanding spacetime (like it happens in our Universe), are ...
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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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How do we know universe is expanding and not light slowing down? [duplicate]
We tend to take some things for granted, for example the light of speed is constant, but what if it isn't? How can we know that light is not slowing down at great distances for example, or that light ...
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Why is the Hubble parameter constant for an accelerating universe?
The Hubble parameter is thought to become constant and to attain a value of about 60 km/s per parsec. So every second a parsec of space grows with 60km. Is this consistent with an accelerated ...
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Distance of distant galaxies
Can two galaxies, one with a redshift of 7 and the other a redshift of 8 have the same angular distance (distance from the Earth during the emission of the observed photons)?
If not why ?
Example: ...
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Does a measuring stick with a size of a billion lightyears in intergalactic space keep the same length in expanding space?
Imagine a measuring stick (a rod or ruler) made of ordinary matter which has a length of a billion lightyears. The space surrounding the ruler expands. Will the ruler keep the same length by the ...
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Will dark energy always repulse observable/dark matter?
We know that the universe is expanding at an increasing accelerated rate, but the ratio of dark energy to observable matter remains constant as dark energy remains constant (please correct me on this)....
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Calculating the "Turnaround Point," where expansion dominates over gravity
I'm trying to understand the point where the expansion of space dominates over gravity, but I'm coming up empty handed when searching the internet. Specifically, I'm trying to find the math for it. I'...
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Can virtual particles with zero energy and non-zero momentum contribute to dark energy?
I know this is actually a physics question, but I can't ask anything there anymore and the same problem walks on my side on other forums... So, I take my chance to ask it here.
A virtual particle is ...
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Why is the CMB's redshift so high?
It is pretty well-established that the CMB was originally emitted around 380,000 years after the Big Bang, at a redshift of ~1100.
The most distant known object is HD1, the light from which was ...
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Expansion rate of an infinite universe at the Big Bang
If the universe is infinitely large, then any two arbitrarily distant points must have been arbitrarily close together at some earlier point in time. Doesn't that mean that the expansion rate of the ...
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How far away from us was Earendel star when it emitted the light that is just now reaching us?
From what I've read, the look back time is about 12.9 billion light years, and the current distance to the Earendel star is approximately 28 billion light years...
How close to us was it when it ...
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Strange plot in Max Tegmark book, Our Mathematical Universe
In Max Tegmark's book, Our Mathematical Universe, we can find (in chapter 5, figure 5.3) the following (horrible and poor quality) plot that is supposed to highlight the extreme sensitivity of the ...
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Can the Event Horizon Telescope been used to find intergalactic distances?
Now that we have the Event Horizon Telescope (EHT), why can't we just guess and check intergalactic distances by changing the EHT's focal length? For instance why don't we take another picture of M87,...
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Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?
When we look in all directions, we see distant objects red-shifted, with the size of the red-shift correlated with the distance from us.
As I understand it, the consensus among cosmologists is that ...
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Can we consider the Universe to be some kind of 3-sphere?
This is probably a naive question. I'm learning a bit of cosmology and I've recently covered the so called angular size-redshift relation, which states that in an expanding Universe the angular size ...
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Why are galaxies thought to get bigger with distance in an expanding universe model?
In an expanding universe model. In addition to galaxies getting fainter with distance, they are also thought to get bigger. Thus the surface brightness of the object should decrease with distance. ...
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Does dark energy make galaxies expand over long periods of time?
Does dark energy expand galaxies slightly over time? I would think this could be verified easily (observe if galaxies far away / further in the past smaller and denser), and might make a good ...
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If we could fly off edge of observable universe what would happen? [closed]
If we could be at the edge of expanding universe in a fast space ship such that we could go beyond the edge, what does the science think we might experience?
Would we still be floating in space?
Would ...
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Can we observe galaxies after their recession velocity exceeds the speed of light? [duplicate]
It doesn't make sense to me that light could ever reach us from a galaxy moving away from us faster than the speed of light. But this video says that it can happen. Is this true? Could someone ...
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In an isolated binary system, can the expansion of the universe balance out collapsing orbit due to gravitational waves?
We know that binary systems slowly lose energy due to gravitational waves from the objects moving through spacetime and that if the objects are compact and massive enough, the mergers happen in time ...
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Local neighbourhood and Superclusters
Recently, I watched a YouTube video on Limits of Humanity, by famous Youtube channel Kurzgesagt. It talked about the local neighbourhood, and it is the only group of galaxies which are gravitationally ...
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How distant were the furthest currently-observable cosmic events when their currently-observed radiation was emitted?
(Edited for clarity. Thanks to James K and Connor Garcia.)
This question about the most distant, observable cosmic objects made me wonder if we know the distance that was between us and them at the ...
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How does the hypothesis of the "inconstant Hubble constant" solve the current crisis in cosmology?
It was published in a paper more or less like two months ago. I'd like to know also if more accurate measurements are necessary to close the gap between the model of the universe and the data reported....
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Formula to calculate round-trip travel time based on current distance to far-away galaxy
Cross-posted from Physics Stack Exchange - original
The question was closed as HW-like there.
The Premise
You travel at a constant velocity towards a far-away galaxy. You then travel back at the same ...
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Because the Universe is expanding, what is it taking up?
It is my understanding that the universe is expanding and that matter takes up space. While the universe only contains small percent of matter, wouldn't expansion indicate that the universe is ...
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How is it possible that a universe with mass does not have curvature?
I may know the answer to my question. Mass must curve the universe but the pressure due to energy density may curve the universe in the opposite direction, leading to a flat universe, if they exactly ...
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Universe expansion data validation
I am not an expert, just a enthusiast, so if possible please keep explanation simple.
That said I have start reading about universe expansion and the idea seems to me revolutionary (the image of an ...
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How many galaxies are predicted in the observable universe? Does it contain dwarfs? Is there any size-ratio diagram?
According to quite recent research the observable universe contains about 2 trillion galaxies ($2 \cdot 10^{12}$). But what is counted there? Does this number also contain dwarf galaxies? According to ...
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Does the radius of your cosmic horizon decrease as velocity increases?
If I was moving at c-1 meters per second, and was observing an object moving 2 m/s away from my starting point as a result of the expansion of the universe rather than classical velocity, would I ever ...
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Why are CMB peak heights sensitive to the physical densities
A very simple question: why should it be that the CMB power spectrum allows constraints to be placed on the combination of parameters
$$\omega_c = \Omega_c h^2$$
$$\omega_b = \Omega_b h^2$$
as opposed ...
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What makes a star? [closed]
What are the properties of a star? How do astronomers classify the properties of stars?
