Questions tagged [space-expansion]
Space expansion is a cosmological phenomenon wherein the proper distance between two spatial points for a given inertial reference frame increases from one moment of time to another. That is, space itself expands; the added distance is not due to relative motion of points or objects.
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Difference between new inflation and chaotic inflation
I'm trying to understand the difference between new inflation and Linde's chaotic inflation. From what I understand, according to the old inflation, during inflation empty space remains empty, so its ...
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How big was the surface of the cosmic background radiation?
The cosmic microwave background radiation is the furthest and oldest visible light in the universe. But the universe has expanded considerably since that light was emitted. At the time that that light ...
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Visibility of our Universe by an Observer outside [closed]
In my own theory/understanding of our universe I believe that EM radiation does not leave the universe because the method /medium for light travel was created during the expansion thus only existing ...
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Are the mass, diameter and age of the Universe frame dependent?
Mass of the observable Universe is known to be $1.50×10^{53}$ kg. Age is approximately known to be 13.7 billion years.The observable Universe is a sphere with diameter of roughly $8.8\times10^{26}$ m.
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What would happen if two super-massive black holes collide faster than the speed of light? [closed]
I know objects can't move through space faster than light. But there's no law against the expansion of the universe increasing the distance between two objects faster than the speed of light. But this ...
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Does inflation theory assume a finite universe?
Inflation theory has it that the early universe was causally connected, and could “mix”, hence explaining relative homogeneity of the CMB. The universe then rapidly expanded and became causally ...
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Can a receding body due to the accelerated spacetime expansion be "rescued"?
Once a body "crosses" the limit where dark energy wins over gravitational forces (Is there a distance from a gravitational source where the influence of gravity and dark energy are balanced ...
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Is Dark Energy Taking Over?
First question, trying to keep it simple 😃
Because it's constant it grows in magnitude as the universe expands, whereas normal matter does not? Is this accurate as far as we know?
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How to derive deceleration parameter in terms of redshift?
How do I get q in terms of $z$ specifically of this form:
I want to derive the second equation from the first but I'm getting an additional $ \frac{a^2}{H^2}\ $ in the second term
$$ q= -\frac{\ddot{a}...
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Dark energy, bound systems and orbits...?
As far as I understand it, dark energy can affect bound systems at cosmological scales (How does dark energy affect the dynamics of galaxy clusters?) effectively modifying their orbits.
This ...
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Is the universe really a closed physical system? [closed]
It is assumed in most physics discussions that the universe is a closed physical system. But is it really? I am defining the universe as the entirety of everything physical, not merely the observable ...
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Andromeda Galaxy and Hubble
When Hubble determined the distance to Andromeda he based his estimation on Cepheids. However, the result was less than half the current value. What was the cause of this error and could another ...
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Does Dark Energy contribute to increase the isothermal temperature of plasma in galaxy clusters?
I have a question about this work called "Dark energy and key physical parameters of clusters of galaxies"
There, towards the end, the authors talk about the isothermal velocities and ...
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If the expansion of space causes the elongation of light waves, why isn't this elongation observed within the Milky Way?
The elongation of light waves occurs not because galaxies are moving away from each other, but because light waves are stretching along with the fabric of expanding space (cosmological redshift). ...
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The equation of motion for the scalar field
Consider a scalar field ϕ with the following Lagrangian density in the FRW scale factor:
$L= (-\frac{1}{2} \partial_{\mu} \phi \partial^{\mu} \phi -V(\phi)) \sqrt{-g}$,
the motion for ϕ in this ...
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Confusion about Hubble law vs. objects freezing at the cosmological horizon
I am puzzled about an apparent contradiction. In a universe with a Hubble law, you see that, the farther an object is, the faster it is moving away from you. On the other hand, you also have a ...
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“Negative energy” definition of “gravitationally bound” in expanding cosmology
First off, I realize that there is already a number of questions relating to gravitational binding in cosmology:
Gravitationally bound systems in an expanding universe
Gravitationally bound systems ...
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Clocks at different redshift: does calculating luminosity distance shift the frame of reference?
Luminosity is energy per time.
When we calculate a luminosity distance, using angular diameter distance times $(1+z)^2$, I think we are correcting the energy (from redshifted photons) by $(1+z)$ and ...
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How to express the linear growth equation in Cosmology in terms of $\partial_a$
I am trying to understand the following claim from a professor, in the context of studying the evolution of the fluid that fills the universe according to Cosmology:
If we take the linear growth ...
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Not an "intelligent design" question: How do galaxies collide given the Big Bang? [duplicate]
If all matter began from one infinitesimally small point, and flew outward from there. How can we have galaxies colliding? Did they make left hand turns or something? Or it is possible multiple ...
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Why is it that the further a galaxy is, the greater is its recessional velocity?
The exam question is:
Explain how red-shift provides evidence for the Big Bang theory.
One of the points in the answer is:
the further away the galaxy is, the greater is their recessional speed
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Why is the cosmic background 4K? Where are the other photons? [closed]
The cosmic background is 4K. Where are the other photons? A 4K photon produced at the big bang is detected by our detector. Time stops for the photon and hence we are seeing the big bang. Shouldn't we ...
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Why are there no enormous galaxies near us?
Recently the James Webb space telescope detected six massive ancient galaxies. They are very old and very far away. But these galaxies must still exist today and be even heavier now. Why can't we see ...
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Is there a distance from a gravitational source where the influence of gravity and dark energy are balanced out?
While gravity is a force that attracts
objects with mass, dark energy (or, alternatively, the accelerated expansion of the universe) is not.
However, I have found numerous articles, forums, questions ...
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Why isn't the curvature scale in Robertson-Walker metric dynamic?
$$ds^2=-c^2dt^2+a(t)^2 \left[ {dr^2\over1-k{r^2\over R_0^2}}+r^2d\Omega^2 \right]$$
This is the FRW metric, here k=0 for flat space, k=1 for spherical space, k=-1 for hyperbolic space. $R_0$ is the ...
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How does dark energy affect the dynamics of galaxy clusters?
Galaxies interact with each other gravitationally (just as every other celestial object) and in many cases they form groups or clusters.
Does the expansion of the universe (or dark energy) affect the ...
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Space expansion or generation [duplicate]
When physicists assert that space is expanding, does this imply the creation of new space? If so, why do they use the term "expansion" instead of "generation"?
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Vector perturbations in an expanding universe
Why vector perturbations in an expanding universe decay while the scalar and tensor perturbations don't?
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Why easiest path from Big Bang to Heat Death is not followed by nature? [closed]
Why after Big Bang it is not going to Heat Death in the easiest path, actually the energy can get distributed uniformly to all directions. Instead we see the energy in Big Bang is being converted to ...
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Momentum in terms of comoving velocity in cosmology
I want to understand why the following relation holds in the context of Cosmology, considering that $m$ is the mass of a particle of the fluid that fills the universe:
$$\vec{p}=am\vec{u}$$
where this ...
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Does the current size of the cosmological sound horizon play a relevant role in the universe?
I am doing some interactive plots about cosmological horizons and in my research I stumbled upon the sound horizon, the baryonic acoustic oscillations and how it had an impact on the formation of the ...
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Has the age of the universe changed in 2023?
I teach high school physics and physical science. I was going through the definitions of theory and law when a couple of my students (of different periods) asked about some recent development that ...
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What is the formalism for calculating the vacuum energy density from the observed data of the expansion of the universe?
Wikipedia states here the calculated effective vacuum energy density value of free space from the observed and collected cosmological constant data of the 2015 Planck telescope satellite mission. But ...
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Are we surrounded by Big Bang? [duplicate]
Maybe the questions is too stupid to be asked or I do not know the technical words, but I could not find any answer to this question.
Here is how I started to think the title:
First I thought of if we ...
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What was the size of the observable universe at the matter-dominated era and its mass density?
For instance, at the scale factor $a=0.5$ and matter dominated era, what was the size of the observable universe and matter density?
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Hypothetically, could the interior of a black hole look exactly like the universe that surrounds us?
I do understand that we can't experimentally verify anything we imagine about the interior of a black hole.
If we were to apply what we know about the physics of the observable universe and assume ...
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What is the expansion of space of one megaparsec in one year?
suppose we know Hubble's constant. In a hypothetical scenario an astronomer finds and confirms Hubble's law for a galaxy 1 mega parsec away.
Next year, how much distance will the hypothetical ...
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What is the correlation between the Hubble tension and Dark Energy?
When Dark Energy was first discovered it was because we noticed that distance type 1A supernovae were dimmer given their perspective redshifts.
However, to determine the Hubble constant in the late ...
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Could you have a universe with part of it collapses and part of it expands forever
Lets imagine you have a universe where the average matter density is extremely close the the boundary between one that will expand forever and one that will eventually re-collapse. Now lets imagine ...
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What causes a big rip?
If dark energy has $w<-1$ you get the Big rip scenario, where dark energy becomes more and more powerful until it eventually rips all matter apart. Why does this occur? Why does having $w<-1$ ...
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Could entropy ever be reversed in the universe with infinite time?
In the far future there will be most likely a point where a maximal state of entropy will be reached in the universe where no more useful work could be done and no structures would form, reaching a ...
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How does the gravitational potential change when using physical instead of comoving coordinates?
If we consider the universe as filled by a self-gravitating fluid, then there will exist an associated gravitational potential $\phi$ and the Poisson equation $\nabla^2=4\pi Ga^2\rho$ will hold, where ...
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Poisson equation in Cosmology at first order in perturbation theory
The book Cosmology by Daniel Baumann states that the Poisson equation for a universe where we consider the effects of both gravity and expansion, expressed in physical coordinates $\vec{r}=a\vec{x}$, ...
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Expansion of Universe and validity of law of conservation of energy [duplicate]
It has been proved by the Red Shift that universe is expanding. But if the universe is actually expanding, it needs energy to do so. I also do not know that with expansion in universe if mass ...
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Poisson equation in universe with gravity and expansion
According to the book Cosmology by Daniel Baumann, the Poisson equation for a static universe (a universe without expansion) where gravitation is neglected is the following, denoting by $\phi$ the ...
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Why the ant on rubber rope paradox does not work in our universe or de Sitter universe?
The ant on rubber rope paradox says that an ant moving along a rubber rope that can infinitely expand will reach the other end of the rope regardless of how fast the rope expands and how slow the ant ...
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Does The Big Bang Require An Infinitesimal Point, Or Is Another Shape Possible? [duplicate]
Einstein's Spacetime has four dimensions. If the size of one of these dimensions is zero, then the four-dimensional 'volume' - or whatever the corollary to 3D volume is called in 4D - would be zero.
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Why would we correlate dark energy to the rate of universal expansion: $dS(x,y,z)/S(x,y,z)$ and not to the flow rate of cosmic time $dt/t$?
Cosmic time, which is the same from one place to another (at a given instant), is it also the same from one moment to the next?
To compare the cosmic time at two different instants,
we would need ...
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Does the universe have an infinite volume? [duplicate]
The implications of a spatially infinite universe is profound, but so are the implications of a finite universe. What we know about this issue?
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How long would take for other galaxies to be unobservable due to Cosmic Expansion?
I heard that if Universal Expansion continues at some point galaxies will be so separated that a future civilization would have no way to know there are other galaxies, for them the Galaxy they live ...
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