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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Why do we form cosmological theories based on old data?

Since the light we receive from distant galaxies may be between 7 and 14 billion light years away, the redshift we see indicates that the universe was expanding at that time (7 to 14 billion years ...
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Super-luminal separation

Suppose there are are 5 bodies separating in space (due to it's expansion), and let us consider that they can emit light. 1st body moves in the -x direction, at the speed of light. 2nd body moves ...
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Cosmological constant theories

Are there any hypotheses on the expansion of the universe, which have a cosmological constant, or some other parameter, that results in a universe with an ever increasing rate of acceleration for the ...
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42 views

Redshift of supernova light curve

I am trying to understand how the width of a supernova light curve depends on the redshift of its component frequencies. Let us make the simple assumption that the light curve is Gaussian. The ...
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123 views

How confident are we that mass is not being lost in the universe?

After reading about the latest super-massive black hole in Nature 518, 512–515 (26 February 2015), I couldn't help but wonder if the accelerating expansion is a result of mass being lost. Would a ...
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How does a particular galaxy's apparent recessional velocity CHANGE as the universe expands?

By this I mean will the light from distant galaxies continue to show red shift (i.e. if you look at light from a particular galaxy now and in 10000 years time, the spectra will have been shifted ...
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Do we need Dark Energy to explain the acceleration of the expansion of the universe?

As far as I know is the discovery that galaxies that are farther away are moving faster from us than galaxies the are closer by. This led to the theory of Dark Energy. The acceleration was speeding ...
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Space is expanding so what is time doing? [duplicate]

Space is expanding and as we know space and time are intrinsically linked to be now known as spacetime. What is happening to time during expansion? Is there more time, longer time or is the time part ...
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91 views

Why the CMB has not been dispersed so far?

Imagine you have a box of black body radiation. What happens if you open the box for a long time? It becomes dispersed and no radiation remains in the box. Now, apply this example to the Cosmic ...
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How much has the universe expanded in total from the onset of inflation until today?

Starting from the onset of inflation, through inflation, reheating, radiation domination, matter domination, the transition toward dark energy domination all the way to today, how many e-folds of ...
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If we can see a galaxy can that galaxy see us?

This is a question about the properties of the expansion of the universe. I can't say it any better than: If we observe a primordial galaxy that existed soon after the Big Bang, does it follow that ...
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Has galaxy merger and universe expansion been proven?

I understand the basic argument for hierarchical merging of galaxies during expansion of the universe. I also understand peculiar motion and the Hubble flow. So I understand what's going on with ...
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What is meant by a “sodium line”?

What speed should a galaxy move with respect to us so that the sodium line at $589.0\ \mathrm{nm}$ is observed at $589.6\ \mathrm{nm}$? In the above question what's meant by a sodium line? The ...
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108 views

What evidence is there of a universe older than 13.8 billion years

I've read an analogy that finding iron-rich galaxies just 900 years after the Big Bang is like finding an old man in a crib in a nursery. We just recently found a supermassive black hole 12 billion ...
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185 views

Is the accelerated expansion of the universe consistent with conservation of energy? [duplicate]

If energy can neither be created nor destroyed, how come the universe is expanding at an accelerating rate? Where does this energy come from?
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Assuming the universe is finite, at some point, CMB should go away, right?

I'm not talking about gradual red-shifting, that happens slowly anyway, but with a universe of finite size, we should actually see Cosmic Background Radiation turn off in a sense, first at a point, ...
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Is there any paper analyzing the validity of Relativity in expanding space? [duplicate]

Big Bang models result from applying Relativity equations to expanding space; however, as Einstein noted, Relativity was not established in expanding space. A basic question arises: is Relativity ...
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56 views

Long rod in an expanding universe

Suppose you have a metal rod, of vast length, floating in space. From it's center-of-mass reference frame it is assumed to be at rest with respect to the CMB. The rod will have some degree of ...
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Even the universe is infinite, it could keep expanding? [closed]

the study showed Cantor, that there are infinite types, the universe would be expanding as well as the possibility of Stephen Hawking. http://phys.org/news/2015-02-big-quantum-equation-universe.html
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How do we know the expansion of the universe is “of space” and not “in space” or “into space” or another less intuitive arrangement?

How do we know the expansion of the universe is "of space" and not "in space" or "into space" or another less intuitive arrangement? For example, what implicit and explicit assumptions underlie the ...
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Is it valid to apply Einstein's Relativity to scenarios involving expansion of space?

IIs it valid to apply Einstein's Relativity to scenarios involving expansion of space? For a practical example of this: Is it legitimate to speak of distant red-shift galaxies as experiencing time ...
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1answer
62 views

Is the Big Bang instant considered a beginning of all the coordinates of our universe? [duplicate]

Is the Big Bang instant considered a beginning of all the coordinates of our universe? If we consider the BB to be the Beginning of of our universe, can we call this the Origin of all of the 3 ...
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3answers
60 views

Can we tell the difference types of recession? [duplicate]

Because of the the Hubble red shift pattern, Cosmologist generally assume that space is expanding. They assume this is a fact because of the observed redshifts and GR says it can be so. But how can we ...
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How tall is the universe?

Let's suppose that I am on a spaceship in low-earth orbit, if I rise my spaceship higher and higher and hover it upwards forever, will there ever come a point where I just can't get up any further or ...
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About a *center of the universe* [duplicate]

I understand that the history of our universe began with an explosion - the Big Bang. Now, I saw a comment in some old post, that "the universe has no center". Is that true? If there was initially a ...
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Can accelerating universe avoid Big Bang?

Expansion of our universe is accelerating. This means that it was expanding less rapidly in the past. Is in accordance with the laws of physics a model of accelerating universe in which the rate of ...
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Expansion of the universe in “everyday live” [duplicate]

According to space.com the universe is expanding with 75km/1Mpc/1s (megaparsec), which comes down to $\beta=2.43\times10^{-18}/s$, a relative rate per second. To put this in perspective: The average ...
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How could the “Big Bang” singularity have actually expanded? [duplicate]

We have mountains of evidence about singularities and how they work, and we have mountains of evidence that the "Big Bang" was the origin of the universe as we know it. But if compressing enough ...
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Why do we theorize that the Big Bang created space? [duplicate]

I just asked this astronomy question about how far away the light is that would show us the beginning of time, the Big Bang. Some answers claim that the light I ask about doesn't exist, because "The ...
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62 views

Did the Earth (amongst other things) travel faster than light?

It's often said that when you look far across space with a telescope you are looking back in time, as the light has only just reached our position in space. However, given that the Earth and many ...
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62 views

Expansion of the universe a thermodynamic process or not?

Can the expansion of the universe be thought of as a thermodynamic process? If so, is it a closed system? Is it a reversible system?
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Question about universe expansion

In general relativity, we cannot determine the global structure of the universe (since it is not flat), therefore all measurements and observations are only meaningful locally. In particular, we can ...
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Why do scientists use a different method from redshift to find the distance of distant galaxies?

The method I am referring to is measuring the brightness of a super nova. Does the redshift method even work at that distance and if it doesn't why not? If it does work why do they prefer to use the ...
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Coordinates for FLRW metric

In GR, coordinate are just a tool for us to describe the physics, they should be equivalent. However, in standard form of FLRW metric, it can be inferred that the universe is expanding, but we can do ...
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Would cosmological redshift be present in the following situation?

I'm trying to understand if cosmological redshift is just a secondary form of doppler redshift, or something else entirely. Suppose the two galaxies in the picture are receding from each other, but ...
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Expanding universe as predicted by the Einstein Field Equation

Without the cosmological constant, the Einstein field equation predicts the universe is expanding. Why is that? It is counter-intuitive because generally gravity should pull things closer and shrink ...
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515 views

How do scientists calculate the percentage of dark energy in the universe?

I can understand how the percentage of dark matter compared to ordinary matter is calculated, because the amount of dark matter has a clear gravitational effect on the ordinary matter in a Galaxy. ...
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Expanding possibilities

How does the nature of space-time and how we are able to interact within it relate to the expansion of space? If Space expansion ceased to be a constant would a body of mass still be able to change ...
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Effect of expansion on time?

We know that for moving body times moves at a slower rate, but can this happen for Universe itself whose rate of expansion is accelerating?
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Where does the dark energy of space expansion come from? [duplicate]

Space has a constant density of dark energy, that means dark energy does not dilute with space expansion. By consequence, any space generated by space expansion does generate new dark energy. ...
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Expanding universe - Creation of Space [duplicate]

Is the expansion of the space between the galaxies caused by stretching of existing space or the creation of new space? The fact that the energy content remains constant, and is therefore not being ...
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Are we comoving observers of space expansion?

In cosmology: A comoving observer is the only observer that will perceive the universe, including the cosmic microwave background radiation, to be isotropic. (Wikipedia) According to this ...
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Tired light red shift hypothesis

Have there been any recent attempts to falsify the tired light hypothesis alternative to the Doppler shift explanation for the red shift, or is it simply ignored like the pilot wave quantum mechanical ...
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The Doppler shift and the apparent speed of galactic rotation with distance

A Doppler redshift would also give the illusion that galaxies were rotating more slowly then they are with the degree of illusory slowing in proportion to the degree of redshift. Do more distant ...
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If space is expanding, how can I see a galaxy 12 billion light years away where it is today?

Assuming space is expanding (and that seems plausible), photons from a galaxy that have been traveling for 12 billion years must have been traveling on a curve to get to us due to the fact that where ...
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Expansion of the Universe: is new space(time?) being created or does it just get stretched?

Is new space(time?) being created as the Universe expands, or does the existing spacetime just get stretched? If it just gets stretched, why do galaxies move along with the expansion instead of just ...
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How could gravity affect the expansion of the universe?

I've read several books which talk about gravity slowing down, halting, or reversing the expansion of the universe. The expansion is often compared to a stretching of space at every point, so that the ...
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Compatibility of twin paradox with the time-dependent Hubble constant

The universe is currently expanding with a speed of about 70 km/sec/Mpc which is today's Hubble constant. As this expression includes two length units, it is also possible to use the unit: $sec^{-1}$, ...
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Estimating the expansion of the universe using light from supernova

I understand that you can tell how far light has traveled by the measuring redshift but how accurate is this and could it be effected by anything like radiation from the sun it must be fairly accurate ...
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How can we detect cosmic background microwave radiation? [closed]

From my understanding this stuff expands at or near the speed of light -- and it's origins are that of the creation of this universe (via big bang). Obviously, our planet does not expand from origin ...