# 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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### Since the universe is expanding, does anything ever occupy the same point in space?

Let's say we can observe expansion in a supercluster. We define origin of our frame of reference at the center of the supercluster. We observe an object/atom at point A at time T. The object is ...
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### At what speed does our universe expand?

Conceivably it expands with the speed of light. I do not know, but curious, if there is an answer. At what velocity, does our universe expand?
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### Virtual particle production in space-time.

Are virtual particles created within existing space-time, or do they create new space-time for them to occupy?
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### How can a quasar be 29 billion light-years away from Earth if Big Bang happened only 13.8 billion years ago? [duplicate]

I was reading through the Wikipedia article on Quasars and came across the fact that the most distant Quasar is 29 Billion Light years. This is what the article exactly says The highest redshift ...
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### Cosmic Microwave Background (CMB) and its relation to Inertial Frames

We know that the CMB is isotropic when viewed outside of the spinning and revolving earth. Is it homogeneous? Can we relate the CMB to an inertial frame in the Newtonian sense (in which space and ...
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### composition of space expansion and movement as a gauge invariance

suppose i have a space-time where we have one point-like object* which we will call movement space probe or $\mathbf{M}_{A}$ for short, and it will be moving with constant velocity $V^A_{\mu}$ in ...
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### Given that matter cannot escape a black hole, how did the big bang produce the universe we see today?

Extrapolation of the expansion of the Universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past. If the matter contained within our ...
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### Is there a consensus on the fate of our universe?

We all know that our universe is inflating from what is known as the Big Bang. However, will our universe continue to inflate at the current rate? Or after reaching a maximum size, will it collapse in ...
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### Why is the observable universe so big?

The observable universe is approximately 13.7 billion years old. But yet it is 80 billion light years across. Isn't this a contradiction?
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### What has been proved about the big bang, and what has not?

Ok so the universe is in constant expansion, that has been proven, right? And that means that it was smaller in the past.. But what's the smallest size we can be sure the universe has ever had? I ...
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### Will the night sky eventually be bright?

I have read that the night sky should have been bright because every spot should end up pointing to a star in the infinite universe but this is not the case because the universe is expanding. I am ...
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### Seeing cosmic activity now, really means it happens millions/billions of years ago?

A Recent report about a cosmic burst 3.8 billion light years away. It is written as though it is happening now. However, my question is, if the event is 3.8 billion light years away, doesn't that mean ...
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### Are scientists missing the point with distant cosmic objects, or is it just me?

I was reading this article this morning: http://www.bbc.co.uk/news/science-environment-13539914 Scientists have discovered a gamma-ray burst whose light has taken 13.14 billion years to reach Earth. ...
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### Have CMB photons “cooled” or been “stretched”?

Introductory texts and popular accounts of why we see the "once hot" CMB as microwaves nearly always say something about the photons "cooling" since the Big Bang. But isn't that misleading? Don't ...
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### Expanding universe

If we know the universe is expanding in whatever direction we look, can't we reasonably estimate where the 'center' of the Universe is? Is the rate of expansions in all directions the same?
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### If the Big Bang theory suggests that the Universe is “expanding” then what is it expanding INTO? [duplicate]

I am a software engineer and not an astrophysicist but I want to know if anyone is working on sorting out what exists outside the universe? So what about outside spacetime? what is there? or shall I ...
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### Distance in cosmology

How can we calculate the change in distance over time between (say) two galaxies that they are at rest in respect to each other? In other words, how do we modify the "classical" equation:  \ddot{\...
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### Do cosmological and Doppler redshift produce different patterns?

For a given black body radiation curve, would the changes to the spectrum resulting from cosmological expansion and those from Doppler effects be distinguishable on the basis of the shapes of the ...
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### If the universe is expanding, what is it expanding into? [closed]

If the universe is expanding, what is it expanding into? When the big bang happened where did it occur? When the big bang happened how did it occur? Where did the energy come from? Energy can not be ...
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### Shear, viscosity and expansion of universe

What is the meaning of expansion, shear and viscosity in context of universe? How can we conclude a result after getting a numerical value of above terms?
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### Redshifting of Light and the expansion of the universe

So I have learned in class that light can get red-shifted as it travels through space. As I understand it, space itself expands and stretches out the wavelength of the light. This results in the light ...
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### Effect of expansion of space on CMB

Is it true that the expansion of space time cause the CMB to become microwaves from a shorter wavelength. If it is has the amplitude been increased? Seeing as the amplitude has decreased; why hasn't ...
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### Star trace in the sky

If the space of universe is expanding at fast rates..(even faster than light) Why we do not see the trace of the stars? A possible answer could be that the stars are only moving away but mantaining ...
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### Expansion of space and gravity

In my previous question I asked how gravity can be represented as dents in space. It seems that it's a metaphor. But I wondered with spac expanding does the effect of gravity get bigger as well, I ...
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### The Big Bang in an infinite universe

If the universe is spatially infinite (and assuming, if it makes a difference, that we don't have eternal inflation), what actually happened 13.7 billion years ago? Was the energy density infinite (or ...
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### Redshifted Photon Energy

A photon emitted from a receding source (Doppler redshift) has less energy when detected at an observer's location. Please explain the energy loss from the perspective of energy conservation.
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### Effect of Cosmological Expansion at the Atomic Level [duplicate]

Possible Duplicate: Why does space expansion not expand matter? Does cosmological expansion have any effects at the atomic level?
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### Why did the universe not collapse to a black hole shortly after the big bang?

Wasn't the density of the universe at the moment after the Big Bang so great as to create a black hole? If the answer is that the universe/space-time can expand anyway what does it imply about what ...
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### How Does Hubble's Expansion Affect Two Rope-Tied Galaxies?

Suppose we have two galaxies that are sufficiently far apart so that the distance between them increases due to Hubble's expansion. If I were to connect these two galaxies with a rope, would there be ...
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### What experiments, other than Hubble Expansion, support the Dark Energy theory?

Dark energy is introduced as a constant inside Einstein's equations. Its primary purpose, from what I understand, is to make Einstein's equations compatible with the accelerating expansion of the ...
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### Why does space expansion not expand matter?

I have looked at other questions on this site (e.g. "why does space expansion affect matter") but can't find the answer I am looking for. So here is my question: One often hears talk of space ...
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### What does it mean that the universe is “infinite”?

This question is about cosmology and general relativity. I understand the difference between the universe and the observable universe. What I am not really clear about is what is meant when I read ...
If all distances are constantly increasing, as Hubble's law say, then lots of potential energies of form ~$\frac{1}{r}$ changes, so how is the total energy of the Universe conserved with Hubble's ...