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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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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3answers
140 views

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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68 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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61 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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58 views

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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29 views

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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44 views

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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1answer
57 views

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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2answers
112 views

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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4answers
531 views

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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2answers
73 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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63 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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119 views

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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48 views

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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184 views

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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2answers
250 views

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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111 views

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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599 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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51 views

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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4answers
83 views

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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106 views

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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1answer
98 views

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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191 views

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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1answer
52 views

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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76 views

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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89 views

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 ...
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603 views

Exploring beyond event horizons

In the expanding universe the velocity of separation between galaxies depends upon how far they are. If they are much far away will they have relative velocity of separation greater than speed of ...
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38 views

How Do we Know How Old the Universe Is? [duplicate]

It is common knowledge that the universe is 13.8 ± 0.037 billion years - but how was this calculated?
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How far away must a galaxy be for its light never to reach us due to the expansion of the universe?

My understanding is that at the present rate of expansion of the universe some galaxies are growing more distant from us at such a rate that light from them will never reach us. My question is how far ...
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119 views

Infinite Universe and Big Bang

A common view now in the physics community is that the Universe is infinite in extent (which makes Hubble sphere an infinitely small part of the Universe). On the other hand, there is the Big Bang ...
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Can Einstein's constant explain expansion?

I read somewhere that Einstein or Newton believed that the universe was completely static, where it neither expanded nor contracted, but simply remained fixed. It was concluded that due to attraction ...
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Do things in the universe get farther apart or bigger? (Amateur)

To start off I would like to say I am a complete amateur and have no experience in physics! I am just a sophomore in high school with some questions. Now that that is out of the way. There are many ...
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49 views

Light speed after the Big Bang

We know that immediately after the Big Bang space was opaque to light. As space expanded, light could travel. However I would think that as space expanded at some de sites the light would be much ...
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142 views

Is the big bang a fact? [duplicate]

I have watched many physics debated and in everyone of them, physicists take big bang for granted. But, is the big bang actually proven, or there are many evidence that indicate that it did happen?
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Space Between Current universe and point of origin [duplicate]

If universe is expanding like a balloon from point zero to current space time. what is there in between the point of origin and current universe. Is there still hot energy in between the current ...
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5answers
854 views

Does our solar system rotate parallel or perpendicular to the direction of the expansion of the universe? [closed]

Or is it a little more complicated than that? A friend recently posted a video on Facebook of a 3D model of the solar system rotating like a corkscrew chasing after the sun. It looks completely ...
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25 views

How is expansion of the Universe consistent with the speed of light? [duplicate]

I have a question that I believe is related to @PetTaxi's question here: How far has a 13.7 billion year old photon travelled, but I didn't want to hi-jack it. My issue is this. I'm assuming the ...
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3answers
222 views

How far has a 13.7 billion year old photon travelled

I've read that the size of the observable Universe is thought to be around ~46 billion light years, and that the light we see from the most distant galaxies were emitted ~13.7 billion years ago as a ...
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23 views

Expansion rate in matter dominated era [duplicate]

Do physicists know what the expansion rate of the Universe was at the beginning of the matter dominated era?
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431 views

Are the distances we measure to objects in the universe incorrect because of their relative motion?

For example the agreed distance to the Andromeda Galaxy is 2.5 million light years, and consequentially, we see the galaxy as it was 2.5 million years ago! (A time interval in which the galaxy must ...
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1answer
230 views

What caused the expansion of the universe to slow down after the inflationary epoch?

As everyone knows, when the big bang happened, the universe expanded at an unbelievable rate and this was called the inflationary epoch (or more popularly cosmological inflation) which lasted for ...
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What will happen to a naked singularity during the Big Rip? [duplicate]

I apologize in advance if some concepts I use are vague, but I am just an enthusiast. I have read that the Big Rip will not rip off black holes because the event horizon will become equal to something ...
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1answer
112 views

Does dark matter in the universe acts as a pulling force or a pushing force?

Scientists have claimed that in this world there are two kinds of forces which help in keeping everything in its place called dark matter and dark energy. But are these two forces act as a pulling ...
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37 views

Is There A 'Leading Edge' to the Universe? [duplicate]

Is there a center to the universe? Did the Big Bang happen at a single location, spreading outwards? Or, was the Big Bang more of a state-change, in which the universe went from super-dense and ...
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119 views

Where's all the light going in the universe?

According to my knowledge, matter can not go faster than light, and light is emitted constantly in the universe from many types of reactions. If this is so, then isn't light constantly getting past ...