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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Does an object's redshift actually decrease with time?

I am trying to determine how an object's redshift (specifically, redshift due just to the expansion of the universe) changes in time. Starting with a definition of the Hubble parameter, $$H \equiv \...
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1answer
82 views

Where does the kinetic energy come from if galaxys are moving apart due to the expansion of the universe?

We know the universe is expanding because of the red shift of far away galaxies, the further away the galaxies are the faster they recede. We also know that the energy in the universe (mass and other ...
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1answer
297 views

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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3answers
451 views

Expansion of the Universe: Conversion of gravitational potential energy to kinetic energy?

Suppose there is an object floating in space which over time begins to fall toward the source of a gravitational field. As it falls, its motion happens to be such that it gets locked in orbit around ...
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2answers
132 views

How fast does space/time travel?

It is said that before the big bang there was no before, as space/time was created in the big bang. The big bang creates a rapid expansion of space/time... so how fast is rapid?
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91 views

Expanding Universe Balloon Analogy - Anything Similar for Time?

It is difficult to imagine the infiniteness of space and how it itself is expanding rather than the universe expanding into something else. A helpful analogy is that of drawing little dots (...
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1answer
110 views

What is the value of the Universe's acceleration? [closed]

Please read this http://www.researchgate.net/publication/282157370_VALUE_OF_THE_UNIVERSE%27S_ACCELERATION Your ideas are welcome.
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1answer
49 views

Explanation and quantum gravity [closed]

Is spacetime accelerating? Is it accelerating within an acceleration ?Or is it a constant? (are different objects or particles influenced by other rates in spacetime compared to one-another and if ...
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4answers
675 views

Could the acceleration of universe expansion be caused by gravity itself?

Dark energy is suggested to be a repulsive force in the universe causing an accelerated expansion. If the amount of mass outside our observable universe is greater than inside (higher mass density), ...
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2answers
156 views

Why does dark energy seem to push things apart? [duplicate]

Ordinary matter acts to slow down the expansion of the universe. That makes intuitive sense, because the matter is exerting a gravitational force, acting to pull things together. Moreover, dark ...
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2answers
93 views

What evidence is there for additional dark energy coming into existence when space increases?

As I understand since cosmological constant is a 'constant' - increasing the space must generate additional dark energy that fills that space This does sound counter-intuitive to me, but I am sure ...
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1answer
93 views

Could observed accelerating expansion be an illusion based on distance?

The thought occurred to me that if we just happened to be born into a time when the the universe started slowing down, it would take some time for us to observe this - especially in more distant ...
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1answer
80 views

If everything in the universe doubled in size overnight, would objects in space appear to move slower? [closed]

I've been struggling with this question for a while. Imagine an object moving from planet A to planet B at a constant speed of lets say 10 m/s. If everything suddenly doubled in size, I would imagine ...
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3answers
234 views

How does dark energy allow the universes expansion to accelerate?

I was wondering how dark energy is effecting the rate at which the universes expansion occurs.
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3answers
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1answer
595 views

How is “little $h$” measured in cosmology? The dimensionless parameter from the Hubble constant, $H_0$

Hubble's law has been well-know for close to a century now. It is written as $v = H_0 d$ where the Hubble constant $H_0$ is the constant of proportionality between recession speed $v$ and distance $...
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2answers
81 views

could anti-matter black hole is sitting at the center of the universe ? that have all the aniti matter [closed]

i am very curious about the space , matter and anti-matter , i am not a scientist but i have few question , can we calculate the speed of expansion of the universe? , i have made some assumption or ...
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2answers
593 views

If the universe is expanding will gravitational attraction eventually go to zero?

Let's assume that we prove that dark matter exists (after all, only about 4 percent of the entire universal mass is atoms, and 22% dark matter, 74% dark energy (I think I got the numbers right)). ...
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6answers
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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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1answer
100 views

How is the speed in Hubble's law determined, if not from the Doppler shift?

Hubble's law originally mentions the speed (i.e. proper motion) of a receding galaxy, as calculated via the Doppler effect from the observed redshift. However, the observed redshift is today explained ...
2
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3answers
211 views

Is it possible that photons lose a small amount of energy over time to become redshifted instead of being redshifted because of an expanding universe? [duplicate]

Can photons lose a small amount of energy over time when traveling large distances due to either weak interactions with magnetic fields (Faraday Effect) or due to the way all objects cool and give off ...
2
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1answer
213 views

Redshift and shapes of galaxy clusters

How does peculiar velocities lead to the observed elongation of galaxy clusters in redshift space, otherwise known as the Fingers of God effect? I have read the relevant Wikipedia page, but cannot ...
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1answer
55 views

Does Schwarzschild metric have cosmological horizon?

Since the space is not expanding in the Schwarzschild metric does that mean that there is no cosmological horizon? Also, what if the Schwarzschild metric was not asymptotically flat and we replace ...
2
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0answers
92 views

When spacetime expands to the point where galaxy clusters are not observable, will there by any interaction?

It's my understanding that in a few billion years, clusters of galaxies won't be able to directly observe one another due to the expansion of spacetime overcoming gravity between those clusters. ...
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6answers
717 views

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 ...
4
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1answer
203 views

Thought experiment: Tethered galaxies - to the extreme [duplicate]

If two rocks were tied together with a tight, absurdly long, non-elastic rope, and placed on planets at either end of Earth's observable universe - or beyond - What would happen? Is the structural ...
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0answers
50 views

Modeling of Big Bang [duplicate]

Well, I’m just an ordinary High School passed student. I had passion towards space-time- relativity and other things related with physics :D I have been watching theories of physics like Big Bang from ...
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1answer
44 views

How does space expansion affect cosmic rays?

As high energy protons travel through expanding space do we measure some physical difference depending on how far they travel before reaching us?
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1answer
49 views

Equations for Big Bang expansion, distance and energy

On the back page of the CPEP poster “The History and Fate of the Universe” a table gives distance scale (size), temperature, and energy (radiation) for seven expansion times (10-43 sec to now). http://...
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3answers
131 views

Is there any situation in which a primordial black hole-sized black hole form AFTER the “Big Bang?”

I have seen that primordial black holes may have formed at the start of the universe due to the density of matter. So, is there any way in which our current Universe could spawn a non-stellar mass ...
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1answer
25 views

What is our confidence with respect to the critical density of the universe? [closed]

How can scientists speak confidently about the critical density of the universe while knowing the majority of matter and energy is foreign and not well understood. Shouldn't more knowledge about dark ...
3
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2answers
245 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. My ...
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2answers
98 views

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 ...
5
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1answer
103 views

Since space expands (and can theoretically contract) faster than light, does that mean that in a big crunch information could travel FTL?

Layperson here. In a theoretical big crunch with space contracting faster than the speed of light, would information be travelling faster than speed of light? Because the points A and B themselves ...
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1answer
56 views

What is the difference between the expansion of space and the Alcubierre drive?

The Alcubierre drive violates causality. As far as I know the expansion of space does not. The usual explanation for why space is allowed to go FTL is that the matter doesn't move. The Alcubierre ...
3
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4answers
670 views

How long does it take for expanding space to double in size?

I have been reading about Hubble's constant and trying to make 'sense' of the theory of the expanding Universe. Is is possible that space in the universe expands uniformly? If so, absent of other ...
4
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1answer
59 views

What is the analogous effect of cosmological redshift for particles with mass?

Due to the metric expansion of space, light emitted from earlier times in faraway parts of the universe and travels for a long time to reach us get progressively redshifted, decreasing the energy of ...
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1answer
95 views

How does the Higgss field change with the expanding universe?

Does the expanding universe really have an effect on the Higgs field? Say, is it like the matter getting diluted with the expanding universe? Or does the expansion does not have any effect on the ...
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3answers
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Does the accelerated rate of expansion of the Universe have any effect on the speed of light in vacuum?

So I was just wondering about this as I finished reading about Michelson-Morley's experiment which disproved the ether theory. My question is since the Universe is constantly expanding and that too ...
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0answers
24 views

Backtracking position [duplicate]

Using a hypothetical photo from a hypothetical telescope, we were able to determine that the farthest galaxy present in the photo is 1 billion light years away. Because we are awesome we were able to ...
2
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1answer
724 views

Misconceptions about the universe - Hubble Sphere

I recently watched Veritasium's (excellent) video "Misconceptions about the Universe". However, he said something (at 2min 25s) which I think is wrong. Can somebody please clarify this one way or the ...
2
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1answer
54 views

Dark age of the universe

during the early universe and just after the habitable epoch,when the universe was finally cooled down allowing the ions to recombine into atoms, comes the Dark Ages who are currently thought to have ...
0
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1answer
127 views

Faster than speed of light [duplicate]

I was watching a Physics TV show, When someone called Alex Filippenko said that when there was the Big Bang, the Space extended at a speed faster than speed of light. He said that it wasn't against ...
2
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2answers
60 views

Cosmology: what is a quantity that is called “$h$” in regard to angular size of a galaxy?

I am trying to solve a Cosmology problem, but a certain quantity $h$ appears in it, of which I do not know the definition (I have never seen it mentioned anywhere before). So I thought maybe someone ...
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0answers
18 views

Consequences of space-expansion in the Universe [duplicate]

Current theories about Universe dimensions and age put them - respectively - at about 90 G light-years wide and 13.8 G years old. To avoid implying that matter travelled faster than light, theories ...
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2answers
82 views

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 ...
5
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1answer
231 views

Speed of light and current dimensions of the universe [duplicate]

I've seen several documentaries explaining that the diameter of the universe is currently estimated at over 90 billion light-years. And which that - in the face of the age of the universe being about ...
0
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2answers
93 views

Special and general relativity and space time

I have a question. I'm reading The Elegant Universe and it's talking about the special and general theory of relativity. One of the things it mentions is that time and the three dimensions of space ...
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2answers
162 views

Where does the energy go when light is redshifted? [duplicate]

Imagine a galaxy millions of lightyears away and, obeying Hubble's law, moving very quickly away from us. Now imagine the same galaxy emitted a green photon in our direction (a photon with a ...
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5answers
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Does entropy increase or decrease as our Universe is expanding?

Scientists say that entropy of our universe is increasing as it is expanding and our universe is cooling down gradually from the time of its birth. If something is getting cooler and cooler, then how ...