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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Size of the universe from CMB?

The CMB is almost 13.8 billion light years away in every direction so the diameter of the visible universe as we actually observe it is 27.6 billion light years, twice the distance light traveled over ...
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Space is expanding but the space around me isn't [duplicate]

Everyone says space is expanding and distances between galaxies growing. But space isn't limited to outside of the earth. Space is everywhere on earth and around me. However I don't notice any ...
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Is it possible to learn about an event that occurred outside of your observable universe?

I have mixed intuitions about this. On one hand, nothing can travel faster than the speed of light and if there is enough space between you and an event then a signal will get stuck in the middle of ...
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Dark Energy Density Paramater For Unlimited Expansion

Suppose that the universe is dominated by matter and dark energy. Let $\Omega_m$ and $\Omega_\Lambda$ denote the respective relative density parameters. Given $\Omega_m$, what does $\Omega_\Lambda$ ...
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91 views

In what manner does momentum of a particle with mass decrease due to spatial expansion?

I've read that the momentum of particles declines due to the universe's expansion. In particular, that $p \propto \frac{1}{a}$, where $a$ is the scale factor. For light, this momentum reduction ...
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Looking at past events by observing sky? [duplicate]

Since solar system (and our galaxy) is constantly in motion at a great speed, is it possible that we can look at our own image as it was sometime ago? Since the light of that age takes sometime to ...
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110 views

Why is the universe expanding while its components actually attract each other?

First of all, what's the difference between gravity & gravitation? Anyway that's not the actual question. If every matter attracts each other toward itself, then wasn't the universe supposed to be ...
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82 views

Gravity's force on space

Here is a quote from Brian Greene, The Fabric of the Cosmos: Space, Time, and the Texture of Reality, p. 273: “The early universe provided an arena in which gravity exerted its repulsive side with ...
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21 views

Ripples from the big bang

A pebble dropped in a pond creates ripples of concentric circles. Each larger circle having infinitely more points than the smaller ones inside. If we use any arbitrary size for the unit "point" with ...
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Can space move? [closed]

I have some questions; I hope you don't mind: $\bullet$ If the space between two distance galaxies is increasing, then is the volumes of space in which the galaxies find themselves also moving apart? ...
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Expanding universe via vaccuum?

I was wondering if anyone looked at the expanding model of the universe in terms of a vacuum pulling the universe out rather than an explosion pushing the universe outwards? Or explain why this model ...
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Backwards in time?

A “Universe Today” article titled “Galaxies Are Moving Away From Us Faster than the Speed of Light” prompted the following question, which the author of the article was unable to answer: “Would such ...
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1answer
195 views

Is the Universe infinite or it's just expanding to infinity?

According to the WMAP data in the past years we can say that our universe is considered flat or at least nearly flat and we also know that flat universe is allowed to be both infinite or finite in ...
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55 views

According to some theories space is constantly expanding but at what granularity? [duplicate]

One idea from cosmology is that galaxies are all moving away from each other. Naively this could be taken to mean that they are expanding into something. Popularly this could be seen as them moving ...
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56 views

The steady state theory, can it now be falsified on particle physics grounds, in addition to CMB data?

The steady state theory is no longer taken seriously by most physicists and the Big Bang theory is supported by an enormous amount of evidence, especially the CMB data. But from a quick scan through ...
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240 views

Has neutrino redshift been observed?

I understand that neutrinos are emitted when supernova explode. I presume that there are quite accurate models that predict the energies of those neutrinos at the time of emission. Has the phenomenon ...
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1answer
54 views

Effect of redshift on energy conservation [duplicate]

Light coming from galaxies that are going away from us is redshifted. Since the energy of a photon is purely dependent on its frequency one may conclude that the energy of these photons decreases. The ...
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1answer
68 views

Do sound waves travel before Big Bang?

So I was reading a Scientific American article about how the universe is spreading apart and how it is getting faster. But in the article there was something that baffled be and it was this "Sound ...
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1answer
41 views

Are the edges of a galaxy moving inwards?

Space is expanding, but as I understand it, galaxies are not since gravity keeps them together. If you think of space becoming bigger, your galaxies just become further apart. But taking the size of ...
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61 views

Why is the expansion of universe continuously increasing? [closed]

If our universe is expanding and the concept of the multiverse is true, then why is the rate of the expansion of the universe increasing? Surely it must decrease?
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69 views

Does a rigid box of gas cool over cosmological timescales?

According to standard cosmology theory the physical momentum $p$ of both massive and massless particles decay like: $$p \propto \frac{1}{a(t)}$$ where $a(t)$ is the scale factor as function of ...
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54 views

Outer Space & Universe Expansion: [duplicate]

Experts agree that the stuff within the universe is moving farther apart from all the other stuff in the universe--much like the dots marked on the outside of a balloon that is being inflated. We ...
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2answers
86 views

Big Bang: Initial velocity of all matter in four dimensions? [closed]

Consider this hypothesis: Two objects A and B, are able to maintain their spatial distance. Object A is near a neutron star, and thus it clock is running at a different speed than object B, and both ...
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3answers
342 views

If the expansion of the Universe accelerates, why its horizon does not shrink?

In de Sitter (expanding) universe to which our universe asymptotically approaches, the higher the rate of space expansion, the smaller the radius of the cosmic horizon. Why then our universe is ...
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2answers
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Interpretation of cosmological redshift

I was trying to understand why we cannot explain the observed redshift of distant galaxies using special relativity and I came upon this article by Davis and Lineweaver. Unfortunately when I arrive ...
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1answer
59 views

Black hole surrounding an object?

When a particle crosses the event horizon of a black hole, at one short moment in time would it appear for that particle as if it was surrounded by a black hole? Regardless of which direction you ...
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1answer
113 views

How does the expansion of the Universe affect Black Holes?

As know our Universe is expanding, which I have always visualised as some stretching of the metric of space-time, which "flattens" it. In the same time. our theoretical perception of Black Holes ...
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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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2answers
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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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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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2answers
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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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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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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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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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2answers
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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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3answers
244 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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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 ...
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3answers
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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 ...
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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 ...
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3answers
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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
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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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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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
26 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 ...
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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 ...
5
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2answers
73 views

Is there a proof that space expanding produces observers at all points that see what we see?

I know that galaxies are moving away from us, and so can see that it's intuitive that if space was expanding, then the astronomical observations from Earth would be the same as at all other points in ...
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2answers
298 views

Isn't the accelerating expansion of the universe intuitive?

I have a question about accelerating expansion of the universe. My understanding is that Hubble said the farther our we look into the universe, the higher the redshift, therefore the faster things ...
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1answer
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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 ...