Questions tagged [expansion]

Questions about the increase with time of distance between two distant points in the Universe.

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1answer
49 views

Why does the Hubble flow does not carry photons with it?

I have this naive question. We know that the expansion of the universe "takes" or "carries" the galaxies with it, separating them, but this doesn't apply to photons. My guess is ...
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3answers
245 views

Is there any proof of space being created?

Is there any proof for space being created? Because I guess an explanation for the dark energy (dark = our understanding of it) could be that there is a gigantic amount of matter/dark matter that we ...
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Do all objects get larger in an “expanding universe”?

I'm envisioning an analogy of the universe as a plane with marbles in that plane to represent different planets. Now, if this plane expands how does this work? I assume that it is not like 'nothing' ...
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If an object 1 billion light years away emits light, does it take more than 1 billion years to reach us because of the expansion of the universe?

From page 7 of the recent (September 26, 2020) edition of Science News Magazine: Detected May 21, 2019, the gravitational waves came from a source about 17 billion light-years from Earth, making this ...
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152 views

Scale factor 0 for expanding universe

Does the FLRW model have a scale factor $0$ at the singularity, meaning that even infinite distances become $0$ there according to the mapping $x \mapsto a(t)x$, for $a(t)=0$? I am asking this ...
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128 views

Universe expansion

I'm reading the book "The theory of everything". In the second chapter it says the Universe is expanding, and we know this because the measurements made using the Doppler effect of other ...
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2answers
92 views

Does time also pass more slowly for a galaxy that is traveling at relativistic speeds, where the speed difference is due to Hubble expansion?

If time passes more slowly, relative to Earth, for a traveler at relativistic speeds, say at .8c, traveling between stars inside this galaxy, does time also pass more slowly for a distant galaxy that ...
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1answer
61 views

Must time pass more slowly, relative to our inertial reference frame, inside galaxies that are currently located at half way to the Hubble Horizon?

Trying to understand simultaneity of events and time-dilation on a Universe scale, I would like to know must time pass more slowly, right now, relative to our current inertial reference frame, inside ...
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How is the Universe's Expansion Accelerating if the Hubble Constant is Decreasing?

I am just getting into the field of cosmology and was wondering what it means practically to say that the Hubble Constant is decreasing while the expansion rate of the Universe is accelerating. I am ...
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3answers
607 views

Cosmological redshift vs doppler redshift

I'm reading Harrison's "Cosmology: Science of the universe" because Harrison focuses on the distinction between cosmological redshift (he calls it expansion redshift) and the Doppler redshift. He ...
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1answer
83 views

How can something infinitely big have expanded from an infinitely small?

Please help me reconcile what I see as contradicting theories: The universe began with the Big Bang and expanded from an infinitesimally small point. The universe is infinite. How can something ...
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1answer
143 views

Why is CMB an evidence of hotter and denser early Universe?

In his book Gravitation and cosmology, Steven Weinberg says that CMB makes it "difficult to doubt that the universe has evolved from a hotter denser early stage". In my understanding, CMB ...
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What was the the value of the Hubble constant at the time of the CMB's 'release' (i.e., 379,000 years after Big Bang)?

What about its value roughly 9 billion years after the Big Bang, when dark energy started to 'take over' and accelerate the expansion of the universe? Is there a timeline or chart somewhere that shows ...
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1answer
135 views

Theoretically could the expansion of the universe affect acceleration due to gravity?

I was wondering if theoretically the universe expanding affects speed or acceleration due to gravity, compared to if space weren't accelerating. The way I have it in my head, something is falling ...
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1answer
40 views

Intuitive explanation for why the Doppler effect (and red-shift) happens?

I was looking for an intuitive explanation as to why the Doppler effect happens. I haven't found any, but this is what I thought: -Waves emitted travel at a constant speed -The source emits a wave -If ...
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3answers
107 views

Intuition about Hubble's Law

I have recently learnt about Hubble's Law and this is my understanding of it: Galaxies move away from us at a rate that is proportional to their distance from us. So, considering an arbitrary unit of ...
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1answer
28 views

Can expansion of space cause the motion of galaxies, does expansion of space do effect motion of our sun around center and earth around Sun?

I'm just wondering that expansion is anyway related to in effecting motion of a star under the galaxies ? Planets are currently revolving around sun in helix motion, if galaxies has motion as well ...
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2answers
106 views

Will the “fabric of space time” rip from expansion?

I'm quite familiar with the fabric of space time theory and as I've been quite lonely these past few weeks, I started thinking that since the universe is expanding and since the "fabric" is the ...
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1answer
218 views

Why can we trust Hubble Time if the rate of expansion is not constant?

The age of the Universe can be estimated from taking the inverse of the Hubble constant: $t_\text{universe} = 1/H_0 =d/v.$ It seems to me this method assumes that any given galaxy has been receding ...
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0answers
54 views

Definition of space - to cope with “space expansion”

I've searched quite a lot but found no satisfying definition, so please: How do we actually define space when talking of "space expansion"? Isn't it just a metric, a dimension we measure, instead of ...
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0answers
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What will be the eventual result of the Milky Ways future mergers?

I am wondering, after the Milky Way merges with Andromeda and other near by dwarf galaxies and globular clusters, will it then merge with galaxies in the Virgo cluster and even Laniakea? And if so ...
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Galaxies stay at same place but it's the space that splits the galaxies apart [duplicate]

Galaxies stay at same place but it's the space that splits the galaxies apart. Is my understanding correct? As per my understanding. Galaxies moving apart at high speed is due to the increase in ...
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125 views

Expansion of the universe speeding up

I know that the expansion of the universe is speeding up, but is there an equation to measure this? Also, what is the cause of this?
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With the expansion of the universe is time also increasing?

With more space being created would there be more time in that new region formed? Is the over all universe increasing in time? This is my first question so go easy on me. PS. Would that also mean that ...
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1answer
74 views

Why is constant velocity drift not an accepted explanation of Hubble expansion?

Edward A Milne at the Oxford University proposed that what Hubble was observing was simply a natural sorting of random galactic motions. If a group of galaxies formed together moving at various ...
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1answer
63 views

Expansion of the universe and visibility of distant galaxies [duplicate]

The universe expands at an accelerating rate, which makes me wonder if at a certain point the speed of expansion between two points will exceed the speed of light. In that case, it might eventually ...
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1answer
57 views

Any theories about universal expansion due to action at the universal event horizon?

I'm curious if there are any theories about the increasing rate of the expansion of the universe that are centered around gravitational pull from matter outside the event horizon of either the ...
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1answer
95 views

Does the gravity oppose to the Universe expansion?

I'm trying to understanding the very basic of the current cosmology. I searched in the old questions but I found nothing that answers specifically to my questions. As far as I understand, we have to ...
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1answer
121 views

At what cosmological redshift $z$, does the recession speed equal the speed of light? How is it calculated?

At what cosmological redshift $z$, does the recession speed equal the speed of light? What equations are used to calculate this number (since at large redshifts, $z=v/c$ won't apply)? [The ...
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2answers
106 views

Why does the Supernova 2006cm give a very different value for the Hubble constant? Why doesn't it increase error bars for the Hubble constant?

The Supernova 2006cm has a redshift of 0.0153 which translates into a recession speed of 4600 km/s. It has a distance modulus of 34.71 which translates into a luminosity distance of 87 Mpc. This ...
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3answers
187 views

Is the eventual heat death of the universe due to the expansion of the universe?

I am reading about the accelerating expansion of the universe and something struck me. The observation that things further away were accelerating away faster and that early observations made it look ...
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1answer
84 views

Why do we expect Type Ia Supernovae to be brighter in a decelerating Universe than what has been observed?

This seminal review paper in the PNAS by Robert P. Kirshner (https://www.pnas.org/content/96/8/4224) says the following: If the universe had been decelerating—–in the way it would if it contained ...
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1answer
185 views

Do gravitationally bound (e.g. orbiting) objects really resist the expansion of space?

Thinking about the expansion of space, it is commonly explained that gravitationally bound objects (like galaxies and galaxy clusters) will not be affected by the expansion of space (dark energy). I ...
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1answer
104 views

Difference between 3D real space and 3D redshift space?

With regards to cosmological simulations (e.g., N-body dark matter only simulations), I've seen people talk about the positions of objects (halos, galaxies) in the simulation in terms of 3D real space ...
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1answer
108 views

Can expansion of space blueshift galaxies with respect to one another?

Suppose we have two galaxies in an otherwise devoid space, and suppose the galaxies are gravitating. Suddenly, dark energy kicks in, and accelerated expansion of space begins ... (1D force diagram. ...
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1answer
153 views

Cosmological redshift - How do we know it's not caused by the observer's time dilation?

Instead of cosmological redshift being caused by the metric expansion of space, why couldn't cosmological redshift be caused by our perspective moving faster in time? Said another way, if the ...
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1answer
295 views

Will intergalactic travel be impossible in roughly 15 billion years?

Even if we (or aliens somewhere in the universe living at that time) somehow invent something that can go just short of the speed of light, will intergalactic travel still be impossible in roughly 15 ...
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1answer
87 views

If the space is expanding near the speed of light or the speed of light, why Andromeda is approaching or coming near to our galaxy (Milky way)? [duplicate]

Space with distance of 1megaparsec is expanding with rate of 70km/s, and if space with a distance of 4296 megaparsec is expanding at rate of 300,720km/s, then why Andromeda is coming to us? Even there ...
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2answers
132 views

Does the expansion of the universe increase with distance?

I read something in a book the other day which has gotten me really confused. They were talking about the expansion of the universe, and if I understood it all, they said that the expansion of the ...
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1answer
226 views

Has the Big Crunch been ruled out?

If the dark energy equation of state $\omega$ evolves with time, and becomes larger, this would result in decelerated expansion and eventually a Big Crunch. If $\omega$ decreases with time, becoming ...
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How are constraints on dark energy improved the most?

Today we have various data available from independent probes to constrain dark energy, i.e. its equation of state $w$. These include Type 1a supernovae, BAO, CMB, large-scale galaxy surveys, etc. Are ...
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1answer
62 views

How is the expansion rate of the universe obtained from Baryon Acoustic Oscillations?

I understand that we can measure the sound horizon from the anisotropies in the CMB. Large galaxy surveys today can construct two-point correlation functions, which reveal peaks at distances equal to ...
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1answer
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how to define the universe itself is expanding greater than than the speed of light?

since we observe galaxies and other steller objects in very tiny tiny scale, and how we can understand that the speed of expansion on universe is higher than the speed of light ? even using the ...
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1answer
189 views

Why hasn't the CMB already receded away faster than the speed of light?

If there are supposedly galaxies, or whole other parts of the universe, that we can't ever see due to them receding away from us faster than the speed of light, then why isn't or hasn't this occurred ...
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2answers
807 views

Gravitational red shift vs Doppler redshift: Is the universe really expanding?

Is it possible that the redshift observed by Edwin Hubble is really from a gravitational redshift and the universe isn't expanding as he has predicted? What I think I know thus far is this: Redshift ...
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0answers
42 views

Is it possible for redshift to be caused by light being somehow slowed down during travel? [duplicate]

In other words, is the assumption, that redshift is caused by universe expansion, definitive? Or are other theories still being considered? Could it be, that light is being slowed down by dark energy, ...
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Expansion of space - how do we end up with an unobservable region?

I've just been answering a question on this issue,in physics SE,and realised that my answer conceals a point I don't myself understand. I understand that The expansion of metric isn't affected by ...
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1answer
88 views

Looking at the Expanding Universe through the lens of relativity [closed]

The basis and most observable metric for how the universe is understood to be expanding at an accelerating rate is the red shift in observable light. I am assuming it has been thought about or maybe ...
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1answer
71 views

What fills the new space created during expansion?

Does it remain void and pushes even more or will virtual particles eventually create normal matter?