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Questions tagged [expansion]

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

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Shouldn't very very distant objects appear magnified?

My understanding of the expansion of space itself is very shaky, but if space itself is expanding, then shouldn't very very distant objects appear magnified? For example these James Webb Space ...
orion elenzil's user avatar
23 votes
5 answers
7k views

How do we know the expansion of the universe is not centered around our position?

It is my understanding that the red shift of galaxies in whatever direction we look shows the universe is expanding in every direction around us. That could be explained in two ways: A (accepted): The ...
armand's user avatar
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22 votes
2 answers
2k views

Where does the energy of light go, when it red-shifts?

When talking about the expansion of the universe, it is said that it can be proven by the red-shifting of light.(As we would need higher than lightspeed to get this redshift by the Doppler effect) I ...
akaltar's user avatar
  • 323
21 votes
2 answers
4k views

What equation tells you how far in space you can go from a point and return?

We know that hubble expansion increases the distance between points in space, and that the cosmological event horizon represents the distance from the observer at which objects are receding faster ...
user52978's user avatar
  • 313
21 votes
2 answers
938 views

Space expansion in layman terms

So far I got to understand the expansion of space is not to be understood as stars drifting further apart through space. There's something more fundamental - e.g. you can't simply measure speed of it, ...
SF.'s user avatar
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21 votes
2 answers
2k views

Are there any galaxies which fell out of sight horizon due to cosmic expansion?

If farthest galaxies run away from us with acceleration making them exceed speed of light, we should expect them to disappear from sky among time with increasing quantity. Did we observe this? Can we ...
Waldemar Gałęzinowski's user avatar
20 votes
1 answer
984 views

On what scale does the universe expand?

According to the theory (or my understanding of it), the universe is not only expanding, but speeding up. If the galaxies are moving apart, are the solar systems within them also moving apart from ...
SteB's user avatar
  • 597
19 votes
2 answers
3k views

Could we (Earth, Humanity, Solar System) be falling into a black hole?

With the expansion of the universe, all objects far away from us appear to be moving away (ie: exhibit Redshift). With distance, this acceleration / redshift also seems to increase (~73,000 (m/s) / (...
G. Putnam's user avatar
  • 299
17 votes
11 answers
4k views

Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?

When we look in all directions, we see distant objects red-shifted, with the size of the red-shift correlated with the distance from us. As I understand it, the consensus among cosmologists is that ...
Brionius's user avatar
  • 331
15 votes
9 answers
6k views

How do we know we're not getting bigger?

Alright so I've been thinking a lot about how the universe expands and I've always wondered if we're getting bigger as well. Since everything would be getting larger at an equal rate (tools of ...
Landon's user avatar
  • 169
15 votes
1 answer
2k views

How many galaxies disappear beyond the Hubble Bubble horizon every year now? [duplicate]

The accelerating expansion of space means that the space between us and far away galaxies expands faster than light can travel through space. There is a horizon of possible observation beyond which ...
LocalFluff's user avatar
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14 votes
1 answer
3k views

Will we start seeing galaxies disappear due to Universe expansion? [duplicate]

Does the fact that universe is currently expanding at an accelerating rate means that far far away objects (FAO) might start disappearing with time, set aside the "red shift"? I'm saying this ...
J. Chomel's user avatar
  • 1,452
14 votes
3 answers
2k views

Does a measuring stick with a size of a billion lightyears in intergalactic space keep the same length in expanding space?

Imagine a measuring stick (a rod or ruler) made of ordinary matter which has a length of a billion lightyears. The space surrounding the ruler expands. Will the ruler keep the same length by the ...
Gerald's user avatar
  • 259
13 votes
4 answers
3k views

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' ...
hashier's user avatar
  • 241
11 votes
6 answers
4k views

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 ...
nosn's user avatar
  • 213
11 votes
2 answers
2k views

In km/h, what actually is the "speed" of Andromeda away from us: cosmologically?

Andromeda is about 2.5 million ly away. Actually, in this universe, at what "speed" (in km/h) are two objects separating cosmologically - I mean strictly due to the "expansion of the universe" - if ...
Fattie's user avatar
  • 946
11 votes
3 answers
8k views

When the universe expands does it create new space, matter, or something else?

I am wondering what exactly is meant when it is said the universe expands. Does it simply create new space for matter to fill, does it also create new matter/dark matter to fill that space, or am I ...
Joey Seibel's user avatar
11 votes
1 answer
550 views

Will gravitational waves too far away ever reach us?

Gravity is the curvature of spacetime, and its effects travel at lightspeed. However, space is expanding; eventually, light from distant galaxies will become more and more redshifted, and we will no ...
Sir Cumference's user avatar
11 votes
1 answer
230 views

Farthest distance two objects are "gravitationally bounded", considering expansion of the Universe

The narrative is: "on greater scales the expansion of the Universe dominates, but on smaller scales gravitationally bounded objects still stay bounded". But how small is meant by "...
Heopps's user avatar
  • 647
10 votes
3 answers
2k views

How far apart has the sun drifted from Alpha Centari due to the expansion of the universe since its formation?

From what I read Alpha Centauri formed 250 million years before the sun which was 4.85 billion years. So how far apart were they when the sun formed vs what they are now? The expansion of the universe ...
Sedumjoy's user avatar
  • 1,201
10 votes
2 answers
1k views

How does the concept of a universe with no center work?

I understand basically that the universe is homogenous (looks the same from every point) and I was told in my astro class that it's supposed to have no center, but how that works boggles my mind. I ...
Pulchritude's user avatar
10 votes
2 answers
2k views

Does the accelerating expansion of the Universe contradict Hubble's law?

Hubble's law gives a linear relationship between the distance to a galaxy and it's recessional speed. Observations of distant type 1a supernovae showed that their red shift (and therefore their ...
Pancake_Senpai's user avatar
10 votes
3 answers
3k 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 ...
user120112's user avatar
10 votes
1 answer
579 views

Does the gravity oppose to the Universe expansion?

I'm trying to understand the very basis of the current cosmology. I searched in the old questions but I found nothing that answers my questions specifically. As far as I understand, we have to think ...
Mark's user avatar
  • 359
10 votes
2 answers
282 views

Expansion of Space

If Space is expanding between the Galaxies then why isn't it also expanding between the Stars within the Galaxies as well ? In fact why isn't Space expanding within our Solar System ?
Peter U's user avatar
  • 1,619
9 votes
6 answers
2k views

Are there other proofs of the expanding universe apart from the redshift?

The theory of the expanding universe is so widely accepted, that the redshift is sometimes used as a measure of distance to far away galaxies. But is it still possible that the redshift is caused by ...
cuckoo's user avatar
  • 800
9 votes
1 answer
2k views

Could there really be a preferential direction to the speed of light?

This question is inspired by a recent video by Veritasium Why no one has measured the speed of light linked below. To summarize the video, Derek points out that it is impossible to measure the one-way ...
asgallant's user avatar
  • 571
9 votes
1 answer
627 views

Local neighbourhood and Superclusters

Recently, I watched a YouTube video on Limits of Humanity, by famous Youtube channel Kurzgesagt. It talked about the local neighbourhood, and it is the only group of galaxies which are gravitationally ...
Kshitij Kumar's user avatar
9 votes
1 answer
691 views

In an isolated binary system, can the expansion of the universe balance out collapsing orbit due to gravitational waves?

We know that binary systems slowly lose energy due to gravitational waves from the objects moving through spacetime and that if the objects are compact and massive enough, the mergers happen in time ...
Justin T's user avatar
  • 3,404
9 votes
1 answer
279 views

How distant were the furthest currently-observable cosmic events when their currently-observed radiation was emitted?

(Edited for clarity. Thanks to James K and Connor Garcia.) This question about the most distant, observable cosmic objects made me wonder if we know the distance that was between us and them at the ...
Glycoversi's user avatar
9 votes
4 answers
727 views

Distinction between metric expansion and objects just moving apart from each other?

I see explanations likes this: Galaxies and other sources, then, are not strictly expanding away from each other but rather are attached to the fixed grid on the expanding fabric of spacetime. Thus, ...
eyenstine's user avatar
8 votes
1 answer
216 views

How far would EGSY8p7 be away now?

Apparently EGSY8p7 is the object with the longest light travel distance, 13.2 gly or a redshift of z = 8.68 (Wikipedia). So the light took 13.2 billion years to travel to us from that object, but we ...
jpp1's user avatar
  • 183
8 votes
4 answers
1k views

Is expanding universe adding potential energy?

A system with two massive bodies has potential energy proportional to their separation. Since the universe is expanding, is the potential (and total?) energy of such a system slowly increasing? What ...
user7779's user avatar
8 votes
2 answers
453 views

Expansion again: where does the energy come from?

Is it sensible to ask for the overall increase in potential energy when looking at the baryonic mass in the universe moving away from each other, that is, moving against the direction of the force ...
Vroomfondel's user avatar
8 votes
2 answers
5k views

Do objects look larger the further away they are, beyond z=1?

I stumbled upon this text which illustrates and says: We find that as the object is moved to higher redshifts its angular size first decreases (as naively expected) but soon begins to increase ...
LocalFluff's user avatar
  • 11.4k
7 votes
3 answers
2k views

How do we work out the light travel time on a cosmic scale?

I just read this article in the AUSTRALIAN SKY & TELESCOPE magazine, Nov/Dec 2022 Issue 140, on P16, KEEP YOUR DISTANCE: How far away are the objects we see in the universe? And on P23: "And ...
Curious Cat's user avatar
7 votes
2 answers
2k views

How long has it been since dark energy started to reverse our slowdown and accelerate the expansion of the universe? 4 billion years ago? 4.5? 5?

Or has it been as long as six billion years? Over the last few years I keep seeing longer and longer numbers... Have researchers noticed something different recently? Or found a mistake in their ...
Kurt Hikes's user avatar
  • 5,177
7 votes
1 answer
845 views

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 ...
Kurt Hikes's user avatar
  • 5,177
7 votes
1 answer
2k views

Evolution of the Hubble parameter

In the lambda-CDM model describing an accelerating Universe, the Hubble parameter is currently decreasing with time. Will it continue to decrease forever?
set5's user avatar
  • 559
7 votes
7 answers
8k views

How can an infinite universe expand?

I understand the expansion of the universe as actually an increase in the ratio of space to matter. Is this a correct understanding? Otherwise, I don't understand how an infinite structure can expand....
Justin Waters's user avatar
7 votes
2 answers
1k views

How can gravity lead to the Big Crunch scenario?

According to modern cosmology, space is expanding, causing proper distances (but not comoving distances) to increase between galaxies. In the Big Crunch hypothesis, gravity halts and reverses the ...
Sir Cumference's user avatar
7 votes
1 answer
333 views

Dark Energy Expansion

The new Cosmos extra features mentions that at about 6,771,500,000 years ago the universe began an accelerated expansion. How do we know this? What evidence do we have for this renewed and accelerated ...
CDspace's user avatar
  • 294
6 votes
2 answers
876 views

Is the age of the Universe really 13.8 billion years?

Ok, I know this has been asked by a lot of people, but my reason for asking this question is a bit different. Please read further. I was watching a video by Fermilab (Start at 6:30, at 8:30 he ...
Deepak Kamat's user avatar
6 votes
3 answers
561 views

Heavy star and redshift

A heavy star should look redshifted, due to gravitational time dilation. How is that incorporated into the calculations of distances to the stars, or is it negligible? How about an entire region of ...
frodeborli's user avatar
  • 1,197
6 votes
2 answers
887 views

Why would galaxies (and galaxy clusters) be unaffected by the expansion of space?

"Gravity holds galaxies and cluster of galaxies together, and they get farther away from each other--without themselves changing in size--as the universe expands." Quoted from the OpenStax ...
GulbenkianD's user avatar
6 votes
3 answers
827 views

Can the Event Horizon Telescope been used to find intergalactic distances?

Now that we have the Event Horizon Telescope (EHT), why can't we just guess and check intergalactic distances by changing the EHT's focal length? For instance why don't we take another picture of M87,...
Caston's user avatar
  • 329
6 votes
3 answers
649 views

How is the Milky Way on a collision course with Andromeda when the universe is expanding? [duplicate]

At some time in the future it is said our galaxy will collide with Andromeda. Yet at the same time the universe is expanding at a ever-accelerating pace. Using the old raisin-in-the-baking-loaf-of-...
iMerchant's user avatar
  • 1,062
6 votes
2 answers
184 views

How does the hypothesis of the "inconstant Hubble constant" solve the current crisis in cosmology?

It was published in a paper more or less like two months ago. I'd like to know also if more accurate measurements are necessary to close the gap between the model of the universe and the data reported....
bestofthebeast's user avatar
6 votes
2 answers
4k views

Redshift for gravitational waves?

According to general relativity, would gravitational waves experience the same sort of redshift that electromagnetic waves experience due to the expansion of the universe? And are there astrophysical ...
dualredlaugh's user avatar
6 votes
1 answer
2k views

Does the universe expand at the same rate everywhere in the universe?

Specifically, I am wondering if some areas of the universe expand faster than other areas and whether the faster expanding areas diffuse the expansion through the slower expanding areas or does the ...
Justin Waters's user avatar

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