Questions tagged [expansion]

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

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21
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2answers
725 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, ...
21
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2answers
1k 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 ...
18
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1answer
655 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 ...
16
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2answers
992 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 ...
14
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1answer
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 ...
11
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1answer
452 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 ...
10
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4answers
2k 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' ...
9
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6answers
693 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 ...
9
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1answer
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 ...
9
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2answers
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 ...
9
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1answer
2k 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 ...
8
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2answers
493 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 ...
8
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3answers
2k 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 ...
8
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2answers
302 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 ...
8
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1answer
227 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 ...
8
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2answers
161 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 ?
7
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1answer
125 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 ...
7
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2answers
780 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 ...
7
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7answers
2k 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....
6
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3answers
467 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 ...
6
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3answers
330 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-...
6
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1answer
91 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 ...
6
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3answers
458 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 ...
6
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2answers
384 views

Is the universe expanding faster than speed of light?

The celestial bodies like stars and galaxies are moving away from each other. How fast are they moving apart? Is that speed more than the speed of light?
6
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2answers
191 views

Is there an objective difference between space expansion and reduction in speed of light

I just read an article about the cosmological model of an inflationary universe. As you probably know it basically states that space itself is subject to an expansion over time. Since there is no ...
5
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3answers
488 views

How did scientists come to the conclusion that it is space that is expanding?

How did scientists come to the conclusion that it is space that is expanding and not galaxies moving away from each other as in a giant explosion?
5
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3answers
916 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 ...
5
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2answers
619 views

Did Gaia actually generate complete light curves for 212 Cepheids in other galaxies?

The recent BBC news item Gaia clocks speedy cosmic expansion says that a recent Gaia measurement of 212 Cepheid variables in other galaxies within the local group yields a Hubble constant of ~73 km/s/...
5
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1answer
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 ...
5
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1answer
113 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 is just a ...
5
votes
1answer
508 views

Is the expansion accelerating or Decelerating?

According to Hubble's Law, the farther a galaxy is, the farther it is moving away. But do we take into account the fact that we are actually looking in the past? For example, there are two galaxies A ...
5
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1answer
336 views

What is driving the expansion of the Universe?

Is it just the momentum from the Big Bang? If yes, how can it account for the acceleration of the expansion? Why isn't the collective gravitational force slowing it down? What part does dark energy ...
5
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1answer
163 views

Is dark energy constant?

Does the "amount" of dark energy in the universe change over time, or is it constant? The dark energy I am asking about is the rate of acceleration of the universe's expansion.
5
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4answers
299 views

Influences from outside the observable universe explaining dark energy and expansion?

Could some influence from outside the observable universe be causing the expansion?
5
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1answer
205 views

Why are galaxies distributed as walls and voids, or spider webs?

I have wondered why the "walls and voids" of the cosmological galaxy distribution seem to resemble a "foam", like rising bread that's ready to fall, with "voids" corresponding to empty bubbles in the ...
4
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3answers
3k views

Are black holes expanding?

We know that it is a commonly heard claim that in every black hole there is a universe. It is also believed that the universe is expanding. If we use both of these, can we conclude that every black ...
4
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1answer
111 views

Can the diminishing energy of the CMBR be the source of dark energy?

I was just told the CMBR energy diminishes with time. Can it be that the lost energy is somehow transferred to spacetime, causing the expansion to accelerate?
4
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1answer
98 views

If the density of nebular distribution increases symmetrically in all directions, how does space curvature explain it?

Edwin Hubble, in The Observational Approach to Cosmology, wrote Thus the density of the nebular distribution increases outwards, symmetrically in all directions, leaving the observer in a unique ...
4
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2answers
119 views

Is dark energy evenly spaced throughout Universe?

Are there certain parts of the Universe that are expanding faster than others? Is there anyway to definitively measure this?
4
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3answers
2k 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 ...
4
votes
1answer
214 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 ...
4
votes
2answers
116 views

Does Flat Universe mean even distribution?

I've read through all the other related answers to "flatness" questions but I need a bit more clarification. I understand that a triangle in a 2D universe would not equal 180 degrees in both a closed ...
4
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1answer
101 views

What accounts into calculating the Hubble constant?

From my understanding, the Hubble constant $H_0$ calculates from observed redshifts $z$ of distant galaxys against their proper distance $D$. The current value appears to be 67.80(77) $\frac{km}{s}Mpc^...
4
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1answer
2k 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 ...
4
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1answer
477 views

How many new galaxies enter the observable universe each day/year/decade?

Each day light has more time to reach our eyes from distant galaxies. In one day, light travels 2.59×10^10 km. So our observable universe (assuming my simple math skills apply here and there isn't ...
4
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1answer
141 views

Is the expansion of the universe proof of the big bang?

Is the expansion of the universe proof of the Big Bang theory? Or are there other proofs?
4
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1answer
520 views

How can the observable universe shrink in a Big Rip?

As far as I know, the Big Rip occurs when the scale factor reaches infinity in a finite time. This will only happen in a universe dominated by phantom energy (i.e. a universe with an equation of state ...
4
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3answers
326 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, ...
4
votes
1answer
270 views

Are galaxies moving away from us faster than before?

Are all galaxies moving away from us at constant speed even those that may be moving in our direction as the space is being formed? How does nothingness appear to push matter? A black hole sucks as ...
4
votes
1answer
249 views

What is the explanation for rapid inflation just after the big bang?

I often hear about cosmic inflation occurring rapidly after the Big Bang, but have never came across any explanation for it. What supposedly caused this inflationary period in the early universe? Also,...