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.

learn more… | top users | synonyms

22
votes
4answers
3k views

How did the universe shift from “dark matter dominated” to “dark energy dominated”?

In order to get dark energy to dominate, wouldn't you first need another form of energy to push the expansion until dark energy could dominate? Otherwise I don't understand how the universe could ...
0
votes
1answer
44 views

Does the FRW metric imply spacetime scales?

The FRW metric can be written in conformal co-ordinates to give: $$ds^2=a^2(\eta)(-d\eta^2+d\mathbf{\Sigma^2}),$$ where $\eta$ is the conformal time and $\mathbf{\Sigma}$ ranges over 3-dimensional ...
0
votes
0answers
30 views

What is the relationship between an expanding universe, an increase in entropy and the the creation of mass?

What is the relationship between an expanding universe, an increase in entropy and the the creation of mass? Could the creation of mass be driven by or in equilibrium with the creation of space?
2
votes
1answer
103 views

If the universe has no center, how it can collapse?

After reading Does the universe have a center? and trying to find a place in my mind for "There exists no center", I asked myself: If there is no center, in what direction our universe will collapse, ...
5
votes
2answers
71 views

On the expansion of space on small distances

After reading this post :Why does space expansion not expand matter? and after posting some comments to Peter Diehr, I was invited to make my argument to a question. The main things one needs from the ...
0
votes
0answers
36 views

Where is the origin of cosmic expansion? [duplicate]

Perhaps, a rudimentary or dumb question, but nevertheless am curious. There is the idea that space is expanding at an exponential rate. From where? If everywhere, why doesn't this rapid creation of ...
3
votes
1answer
70 views

Hubble's constant measured by observer approaching light speed

I recently read about expansion of the universe and I can't figure out if Hubble's law (and other models of expansion of the universe) is compatible with the theory of relativity. My question is: In ...
7
votes
1answer
112 views

Was the matter-energy content of our universe always distributed in the same ratios?

Currently, Dark energy (68.3%) and Dark matter (26.8%) together constitute about 95.1% total matter-energy content of the universe while only 4.9% is ordinary baryonic matter. Was this always the case?...
7
votes
3answers
154 views

Considering dark energy and other factors, what is the most distant object light could reach?

If we send a photon from Earth at this moment, what is the most distant object that it could reach? This question is partly inspired by this video which states we cannot ever travel beyond our local ...
4
votes
1answer
203 views

The CMB and the Hubble comoving radius

I have been thinking on this for a while and i don't get it. My point is, the comoving Hubble radius $(aH)^{-1}$ is the distance at wich the universe expansion begins to be superluminical. In an ...
2
votes
3answers
471 views

Have CMB photons “cooled” or been “stretched”?

Introductory texts and popular accounts of why we see the "once hot" CMB as microwaves nearly always say something about the photons "cooling" since the Big Bang. But isn't that misleading? Don't ...
6
votes
4answers
409 views

Can the cosmological constant change with time?

This post is a specialization of the post: Can the proportion of dark energy change? Can the cosmological constant change with time? If so, is there a measurement of this evolution up to now, and ...
1
vote
3answers
176 views

Is the Universe being dragged into a singularity rather than expanding?

Recently I've read that the expansion of the Universe as observed is not exactly uniform as proposed by Hubble. Therefore is it possible that instead of space expanding in all directions all matter is ...
-1
votes
2answers
78 views

Universe Expanding

Quick question that I was just hoping to get some clarification on. Current theories state that the universe is expanding; with those planets farther away moving away from us at a faster rate. Is it ...
0
votes
0answers
29 views

Space expanding within atoms [duplicate]

I'm hoping that "all questions are good questions." I'm a layman enthusiastically trying to comprehend cosmology and physics, and the more I learn the more questions I have. My understanding is that ...
1
vote
0answers
53 views

The reason for the fading of galaxies?

Galaxies that are greater than a distance of c/H metres from Earth have recessional velocities exceeding the speed of light and begin to fade. Thus, theoretical astronomers 3 trillion years the future ...
0
votes
2answers
71 views

Cosmic Scale Factor $R$ and redshift

I'm slightly confused by an idea of redshift: If we assume the distance between two points is given by: $$d = R Δx$$ we can assume that $$λ_0 = R_0 Δx$$ And when we receive the emission it will ...
2
votes
1answer
62 views

Cosmic inflation and space flatness

I am new here, an avid Physics reader, but have lots of questions and doubts on which I'd like to get the help of a pro physicist. Here goes some about the theory of Inflation: a) after the first ...
1
vote
1answer
61 views

Many questions about expanding of the space

Sorry if my grammar is a bit off. But I have few questions about space and its expansion. If space expands faster and faster all the time, will there be a time when we cannot see further than "hubble ...
3
votes
1answer
57 views

How is a result of no time variation in the gravitational constant $G$ related to a measurement of no local expansion?

In this answer @PhillS linked to the paper Progress in Lunar Laser Ranging Tests of Relativistic Gravity which has given me a great start. While its main focus is on the Equivalence Principle (EP) ...
0
votes
1answer
40 views

Expansion of the Universe and Conservation of Energy [duplicate]

How the expansion of the universe doesn't violate the principle of the conservation of energy? If we would put a spring between two objects, the distance would get bigger between them, so would the ...
3
votes
2answers
218 views

How do we know that the galaxies the farthest away from us are actually speeding up?

What i mean is Hubble proved that the galaxies the farthest away from us were moving away faster than the galaxies closer to us. I have a basic understanding of red shift. I've always wondered (and ...
-1
votes
1answer
73 views

What is a simple explanation to the fact that the universe is expanding? [closed]

How can we prove that the expansion of the universe is actually occurring to highschool children?
-1
votes
2answers
55 views

How can we find out the distance to a galaxy using redshift?

As redshift occurs due to Doppler effect and universe expansion, how do we know what part of the shift is responsible for which, in order to determine the distance to the object emitting the waves? Is ...
5
votes
4answers
679 views

Before the Big Bang

I've heard this saying before I don't know about anyone else. It says, "What ever was before the Big Bang is something physics can't explain..! Is this saying true (accurate)?
1
vote
3answers
71 views

What evidence is there that universe will not shrink again?

There are theory that universe eternally expanding and shrinking, so that every event and our lives will repeated again. At the other hand some scientists thinks that it will not shrink again because ...
1
vote
0answers
32 views

Curisioty about universe [duplicate]

I am a bachelor student and I have a question going round my mind about the universe. Every one says that the universe is ever expanding and it is also said that the vast possible space is also the ...
2
votes
2answers
296 views

How does a particular galaxy's apparent recessional velocity CHANGE as the universe expands?

By this I mean will the light from distant galaxies continue to show red shift (i.e. if you look at light from a particular galaxy now and in 10000 years time, the spectra will have been shifted again)...
5
votes
1answer
61 views

Did our Universe experience a curvature dominated phase?

So, my question is simple: did our Universe experience a curvature dominated phase? Or, rather, could our Universe have experienced a curvature dominated phase? This seems quite shruggish, at first ...
6
votes
2answers
114 views

Scanning the universe - edit: expanding or shrinking

I know that this may sound as a very basic question, but how come that we can detect CMB radiation, light or gravitational waves from the big-bang era? Shouldn't this radiation has overtaken us a ...
0
votes
2answers
82 views

Dark energy and virtual particles

If space time is accelerating away from itself everywhere due to dark energy, could this acceleration be the cause of virtual particles, essentially Unruh radiation?
0
votes
1answer
62 views

Rate of change of temperature of the Universe

Temperature of the whole universe is about 2.7K base on the wmap satellite. I know that temperature has to decrease to time and I have difficult time finding references for rate of change of ...
1
vote
0answers
26 views

Why don't big bang photons conserve mass and energy? [duplicate]

A photon from the big bang has lost most of its momentum and energy. What does it push against? Does it break the 'laws' of conservation of energy and momentum? Is there any possibility that momentum ...
0
votes
2answers
100 views

How is this conflict about age of the universe resolved?

In a previous Phys.SE question, Does a spaceship travelling at near lightspeed see the universe aging slow or fast?, the answer (which was followed by a proof involving co-moving reference frames) was ...
1
vote
2answers
85 views

If gravitons are 'real' and analogous to photons are they also being 'stretched' by the universe's expansion?

Since photon wavelengths are stretched by our expanding universe, appearing to us as a redshift, would graviton wavelengths similarly be stretched? For that matter, do gravitons even have a ...
3
votes
2answers
200 views

If space can expand faster than light why can't gravitational wave?

I heard that gravitational wave is the measure of stretchiness of space time, so since there is no limit to how fast space can stretch what about gravitational wave?
2
votes
1answer
85 views

Why can't our expanding universe be an imploding universe that appears expanding relative to us? [closed]

Galaxies moving away from us is our proof of an expanding universe. However, if the universe was contracting towards a black hole we would see a galaxy ahead of us accelerating faster towards that ...
1
vote
1answer
69 views

Expanding space and red shift

Assuming space is really expanding - Due to expanding space, distant galaxies are supposed to be moving away from us. When light leaves a distant galaxy, it's wavelength is red shifted to begin with ...
0
votes
3answers
451 views

Tired light red shift hypothesis

Have there been any recent attempts to falsify the tired light hypothesis alternative to the Doppler shift explanation for the red shift, or is it simply ignored like the pilot wave quantum mechanical ...
5
votes
2answers
286 views

Would cosmological redshift be present in the following situation?

I'm trying to understand if cosmological redshift is just a secondary form of doppler redshift, or something else entirely. Suppose the two galaxies in the picture are receding from each other, but ...
5
votes
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 ...
1
vote
1answer
66 views

What are the pieces of evidence that universe is expanding? [duplicate]

Do we have any other evidence other than red shift? Is anyone trying to disapprove inflation? Also, can red shift occur because of large distance, not only because two objects are going farther from ...
-2
votes
2answers
101 views

What causes the expansion of space? [closed]

What is causing space to expand? Is it due to some kind of innate property or is it due to some force? I did a google search on this and found lots of articles explaining that space is expanding ...
0
votes
2answers
51 views

How Can a Singularity contain different things? [closed]

According to the Big Bang model, space and everything in it was squeezed into a infinitely small point which subsequently expanded. But if everything is squeezed into a point of zero size than there ...
2
votes
2answers
42 views

How object's movement is separated from the space-time movement?

In Issues related to expansion of the universe while space-time itself is moving how it is possible to calculate the speed of an moving object? In other words how object's movement is separated from ...
2
votes
3answers
172 views

Why is speed of light a constant while distance in space is not?

Disclaimer: I asked this at Astronomy.SE, but got no answer whatsoever, so I am trying my luck here. As you probably know current state-of-the art physics (i.e. gravitational waves, cosmic expansion) ...
-1
votes
1answer
75 views

Wouldn't it take an infinite amount of time to create an infinite universe? [duplicate]

I have heard many people say that the universe is possible infinite. But, if it takes time and energy to create bodies such as planets and stars and the universe has only existed for 13.7 billion ...
1
vote
2answers
105 views

Standing wave on a circle [closed]

Suppose that we have a standing wave on a circle. I heard that by gradually increasing the radius of the circle, the wavelength will also increase to keep the standing wave. Is it right? If yes, what'...
3
votes
3answers
147 views

Is General Relativity compatible with relative speeds bigger than $c$ between two inertial frames?

My question is motivated by a remark done by Tegmark in his book "Our Mathematical Universe". He says that GRT does not prove that relative speeds between material points are always smaller than c. It ...
0
votes
2answers
70 views

Don't rulers expand at the same rate as the universe they measure? [duplicate]

If you placed a giant ruler between the sun and our nearest star for example, wouldn't the divisions on the ruler expand at the same rate as the universe - therefore maintaining a constant distance? ...