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

0
votes
1answer
28 views

Could the universe really be expanding at a constant rate?

I was just thinking, sorry if this idea is idiotic, but since we know galaxies move away from each other at an accelerating rate, could this be due to a weakening gravitational force between galaxies? ...
0
votes
1answer
19 views

Energy conservation in Hubble Expansion

So space expands due to Hubble Flow. Some light is observed, which is seen to be red-shifted due to the space expansion. It is less energetic. Where did the energy go?
5
votes
1answer
125 views

The naive idea of the big bang

Many people think that according to big bang cosmology, first there was empty space, then there was an explosion in the middle of the emptiness, and now all the galaxies are flying away from that ...
0
votes
0answers
36 views

(naive?) interpretation of Hubble's Law

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) ...
0
votes
1answer
124 views

Is there any observational test that could be done to approve\ disapprove the Tired Light theory? [closed]

Tired light is alternative explanation for the redshift-distance relationship and for the metric expansion of space. The suggestion is if photons lost energy over time through collisions with other ...
1
vote
3answers
101 views

Observing a point 13.82b ly away, 1b years ago

I understand that we can observe far away galaxies to get an idea how the universe looked like in the past. Assuming the universe is 13.82b years old, would it be correct to say that if we looked at ...
3
votes
0answers
52 views

Red shift and expansion of universe [duplicate]

We have been led to believe that in the theory of universe expansion, the farthest object is moving faster away from us than the nearest object, attributing the difference to red shift. Question: is ...
11
votes
4answers
2k views

Height Issues of the Time Traveler [duplicate]

A person from the year 2250 goes back in time. They go back 60 Million years, because they want to observe dinosaurs. Imagine their surprise when they see T-Rex's running around like little ...
0
votes
2answers
80 views

Expansion of the Universe [duplicate]

At what speed is our solar system expanding, and if it is, why don't the positions of the sun and planets change, or grow farther apart? Why is the Big Dipper still where it is?
1
vote
0answers
30 views

How did people think of the universe before Hubble? [closed]

Did they think the universe had always existed? And was there even any serious scientific inquiry into the question, or was it pure speculation?
0
votes
0answers
29 views

Non-homogeneous expansion of the observable universe

This question may be more philosophical than cosmological, but here goes. Given that expansion of the observable universe is based on secondary data, i.e., we haven't actually measured the expansion ...
0
votes
2answers
93 views

Redshift of distant galaxies: why not a doppler effect?

How can I explain to my 17 year old pupils that the observed redshift of distant galaxies cannot be interpreted as a doppler effect and inescapably leads to the conclusion that space itself is ...
9
votes
1answer
180 views

Space time expansion near galaxies

I understand that on galactic scales, the expansion of space time has no appreciable effect, gravity being dominant and thus distance between stars remains fixed despite universal expansion. Can ...
0
votes
1answer
43 views

Using wormholes to see out of the visible universe

As is commonly known, using our telescopes, we can only see so much of the universe because of its faster than light expansion. However, although under normal circumstances it is impossible to see ...
4
votes
2answers
78 views

Is space expanding equally in every direction?

Does space expand equally in every direction, so that it draws a perfect sphere or is expansion asymmetric, so it creates "bubbles" (when seen from the outside)?
1
vote
1answer
32 views

Photon outside of Hubble sphere from perspective of comoving frame

I understand that there have been alot of questions on Hubble sphere, but I seek a more direct answer to this confusion that I have because I still can't resolve it after going through the posts. ...
3
votes
2answers
39 views

Were more stellar objects part of our observable universe in the past? [duplicate]

In the past, i.e. a billion years ago, if the universe is larger than our observable universe, would there have been more objects in our observable universe that have now accelerated beyond it?
0
votes
0answers
31 views

Accelerated expansion of the universe

Let us first consider space time as a fabric, i.e. from a General relativity point of view. Know let's refresh the fact that the radius of OUR observable universe is increasing its length at the speed ...
1
vote
2answers
65 views

Relative motion of an arbitrary volume of space ( is space static or dynamic?) [closed]

Do physicists consider space as being "static" or "dynamic" ? Hi I asked a question about whether space can move, and from the answer, I realized I was not precise enough and did not actually ask ...
4
votes
1answer
72 views

Implications of observable Universe growing indefinitely [closed]

Why, if the observable Universe becomes infinitely large in proper units as time goes to infinity, the objects in space, that we can actually observe, become fewer? I don't know how to use ...
5
votes
0answers
134 views

If spacetime is discrete: what would space expansion mean? [closed]

How is space expansion explained in physical theories where spacetime is quantized? Discrete spacetime is claimed in some candidate theories of quantum gravity like loop quantum gravity and algebraic ...
1
vote
1answer
62 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 ...
5
votes
7answers
253 views

If space is “expanding” in itself - why then is there redshift?

The "kid's" way of understanding the expanding universe is that: "space" is totally "ordinary", and all the galaxies are expanding through it (like an explosion). Of course, that's wrong. The usual ...
0
votes
0answers
50 views

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 ...
0
votes
1answer
38 views

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 ...
3
votes
5answers
183 views

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 ...
0
votes
0answers
28 views

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 $\Omega_\Lambda$ ...
4
votes
1answer
85 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 ...
0
votes
3answers
26 views

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 ...
1
vote
0answers
54 views

Is spacetime elastic or inelastic [closed]

If spacetime is nonelastic and the zero mass curvature is zero than local perturbations of spacetime by mass describable as circumference -2r(pi)is less than zero must be balanced by areas of ...
0
votes
3answers
87 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 ...
0
votes
0answers
80 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 ...
0
votes
1answer
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 ...
4
votes
0answers
141 views

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? ...
0
votes
2answers
46 views

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 ...
1
vote
2answers
106 views

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 ...
0
votes
1answer
97 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 ...
1
vote
1answer
47 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 ...
1
vote
0answers
33 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 ...
4
votes
2answers
213 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 ...
1
vote
1answer
38 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 ...
0
votes
1answer
58 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 ...
0
votes
1answer
36 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 ...
-1
votes
1answer
51 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?
1
vote
1answer
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 ...
0
votes
0answers
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 ...
-1
votes
2answers
61 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 ...
5
votes
3answers
283 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 ...
2
votes
2answers
80 views

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 ...
0
votes
1answer
52 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 ...