Expansion of space Definition and 71 Threads

What is the maximal comoving distance that a probe can reach depending on its speed? If the probe travels at light speed, the maximal comoving distance that it can reach is 5 Mpc, which is called the cosmic event horizon. But what if it travels at some other speed?

I am trying to find some sources about time dimension expansion during spacetime expansion. Why do We assume that only spacial dimensions expand? I only found a lot of weird arguments. Btw, temporal dimension expansion does not mean that second was shorter in the past. Similarly to spacial...

TL;DR Summary: Express through the Hubble constant the force that acts on the hydrogen atom due to the expansion of the universe We have a hydrogen atom, in a gravitationally bound system nothing interesting happens to it. Let's put it in an empty world with only an electron and a proton...

I the lambda-CDM model, is the expansion of spacetime uniform around all of spacetime, is there a smooth transition between expanding parts of spacetime (the voids) and non-expanding parts of spacetime, or is there a sharp distinction between expanding and non-expanding parts of spacetime. Is...

I found this article* about the behavior of quasar outflows in cosmology and how they can create a magnetic field. In section 2.1.4., the authors say that when a quasar produces a "wave" or an outflow, the material will be emitted with energy coming from both the quasar itself and the Hubble...

I was reading this interesting article [1] which talks about particle production in an expanding universe. Usually this process is proposed to have occurred in the early universe, when the expansion was in the inflationary phase and it was so powerful that matter was created in particle...

Please explain how we know that it is space itself that is expanding rather than an expansion due to an explosion such as the big bang. In either case wouldn’t every object appear to be moving away from us? How do we determine that space/ time is expanding? Tex

I first apologize if this has been posted more than once; sorry. There is a lack of clarity at my end as to whether I am logged on here? Say we have two galaxies, the Milky Way (MW) and galaxy A separated along a straight line 20 x the radius of the Universe visible to us. If I understand...

Hi, may I ask a question, please? Say we have two galaxies, the Milky Way (MW) and galaxy A separated along a straight line 20 x the radius of the Universe visible to us. If I understand correctly then the rate of the physical expansion of space between MW and A could be at the rate of say...

On a long trip the photon goes, but it occupies a wavelength of space at any particular time. If the space between start and finish (inspection) is expanding all the way all the journey time, then most of the expansion has no effect on the photon. Like eg second tenth is section currently passed...

How would the expansion on a scale of 10 kpc be measured, by a red or blue shift? How can expansion of space be differentiated from the velocity of stars? It seems that the expansion of space weakens the effects of gravity?

Space evidently is expanding, so we say that the very fabric of space time is expanding uniformly in all directions, so two questions 1)originally this expansion was driven by the energy content within the universe aka the dense hot matter , versus nowdays the acceleration is picking up speed...

I am wondering if an object can fall into a black hole at faster that the speed of light. I have heard that the expansion of the universe can make distant galaxies appear to recede from one another at velocities faster than the speed of light.

 Intuitively, this makes sense to me. I am...

I was talking to a graduate physics student about the issue of energy conservation in an expanding universe. I paraphrased the argument against energy conservation as follows - Suppose we have a photon in outer space that is very far from earth. The universe is expanding (by this I meant that in...

I've been trying to wrap my head around the geometry of the expansion of space, from Science Channel shows I vaguely understand the "every point in space is moving away from every other point in space" and iirc this was uniformly so. Is that correct? If not ignore the rest of this post I suppose...

Imagine that the CMB did not exist. What observational evidence exists to support the theory of the metric expansion of spacetime, as opposed to having a static spacetime and it's the matter distribution that is expanding - as it would in an explosion?

Before I get to a question that's been on my mind for a while, I would like to make it clear that I am a high school student with no understanding of physics beyond my school's curriculum and some books that I've read, so excuse me if this sounds rather absurd. I know that the expansion of...

How does knowing that galaxies are all moving away from each other and the farthest ones are moving more quickly prove that space is itself expanding and not just that the galaxies are moving through it?

Light can get red-shifted due to expansion of space, this leads to a loss of energy. Would it be possible that this energy is what's causing the universe to expand in the first place?

We are told that space is expanding and that the rate of expansion is speeding up. However, as relativity shows that space and time are inextricably linked, does this mean that time is expanding too?

Then is potential energy infinite (potential energy=energy that can be created)

universe is expanding since the bigbang so therefore space is expanding, but apparently dark energy remains constant, it apparently isn't getting diluted as the universe expands is energy being created, specifically the energy in vacuum?

Prof. Brian Schmidt got the Nobel Prize for his work in expansion of the universe which he did in 1998. His team was able to figure out that earlier in the past, the universe's expansion rate was slower than it is right now and it's actually increasing day by day. However, wasn't the same thing...

It is my understanding from reading a few threads that remote clusters don't have any "speed" relative to us, they are simply moving away. Does this mean they have no momentum? And if that is true, does that imply that they have no mass (in this context, not in a local context). And if that is...

Since Edwin Hubble proposed distant galaxies move apart from each other as spectra of each galaxy is shifted towards the red end. this created the law that universe is expanding exponentially since big bang. and these galaxies spectra are due to stretching of wavelength of light incident from...

Hi all, After the 'big bang' it is said that space is expanding. Atom is almost 99% space then why are they not expanding, same can go with all the stars and galaxies and all stuffs. Hope this is not sounding crazy. If so pls forgive me. Cheers.

I read that the mass of the universe slows the expansion of the universe. I also heard that if the mass of the universe was above a critical value the universe would contract. I believe this is called the big crunch scenario. And that it is currently not considered a probable scenario. Is this...

Fellow Nerds, I'm looking for a quantitative relationship between the gravitational strength of a point on a field and the speed of expansion of space at that point. Given a cosmological constant and a metric, is it possible to pinpoint a certain point of space and ask how quickly that space is...

Hello everyone, My question is: The big bang model proposes that the rate at which the universe is expanding is now decelerating. The inflationary theory proposes that the speed of expansion and separation started out slow and now it is accelerating. But as we know, recently it has been found...

Space is expanding, which separates objects from each other in space. Won't this add potential energy? Doesn't this violate the law of conservation of energy? But if it does not, how can space be added without adding potential energy?

I have a paradox that I don't know the answer to. Special relativity has no preferred frame, but it seems like adding an exponential expansion to space introduces such a frame. The Setup Suppose we're in a universe with a much faster expansion rate, where the space between any two objects...

I am writing this thread because I have too often had to explain this and I basically wanted to have a resource available to direct folks to, and, frankly, the Wikipedia topics on this are pretty vague on the explanation. Any questions, comments, or corrections are greatly appreciated. So, here...

A very fundamental doubt. Was inflation expansion of just space or the universe with whatever the state of matter it had?

I know that expansion of space operates farther away from our Local Group of galaxies. But the reason for not considering expansion in our galactic neighborhood is: A. The space expands everywhere, the expansion is just too small close to us so we don't need to talk about it. or B. The space...

If the expansion of space in the macrolevel is faster than the speed of light then it should have "more" than infinite rapidity. How does that work out? Thanks.

Is it possible that the forces behind the expansion of space could at some point overcome the fundamental forces holding our molecules together?

So what I don't get about the expansion of space, and what I'm assuming one of you can explain to me, is that it seems like if space were expanding, how would we have any way of noticing it? It seems like as the distances between particles expands, so must the size of the particles themselves...

As far as I know, the main argument for the statement that the universe is expanding is that the velocities of galaxies increase proportional to the distance. This together with the cosmological principle indicates that every point in the universe observes the same thing, something that is...

NOTE: I am not a cosmologist, so if any of my statements are not correct please tell me. When we observe distance galaxies we can measure how fast they move away using the red-shifting of their light. So how do we know space itself is expanding vs the galaxies are just moving away relative to...

Sigh. My first post. I wrote rather long message here and as I tried posting it, "you need to login" - and it vanished. :( Anyways. I have no high physics/math education but still I consider myself enthusiasts. So be gentle! :) Consider the following "my way of filling sudokus", just thinking...

Hi, I made a (rough) calculation of how far the Moon would be moving away from Earth according to Hubble's law = 72.6 (km/s)/Mpc -- 1 megaParsec = 3.08 × 1022 m ≈ 4 × 1022 m Distance between Moon and Earth ≈ 4 x 108 m Expansion rate ≈ 7.2 104 (m/s)/4 × 1022 m = 7.2 (m/s)/4 × 1018...

If space is expanding and I put a ruler inside this expanding space, the ruler should expand with the space. Therefore, inside this expanding space two particles would always measure, to an observer with the ruler inside the same space, the same distance away, even as that space expands since...

I have always been puzzled by how we see an object from the past and can tell what it is doing now if it is billions of light years away. Given that; 1. the shift in the measurement of the light spectrum indicates the speed at which an object is retreating or getting closer. 2. that...

I'm coming with a good background in Big Bang expansion as the following sci-am article shows (which I've mastered): http://space.mit.edu/~kcooksey/teaching/AY5/MisconceptionsabouttheBigBang_ScientificAmerican.pdf What I'd like to understand is this. Expansion can only be felt in unbound...

I realize that because of gravity and the relatively high density of our place in the universe compared to the voids, cosmologists generally agree expansion isn't really significant, but I don't understand why this is so. If the universe is expanding, then why isn't the space between every atom...

Hi. So if the space in the Universe is expanding, does that mean that the space existing between me and my monitor, or the space between object A and object B is also expanding in some sense?

I'd like to understand accelerating expansion better. It seems that space is interjected proportionately where there is low density (intercalated is the term in biology). Can this interjection of space be sent back where it came from when that area of space becomes more densely populated?

Since I see the Big Bang was the beginning of space; if space is infinite, does that mean that space can expand at an infinite rate? (Thanks in advance from this layman; I've started Brian Greene's "Hidden Reality" and despite laymen being it's target audience, I'm stuck on this question.)

question 1. i need some help understanding this. it is proven that the universe is infinitely expanding correct? what is the exact reason for that? question 2. i have a couple questions on dark matter. does dark matter give off its own gravity bending space-time, I am assuming ?

From what I understand the beginning of the universe was period of rapid expansion. I've been told that this expansion is not to be thought of as the universe expanding into an empty space and filling things up but space expanding instead? Is there something off with this and if not how...