B Is space stretching or is new space being created?

[Dale]

I'll never have the slightest clue on this question because the explanation in layman's terms is completely wrong

IMO, the problem is that you are not asking a physically meaningful question.

You have heard two different ways of describing the same thing and think that only one can be right. But physics doesn’t work that way. It doesn’t say only one description is right. In fact, a lot of modern physics is specifically based on the equivalence of different descriptions.

The only way that physics can choose between two descriptions is if they describe different measurements.

 

[Nugatory]

it appears that I'll never have the slightest clue on this question because the explanation in layman's terms is completely wrong

It’s not that dire. The physical fact is that two objects initially at rest relative to one another will drift apart unless there is some force that tends to hold them together. We don’t need to think in terms of space stretching or being created to understand this.

 

[PeroK]

Well gentlemen (and I use the word loosely) it appears that I'll never have the slightest clue on this question because the explanation in layman's terms is completely wrong. My math is limited to 2 + 2 can equal 5 if the value of two is large enough.

Accept it from those who know? The last time I did that I lived with a lie for 65 years (as have all of you) but that's off topic. I'll call this one closed because it's dead-ended for me. Thanks for trying.

Yours is a common dilemma. If you cannot or will not learn the required mathematics to study modern physics as an undergraduate student would, then you do have to accept explanations without fully understanding them.

The purpose of this site is to provide the next level of understanding, where possible, beyond popular science. If you are happy with what popular science tells you, then fine. But, it is a deadend. It doesn't allow you to think for yourself beyond what you have been told.

If you study physics as an academic subject, then you have the tools to explore the subject for yourself. Many people who read popular science are unhappy at this situation. But, the physics students puts in hundreds of hours of study to learn the subject. And, from the very start is required to solve problems for themselves and apply what they have learned. The popular science reader learns passively, and is never asked to roll their sleeves us and spend hours solving problems for themselves.

You can be as skeptical of this state of affairs as you like, but there it is.

One final point. The question of whether space is physically stretched is at best superficial. You're getting absorbed by a question that is ultimately of no relevance. There is a huge body of knowldege in the realms of GR and Cosmology. To me, that's what's sad. There is so much to learn in modern physics, but you've ended up foundering on a question that isn't even a question that physicsts are concerned with. You haven't even scratched the surface of what there is to learn about Cosmology, but have been stopped in your tracks by an irrelevant concern.

That we do not share your concerns is not our problem. That's your problem and prevents you from learning further.

 

[sophiecentaur]

you'd have double the space between everything.

. . . . . or even eight times?

 

[Jonathan Scott]

Consider the analogy of a 1-dimensional universe shaped like a cone, where the distance along the axis from the point is time and space at a given time forms a circle around the cone. If you move the circle towards the wider end of the cone, is new length being created or is existing length stretching? I would not consider either option meaningful. If you draw straight lines on the cone starting from the point to representing the paths of galaxies, they get further apart, so the gaps between galaxies are increasing. However, if you draw two parallel lines on the cone and it is made of flat material, the lines remain parallel into the future, so objects (including galaxies) do not grow or shrink as a result of the expansion of the universe. (If the rate of expansion changes, which is probably true for the actual universe, it gets more complicated, but I think the analogy is still helpful).

 

[ShadowKraz]

No, when you increase the resolution, you, of necessity and by definition, increase the number of pixels. Not a good analogy anyway because the Universe, the screen in your analogy, is getting larger.

Those are just analogies, which help to intuitively understand it in terms of everyday concepts, but neither is exactly true. Here is a third analogy, which I find quite appealing. The universe expansion is like changing the resolution of the computer screen. When you increase the resolution, the size of the screen and the number of pixels remain the same.

 

[Herman Trivilino]

My understanding of dark energy is that particles come into existence, exert and outward force, then vanish.

That's your problem. There is no accepted explanation to a mystery, that's what makes it a mystery. People can't answer a query based on a premise that isn't even wrong.

 

[ShadowKraz]

On looking at the maths with a limited understanding of it (somehow calculus defeated me in my college days), I leapt, with the help of someone who does understand the maths, from the misleading balloon analogy to thinking that while space expands it doesn't expand into anything, that there is no boundary as we think of one based in everyday experience. It seems counterintuitive, but that's only because it does not relate to the ordinary everyday physics we experience directly. Letting go of that, it suddenly made sense. Nothing is 'created', space is bigger simply because it is bigger. Again, it seems counterintuitive but only because we are so rooted in the everyday mundane physics.

 

[phinds]

from the misleading balloon analogy

try this:

Learn Inflation Balloon Analogy

 

[ShadowKraz]

try this:

Learn Inflation Balloon Analogy

Been there, read that, moved beyond.
It does help folks mired in the balloon analogy, however, I'm not mired in it.
But thank you.

 

[sbrothy]

[...] what is the measurable difference between creating space and stretching it? [...]

I (think I) know the thread is officially dead but I couldn't resist:

If there's no agency behind LLMs but you can't tell the difference what is the difference?

(Tongue-in-cheek, as so often with me.)

 

[marees]

What you can measure is the curvature of spacetime. That leaves you with a more agnostic, mathematical approach that says that if we measure time in a certain way (technically using comoving coordinates), then the measured distance between distant objects generally increases over time.

So if I understood this correctly

Curvature of spacetime depends on mass
It is only spacetime that "expands" & not mass
Hence the curvature near a mass is not distorted much, but away from the Mass should we observe a "diluting" of the spacetime curvature ?

 

[PeroK]

So if I understood this correctly

Curvature of spacetime depends on mass
It is only spacetime that "expands" & not mass
Hence the curvature near a mass is not distorted much, but away from the Mass should we observe a "diluting" of the spacetime curvature ?

The expansion of space is a description of the overall geometry of spacetime across the whole universe. This is measured on the largest cosmological scales. In this model, galaxies (or even galaxy clusters) are treated as point particles.

The curvature of spacetime near a massive body is a different case. This a local curvature and is not directly related to the overall expansion of space.

 

[marees]

The expansion of space is a description of the overall geometry of spacetime across the whole universe. This is measured on the largest cosmological scales. In this model, galaxies (or even galaxy clusters) are treated as point particles.

The curvature of spacetime near a massive body is a different case. This a local curvature and is not directly related to the overall expansion of space.

Would backreaction play a role in accelerating the expansion of space ?

https://cqgplus.com/2016/01/20/the-universe-is-inhomogeneous-does-it-matter/

 

[PeroK]

Would backreaction play a role in accelerating the expansion of space ?

https://cqgplus.com/2016/01/20/the-universe-is-inhomogeneous-does-it-matter/

https://en.wikipedia.org/wiki/Inhomogeneous_cosmology

 

[ShadowKraz]

What is bothering me is that I can perceive the expansion of the Universe in my mind's eye but can't come up with a clear description of it in plain language. What doesn't bother me is that no one else can either.

 

[timmdeeg]

What is bothering me is that I can perceive the expansion of the Universe in my mind's eye but can't come up with a clear description of it in plain language. What doesn't bother me is that no one else can either.

Perhaps this helps:

https://www.astro.ucla.edu/~wright/cosmology_faq.html#MX

Are galaxies really moving away from us or is space just expanding?​

This depends on how you measure things, or your choice of coordinates. In one view, the spatial positions of galaxies are changing, and this causes the redshift. In another view, the galaxies are at fixed coordinates, but the distance between fixed points increases with time, and this causes the redshift. General relativity explains how to transform from one view to the other, and the observable effects like the redshift are the same in both views. Part 3 of the tutorial shows space-time diagrams for the Universe drawn in both ways.

So, the view of stretching space is not invariant.

 

[Dale]

What is bothering me is that I can perceive the expansion of the Universe in my mind's eye but can't come up with a clear description of it in plain language. What doesn't bother me is that no one else can either.

I don't think that the plain language description is important. What is important for physics is an experimental description. Plain language can describe many non-physical things. Experiments are what we use to ground our descriptions in the physical world.

What measurement would be different in the two cases? I think that the answer to that is "no measurement would be different". So the question about the two cases is non-physical.