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But apparently we don’t live in a void, we live in a big glob of higher density galaxies, the Laniakea supercluster.
https://arxiv.org/pdf/2311.00215.pdf
MOND hasn’t been having the rosiest of time lately. https://academic.oup.com/mnras/article/527/3/4573/7342478?lo...
Doesn't sound like the paper's (the one you linked) authors don't necessarily agree with your summary. From the discussion on page 16:
These results seemingly worsen the recently established tension between the inferred value of H0 from early and late times Universe probes, which has been argued to potentially be the sign of new cosmological physics (see for example Refs. [78–83]). This might appear to be in contradiction with the possibility, explored for example in Refs. [74, 84– 93], that local gravitational physics could alleviate the Hubble tension. Amongst these, a class of models achieve a lowering of H0 under the assumption that we live in an underdense region, whose inner expansion rate is on average larger than the background one. Some results in the literature, see for example refs. [94–96], seem to corroborate the latter assumption finding evidence of local voids which averaged on spheres of r ≳ 100Mpc have density contrasts of δ ≤ −0.1, unexpected within the ΛCDM model. Computing the average density contrast of a sphere centered in Laniakea with radius r ≈ 110 Mpc (i.e. the average distance of the boundary of the ellipsoid from the center) using the CF4 reconstruction we found δ ∼ −0.06, within the prediction of the concordance model (see for example Fig. 6 of Ref. [55]). However, this sphere is not centered in the Milky Way, which might explain why the result differs from the aforementioned ones. Indeed, overdensities such as Laniakea are surrounded by voids (from which they have collected matter), and therefore any sufficiently spherical average will include these under-dense regions. On the other hand, Refs. [55, 79, 97] also found no evidence of any large void or overdensity, thus disfavoring a local resolution of the Hubble tension. Our analysis corroborates these results, suggesting instead that the tension is likely to be (slightly) worsened by Laniakea’s backreaction. An important caveat, however, is that our analysis does not exclude the possibility that large voids in the annular region between 110 − 400 Mpc outside Laniakea could balance and overcome the backreaction from Laniakea, like a rather picturesque Matryoshka doll. Alternative modelling choices accounting for the impact of these voids are therefore required to fully understand the impact our cosmic environment’s gravitational backreaction, which will be the focus of forthcoming studies.
Dr. Becky has a nice explainer video of the first paper.
I dont know why but my mind enters an endless loop when thinking about the vastness of space and where that space exists. Almost as if it reaches the end of human imagination. I can imagine the multiverse, but i cant imagine the “nothingness” in which they exist. I cant imagine where everything came from and where it goes. It makes no sense. I understand the explanation of physics and time, the big bang, expansion, but where the heck does it all exist in? The void of what? What are they expanding into? I understand matter existing in the universe, but where is the universe expanding in? What are the laws of that “in”? That void exists in something but what does the something exist in? It’s almost as weird as if nothing ever existed yet it exists.
It is not expanding inside of something.
The picture I've been given is living on the surface of a balloon. Draw a few dots on the surface, blow in the balloon. Every points expands away from every other point.
Of course with a balloon there is always an outside, but the point is that it isn't expanding like if it were pushing against an external wall.
It's expanding everywhere. It's expanding in the space between your fingers. If you look there, it's not pushing against any outside. There is just more space per space, the longer you let it age.
I understand what you mean and I can easily get this feeling when looking at the night sky on a clear night. I have to quickly abort the loop because it's not very pleasant.
"I dont know why but my mind enters an endless loop when thinking about the vastness of space and where that space exists."
Change 'where' to 'whether' and everything will fall into place.
While we're all throwing out our whacky idea laundry in front of people I presume actually know what they're talking about:
I've wondered for many years if our universe isn't like a supersaturated (SS) solution (1), where mass/energy and the fabric of space-time itself can eventually combine and settle into a balanced but very precarious state, like an SS solution comprised of Mass-Energy-Space-Time [MEST] as a single "fabric" (which perhaps was the state of the universe prior to the big bang, and will be again after the universe' heat death).
Say this large swath of peaceful-yet-highly unstable MEST fabric is perturbed slightly (like dropping a seed crystal in a SS solution) - then matter, energy space and time precipitate outward in a rapidly evolving chain reaction. The horizon of this chain reaction would be a place where matter and energy particles are continually being generated (liberated) from the serene METS fabric, which generates a gravitational pull in all directions.
So, all of the mass in our universe is actually being pulled outward, and because this precipitation horizon is expanding (growing in surface area), it generates an increasing amount of matter and hence an increasing amount of gravity that ultimately pulls matter within this horizon outward - at an accelerated rate. Perhaps the big bang was really, instead, a 'big fizz' - chain reaction of precipitated matter and energy from an initial supersaturated MEST fabric.
Or maybe I'm just full of silly nonsense. Either way, would love to hear an actual astrophysicist 's take on that idea. Maybe gently tear it to shreds:)
Seems like you are picking up on the intuition of cosmic inflation of quark gluon plasma.
The degenerate matter state is like a partial order of time. https://en.wikipedia.org/wiki/Causal_sets
The first part of your idea sounds a lot like a false vacuum decay which is metaphorically a lot like a supersaturated solution.
This article starts from an infinity of axioms that all have to be true for that single statement of the title to have even a small chance of making sense.
It is a purely speculative article.
Sometimes I think about how everything Ive ever known is a tiny invisible spot on a little wet rock hurtling through an empty nightmare abyss.
I do disagree with nightmare, but it's all in perspective. More like an infinitely deep well of incomprehensible potential to me. Deep water is scary but a well is life giving. It's a little bit of both
I read that sentence as poetry. Beautiful.
FYI their definition of “void” is “slightly below average density”
Thanks—I've replaced the void with that in the title above.
"Slightly" can mean such gigantic numbers still on this scale. Still interesting if this is the case
I listen to this before seeing this post:
https://www.youtube.com/watch?v=-kTe0xRAU1w
Seems more concerns about the issue of cosmological constant and its disagreement with observation and current model.
Interesting solution.
I have a theory in my head for years now. It is probably wrong, but here it comes:
In an infinite universe the total amount of gravity that affect us in one point in space is defined by the event horizon if we assume that gravity travels with light speed. Every atom in the universe has a very small influence on us. But this event horizon expands with light speed all the time. I wonder if this could lead to very small but permanent increasing gravitational pull from all directions at once. In other words, and increasing inflation.
I don't know what theory of gravity you are trying to use, but it isn't the correct one.
In our actual model of the universe, using the correct theory of gravity, the "total amount of gravity" affecting us (or any point) from the rest of the universe (i.e., once we factor out local influences like our solar system and our galaxy) is zero. That is because the average matter distribution in the universe is the same in all directions from us, so the "gravity" from it cancels out. The average matter distribution in the universe affects its overall rate of expansion over time, but this is not the same as the kind of "gravity" you are thinking of.
Also, while our universe does have a cosmological horizon (due to accelerating expansion), this horizon does not work the way your hypothetical "event horizon" does.
In short, your "theory" is not even wrong, because it doesn't even start from a correct underlying theory of gravity.
You're on the path to coming up with Mach's Principle[0].
The force of gravity is reduced by the inverse square of the distance (newton's law). Thus as space expands, and matter red shift away from us, the force of gravity reduce over time. The maximum force of gravity was just after the big bang.
Does this account for all the extra space being created - from what I have understood from "always right" youtube videos - parts of the universe are moving away from us with speed greater than the speed of light (or more precise the space between the points is increasing at rate higher than C, no actual movement is being done)
Sort of like a pair of ice climbers, where one climbing up and securing themselves allows the other climber to safely climb higher. Eventually we can't see the ice climbers anymore, but that doesn't mean they aren't still helping each other climb higher.
Increasing gravitational force would result in a contracting universe, not an expanding one, I think.
it grow. we grow?
Question - what are the conditions in the denser parts of the universe for earth style life?
At the mentioned 25% higher density, probably no significant difference.
Why would distance from earth influence the speed of expansion of a distant galaxy?
Does that suggest that our awareness of the galactic bodies itself is somehow influencing them, as in the double-slit experiment?
> our awareness of the galactic bodies itself is somehow influencing them, as in the double-slit experiment
In the double slit experiment, the awareness is not influencing the outcome. The act of measuring is. Pretty sure the act of measuring the galactic bodies has no impact on them in any meaningful way.
Galaxies themselves aren't expanding, they're gravitationally bound. Galaxies are moving apart from one another, however.
The issue is that not all galaxies are moving away from us. The ones that are closer to us have a lot of peculiar velocity [1]. This means they can be moving toward us or moving tangentially to us or any other direction. If we want to characterize the expansion of the universe as a whole, we need to account for this in our models. It turns out to be a lot more complicated than we previously thought.
The crisis in cosmology (aka the Hubble tension [2]) is that our two means of characterizing the expansion of the universe, models of the cosmic microwave background (CMB) and measurements on the cosmic distance ladder using standard candles (Cepheid variables [3] for up-close measurements, Type Ia supernovae [4] for more distant measurements) disagree with one another, and that disagreement is getting worse, not converging.
[1] https://en.wikipedia.org/wiki/Peculiar_velocity#Cosmology
[2] https://en.wikipedia.org/wiki/Hubble%27s_law#Hubble_tension
> Does that suggest that our awareness of the galactic bodies itself is somehow influencing them, as in the double-slit experiment?
"Awareness" is not a thing, not even in the double slit experiment. The term 'measurement' refers to a specific kind of interaction that bridges quantum systems with classical systems, although I believe a good case could be made that these waveforms never actually fully collapse.
Likewise, if there is anything special about Earth's position in the greater cosmos, it would be a trick of perspective or perception - unless there are any completely disruptive new discoveries about the nature of reality. However, my money would be on the fact that the universe is simply not as uniform as we thought.
At any point in space, a celestial object at distance d will tend to appear to move away from you faster than an object at a distance less than d. The only thing special about the Earth here is that it happens to be where we live.
This observation is the reason we think the universe is expanding.
As an analogy, consider the 2 dimensional surface on the surface of a balloon. As you inflate the balloon, the distance between any 2 points increases, and it increases more the farther away the points are from each other.
> Why would distance from earth influence the speed of expansion of a distant galaxy?
It wouldn't - but it may influence how we measure distance. If we're using the wrong distance measurements then we're calculating the speed of expansion incorrectly.
It's distance between any two points, however the distance measuring techniques to which we have access can only be performed by astronomers on Earth. Hence, one of those points will be Earth.
no it's because space itself is expanding which causes things more distant from each other to be moving away from each other faster, the wikipedia article about hubbles law has a graphic illustrating the priciple with bread https://en.wikipedia.org/wiki/Hubble%27s_law
One alternative explanation is that the expansion of the universe is slowing down.
We should call it "space"
Don't say that too loud or somebody will show up and say we should call it "tab."
The management called. It's too long. They'd like to shorten it to " " to keep it cool with the kids.
Space does not imply low(er)-density, void does.
Because of galactic-scale NIMBY zoning.
Without twerking the laws of gravity, I posit I do not live in a giant void.
Am I right?
Please tweak the laws of gravity, but never twerk them.