I vaguely recall that the observable universe looks a lot like foam. And even more vaguely, that maybe this reflects inflationary expansion of random fluctuations in the early universe.
So maybe this apparent connectivity over implausible scales just reflects the fact that stuff used to be much closer together.
Edit: There's a great sequence on inflation in Takashi Miike's "God's Puzzle".
We used to think so, yes. But our telescopes have improved a lot since then, and we're now able to see with much more detail, our 3D positioning is better too.
We've recently observed that the universe, at the largest scales of what's observable to us, looks like this: https://i.stack.imgur.com/lFnDf.jpg
That's what I meant by "foam". And remember that those are ~2D slices. In 3D, there are voids, with thin intervening walls, and stringy stuff where walls intersect.
It's dark matter that probably defines that structure. And so that dark matter could be moving, in coherent patterns at extremely large scales. But there's nothing necessarily supraluminal about it. It could just be moving in the same patterns that it did when it was hugely smaller. But then, I have zero clue about how conservation of angular momentum works during inflation.
If that were the explanation, we wouldn't expect to see perturbations in cosmic scale motion propagating supraluminally.
Oh sorry I didn't catch that (not a native speaker). When thinking of "foam" I see a uniform, homogenous noisy structure and I was pretty sure this was the name given to our former such view of the universe. My bad! (although I'd say, if "foam" is used to described these pictures, it's a pretty bad choice of adjective by scientists imho. "Galactic tissue" or "tissue-like walls" makes more sense to the layman imho).
Indeed, it's not "probably" dark matter, it is by the very definition of what we call dark matter. It's important to keep that in mind, when we name unknown phenomena it's just a 'placeholder' so to speak. Like X. So X explains the motion of galaxies, and we intuitively called X dark matter. Assuming there is an X, then there is dark matter (what it actually is is another question, could be "white energy" or fluffly creatures from the 6th dimension for all we know, but we call it dark matter for now).
So based on this, I always wonder: is it our observation or maybe interpretation thereof that's flawed? Are there 'effects' that make us see and infer things that are slightly 'off' maybe? (like the discrepancy with dark energy measurements for instance, it appears recently that there might not be accelerating expansion and the increasing redshift is due to errors in our calculations, i.e. we created "dark energy" out of a mistake and now it's possibly going to "disappear" as an idea because it's not needed anymore to explain anything).
As for inflation etc. These are also mathematical concepts that fit the observation, the clues; it however might not be the only possible model that works, we also might not have a correct interpretation (layman words) for it. Like we've got QED/QCD and we're still unable to describe in layman terms because it's illogical, paradoxical. Sometimes our idea of "simplest interpretation" is just that, an idea, and reality is a bit more complex, even if the simple equations may work as terms simplify (see how we "add" zero-value or unit-value arguments to some equations in physics to solve the math, it really begs the question if the "thing" you add actually exists, speaks of a real phenomena). I know Einstein was pretty unhappy about the picture painted by Λ... ;-)
About supraluminal anything (I assume you mean speed > c), I personally don't think it wise to postulate things that physics rule out explicitely. Inflation doesn't do that though, since it's spacetime expanding and that's not constrained by c.
I'm no physicist, and foam is just my analogy. I could have also said bread, because it's basically foam. Or even soap bubble foam. And yes, biological tissue, which is fundamentally an emulsion of oil in water.
That's a great point about dark matter, that it's just a placeholder. There could be stuff that only interacts through gravity. Or it could just be that there's a constant gravitational force that dominates at large distances.
TFA describes evidence that such properties as galactic rotational axes are correlated on extremely large scales. And if there are connections, they must be something that we can't see. So "dark matter" is the obvious candidate.
The other issue is how stuff can be correlated over distances that are too great for forces at the speed of light to correlate them quickly enough. Although TFA doesn't explicitly say that, I can't think of what else about those connections is so surprising. Given that the large-scale structure is so well known.
That's what got me thinking that inflation could account for it. I was thinking of stuff like shedding of vortices from rapidly moving objects in fluids. As they expand, features that arose at small scales in the boundary layer expand to far larger scales. Indeed, to scales that are large enough to be puzzling, if we had observed them in isolation.
That's simple minded, I know. But then, I'm no physicist.
I'm no physicist either. Maybe I wish I were, though. And no, your ideas here are everything but simple-minded, imho. On the contrary, being a non-expert lets you play with things with much more freedom than otherwise (like sci-fi authors), and then actual physicists can take over, sort out the testable and go with their own gut feeling.
(note: I assume TFA = Trend Filtering Algorithm, please correct if I'm wrong).
> galactic rotational axes are correlated on extremely large scales
I think "correlation does not imply causation". While this is a plague in economics, psychology, sociology, biology (non-exact sciences), it also applies in physics. We really don't know in this case, we just observe what you said but "correlation" is bias that typically hinders actual research, experiments — it's the idea that you'll see what you want to see and even design the experiment to show it, which is a very slippery slope, basically a form of "confirmation bias".
I want to stress that I in fact agree with you, in sentiment and analysis, but I'm just voicing my internal "devil's advocate" voice here: mental models and frameworks that are wrong, and not only make my intuition thus false, but deeper than that prevent me from seeing other solutions, from 'forking' every step of the way according to new data.
I guess I'm prefacing my conclusions here:
- there is no "dark matter", there is X that explains a bunch of discrepancies between theory and observation. Each such discrepancy could be explained by a different X (Y, Z...) or a sub-part of X (like mass relates to gravity, but also density, thus heat profile, etc).
- there is always a "fundamental correlation" between literally everything (aren't each and every organ of our body, every inch of this Earth the literal 'children' of supernovae and neutron stars explosions and black hole cataclysms?)
The hard part is to find first-degree (i.e. direct) relations, of the kind described by physics equations. It's not always discrete and binary, but it can be done — for instance I can tell you that "hunger" among the population is as certain a path as it gets to revolution. Not sadness, not lack of freedoms, not violence physical or mental, not even cataclysms have a firmer grasp on rebellion than the empty stomach of our children. It's as direct a path from A (hunger) to B (revolution) as you can get, statistically in all of history (you have days before people rebel, a very few weeks at most).
The alignment of galaxies are obviously related to something, which might yet leave individuals otherwise independent — like metal rods align, each of their own "volition", with a magnetic field; there is no correlation between the rods but rather a macro phenomena. Functionally a vector space wherein rods exist, not a function from rod i to rod j for any (i,j). Galaxies might work this way too — this is my intuition. No spooky supraluminal action at a distance, just a "gravitational polarity X" that averages to orienting space locally at large-enough scales. At a higher scale in 3D, it's probably more about tangents lines (i.e. said "polarity" is of the flow, the streams of galaxies, possibly "dark matter" which is a Y here, possibly distinct from the X phenomena) than a macro-universal sense of rotation (although it's a perfectly valid solution too, indeed many symmetries are broken for our cosmos to exist, namely anti/matter, causality, or chirality.)
Rotation discrepancy could be related to X and/or Y or yet another Z phenomena (my money is on the supermassive blackhole in the center, which I think we're not fully understanding all effects yet, far from it, but meh it's bias and subjectivity on my part).
[Btw, since you seem to like this kind of discussion, I'd strongly recommend you follow Anton Petrov on YouTube[1]. He's a wonderful young scientist who makes short 5-15 minutes videos on new astrophysics / astronomy papers every day or so. For me, it's just the best way I've ever had to 'quickly' keep track of the latest observations and theories, while hearing the explanation and questions of an expert. Dr Becky[2] is another newcomer in the field of intelligent vulgarization, and she's on a path to awesomeness as well.]
I've been into these things since my teenage years (late 1990s) and it's incredible how much more observation we have now, how much more material there is to think about. It's a truly great time for space amateurs.
I agree about the "correlation does not imply causation" plague. It's especially problematic for purely observational sciences, where experiments are impossible or unethical. Prototypically for epidemiology, but also for astronomy and cosmology. And yes, it's a slippery slope, even for experimental sciences.
I get what you say about the alignment of metal rods in magnetic fields. So yes, there could be some gravitational polarity over extremely large scales.
I see that I was getting stuck on the idea that changes can't propagate faster than light, no matter what the mechanism. But now I get how arbitrarily separated stuff can be similarly affected by a given source. For example, there was a recent article about hot gas "sloshing" in a galaxy cluster.[0]
Yeah, the faster-than-light topic is actually a very, very tricky one, even for seasoned astro-peeps it seems.
I didn't mention PBS Spacetime[1] but it's probably the best place to start for best-in-class high level mojo in astrophysics. Tons of back-catalog. Really great quality production. Less 'newsy', more 'substance' than the other two I mentioned (these are my trio on the topic).
Case in point: they do a fantastic job at explaining, notably time shenanigans. They basically made it click for me, notably for FTL (Faster-Than-Light) space expansion, cosmic inflation, etc. Fantastic-everything about them, can't recommend enough.
One thing, though: my best way of framing the FTL limit is in terms of a speed limit (c) to transfer "information". This is why entanglement is a valid principle, it does not violate c because entanglement cannot be used to transfer information faster than light[2].
So "structure" can change arbitrarily fast, from the perception of its objects, its contents; but "information", the contents, the objects, they are bound by c and all the rules actually defined by said structure.
I really don't know if that's the correct view, but it seems to work to explain (actually rule out) most light-speed paradoxes, so...
In these pictures[1], each individual 'dot' is a whole galaxy's worth of dark matter (and here[2] are said galaxies).
So you may view galaxies as "neurotransmitters" of the universe, maybe. Or hormones. The big luminous nodes are the neurons, where all 'dark matter synapses' converge.
Perhaps what happens when over the short course of a few billion years, some "life" is taken from one node to another, is just a cosmic neuron doing its thing. Perhaps said life is just the equivalent of some positive ion charge, and it ends up blowing up the node into a huge black hole and that's just the universe doing "two minus one" (cataclysmic event = "remove 1" from the neuro-galactic graph, just the time of a thought.) Maybe treants had it right all along.
This is exactly what I thought. Sorry to not be able to comment more usefuly... I was looking for a comment already stating my idea before writing it down and i found it here.
So maybe this apparent connectivity over implausible scales just reflects the fact that stuff used to be much closer together.
Edit: There's a great sequence on inflation in Takashi Miike's "God's Puzzle".