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On the Motion of Galaxies

#1
Astrophysicists have known for a while that there was a place in space, which they've called the Shapley Attractor, that is pulling thousands of galaxies toward it.

Now it seems there's another part of space that gives the appearance of "pushing" galaxies away from its center. It's being called the Dipole Repeller as it acts like the other pole of a magnet from the Shapley Attractor.

What's weird -- beyond "why are there attractors and repellers in the first place?" -- is that the force operating at the Dipole Repeller can't be gravity as that's an attractive force: it can only pull masses toward each other. The article linked above suggests that the Dipole Repeller only looks like it's pushing galaxies away because it's an area of low mass. But this fails to ask how such a thing can persist if "nature abhors a vacuum" is a sound general principle. Why wouldn't an area of low mass "want" to be filled by mass to equalize that (for lack of a better word) pressure, appearing as a center of attraction?

Reality is just plain weird.
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Re: On the Motion of Galaxies

#2
Flatfingers wrote:But this fails to ask how such a thing can persist if "nature abhors a vacuum" is a sound general principle.
It isn't. :ghost:
Well, it is, but only in a fluid, in a constant gravitational potential.
On large scale, gravity is much stronger than fluid pressure. (which is why we have an athmosphere at all)
(After all, if nature abhors a vacuum, why is 99.999... percent of the universe filled with one?)
Flatfingers wrote: Why wouldn't an area of low mass "want" to be filled by mass to equalize that (for lack of a better word) pressure, appearing as a center of attraction?
Because there is no pressure - gravity tends to clump things up, not spread stuff out, as stuff is attracted to stuff, not to not-stuff.
Warning: do not ask about physics unless you really want to know about physics.
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Re: On the Motion of Galaxies

#4
Well, let's put it a different way: why would one part of space have a central area containing less mass than other places?

In other words, why wouldn't a gravity-based attractor draw matter from all surrounding locations equally? How could there be a centralized, probably spherical, lack of matter?

Just putting these questions out there for speculation. :)
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Re: On the Motion of Galaxies

#9
They're just trolling us. :squirrel:

"Hey Bob, what you up to?"
"Oh, just my gravity machine! I'm totally wrecking the calculations of the guys in Universe C-137!"
"Bahaha, that's awesome! Let me try!"
"Okay, here!"
"Lulz, wow, lookit that, now they're inventing some kind of space-magic called dark matter to explain what we're doing"
"xD Lol, morons"
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Re: On the Motion of Galaxies

#11
Flatfingers wrote:Well, let's put it a different way: why would one part of space have a central area containing less mass than other places?

In other words, why wouldn't a gravity-based attractor draw matter from all surrounding locations equally? How could there be a centralized, probably spherical, lack of matter?

Just putting these questions out there for speculation. :)
If I have to guess, because the formation of structures is all but neat. Matter tends to clump up in a large "web" of stuff, and round holes in it are fairly common.
You can see what I mean in this neat video of the EAGLE simulation: :)
https://www.youtube.com/watch?v=-awYNyznf58
Warning: do not ask about physics unless you really want to know about physics.
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Re: On the Motion of Galaxies

#12
The clumping phenomenon is pretty well recognized. That's an excellent simulation of the effect.

What seems to be going on here, as shown in the diagram, looks more like some different kind of post-clumping effect exerted over a much larger volume than the "local" gravity of galaxies.

In fact -- and I know how nutty this sounds, but I give it no more weight than idle speculation -- the diagram of galactic motions has a familiar look:
Image It's as though a stupendously large horseshoe magnet, but acting on gravity (and at gravity's scale) rather than magnetism, were poking through into our universe. Where the endpoints emerge creates a monstrous (but low-intensity relative to galactic gravity) gravity field through which matter flows directionally, similar to the directional flow of charged particles through a magnetic field. Where there's clustering (as in our own Local Group of galaxies), these are small distortions of the large-scale gravity field by more localized gravity generated normally by large mass concentrations.

(Note: I see that something called "negative mass" has been proposed, but I'm not equipped to assess whether that's plausible or pseudo-scientific gibberish. If plausible, it would be an explanation for the Dipole Repeller, but not the Shapley Attractor.)

Again, I know how peculiar all this sounds. A colossal "gravity magnet" poking at two points into our universe? It's not like I'm going to magically understand something that would make roomfuls of PhDs in astrophysics exclaim, "Why didn't we think of that?!" I do have a sense of proportion. ;)

And yet... I look at that diagram, and I factor in the recent confirmation of gravity waves by the LIGO sites, plus gravity fields... and I get "well, why couldn't it be a gravity dipole?"

And now I need to know whether the universe can be seen to contain other attractor/repeller pairs.
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Re: On the Motion of Galaxies

#13
It'd be cool if it was something akin to a tractor beam. A couple years ago, some Austrailian physicists made a 'tractor beam' using waves in a water tank. Different patterns of waves, they found, were able to manipulate objects- pushing and pulling them around the tank.

What if gravitational waves could produce similar results, and there was some super funky phenomenon acting as a gravitational wave generator that was producing gravitational waves in such a manner that they pushed things away from the Dipole Repeller and towards the Shapley Attractor? That would be cool, but I have no idea if it is reasonable to apply the properties of water waves to gravitational ones.
Libertas per Technica
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Re: On the Motion of Galaxies

#15
...

Sometimes I really don't know how to deal with you guys. Here I am, taking the time to share some neat information and some obviously speculative ideas. Is it really necessary, or helpful, or encouraging in any way, to make no response other than to go looking for things that in your opinion have failed to be utterly complete and perfectly accurate?

"Geez, I guess Flatfingers just can't tolerate being corrected." Bollocks. It's a point of honor for me to admit when I'm wrong, and I am wrong sometimes, just like everyone is wrong sometimes. But the correction ought to matter.

If I'm clearly wrong on some fact that is important to the overall concept being considered, that's one thing. But this nit-picky stuff, that seems to have no purpose other than "ha-ha, gotcha!" just makes me want to stop trying to say anything.

Call that whatever you want.

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