Cage Match: Gravity Leakage vs. Dark Matter

March 1, 2005 5:10 PM

In 1962, Thomas Kuhn published The Structure of Scientific Revolutions. It questioned not only the "progressive" model of scientific history, but also bled over into other disciplines and brought into question human perception of just about everything else. (coining the questionable phrase "paradigm shift" in the process.)

One of the most interesting shifts came in the battle about the (not totally forgotten) aether. A modern day equivalent might be "dark matter," an undetected form of matter that explains some of the quirky behavior of gravity. Or, it could all be gravity leakage.
Let the battle begin! (The winner might just set the course of astrophysics for the next generation, or even lead to the holy grail.)
(see also here.)
posted by absalom (26 comments total)

Is dark matter somehow a less palatable mechanism than an ad hoc number of dimensions?
posted by jungturk at 5:40 PM on March 1, 2005

Just a short note that theories with extra dimensions are testable, but so far we have no positive results. The idea is a attractive, however, because it offers an explanation of the relative weakness of gravity compared with the other forces.

Not to nit pick, but nothing about cold dark matter is quirky with respect to gravity--in fact, just the opposite--we don't know why it gravitates like ordinary matter but isn't glowing or absorbing light like ordinary matter. The quirky stuff absalom is likely speak of is what's been termed "dark energy" (that is, whatever is responsible for the current acceleration of the expansion of the universe). And lastly, this debate has little to do with the original proposition of an aether¹.

¹ The aether was proposed as a medium responsible for the transmission of electromagnetic waves--light--which we know now does not exist. Light persists in the vacuum.
posted by fatllama at 5:45 PM on March 1, 2005

the paradigm shift is totally one of my favourite concepts. I particularly like the idea that what can start as a single anomaly from a system can eventually accumulate into a rival paradigm of its own.

I imagine this like a single person subverting the moral code, and eventually it accumulates into a criminal underclass. Different paradigms are supposed to be incommensurable, i.e. you can't really compare them. But you can get an arms race between the two paradigms, and thus symbiosis (is this a meta-paradigm?)
posted by leibniz at 5:53 PM on March 1, 2005

I disagree with the view that dark matter is a paradigm shift, since that would imply that dark matter subverts the existing scientific theories of cosmology, for example. In fact, the situation is the opposite -- dark matter is the solution generated by the current paradigm to address oddities in existing cosmological theories.
posted by blahblahblah at 5:58 PM on March 1, 2005

My understand was that aether was a bootstrap, something pulled out of the blue that "could never be proven" that explained a dificult to explain phenomenon (creationism would be another example).

Dark matter though, is something that was found to show up in calculations, just like black holes were, but is believed to be difficult if not impossible to show/find/see (as coincidentally black holes were at one point).

Am I not correct?
posted by furtive at 5:59 PM on March 1, 2005

My understand was that aether was a bootstrap, something pulled out of the blue that "could never be proven" that explained a dificult to explain phenomenon

Actually - Ether was, at the time, a scientifically credible hypothesis. Light is, classically, a wave, but, unlike other waves (such as sound), there is no apparent medium through which it travels. Ether was hypothesised as an invisibile medium for the light to travel through (since scientists' knowledge of waves, at the time, seemed to require some medium).

There was actually some rather sophisticated theories of how this ether would behave (it would have to be an extremely odd material - since theory demanded it be extremely rigid despite not interfering with the movement of massive bodies). What finally disproved the existance of Ether was an elegant, and famous, experiment done by Michelson and Morely in Cleveland in 1887. Here's what looks like a good summary of that experiment. Later, more sophisticated, theories of light buried the ether concept once and for all, not long thereafter.
posted by kickingtheground at 6:13 PM on March 1, 2005

aether wasn't pulled out of the blue - to that point, all energetic waveforms were expected to have to propagate through something, and the aether was proposed to be the medium through which electromagnetic fields propagated (pardon the gross simplification of the aether arguments). the disproof of the aether (michelson-morley) was extremely disconcerting to the norm because it was downright nonsensical - WTF was electromagnetic propagating through if it wasn't the cosmic goo?

as for the testability of dark matter, some of its hypotheses are quite testable, and in fact within the past week we've seen news stories which suggest that the stuff's just right down the universe from us.
posted by jungturk at 6:15 PM on March 1, 2005

bleh...good preemptive synopsis, ktg...
posted by jungturk at 6:16 PM on March 1, 2005

Don't listen to the naysayers, furtive; you're toally right. In terms of what they're doing for their respective theories, aether and dark matter are nothing alike. Aether was intended to be an underlying explanation for action at a distance. In effect, our forefathers worked out a scientific theory, and decided that they needed something out there to explain their mathematical formulae, so they introduced aether. There were three other main competing theories, none of which had any metaphysical hope of being proven over another. Newton's Principia turned science on its head, because he realized that science should not be concerned with underlying explanations, and concentrated solely on the math. There was a lot of resistance to his theory of gravity on its publication because it provided no explanation for action at a distance. We still don't have an underlying explanation for it. No big deal. A lot of researchers in quantum theory are concerned with unifying wave and particle theories of light, and in so doing, they're hoping for a pre-Newtonian explanation. To think that there is a true explanation, or even that the two theories can be reconciled at all, is pure metaphysical overreaching.

Dark matter, on the other hand, is borne precisely out of our math. We found we could make better calculations and predictions by introcucing it as a substance, so we did. A lot of progress in physics is made when physicists stop throwing out recalcitrant numbers as noise and nominalizing them as objects instead. There's a very fine line between physical and mathematical entities. What is dark matter really? There's no answer and no need to ask the question. In this sense, dark matter is doing the exact opposite for its theory as what aether was doing.

I guess this is debatable, but I don't think either aether or dark matter are that intimately connected with paradigm shifts; both grew out of normal science in their respective theories and not very much restructuring of our total science had to occur. Kuhn drew strong lines between normal science and revolutionary science... revolutions happen when the science occuring afterward does not and cannot even talk about the same ontological enitities as the previous science. I disagree with him on this point, but from his perspective, I don't think the introduction of dark matter would have constituted a paradigm shift.
posted by painquale at 6:31 PM on March 1, 2005

fatllama: To my way of thinking, the aether angle comes from the fact that there is now a competeing theory in regards to why the universe expands as it does that does *not* require dark matter. Until just recently, there was no direct evidence *at all* of the existance of dark matter *outside* of math. If the alternate theory (gravity leakage) turns out to have merit, the dark matter paradigm will be overturned and a whole new model will have to be created. (Much like new models were forced to be created after the breakdown of the aether model)
posted by absalom at 7:47 PM on March 1, 2005

Kuhn took special pains in Structure to explain that during paradigm shifts, people don't "see it coming" as it were. The shift takes some time -- it's not a solid state switch where one second the aether is the accepted theory and then tomrrow we all wake up and see the world differently. So during that period of upheaval (it usually lasts for a couple of years to a couple of decades), we see further and further holes or problems in the current theory. In other words, the theory's predictive power is diminished. And the old tools (Kuhn is interested in the tools of science, both physical tools, like telescopes, and, to a lesser extent, mathematical or analytical tools) become less useful. This is, in my opinion (and IANAAstroPhysicistOrCosmologist), exactly what's happened with the theory of gravity.

The theory does a fine job of explaning what happens on earth and in our solar system. The theory does a rotten job (truly horrid -- have you seen how much dark matter would be required to "balance" out the universe?) of predicting or explaining what we see in terms of galaxies and galaxy clusters. There is not enough star matter (the stuff we see) to hold together the galaxies, clusters, and super clusters. Not nearly enough (5 - 20%, depending on who you talk to and how massive the supermassive black holes are).

And so you're left with two potential hypotheses: either there is a mysterious, invisible, un-detectable, matter in the universe or, more likely, your theory is fucked.

painquale, I think Kuhn would have allowed for "science" (the big thing) to be subdivided into the various disciplines. So that a revolutionary period in one science (biology) might not have a big impact on scientists in other areas. I also believe that the ontological stuff that Kuhn is talking about would be damn hard to spot if you're in the middle of the revolution. Without some time for the significance of discoveries to become apparent, it's hard to see when the break-points really occured. FWIW, I think that the Aether was DIRECTLY related to the wave-particle duality of light and this discover fueled Einstein's and others' work in the first part of the 20th century. As such, it was a break-point, or paradigm shift.
posted by zpousman at 8:13 PM on March 1, 2005

absalom, good post btw! This is what MeFi is best at, IMO.
posted by zpousman at 8:14 PM on March 1, 2005

If the alternate theory (gravity leakage) turns out to have merit, the dark matter paradigm will be overturned and a whole new model will have to be created.

Guys, you are confusing "dark energy" and "dark matter"

Dark matter arose as an explanation as to why galactic clusters seem bound so tightly. In this sense Gravity appears to be stronger than our calculations would indicate so the assumed explanation is that we are missing some matter.

Dark energy is tied up with the cosmic expansion and presupposes something that is either making Gravity weaker at larger distances.

Now there are some other theories out there trying to unite the two as different aspects of the same thing (cf. some quintessence models) they are not the same thing.

From the news article (havent had time to read the journals), it appears that "gravity leakage" is being offered as an alternative to dark energy but not as an alternative to dark matter.
posted by vacapinta at 8:23 PM on March 1, 2005

Aether may actually exist. But to explain its existence, you have to use an even trendier word than "paradigm", that being the word "virtual". That is, instead of thinking of aether as a physical thing, a construct of energy like every other physical thing, think of it as an abstract.

You have seen how massive bodies, like stars, make indentations in the space-time continuum, represented by a 2-D grid. Well, they are not distorting some thing, but instead, they are distorting empty space. They change "virtual" space-time. So what do they change?

"Virtual" aether.

Now, extrapolate this to the universe as a whole. A vast amount of empty space distorted by the energy within, but in such a way that the distortion 'evens out' into a universal constant, unless you are near a massive body. This being said, no matter *where* you are in the universe, this distortion constant affects your space-time.

This is not that radical of a notion, as at least one form of energy, gravity, also has a universal constant.

The irony comes when you build theories based upon one theory or the other. Either aether exists in some form or it doesn't. But you can build a substantial model of reality based on either belief.
posted by kablam at 8:23 PM on March 1, 2005

vacapinta is correct; this theory has nothing to do with dark matter.

I wrote the rest of this for another board; normally I wouldn't cross-post, but it's relevant and the other board's not that famous.

The expansion of the universe is accellerating faster than, at first glance, it seems like it should -- the universe as a whole is acting as though there's less matter in it than other observations indicate.

(Brief sidetrack: the expansion of the universe, from the time of the big bang to the very end, is a little like throwing a ball in the air: if the ball's light enough, you can throw it so hard it escapes earth gravity and never comes down; if it's not -- which is to say, if there's too much matter in it -- you can't. The current situation is like if you hefted an anvil above your head and it just kept going up.)

One way of explaining this is assuming a pervasive repulsive force, dark energy. Dvali has proposed another way: if gravity itself doesn't act like we thought it does, then maybe there's the same amount of matter it looks like there is, after all.

His work rests on string theory, which posits 11 spatial dimensions. We can only imagine 3 dimensions, though, so here's an (oversimplified) analogy: pretend the universe as we know it looks one-dimensional -- which is to say, a line. But it's actually not a line, not one-dimensional; what seems to be a line is actually a very thin cylander, like a telephone wire: three dimensional, but dimensions 2 and 3 are so small that you can't see them until you get close.

The extra dimensions of string theory are the same: they're there (if the theory is correct) but too small to see.

(If you're wondering how dimensions can have a size at all, think of the arcade game Asteroids: go far enough to the right and you're back on the left side of the screen. You can keep going in one direction as long as you like, but you'll end up retracing your steps. The universe may be the same way: travel far enough in any direction and you'll come back to earth. If so, the dimension you travelled in has a definite size (a few trillion light years, perhaps), just as the Earth has a circumference.)

Over long distances, however, the existance of these dimensions can perceptibly change the motion of particles (they'll slide all around the outer edge of the cylindrical telephone wire instead of moving straight along it) and since gravity can be thought of as being transmitted by particles called gravatons, it'll weaken with distance more than would otherwise be expected.
posted by Tlogmer at 8:46 PM on March 1, 2005

"Virtial" aether?

It sounds like you're trying to claim that the curvature of spacetime is based on the notion of it curving around something - much like rolling up a sheet of paper and calling the resulting cylinder a curved surface.

However, that's making the assumption that the curvature of spacetime is due to its embedding into "something else", which is certainly not required. You can have a purely intrinsic notion of curvature with no reference to any embedding.

Did I read what you meant right?
posted by vernondalhart at 8:50 PM on March 1, 2005

zpousman: I think Kuhn would have allowed for "science" (the big thing) to be subdivided into the various disciplines. So that a revolutionary period in one science (biology) might not have a big impact on scientists in other areas.

Hmmm. Maybe you're right... I don't know if I've thought about what Kuhn would have thought about scientific localization. Kuhn was definitely a holist, taking a hard-line stance on the Quine-Duhem hypothesis, and it's still a debatable question as to how you can change any one concept within a holist semantic network without changing every other concept. The reason pre- and post- revolutionary theories are incommensurable for Kuhn is because when you alter your scientific concepts, you simultaneously alter your scientific standards... and those scientific standards presumably affect all of science. This lends me to believe that he might have thought that changing comething in one area changed everything. Otherwise, he might have admitted that scientific goals and norms could be isolated in their own little semantic pocket, and this was absolutely not a conceivable option for him. But then, Kuhn's theories of reference and semantics were pretty naive (at least at the time when he wrote Structure).

I also believe that the ontological stuff that Kuhn is talking about would be damn hard to spot if you're in the middle of the revolution.

Oh yeah, absolutely. You might be right; dark matter might be leading up to a complete overhaul of astrophysics. But that's also true of connectionism in neurology, quantum theory in physics, etc. I'm just being conservative and saying that, from our vantage point, dark matter still looks like normal science, and we shouldn't get too far ahead of ourselves and brand it a revolution yet.

FWIW, I think that the Aether was DIRECTLY related to the wave-particle duality of light and this discover fueled Einstein's and others' work in the first part of the 20th century. As such, it was a break-point, or paradigm shift.

Well, when I was talking about aether, I was talking about the ancient stuff that existed from antiquity up to Newton... post-Newton, its concept changed its form to become luminiferous aether -- at least a halfway respectable scientific entity. I don't know enough about luminiferous aether to know if was built into the scientific tradition or if it was just a short-lived garden path like phlogiston.
posted by painquale at 8:57 PM on March 1, 2005

kablam: You have seen how massive bodies, like stars, make indentations in the space-time continuum, represented by a 2-D grid. Well, they are not distorting some thing, but instead, they are distorting empty space. They change "virtual" space-time. So what do they change?

"Virtual" aether.

If the point here is that aether is just a thought experiment or metaphor we use to explain gravity, then that's fine; but we should not call it real or say that it exists in any sense. We may as well say "imagine that the universe is full of water" to help get our imaginations off the ground. And if our calculations start making our virtual aether look especially weird, we should not get upset (which is why scientists who try to determine if light IS a wave or IS a particle because it must be one are barking up the wrong tree. It can be an exceptionally weird amalgam of the two. As long as we're still able to make predictions by means of calculations, we haven't lost anything.)
posted by painquale at 9:05 PM on March 1, 2005

vacapinta (as usual), and Tlogmer have it just right. And I think blahblahblah has the right attitude w.r.t. any paradigm shift this implies--none.
posted by fatllama at 9:50 PM on March 1, 2005

which is why scientists who try to determine if light IS a wave or IS a particle because it must be one are barking up the wrong tree.

This is the second time you've mentioned this in the thread, and I'm tremendously curious. Who are these physicists who do not accept wave/particle duality? I was under the impression the impression that this has been essentially a settled point for nearly a century. I must admit, however, that I don't follow cutting-edge science, and so I could very well be wrong.
posted by kickingtheground at 9:51 PM on March 1, 2005

the impression the impression

blech.
posted by kickingtheground at 9:55 PM on March 1, 2005

This is a very interesting thread. I just had a quick point, in response to something painquale said:

>it's still a debatable question as to how you can change any one concept within a holist semantic network without changing every other concept

I think it's possible to accept the changes if there's a corresponding switch in the rules of semantics. And it's happened before, in the discovery of catalytic RNA.

It's a biological example but simply, through evidence, exploded a few myths and changed the rules effectively -- I'll go away now.
posted by gsb at 9:58 PM on March 1, 2005

kickingtheground: Who are these physicists who do not accept wave/particle duality?

Yeah, there probably are none any more. But there were! There were huge camps. And they were barking up the wrong tree. Wrong tense.
posted by painquale at 10:50 PM on March 1, 2005

actually the wave/particle thing came up again recently.

as ever, when kuhn is mentioned, it's just people from the arts getting their pants in a knot at the idea that science changes.
posted by andrew cooke at 3:03 AM on March 2, 2005

Off topic:
To the extent that at least a couple of y'all must be in physics, would you MIND shifting your paradigms into high gear? I want my damn FTL space ship! Okay? I ain't getting any younger!

(alternatively, you could buy time by extending my life, which is cool, too)

And whoever responds by saying "Its impossible" has to stay after school and wash blackboards.
posted by Goofyy at 4:09 AM on March 2, 2005

vernondalhart: your "rolled up paper creating a virtual cylinder" analogy is a reasonable one. The paper of the cylinder is the only thing that defines the space inside of the roll, but it does create a "virtual cylinder space" that in some ways mimics a cylinder made of a solid object.

Unlike gravity, which is a form of energy, the space-time that gravity affects is not entirely defined. It is the hard to imagine an example of "something" affecting "nothing." And, conversely, when "something" enters the affected time-space, that this time-space "nothing" affects "something".

There are theories that time is a form of energy, and that time and space can be treated as the same thing. But they are *not* the same thing as gravity. This again, leads to an aethereal theory: that time-space is composed of, or filled with, "something" that can be acted on by gravity.

And this energy, whatever it is, behaves so much like aether, that we can just as well call it "aether."
posted by kablam at 10:44 AM on March 2, 2005