Daily Archives: 2011.10.4 23:37

Gravity: Not what it does, what it causes

In addition to the LibreCAD thing, OS support stuff, etc. I’m also working on an ERP solution for my clients. This solution has an enormous number of obvious advantages over the way they are using software right now, but it requires me as an individual to understand how their business works better than any individual in that company does (or at least it seems that way after talking with all the different section leaders over there). My thinking about their problems and how to model them accurately in an ERP system leads me back to the problems that can be solved in my own company by a similar system, which leads me to the idea of generalization of functions and rules. This is, of course, the goal of good software design, but without spending some time reflecting on the nature of problems, the nature of data, and the nature of computing it is impossible to identify the parts that can be correctly be said to be general to all problems of a similar type, and what elements remain that make the specific problem at hand unique and identify it as that specific problem and not the same problem also found somewhere else.

This is, in a sense, what must be done when designing general functions, or correct object design, or deciding what utilities and handy tools should be considered to be “system utilities” and what other are just niche applications or personal tools. The concept of classification implies description, and at a certain level specifying a problem implies the ready resolution of the same problem (pretty neat!). But many times we get the identification of the problem wrong. More correctly, we inadequetely or incorrectly specify a problem and then develop whatever solution naturally follows from this mistaken version of the problem as we (wrongly) understand it.

As I was driving home in the rain today I was thinking about this — both the nature of the specific problems my ERP system needs to solve for the customer and the nature of problem classification itself. This led to a thought on how the precise, yet incorrect understanding of problems can lead to silly things like the widely misquoted statement “mathematics/physics states that bees can’t fly.” But quite clearly they do — which means neither mathematics nor physics is what says bees can’t fly, but rather an inaccurate mathematical model of flight predicts that bees can’t fly. But the misquote above is the more popular concept (its more fun, anyway, because it leaves the door open to magical thinking and the world of foolish mystery). The problem with this thinking is not just that it misleads people into thinking that math and physics don’t work — it also personifies math and physics (as in, creates the idea that “they” are beings of some sort who would attempt to prevent bees from flying as if the “can’t” in the misquote relates to the idea of permission) in a way that is weird and leads to more wrong thinking later. That idea led me down a mental journey into physics and I recalled an article I read recently about M-theory, gravity and General Relativity — and, specifically, the parts in the article that relate to the idea that gravity might be repulsive at great distances.

So… Gravity, at great distances, is it repulsive? Does this make sense? Or is there, perhaps, a misconception of the problem space here? There quite definitely is a miconception of the problem — that is evident in our inability to describe gravity in a mathematically consistent way that reconciles relativity with quantum physics. But what sort of misconception? I’m not part of the physics community, but from the way articles written for the layman put things (which is highly suspect) it seems as though people are personifying gravity a bit much. In other words, they are looking for what gravity “does” and from that trying to derive an accurate model of how gravity does that instead of thinking about what gravitiy “is” and then following the path of consequences to its existence.

The four basic forces (weak atomic, strong atomic, electromagnetic and gravity) are fairly well established. Interactions of things (space/matter/energy) those forces have to explain all phenomena — and so far pretty much do, which indicates that this is likely a correctish concept of the way things are. There doesn’t seem to be room for a fifth basic force, though there may be room for more things or types of things with which they might interact or ways they might interact (that is, unthought of dimensions, unobserved particles, etc, but not new forces themselves).

So… Gravity. It a sense it is a side effect of what happens when you concentrate mass in a single place. We say it “curves” space, though the way I tend to picture this in my mind is more of compression that bending, because bending can only happen to things that are truly unbounded, and space seems to be bounded by itself. The most common demonstration is to take a taught, suspended sheet and place something heavy on it, and then say “like this, it bends the surface down” and then the path of a marble on the sheet when rolled across tends towards the heavy thing. But this is a massive oversimplification.

If we take the suspended sheet as a 2D object then the downward direction that it bends to when something is placed on it represents a third dimension for that thing to bend “to” — hence it is bendable because it is unbounded in a new direction. The situation with space and gravity doesn’t seem to be the same because while we are fairly certain there are far more than 3 simple dimensions, we’re not being told to imagine that space itself bends in a 4th extra direction due to the influence of gravity/the presence of mass.

Another problem is the reason for the bending. Space is being directly influenced by the presence of matter via gravity, wheras the sheet is being influenced by something pressing on it. In other words, to get something to bend in an extra direction/new dimension it must be pushed, not contracted. So space under the influence of gravity behaves more the way that a wet cotton sheet contracts towards a spot that warm, dry air is applied to while the wet remainder stays lose and stretched out than the way that a sheet with something heavy on gets forced down in a single spot by the heavy thing.

And another problem with this sheet example is the rolling of the marble in an attempt to explain how things get drawn toward “gravity wells” in the same way the marble gets drawn to the lower points of the sheet. In the case of gravity the path of something under the influence of inertia is to continue moving in a straight line. But the straightness of that line is through space and gravity has contracted space into a smaller area than it normally would have been (or at least it appears so) and so the “straight” line is now curved relative to things that aren’t as local to the mass as the moving thing is. With the sheet example the path of the marble is actually longer than the original path, so this is a mis-example.

So this explanation and concepts derived from it are wrong. Now let’s return to the 2D sheet, because the number of dimensions really isn’t important here. If we were to draw a straight grid on it (or just a bunch of uniformly even or uniformly random dots), get it wet and then apply a hairdryer to a single part of it, we would start to see a subtle warping of the lines on the sheet, though over the whole sheet the size and general shape of things would remain the same. Now if we traced a line from one side to the other we would continue on that line just fine, but our path would bend toward the point we applied the hairdryer (interestingly, using a bounded space/area the path bends, but the medium itself does not, it just contracts in an area).

A more extreme example (and the one that came to mine while driving) was the shrink wrap we used to use when I was a teenager working at a video store. We would put items for sale into a polymer bag, and then blow hot air on the bag to make it shrink down. Being michievious kids we would sometimes experiment on down times with the stuff, and found that you could really make some weird things happen by blasting select spots of a large, flat sheet of the wrap material when spread out against the wall or floor. We were forcing local contractions on a self-bound 2D plane when we did this on material that was stretched out flat.

What does this have to do with gravity and localized attraction vs distant repulsion? Everything. If we blow hot air at points opposite one another on the same stretched out sheet the wrap material in between the two sheets get stretched tigher. Anything point that is closer to one point than another is pulled away from the center and toward the opposite point — relatively speaking this means that a point that is distant enough from one spot is traveling away from it. And this happens despite the fact that our actual influence on the sheet is constrictive in nature — all pull and no push. If space behaves in anything approaching this, then gravity can easily have a secondary effect of causing points beyond a certain distance from one another to grow further apart and yet not have any properties of repulsion at all. This increasing distance of points beyond a certain distance also does not require that the sheet continues to expand overall, either. That the universe itself likely is expanding just confuses the issue a bit more.

To a tiny observer on a whirling rock out in deep cold space this effect could definitely look forbiddingly like an unfriendly “push” effect to gravity. If that observer were prone to personify elements of existence (in other words, assign blame for effects on them) then it would be very natural to blame the observed possible increasing rate of expansion of the universe on a property of gravity rather than on an indirect effect or condition that it causes. One effect per force makes more sense than having a magical force that somehow exhibits one behavior in one place and yet another in another place.

Of course, the mental idea above that space doesn’t “bend” is going to probably bother people who carry with them a mental model of space as a bendy thing, and of blackholes as places where space “folds back on itself” when contraction is really the issue. The mental picture of a black hole just gets all screwy then — but this is probably more correct, not less. Anyway, with teeny tiny dimensions apparently being all over yet so small in scale, yet so universal because they represent entire dimensional planes that have been prevented from much direct interaction with our normal Euclidian(ish) selves, it seems likely that perhaps the folded up space stuff that makes up matter and energy might just be manifestations of tiny black holes compressed in directions that are just not a part of our 3 spacial dimensions, and all those black holes bubbling in and out of existence could have a lot to do with the basics of why/how all subatomics are unstable, yet predictably so. But that is a whole different discussion.

I am completely unqualified to make any statements about physics anyway, but these were the thoughts that went through my mind as I drove home in the rain. Unfortunately I’ll probably never have the time to really study physics, so the common crap written in the press for the layman (this includes most “science magazines” as well) are all I’ll likely ever get a chance to read and be mislead into dumb mental models like the ones above by.