To this point we have not discussed anything new; only clarified the importance of thinking of gravity in the correct context. Rather than visualizing gravity as the attraction of two bodies, we are now thinking of bodies such as stars and planets traveling along the inside of Gravity Wells - a well-known concept. This means, we have only restated the problem in less abstract, less obscure terms.
It turns out that this analogy holds up remarkably well; like rolling a marble along the inner surface of a physical bowl, it will travel around the bowl until it eventually loses momentum and settles to the bottom, or if it is tossed too hard, roll over the edge of the bowl and escape it altogether. If the marble could somehow be rolled with just the right force (momentarily overlooking friction), it could settle into a point of equilibrium, having just the right amount of angular velocity to maintain a constant distance from the bottom of the bowl and its outer edge.
This perfect velocity, of course, is entirely dependent on the mass of the marble, the slope of the inner surface of the bowl (and, in this analogy, the force of gravity acting upon the marble). If we took the same marble, for example, and tossed it with the same velocity around the inside of a much shallower saucer, that same momentum would cause the marble to escape.
Returning to stars within galaxies, the problem boils down to not being able to explain why the gravity wells underlying them are so deep. In other words, the matter within galaxies does not actually behave strangely at all, we are only struggling to understand the shape of the bowls beneath them. This is very much like finding a deep depression in the center of a trampoline, around which we can roll a tennis ball, but with no bowling ball to account for it. Such an anomaly would hardly be any less mystifying on the scales of trampolines than it is at galactic scales - it would compel us to begin investigating possible causes. Is the trampoline sagging because it is not taut enough, or is some other force acting on it?
So, we must now begin questioning whether the depth of these gravity wells has anything to do with the matter within them. For instance, if we sprinkled tiny bits of Styrofoam on the surface of water draining from a kitchen sink, there would come a point where the water would begin to take the form of a whirlpool. When this happened, the Styrofoam bits would then reflect that underlying structure. If we were to attempt to understand the behavior of the Styrofoam without first understanding the nature and behavior of the water upon which it was floating, we would be eternally mystified.
This analogy seems to hold true for the stars and spiral arms within galaxies as well. If we view them as floating debris upon an underlying, and somewhat independent structure (gravity wells), then suddenly the question of Dark Matter begins to dim even more. If another force, besides mass, can bend space into something akin to gravity wells, what could it be? Have we overlooked something?
We may have, and maybe only because it is too obvious to notice.
It turns out that this analogy holds up remarkably well; like rolling a marble along the inner surface of a physical bowl, it will travel around the bowl until it eventually loses momentum and settles to the bottom, or if it is tossed too hard, roll over the edge of the bowl and escape it altogether. If the marble could somehow be rolled with just the right force (momentarily overlooking friction), it could settle into a point of equilibrium, having just the right amount of angular velocity to maintain a constant distance from the bottom of the bowl and its outer edge.
This perfect velocity, of course, is entirely dependent on the mass of the marble, the slope of the inner surface of the bowl (and, in this analogy, the force of gravity acting upon the marble). If we took the same marble, for example, and tossed it with the same velocity around the inside of a much shallower saucer, that same momentum would cause the marble to escape.
Returning to stars within galaxies, the problem boils down to not being able to explain why the gravity wells underlying them are so deep. In other words, the matter within galaxies does not actually behave strangely at all, we are only struggling to understand the shape of the bowls beneath them. This is very much like finding a deep depression in the center of a trampoline, around which we can roll a tennis ball, but with no bowling ball to account for it. Such an anomaly would hardly be any less mystifying on the scales of trampolines than it is at galactic scales - it would compel us to begin investigating possible causes. Is the trampoline sagging because it is not taut enough, or is some other force acting on it?
So, we must now begin questioning whether the depth of these gravity wells has anything to do with the matter within them. For instance, if we sprinkled tiny bits of Styrofoam on the surface of water draining from a kitchen sink, there would come a point where the water would begin to take the form of a whirlpool. When this happened, the Styrofoam bits would then reflect that underlying structure. If we were to attempt to understand the behavior of the Styrofoam without first understanding the nature and behavior of the water upon which it was floating, we would be eternally mystified.
This analogy seems to hold true for the stars and spiral arms within galaxies as well. If we view them as floating debris upon an underlying, and somewhat independent structure (gravity wells), then suddenly the question of Dark Matter begins to dim even more. If another force, besides mass, can bend space into something akin to gravity wells, what could it be? Have we overlooked something?
We may have, and maybe only because it is too obvious to notice.