Inertial effects are felt when there is a change in constant straight motion- acceleration, rotation, changing direction etc.
This inertial effect that Newton showed was a direct attack on Descartes position in which he stated that objects are at true rest when they rest relative to their surroundings, but it also attacks the relationist, for the relationist claims that all motion is relational, so to explain the inertial effect, the relationist must hold that the bucket example is explicable by saying that the bucket is rotation relative to something. But what? Turning the Earth around the bucket may not cause this. There is no relation between the Earth and the water to make this happen, but this can be applied to the absolutist too. How can rotation in relation to absolute space cause inertial effects? How can immaterial space have a material effect? We cannot appeal to such things as the Sun and Earth to explain this effect for as a reference frame, they too are in rotation, so how can they explain the effects on other things. But if we were to turn the whole universe around the bucket, surely the inertial effect would happen? If it did, there would be no need for absolute space.
Then again, how can the universe have these immediate effects on the water?
Newton says the relationist cannot explain inertial effects as they are present independent of relational motion, but it seems to me they can be explained relationally.
Newton’s third laws, that actions and reactions are equal are problematic to the absolutist.
In the two globes example, we could say that, relationally, each globe is constantly moving away from the location it was previously at. This location is not in absolute space; it is just where the object is. There is somewhere 2cm away from where the globe is. Although nothing is there, as soon as we conceptualize the possibility of something being there, we can conceive of things moving in relation to this location, therefore, the globes will be moving in relation to this location. The globes can be moving truly, even though it cannot be observed. Just as if there are two cars in the universe. Relationally, they are both moving away from each other, but truly, the inertial effect felt in one of the cars shows it is truly at motion in relation to the other car, even though this cannot be observed. The inertial effect tells us which object is in true motion, but does in no way imply absolute space. So, the inertial effect on the globes shows us that the globes are moving, and as movement must be in relation to something, it is in relation to possible locations, or past locations, not real places in absolute space.
Similar position put forward in the book ‘A Box With No Sides’ (p49), but apparently this leads to problems with time and space, for if motion not relative to anything material were possible, how could we explain the succession of time? In defining position, we have presupposed time, and in defining time, we presuppose position, leading to a circular argument, so it is best to stick to understanding relative motion as motion relative to other objects (seems odd. How does this explain the 2 globes example? Mach would say there is another way to explain the apparent centrifugal force)
Inertial effects imply ‘true’ motion, not ‘absolute’ motion. If one object is in the universe, with no inertial effects, it could either be at true motion, or true rest. There is no way to tell, but this does not mean we have to introduce absolute space into the picture. There is no need to posit anything infinite here.
‘Berkeley suggested that, lacking any point of reference, a sphere in an otherwise empty Universe could not be conceived to rotate, and a pair of spheres could be conceived to rotate relative to one another, but not to rotate about their center of gravity’ – this seems wrong. If a single sphere had an inertial effect (i.e. being ‘squashed’) this implies true rotation, not absolute rotation. Completely misses the point of inertial effects.
Mach- ‘proposes that mechanics is entirely about relative motion of bodies and, in particular, mass is an expression of such relative motion. So, for example, a single particle in a Universe with no other bodies would have zero mass.’ So, for the rocket example, the passenger would have no gravitational nor inertial mass, so would feel no inertial effect. In the bucket example, we can apply the same line of thought. This example only really works if we imagine the bucket alone in the universe, for otherwise we could conceive of the universe being rotated around the bucket and the inertial effect being caused, thus reducing this to a relational explanation. If the bucket were on its own in the universe, there would be no inertial effect, because, as Mach points out, it would have zero mass, and without mass, there can be no inertial mass, thus no inertial effect. The absolutist could say that space gives mass, but this is counter to scientific observations such as when we go into space, and mass is depleted the further we recede from massive objects.
‘Absolutism is unnecessarily extravagant theory, introducing something that explains nothing’
