Ontology of Space and its Effects on Scientific Theories
Aamod Kore - 110050004 Anushrut Sharma - 110260014 C. Yeshwanth - 110050083
Overview
● The ontological properties of space have long been a cause for numerous arguments in the philosophical community
● The philosophical viewpoints held by scientists have a strong impact on the nature of their theories of motion
● The 3 most general notions of space are that space: ○ Is an independent entity not conditioned on the existence of any other entity/object ○ Is an entity that exists but is only a property of the other entities present in reality ○ Is a purely subjective notion that does not actually exist in reality
Motion
● Space as an “entity” is hard to analyze on its own
● Empirical evidence based on the behavior of objects in motion has been used to argue for one viewpoint over the other
● This has inevitably led to the notion that a proper understanding of motion is important to reason about the existence of space
● Therefore, theories of motion inherently make some assumptions on the nature of space and this is indicative of notions that the scientist holds on the same subject Aristotle (384-322BC)
● Aristotle proposed a simple theory explaining why heavier objects fell down while lighter objects moved up
● This behavior is part of the object’s ‘nature’ or ‘form’
● Objects move towards or away from the ‘center of the universe’
● He never explains whether this center is an absolute or relative position
● Issues arising in the analysis of this theory deal with the notions of relative or absolute space Descartes (1596-1650)
● Descartes proposes a theory based on relative quantities
● Space and matter are the same thing
● This precludes the possibility of vacuum
● How does Descartes define motion?
● Motion is determined relative to other bodies
● ‘Proper’ motion (a Privileged Frame) is determined by a change in position with respect to its immediate surroundings Enter Newton’s Bucket
● Newton attacked Descartes' notions of motion using the “water-bucket” argument: ○ a bucket of water hanging from a cord is set spinning about the cord's axis, ○ the same bucket and water when they are rotating at the same rate
● In the first case, when it is in motion relative to its immediate surroundings — the inner sides of the bucket ● In the second one, when it is at rest relative to its immediate surroundings ● The mechanically relevant meaning of rotation is not that of ‘proper’ motion
Newton’s Theory of Space and Motion
● A privileged frame of motion cannot be one involving relative quantities
● Newton postulated the existence of an absolute temporally enduring, rigid, 3-dimensional Euclidean space
● So according to Newton, the rate of true rotation of the bucket (and water) is the rate at which it rotates relative to absolute space.
● This view of absolute space was widely accepted for more than two centuries due to the lack of any competing theory Inertial Frames
● Newton’s First Law - In an inertial frame, an object remains at rest or continues to move at a constant velocity, unless acted upon by an external force
● The definition of an inertial frame by Newton is tautological:
o The first law is valid only in inertial frames of reference o Inertial frames are those in which the first law is valid
Ernst Mach (1838 – 1916)
• Mach was an Austrian physicist and philosopher
• Major influence on logical positivism, and pragmatism
• Criticized Newton’s idea of space and motion
Mach’s critique of Newton
● “No one is competent to predicate things about absolute space and absolute motion; they are pure things of thought, pure mental constructs, that cannot be produced in experience.”
● Motion of a body K can only be talked about relative to other bodies A, B, C and so on
● Any attempt to explain the behaviour of K in the absence of A, B, C will lead to a two-fold error - firstly, we cannot know how K would act in the absence of A, B, C and secondly, no prediction about the motion of K in the absence of A, B, C can be scientifically tested and hence lacks any scientific significance Mach’s critique of Newton
● Newton’s bucket experiment tells us that noticeable centrifugal forces are produced due to relative motion with respect to the earth and celestial bodies
● “The one experiment only lies before us, and our business is, to bring it into accord with with the other facts known to us, and not with the arbitrary fictions of our imagination.”
Mach’s Principle
● Measuring Earth’s spin about its polar axis by observing the rising and setting of stars and by the period of a Foucault pendulum gives the same answer and this led Mach to postulate that the notion of absolute space in Newton’s mechanics is nothing more than background of distant stars.
● Law of inertia is independent of absolute space
● Local inertial frames are determined by the large scale distribution of matter in the universe
● “When we say that a body preserves unchanged its direction and velocity in space, our assertion is nothing more or less than an abbreviated reference to the entire universe.” Mach’s Principle
The basic principles that distil the idea of Mach’s theorization of physics (“Machian physics”) –
• It should be based entirely on directly observable phenomena (positivism)
• It should eschew absolute space and time in favour of relative motion
• Any phenomena that would seem attributable to absolute space and time (e.g. inertia, and centrifugal force) should instead be seen as emerging from the large scale distribution of matter in the universe. Mach’s influence on contemporary physicists
● Albert Einstein was heavily influenced by Ernst Mach in the formulation of General Theory of Relativity
● The Principle of General Covariance is a direct consequence of Mach’s principle
● The well known competitor of General Relativity, the Brans - Dicke theory, is also based on Mach’s principle Challenges to Mach’s Principle
● The Vacuum solutions (FRW) of Einstein’s equations are not compatible with Mach’s principle
● The dynamic nature of vacuum in Quantum Field theory also contradicts Mach’s principle
References
1. Huggett, Nick and Hoefer, Carl, "Absolute and Relational Theories of Space and Motion", The Stanford Encyclopedia of Philosophy (Fall 2009 Edition), Edward N. Zalta (ed.), URL =