Are space and/or time considered abstract objects or concrete objects? They seem causally inert yet more real than the typical abstract objects we think of.

  • I don't know what is meant by 'abstract object'. Do you mean 'conceptual imputation'? Or maybe 'mental creation'? It is a common view that all physical objects are conceptual imputations, and the space-time that contains them. So the answer to the question will depend on who you ask.The perennial view would be that there is no such thing (metaphysically-speaking) as a 'concrete object'. This would be why they can all squeezed into a black hole – PeterJ Apr 13 '19 at 9:25
  • There is no short or agreed upon answer to this, the nature of space and time is actively debated to this day, see SEP survey. The interpretations range from concrete entities (substantivalism), to relational abstractions (Leibniz), to artifacts of our perception (Kant), to theoretical constructs (string theory). – Conifold Apr 13 '19 at 11:38

The discovery of gravitational waves in 2016 shows that spacetime is a physical object. The gravitational masses of two merging black holes act on spacetime.

Since 100 years we know the bending of light by curved spacetime. Hence spacetime acts on other physical objects like light rays.

Therefore, spacetime is accepted for membership in the ontology of physics.

  • The ontology of physical objects is not understood in physics any better than that of space-time, so using one to ground the naive reality of the other is not possible,.Also, physics does not have an ontology. 'Ontology' is another word for metaphysics. If you mean that physicists usually assume naive realism then fair enough, but this is a metaphysical conjecture and not necessary for physics. . – PeterJ Apr 13 '19 at 9:21
  • @PeterJ My intention is to emphasize: Spacetime has the same ontological status like other physical objects, e.g., like electromagnetic field. Spacetime acts and reacts. - Equating ontology with metaphysics narrows down the meaning of ontology. Ontology covers any discipline which studies the taxonomy of the concepts used in a given science, asking: Which key concepts do we use and how do they relate to each other? – Jo Wehler Apr 13 '19 at 10:02
  • i think I was saying that space-time has the same ontological status as physical objects. My use of 'ontology' is standard. Physics does not study ontology, or not beyond a certain point. It tells us how things behave not what they are, and not even if they are. Thus physics cannot address the question of whether Realism is true or false. This is not a criticism, just the way things are given the scientific method. Ontology as a fundamental study is metaphysics. – PeterJ Apr 13 '19 at 10:53

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