Relativity is a form of symmetry and for that reason already of fundamental importance for science. Symmetry means: You can change something in some quite fundamental way, for example rotate the whole circle, and yet, the result is in some other important way the same, the circle is in all ways we can notice as it was before the rotation. The law of the conservation of energy is such symmetry: We transform local chemical energy into non-local kinetic energy and back, yet its mass stays the exact same throughout. We usually call ‘Relativity’ a symmetry that involves transforming the observer/describer and his perspective. They are mainly:

    Galilean relativity of 1632 claims that all laws of physics we can find are the same no matter we research in one (closed) laboratory or in another, similar one that moves away from the first laboratory with a great velocity.
    Modern relativity (Poincare, Lorentz, Einstein, Everett) is similar but updates Galileo, mainly by presenting another geometry that is in several ways more symmetric (= more relative, more rotations), more general. Ordered according to generality: Special Relativity Theory, General Relativity Theory, Many-World Geometry.
    Description Relativity is about transforming theories into apparently very different, seemingly mutually exclusive, contradicting theories/descriptions, such as string theories with more dimensions, all however describing the same phenomena as they are experienced by the observers that the descriptions “describe describing” (it is here that ‘phenomenology’ is a sub-field in high energy physics and string theory and other fields rather than only philosophy).

    One example for “Relativity of Relativity”, without such being the silly kind of post-modern philosophy, is Description Relativity as it applies to Modern Relativity: We can describe a Geometry of space-time as if it is a given unchanging shape with four or many more dimensions (I), or we can describe an Einstein-Ether (substance-like or already a computational substrate such as the Game of Life (GOL)) in which the observed relativity emerges (II), or we can also describe a brain trapped in a Virtual Reality (VR), such as ‘quantum solipsism’ (III).

    After teaching a course often discussing Ether versus Geometry, which always still today leaves a suspicion about whether somebody actually understands basic modern relativity theory, the students’ peaked and explicitly stated interest confirms that I neglected VR. VR versus Geometry is even more interesting and convincing in many ways, not only because it is “more sexy” to talk about suchlike, as much of it is of course fashion; after all, Plato and religion already thought about VR, using “God” instead of “Administrator of the host computer”.

    The ‘Remove-by-Keeping Method’ that deals with systems of constants and measurement units [Ref 1] shows that the parameter “(v/c)”, equal to speed v divided by speed of light c, results from both, either a geometry where times are distances “(ct)” or a (perhaps fundamentally solipsist quantum) VR where all spatial distances are delay times “(x/c)”, although the new parameter “(v/c)” has then two radically different interpretations for what it is. Relativity emerging in ether provides yet another reason for why “(v/c)” can be bound to not exceed unity, why (v/c) is smaller or equal to 1. However, the feasibility of modern relativity being emergent is immediately obvious with VR. That modern relativity can emerge in ethers, which also includes computational substrates such as the Game of Life (GOL), is far less obvious, especially if also demanding that the observer experiences quantum physics.

    If I wanted ether instead of VR in the Remove-by-Keeping example of (v/c), it needs first elaborating how the observers are made from excitations of the ether, how therefore observers obtain a constant speed of light, and some hand-waving about that black holes and cosmology did not already make the ether obsolete anyway.

    Focusing more on VR early prepares better for discussing VR later in other sections such as on error statistics, uncertainty, quantum theory, emergence of consciousness and philosophy of mind. What is essentially the same course once again is actually a different, better course of lectures. But since it is a course to facilitate fundamental critical thinking as it is important and advantageous for the applied scientist, mentioning ether is mandatory simply for how misunderstood and vilified ether still is, a great historical example for the fundamental problems of science such as the scientific community as an evolved social structure of Darwinian cruelty.

Ref 1: S. Vongehr: “Fundamental Science for Applied and Social Science Students.” Lecture Notes, Nanjing University (2018)