This question came up in regards to another thread (and often comes in the desperate defence of YEC timelines). There are lots of confusion about what relativity says about this matter as well more modern speculations of modern theoretical cosmologists.
Let's first think about locations in space in ordinary Newtonian physics. Consider, say New York. Relative to Roger, who lives in Chicago, the location of New York in terms of North-South-East-West will be different for him than if he lives in Washington. Does this mean locations of places on earth is subjective or illusions? No it does not. Because between any two locations, the direction and distance is invariant. Thus the direction and distance between New York and Chicago is invariant and the direction and distance between New York and Boston is also invariant. It's John's position and orientation that has changed, not the locations themselves.
Thus, mathematically, the distance ΔR between any two points A and B is the same regardless of which coordinate system one chooses and how that coordinate system is oriented. It is given by
ΔR= Sqrt( Δx^2 + Δy^2 + Δz^2)
and is the same regardless of the coordinates one chooses. This is what makes spatial locations objective in Newtonian physics.
In Special Relativity, the focus is on events. Events are happenings that "happen" at specific locations in space and specific moment of time (t, x, y, z). The matrix in which events are located are therefore no longer three dimensional space but four dimensional space-time. And here too one is to objectively measure the unique spacetime distance ΔS between any two events in space-time which is invariant for all observers and all choice of the coordinates system. This space time distance between two events E1 and E2 is given by
ΔS^2 = (cΔt)^2 - Δx^2 - Δy^2 - Δz^2
Here c is the constant speed of light in vacuum and Δt, Δx etc. are the differences in time and x, y, z locations between the two events as measured from any specific inertial coordinate frame. The most important thing here is that no matter what inertial coordinate frame is chosen the value ΔS^2 is the same in all of them and hence it is an objective and invariant measure of space-time distance between any two events in physics.
So, we have hit upon something that is indeed objective and independent of measurement conditions. In the next post I shall look at what this means for the reality of time.
Let's first think about locations in space in ordinary Newtonian physics. Consider, say New York. Relative to Roger, who lives in Chicago, the location of New York in terms of North-South-East-West will be different for him than if he lives in Washington. Does this mean locations of places on earth is subjective or illusions? No it does not. Because between any two locations, the direction and distance is invariant. Thus the direction and distance between New York and Chicago is invariant and the direction and distance between New York and Boston is also invariant. It's John's position and orientation that has changed, not the locations themselves.
Thus, mathematically, the distance ΔR between any two points A and B is the same regardless of which coordinate system one chooses and how that coordinate system is oriented. It is given by
ΔR= Sqrt( Δx^2 + Δy^2 + Δz^2)
and is the same regardless of the coordinates one chooses. This is what makes spatial locations objective in Newtonian physics.
In Special Relativity, the focus is on events. Events are happenings that "happen" at specific locations in space and specific moment of time (t, x, y, z). The matrix in which events are located are therefore no longer three dimensional space but four dimensional space-time. And here too one is to objectively measure the unique spacetime distance ΔS between any two events in space-time which is invariant for all observers and all choice of the coordinates system. This space time distance between two events E1 and E2 is given by
ΔS^2 = (cΔt)^2 - Δx^2 - Δy^2 - Δz^2
Here c is the constant speed of light in vacuum and Δt, Δx etc. are the differences in time and x, y, z locations between the two events as measured from any specific inertial coordinate frame. The most important thing here is that no matter what inertial coordinate frame is chosen the value ΔS^2 is the same in all of them and hence it is an objective and invariant measure of space-time distance between any two events in physics.
So, we have hit upon something that is indeed objective and independent of measurement conditions. In the next post I shall look at what this means for the reality of time.