I've recently gotten marred down in another debate over eternalism vs presentism via private email. It's a debate I generally like having because it's one I know I can win. Plus it's a great way to get to know Special Relativity, one of the coolest and most fascinating scientific theories. What I want to emphasize here is what one has to deny in order to deny eternalism and hold to either presentism or possibilism, because it's not always apparent to those who do so.
In order to deny eternalism, one has to deny one or both of the following. They have to either:
- Deny that the speed of light travels at constant speed regardless of the speed of the light source.
- Deny that we can accurately measure two non-parallel distances as being of equal length with any physical instrument, such as a ruler or tape measurer, or even sense in any way that they are equal or unequal.
The reason why is because logic demands it.
If...
(1) the speed of light is constant for all observers and isn't changed depending on whether or not the light source is moving,And...
(2) we are able to physically measure two perpendicular distances accurately using any device such as a ruler or tape measurer,Then...
(3) if two beams of light travel an equal distance to a single point and arrive at the same time, they must have been emitted at the same time and the events that emitted them must have been ontologically simultaneous.And...
(4) if two beams of light travel an equal distance to a single point and arrive at different times, they must have been emitted at different times and the events that emitted them must have not been ontologically simultaneous.In order to deny (3) and (4) you must deny either (1) or (2) or both (1) and (2). There is no other logically possible way to do so.