Sunday, April 23, 2017

Here's What You Have To Believe In Order To Deny Eternalism

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:
  1. Deny that the speed of light travels at constant speed regardless of the speed of the light source.
  2. 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 denier of eternalism must accept one or both; there is no logical way to deny at least one and still deny eternalism.

The reason why is because logic demands it.

(1) the speed of light is constant for all observers and isn't changed depending on whether or not the light source is moving,
(2) we are able to physically measure two perpendicular distances accurately using any device such as a ruler or tape measurer,
(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. 
(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.

Some people, who are so deeply inclined to hold to presentism or possibilism, which both require an objective reference frame, will indeed try to deny (1) or (2) or both. To deny (1) is to deny the second postulate of Special Relativity, which is to effectively deny the theory, since the postulate is absolutely fundamental to the theory. To deny (2) would force you to believe that we cannot accurately measure two non-parallel distances equally (such as r1 and r2 above), even if we use the same ruler to do so, or split the same ruler in half and use each side to measure the two distances. On presentism, it must be the case that one distance is longer than the other even though we empirically measure the two distances to be exactly equal length using the same measuring device, if you don't deny (1).

This forces you into believing that nature and our senses are tricking and deluding us into seeing them measured as equal and thinking they are, but they are really objectively unequal, even as the laws of physics are the same for all non-accelerating observers (the first postulate of Special Relativity). This is because if you accept that the speed of light is constant for all observers regardless of a light source's movement, the only way you can deny that the two events that emitted the two light sources are ontologically simultaneous, would be if they each had to travel different distances to reach the single point at the same time. Only then can they reach the same point at the same time and not have started out ontologically simultaneous.

And yet, as in the image above, we empirically measure r1 to be the same distance as r2 using every possible way to get the most accurate measurements the best engineers or scientists could use. This view forces one into a radical denial of empirical evidence that has many consequences. For example, the recent LIGO experiments that confirmed the existence of gravitational waves relied on precisely measuring the speed of light beams extremely accurately as they traveled down two perpendicular equal length tubes to within a thousandths of the width of a single proton. But according to the denier of (2), those two arms of the LIGO aren't really equal, they just seem equal. Nature is really tricking us into seeing and thinking they are and we cannot really trust our senses. If fact, the accuracy of all of our senses is up in the air.

So here is where the important part of the denial of eternalism enters: what's more rational, (a) accepting every empirical test showing that the speed of light is constant and accepting that we can indeed measure distances accurately, or (b) denying our senses and the empirical evidence and believing that nature is just tricking us into thinking the speed of light is constant, and/or that our empirical measurements of length and distance are accurate?

To deny eternalism forces you into thinking the latter; there is no possible way to avoid it. I argue that it takes more faith to believe in something which you have no empirical evidence for and that forces you to deny empirical evidence, and that such a position is far less rational. It is akin to believing angels push the planets along their orbits or that demons cause weather patterns but in a way that can never be detected, and would always look as if it's not the case.

I don't have enough faith to be a presentist.

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