Reducing Presentism to Solipsism

Presentism: the past is a memory; the future is a possibility; the present is the only reality. Objects in the past or the future do not actually exist; they are constructions in our minds. Let's suppose this theory of time is correct, and look at the example of the Sun. The sunlight that hits Earth is about 8 minutes old. When you look up during the day, you're not seeing the Sun; you're actually seeing photons that were created from reactions in the Sun 8 minutes ago. The Sun that you see exists in the past, and so according to presentism, it does not have objective reality. "But," you can ask, "does the Sun exist in the present?" There is no way to tell if the Sun exists in the present. You would know 8 minutes from now, if you still see it shining in the sky. But that's in the future, and mere speculation (a good bet though if you go by the laws of physics). Therefore, it is unknowable whether the Sun exists in the present. This explanation becomes obvious if we take the "light-cone" picture used in special relativity and remove the past and future light cones.

Since all of our interactions with external objects rely on signals that takes time to travel, we can extend the example of the Sun to everything we see, hear, or otherwise sense. Nothing at all can be known about the present except for what's at the origin, the observer: our own minds. And that's how the theory of presentism can be reduced, with a little help from physics, to the philosophical idea of solipsism.