IT'S A HOMOCENTRIC UNIVERSE:

In a philosophical sense, we're taught to doubt and question everything. Even the reality of ourselves and our own experiences are up for debate, as we have to make certain assumptions about how trustworthy our sensors -- and our own senses, for that matter -- actually are in order to arrive at any satisfactory conclusions. Sure, certain things might appear real, but isn't it possible that those appearances are deceiving, and that quantities or concepts that we take for granted might be nothing more than very convincing illusions?

From a physical, scientific perspective, however, these sorts of questions take on a different meaning. We've learned lots of surprising and counterintuitive lessons from our investigations of time. Time is relative, not absolute. Time always marches forwards, not backwards, but we still lack an explanation for the arrow of time. Thermodynamically, the Universe has an arrow of time, which "flows" in the same direction as increasing entropy. And when we investigate the Universe on a fundamental level, it turns out that time may not be fundamental at all.

But existence itself? It's very, very difficult to take that property away from time and to still wind up with a Universe consistent with what we observe.

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