Suppose I described a tree to someone who had never seen anything like it. I might say it was a giant creature with countless sprawling arms that never moved, and its body was full of intricate vessels that extracted water from the ground imperceptibly. Most fantastic of all, it had the power to transform light and air into its food, and grew to its great size without taking its bulk from the earth or any other solid thing. Nonetheless, its body was rigid, pound-for-pound stronger than steel, yet lighter than water.

The person being told this might be forgiven for taking this as a tall tale or myth, and the same is true for any natural object. Everything seems impossible or fantastic if we never experienced anything similar. If you saw nothing but cosmic dust, you might never imagine that there could be such a thing as a star. If you saw a barren planet, you might never guess that there could be such a thing as life. If you saw only bacteria, you might never deduce the possibility of more complex organisms. We are able to explain the complex in terms of the simple only after the fact. We have a poor record of determining in advance what is possible or impossible.

If all you knew was physics, you likely would not be able to derive much chemistry. Anything beyond the hydrogen atom is computationally problematic. The few unknown things we have been able to predict are mostly simple structureless entities like fundamental particles and black holes. Everything else comes as a surprise to us. No cosmologist or astronomer anticipated the existence of quasars or pulsars. As with most new things, we first observe them and then try to explain them.

After a long history of discovering things thought to be impossible, if they were ever imagined at all, we should realize how unreliable it is to claim that something is impossible simply because it is outside of our experience. Everything is impossible when abstracted from experience. It is only familiarity that makes these impossible things no longer fantastic.