Well we&#x27;ve accounted for about 5% of the universe--the stuff we know about.<p>Dark matter (about 25%) seems to only interact gravitationally, which means that we&#x27;ve just, today, proven that we have an instrument that could possibly observe it directly. To date, all our evidence for dark matter is indirect--observing the otherwise unexplained behavior of normal matter. Today is the gravitational equivalent to Galileo pointing his first telescope at the night sky.<p>Dark energy (about 70%) still seems to be a total mystery.<p>And of course there is our inability to reconcile quantum mechanics with gravity. With each further proof of the correctness of each of those theories, the mystery of their apparent incompatibility deepens.<p>All of these factors lead me to believe that we may still have a long way to go in our understanding of the physical universe. I hope I&#x27;m right.<p>This is also why I believe it is so important to pursue nuclear energy. If we do invent further theories and experiments, it&#x27;s likely that they will require even greater energy levels than we can create now, and potentially imply even greater dangers. If we can&#x27;t learn to manage nuclear physics in a practical, routine way, we&#x27;ll never have a hope of going beyond it (if indeed there is a &quot;beyond.&quot;)