The Importance of Light Transparency

The key to transparency is that sometimes light doesn't interact with the thing that's there. Rutherford shot alpha particles, which are helium nuclei at a very thin tissue of gold. He expected it to mostly just pass through, occasionally get distorted a little bit by forces. What he found was that one in eight thousand times, thealpha particle, the helium nucleus, bounced right back. That told him that the sheet of gold actually was made out of a grid of hard nuclei.