5 / The Cave

I had been walking for a day and a half when I found the cave. I had decided to follow the ridge-line North. Uphill, towards one of the five peaks on the map, it had been hard going. I knew though that on the other side of the mountain the peninsula began and at the end of the peninsula was the beach and that beach = ocean.

Heading North

Beach = ocean! That’s what had redirected my mind every time it had wandered. It was amazing that a simple fact could be so comforting. I welcomed that gift from the World of Science; out in the open, last night had been cold again. I needed shelter tonight. That’s half the reason why, when I came out of the tree-line and saw the mid-afternoon sun shining on the entrance of the cave near the peak, it would remain in my mind for a long time to come.

The other half of the reason I could never have guessed. “Hello…” I sounded, “Hello?!” No reply. I took that as my invitation to enter. As I began cautiously into the tunneled entrance of the cave, I noticed that it zig-zagged in a way that let the slightest ray of light from the outside carry on through.

The cave entrance/tunnel

Spellbound, I followed that ray of light until the cave opened up into an internal cavern. Then, my feet stopped, my eyes blinked and my mind exploded. For, the little ray of light expanded towards the back wall and, there, it was projecting a stunning image. I was looking at the very view that I had seen whilst looking out at the world from in front of the cave moments earlier. I stared, gobsmacked at what I had discovered, but I couldn’t help but feel that something was wrong.

“It’s upside-down.” Came a voice from the shadows. I almost hit my head on the roof of the friggen cave in fright! I had been too absorbed in the image to realise that someone else was present.

“You have found my movie theatre.” said the scientist stepping into more light.

I couldn’t muster a reply.

“The cave has formed a natural camera obscura.” he explained, “‘Camera’ is Latin for ‘vaulted room’ and ‘obscura’ is Latin for ‘dark’ – meaning ‘dark room’ together. The camera obscura was an early optical  invention that has paved the way for photography and the cameras we have today. A hole – like the one at the entrance – lets light from the outside pass inside and it projects an image onto the opposite side of the room as you can see. The light travels in a straight line through the hole so the top of the scene outside projects at the bottom of the image inside.”

It was hard to believe but the image on the wall of the cavern was becoming even more intriguing as the scientist spoke and he wasn’t done yet.

“The size of the hole determines the sharpness and brightness of the image,” he continued, “Just like adjustment of the aperture on a camera. Generally, the smaller the hole the sharper the image but the image also gets dimmer. Too small though and the light waves can’t pass cleanly through the hole – they undergo diffraction and spread out inaccurately. We are most fortunate that the size of the hole at the entrance here is perfect for the dimensions of this cavern.”

I was speechless as a sponge but had almost absorbed as much as I could. The scientist was aware of this.

“You know,” he concluded,  “The camera obscura – this cave – in principle, is just a big version of what happens in our human eyes. The pupil is the hole and the retina is the back wall. Our brains are just conditioned to flip the projected image so that we perceive things the right way up.”

The human eye as a camera obscura from Rene Descartes ‘La Dioptrique’ (1637)

There was a long silence as the scientist let the information soak in.

“I thought you said I had to discover this world in my own way.” I managed eventually.

“Yes,  and you have been doing that haven’t you?” he replied. “Haven’t you learned a lot in the last few days?”

Well, yes…” I said, “But I have been thinking quite deeply about it all, too much probably, I’m a little worried I spend more time lost in my own head than exploring this world. I haven’t got that far after all.”

“It is good you have run into me again then.” The scientist said. “Personally, I think you have done well to get here. It is easy to get stuck in your own head and it is silly to think you are without the help of those you have met along the way. Have you still got the map?”

I pulled it out of my pocket. Proof.

“Where are you going?” he asked.

“To the beach,” I answered without hesitation, “I need to be with the ocean.”

“Good,” he said. “You will find that it needs you too.”