Shedding a Some Light on the Heart
Have you ever shone a bright flashlight through your hand on a dark and stormy night and marvelled at the almost x-ray-like appearance you see as the light passes through it?
Have you ever shone that same flashlight beam on that cheery campfire burning at your campsite only to be disappointed at how the cheerfully glowing red and orange embers turn to boring and slightly dismal grey ash?
Have you ever taken that same flashlight - so bright at night - and lit it in the sunny light of day only to find the beam cast by it on the wall or sidewalk to be hardly discernible?
A lot of that has to do with how we see light and how adjustable our marvellous eyes are to varying amounts of light. Our eyes adjust to the dark of night and make the flashlight bright to us in the night while adjusting so we are not blinded by daylight.
Getting back to the matter at hand - the light through the hand. Of course it is much harder to do the flashlight beam through the hand thing during the light of day - the light provided by the Sun overwhelms the light provided by the flashlight and what might pass through the flesh and bone of the hand. Light still goes through the hand though, but not just the flashlight beam. Consider the light from the so much brighter Sun!
We might not be able to see the light from the Sun passing through our bodies like the light from the flashlight through our hand at night, but I am sure that it would penetrate even deeper into our bodies. That we can't see it from the other side I figure has to do with just how much light is around in the daytime hiding the dim light that would pass through. That light would be dim like that of the campfire embers - visible in dark of night, but paled by day.
When I was growing up I though that rib cages were nearly solid walls of bone, like the planks of a ship side-by-side protecting the lungs and heart. It was only later studying a bit of anatomy that I learnt the gaps seem to be larger than the sections of bone in most critters. The heart and lung must not be hidden behind walls of bone but in open cages. The flesh of the chest is not too many inches thick before the lungs and heart. I can imagine if a person were to stand inside the lung, that perhaps in a room in a house at night lit by TV or end table lamp that it might be a dark place. But it the daylight - the much, much brighter sunlight must glow through the chest-wall lighting up the place with a warm red glow.
I think that on a sunny day, providing we are not covered in too many layers of tinfoil the daylight must even touch our hearts.