Always asked myself this…
Physician friend explained that to me but i dont get it, thats why ELI5…
In: 333
An objects transparency isn’t necessarily determined by it’s thickness. Transparency DOES tend to decrease as things get thicker but there way more important details to consider first.
Whether or not something allows light through it is dependent on its molecular structure. Molecules of different shapes, sizes, energies, and other properties will make some light get absorbed, some reflected, and some not react at all.
The cool part is this extends beyond visible light to other electromagnetic radiation such as radio waves, x-rays, gamma rays, and everything in between. You for example are opaque to most visible light (though you can see a flash light through the thin parts of your skin) but you are almost completely transparent to x-rays! What’s the exception? Your bones which is why they show up on the film and nothing else.
On the other end of the spectrum, infrared light is lower energy can come from distant stars and galaxies. When we try to observe them with normal telescopes, that visible light can be blocked by space dust. The brand new James Webb Space Telescope is specifically designed to look through that dust at the infrared instead.
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