Why can’t visible light pass through solids?


X rays can go through solids.
Radio waves can go through solids.
And both of these are on either side of visible light in the spectrum. Why can’t visible light go through solids?

In: Physics

It can. Look at your window. Ask yourself if its a solid, liquid, or gas. And then reevaluate this question.

On a technical level it’s because atoms and molecules are sortof tuned to be able to catch at remit different wavelengths of photons.

On a practical level it’s essentialy because you’re made of very similar stuff to most other stuff. It’s hard for eyes to detect photons that tend to pass through them. That and the sun emits most of it’s light in the visible range so it’s the most useful range for things to evolve to use to see.

Like if we evolved on a planet with a cooler sun that mostly emitted IR, we’d probably be calling some section of the IR spectrum visible light.

It can, Look at glass, diamonds, any see through gemstone, crystals.

What determines if light can pass through an object isn’t whether it is solid liquid or gas, but the specific material properties of that object. Things like glass are solids, but form a crystalline structure that allow light to pass through.

On the opposite end of the spectrum is Lead, which is extremely dense with many many electrons that are really good at absorbing light radiation, including x rays.

Some liquids like water are see through, some liquids like mercury are not.

it isnt the phase of an object, but its material properties.

All EM waves can pass through solids. It’s just that, depending on the material and the EM wave, it’s more or less likely to get absorbed on its way through. Done materials like glad let all visible light through, for example.

Radio waves can make it through most materials because they are low frequency and have a low chance of hitting anything as they pass through a material.

Waves closer to visible light can get absorbed by many materials more easily, hence why everything doesn’t look slightly transparent.

X-rays also tend to get absorbed, which is part of why they are so damaging. It’s also part of the point, as they get blocked more by your bones than your flesh, which is how you can see your skeleton with x-rays. You could theoretically use visible light for this as well, but because there is so much visible light already in the world, it would be difficult to pick out the few waves that would make it through your body. X-rays, by contrast, don’t generally occur naturally.

Try this, turn on your cell phone’s flashlight, put your finger over the LED, and then look at your fingertip. Next, summon the strangest voice you can and say “phone home”. Not that that last step helps with seeing the visible light passing through your finger, but it helps, just trust me.

It’s stranger for light, radio waves, etc. to get _stopped_ by matter than to pass right through it. There are some materials that are opaque to X-rays (lead, your bones), and some materials that are transparent to visible light (diamonds, glass). But the _default _ reaction electromagnetic radiation has when encountering matter is to pass right through it… _unless_ it hits an atom with an electron that can absorb exactly the frequency of the radiation. Then, instead, the photon is absorbed, exciting the electron, and then re-emitted when the electron de-excites.

Imagine everything on the spectrum like ridged wavey noodles. And now imagine solids like sieves, different sources of energy have varying wave lengths thus some can not fit through sieve and others can.

Look at a microwave door, light can escape from inside, yet the microwave can not yet you can see through the microwave door. Its cause microwaves have really big wave lengths. This is how material can either penetrate or be blocked.

This works to the molecular level as well, why lead can block gamma rays, x-rays etc.