Eli5 Why is water see through?

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My 4 year old asked me and I think it’s a rather good question that I would like to answer so she understands. Thanks 🙏🏻

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38 Answers

Anonymous 0 Comments

It’s a little bit backwards. Life needed to be able to see through water, so it created eyes that could see the light that water was clear to.

That might need some explanation. All things are “clear” to some kinds of light and “opaque” to other light. Like how an X ray can go right through your skin and see your bones. It’s that way for all light, including visible light.

So there was always some wavelength of light that made water “clear”. And some of those wavelengths are the visible light spectrum.

So when life evolved in the ocean, and eyes developed, it was very useful to be able to see the light that could pass through the water. And so you get eyes that can see in the ocean.

Edit: so the phrase I’d use for the actual 4 y/o is “It’s see-through because eyes were specially made to see through water” or if you want it to sound more awesome but less helpful, “because your eyes are like x-ray goggles for water”

Anonymous 0 Comments

It’s a little bit backwards. Life needed to be able to see through water, so it created eyes that could see the light that water was clear to.

That might need some explanation. All things are “clear” to some kinds of light and “opaque” to other light. Like how an X ray can go right through your skin and see your bones. It’s that way for all light, including visible light.

So there was always some wavelength of light that made water “clear”. And some of those wavelengths are the visible light spectrum.

So when life evolved in the ocean, and eyes developed, it was very useful to be able to see the light that could pass through the water. And so you get eyes that can see in the ocean.

Edit: so the phrase I’d use for the actual 4 y/o is “It’s see-through because eyes were specially made to see through water” or if you want it to sound more awesome but less helpful, “because your eyes are like x-ray goggles for water”

Anonymous 0 Comments

Things are see through because light is able to pass through them relatively uninterrupted. Things are opaque because a portion of the light hitting it will bounce off instead of passing through. The object’s color will be the portion of light that bounces off and into your eye.

Anonymous 0 Comments

Things are see through because light is able to pass through them relatively uninterrupted. Things are opaque because a portion of the light hitting it will bounce off instead of passing through. The object’s color will be the portion of light that bounces off and into your eye.

Anonymous 0 Comments

For a less inside-out answer (although still good to know / keep in mind), see link. Basically, water doesn’t have any mechanisms that strongly absorb photos in the visible spectrum. A lot of materials (like pure gas out in space) “require” photons of specific energy to change state in some way, so have very specific absorption lines. The more complex the molecule, generally the broader and more complex the absorption bands.
“The absorption of electromagnetic radiation by water spans a wide range of physical phenomena, characteristic of the general interaction of radiation with matter. It absorbs strongly in the microwave region by excitation of molecular rotations. In the infrared it exhibits strong absorptions from vibrations of the water molecule. As you go above the visible through the UV toward x-rays, it successively absorbs by photoelectric effect, Compton scattering and finally pair production.”
(Additional info via hyperlinks in original.)
http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.html

Anonymous 0 Comments

For a less inside-out answer (although still good to know / keep in mind), see link. Basically, water doesn’t have any mechanisms that strongly absorb photos in the visible spectrum. A lot of materials (like pure gas out in space) “require” photons of specific energy to change state in some way, so have very specific absorption lines. The more complex the molecule, generally the broader and more complex the absorption bands.
“The absorption of electromagnetic radiation by water spans a wide range of physical phenomena, characteristic of the general interaction of radiation with matter. It absorbs strongly in the microwave region by excitation of molecular rotations. In the infrared it exhibits strong absorptions from vibrations of the water molecule. As you go above the visible through the UV toward x-rays, it successively absorbs by photoelectric effect, Compton scattering and finally pair production.”
(Additional info via hyperlinks in original.)
http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.html

Anonymous 0 Comments

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Anonymous 0 Comments

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Anonymous 0 Comments

I think for a 4 year old, just explain that light can go through it and light can’t go through other things. If she actually does want to know why it goes through some things and others, then you can busy out the material science questions

Anonymous 0 Comments

I think for a 4 year old, just explain that light can go through it and light can’t go through other things. If she actually does want to know why it goes through some things and others, then you can busy out the material science questions