Cara Giovanetti
@idontevencara.bsky.social
I study dark matter, cosmology, and particle physics for a living at UC Berkeley and Lawrence Berkeley National Lab. On the weekends I write explainers about surprising places physics shows up in the natural world.
caragiovanetti.com
caragiovanetti.com
And so that energy makes the combined droplet spring off the gecko’s skin! This has the added benefit of taking dirt and microbes along with the water, keeping the gecko clean, and some insects even use this strategy to stay clean too. If only I could put micro-hairs on my kitchen windows…
8/8
8/8
December 7, 2025 at 11:08 PM
And so that energy makes the combined droplet spring off the gecko’s skin! This has the added benefit of taking dirt and microbes along with the water, keeping the gecko clean, and some insects even use this strategy to stay clean too. If only I could put micro-hairs on my kitchen windows…
8/8
8/8
If these two droplets combine (often because the droplets grow because of humidity in the air), the whole system suddenly has way more energy than it ought to—the two-droplet configuration had more energy than the mega-droplet configuration should, and that extra energy has to go somewhere…
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7/8
December 7, 2025 at 11:08 PM
If these two droplets combine (often because the droplets grow because of humidity in the air), the whole system suddenly has way more energy than it ought to—the two-droplet configuration had more energy than the mega-droplet configuration should, and that extra energy has to go somewhere…
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7/8
But what if there are two water droplets? The energy of this system is defined by the area of the interface between the water and the gecko skin—the more area, the higher the energy. Two separate droplets have more energy than one big droplet:
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6/8
December 7, 2025 at 11:08 PM
But what if there are two water droplets? The energy of this system is defined by the area of the interface between the water and the gecko skin—the more area, the higher the energy. Two separate droplets have more energy than one big droplet:
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6/8
That’s a bit of an overstatement—the geckos don’t exactly “make” the water do anything, since this is a passive process. When water forms a perfect sphere on the gecko’s skin, it’s stable: there’s no excess energy or force in the system that makes the water droplet want to move around.
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5/8
December 7, 2025 at 11:08 PM
That’s a bit of an overstatement—the geckos don’t exactly “make” the water do anything, since this is a passive process. When water forms a perfect sphere on the gecko’s skin, it’s stable: there’s no excess energy or force in the system that makes the water droplet want to move around.
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5/8
Okay, but surely if enough water gathered on the gecko it would start to get wet, right?
Geckos prevent this eventuality by making water literally jump right off of them.
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Geckos prevent this eventuality by making water literally jump right off of them.
4/8
December 7, 2025 at 11:08 PM
Okay, but surely if enough water gathered on the gecko it would start to get wet, right?
Geckos prevent this eventuality by making water literally jump right off of them.
4/8
Geckos prevent this eventuality by making water literally jump right off of them.
4/8
Geckos achieve these large contact angles, or beading, with specialized hairs on their skin. Air gets trapped between these tiny hairs, which makes it difficult for water to spread out and penetrate down to the lower surface of the gecko’s skin.
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3/8
December 7, 2025 at 11:08 PM
Geckos achieve these large contact angles, or beading, with specialized hairs on their skin. Air gets trapped between these tiny hairs, which makes it difficult for water to spread out and penetrate down to the lower surface of the gecko’s skin.
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3/8
First—what does it mean to be wet?
Turns out physicists defined this long before the is-water-wet-wars started: a wet surface has a small “contact angle” with water, meaning the water doesn’t bead up.
Take a look at the water on a gecko’s skin—looks more like the “non-wetting” case, right?
2/8
Turns out physicists defined this long before the is-water-wet-wars started: a wet surface has a small “contact angle” with water, meaning the water doesn’t bead up.
Take a look at the water on a gecko’s skin—looks more like the “non-wetting” case, right?
2/8
December 7, 2025 at 11:08 PM
First—what does it mean to be wet?
Turns out physicists defined this long before the is-water-wet-wars started: a wet surface has a small “contact angle” with water, meaning the water doesn’t bead up.
Take a look at the water on a gecko’s skin—looks more like the “non-wetting” case, right?
2/8
Turns out physicists defined this long before the is-water-wet-wars started: a wet surface has a small “contact angle” with water, meaning the water doesn’t bead up.
Take a look at the water on a gecko’s skin—looks more like the “non-wetting” case, right?
2/8
My apartment’s been unseasonably humid, and I’ve been doing what I can to keep things dry to prevent mold. It’s got me thinking about animals that live in wet climates—how do they stay dry?
Some geckos get by with hairs on their skin that literally rocket water off of them.
1/8 ⚛️🧪
Some geckos get by with hairs on their skin that literally rocket water off of them.
1/8 ⚛️🧪
December 7, 2025 at 11:08 PM
My apartment’s been unseasonably humid, and I’ve been doing what I can to keep things dry to prevent mold. It’s got me thinking about animals that live in wet climates—how do they stay dry?
Some geckos get by with hairs on their skin that literally rocket water off of them.
1/8 ⚛️🧪
Some geckos get by with hairs on their skin that literally rocket water off of them.
1/8 ⚛️🧪
buddy I am a physicist I am not supposed to know what PCR is
December 4, 2025 at 6:24 AM
buddy I am a physicist I am not supposed to know what PCR is
I used to think the spammy papermill invitations in physics were bad, but nothing has decimated my inbox like publishing an ***opinion piece*** in a biosciences journal
December 4, 2025 at 6:12 AM
I used to think the spammy papermill invitations in physics were bad, but nothing has decimated my inbox like publishing an ***opinion piece*** in a biosciences journal
Not all individuals’ sails curve the same way, and that’s the magic of their body plans.
If you cup each of your hands in front of a powerful fan, each of your hands will be pushed out in a different direction. The same thing happens to the Man o’ War when a strong wind blows.
4/5
If you cup each of your hands in front of a powerful fan, each of your hands will be pushed out in a different direction. The same thing happens to the Man o’ War when a strong wind blows.
4/5
December 1, 2025 at 3:54 AM
Not all individuals’ sails curve the same way, and that’s the magic of their body plans.
If you cup each of your hands in front of a powerful fan, each of your hands will be pushed out in a different direction. The same thing happens to the Man o’ War when a strong wind blows.
4/5
If you cup each of your hands in front of a powerful fan, each of your hands will be pushed out in a different direction. The same thing happens to the Man o’ War when a strong wind blows.
4/5
At the top of the Portuguese Man o’ War, there’s a sack full of air and carbon monoxide, which helps the Man o’ War float. And on top of this sack, there’s a crest, which can catch the wind and move the Man o’ War about as it hunts for prey. But if you look closely, the sail is a bit curved.
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3/5
December 1, 2025 at 3:54 AM
At the top of the Portuguese Man o’ War, there’s a sack full of air and carbon monoxide, which helps the Man o’ War float. And on top of this sack, there’s a crest, which can catch the wind and move the Man o’ War about as it hunts for prey. But if you look closely, the sail is a bit curved.
3/5
3/5
Like many animals that look like jellyfish, the Man o’ War is not a jellyfish. Instead it’s a member of an obscure order of organisms called siphonophores. In addition to their weird looks, siphonophores are colonial organisms, meaning they’re composed of specialized clones called zooids.
2/5
2/5
December 1, 2025 at 3:54 AM
Like many animals that look like jellyfish, the Man o’ War is not a jellyfish. Instead it’s a member of an obscure order of organisms called siphonophores. In addition to their weird looks, siphonophores are colonial organisms, meaning they’re composed of specialized clones called zooids.
2/5
2/5
Why does this animal look so weird? Did it really need to be so asymmetrical?
It’s called a Portuguese Man o’ War, and its funky body plan might just help it avoid total annihilation.
1/5 ⚛️🧪
It’s called a Portuguese Man o’ War, and its funky body plan might just help it avoid total annihilation.
1/5 ⚛️🧪
December 1, 2025 at 3:54 AM
Why does this animal look so weird? Did it really need to be so asymmetrical?
It’s called a Portuguese Man o’ War, and its funky body plan might just help it avoid total annihilation.
1/5 ⚛️🧪
It’s called a Portuguese Man o’ War, and its funky body plan might just help it avoid total annihilation.
1/5 ⚛️🧪
Airflow is important in shaping the response of these neurons to different kinds of molecules. Some of these molecules take a long time to bind to these neurons and produce a signal in the brain, while others bind very quickly.
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4/7
November 22, 2025 at 4:06 PM
Airflow is important in shaping the response of these neurons to different kinds of molecules. Some of these molecules take a long time to bind to these neurons and produce a signal in the brain, while others bind very quickly.
4/7
4/7
How does your nose even work in the first place? You—and pretty much everything that can smell—have specialized neurons deep in your nasal cavity. When an odor molecule enters your nose, it binds to these neurons, which then send different signals to the brain depending on what triggered them.
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2/7
November 22, 2025 at 4:06 PM
How does your nose even work in the first place? You—and pretty much everything that can smell—have specialized neurons deep in your nasal cavity. When an odor molecule enters your nose, it binds to these neurons, which then send different signals to the brain depending on what triggered them.
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2/7
Hope you’re staying healthy this cold and flu season! Have you ever wondered why one side of your nose might feel more congested than the other when you get sick?
It’s an unfortunate side-effect of the way your nose is built to process smells.
1/7 ⚛️🧪
It’s an unfortunate side-effect of the way your nose is built to process smells.
1/7 ⚛️🧪
November 22, 2025 at 4:06 PM
Hope you’re staying healthy this cold and flu season! Have you ever wondered why one side of your nose might feel more congested than the other when you get sick?
It’s an unfortunate side-effect of the way your nose is built to process smells.
1/7 ⚛️🧪
It’s an unfortunate side-effect of the way your nose is built to process smells.
1/7 ⚛️🧪
"hahaha okay somebody's up late in Berkeley. Thank goodness I still have access to NYU's cluster--"
November 17, 2025 at 2:16 AM
"hahaha okay somebody's up late in Berkeley. Thank goodness I still have access to NYU's cluster--"
"Surely I won't have to wait that long for a GPU on a Sunday night!"
Berkeley's cluster:
Berkeley's cluster:
November 17, 2025 at 2:12 AM
"Surely I won't have to wait that long for a GPU on a Sunday night!"
Berkeley's cluster:
Berkeley's cluster:
The Reynolds number of glacial ice is estimated to be 0.0000000000001--one over 10 trillion! And that’s not even near some of the lowest Reynolds numbers on the planet—the earth’s mantle has a Reynolds number that’s about 10 billion times smaller!
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5/6
November 16, 2025 at 9:28 PM
The Reynolds number of glacial ice is estimated to be 0.0000000000001--one over 10 trillion! And that’s not even near some of the lowest Reynolds numbers on the planet—the earth’s mantle has a Reynolds number that’s about 10 billion times smaller!
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5/6
Physicists characterize fluid flows with Reynolds numbers, which compare inertial forces in a fluid (force from the fluid’s own momentum) to viscous forces (frictional from layers of the fluid moving over each other). A low Reynolds number means viscous forces win out, and the flow is smooth.
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4/6
November 16, 2025 at 9:28 PM
Physicists characterize fluid flows with Reynolds numbers, which compare inertial forces in a fluid (force from the fluid’s own momentum) to viscous forces (frictional from layers of the fluid moving over each other). A low Reynolds number means viscous forces win out, and the flow is smooth.
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4/6
I grew up in northern New Jersey, where most of the terrain was shaped by glacial movement from up to 800,000 years ago; whenever we’d go hiking and see these grooves in the rocks, we knew the ridge we were on was formed by glaciers scraping by eons ago.
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3/6
November 16, 2025 at 9:28 PM
I grew up in northern New Jersey, where most of the terrain was shaped by glacial movement from up to 800,000 years ago; whenever we’d go hiking and see these grooves in the rocks, we knew the ridge we were on was formed by glaciers scraping by eons ago.
3/6
3/6
Make no mistake, glacial ice is a solid, but it’s a solid that flows! Glaciers are so heavy that they deform under their own weight—on geological timescales, they can even retreat or flow downhill, shaping the landscape in their wakes.
2/6
2/6
November 16, 2025 at 9:28 PM
Make no mistake, glacial ice is a solid, but it’s a solid that flows! Glaciers are so heavy that they deform under their own weight—on geological timescales, they can even retreat or flow downhill, shaping the landscape in their wakes.
2/6
2/6
When we think about fluids, there are a handful of substances that usually come to mind—things like water, air, cheez whiz, etc.
But that’s not all there is to it—even glacial ice is a fluid.
1/6 ⚛️🧪
But that’s not all there is to it—even glacial ice is a fluid.
1/6 ⚛️🧪
November 16, 2025 at 9:28 PM
When we think about fluids, there are a handful of substances that usually come to mind—things like water, air, cheez whiz, etc.
But that’s not all there is to it—even glacial ice is a fluid.
1/6 ⚛️🧪
But that’s not all there is to it—even glacial ice is a fluid.
1/6 ⚛️🧪
And pit vipers might not be the only animals to do this! While maintaining a system near its bifurcation is tricky, the animal kingdom is full of examples of animals being way more sensitive to different stimuli than we expect, and this would be a pretty robust mechanism to achieve that.
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6/6
November 9, 2025 at 12:52 AM
And pit vipers might not be the only animals to do this! While maintaining a system near its bifurcation is tricky, the animal kingdom is full of examples of animals being way more sensitive to different stimuli than we expect, and this would be a pretty robust mechanism to achieve that.
6/6
6/6