How do we define a second? #shorts #science

How do we define a second? It used to be as a fraction of the length of a day, i.e. how long it takes Earth to turn once on its axis. But that wasn’t precise enough for scientists, especially since the length of Earth’s day changes! So instead, since the 1950s the second has been defined by the number of spin transitions of electrons in a Caesium atom.

👩🏽‍💻 I'm Dr. Becky Smethurst, an astrophysicist at the University of Oxford (Christ Church). I love making videos about science with an unnatural level of enthusiasm. I like to focus on how we know things, not just what we know. And especially, the things we still don't know. If you've ever wondered about something in space and couldn't find an answer online - you can ask me! My day job is to do research into how supermassive black holes can affect the galaxies that they live in. In particular, I look at whether the energy output from the disk of material orbiting around a growing supermassive black hole can stop a galaxy from forming stars.

[ryanmcgowan]

So indirectly, a meter is officially defined as the distance light travels in 30.663318988498... cesium atom oscillations.

[mosatsoni]

“What time is it exactly?”
“Hold on, let me get my cesium and a flashlight”

[AmythefirstA]

I saw the kid diving into the pool to escape a tsunami and couldn't pay attention to the rest of the video. 😅

[WilliamWizer]

a second is what I ask for after finishing any good meal.

[YoungGandalf]

A second is one Mississippi.

Edit: I'm not sure what the equivalent word of measure is in Dr. Becky's part of the world.

[nothingsurprisesmeanymore]

The guy with the clicker counting the rotations is the real hero 🏆

[morryDad]

According to my kids reaction time when I call them, 1 second is about 10 minutes long.

[NostalgicTribe]

Seconds changed depending on if you are in school or if you work but on off days, hours go by in minutes.

[jonathanlafrance]

I could listen to you for hours. You’re SO SMART and CHARMING!

[ralfsenger]

Thanks for explaining it. I always heard about the oscillation of atoms or electrons but didn't see a good explanation of it

[skepticusmaximus]

A second is the period of time between which the light turns green, and the impatient bastard behind you honks his horn.

[Raven.flight]

Somewhere someone has the job of counting those flips. And I thought my job sucked.

[jonnyskybrockett]

Learned this in distributed systems class. Most space stations have a cesium clock, and there are a few cesium clocks on earth that are in control by various governments and massive companies. The massive companies use it to maintain the same time across all computer clocks. There’s some hierarchy, but every computer has the capability to resync their clocks with cesium time once every day/week/month (arbitrary time, but it syncs).

[meretrix]

Hang on, gimme a second, I gotta think on it.

[caleb]

I literally just read this in my physics text book yesterday. I was reading about how we measure a second, meter, and kg. Incredibly interesting information.

[Ed]

"At just the right frequency" great, how do we define frequency? Well that's the number of vibrations in a

[varshinisubramanian]

Could you talk about the slowing down of Earth's rotation in more detail in a future video? Thank you in advance!

[lancelotandmerlin]

i don’t really understand how we are able to measure that it’s so fascinating

[troubledsole]

One second on your vacation is much faster than a second during rush hour at a stoplight in Boston.

[quincysantomieri]

Anybody else worried about that kid? Escaping a tsunami by jumping into a swimming pool seems like a questionable decision.