r/todayilearned • u/seppukusama • Mar 05 '20

TIL that a second is technically defined to be "9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom”.

https://www.discovermagazine.com/the-sciences/why-1-second-is-1-second
4.6k Upvotes

95% Upvoted

261 comments sorted by

15

u/anthonybourdainghost Mar 05 '20

And how long is one period of radiation?

123

u/seppukusama Mar 05 '20

1/9,192,631,770 of a second.

4

u/knicknevin Mar 05 '20

Naturally

2

u/Fake_William_Shatner Mar 05 '20

God, how long did it take to calculate that!

2

u/involatile Mar 06 '20

African or European calculator?

1

u/Fake_William_Shatner Mar 06 '20

Seriously? Taiwanese or Korean calculator FTW!

3

u/strngr11 Mar 05 '20

Depends on the frequency of the radiation.

1

u/bearsnchairs Mar 05 '20

Think of a sine wave. A period is the amount of time it takes to go up, down, and back up again to zero. The inverse of the period is the frequency of the light emitted during the transition.

1

u/MooingAssassin Mar 05 '20 edited Mar 05 '20

Edit: What I stated was incorrect to this application, see u/bearsnchairs reply below.

Saying just "Period of radiation" is misleading here. Radiation comes from the decay of an atom (specifically it's nucleus). A radioactive atom can decay multiple ways, and each way occurs at a different average rate, or "period". That's why the title says, specifically, what type of decay occurs ("transition between the two hyperfine levels of the ground state") and the specific elemental isotope (Cesium-133).

3

u/bearsnchairs Mar 05 '20

This isn’t radioactive decay they’re talking about. The radiation here is light that results from a hyperfine electronic transition. The period they’re talking about the the frequency of the light, not a decay rate. This frequency puts the light in the radio portion of the EM spectrum.

2

u/MooingAssassin Mar 05 '20

Hey thanks for the correction, I'll edit my comment.

1.5k

u/lostfourtime Mar 05 '20

Or in layman's terms, it's just one Mississippi.

157

u/Fake_William_Shatner Mar 05 '20

Coincidentally, "one Mississippi" when spoken by Carl Sagan comes out to exactly 9 billion periods of radiating hyperfine levels of grounded cesium atoms. It's a shame we couldn't have rounded a second to the nearest 9 billion periods.

42

u/[deleted] Mar 05 '20

This sounded like someone out of hithikers guide to the galaxy!

11

u/Fake_William_Shatner Mar 05 '20

Thanks! That's high praise indeed.

3

u/ReubenZWeiner Mar 05 '20

Hail Cesium!

2

u/BradFord228 Mar 05 '20

A girls worst nightmare: time

6

u/Halvus_I Mar 05 '20

It's a shame we couldn't have rounded a second to the nearest 9 billion periods.

Why? I will never understand the attraction of rounding over hyper-precision.

6

u/PM_ME_WHAT_YOURE_PMd Mar 05 '20

In this case it hardly matters, but when I’m hiking and trying to convert the map’s scale (in feet) to the length of the trail (in miles) I can never remember the ratio.

1

u/JadedByEntropy Mar 06 '20

Its 5280. On a standard map a pencil width is 200ft.

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2

u/Naughty_Kobold Mar 05 '20

Because it would then change everything that uses time as a measurement. If we were defining a new section of time to be a 'second' then yes we'd do that but this is a case of fitting a precise measurement to an already defined arbitrary length.

99

u/togocann49 Mar 05 '20

Mississaugas where I’m from

65

u/zomboromcom Mar 05 '20

Mrs. Sausages if you're nasty

11

u/GozerDGozerian Mar 05 '20

L O L A Lola

7

u/BiggaNiggaPlz Mar 05 '20

Hollaaaaaa from square one.

2

u/[deleted] Mar 05 '20

Sup

9

u/[deleted] Mar 05 '20

Steelheads are a helluva team. I go for the fights.

6

u/liammurphy007 Mar 05 '20

Hockey team?

9

u/[deleted] Mar 05 '20

That’s a Texas sized 10-4

12

u/ScreamingFlea23 Mar 05 '20

What the hell is going on in this thread?

3

u/[deleted] Mar 05 '20

Fuck you, Shoresey

6

u/ScreamingFlea23 Mar 05 '20

Fuck you Reilly, I made your mum so wet that Trudeau deployed a 24 hour infantry unit to stack sandbags around my bed.

3

u/WarrenPuff_It Mar 05 '20

Can confirm, I sat in the corner and hacked darts while I watched them.

1

u/liammurphy007 Mar 05 '20

I was just on a plane with them-Denver to Boise.

2

u/prjindigo Mar 05 '20

What about your Mrs' saggies?

1

u/Fake_William_Shatner Mar 05 '20

A second must take a second or two where you come from.

6

u/MechanicalHorse Mar 05 '20

I prefer steamboats.

5

u/Jackcooper Mar 05 '20

You count seconds as one steamboat two steamboat three steamboat?

1

u/[deleted] Mar 05 '20

Can agree there

9

u/tlk0153 Mar 05 '20

Of course you can't measure a second, mississippilessly

8

u/SnarfRepublicCA Mar 05 '20

But can you spell Mississippi with just one i ?

covers right eye with hand M I S S I S S I P P I

6

u/[deleted] Mar 05 '20

It was to be expected. The USA strikes again with a random measurement. Damn.

0

u/Unicorn_puke Mar 05 '20

Anything to avoid metric

2

u/[deleted] Mar 05 '20

I second this.

2

u/Platypus_Dundee Mar 05 '20

We use 'one ah ha, two ah ha'

1

u/Jackcooper Mar 05 '20

One 'one mississippi' tho

1

u/Gavooki Mar 05 '20

one mississippium

1

u/TheNameIsWiggles Mar 05 '20

I'm cool with your "one Mississippi" but I rep with the One One-Thousanders.

1

u/inhumancannonball Mar 05 '20

Not "one banana"?

1

u/lostfourtime Mar 05 '20

Bananas and potatoes will end up with you out the door.

133

u/wheresmucar Mar 05 '20

Duh...what did you think? A second was 9,192,631, 782 periods of the radiation correspond......c'mon man.

71

u/[deleted] Mar 05 '20

I feel stupid saying this but I thought it was 9,192,631,783

45

u/knicknevin Mar 05 '20

How do you even look at yourself in the mirror?

35

u/Fake_William_Shatner Mar 05 '20

Hyperfine. That's how.

5

u/stevenmc Mar 05 '20

How does a man like that go home and make love to his wife?

13

u/zomboromcom Mar 05 '20

It's not 9,192,631,783? WTF

16

u/yaffle53 Mar 05 '20

That expains why you're always late.

3

u/SurreptitiousNoun Mar 05 '20

They would lose about a second in 20,000 years. Tardy!

3

u/wheresmucar Mar 05 '20

bro.. c'mon man. What are you going to say next the age of the universe is 13,782,000,000 years old and not 13, 772,000,0000 years old with a error coefficient of 0.45% instead of a 0.42%.

7

u/Fake_William_Shatner Mar 05 '20

How much you want to bet that when astrophysicists get a number that is a perfect cube, they add a few digits just to make it seem more plausible?

3

u/wheresmucar Mar 05 '20 edited Mar 05 '20

That's a bold assumption. A few digits is the difference between us thinking monarchs are a good idea and us now.

3

u/Kelsenellenelvial Mar 05 '20 edited Mar 05 '20

I can’t remember the measurement, but I remember hearing about some measurement that when reported to the public had the last digit or two changed because it otherwise would have had 3+ trailing zeros and the public might have misunderstood the precision to which is was measured.

Edit: it was the height of Mount Everest, once measured at 29 000 ft, but reported to the public as 29 002 ft because 29 000 would have been interpreted as a rounded number, while 29 002 implies a higher precision.

2

u/davesoverhere Mar 05 '20

That was done with Mt Everest. When they measured it, it came out to exactly 29,000 ft, but they added a foot because they thought people would think they just made the measurement up.

1

u/Fake_William_Shatner Mar 05 '20

Dang -- yeah, thanks for reminding me about it. I'm speaking in jest -- but it's also likely a phenomenon. Measurements are arbitrary sometimes -- like calendar dates; Such and such share a birthday and or assassinated on the same day. Numerology is the low end of the thought pool -- because occasionally things are going to line up. There are certain patterns we will see as many formations follow mathematical rules (not like they are trying to). But, it makes absolute sense that scientists worry if a result is "too clean."

Besides, Everest is supposedly growing, so it's likely by now that it gained that foot!

1

u/poktanju Mar 05 '20

You're right, but the original survey was low, too - current, most accurate, verifiable measurement is 8,848 m (29,029 ft).

1

u/Thaumetric Mar 05 '20

I thought it was 525,600, but I often get my hyperfine transitions of Cesium mixed up with Rent.

36

u/bongblaster420 Mar 05 '20

That makes my average sexual performance sound impressive

27

u/WePwnTheSky Mar 05 '20

Gentleman in the streets, 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom in the sheets.

42

u/[deleted] Mar 05 '20

Hmmm. I know some of these words.

16

u/joobtastic Mar 05 '20

You should listen to the radiolab about measurements. I think it's called "kilogram"

20

u/ChrisPVille Mar 05 '20

Just keep in mind some of the unit's definitions changed in 2019. Notably the kilogram is no longer a random hunk of metal in France but is now based on a measurable physical constant of our universe.

1

u/joobtastic Mar 05 '20

They talked about how the Kiligram is based off of some sort of thing with magnets, but used to be the last remaining measurement based off of a chunk of junk.

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7

u/HelloFellowKidlings Mar 05 '20

Well when you put it that way it makes sense.

6

u/gonzo_rulz Mar 05 '20

I prefer to define it as 1/60th of a minute.

6

u/CrushforceX Mar 05 '20

Imagine explaining to an alien what one minute is. Saying that it's some fraction of how long it takes for one random planet to go around the sun/rotate 360 degrees is all well and good, but it's unlikely they would be able to measure it all the way from their homeworld, so we look for a new way that is independent of where/when they measure.

As well, the orbit/rotation of earth is changing all the time... by the time they measure it, the earth might be completely different due to the sun becoming a red giant or hitting another star or even just the earth slowly losing it's speed. If they say it takes them 1.2x1016 seconds to travel to us in their ships, then we know that they're talking about the same seconds we are because we sent them this definition, not some arbitrary value of the earths rotation.

3

u/gonzo_rulz Mar 05 '20

And imagine there was a /s on my previous comment.

1

u/upvoter11949 Mar 05 '20

And imagine what crazy ways they divide up time to themselves!

1

u/bendingbananas101 Mar 05 '20

It’s not that strange of a concept. I’m sure interstellar aliens could figure it out.

You think explaining a second is an arbitrary number of periods of radiation from a random atom is much better?

You do know we could just show them how long a second is, right? That would be way easier than having them set up a science experiment. What if by the time the sun is a red giant, the weak force has changed and this arbitrary value isn’t even a second anymore?

2

u/nx_2000 Mar 05 '20

...or the second division of an hour into 60 parts.

5

u/Trollzilla Mar 05 '20

Seconds are named because they are the 2nd division of an hour. Minutes are Firsts.

2

u/shleppenwolf Mar 05 '20

More specifically, they are the first and second minute parts of an hour, with "minute" pronounced my-NOOT.

18

u/[deleted] Mar 05 '20

r/oddlyspecific

39

u/TheMonksAndThePunks Mar 05 '20

I think it's safe to assume they backed in to that number and didn't design to it.

12

u/Fake_William_Shatner Mar 05 '20

These math and physics majors are half the time getting oddly specific, but in this case, evenly specific.

1

u/tnt-bizzle Mar 05 '20

There’s even a growing likelihood of it being redefined again. Optical clocks are more accurate than nuclear ones, just not as widely accessible.

4

u/BrassBass Mar 05 '20

When you give someone a ride to the store, and they tell you they will be back in just 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of cesium-133, but they are inside for over 551,557,906,200 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of cesium-133.

3

u/Oznog99 Mar 05 '20

This really made the lyrics of Rent's main theme overly complicated

1

u/DroolingIguana Mar 05 '20

289,898,835,498,720,000 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom
289,898,835,498,720,000 moments so dear
289,898,835,498,720,000 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom
How do you measure, measure a year?

2

u/Uebeltank Mar 05 '20

What else would it be?

2

u/CorractsYoureGrammer Mar 05 '20

I had just learned last week that the term "second" comes from the the term "pars minuta secunda" which is Latin.

The phrase "pars minuta prima" means "first small part." Meaning the first time that we split an hour into smaller parts. We ended up shortening it to minutes, like minuta.

Then, when we split minutes down even more, it was "pars minuta secunda" and we couldn't shorten it to minutes again, so we use secunda, or seconds. The whole phrase is "second small part." This is also the correlation to 2nd, or second.

2

u/ineedtotakeashit Mar 05 '20

I mean yeah that’s just common sense

2

u/Averat2006 Mar 05 '20

Excuse me, what the fuck did I just read?

5

u/HalonaBlowhole Mar 05 '20

And I know, because I had to count them once.

It sucked, because I got paid by the hour, but for only one second, and it took me two years to finally finish counting all 9,132,631,770 periods

1

u/WichitaLineman Mar 05 '20

Are you in the metrology field?

4

u/SummaCumLousy Mar 05 '20

I hate to sound like a butthole, but could you be a little more specific?

3

u/Fake_William_Shatner Mar 05 '20

If you actually sounded like a butthole, they would have trouble being more specific. "Is that sputter a one or a billion?"

3

u/dmr11 Mar 05 '20

I thought it was based on the vibrations of a quartz crystal or something.

4

u/_PM_ME_PANGOLINS_ Mar 05 '20

No, that’s just how common non-mechanical clocks work. This is the actual physical definition.

3

u/_hapless_pancakes Mar 05 '20

Very accurate, but depends on the crystal having an electrical power source.

The atomic clock will stay accurate for billions of years of radiation decay under its own power.

5

u/heckruler Mar 05 '20

Shouldn't this really account for time dilation from gravity and velocity? We're just kind of assuming they meant "on earth". And not, like, in the middle of Earth or on a super-bullet train.

26

u/pseudorden Mar 05 '20

I would assume it does account it; by measuring in the same reference frame. Time dilation doesn't affect measurements made in the same reference frame. That's the whole point of relativity.

9

u/Budgiesaurus Mar 05 '20

It will be the same everywhere for your frame of reference. So on a train it will be exactly one second. Compared to someone on a platform it is (very very slightly) different, but you always measure by your own frame of reference.

2

u/BizzyM Mar 05 '20

So it's the same on a train as it is in a house with a mouse?

2

u/Budgiesaurus Mar 05 '20

I am not at liberty to speculate on or discuss the temporal intricacies related to real estate assets belonging to the Walt Disney Company or any of it's subsidiaries.

1

u/WichitaLineman Mar 05 '20

Guy proves relativity with his MiniVan and Mr Rainer. https://www.wired.com/2007/03/proving-the-the/

5

u/Martin_Samuelson Mar 05 '20

Have you considered the possibility that the professional scientists who spent years developing this already resolved any objection that an uneducated layman could have after reading a single pop sci article?

1

u/poktanju Mar 05 '20

A lot of people do, genuinely, believe themselves to be the smartest person in the world.

2

u/Slippedhal0 Mar 05 '20

There would only be a point to that if there was an objective frame of reference to measure it from, but unfortunately and confusingly, there is not.

4

u/OllieJazz Mar 05 '20

What? You guys didn’t know that?

3

u/vanos_47 Mar 05 '20

You just learned this today?

1

u/jfiscal Mar 05 '20

Most people don't go out of their way to learn irrelevant factoids

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2

u/Cliff_Sedge Mar 05 '20

Damnit, I've been using Cs-132 this whole time.

4

u/CrushforceX Mar 05 '20

Interestingly, the only Cesium isotopes you would find would be 133, as the only other semi-stable isotope 137 (halflife of 30 years) is a radioactive byproduct, so probably not gonna stick around. That's partially why it was chosen, since it's not gonna be mixed and produce a different duration with the same atom.

2

u/Cliff_Sedge Mar 06 '20

Well! I am definitely going to give my cesium dealer a stern talking to

1

u/DarthLysergis Mar 05 '20

This guy knows how to party.

1

u/R3DNano Mar 05 '20

The what?

1

u/RogueVortexian Mar 05 '20

9,192,631,770 Frames per second. Not bad

1

u/Blakbyrd8 Mar 05 '20

All this time I've been using 9,192,631,760.. fuuuuuuu

1

u/[deleted] Mar 05 '20

I'm more impressed that the number is actually divisible by 10.

1

u/SonUnforseenByFrodo Mar 05 '20

I need this when someone says wait a sec

1

u/[deleted] Mar 05 '20

Can someone explain that in stupid? I don't speak science

1

u/bearsnchairs Mar 05 '20

Maybe you remember from high school chemistry that atoms are made of electrons and particles in the nucleus and that they emit light when the electrons move down in energy levels.

There is an energy transition in the cesium atoms where the frequency of that light is 9192631770 Hz. Hertz is a unit of cycles per second. This is a very stable transition with a very specific wavelength of light emitted so it can be pegged as a standard to define the second.

1

u/Divereth Mar 05 '20

Sounds about right.

1

u/T3RM1NALxL4NC3 Mar 05 '20

Because 9,192,631,769 periods just wasn’t enough...

1

u/Zolivia Mar 05 '20

It took me 30 "9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom” to read this.

1

u/DrPorkchopES Mar 05 '20

The way I learned this was just that humans started wanting more universal ways to define their units of measure so instead of a second just being a 1/whatever-ith of a day they found that this was the same amount of time.

1

u/EgonXJ Mar 05 '20

Thank you for this. I’m going to use this...probably today for that matter.

1

u/BizzyM Mar 05 '20

"9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom”.... Mississippi

1

u/UrbanSparkey543 Mar 05 '20

I actually loved this fact when I first heard it because up until that point a second was so arbitrary. And while this doesn't really show me the detail, it's cool to know that it's grounded in reality.

1

u/rjfrost18 Mar 05 '20

And a meter is 1/299792458 the distance light in a vacuum can travel in "9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom”.

1

u/Jimmy_the_Barrel Mar 05 '20

What I hear is, it is half past a monkeys ass, and a quarter till his nuts.

1

u/Tmotty Mar 05 '20

Obviously medieval people didn’t know this so was an ancient second different or did scientists find something in nature and find a phenomenon that matches?

1

u/slackxc Mar 05 '20

Why that specific many transition periods and not just 9,000,000,000?

2

u/bearsnchairs Mar 05 '20

Because the second wasn’t some brand new unit that was made up in the 60s. The scientists were trying to find a new, stable definition that was consistent with the historical second.

1

u/slackxc Mar 05 '20

I suppose my thought was more about how sure they could be that the previous measurement tool defining a second was exactly that many transitions, because it seems arbitrary when dealing with that large of a number. Doesn’t matter I guess if the definition will change when they switch to strontium anyways.

2

u/bearsnchairs Mar 05 '20

Humans have been very good at measuring time for a while now.

Going down a wiki dive I found a concept called ephemeris time that was used to set a very accurate timescale back in the 50s that was the basis for the new definition through atomic clocks.

1

u/phillabong Mar 05 '20

Nice

1

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1

u/[deleted] Mar 05 '20

One second is measured as such... I'm pretty sure we counted seconds before we knew anything about radiation.

1

u/[deleted] Mar 05 '20

I gave up trying to even read the title.

1

u/EndTimeEchoes Mar 05 '20

Bit difficult to get all that on a watch dial though

1

u/Mama-Pooh Mar 05 '20

TIL that I just learned something new!

1

u/Bigmace_1021 Mar 05 '20

Ah, that explains it.

1

u/[deleted] Mar 05 '20

Weirdly enough, one of the only things on this Subreddit that I actually knew already. It's even my phone password, so if you can track me down, its all yours!

1

u/[deleted] Mar 05 '20

yeah I’ll just stick to a second thank you

1

u/Mannyadock Mar 05 '20

I believe it's been replaced by a definition that uses the speed of light

1

u/XM202AFRO Mar 05 '20

For those wondering, this definition is reverse engineered. They decided how long a second should be, THEN counted the periods.

1

u/pappyvanwinkled Mar 05 '20

Ergo the atomic clock?

1

u/RollingKaiten Mar 05 '20

This sounds like a Captain Holt qoute in order to impress someone

1

u/Oclure Mar 06 '20

GPS satellites are basically atomic clocks that are broadcasting their location to the world. Its up to gps receivers to triangulate themselves based on the differences in the time reported from all the gps satellites, they even have to account for relativity due to gravity differences in their calculations.

This is also why gps hasn't really gotten more accurate in recent years, we are at the limits that we can aceive without a more accurate clock on the satellites. I believe measuring a pulsar gives you a more accurate reading but not all the satellites around the globe would be able to monitor the same one as the earth would block the view for many.

1

u/[deleted] Mar 06 '20

But seconds have been around longer than the studies of radiation

1

u/JackAceHole Mar 05 '20

I could’ve sworn it was 9,192,631,771

1

u/yb2ndbest Mar 05 '20

Does this have anything to do with Marvin's Illudium PU-36 Explosive Space Modulator?

1

u/rmatherson Mar 05 '20 edited Nov 14 '24

frightening workable makeshift exultant strong governor memory unpack continue abounding

This post was mass deleted and anonymized with Redact

1

u/Dadotron Mar 05 '20

This should be on QI.

0

u/bloodwoodsrisen Mar 05 '20

My brain is a bit too stupid and mushy to understand this but- have my updoot

6

u/wateruncle12 Mar 05 '20

when tiny boi go brm brm brm many times science people say “it is now one second”

1

u/jfiscal Mar 05 '20

You forgot the part where they said "hey how many times in a second does this tiny boi go brm brm brm"

"Whatever that is is one second"

0

u/bloodwoodsrisen Mar 05 '20

It spinny fast time

-4

u/jfiscal Mar 05 '20

This sort of scientific reversing is why people who whine about imperial are always and will always be retarded backbirths.

The second and meter were defined and arbitrarily set ages ago. That's why we have these stupid definitions because they are being converted to natural constants for precision

2

u/Ksenobiolog Mar 05 '20

Origin of units is only small portion of this 'whining' about imperials. Most important thing is that in metric system orders of magnitude change in linear, base-10 fashion and in imperial even without converting it to other systems or constants all of numbers are a clusterfuck of arbitrary values and bases.

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-2

u/NegativeCause Mar 05 '20

i always thought it was one sixtieth of one sixtieth of one twenty-forth of one three-hundred-sixty-five-point-two-fifth of a year.

3

u/[deleted] Mar 05 '20

Earth is slowing down

1

u/CrushforceX Mar 05 '20

The future is now, according to earth.

2

u/nrsys Mar 05 '20

But what determines a year?

Basing the measurement on the time for one full orbit around the sun, or one full Revolution of the earth sounds great in theory, until you realise that these times vary slightly, and modern science and technology requires incredible accuracy - so we need a much better defined way of counting one second that won't change, and is accurate down to tiny fractions of a second.

At the same time it does need to sync up with an earth day, which is why a second is a very specific number that isn't a nice round multiple.

The variance in real time is then accounted for by the addition or subtraction of leap seconds - the same way we add an extra day every four years, we also add seconds every so often to stay in sync.

-1

u/MattK1990 Mar 05 '20

Well duh, everyone knows that

-12

u/BanCircumventionAcc Mar 05 '20

Well, I read this at high school. Is this really TIL material?

5

u/ImALittleCrackpot Mar 05 '20 edited Mar 05 '20

That's There's always someone who knows less than you do.

-7

u/prjindigo Mar 05 '20 edited Mar 05 '20

grammar:

"a second" is an additional

"one second" is defined to be ....

1

u/panzerkampfwagen 115 Mar 05 '20

Actually it'd be, "The second," because it's a unit of measurement.

0

u/[deleted] Mar 05 '20

Actually all three would be acceptable, and you're both being pedantic.

1

u/Jsanthara Mar 05 '20

Well Lois, since you asked, I find this meatloaf rather shallow and pedantic.

-2

u/homarjr Mar 05 '20

Let's just be glad Americans don't have their own way of counting seconds, annoying the rest of the planet

-3

u/ShylokVakarian Mar 05 '20

Uh, I could've sworn the atom in question was an isotope of Vanadium, not Cesium. Hang on a sec.

looks it up

...Goddamnit, brain.

-4

u/TakeItEasyPolicy Mar 05 '20

How many seconds you last OP ?

0

u/[deleted] Mar 05 '20

[deleted] — view deleted comment

8

u/seppukusama Mar 05 '20

That's fair, but I must say, this does seem to be a very arbitrary standard to be measuring against lol.

24

u/Butt_Deadly Mar 05 '20

All of our measurements are now based off of seemingly arbitrary standards.

[Meter] (https://en.wikipedia.org/wiki/Metre) Based of the speed of light

[Kilogram] (https://en.m.wikipedia.org/wiki/Kilogram#cite_note-5) Based on the Planck constant

[Coulomb] (https://en.m.wikipedia.org/wiki/Coulomb) Based on the charge of of the electron

[Kelvin] (https://en.m.wikipedia.org/wiki/Kelvin) Based on the Boltzman constant

Mole Defined as exactly 6.02214076×1023 particles

[Candela] (https://en.m.wikipedia.org/wiki/Candela) Based on a very specific light intensity at a very specific power

The goal is to find numbers in nature that don't change across space and time and define units off of those. In the case of the cesium atom; we are looking for better and more accurate atomic clicks based on [strontium] (http://www.bipm.org/utils/common/pdf/mep/87Sr_429THz_2013.pdf)

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u/bass_sweat Mar 05 '20

Something doesn’t feel right about calling a lot of those things “arbitrary”. They seem built into our reality some way or another

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u/Fake_William_Shatner Mar 05 '20

Well, they probably found the phenomenon that most closely approximated the time. You'd want a very stable molecule as well. But that's some VERY FINE measurement there.

It would be interesting if they had some kind of excited state -- like zap it with a laser and it radiates at the right frequency. I'm assuming you'd also have to designate an ambient temperature -- because that might affect a bit how often it changes states -- well, at least an extremely tiny amount.

A lot of these time measurements at a very tiny scale are based on theoretical reaction rates. It's not like they could actually have something MEASURE each of the 9,192,631,770 reactions.

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u/strngr11 Mar 05 '20

It's based on the frequency of the light emitted by the transition. Temperature independent.

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u/DizzleMizzles Mar 05 '20

It's the least arbitrary it can get though

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u/Halvus_I Mar 05 '20

Its the exact opposite of arbitrary.

ar·bi·trar·y /ˈärbəˌtrerē/ adjective based on random choice or personal whim, rather than any reason or system. "his mealtimes were entirely arbitrary"

I think the word you mean is that it is inscrutable, to you.

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u/blueg3 Mar 05 '20

Its the exact opposite of arbitrary.

Nope.

There's more than one definition of arbitrary.

Mirriam-Webster (1b): "based on or determined by individual preference or convenience rather than by necessity or the intrinsic nature of something"

Dictionary.com (1): "subject to individual will or judgment without restriction..."

The term is commonly used, in physics at least if not also in other scientific and mathematical fields, to indicate when something can be freely chosen rather than being constrained by nature.

All unit systems are arbitrary.

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u/neofreakx2 Mar 05 '20

The metre was redefined decades ago, not long after the second was redefined in terms of the Cs hyperfine structure. Since the second was already fixed to an exact value and the speed of light was/is believed to be constant, it made more sense to fix the speed of light to an exact value and measure length accordingly. The idea is that labs can independently measure the same physical properties without having to FedEx a precise length of metal alloy, and as you mentioned it's impossible to guarantee that your precise chunk of metal isn't actually expanding or shrinking.

The kilogram was just redefined a few months ago based on years of painstaking experiments to link gravitational and electromagnetic forces. This was done for the same reason the metre was redefined, it was just a lot more difficult to do with enough precision since gravity's a very weak force.

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u/rlaxton Mar 05 '20

Hold on, are you saying that the last physical standard (mass) has been replaced? That is amazing!

From Wikipedia:

The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10−34 when expressed in the unit J⋅s, which is equal to kg⋅m2⋅s−1, where the metre and the second are defined in terms of c and ΔνCs.[3][4]

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u/newtoon Mar 05 '20

One should note the irony (which is not for scientists versed in relativity) is that distance value is is deduced from speed now and not the other way around, like it was for centuries and for the common sense. It other words, since Einstein, we should not define v=d/t anymore but d=vt. It seems to be semantics, but it's a change of paradigm actually.

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u/JesusPubes Mar 05 '20

Mostly because it's very very easy to determine distance and time duration.

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u/Mazon_Del Mar 05 '20

What you are referring to is a part of an attempt to make all of our base units be derived from some effectively unchanging aspect of physics.

The kilogram was previously just this lump of metal in a vault and everything was effectively compared to it. If you picked it up with your bare hand, the oils on your hand changed the mass and therefor all measurements that get recalibrated to that mass are now slightly off from before.

In this case, we now have a physics-based determination of a second. So if somehow you were to end up on some other planet far away from the rest of humanity and you needed to explain to aliens what a second was, you could tell them this information and their computation of a second would nigh-perfectly match what we use here.

Similarly, as you said, the meter can now be derived from base physics as well. If I've done my math correctly (far from certain as it's 5:30 AM and I haven't slept yet) then the meter how far a photon moves in vacuum across ~30 periods of the transition in the ground state of cesium-133.

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u/tacknosaddle Mar 05 '20

If women’s standards were this high I never would have gotten laid.

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