Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

An old artifact kept in a vault outside Paris is no longer the standard kilogram

news.mit.edu

Post reply on HN
Print view View original

121–130 of 155 posts

Re: An old artifact kept in a vault outside Paris is no longer the standard kilogram

#121

Post by JohnJamesRambo »

saalweachter wrote: post #113
jelder wrote: post #81

The new reference kilogram is an engineering marvel, but I’ve always wondered this: why didn’t they just build a reference gram instead? Seems like that would be at least a thousand times easier to pull off.

Basically, it's part of the lie of the mythology of the metric system. The metric system did some great things (eliminated the use of measures that depended on the substance being measured, dry pints vs wet pints, bushel of wheat versus bushel of oats; simple relationship between units of length, area and volume), some things that were already common at the time (eliminated regional definitions of units; related the…

As a scientist I've gotta say...how are metric prefixes bad? I couldn't do my job without them every day.

Re: An old artifact kept in a vault outside Paris is no longer the standard kilogram

#122

Post by not2b »

Etheryte wrote: post #91
StavrosK wrote: post #78

Earlier quoted context omitted.

What about the imperial units? Are those defined against metric as well?

A quick glance at Wikipedia seems to indicate so, but I didn't go over every base unit.

Yes, for example an inch is now defined as precisely 2.54 cm, so a foot exactly 30.48 cm, a mile is exactly 1609.344 m.

Re: An old artifact kept in a vault outside Paris is no longer the standard kilogram

#123

Post by saalweachter »

JohnJamesRambo wrote: post #121
saalweachter wrote: post #113

Earlier quoted context omitted.

Basically, it's part of the lie of the mythology of the metric system. The metric system did some great things (eliminated the use of measures that depended on the substance being measured, dry pints vs wet pints, bushel of wheat versus bushel of oats; simple relationship between units of length, area and volume), some things that were already common at the time (eliminated regional definitions of units; related the…

As a scientist I've gotta say...how are metric prefixes bad? I couldn't do my job without them every day.

As a scientist, use scientific notation off the base units; you eliminate opportunities for confusion. The prefixes don't really add anything.

The Sun is 1.5 x 10^11 meters from the Earth.

Calling it 1.5 x 10^8 kilometers doesn't help you visualize the distance better, nor calling it 150 gigameters. Now you have three numbers that mean the same thing floating around, and if you accidentally write 1.5 x 10^8 m somewhere instead of km, or read 1.5 x 10^11 km as m, you've just introduced a thousand-fold error.

Common units (eg, Angstrom) make sense when you do not need to convert between them; it's convenient if they are easily convertible to your standard unit, but having mg and ug and g and kg floating around is just an unnecessary headache, you inevitably accidentally interpret a microgram dose as a milligram dose from time to time and poison a patient or eight.

Re: An old artifact kept in a vault outside Paris is no longer the standard kilogram

#124

Post by saalweachter »

0xffff2 wrote: post #120
saalweachter wrote: post #113

Earlier quoted context omitted.

Basically, it's part of the lie of the mythology of the metric system. The metric system did some great things (eliminated the use of measures that depended on the substance being measured, dry pints vs wet pints, bushel of wheat versus bushel of oats; simple relationship between units of length, area and volume), some things that were already common at the time (eliminated regional definitions of units; related the…

This reply doesn't seem to address the comment it's replying to at all...

The answer to the question "why is the unit weight the kilogram instead of the gram" is "because the kilogram is about 2 Parisian pounds, which is what everyone at the time actually cared about".

Re: An old artifact kept in a vault outside Paris is no longer the standard kilogram

#125

Post by jschwartzi »

saalweachter wrote: post #123
JohnJamesRambo wrote: post #121

Earlier quoted context omitted.

As a scientist I've gotta say...how are metric prefixes bad? I couldn't do my job without them every day.

As a scientist, use scientific notation off the base units; you eliminate opportunities for confusion. The prefixes don't really add anything. The Sun is 1.5 x 10^11 meters from the Earth. Calling it 1.5 x 10^8 kilometers doesn't help you visualize the distance better, nor calling it 150 gigameters. Now you have three numbers that mean the same thing floating around, and if you accidentally write 1.5 x 10^8 m somewhe…

Unless you need to make a dial on a physical piece of equipment. In that case it's helpful not to have to append x10^N to all of your numbers.

Re: An old artifact kept in a vault outside Paris is no longer the standard kilogram

#126

Post by cygx »

saalweachter wrote: post #123
JohnJamesRambo wrote: post #121

Earlier quoted context omitted.

As a scientist I've gotta say...how are metric prefixes bad? I couldn't do my job without them every day.

As a scientist, use scientific notation off the base units; you eliminate opportunities for confusion. The prefixes don't really add anything. The Sun is 1.5 x 10^11 meters from the Earth. Calling it 1.5 x 10^8 kilometers doesn't help you visualize the distance better, nor calling it 150 gigameters. Now you have three numbers that mean the same thing floating around, and if you accidentally write 1.5 x 10^8 m somewhe…

Personally, I find the prefixes helpful when memorizing approximate values, eg for back-of-the-envelope estimates (proton mass is 1GeV, electron mass is .5MeV, room temperature is 25meV, h_bar c is 197 MeV fm, ...)

Re: An old artifact kept in a vault outside Paris is no longer the standard kilogram

#127

Post by Loughla »

jcliffio wrote: post #118
jelder wrote: post #81

The new reference kilogram is an engineering marvel, but I’ve always wondered this: why didn’t they just build a reference gram instead? Seems like that would be at least a thousand times easier to pull off.

I love that everyone took this as a serious comment.

It's either the best unintentionally punny question or the best unintentionally serious pun in history.

Either way, I'm loving this.

Re: An old artifact kept in a vault outside Paris is no longer the standard kilogram

#128

Post by swiley »

Etheryte wrote: post #89
jelder wrote: post #81

The new reference kilogram is an engineering marvel, but I’ve always wondered this: why didn’t they just build a reference gram instead? Seems like that would be at least a thousand times easier to pull off.

As covered in the article, the reference object loses some of it's atoms every time it is handled. The smaller the reference object, the larger the relative error induced this way.

Not just that, it's probably just the surface (or near surface) that sublimes. The surface only increases with the square of the radius while the volume increases with the cube. so multiplying the volume by 27 only multiplies the surface by 9.

Re: An old artifact kept in a vault outside Paris is no longer the standard kilogram

#129

Post by cs02rm0 »

jelder wrote: post #81

The new reference kilogram is an engineering marvel, but I’ve always wondered this: why didn’t they just build a reference gram instead? Seems like that would be at least a thousand times easier to pull off.

Apparently they were going to go a different way, but this saved them a ton.

Re: An old artifact kept in a vault outside Paris is no longer the standard kilogram

#130

Post by gubbrora »

lelf wrote: post #55

Definition of mole changes too. One mole contains exactly 6.022 140 76×10²³ elementary entities (as opposed to the number of atoms in 12 grams of ¹²C). Effective 20 May 2019.

The real wtf is that we had a unitless unit, ie a number whose value changes over time with some reference object.
Post reply on HN