tag:blogger.com,1999:blog-4212234230338648875.post4491673539994439318..comments2024-03-27T20:43:05.862-07:00Comments on The Eternal Universe: Should We Redefine The Kilogram?Joseph Smidthttp://www.blogger.com/profile/02583891162785742138noreply@blogger.comBlogger11125tag:blogger.com,1999:blog-4212234230338648875.post-92180563511712438762010-09-15T11:26:49.428-07:002010-09-15T11:26:49.428-07:00@Bill: There are copies of it.@Bill: There are copies of it.peterfireflyhttps://www.blogger.com/profile/05050847835479172236noreply@blogger.comtag:blogger.com,1999:blog-4212234230338648875.post-983598000195566232010-09-14T16:27:32.290-07:002010-09-14T16:27:32.290-07:00Look up NIST. They do this day in and out.
I lik...Look up NIST. They do this day in and out.<br /><br />I like Madhatter's way of thinking, though...Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4212234230338648875.post-20173967028661527852010-09-14T13:22:08.343-07:002010-09-14T13:22:08.343-07:00I think a lot of people are looking at different w...I think a lot of people are looking at different ways to <a href="http://articles.latimes.com/2008/apr/17/science/sci-kilogram17" rel="nofollow">redefine</a> the <a href="http://en.wikipedia.org/wiki/Kilogram#Proposed_future_definitions" rel="nofollow">kilogram</a>. Re-defining units is something that happens from time to time in SI. (See <a href="http://www.sizes.com/units/meter.htm" rel="nofollow">here</a>, <a href="http://www.iscanmyfood.com/hd/index.php?t=Redefinition+of+the+metre+in+1983" rel="nofollow">here</a> and <a href="http://www.npl.co.uk/science-technology/time-frequency/optical-frequency-standards-and-metrology/units/secondary-representations-of-the-second" rel="nofollow">here</a>.) <br /><br />In reality, the definition probably has next to no practical value. Even though if that platinum cylinder in France suddenly split in half, <i>technically</i> the numerical value of everyone's mass would suddenly double, what would most likely <i>actually</i> happen is that some technician / caretaker would see the problem, grumble under his breath in French, take the thing out of its casing, and have it re-cast such that it would have the mass of exactly 1 kg as measured by some electronic analytical balance in that lab. (Granted, I might be oversimplifying a bit, but minus the scientific media blitz that would surely ensue if word got out, I imagine that the situation would actually be dealt with similarly to this.) This is why it is kept underground in a temperature and humidity-controlled vault. (Actual picture <a href="http://www.bipm.org/en/scientific/mass/prototype.html" rel="nofollow">here</a>.) <br /><br />The issue of how to deal with uncertain definitions is something that we are having to deal with for other units as well. We are getting to the point in atomic physics, where we can tell the difference in frequency between a <a href="http://en.wikipedia.org/wiki/Second#International_second" rel="nofollow">Cesium transition</a> in an atom in Boulder, Colorado, and one in Champaign, Illinois. (They will be slightly different because the local acceleration due to gravity is slightly different, and this has relativistic consequences.) Will we need to define the second not only by what transition in what atom, but by where or under what conditions that atom is in? <br /><br />Should we re-define the kilogram? Probably. Will it make a huge difference? I doubt it. What should we use to re-define the kilogram? Well, a definition like that should be (1) stable, and (2) practically measurable with high precision. A lot of people like counting atoms. Another way we could do it is in terms of fundamental constants. The meter is currently defined by defining a value of <i>c</i>. We could just as easily define the kilogram by defining a numerical value for <i>G</i> or <i>h</i> or h-bar (sorry, I don't know how to typeset that one here). <br /><br />Anyways, good stuff to think about. As always, great post.Billhttps://www.blogger.com/profile/02573106204390814039noreply@blogger.comtag:blogger.com,1999:blog-4212234230338648875.post-38088219940833212822010-09-14T12:08:42.123-07:002010-09-14T12:08:42.123-07:00Nick,
You make a good point. My guess is the pr...Nick, <br /><br />You make a good point. My guess is the practicalness of using carbon. I mean, carbon-12 is plentiful, stable, not-dangerous and a solid at room temperature.Joseph Smidthttps://www.blogger.com/profile/02583891162785742138noreply@blogger.comtag:blogger.com,1999:blog-4212234230338648875.post-40618796012801246462010-09-14T12:04:15.657-07:002010-09-14T12:04:15.657-07:00Here's an off-the-wall question - why do we li...Here's an off-the-wall question - why do we like carbon so much? I understand that it's a great element, but we already define the "mole" using carbon. Carbon seems to be causing global warming. Maybe we should spread the love around and use a less-popular element to define the kilogram. My vote is 1 kg = 3.44181374 × 10^24 yttrium atoms.Anonymoushttps://www.blogger.com/profile/17367937708444729356noreply@blogger.comtag:blogger.com,1999:blog-4212234230338648875.post-60233651474658615462010-09-14T12:01:55.241-07:002010-09-14T12:01:55.241-07:00"Holden wrecks and boiling diesels steam at 4..."Holden wrecks and boiling diesels steam at 45 degrees"<br /><br />An Australian song that always reminds me that we are different and behind the times here in the States.Stannoreply@blogger.comtag:blogger.com,1999:blog-4212234230338648875.post-45855678482317658042010-09-14T11:59:14.478-07:002010-09-14T11:59:14.478-07:00Joe,
I've gotten pretty good at thinking in S...Joe,<br /><br />I've gotten pretty good at thinking in SI (or CGS, crazy astronomers) units for everyday things such as speeds, masses, distances, etc., but the one I can never seem to wrap my brain around is temperature for some reason. I even spent 2 years in Brazil converting temperatures back to Fahrenheit and I still can't "think" in Celsius (or Kelvin).Anonymoushttps://www.blogger.com/profile/17367937708444729356noreply@blogger.comtag:blogger.com,1999:blog-4212234230338648875.post-28588949920959928172010-09-14T11:51:47.480-07:002010-09-14T11:51:47.480-07:00Stan,
What confuses me is when we have visitors ...Stan, <br /><br />What confuses me is when we have visitors to the group who walk in and say: "Wow, what nice weather here, I think it is supposed to be 24 degrees today." It always takes me a second to remind myself where they are getting a number like that since it is *never* in the 20s here. :) (Seriously, I don't think once in the entire 3 years I've been here, even as the low.)Joseph Smidthttps://www.blogger.com/profile/02583891162785742138noreply@blogger.comtag:blogger.com,1999:blog-4212234230338648875.post-1165683327640205502010-09-14T11:42:18.694-07:002010-09-14T11:42:18.694-07:00What's a kilogram? Yes, I am an American.What's a kilogram? Yes, I am an American.Stannoreply@blogger.comtag:blogger.com,1999:blog-4212234230338648875.post-41993551665356385432010-09-14T11:40:47.043-07:002010-09-14T11:40:47.043-07:00Quantum_Flux,
I guess we could do that too.Quantum_Flux,<br /><br />I guess we could do that too.Joseph Smidthttps://www.blogger.com/profile/02583891162785742138noreply@blogger.comtag:blogger.com,1999:blog-4212234230338648875.post-84239376376584925402010-09-14T11:39:27.029-07:002010-09-14T11:39:27.029-07:00Why not just use that cylinder of platinum and est...Why not just use that cylinder of platinum and estimate how many atoms of platinum it is?Quantum_Fluxhttps://www.blogger.com/profile/09383025356536602044noreply@blogger.com