NIST Posts Adjusted Values of the Physical Constants, Tweaking Gravity to Make Science More Precise

By Clay Dillow Posted 07.21.2011 at 11:00 am 12 Comments

The Precisely Milled International Prototype Kilogram Don't you go a'changin'. GregL via Wikimedia

Did you feel that? Gravity just got a little weaker. The National Institute of Standards and Technology has just posted the latest internationally recommended adjustments to the values for the fundamental constants of nature. The results: Gravity is a bit weaker, the electromagnetic force a smidgeon stronger, and the whole of physics a little less uncertain.

The NIST and its international partners reconsider the values placed upon the fundamental constants every four years to take into account advances in technology and science that beget better, more accurate values for things like the speed of light, the Newtonian constant of gravitation (G), the Planck constant, and other values preceded by famous names.

The real news here isn’t really that we’ve discovered anything new but that science on the whole has reduced uncertainty, and that in turn impacts all physical science going forward. For instance, uncertainty in the constant alpha (that’s the fine-structure constant or the electromagnetic constant) has been reduced by 0.3 parts per billion, or cut in half based on the last evaluation of the constants in 2006.

Going forward, this adjustment to alpha will make a difference in (and--if the adjustment is correct--reduce the uncertainty of) all kinds of physics. The same is true for various other constants (there’s a nice overview of the heavy hitters here) like the radius of a proton or the Rydberg constant (relating to the atomic spectra in spectroscopy and thus far the most accurately measured fundamental constant--we think), whose values are still not completely “certain” but have been sharpened to introduce less and less uncertainty over the years.

But this year’s realignment of the constants will ripple through the world as we understand it more than most. In October a worldwide vote will redefine the most basic units in the International System of Units (SI) exclusively in light of these fundamental constants. That means that while more nebulous concepts like the G are getting a tiny adjustment now, that change will soon impact more concrete units like the kilogram.

Just think: in October you may gain or lose a tiny yet measurable bit of weight without so much as lifting a finger. Just don’t let it go to your head, which will still likely be busy trying to wrap itself around all of this.

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12 Comments

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LiveBetter

07/21/11 at 1:04 pm

Is it related to Half Life period, where the mass is getting reduced.

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mathew Rush

07/21/11 at 1:10 pm

What dose NIST know of gravity? Building 7 any one?

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Torbjörn Larsson_OM

07/21/11 at 2:33 pm

I don't think this article analyze the ramifications correctly.

Isolated measurements, that can be more precise than our measurements of parameters relating to fundamental constants, aren't much affected. However constructing equipment for the task and communicating the result is eased. (And greatly compared to having no standards!)

The (invisible, important) ripple effect is dead on though.

@ LiveBetter:

No, radioactive half life is set by physics regardless of our measurements of it. Especially we don't usually measure reduced mass AFAIK, it is easier and as you hint more accurate to measure isotope ratios. I.e. measure how many atoms have decayed and how many remains to decay, but by weight.

Some of these measurements are self-calibrating (isochronous, IIRC the term) so how badly we try, mistakes are caught. Our expression of how many decays there is on average over a time period would change to compensate if we changed the time period of measurement in such cases. I.e. change the period, and the number of decays per period changes. But the physical value of half life stays the same.

What can change our expression, but not the physical value of half life, is if our calibrated value for the time period changes. I.e. change the value of the second, and the number of decays per second changes. But the physical value of half life stays the same.

@ mathew Rush:

NIST knows as much as is known in physics, but especially they know how to measure gravity (or other things) really well over a long time period. In physics term, they kick serious ass.

Gravity is one of those fundamental forces and its constant one of those fundamental parameters that are considered for overhaul of measurement. It is the last parameter to have a real physical artifact (a prototype weight) used for measurement, instead of using a measurement that can be repeated elsewhere. We are on the verge of knowing how to remedy that. (It is googleable.)

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Torbjörn Larsson_OM

07/21/11 at 2:36 pm

@ BubbaGumb: So either NIST disproves gods, or your comment disproves the practice of inserting religious blather into discussions of science. Why, thank you!

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Dj_Janx

07/23/11 at 5:07 am

Hearts vs feathers- i guess heavens a pretty lonely place them!

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Aldrons Last Hope

07/25/11 at 1:14 pm

@matthew Rush....right with you NIST is a joke after the the blown WTC and building 7 investigations.

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Peter10

07/25/11 at 5:01 pm

I'd like to see a pic of a standard pound, a standard inch, foot, degree Fahrenheit, etc. and their exact scientific definitions. Many so-called "serious scientific" articles keep on using those archaic units for weight, distance, temperature and size.
WHY??? This is costing billions in mistakes (...crash of mars probe caused by metric/imperial) and time lost to convert one to the other.

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fisherworldjm

07/28/11 at 10:48 pm

Uh, why should they do that? Altering constants is a big deal - Now all my calculations are messed up! T_T
Fisher Capital Management

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fisherworldjm

07/28/11 at 10:52 pm

Uh, why should they do that? Altering constants is a big deal - Now all my calculations are messed up! T_T
www.fishercapitalmanagement-worldnews.com/

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