Four out of seven base SI units will be redefined in one day.
Shift from physical artifacts to fundamental constants of nature.
The kilogram is the last SI unit defined by a physical object.
Current Definition of the Kilogram
Defined since 1799 as the mass of a metal cylinder in Paris (International Prototype Kilogram or "Big K").
Issues:
Divergence in mass of identical cylinders.
Limited access to the physical prototype.
New Standard Based on Planck's Constant
Proposal to fix Planck's constant to an exact value.
Planck's constant relates photon frequency to energy and is involved in mass through E=mc².
Current uncertainty in the value of Planck's constant.
Measurement Techniques
Various methods to measure Planck's constant:
Watt balance: Balances weight with electromagnet force.
Creation of an extremely round silicon object for precise measurements.
Comparison of findings from physics and chemistry to establish a consistent value for Planck's constant.
Implications of the Redefinition
Changes to other units:
Mole: Redefined based on Avogadro's constant.
Ampere: Redefined based on the charge of an electron.
Kelvin: Redefined using Boltzmann constant.
Overall impact on daily life: Minimal for most people.
Goal: Ensure consistency and reliability in measurements.
Minor Changes
Volt will change by about one part in ten million; resistance will change slightly less.
Update necessary due to discrepancies in prior measurements of Planck's constant.
Importance of Measurements in Science
Measurements are foundational in science, allowing for observations and discoveries (e.g., Kepler, Higgs boson, gravitational waves).
The new definitions mark a significant advancement from reliance on physical objects to abstraction based on nature.
The transition allows for incredibly precise measurements universally.
Conclusion
The shift represents a leap in scientific measurement, moving from physical artifacts to constants of nature, enhancing the ability to ascribe numerical order to the universe.