¡El kg ha Muerto! - Redefinición del Kilogramo

Scientific concepts / nature phenomena / discoveries presented

• SI unit redefinition (2018 vote in France)

  • On Nov 16, 2018, representatives from nearly 60 countries voted to redefine SI units so they are based on fixed fundamental constants of nature, not physical artifacts.
  • The video focuses on redefinitions of four SI base units:
    • kilogram (kg)
    • kelvin (K)
    • mole (mol)
    • ampere (A)

• Problem with the former kilogram definition (artifact-based)

  • The kilogram had been defined using a platinum–iridium cylinder (an international prototype) kept in Paris.
  • Cylinders intended to be identical can show mass differences, suggesting the artifact standard is not perfectly stable.
  • Access difficulty to the Paris artifact makes the definition inconvenient to realize accurately elsewhere.

• New kilogram definition via Planck’s constant

  • The redefinition uses Planck’s constant (h) as an exact fixed value.
  • The video links concepts such as:
    • (h) relating photon frequency to energy
    • mass–energy equivalence tying energy to mass
  • Strategy for removing uncertainty: rather than treating (h) as uncertain, (h) is fixed exactly—so the Paris cylinder is no longer required to match exactly 1 kg.

• Precision measurement of Planck’s constant (multiple methods)

  • Scientists use different experimental approaches to measure (h) precisely, then agree on a fixed value consistent with the combined results.
  • Kibble balance (Kyb balance)
    • Compares the weight of a kilogram against electromagnetic force to determine (h).
  • Silicon sphere method (Avogadro-related)
    • Uses specially engineered silicon with a precisely characterized crystal structure to count atoms in a nearly spherical object, supporting the determination of constants and consistency checks.

• Coupled consistency of other units (dependent constants)

  • Mole (Avogadro’s constant (N_A))
    • Historically tied to 12 grams of carbon-12, inheriting uncertainty from the kilogram.
    • After redefinition, the plan is to fix (N_A) so it is consistent with the fixed (h).
  • Ampere (electron charge)
    • Redefined using the fixed electric charge of an electron, rather than depending on the kilogram.
  • Kelvin (Boltzmann constant (k_B))
    • Defined using (k_B), which connects gas temperature to the average kinetic energy of molecules.

• Small changes to electrical and resistance standards due to “Planck-constant lock-in”

  • The video notes that in 1990, electrical metrologists stopped updating Planck’s constant and kept an earlier value to avoid changing instrument definitions.
  • After the newer redefinition, some electrical standards (including resistance, and a “bolt” reference likely meaning related voltage/derived standards) require minor updates on the order of about 1 part in ten million or slightly less.

• Scientific/measurement philosophy (context, not a new phenomenon)

  • The video emphasizes that measurement standards underpin science.
  • Moving from artifact-based units to constant-based units improves reliability and universality.

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Methods / methodology outlined

• International standard redefinition process

  • A vote by ~60 countries to fix constants defining multiple SI base units.

• Measuring Planck’s constant ((h))

  • Kibble (Kyb) balance
    • Compare mass/weight to electromagnetic force to derive (h).
  • Silicon-based atomic counting
    • Engineer highly characterized silicon spheres and use crystal structure/atom counting to support constant determination and cross-checks.
  • Cross-technique consistency
    • Combine physics-based and chemistry-based routes (including the Avogadro’s constant approach) to arrive at a globally consistent fixed value of (h).

• After redefining (h): update other constants

  • Fix Avogadro’s constant (N_A) for mole consistency.
  • Fix electron charge for the ampere.
  • Fix Boltzmann constant (k_B) for the kelvin.

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Featured researchers / sources (named)

• Max Planck (Planck’s constant)
• Avogadro (Avogadro’s constant / Avogadro’s method context)
• Charles-Augustin de Coulomb (implied via “electron charge”; no specific person named in subtitles)
• Kepler (mentioned in analogy regarding planetary orbits)
• Tien Cobra Hath (mentioned in analogy; appears to be an auto-generated/incorrect name)
• CERN (institution mentioned; related to the Higgs boson context)
• Higgs boson (discovery referenced; no researcher names in subtitles)
• LIGO / gravitational waves (gravitational waves referenced; no researcher names in subtitles)