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Fundamental physics,
in proportion.

Explore measured constants, characteristic particle scales and theoretical physical reference points.

19 entries in this category, ordered by name.

19 measured entities

Browse fundamental physics

Bohr radius52.92 pmThe Bohr radius is a fundamental physical constant representing the most probable distance between the nucleus and the electron in a hydrogen atom according to early quantum theory.

Caesium-133 clock transition108.8 psThe caesium-133 clock transition is the specific change in energy state of a caesium-133 atom that defines the duration of one second in the International System of Units.

Electron9.109 × 10⁻³¹ kgAn electron is a fundamental subatomic particle with a negative electric charge, found in atoms and responsible for electricity and chemical bonding.

Hydrogen 21 cm hyperfine transition5.873 × 10⁻⁶ eVThis is a change in the energy state of neutral hydrogen atoms that produces or absorbs radio waves, widely used in radio astronomy.

Neutron1.675 × 10⁻²⁷ kgA neutron is a type of subatomic particle found in atomic nuclei, carrying no electric charge and playing a key role in holding nuclei together.

Photon pressure thrust per kilowatt6.7 × 10⁻⁶ NPhoton pressure thrust per kilowatt is the force generated when one kilowatt of light is absorbed or reflected, due to photon momentum.

Planck length1.616 × 10⁻³⁵ mThe Planck length is a scale formed from fundamental physical constants.

Planck mass21.76 µgThe Planck mass is a theoretical mass scale derived from fundamental constants, significant in discussions of quantum gravity.

Planck temperature1.417 × 10³² KThe Planck temperature is a theoretical temperature scale at which quantum gravitational effects are expected to become important.

Proton1.682 fmA proton is a positively charged particle found in the nucleus of atoms, made up of quarks.

Radiation pressure on a laser mirror7 × 10⁻⁶ NRadiation pressure on a laser mirror is the force exerted by a laser beam as its photons strike and reflect from the mirror.

Raindrop aerodynamic drag0.0003 NRaindrop aerodynamic drag is the force exerted by air resistance on a falling raindrop as it moves through the atmosphere.

Single DNA molecule stretching force5 × 10⁻¹¹ NSingle DNA molecule stretching force is the force required to extend a single DNA strand under controlled laboratory conditions.

Snowflake aerodynamic drag1 × 10⁻⁶ NSnowflake aerodynamic drag is the resistive force experienced by a falling snowflake as it moves through air.

Soap film pull on a wire0.006 NSoap film pull on a wire is the force created by the surface tension of a soap film stretched across a wire frame.

Strontium-87 optical clock transition1.779 eVThe strontium-87 optical clock transition is an energy change between two quantum states of strontium atoms that can set the timing of an optical atomic clock.

Thrust of a gridded ion engine0.09 NThe thrust of a gridded ion engine is the force generated by accelerating ions through electrostatic grids to provide propulsion in space.

Thrust of a Hall-effect satellite thruster0.1 NThe thrust of a Hall-effect satellite thruster is the force produced by accelerating ions with a magnetic field to propel a spacecraft.

Thrust of an ionocraft lifter0.2 NThe thrust of an ionocraft lifter is the upward force generated by moving ions through air using high voltage, allowing the device to lift itself.

A characteristic wavelength, radius or theoretical scale is not automatically a hard-edged object diameter. The recorded property defines exactly what is compared.

Entries: 19
Main measurement family: Weight & gravity
Measurements include: Length
One cycle
Mass
Single-photon transition energy
Force
Temperature

For examples of weight & gravity, try Single DNA molecule stretching force (5 × 10⁻¹¹ N) or Thrust of an ionocraft lifter (0.2 N). These are starting points for exploring, not limits for the whole category.