Public index · Physics
Hydrogen line
1420.405… MHz
Measured
Neutral-hydrogen hyperfine transition
The 21-centimetre line sits at 1420.405751768 MHz. It is not 42.
What it supports
A laboratory and radio-astronomy frequency. The Book’s 1420 plate is a door to this measurement.
What it does not
Not 42, not 420, not a consciousness frequency. 1420 is its own family.
ExactnessExact
Form1420
UnitMHz
Strengthhard