One of the central concepts in spectroscopy is a resonance and its corresponding resonant frequency.
Like if you run your finger around a wine glass at the right speed/frequency — it resonates.
Resonances were first characterized in mechanical systems such as pendulums. Mechanical systems will vibrate more when they are driven at their resonant frequency.
Sometimes by physical phenomena like wind.
Peak resonant frequencies have a similar appearance on a graph — even at different frequencies.
In quantum mechanics, the resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom via an oscillatory source of energy, such as a radio wave.
The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states.
“If you want to find the secrets of the universe, think in terms of energy, frequency, and vibration.” ― Nikola Tesla
