Sources
For grown-ups sitting beside the walk. Teaching pictures are labeled as models. Generated atmosphere is never evidence.
observed
Ordinary hearing is a response to pressure waves in a medium, usually air.
Standard acoustics. In vacuum there is no air to compress, so a clap cannot arrive as sound.
Limit: Does not cover every vibration a body can feel through bone or a wall.
measured
Visible light is electromagnetic radiation. Photons can cross vacuum.
Maxwell, quantum optics, astronomy. Starlight is a working example.
Limit: Does not require a child to master photon language on first look.
measured
Radio is the same electromagnetic family as light, at longer wavelength.
Radio engineering and astronomy. Wi-Fi, broadcast radio, and spacecraft links are radio-frequency electromagnetic signals.
Limit: Does not mean radio is sound. Speakers later turn some radio programs into sound.
measured
The ground-state hyperfine transition of neutral hydrogen has a rest frequency of 1420.405751768(2) MHz, a vacuum wavelength of about 21.106 cm.
Laboratory spectroscopy of the 21 cm line. NRAO teaching often writes 1420.405752 MHz. The laboratory rest frequency is 1420.405751768(2) MHz.
Limit: Observed frequency shifts with the line-of-sight component of Doppler motion. The rest value is not always the frequency on the dial.
documented
Hendrik van de Hulst predicted the 21 cm line in 1944. Ewen and Purcell detected it in 1951, with independent confirmation that year.
van de Hulst (1945); Ewen & Purcell, Nature 168 (1951).
Limit: Later HI surveys mapped spiral structure. A teaching sky in this app is a model, not a live observation.
documented
Some LIGO/Virgo searches have included frequencies around 1420 Hz, inside bands that run from tens of hertz into the kilohertz. That does not give 1420 Hz a special gravitational-wave meaning merely because hydrogen sits at 1420 MHz.
LIGO/Virgo all-sky continuous-wave searches (example published band 20 to 1726 Hz) and LIGO public education on audio translations.
Limit: Search bands change with detector and analysis. 1420 Hz is not a hydrogen gravitational-wave line.
measured
A nerve impulse along an axon is an action potential (a traveling electrical change). Transmission across most human synapses is chemical, by neurotransmitter. Some synapses are electrical.
Cellular neuroscience. Queensland Brain Institute primers on action potentials and synapses.
Limit: The app does not claim wall-socket electricity. Speeds vary with myelin and axon diameter.
measured
Smell begins when odorant molecules bind receptors in the olfactory epithelium.
Olfactory receptor biology.
Limit: A single odorant molecule can interact with a receptor. That is not the same as saying one molecule reliably produces conscious smell.
documented
Animals send information with light, sound, vibration, chemicals, and electric fields. A signal is produced to be received. A cue can inform without having been sent for you. What was sent is a different question from how an animal finds its way.
Animal communication literature. This room does not replace a navigation atlas.
Limit: Whale song meaning is not fully known. Do not pretend a complete dictionary.
documented
NASA states that on 18 November 2026 at 2:16:07 a.m. PST, Voyager 1 will be one light-day from Earth: about 16.094 billion miles, the distance light travels in 24 hours. A command then needs 24 hours to arrive. A reply needs another 24 hours to come home.
NASA Voyager: Where Are Voyager 1 and 2 Now? (updated 2026).
Limit: The exact light-time changes continuously as the spacecraft recedes. This app does not pretend to be a live ranging clock.
documented
Gravitational waves are ripples in spacetime, not sound waves in air. LIGO can translate strain data into audio frequencies humans can hear. LIGO education is explicit that the wave itself is not ordinary sound.
LIGO Laboratory and GWOSC audio notes: gravitational waves are not sound; data are whitened and bandpassed for listening.
Limit: The playable chirp in this app is a teaching synthesis, not the GW150914 data file.
measured
GW150914 was a binary black hole merger. The signal's frequency rose from about 35 Hz to about 250 Hz in a fraction of a second.
Abbott et al., Phys. Rev. Lett. 116, 061102 (2016), and LIGO education summaries.
Limit: Masses, distance, and waveform details belong to the paper. The room teaches the carrier, not a full catalog of events.
inferred
A candidate can be noise. Repetition, filtering, independent detectors, and controls raise confidence. None of them guarantees you are right.
Detection statistics as used in radio astronomy and gravitational-wave searches.
Limit: This room is an intuition pump, not a statistics course.
inferred
Information can be present without a sender. A message implies encoding for a receiver. Starlight and tree rings inform. They are not letters.
Philosophy of information and scientific practice. Project teaching distinction, labeled as such.
Limit: Definitions vary across fields. The room keeps the distinction practical for a child.