Human radio bubble
Drag the slider — Earth’s radio signals expand at the speed of light into the galaxy.
Guglielmo Marconi transmits the first long-distance radio signal. A sphere of electromagnetic radiation begins expanding from Earth at the speed of light — it will never stop.
Signal recon — 01
Broadcast of Humanity: The expansion of the radio sphere
Humanity has been announcing its presence to the galaxy for over a century. Traveling at 299,792 km/s, our electromagnetic footprint is now a sphere roughly 120–131 light-years in radius — and growing by one light-year every single year, forever.
Radius today
From first ionosphere-escaping transmissions, ~1901
Expansion rate
Stars enclosed (est.)
Uncertain — depends on how many dim red dwarfs are counted
A note on the start date
The bubble’s origin is genuinely debated. Marconi’s 1895 experiments used low-frequency transmissions that were largely reflected back by the ionosphere and never reached space. The first signals that plausibly escaped Earth were Marconi’s 1901 transatlantic crossing and Fessenden’s 1906 voice broadcast — both at higher frequencies. Using 1895 as the origin inflates the radius by ~6 light-years. The honest answer is the bubble is somewhere between 120 and 131 light-years across, depending on which transmission you count as the start.
The 4 pillars of interstellar leakage
Not all radio waves escape Earth equally. The physics governing what leaks out — and whether it could ever be detected — comes down to four fundamental constraints.
Radio waves are electromagnetic radiation — they travel at the speed of light. Our bubble expands by exactly one light-year every year without exception. There is no mechanism to slow, stop, or recall these signals. Every transmission ever made is still out there.
Power density thins by the square of the distance. A signal 10 ly away has 1/100th the strength of one at 1 ly. By 50 ly, standard FM radio is mathematically indistinguishable from cosmic background static — the universe is simply too loud.
Earth’s ionosphere acts as a mirror for low-frequency signals. AM radio waves (below ~30 MHz) bounce back to the surface and never reach space. Only high-frequency VHF and UHF bands penetrate the ionosphere and escape into the interstellar medium. This is why the bubble’s effective start is later than 1895.
Our Sun is a colossal radio emitter. Earth’s leaked signals are billions of times weaker than the solar flux at any interstellar distance. A receiver at Proxima Centauri would need an antenna array several kilometers across just to pull a TV carrier wave out of the Sun’s magnetic noise.
Anatomy of the broadcast of humanity bubble — 1895 to present
The radio sphere is not a uniform shell. It is a layered archive — each concentric band corresponds to a different era of human broadcasting, with wildly different signal strengths, frequencies, and detectability profiles.
1895 – 1919
Outer edgeThe Marconi era
The outermost shell carries faint, low-frequency Morse code pulses — almost certainly reflected back by the ionosphere and never truly escaped. The first transmissions that plausibly breached the ionosphere were Marconi’s 1901 transatlantic signal and Fessenden’s 1906 Christmas Eve voice broadcast. These signals were pioneering but extraordinarily weak. Interstellar hydrogen clouds and the inverse square law almost certainly dispersed them into undetectable noise within a few light-years of Earth.
Bubble radius at end of era: ~24 ly
1920 – 1949
AM broadcast eraCommercial radio
The rise of commercial AM broadcasting sent a continuous electromagnetic hum across continents. These low-frequency signals are largely blocked by the ionosphere, and what escapes is quickly attenuated. The bubble grew to roughly 54 ly by 1949, but the signal quality reaching those distances was too poor to carry meaningful structure. Alpha Centauri received the faintest echo of the 1930s — nothing a receiver could confidently attribute to intelligence.
Bubble radius at end of era: ~54 ly
1950 – 1979
Peak loudnessAnalog television, military radar, and Arecibo
This is the loudest band of the human radio bubble. High-power analog television — broadcasting at VHF and UHF frequencies — penetrates the ionosphere with ease and carries coherent, high-energy signals. Cold War military radar installations swept the sky with pulses powerful enough to be detectable at significant distances if aimed directly. On November 16, 1974, the Arecibo Observatory in Puerto Rico transmitted a precisely encoded 3-minute message toward globular cluster M13, 25,000 light-years away — our most powerful and intentional interstellar signal ever sent. Sirius is receiving our earliest television test patterns. Vega is receiving broadcasts from around 2001 right now.
Bubble radius at end of era: ~84 ly
1980 – 2009
Late analogSatellites, planetary radar, and transition
Planetary radar systems like the Goldstone facility continued pulsing concentrated beams across the sky. The bubble grew past 80 ly, enclosing tens of thousands of star systems. Satellite communications emerged — though their tight directional beams rarely spray signal sideways into open space. The transition from analog to digital broadcasting began, marking the start of Earth’s electromagnetic quieting.
Bubble radius at end of era: ~114 ly
2010 – present
Inner shellDigital silence
The most recent layers of the bubble are, paradoxically, the quietest. Digital compression produces signals that are statistically indistinguishable from white noise to any receiver without the encoding key. Fiber optics route vast swaths of communication underground, never touching the air. Starlink and modern satellite constellations use phased-array beams so tightly focused they barely spray any signal sideways. Earth’s radio signature — from the perspective of the cosmos — is fading.
Bubble radius today: ~120–131 ly
The digital silence paradox
As humanity becomes more connected than at any point in history, we are simultaneously becoming electromagnetically invisible. The 1970s were our loudest decade — a civilization shouting into the void with a billion television sets and continent-spanning radar arrays. Today, those same data flows move through glass fibers buried underground, or ride compressed digital packets that look like random noise to an unencoded receiver. To a radio telescope at Vega pointing at our solar system, Earth peaked thirty years ago and is going quiet.
What civilizations could actually receive
Distance is only part of the detection problem. Signal type matters enormously. Here is what different eras of human broadcasting would look like to a sufficiently advanced receiver at various interstellar distances.
Notable stars — what they’re receiving now
Each star enclosed by the bubble is currently receiving a different era of human history. The signal arriving at any given star left Earth exactly as many years ago as the star is light-years distant. All “receiving” years are calculated from 2026.
Alpha Centauri
4.37 ly — signal reached ~1906
Receiving transmissions from 2022. Saturated in modern digital signals — statistically indistinguishable from noise without the encoding key. Has passed through every era of our broadcasting history.
Sirius
8.6 ly — signal reached ~1910
Receiving our 2017–18 broadcasts — early digital compression era. The moon landing passed Sirius back in 1977–78. It has already experienced every era from Morse code through peak analog TV.
Vega
25 ly — signal reached ~1926
Receiving broadcasts from 2001. In the tail end of our analog television era — some of the strongest and most structured signals Earth ever produced. Vega is currently hearing us near peak loudness.
Pollux
33.7 ly — signal reached ~1935
Receiving broadcasts from 1992. Squarely in the Cold War and peak-radar era — some of humanity’s most energetic and coherent transmissions are passing through this system right now.
Arcturus
36.7 ly — signal reached ~1938
Receiving broadcasts from 1989. The Berlin Wall fell on live television, and those signals are currently passing through this system — some of the most widely broadcast events in human history.
Capella
42.9 ly — signal reached ~1944
Receiving broadcasts from 1983. Mid-Cold War peak. Space Shuttle launches, Reagan-era radar, and some of the most powerful television transmissions in US history are passing through now.
Aldebaran
65 ly — signal reached ~1966
Receiving broadcasts from 1961. Early Space Age television — John Glenn’s orbit, early moon mission coverage, and the first widely broadcast manned spaceflight. A civilisation here would be watching humanity leave the cradle.
Regulus
79.3 ly — signal reached ~1980
Receiving broadcasts from 1947. Early postwar television experiments and military radar tests. The signal here is faint but it carries the first structured, coherent transmissions Earth ever produced at useful frequencies.
The recon zone
Passive detection of accidental electromagnetic leakage is realistically only feasible within roughly 50–100 light-years — what some researchers call the “recon zone.” Beyond that, the inverse square law and solar noise floor make detection implausible with any antenna of physically reasonable size. Deliberate targeted transmissions are an entirely different matter: the 1974 Arecibo message, with an effective isotropic radiated power of 20 trillion watts, would be detectable anywhere in the galaxy by a receiver of comparable size — but only if pointed directly at the source at the right moment.
The solar interference problem
The single greatest obstacle to detecting Earth’s broadcasts from another star system is not distance — it is our own Sun. The Sun emits radio waves across the entire electromagnetic spectrum at intensities that dwarf anything humanity has ever transmitted. Earth’s total broadcast output at any moment is somewhere between a billion and a trillion times weaker than the solar radio flux measured from interstellar distances.
To isolate Earth’s signal from the Sun’s noise at even 4 light-years, a receiving civilization would need a telescope array with a collecting area comparable to a small moon. The engineering challenge is not impossible for a sufficiently advanced civilization — but it illustrates why passive detection of leakage radiation is extraordinarily difficult even in principle, and why SETI researchers focus on deliberate, narrow-band transmissions rather than leakage.
Radar remains our most detectable unintentional output. Directional radar systems concentrate enormous energy into narrow beams. When those beams sweep past a star system, the brief pulse can exceed the solar flux for that frequency — making them detectable at distances of hundreds of light-years by a sufficiently large receiver pointed in the right direction at the right moment.
Earth leakage vs solar noise
10⁹ – 10¹² times weaker
Arecibo 1974 peak EIRP
20 trillion watts
Passive leakage detection range
~50–100 ly
Arecibo message detection range
Galaxy-wide (if aimed at receiver)
A permanent archive
Even if humanity ceases to exist tomorrow, the radio bubble does not. It is a physical object — a thin, expanding electromagnetic shell moving at the speed of light through the interstellar medium. No force in the known universe will stop it. It carries every television broadcast, every radar pulse, every carrier wave ever transmitted, growing fainter with each passing light-year but never truly gone.
In 500 years, the bubble will have reached the Pleiades. In 25,000 years, signals from today will wash over the dense star fields at the galactic core. In a billion years, attenuated beyond any conceivable detection, the sphere will still be expanding — an artifact of a civilization that briefly lit up the electromagnetic spectrum of its star system, then went quiet.
We did not choose to announce ourselves. We simply turned on the lights.
🗿 Dwarf Planet Registry
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✨ Universal Star Census
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🌑 Why is Space Black?
Understand the Redshift effect and why deep space signals eventually fade into invisible wavelengths.