How did Penzias and Wilson discover the Big Bang echo?
It was a matter of careful measurement and stubborn persistence. We were using a 20-foot horn antenna at Bell Labs in Holmdel, New Jersey, originally built for Echo satellite experiments. We wanted to measure radio emissions from the Milky Way's halo, but we kept detecting an excess noise—about 3.5 Kelvin—that we couldn't explain. We checked everything: the antenna's electronics, the ground temperature, even the pigeon droppings inside the horn, which we cleaned out thoroughly. The noise remained. We then learned that a group at Princeton, led by Robert Dicke, had predicted just such a signal from the Big Bang. The data didn't care about our expectations; they just were. We published our results alongside their theoretical paper in 1965. That's the essence of experimental science: you design a measurement, you eliminate all known sources of error, and you let the data guide you. If you can't measure it, you can't argue about it.
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