Soru

Passage

In $1964$, two radio astronomers, Arno Penzias and Robert Wilson, were conducting research at the Bell Telephone Laboratories in Holmdel, New Jersey. Their primary objective was to measure the intensity of radio waves emitted by the halo of our galaxy, the Milky Way. To accomplish this, they utilized a state-of-the-art instrument known as the Holmdel Horn Antenna. This massive, $20$-foot horn-shaped reflector had been constructed in $1959$ for NASA’s Project Echo, a satellite communication initiative, but it had recently become available for astronomical research. Because of its unique design, which shielded the receiver from thermal radiation emitted by the ground, it was exceptionally suited for detecting incredibly weak cosmic signals.

However, when Penzias and Wilson began calibrating the antenna, they encountered an unexpected obstacle. Regardless of where they pointed the horn, they detected a persistent, low-frequency static hum that was far stronger than expected. The noise was equivalent to a temperature of about $3.5$ Kelvin (approximately minus $270$ degrees Celsius). This background radiation did not change when they rotated the antenna, nor did it vary between day and night, or as the seasons shifted. The uniformity of the signal suggested that its source could not be localized within our galaxy, let alone within the solar system.

Determined to isolate the cause of this interference, the two scientists embarked on a rigorous process of elimination. They initially suspected that the noise was generated by human activity, specifically broadcasting from nearby New York City. However, pointing the antenna directly toward the metropolis yielded no increase in the static. They then investigated whether the signal was caused by radar systems, atmospheric testing, or even extraterrestrial broadcasts. Each of these hypotheses was systematically tested and rejected. They also examined the antenna's electrical components, checking for loose connections or faulty wiring, but found the system to be in perfect working order.

Upon closer physical inspection of the horn antenna, Penzias and Wilson discovered a more terrestrial source of potential interference: a pair of pigeons had taken up residence inside the narrow throat of the horn. The birds had built nests and coated the interior aluminum surfaces with a sticky layer of droppings, which Penzias later referred to as "white dielectric material." Believing that this debris was causing the unwanted electrical resistance, the scientists evicted the pigeons, captured them, and shipped them away. They then climbed inside the horn and meticulously scrubbed away the droppings. Despite these efforts, and the subsequent installation of a liquid-helium cooling system to reduce internal thermal noise, the mystery hum persisted, remaining just as strong and steady as before.

Unbeknownst to Penzias and Wilson, a team of theoretical physicists at nearby Princeton University, led by Robert Dicke, was searching for the very signal the Bell Labs astronomers were trying to eliminate. Dicke, along with his colleagues Jim Peebles and David Wilkinson, had hypothesized that if the universe had expanded from a hot, dense singularity—the Big Bang—there should be a faint, uniform leftover radiation permeating all of space. Over the course of nearly $14$ billion years, this radiation would have cooled and stretched into the microwave portion of the electromagnetic spectrum.

When Penzias contacted Dicke to discuss the anomalous hum, the connection was immediately made. Dicke famously turned to his colleagues and remarked, "Well, boys, we've been scooped." The Holmdel Horn Antenna had accidentally detected the cosmic microwave background (CMB) radiation, the ancient echo of the early universe. This landmark discovery, which occurred in $1964$ and was published in $1965$, provided the first concrete evidence supporting the Big Bang model over the competing Steady State theory. In recognition of their monumental contribution to astrophysics, Arno Penzias and Robert Wilson were awarded the Nobel Prize in Physics in $1978$.

According to the passage, the persistent hum that Penzias and Wilson detected disappeared completely after they cleaned the pigeon nests and droppings from the antenna.