The cosmic microwave background is a uniform 2.7 Kelvin radiation that permeates the entire universe. Although postulated almost 50 years before, Penzias and Wilson discovered the cosmic microwave background accidentally in the 1970s. Working at Bell Labs, these two scientists were using a radio telescope to observe distant stars. They found, however, that no matter where they pointed their telescope they observed an approximately 3 Kelvin background signal. After convincing themselves that this signal was real and not some artifact of their instrument, they consulted with a team at Princeton University that had been searching for the cosmic microwave background. The Princeton team confirmed what Penzias and Wilson had found. Apparently, Penzias and Wilson had accidentally stumbled upon the oldest observable relic of the early universe.

Why does the cosmic microwave background exist? Just an instant after the Big Bang, all matter in the universe was so energetic, or hot, that it existed as free particles known as "quarks." In the fractions of a second following, the universe expanded and cooled until the quarks lost enough energy to form electrons, protons, and neutrons. Photons, the smallest particles of light, also filled the universe and were so energetic that they "bounced" off electrons, keeping the electrons and protons from forming atoms. After approximately 400,000 more years, the photons lost enough energy that atoms could form readily, eventually themselves cooling to 2.7 Kelvin.

Which of the following most accurately expresses the author's intent in writing the passage?

(A) To describe the discovery and reason for the cosmic microwave background
(B) To explain how science discoveries can be made accidentally
(C) To argue that the cosmic microwave background is the oldest observable relic of the universe
(D) To defend the work of Penzias and Wilson
(E) To support the theory of the Big Bang using the cosmic microwave background



According to the passage, which of the following events occurred first after the Big Bang?

(A) The universe expanded and cooled until atoms formed.
(B) Photons streamed unimpeded through space.
(C) All matter existed as particles known as "quarks."
(D) The cosmic microwave background cooled to 2.7 Kelvin.
(E) Atomic nuclei, composed of protons and neutrons, formed.



According to the passage, with which of the following would the author most likely agree regarding the discovery of Penzias and Wilson?

(A) It was not as important as the signal for which they were originally searching.
(B) The telescope belonging to Penzias and Wilson was more sensitive than that of the Princeton team.
(C) Penzias and Wilson would not have discovered the cosmic microwave background if it had been more than 3 Kelvin in temperature.
(D) Penzias and Wilson did not initially understand the implications of their results.
(E) Penzias and Wilson did not believe that their signal was real when they took their discovery to the Princeton team.