Why is the cosmic microwave background (CMB) so cold if the early universe was so hot?
a. Enough time has passed for matter in the universe to release enough heat to cool down.
b. The CMB constantly interacts with atoms, which effectively cool down the photons.
c. The expansion of the universe has redshifted those photons to an effectively cooler temperature.
d. Misleading; The Big Bang was initially hot but the CMB was released from cold material much later on.
C
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A full Moon is just now rising. Approximately what time of day is it?
A. 6 PM (sunset) B. It could be any time of day C. 6 AM (sunrise) D. Noon E. Midnight
How did Brahe measure highly accurate planetary positions?
A) By careful measurements of the brightness of the planets, as seen from Earth. B) With larger and more elegant sighting instruments. C) By his invention of the technique know as triangulation (measuring the distance between 2 points, and measuring 2 angles, to determine the distance to a 3rd point). D) With the recently-invented telescope. E) With a new type of telescope that used mirrors instead of lenses.
What does this diagram represent?
A) a particle and antiparticle colliding and converting all their mass into photons B) two photons spontaneously turning into a particle and an antiparticle C) a blue electron and a red electron turning into to pink light rays D) a particle of ordinary matter and a particle of dark matter colliding and becoming two photons of dark energy
What is the cause of a magnetic field about a permanent magnet and about a current-carrying wire?
What will be an ideal response?