The Big Bang model posits that the universe was created in a primordial fireball between 10 and 20 billion years ago. The model attempts to reconstruct the behavior of the early universe using only the rules of general relativity, elementary particle physics, and basic thermodynamics. Matching these claims with observations of the universe today shows its validity.
The Big Bang produced a universe made almost entirely of hydrogen and helium. For the first few seconds of the universe’s existence, its temperature was so high—over 10 billion degrees—and energetic electrons, neutrinos, and positrons so abundant that subatomic particles such as neutrons and protons were constantly transmuted into one another. As the universe cooled, these transmutations ceased. Most of the matter took the form of the most stable particle, the proton, leaving a universe where the ratio of protons to neutrons was about seven to one.
After a few minutes, the temperature of the universe fell to about 1 billion degrees, cool enough for these protons and neutrons to bond and form nuclei. Deuterons were formed as each neutron found a proton partner. Most deuterons then joined another deuteron to form a helium nucleus. As the universe continued to expand and cool, its density became too low to allow further fusion into heavier elements, and so almost all the neutrons were incorporated into helium. Only 0.01 percent of the deuterons formed remained unpaired, and an even smaller percentage had fused into elements heavier than helium, such as lithium.
Because only one neutron was formed for every seven protons, six-sevenths of all protons remained isolated. These remaining protons formed hydrogen nuclei containing one proton each. The Big Bang model predicts that about three-quarters of the total mass of the universe will be hydrogen and the remaining quarter helium. This simple prediction matches observations very well.
Q1). The author is primarily concerned with
○○ explaining how the evolution of the universe is incompatible with the implications of the Big Bang model.
○○ chronicling the events that followed the creation of matter by the Big Bang.
○○ explaining how helium was formed in the early life of the universe.
○○ illustrating specific propositions of a model and showing how they have been supported by observation.
○○ showing how the ratios of protons to neutrons created in the Big Bang dictated the final ratio of hydrogen to helium in the universe.
Q2). In the fourth paragraph, the author introduces information about the Big Bang model’s prediction for the molecular composition of the universe in order to
○○ obviate the claim that six-sevenths of all protons remained isolated.
○○ show that the remaining quarter of the total mass of the universe must be helium.
○○ provide evidence for the veracity of the Big Bang model.
○○ describe the means by which remaining protons formed hydrogen nuclei.
○○ predict the results of a Big Bang.
Q3). According to the passage, which of the following was true during the first few seconds of the universe’s existence?
I. The great majority of neutrons were incorporated into helium molecules.
II. The temperature was not high enough to allow for the formation of deuterons.
III. Vast numbers of subatomic particles rapidly metamorphosed into other types of particles.
○○ None
○○ I only
○○ III only
○○ II and III only
○○ I, II, and III
Q4). The author uses the first paragraph to introduce
○○ a scientific model that the passage will show to be supported by modern evidence.
○○ a theory of the origin of the universe that the passage will describe and attempt to refute.
○○ a description of the theoretical basis for a scientific model and the modern evidence undermining it.
○○ an attempt to use recent evidence to revive a discarded scientific model.
○○ a detailed description of an appealing but unsupported theoretical model.
Q5). The author would most likely agree with the position that
○○ models of the creation of the universe that were made before the Big Bang model was created failed because they did not take into account the behavior of subatomic particles.
○○ no credence can be given to a scientific model unless it is possible to produce supporting data through a series of controlled experiments.
○○ the Big Bang was part of a cycle of expansion and contraction in the universe.
○○ it is beneficial to use the statistical evidence at hand when judging the veracity of scientific models for which the process cannot be repeated in a laboratory.
○○ the simplicity of the Big Bang theory accounts for its accuracy.
Q6). According to the passage, a helium nucleus
○○ could only be created early in the universe’s history.
○○ has a low density due to the cooling and expansion of the universe.
○○ is more stable than a lithium nucleus.
○○ has four times the mass of a hydrogen nucleus.
○○ consists of exactly two neutrons and two protons.