According to the theory of gravitation, every
particle of matter in the universe attracts every other
particle with a force that increases as either the mass of
the particles increases, or their proximity to one
(5) another increases, or both. Gravitation is believed to
shape the structures of stars, galaxies, and the entire
universe. But for decades cosmologists (scientists who
study the universe) have attempted to account for the
finding that at least 90 percent of the universe seems to
(10) be missing: that the total amount of observable
matter—stars, dust, and miscellaneous debris—does
not contain enough mass to explain why the universe is
organized in the shape of galaxies and clusters of
galaxies. To account for this discrepancy, cosmologists
(15) hypothesize that something else, which they call “dark
matter,” provides the gravitational force necessary to
make the huge structures cohere.
What is dark matter? Numerous exotic entities
have been postulated, but among the more attractive
(20) candidates—because they are known actually to
exist—are neutrinos, elementary particles created as a
by-product of nuclear fusion, radioactive decay, or
catastrophic collisions between other particles.
Neutrinos, which come in three types, are by far the
(25) most numerous kind of particle in the universe;
however, they have long been assumed to have no
mass. If so, that would disqualify them as dark matter.
Without mass, matter cannot exert gravitational force;
without such force, it cannot induce other matter to
(30) cohere.
But new evidence suggests that a neutrino does
have mass. This evidence came by way of research
findings supporting the existence of a long-theorized
but never observed phenomenon called oscillation,
(35) whereby each of the three neutrino types can change
into one of the others as it travels through space.
Researchers held that the transformation is possible
only if neutrinos also have mass. They obtained
experimental confirmation of the theory by generating
(40) one neutrino type and then finding evidence that it had
oscillated into the predicted neutrino type. In the
process, they were able to estimate the mass of a
neutrino at from 0.5 to 5 electron volts.
While slight, even the lowest estimate would yield
(45) a lot of mass given that neutrinos are so numerous,
especially considering that neutrinos were previously
assumed to have no mass. Still, even at the highest
estimate, neutrinos could only account for about
20 percent of the universe’s “missing” mass.
(50) Nevertheless, that is enough to alter our picture of the
universe even if it does not account for all of dark
matter. In fact, some cosmologists claim that this new
evidence offers the best theoretical solution yet to the
dark matter problem. If the evidence holds up, these
(55) cosmologists believe, it may add to our understanding
of the role elementary particles play in holding the
universe together.
1. Which one of the following most accurately expresses the main idea of the passage?(A) Although cosmologists believe that the universe is shaped by gravitation, the total amount of observable matter in the universe is greatly insufficient to account for the gravitation that would be required to cause the universe to be organized into galaxies.
(B) Given their inability to account for more than 20 percent of the universe’s “missing” mass, scientists are beginning to speculate that our current understanding of gravity is significantly mistaken.
(C) Indirect evidence suggesting that neutrinos have mass may allow neutrinos to account for up to 20 percent of dark matter, a finding that could someday be extended to a complete solution of the dark matter problem.
(D) After much speculation, researchers have discovered that neutrinos oscillate from one type into another as they travel through space, a phenomenon that proves that neutrinos have mass.
(E) Although it has been established that neutrinos have mass, such mass does not support the speculation of cosmologists that neutrinos constitute a portion of the universe’s “missing” mass.
2. Which one of the following titles most completely and accurately expresses the contents of the passage?(A) “The Existence of Dark Matter: Arguments For and Against”
(B) “Neutrinos and the Dark Matter Problem: A Partial Solution?”
(C) “Too Little, Too Late: Why Neutrinos Do Not Constitute Dark Matter”
(D) “The Role of Gravity: How Dark Matter Shapes Stars”
(E) “The Implications of Oscillation: Do
Neutrinos Really Have Mass?”
3. Based on the passage, the author most likely holds which one of the following views?(A) Observable matter constitutes at least 90 percent of the mass of the universe.
(B) Current theories are incapable of identifying the force that causes all particles in the universe to attract one another.
(C) The key to the problem of dark matter is determining the exact mass of a neutrino.
(D) It is unlikely that any force other than gravitation will be required to account for the organization of the universe into galaxies.
(E) Neutrinos probably account for most of the universe’s “missing” mass.
4. As described in the last paragraph of the passage, the cosmologists’ approach to solving the dark matter problem is most analogous to which one of the following?(A) A child seeking information about how to play chess consults a family member and so learns of a book that will instruct her in the game.
(B) A child seeking to earn money by delivering papers is unable to earn enough money for a bicycle and so decides to buy a skateboard instead.
(C) A child hoping to get a dog for his birthday is initially disappointed when his parents bring home a cat but eventually learns to love the animal.
(D) A child seeking money to attend a movie is given some of the money by one of his siblings and so decides to go to each of his other siblings to ask for additional money.
(E) A child enjoys playing sports with the neighborhood children but her parents insist that she cannot participate until she has completed her household chores.
5. The author’s attitude toward oscillation can most accurately be characterized as being(A) satisfied that it occurs and that it suggests that neutrinos have mass
(B) hopeful that it will be useful in discovering other forms of dark matter
(C) concerned that it is often misinterpreted to mean that neutrinos account for all of dark matter
(D) skeptical that it occurs until further research can be done
(E) convinced that it cannot occur outside an experimental setting
6. Which one of the following phrases could replace the word “cohere” at line 30 without substantively altering the author’s meaning?(A) exert gravitational force
(B) form galactic structures
(C) oscillate into another type of matter
(D) become significantly more massive
(E) fuse to produce new particles
7. The passage states each of the following EXCEPT:(A) There are more neutrinos in the universe than there are non-neutrinos.
(B) Observable matter cannot exert enough gravitational force to account for the present structure of the universe.
(C) Scientific experiments support the theory of neutrino oscillation.
(D) Neutrinos likely cannot account for all of the universe’s “missing” mass.
(E) Dark matter may account for a large portion of the universe’s gravitational force.