*We know, however, that the universe must also contain what is called the dark matter, which we cannot observe directly. One piece of evidence comes from the spiral galaxies. These are enormous pancakeshaped collections of stars and gas. We observe that they are rotating about their centers, but the rate of rotation is so high that they would fly apart if they contained only the stars and gas that we observe directly. There must be some unseen form of gravitational attraction whose matter is great enough to hold the galaxies together as they rotate*.
Another piece of evidence for dark matter comes from clusters of galaxies. We observe that galaxies are not uniformly distributed throughout space; they are gathered together in clusters that range from a few galaxies to millions. Presumably these clusters are formed because the galaxies attract each other into groups. However, we can measure the speeds at which individual galaxies are moving in these clusters. *We find they are so high that the clusters would fly apart unless they were held together by gravitational attraction. The mass required is considerably greater than the masses of all the galaxies. It follows, therefore, that there must be extra dark matter present in clusters of galaxies.* So, the only way we can detect dark matter would be by its effect on bright matter.
The main candidates of dark matter would be remnants left over from the early stages of the universe. One possibility is elementary particles. There are several hypothetical candidates, particles which we think might exist but we haven’t actually detected them yet. But the most promising case is a particle for which we have good evidence, the neutrino. The neutrino was thought to have no mass of its own, but observations have suggested that the neutrino may have a small mass. *If this is confirmed and the mass of the neutrino is found to be of right value, neutrinos would provide enough mass to bring the density of the universe up to the critical value*.
Vocabulary Notes
1.to estimate – to calculate
2.to add up – if you add up several numbers, you calculate their total
3.to add in – if you add in something, you include it as a part of something else
4.the total – the number that you get when you add a series of figures together
5. enormous – very large
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6.presumably – most probably
7.to require – to need
8.extra – additional
9.a remnant – a small part that was left of what was destroyed
10.promising – perspective
11.to confirm – to prove
POST-READING TASK
(To be done at home in writing)
\
I. Put in the prepositions.
1.We can try to estimate the average density … the universe … observations.
2.One piece … evidence … dark matter comes …the spiral galaxies.
3.These are enormous pan-shaped collections … stars and gas.
4.They are rotating … the centers.
5.Another piece … evidence … dark matter comes … clusters of galaxies.
6.Galaxies are not uniformly distributed … space.
7.Clusters … galaxies range … a few galaxies … millions.
8.We can measure the speed … which the individual galaxies are moving.
II. Study grammar point IV and do an exercise. Change the sentences according to the model:
S + (is believed; is supposed; is expected; is considered; is known; is proved) + to V
1.The universe must contain some matter which we cannot observe directly.
2.One piece of evidence comes from spiral galaxies.
3.Spiral galaxies are enormous pancake-shaped collections of stars and gas.
4.Another piece of evidence for dark matter comes from clusters of galaxies.
5.The speeds at which individual galaxies are moving are so high that the clusters would fly apart unless they were held together by gravitational attraction.
6.The mass required is considerably greater than the masses of all the galaxies.
7.The main candidates of dark matter are elementary particles.
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8. The neutrino is the most promising candidate.
III. A paragraph is a micro text. Cut down each paragraph of the passage to the topical sentence and write a summary.
IV. Do you have any information about dark matter which is not given in the passage? Write a paragraph.
CLASS EXERCISES
Exercise 1 (do it yourself)
Make up simple sentences using the below words and expressions. Follow the passage.
1.to contain dark matter
2.to observe dark matter directly
3.an enormous pan-shaped collection of stars and gas
4.to rotate about its centre
5.to be uniformly distributed throughout space
6.to be gathered together in clusters
7.to range from to
8.to detect dark matter
9.to suggest
10.to bring up to
Exercise 2
a.Formulate questions to the sentences you made up in exercise 1.
b.In groups ask the formulated questions and give answers.
Exercise 3 (in groups) Sharing ideas
1 How can we estimate the average density of the universe?
2.Where do the pieces of evidence of dark matter come from?
3.What is a spiral galaxy?
4.How do astronomers account for the fact that the spiral galaxies do not fall apart as they rotate?
5.How are galaxies distributed throughout space?
6.How many galaxies are there in a cluster?
7.What mechanism collects stars in clusters?
8.At what speed are individual galaxies moving in these clusters?
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9.Why do the clusters not fall apart?
10.What is the proportion between the mass of all the galaxies and the mass required for the galaxies to form clusters?
11.Why do astronomers call extra matter ‘dark matter’?
UNIT 4
BLACK HOLES
“Turn to Stephen Hawking if you would look outward, to the ends of the universe”
Independent on Sunday
PRE-READING TASK Study some grammar points.
I. N + to V; N + to be V3
An infinitive after a noun characterizes it and expresses an action which must be done or could be done in the future.
Study the sentences.
1.The universe is a puzzle to be guessed.
2.This is a much more difficult question to answer.
3.Because my father was a scientific researcher, I felt that scientific research was a natural thing to do when one grew up.
II. Active and Passive
A verb has two categories: tense (past, present and future) and voice
(active and passive). There are two infinitives: active to V and passive to be + V3.
On the basis of an active infinitive we form active sentences and use active when it is important who or what does the action.
On the basis of a passive infinitive we form passive sentences and prefer passive when it is not important who or what does the action.
In passive sentences we use be (is, are, was, were, has been, will be, etc) + V3.
Study the sentences.
1. In the 1930s quantum mechanics was applied with great success to systems such as atoms or molecules, which have only a finite number of degrees of freedom.
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2.The problem has been overcome.
3.The interactions are divided into four categories and are represented by integer-spin fields.
Note: In passive sentences modal verbs are followed by be + V3
Study the sentences.
1.I want to discuss the possibility that the goal of theoretical physics might be achieved in the not-too-distant future.
2.The values of these quantities cannot be predicted by our theories. Instead, they have to be chosen to agree with observations.
III. Would
a. Would is used to talk about the natural course and behavior of things and events as a result of some action. It is the less definite form of
will.
Study the sentence.
If the electrons are in orbit around the nucleus, electromagnetic waves would carry away energy and would cause the electrons to spiral into the nucleus.
b. We also use would, if we imagine the situation. We can also use could = would be able to
Study the sentence.
In this state the electron couldn’t radiate energy in the form of electromagnetic waves because there would be no lower energy state.
IV. We use that (those) to refer to a thing (things) that has been mentioned before.
Study the sentences.
1.The key physical properties of Mars are remarkably similar to those of Earth.
2.The Mar’s axis is tilted to a similar degree as that of Earth.
3.The difference between the classical physics and the modern one is that between logical and illogical physics.
Give Russian correspondence:
as (in the process), an effect (an action), to have an effect on (to influence something), eventually (finally), about (approximately), both ….. and, then (in this case), according to, until, a few (some, several), so (thus, therefore, hence), fails to V (is unable to V)
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