Physics: Quantum Theory and Relativity

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Quantum Theory and Relativity :: Quantum Theory and RelativityDuring the early decades of the 20th century, the field of theoretical physics was revolutionized by some startling new discoveries. These discoveries-quantum theory and relativity-had profound implications for our understanding of the universe and for the development of new technology. Quantum theory is concerned with the absorption and emission of energy by matter, and with the wavelike motion of matter.

This area of physics was developed by several scientists over a period of about thirty years, beginning at the start of the 20th century. Before the development of quantum theory, physicists had believed that energy could be absorbed or emitted in any amount, and that matter occupied a definite location in space. However, quantum theory showed that these conceptions were inaccurate. According to quantum theory, energy can only be absorbed or emitted in certain, discrete amounts, which are called quanta.

It is as if energy is transported in small “packets” that only exist in particular sizes. This finding can be seen in the frequencies of light and other radiation that are emitted by different kinds of atoms. Each atom only emits radiation having certain frequencies. These frequencies correspond to the amounts of energy that are released when the electrons that orbit around the nucleus of an atom move from a higher orbital path to a lower orbital path.

Another astonishing feature of quantum theory is that matter can exist both as a particle and as a wave. Experiments have shown that the electrons of an atom can behave as waves; for example, electrons can diffract, or bend, in the same way that light waves bend. One surprising implication of this wavelike property is that the precise location of a particle cannot be known with certainty. The other major discovery of the early 20th century physics was the theory of relativity.

Unlike quantum theory, relativity was largely the work of one man, a physicist named Albert Einstein. Einstein demonstrated that the speed of light is constant, regardless of the motion of the observer. Einstein showed that, contrary to the assumptions of classical physics, time and motion are not constant, but relative to the observer. If a spaceship could move at an extremely high speed, time would pass considerably more slowly on that spaceship than for people who stayed on the earth. Moreover, the spaceship will appear to become shorter as its speed increases, and the mass of the spaceship would increase as its speed increased.

One of the bewildering ideas from Einstein’s theory of relativity is the notion that time can be added to the three dimensions of space-length, width, and height-as a fourth dimension. According to the theory of relativity, massive objects cause a distortion, or warping, of this four-dimensional space-time continuum.

But because the speed of light is constant, light will follow a straight line through space-time, and its motion will appear to be warped as it moves through space that is distorted by massive objects such as stars or planets. Another astonishing implication of the theory of relativity is that matter and energy are interchangeable.

This is the basis for Einstein’s famous formula, E = mc2, which states that energy equals mass times the speed of light squared. This idea is the basis for atomic energy, which allows for the release of energy by destroying a small amount of matter when the nucleus of an atom is divided, or split.

Today, thanks to the efforts of Einstein and the other physicists of the early 20th century, the study of theoretical physics is based largely on the ideas of quantum theory and relativity. Also, much of our modern technology-from electronics to nuclear power-is based on the ideas that were developed during this exciting period in the history of science.


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Einstein’s theory of the universe based on the principle that all movement is relative and that time is a fourth dimension related to space

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the relationship in physics between time, space, and movement according to Einstein’s theory


source 1
very great; felt or experienced very strongly
profound changes in the earth’s climate
My father’s death had a profound effect on us all.
The news came as a profound shock.
The report has profound implications for schools.
Her sense of disappointment was profound.

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having a strong influence or effect
profound effect/influence/impact/consequence etc Tolstoy’s experiences of war had a profound effect on his work.
The mother’s behaviour has a profound impact on the developing child.
profound changes in society


source 1
the process of a liquid, gas or other substance being taken in
Vitamin D is necessary to aid the absorption of calcium from food.

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a process in which something takes in liquid, gas, or heat
absorption of
the body’s absorption of iron

emission source 1
the production or sending out of light, heat, gas, etc
the emission of carbon dioxide into the atmosphere
emission controls

source 2
a gas or other substance that is sent into the air:
Britain agreed to cut emissions of nitrogen oxide from power stations.


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physical substance in general that everything in the world consists of; not mind or spirit
to study the properties of matter

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the material that everything in the universe is made of, including solids, liquids, and gases:
particles of matter

definitesure or certain; unlikely to change
Can you give me a definite answer by tomorrow?
Is it definite that he’s leaving?
I’ve heard rumours, but nothing definite.
a definite offer of a job
I’m not sure—I can find out for definite if you like.
That’s definite then, is it?
They have very definite ideas on how to bring up children.


source 1
emit something (formal)
to send out something such as light, heat, sound, gas, etc
The metal container began to emit a clicking sound.
Sulphur gases were emitted by the volcano.

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to send out gas, heat, light, sound etc:
The kettle emitted a shrill whistle.

conceptionsource 1
an understanding or a belief of what something is or what something should be
Marx’s conception of social justice
He has no conception of how difficult life is if you’re unemployed.

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an idea about what something is like, or a general understanding of something [↪ concept]
conception of the conception of parliamentary democracy
changing conceptions of the world
have (no) conception of something They have no conception of what women really feel and want.

inaccuratesource 1
not exact or accurate; with mistakes
an inaccurate statement
inaccurate information
All the maps we had were wildly inaccurate.
Statistical graphs may be inaccurate and misleading.
Opposite: accurate

Usage note: mistakeerror inaccuracy slip howler misprint
These are all words for a word, figure or fact that is not said, written down or typed correctly.
mistake a word or figure that is not said or written down correctly: It’s a common mistake among learners of English. spelling mistakes
error (rather formal) a word, figure, etc. that is not said or written down correctly: There are too many errors in your work.
 Error is a more formal way of saying mistake.
inaccuracy (rather formal) a piece of information that is not exactly correct: The article is full of inaccuracies.
slip a small mistake, usually made by being careless or not paying attention
howler (informal, especially British English) a stupid mistake, especially in what somebody says or writes: The report is full of howlers.
 A howler is usually an embarrassing mistake which shows that the person who made it does not know something that they really should know.
misprint a small mistake in a printed text
a(n) mistake/error/inaccuracy/slip/howler/misprint in something
to make a(n) mistake/error/slip/howler
to contain/be full of mistakes/errors/inaccuracies/howlers/misprints

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not completely correct [≠ accurate]:
A lot of what has been written about him is inaccurate.
inaccurate information/data etc
He was fined $300,000 for making inaccurate statements to Congress.


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independent of other things of the same type
Synonym: separate
The organisms can be divided into discrete categories.

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clearly separate:
The change happens in a series of discrete steps.


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the rate at which a sound or electromagnetic wave vibrates (= moves up and down)
a high/low frequency

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the number of radio waves, sound waves etc that pass any point per second:
This station broadcasts on three different frequencies.
high/low frequency Dolphins produce a high frequency sound.
the frequency range of the human ear


source 1
a line along which somebody/something moves; the space in front of somebody/something as they move
Synonym: way
He threw himself into the path of an oncoming vehicle.
The avalanche forced its way down the mountain, crushing everything in its path.
Three men blocked her path.

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the direction or line along which something or someone is moving
in something’s/somebody’s path The tornado destroyed everything in its path.
into the path of something She walked into the path of an oncoming vehicle.


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very surprising; difficult to believe
Synonym: amazing
She ran 100m in an astonishing 10.6 seconds.
I find it absolutely astonishing that you didn’t like it.

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so surprising that it is difficult to believe [= amazing]:
an astonishing decision
their astonishing success

WORD FOCUS: surprising very surprising: amazing, extraordinary, astonishing, astounding, staggering, startling

diffractsource 1
diffract something (physics)
to break up a stream of light into a series of dark and light bands or into the different colours of the spectrum

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to bend light or sound waves as they pass around something or through a hole [↪ refract]


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clear and accurate
Synonym: exact
precise details/instructions/measurements
Can you give a more precise definition of the word?
I can be reasonably precise about the time of the incident.

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precise information, details etc are exact, clear, and correct [= exact]:
precise sales figures
It was difficult to get precise information.
‘She’s a lot older than you, isn’t she?’ ‘Fifteen years, to be precise.’


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to show something clearly by giving proof or evidence
demonstrate that… These results demonstrate convincingly that our campaign is working.
demonstrate something (to somebody) Let me demonstrate to you some of the difficulties we are facing.
demonstrate how, what, etc… His sudden departure had demonstrated how unreliable he was.
demonstrate somebody/something to be something
The theories were demonstrated to be false.
it is demonstrated that… It has been demonstrated that this drug is effective.

Usage note: evidenceGiving proof
There is clear evidence that TV advertising influences what children buy.
It is clear from numerous studies that TV advertising influences what children buy.
Recent research demonstrates that TV advertising influences children’s spending habits.
Many parents think that TV advertising influences their children. This view is supported by the findings of a recent study, which show a clear link between television advertisements and children’s spending habits.
The findings also reveal that most children are unaware of the persuasive purpose of advertising.
There is little evidence that children understand the persuasive intent of advertising.
The results contradict claims that advertising is unrelated to children’s spending habits.
Manufacturers argue that it is difficult to prove that advertising alone influences what children buy.

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to show or prove something clearly:
The study demonstrates the link between poverty and malnutrition.
demonstrate that Hitchcock’s films demonstrate that a British filmmaker could learn from Hollywood.
demonstrate how/what/why etc This section will attempt to demonstrate how the Bank of England operates.
The government now has an opportunity to demonstrate its commitment to reform.


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that does not change
Synonym: fixed
travelling at a constant speed of 50 m.p.h.
Ross was his most constant and loyal friend.

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happening regularly or all the time:
There was a constant stream of visitors to the house.
Amy lived in constant fear of being attacked.
He kept in constant contact with his family while he was in Australia.


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a belief or feeling that something is true or that something will happen, although there is no proof
an underlying/implicit assumptionWe need to challenge some of the basic assumptions of Western philosophy.
We are working on the assumption that everyone invited will turn up.
It was impossible to make assumptions about people’s reactions.
His actions were based on a false assumption.
She arrived at college with a whole set of assumptions inherited from her family.

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something that you think is true although you have no definite proof
assumption that A lot of people make the assumption that poverty only exists in the Third World.
My calculations were based on the assumption that house prices would remain steady.
We are working on the assumption that the conference will take place as planned.
assumption about People make a lot of assumptions about me.
underlying assumption (=a belief that is used as the basis for an idea, but which may not be correct)


source 1
contrary to something different from something; against something
Contrary to popular belief, many cats dislike milk.
The government has decided that the publication of the report would be ‘contrary to the public interest’.
Contrary to expectations and the weather forecast, we had a fine day for the experiment.

source 2
contrary ideas, opinions, or actions are completely different and opposed to each other:
Two contrary views emerged.
The men shouted contrary orders.
contrary to The government’s actions are contrary to the public interest


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making you feel confused because there are too many things to choose from or because something is difficult to understand
Synonym: confusing
a bewildering array/range
There is a bewildering variety of software available.

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confusing, especially because there are too many choices or things happening at the same time
a bewildering variety/array/range a bewildering variety of choices

notion source 1
an idea, a belief or an understanding of something
notion (of something) a political system based on the notions of equality and liberty
She had only a vague notion of what might happen.
He has no notion of the difficulty of the problem.
notion (that…) I have to reject the notion that greed can be a good thing.

source 2
an idea, belief, or opinion
notion of misguided notions of male superiority
The traditional notion of marriage goes back thousands of years.
She had only a vague notion of what she wanted to do.
notion that the notion that human beings are basically good
She had no notion what he meant.
accept/challenge/reject etc a notion They reject the notion of group guilt.


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a measurement in space, for example the height, width or length of something
We measured the dimensions of the kitchen.
computer design tools that work in three dimensions

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the length, height, width, depth, or diameter of something:
a rectangle with the dimensions 5cm x 2cm
dimension of We’ll need to know the exact dimensions of the room.


to change the shape, appearance or sound of something so that it is strange or not clear
a fairground mirror that distorts your shape
The loudspeaker seemed to distort his voice.

warpsource 1
to become, or make something become, twisted or bent out of its natural shape, for example because it has become too hot, too damp, etc
The window frames had begun to warp.

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if something warps, or if heat or cold warps it, it becomes bent or twisted, and loses its original shape:
The door must be warped. It won’t close properly.


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a series of similar items in which each is almost the same as the ones next to it but the last is very different from the first
Synonym: cline
It is impossible to say at what point along the continuum a dialect becomes a separate language.

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a scale of related things on which each one is only slightly different from the one before:
The Creole language is really various dialects arranged on a continuum.
All the organisms in an ecosystem are part of an evolutionary continuum.

to multiply a number by itself

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the part of an atom that contains most of its mass and that carries a positive electric charge

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the central part of an atom, made up of neutrons, protons, and other elementary particles


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to divide, or to make something divide, into two or more parts
split something (into something) She split the class into groups of four.
split (into something) The results split neatly into two groups.
Slate splits easily into thin sheets

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also split up [intransitive and transitive] to divide or separate something into different parts or groups, or to be divided into different parts or groups
split into Can you split into groups of three now?
split something into something
The book is split into six sections.