It is currently 26 May 2019, 11:05
My Tests

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Classical physics defines the vacuum as a state of absence:

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
1 KUDOS received
Founder
Founder
User avatar
Joined: 18 Apr 2015
Posts: 6647
Followers: 107

Kudos [?]: 1275 [1] , given: 6017

CAT Tests
Classical physics defines the vacuum as a state of absence: [#permalink] New post 12 Jan 2019, 07:24
1
This post received
KUDOS
Expert's post
00:00

Question Stats:

99% (08:24) correct 0% (00:00) wrong based on 7 sessions
Classical physics defines the vacuum as a state of absence: a vacuum is said to exist in a region of space if there is nothing in it. In the quantum field theories that describe the physics of elementary particles, the vacuum becomes somewhat more complicated. Even in empty space, particles can appear spontaneously as a result of fluctuations of the vacuum. For example, an electron and a positron, or antielectron, can be created out of the void. Particles created in this way have only a fleeting existence; they are annihilated almost as soon as they appear, and their presence can never be detected directly. They are called virtual particles in order to distinguish them from real particles, whose lifetimes are not constrained in the same way, and which can be detected. Thus it is still possible to define the vacuum as a space that has no real particles in it.

One might expect that the vacuum would always be the state of lowest possible energy for a given region of space. If an area is initially empty and a real particle is put into it, the total energy, it seems, should be raised by at least the energy equivalent of the mass of the added particle. A surprising result of some recent theoretical investigations is that this assumption is not invariably true. There are conditions under which the introduction of a real particle of finite mass into an empty region of space can reduce the total energy. If the reduction in energy is great enough, an electron and a positron will be spontaneously created. Under these conditions the electron and positron are not a result of vacuum fluctua-tions but are real particles, which exist indefinitely and can be detected. In other words, under these conditions the vacuum is an unstable state and can decay into a state of lower energy; i.e., one in which real particles are created.

The essential condition for the decay of the vacuum is the presence of an intense electric field. As a result of the decay of the vacuum, the space permeated by such a field can be said to acquire an electric charge, and it can be called a charged vacuum. The particles that materialize in the space make the charge manifest. An electric field of sufficient intensity to create a charged vacuum is likely to be found in only one place: in the immediate vicinity of a superheavy atomic nucleus, one with about twice as many protons as the heaviest natural nuclei known. A nucleus that large cannot be stable, but it might be possible to assemble one next to a vacuum for long enough to observe the decay of the vacuum. Experi-ments attempting to achieve this are now under way.
17. Which of the following titles best describes the passage as a whole?

(A) The Vacuum: Its Fluctuations and Decay
(B) The Vacuum: Its Creation and Instability
(C) The Vacuum: A State of Absence
(D) Particles That Materialize in the Vacuum
(E) Classical Physics and the Vacuum

[Reveal] Spoiler: OA
A


18. According to the passage, the assumption that the introduction of a real particle into a vacuum raises the total energy of that region of space has been cast into doubt by which of the following?

(A) Findings from laboratory experiments
(B) Findings from observational field experiments
(C) Accidental observations made during other experiments
(D) Discovery of several erroneous propositions is accepted theories
(E) Predictions based on theoretical' work

[Reveal] Spoiler: OA
E


19. It can be inferred from the passage that scientists are currently making efforts to observe which of the following events?

(A) The decay of a vacuum in the presence of virtual particles
(B) The decay of a vacuum next to a superheavy atomic nucleus
(C) The creation of a superheavy atomic nucleus next to an intense electric field
(D) The creation of a virtual electron and a virtual positron as a result of fluctuations of a vacuum
(E) The creation of a charged vacuum in which only real electrons can be created in the vacuum's region of space

[Reveal] Spoiler: OA
B


20. Physicists' recent investigations of the decay of the vacuum, as described in the passage, most closely resemble which of the following hypothetical events in other disciplines?

(A) On the basis of data gathered in a carefully controlled laboratory experiment, a chemist predicts and then demonstrates the physical properties of a newly synthesized polymer.
(B) On the basis of manipulations of macroeconomic theory, an economist predicts that, contrary to accepted economic theory, inflation and unemployment will both decline under conditions of rapid economic growth.
(C) On the basis of a rereading of the texts of Jane Austen's novels, a literary critic suggests that, contrary to accepted literary interpretations, Austen's plots were actually metaphors for political events in early nineteenth-century England.
(D) On the basis of data gathered in carefully planned observations of several species of birds, a biologist proposes a modification in the accepted theory of interspecies competition.
(E) On the basis of a study of observations incidentally recorded in ethnographers' descriptions of non-Western societies, an anthropologist proposes a new theory of kinship relations.

[Reveal] Spoiler: OA
B


21. According to the passage, the author considers the reduction of energy in an empty region of space to which a real particle has been added to be

(A) a well-known process
(B) a frequent occurrence
(C) a fleeting aberration
(D) an unimportant event
(E) an unexpected outcome

[Reveal] Spoiler: OA
E


22. According to the passage, virtual particles differ from real particles in which of the following ways?

I. Virtual particles have extremely short lifetimes.
II. Virtual particles are created in an intense electric field.
III. Virtual particles cannot be detected directly.

(A) I only
(B) II only
(C) Ill only
(D) I and II only
(E) I and III only

[Reveal] Spoiler: OA
E



23. The author's assertions concerning the conditions that lead to the decay of the vacuum would be most weakened if which of the following occurred?

(A) Scientists created an electric field next to a vacuum, but found that the electric field was not intense enough to create a charged vacuum.
(B) Scientists assembled a superheavy atomic nucleus next to a vacuum, but found that no virtual particles were created in the vacuum's region of space.
(C) Scientists assembled a superheavy atomic nucleus next to a vacuum, but found that they could not then detect any real particles in the vacuum's region of space.
(D) Scientists introduced a virtual electron and a virtual positron into a vacuum's region of space, but found that the vacuum did not then fluctuate.
(E) Scientists introduced a real electron and a real positron into a vacuum's region of space, but found that the total energy of the space increased by the energy equivalent of the mass of the particles.


[Reveal] Spoiler: OA
C


_________________

Get the 2 FREE GREPrepclub Tests

Moderator
Moderator
User avatar
Joined: 22 Oct 2018
Posts: 43
Followers: 5

Kudos [?]: 45 [0], given: 5

CAT Tests
Re: Classical physics defines the vacuum as a state of absence: [#permalink] New post 13 Jan 2019, 22:10

+1 kudos to the posts containing answer explanations of all questions

4 KUDOS received
Intern
Intern
User avatar
Joined: 30 Jan 2019
Posts: 5
Followers: 0

Kudos [?]: 15 [4] , given: 0

Re: Classical physics defines the vacuum as a state of absence: [#permalink] New post 08 Mar 2019, 22:57
4
This post received
KUDOS
4 mins 57 secs... all correct! Wohooo :cool: The kind of passage that I like...straightforward and well written with some information to learn at the end of it. :-)

Classical physics defines a vacuum as an absence of stuff. But quantum field theories define it in more complicated terms. In normal vacuum some particles are created and they disintegrate really fast (so much so that we cannot even observe them!) this is still vacuum but not as defined by classical phy. So now vacuum is anything without "real" particles.

Suddenly, the passage starts talking about the energy of vacuum and states we ought to assume it to have the lowest possible energy. Goes on to add when a normal particle is added to vacuum its energy rises and these fluctuations ( electron-positron created and then destroyed) however, A surprising result of some recent theoretical investigations says that sometimes when particle added - energy reduces! This is said to happen when vacuum is permeated by a strong electric field and in such cases, electron-positron are created but this time they do not self-destruct and hence are real.

Finally, passage talks about how this "theoretical" finding can possibly be tested. If vacuum was next to an atomic nucleus with twice the protons than currently found in nature and reveals that experiments are being carried out to conduct such an experiment.


Really weird question if you do not understand the main point - vacuum is being discussed with two aspects in mind - normal vacuum (with its fluctuations) and special vacuum decay by being next to nucleus and possible theory being confirmed by experiment
Which of the following titles best describes the passage as a whole?
(A) The Vacuum: Its Fluctuations and Decay Crystal clear choice among the given options
(B) The Vacuum: Its Creation and Instability No, the creation of vacuum is out of scope.
(C) The Vacuum: A State of Absence TRAP? only the first line could lead to this one but does not summarize the passage well
(D) Particles That Materialize in the Vacuum too detailed to be the title
(E) Classical Physics and the Vacuum TRAP - even though this is the start - we are talking about other things throughout the passage

Cleverly worded detail question
According to the passage, the assumption that the introduction of a real particle into a vacuum raises the total energy of that region of space has been cast into doubt by which of the following?
(A) Findings from laboratory experiments Nope, the finding is based on theory and we are trying to conduct experiments to verify it.
(B) Findings from observational field experiments Discard for same as above
(C) Accidental observations made during other experiments Again, no observations.
(D) Discovery of several erroneous propositions is accepted theories Again, no discoveries from erroneous propositions - not mentioned.
(E) Predictions based on theoretical' work Perfect - verbatim from the passage

Options on this one are tricky because they have two parts - charged vacuum and particles - we need to be clear that a charged vacuum "decays" and creates "real" particles
It can be inferred from the passage that scientists are currently making efforts to observe which of the following events?
(A) The decay of a vacuum in the presence of virtual particles Nope - decay is in the presence of a charge and results in real particles
(B) The decay of a vacuum next to a superheavy atomic nucleus Right - even though this has less info than the other options this is correct
(C) The creation of a superheavy atomic nucleus next to an intense electric field 180 opposite choice - we are not creating the atomic nucleus ( even if we are that is not the point, it is only a means to an end)
(D) The creation of a virtual electron and a virtual positron as a result of fluctuations of a vacuum similar to option one
(E) The creation of a charged vacuum in which only real electrons can be created in the vacuum's region of space MAJOR TRAP - a lot of words that we are looking for but again not the crux of what is happening in the experiment - we are doing the experiment for "decay of vacuum"

We are looking for the following structure: Theoretical finding -> possible in real-world -> requires some experiment to possibly confirm it
Physicists' recent investigations of the decay of the vacuum, as described in the passage, most closely resemble which of the following hypothetical events in other disciplines?
(A) On the basis of data gathered in a carefully controlled laboratory experiment, a chemist predicts and then demonstrates the physical properties of a newly synthesized polymer. Again , data gathered first is reverse of what we are trying to do.
(B) On the basis of manipulations of macroeconomic theory, an economist predicts that, contrary to accepted economic theory, inflation and unemployment will both decline under conditions of rapid economic growth. The first few words are a giveaway and the rest of the option confirms. Still, we need to look at other options and rule them out
(C) On the basis of a rereading of the texts of Jane Austen's novels, a literary critic suggests that, contrary to accepted literary interpretations, Austen's plots were actually metaphors for political events in early nineteenth-century England. Rereading of texts is not a theoretical finding - discard.
(D) On the basis of data gathered in carefully planned observations of several species of birds, a biologist proposes a modification in the accepted theory of interspecies competition. Data gathered first - discard fast :-)
(E) On the basis of a study of observations incidentally recorded in ethnographers' descriptions of non-Western societies, an anthropologist proposes a new theory of kinship relations. Discard fast for same reason as above.

finally a straightforward question from the passage
According to the passage, the author considers the reduction of energy in an empty region of space to which a real particle has been added to be

(A) a well-known process not at all. 180 opposite
(B) a frequent occurrence same as above
(C) a fleeting aberration fleeting word is TRAP - the real particles created are long lasting - abberation again is clumsy - it is surprising find.
(D) an unimportant event then why would we discuss it? Not mentioned so discard.
(E) an unexpected outcome Perfect - infact this is verbatim from the passage ( marked in purple above)

Easy-cheesy detail question :-)
According to the passage, virtual particles differ from real particles in which of the following ways?

I. Virtual particles have extremely short lifetimes. CORRECT
II. Virtual particles are created in an intense electric field. OPPOSITE
III. Virtual particles cannot be detected directly. CORRECT

(A) I only
(B) II only
(C) Ill only
(D) I and II only
(E) I and III only Tick.

Start your critical reasoning engine - we want to look out for anything that goes against the theory mentioned
The author's assertions concerning the conditions that lead to the decay of the vacuum would be most weakened if which of the following occurred?
(A) Scientists created an electric field next to a vacuum, but found that the electric field was not intense enough to create a charged vacuum. Not against the theory - discard
(B) Scientists assembled a superheavy atomic nucleus next to a vacuum, but found that no virtual particles were created in the vacuum's region of space. TRAP - we are not looking for virtual particles at all - but for real ones. Discard.
(C) Scientists assembled a superheavy atomic nucleus next to a vacuum, but found that they could not then detect any real particles in the vacuum's region of space. PERFECT - a needle in a haystack - need to stay focussed and look out for what we know about the theory and then negate it.
(D) Scientists introduced a virtual electron and a virtual positron into a vacuum's region of space, but found that the vacuum did not then fluctuate. Opposite of what makes up the experiment. Discard.
(E) Scientists introduced a real electron and a real positron into a vacuum's region of space, but found that the total energy of the space increased by the energy equivalent of the mass of the particles. Discard for same reason as above!

Phew! That was one long post. Hope the explanations are helpful. :-)
_________________

Regards,
Gladi



“Do. Or do not. There is no try.” - Yoda (The Empire Strikes Back)

Re: Classical physics defines the vacuum as a state of absence:   [#permalink] 08 Mar 2019, 22:57
Display posts from previous: Sort by

Classical physics defines the vacuum as a state of absence:

  Question banks Downloads My Bookmarks Reviews Important topics  


GRE Prep Club Forum Home| About| Terms and Conditions and Privacy Policy| GRE Prep Club Rules| Contact

Powered by phpBB © phpBB Group

Kindly note that the GRE® test is a registered trademark of the Educational Testing Service®, and this site has neither been reviewed nor endorsed by ETS®.