Since the inception of quantum mechanics, the many counter-intuitive

Question

Since the inception of quantum mechanics, the many counter-intuitive aspects and results of the theory have provoked strong philosophical debates and many interpretations. Even fundamental issues, such as Max Born's basic rules concerning probability amplitudes and probability distributions, took decades to be appreciated by society and many leading scientists. Indeed, the renowned physicist Richard Feynman once said, "I think I can safely say that nobody understands quantum mechanics."

The Copenhagen interpretation—due largely to the Danish theoretical physicist Niels Bohr—remains the quantum mechanical formalism that is currently most widely accepted amongst physicists, some 75 years after its enunciation in the first quarter of the 20th century. According to this interpretation, the probabilistic nature of quantum mechanics is not a temporary feature that will eventually be replaced by a deterministic theory, but instead must be considered a final renunciation of the classical idea of "causality". It is also believed therein that any well-defined application of the quantum mechanical formalism must always make reference to the experimental arrangement, due to the complementarity nature of evidence obtained under different experimental situations.

Albert Einstein, himself one of the founders of quantum theory, disliked this loss of determinism in measurement. Einstein held that there should be a local hidden variable theory (also known as the local realism idea) underlying quantum mechanics and, consequently, that the present theory was incomplete. He produced a series of objections to the theory, the most famous of which has become known as the Einstein-Podolsky-Rosen paradox. John Bell showed that this "EPR" paradox led to experimentally testable differences between quantum mechanics and local realistic theories. Experiments have been performed confirming the accuracy of quantum mechanics, thereby demonstrating that the physical world cannot be described by any local realistic theory. The Bohr-Einstein debates and the experiments that followed provide a vibrant critique of the Copenhagen Interpretation from an epistemological point of view.   1 
 1. According to the passage, Einstein’s position regarding determinism in quantum mechanics was ___________________.

(A) unverifiable
(B) incomplete
(C) promising
(D) incorrect
(E) unfounded

2 
 2. According to the passage, all of the following are true about the Copenhagen interpretation except:

(A) It puts an important emphasis on the experimental arrangement
(B) It redefines the interpretation of cause and effect
(C) It was critiqued by both Einstein and Bohr
(D) It is well regarded in the scientific community
(E) It is difficult to understand

3 
 3. Which of the following can be inferred about the local hidden variable theory?

(A) It replaced most components of quantum theory
(B) It was mostly in line with John Bell’s discoveries
(C) It was proven by the Einstein-Podolsky-Rosen parado
(D) It predicted more determinism in measurement than quantum theory
(E) It agreed mainly with the predictions of Niels Bohr

4 
 4. The primary purpose of the passage above is to:

(A) Show that Einstein was wrong about quantum mechanics
(B) Discuss an important debate on one of the most challenging scientific theories of the 20th century
(C) Highlight the importance of quantum mechanics in the field of physics
(D) Illustrate how perplexing quantum mechanics is for scientists
(E) Argue that the Copenhagen interpretation is correct

5 
 5. Which of the following can be inferred about the Copenhagen interpretation of quantum mechanics?

(A) It views the probabilistic nature of quantum mechanics as temporary.
(B) It involves some loss of determinism in measurement.
(C) It was widely accepted when it was enunciated 75 years ago.
(D) It views the experimental arrangement as unimportant.
(E) It rejected many of Albert Einstein’s views and theories.

6 
 6. According to the passage, it can be inferred that Albert Einstein believed all of the following EXCEPT:

(A) the local hidden variable theory was an essential component in a complete theory of quantum mechanics.
(B) Niels Bohr was incorrect in some part of his interpretation of quantum mechanics.
(C) the Copenhagen interpretation of quantum mechanics was incomplete.
(D) experimentally testable differences exist between quantum mechanics and local realistic theories.
(E) some components of the quantum mechanics theory were correct.

7 
 7. The passage suggests which of the following:

(A) Niels Bohr and Max Born would most likely agree on rules concerning probability amplitudes
(B) Richard Feynman and Albert Einstein would most likely disagree about the difficulties relating to quantum mechanics
(C) Niels Bohr and Albert Einstein would most likely disagree about most aspects of quantum mechanics
(D) John Bell and Albert Einstein would most likely disagree about quantum mechanics
(E) Albert Einstein and Niels Bohr would most likely disagree about determinism in measurement

HarishLearner · Answer

Q1 - Answer D.

Reasons:

Einstein did not accept the probabilistic nature of quantum mechanics. According to the Copenhagen interpretation (para 2) (line 4) "the probabilistic nature of quantum mechanics is not a temporary feature that will eventually be replaced by a deterministic theory, but instead must be considered a final renunciation of the classical idea of "causality".

But Einstein felt that - (para 3) "Albert Einstein, himself one of the founders of quantum theory, disliked this loss of determinism in measurement. Einstein held that there should be a local hidden variable theory (also known as the local realism idea) underlying quantum mechanics and, consequently, that the present theory was incomplete."

Same Para -3, Line 8 - "Experiments have been performed confirming the accuracy of quantum mechanics, thereby demonstrating that the physical world cannot be described by any local realistic theory."

Clearly the experiments have proved that Einstein was wrong in postulating a local hidden variable theory(aka local realism idea). So yes, Choice D - incorrect- is the correct answer.

------------------------------------

Choice A - unverifiable - is wrong because EPR paradox was verified by John Bell and it led to " testable differences between quantum mechanics and local realistic theories. "

Choice B - incomplete - is wrong, because nowhere is it stated or implied that his objections were incomplete. Rather they were proven wrong.

Choice C - promising - is wrong because Einstein was proven wrong. (Penultimate Sentence of the Last Para - "Experiments have been performed confirming the accuracy of quantum mechanics, thereby demonstrating that the physical world cannot be described by any local realistic theory."

Choice E - unfounded - is wrong because Einstein was proven wrong - Also we cannot say his objections were unfounded - there was some basis for his objections.

HarishLearner · Answer

Question - 2. Answer C.

Choice A - supported by Para 2, Last sentence - "It is also believed therein that any well-defined application of the quantum mechanical formalism must always make reference to the experimental arrangement, due to the complementarity nature of evidence obtained under different experimental situations."

Choice B - supported by Para 2, 2nd sentence - "According to this interpretation, the probabilistic nature of quantum mechanics is not a temporary feature that will eventually be replaced by a deterministic theory, but instead must be considered a final renunciation of the classical idea of "causality". "

Choice C - not supported - in fact Bohr and Einstein were opponents - so it is the correct answer.

Choice D - supported by Para 2, 1st sentence - "The Copenhagen interpretation - due largely to the Danish theoretical physicist Niels Bohr - remains the quantum mechanical formalism that is currently most widely accepted amongst physicists, some 75 years after its enunciation in the first quarter of the 20th century. "

Choice E - supported by Para 1, last sentence - "Indeed, the renowned physicist Richard Feynman once said, "I think I can safely say that nobody understands quantum mechanics."

HarishLearner · Answer

Q3 - Answer - D.

What is the local hidden variable theory and how was it born?

"According to this interpretation, the probabilistic nature of quantum mechanics is not a temporary feature that will eventually be replaced by a deterministic theory, but instead must be considered a final renunciation of the classical idea of "causality".

Einstein had difficulty in accepting the loss of determinism in quantum mechanics - "Albert Einstein, himself one of the founders of quantum theory, disliked this loss of determinism in measurement. Einstein held that there should be a local hidden variable theory (also known as the local realism idea) underlying quantum mechanics and, consequently, that the present theory was incomplete." Essentially, Einstein did not believe that probabilistic interpretation was a temporary feature, but held that there was a local hidden variable theory.

This this pits probabilistic nature and loss of determinism of QM against the local hidden variable theory, therefore, the implication is the local hidden variable theory or local realism will bring back the determinism. Hence Choice D is correct.

_____________________________________________

Choice A - is wrong because Hidden Variable Theory (HTV) was only supposed to put an end to (replace) the probabilistic nature of QM and not replace most components.

Choice B - is wrong because it is the exact opposite answer - It was  not  in line with John Bell's discoveries -"Experiments have been performed confirming the accuracy of quantum mechanics, thereby demonstrating that the physical world cannot be described by any local realistic theory."

Choice C - is wrong because it is the exact opposite answer - it was not proven by EPR Paradox - "John Bell showed that this "EPR" paradox led to experimentally testable differences between quantum mechanics and local realistic theories." - clearly proving that EPR Paradox did not get rid of probability of QM (which was the aim of HTV).

Choice E - is wrong because it is the exact opposite answer - "According to this interpretation, the probabilistic nature of quantum mechanics is not a temporary feature that will eventually be replaced by a deterministic theory....."

HarishLearner · Answer

Q.4 - Answer B.

I think this can be easily established by eliminating all others.

Its too much to say the primary purpose was to prove Einstein wrong, as he makes his appearance only in the last paragraph, and only as a contender of QM's probabilistic nature.Hence Choice A is wrong.

Choice C is wrong because no attempt is being made to highlight the importance of QM within the domain of physics.

Choice D is wrong because there is only quote by Richard Feynmann which talks about the perplexity of QM.

Choice E is wrong because no attempt is made to establish the correctness of Copenhagen Interpretation vis-a-vis other interpretations.

dcummins · Answer

I don't think Question 1's answer is right.

Einstein argued against the loss of determinism.
According to the passage, Einstein’s position regarding determinism in quantum mechanics was "Incorrect"

VeritasKarishma  the question should be reworded to "According to the passage, Einstein’s position regarding determinism  is that  quantum mechanics  absence of determinism  was "Incorrect"

It makes no logical sense to say "incorrect" - this can't be supported in the passage. For all we know Einstein was right.

The official explanation even contradicts the answer to the question. 
"In that paragraph, you learn that Einstein developed a local realism theory to object to a part of the quantum theory relating to determinism in measurement. Later in the paragraph, you learn that experiments showed the local realism theory was experimentally inconsistent with quantum mechanics. This implies that local realism theory was wrong. The correct answer is thus (D)."

So if local realism theory is wrong then Einstein is right.... lol, so how can he be "incorrect".

I think the question just needs to be better worded - thats the path of least resistance here.

Secondly, I think Question 2, answer choice E should be reworded to something else. The answer choice makes too much of a leap for a detail question. These are details the reader can support from the passage.

Here's the official explanation "Choice (E) takes a small inference in order to make sense. At the end of the first paragraph, the author references Richard Feynman, who stated that he thought that no one really understood quantum mechanics. Similarly, the author calls quantum mechanics “ counter-intuitive .” Since the Copenhagen interpretation is an interpretation of quantum mechanics, you can conclude that the author would feel the same way about the Copenhagen interpretation."

COUNTER-Intuitive does not mean no one understood it. Look at how counter-intuitive is used in the sentence. "Countintuitive aspects" of the theory implies the theory either went against some prevailing idea or the theory seemed impractical / not conducive to progression of Quantum mechanics.

The people in the passage are physicists - who else is going to care about the Copenhagen experiment? AND based on the passage the physicists clearly understand the copenhagen experiment since they were able to critique it. Even moreso, we are told "mains the quantum mechanical formalism that is currently most widely accepted amongst physicists" --> this completely goes against answer choice E.

Bottom-line, change answer choice E please... because it cannot be supported.

dcummins · Answer

OFFICIAL EXPLANATIONS 
 
 1. According to the passage, Einstein’s position regarding determinism in quantum mechanics was ___________________.
 
Solution: D

As with any specific question, the key to success in this question is to quickly consult your mental map of the passage to find where relevant information is contained and closely read that information. In this case, you are looking for information on Einstein and determinism in quantum mechanics – that should lead you to the third paragraph.

In that paragraph, you learn that Einstein developed a local realism theory to object to a part of the quantum theory relating to determinism in measurement. Later in the paragraph, you learn that experiments showed the local realism theory was experimentally inconsistent with quantum mechanics. This implies that local realism theory was wrong. The correct answer is thus (D).

For (A), his position was verified to be incorrect via experimentation, so you cannot say it was unverifiable. For (B), Einstein believed that the theory of quantum mechanics was incomplete. This word was not used to describe local determinism. (C) and (E) are both contradicted in the passage as Einstein’s view cannot be described as unfounded and promising if experiments later proved it to be wrong. The correct answer is (D).

2. According to the passage, all of the following are true about the Copenhagen interpretation EXCEPT:
 
Solution: C

For any except question, your job is to find specific information in the passage to either confirm or refute each answer choice. Since you are looking for information about the Copenhagen interpretation, you will mainly be looking in the second and third paragraphs for relevant information.
Choice (A) can be easily found in the text – the last sentence of the second paragraph states that any use of quantum mechanical formalism must make reference to the experimental arrangement. You can therefore eliminate choice (A).

Choice (B) can also be found in the text. In paragraph 2 it states that the Copenhagen interpretation involved a “renunciation of the classical idea of “causality”.” You can therefore also eliminate answer choice (B).

Choice (C) is correct: in the passage you learn that Bohr helped form the Copenhagen interpretation so he clearly agreed with it, whereas Einstein critiqued it, so he clearly did not. As a result (C) is correct as they did not both critique it.

Choice (D) also has evidence within the passage – since the Copenhagen interpretation is the most widely accepted view, it must be well regarded within the scientific community, so you can eliminate (D).

Choice (E) takes a small inference in order to make sense. At the end of the first paragraph, the author references Richard Feynman, who stated that he thought that no one really understood quantum mechanics. Similarly, the author calls quantum mechanics “counter-intuitive.” Since the Copenhagen interpretation is an interpretation of quantum mechanics, you can conclude that the author would feel the same way about the Copenhagen interpretation.

Choice (C) is correct.

3. Which of the following can be inferred about the local hidden variable theory?
 
Solution: D

Explanation: The local hidden variable theory is discussed in the third paragraph. Consider these sentences: “Albert Einstein, himself one of the founders of quantum theory, disliked this loss of determinism in measurement...(AND) held that there should be a local hidden variable theory (also known as the local realism idea)” From that you can conclude that the local hidden variable theory would have more determinism in measurement, as that was why it was devised. Answer is (D). For (A), the local variable theory only attacked one component of quantum theory not most. For (B), it was later learned to be incorrect based on John Bell’s work. The Einstein-Podolsky-Rosen paradox was used in an attempt to contradict quantum theory and never proved the local hidden variable theory. For (E) it disagreed with those predictions. Answer is (D).

5. Which of the following can be inferred about the Copenhagen interpretation of quantum mechanics?

The Copenhagen interpretation was primarily discussed in the 2nd paragraph (and in the 3rd) so you should focus your attention there.

(A) is contradicted in the second sentence of the second paragraph. It says that according to this interpretation the probabilistic nature is NOT temporary.

(B), the correct answer , requires that you leverage the first sentence of the 3rd paragraph in combination with the second paragraph. In that sentence you learn that “Albert Einstein...disliked this loss of determinism in measurement” in reference back to the Copenhagen interpretation. From that you know that the Copenhagen interpretation involved some loss of determinism.

For (C), you learn in the passage that it is widely accepted today, but you have no idea if that was the case 75 years ago.

(D), like (A), is directly contradicted in the 2nd paragraph – it states that the arrangement IS important.

For (E), you know that Albert Einstein did not like the loss of determinism in the Copenhagen interpretation, but you have no idea if the Copenhagen interpretation rejected MANY of his views and theories.

Correct answer is (B).

6. According to the passage, it can be inferred that Albert Einstein believed all of the following EXCEPT:

From your mental map of this passage, you should recognize that for this question, you need to look mostly in the last paragraph since that is the only place where Einstein is mentioned. As with any EXCEPT question, your job is to find evidence in the passage for or against each answer choice and carefully use process of elimination.

Choice (A) can be confirmed based on this sentence: “Einstein held that there should be a local hidden variable theory underlying quantum mechanics and, consequently, that the present theory was incomplete.” Since Einstein believed that without local hidden variable theory, quantum theory is incomplete, he must believe that it is essential to quantum theory. Because (A) is supported by the passage, it can be eliminated.

For (B), Einstein had issues with some part of the Copenhagen interpretation (he believes that it is incomplete), and therefore with the ideas of Bohr, one of its primary architects. The passage also references the “Bohr-Einstein debates” at the end of the last paragraph. From this you know Albert Einstein clashed about some part of theory and that Einstein believed that Bohr was incorrect about some portion of his interpretation. You can therefore eliminate choice (C).

(C) is fairly easy to prove as it is explicitly stated in the second sentence of the last paragraph and can be eliminated.

(D), the correct answer, is tricky. While it is discussed in the last paragraph, you do not know if Einstein believed it. It was John Bell who showed these experimentally testable differences and that those differences contradicted Einstein. However, the passage doesn’t mention whether Einstein accepted Bell’s work. Thus (D) is the one choice that you cannot conclude regarding Einstein’s beliefs.

For (E), since Einstein was one of the founders of quantum mechanics, you can be sure that he agreed with some of its components.

The correct answer is (D).

7. The passage suggests which of the following:

To answer this question, you must examine each agreement/disagreement in the answer choices and look for confirmation in the passage.

(E) is the only one that is guaranteed because  determinism in measurement  was the exact portion of the quantum theory that the two men disagreed upon.

For (A), no information is given about how Bohr feels about Born’s rules. Likewise in (B), no comparison is given between Feynman and Einstein.

(C) and (D) are both too strong as Bohr and Einstein almost surely do agree about many aspects (they were both involved in its development) but just disagree about determinism in measurement, and Bell and Einstein may or may not agree on quantum mechanics.

All you know is that Bell determined that it would be possible to see who is correct.

Answer is (E).

KarishmaB · Answer

Question 1 and answer are perfectly correct.

1. According to the passage, Einstein’s position regarding determinism in quantum mechanics was ___________________.

(A) unverifiable
(B) incomplete
(C) promising
(D) incorrect
(E) unfounded

Einstein's position -  "Einstein did not like loss of determinism. He held that there should be local realism idea underlying quantum mechanics (presumably brings in determinism) and, consequently, that the present theory was incomplete." 
Einstein's position was that there must be determinism (an LRT) underlying QM. His position was that QM is incomplete.

Later we learn in the passage:  "EPR" paradox led to experimentally testable differences between quantum mechanics and local realistic theories. Experiments have been performed confirming the accuracy of quantum mechanics, thereby demonstrating that the physical world cannot be described by any local realistic theory.

There were testable differences between QM and LRT. Experiments show that QM is accurate and no LRT can be accurate. 
Hence, experiments show that Einstein was wrong about LRT. So Einstein was wrong about determinism in QM.

KarishmaB · Answer

2. According to the passage, all of the following are true about the Copenhagen interpretation except:

(A) It puts an important emphasis on the experimental arrangement
(B) It redefines the interpretation of cause and effect
(C) It was critiqued by both Einstein and Bohr
(D) It is well regarded in the scientific community
(E) It is difficult to understand

You need to understand the passage in its entirety to get that (E) is well supported.

First paragraph says that nobody understand QM as per Richard Feynman. That QM has counter-intuitive aspects.

Paragraph 2 says that Copenhagen interpretation remains the quantum mechanical formalism that is currently most widely accepted. 
So what is QM? It is explained by the Copenhagen interpretation. As per Copenhagen interpretation, QM is probabilistic, not deterministic.

Paragraph 3 says that Einstein himself did not like the loss of determinism and was proved wrong. Loss of determinism must be one of the counter intuitive aspects of QM (which is the same as Copenhagen interpretation since it explains QM)

Then we can safely say that Copenhagen interpretation is difficult to understand.

Also, (C) is certainly wrong so the question and options are all fine. You are always looking for the best option.

dcummins · Answer

Hi  VeritasKarishma

"Experiments show that QM is accurate and no LRT can be accurate" is a bit of a stretch when we are only told that there are testable differences.
I don't think there is sufficient enough information in the passage to actually say Einstein was incorrect. Really. It's way too much of a stretch based on the info you brought to light.

dcummins · Answer

Hi  VeritasKarishma

I agree that (C) is incorrect. And yes I know we need to look for the best option. But the inferences and deductions you made in your explanation just can't be supported.

The logic in what you brought to light here isn't conclusive enough to say the people "don't understand" things.
Just because Einstein didn't like the loss of determinism doesn't mean the theory was difficult to understand.

To the contrary, we are explicitly told in this passage that the Copenhagen theory is the theory most regarded in the community - so logically if something is MOST regarded then MOST the people at least understand it, Otherwise how can people regard something with importance if they don't understand it.

KarishmaB · Answer

The argument very clearly states: Experiments have been performed confirming the accuracy of quantum mechanics, thereby demonstrating that the  physical world cannot be described by any local realistic theory .

You have to take premises to be true, even if you do not agree with them.

KarishmaB · Answer

dcummins

"A is difficult to understand" and "People do not understand A" are different things.

Richard Feynman said that no one understands QM (mentioned in the passage to show that QM is not easy to understand and not intuitive).

Option (E) ONLY SAYS that QM is hard to understand. People do not find it intuitive (depicted by Einstein example). Option (E) does not say that people do not understand QM.

dcummins · Answer

@veritasprepKarishma

But we are asked about the The Copenhagen interpretation specifically and what we know of that is it "remains the quantum mechanical formalism that is currently most widely accepted amongst physicists".

If the question asked what is true about "quantum mechanics" then E would make more sense.

I understand the the C Interpretation is a derivative of QM, but the only people who care about QM in general are the people mentioned in the passage.

Through POE one could get to E, but even then I don't think its an overly great question or answer.

KarishmaB · Answer

dcummins  - Quantum mechanics (QM) means nothing without Copenhagen interpretation (CI) since CI tells you what QM is. It explains what QM is - probabilistic behaviour of sub atomic particles (not deterministic). You can't separate one from the other. QM is difficult to understand because CI is difficult to understand.

I think we have spent enough time on this question.

0212 · Answer

Can anyone explain Q7? Why cant option C be the answer?

bM22 · Answer

Hi  0212 ,

Option C cannot be the correct answer as we cannot infer that Niels Bohr and Albert Einstein disagreed with  most aspects  of the quantum mechanics. They did not agree with the determinism in measurement in quantum mechanics, as can be inferred from the lines:

By Neil Bohr: "According to this interpretation,  the probabilistic nature of quantum mechanics is not a temporary feature that will eventually be replaced by a deterministic theory , but instead must be considered a final renunciation of the classical idea of "causality"."

and

"Albert Einstein, himself one of the founders of quantum theory,  disliked this loss of determinism in measurement ."

Thus option E can directly inferred from the passage.

Hope This Helps.
Thanks.

VerbalBot · Answer

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