CAT 2021

Slot 3

VARC

Question & Solution

A: We cannot infer that the 'arrow of time' has not been tested for atomic clocks. Option A can be eliminated.

B: It has been given in the Option that since quantum computers place more emphasis on their clock's accuracy, they would produce more heat.

The researchers found that as they increased the clock’s accuracy, the heat produced in the system grew, increasing the entropy of its surroundings by jostling nearby particles...

The passage supports this inference. B is the answer.

C: The relationship that the researchers found is a limit on the accuracy of a clock, so it doesn’t mean that a clock that creates the most possible entropy would be maximally accurate - hence a large, inefficient grandfather clock isn’t more precise than an atomic clock.

The passage gives a specific example of an inefficient grandfather clock. We cannot infer whether all grandfather clocks are efficient or not.

D: The clock consists of a 50-nanometre-thick membrane of silicon nitride, vibrated by an electric current.

The clock uses electric current to produce vibrations and not the other way around. Option D can be eliminated.

There is an evident confusion between Option B and Option C; however, the official answer key marked Option B as the correct choice. Let us try to rationalise this decision. Options A and D can be understood from the passage:

Option A follows from {...We can’t be sure yet that these results are actually universal, though, because there are many types of clocks for which the relationship between accuracy and entropy haven’t been tested...}

Option D follows from {...Understanding this relationship could be helpful for designing clocks in the future, particularly those used in quantum computers and other devices where both accuracy and temperature are crucial, says Ares...}

Option C: Pay heed to the following excerpt from the passage - {...The relationship that the researchers found is a limit on the accuracy of a clock, so it doesn’t mean that a clock that creates the most possible entropy would be maximally accurate - hence a large, inefficient grandfather clock isn’t more precise than an atomic clock. “It’s a bit like fuel use in a car. Just because I’m using more fuel doesn’t mean that I’m going faster or further,” says Huber...}

A simple correlation is being highlighted: higher accuracy means higher entropy; however, this does not necessarily imply that higher entropy translates to higher accuracy. The example of a grandfather clock is highlighted to emphasise this point: we will come across higher entropy in this case, but it does not mean that the grandfather clock is any more accurate than an atomic clock. In a way, the author tries to point out that the accuracy could very well be similar. This accuracy is not in absolute terms but in the way accuracy is defined by the author earlier in the passage. Thus, in a way, Option C matches the idea conveyed by the author

Option B: Pay heed to the following excerpt from the passage - {...The researchers found that as they increased the clock’s accuracy, the heat produced in the system grew, increasing the entropy of its surroundings by jostling nearby particles . . . “If a clock is more accurate, you are paying for it somehow,” says Ares. In this case, you pay for it by pouring more ordered energy into the clock, which is then converted into entropy. “By measuring time, we are increasing the entropy of the universe,” says Ares...}

The discussion about the price paid appears to be distinct from the earlier segment wherein the author states that when we push for higher accuracy, we will come across more heat. While talking about the cost at which higher accuracy is achieved, the author states that we "pour in" more 'ordered energy' and this subsequently leads to higher entropy. Hence, the focus seems to be on the connection between accuracy and entropy than between heat and its role in creating higher accuracy. We cannot conclusively infer that the "ordered energy" stated in the latter half refers to the "heat" mentioned earlier on. Thus, claiming that heat is the price we pay for generating higher accuracy might be difficult to substantiate. Hence, Option B is distorted. 

The relationship that the researchers found is a limit on the accuracy of a clock, so it doesn’t mean that a clock that creates the most possible entropy would be maximally accurate - hence a large, inefficient grandfather clock isn’t more precise than an atomic clock. “It’s a bit like fuel use in a car. Just because I’m using more fuel doesn’t mean that I’m going faster or further,” says Hube

In the above excerpt, the author gives an example that though a large, inefficient grandfather clock would produce more entropy, it is not necessarily more precise than an atomic clock. Hence, if a clock produces more entropy, it does not mean that it would be more precise than a clock that produces less entropy. Then the mentioned statement is given as an example. If a car is going faster or further, it will definitely use more fuel. But if a car is using more fuel, then the converse is not true. It could just be possible that the mileage of the car is low. Option A comes the closest to capturing this idea, and hence, is the answer. 

The maximum accuracy of a clock is directly related to how much disorder, or entropy, it creates every time it ticks.

The author highlights in the beginning of the passage that the accuracy associated with measuring time is directly related to how much entropy it creates while ticking. The author then goes on to talk about the relationship between accuracy and entropy, and how quantum mechanics and thermodynamics come in play here. Thus, the main keywords are the measurement of time, accuracy and entropy. Option C is the answer.

Electric current is just a small part of an example presented in the passage. Option A can be eliminated. The same is the case for Silicon Nitride and Membrane. These are just keywords associated with a particular experiment/example presented in the passage and are not important for the passage as a whole.