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Sajjad1994
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Standard model particle interactions obey typical conservation of mome Updated on: 07 Aug 2025, 10:56
Originally posted by Sajjad1994 on 07 Aug 2025, 10:55.
Last edited by Sajjad1994 on 07 Aug 2025, 10:56, edited 1 time in total.
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Question 1
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Standard model particle interactions obey typical conservation of momentum and energy laws as well as conservation laws. The model has been thoroughly probed and has led to spectacular results such as the precision measurement of the anomalous magnetic moment of the electron (analogous to measuring the distance between New York and Los Angeles to the width of a human hair). Despite its success, the standard model does not contain any particle that could act as the dark matter. The only stable, electrically neutral, and weakly interacting particles in the model are the neutrinos. Can the neutrinos be the missing dark matter? Despite having the “undisputed virtue of being known to exist” (as put so well by Lars Bergstrom), there is a major reason why neutrinos cannot account for all of the Universe’s dark matter. A neutrino-dominated universe would have inhibited structure formation and caused a “top-down” formation (larger structures forming first, eventually condensing and fragmenting to those we see today). However, galaxies have been observed to exist less than a billion years after the Big Bang and, together with structure formation simulations, a “bottom-up” formation (stars galaxies, then large galaxies, then clusters, etc.) seems to be the most likely. While neutrinos do account for a small fraction of dark matter, they clearly cannot be the only source.
1. It can be inferred from the passage that a hypothesis using neutrinos for the missing dark matter in the standard model would include which of the following elements?

Indicate all that apply.

A. A structural model of the universe in which the average distance between galaxies increased over time.
B. A justification for the “top-down” universe formation that includes a new weakly interacting particle.
C. An inconsistency regarding the conservation of energy when used for measurements at the atomic level.


2. It can be inferred that the author of the passage mentions “large galaxies” (Highlighted) primarily in order to

A. explain another benefit of using the standard model to explain particle interaction
B. identify a probable source of missing dark matter
C. help account for the accuracy of the standard model in measuring distance
D. indicate how cosmic structures have followed a model in which larger structures disintegrate
E. point out a factor that contradicts a model using neutrinos as the universe’s missing dark matter

ShowHide Answer Question #1
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A
ShowHide Answer Question #2
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E
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Standard model particle interactions obey typical conservation of mome 23 Aug 2025, 00:29
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Official Explanation

1. It can be inferred from the passage that a hypothesis using neutrinos for the missing dark matter in the standard model would include which of the following elements?

The author says that “a neutrino-dominated universe would have ... caused a ‘top-down’ formation,” and then follows by explaining that, in a top-down formation, larger structures would have formed, then broken apart, supporting the statement that the average distance between galaxies would grow as time passed.

Answer: A
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Standard model particle interactions obey typical conservation of mome Updated on: 23 Aug 2025, 00:41
Originally posted by Sajjad1994 on 23 Aug 2025, 00:38.
Last edited by Sajjad1994 on 23 Aug 2025, 00:41, edited 1 time in total.
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Official Explanation

2. It can be inferred that the author of the passage mentions “large galaxies” (Highlighted) primarily in order to

The mention of large galaxies is part of the author ’s description of a sequence of events in the “bottom-up” theory, which he claims to explain the universe and which he uses to argue against a model using neutrinos as the main source of dark matter.

Answer: E