In astronomy the term "red shift" denotes the extent to which light

Hello again, imSKR. I will respond directly to your questions below.


Yes, I agree with this. Shift and extent do indeed carry different meanings, and choice (C) does not provide an idiom that works within the shell of the sentence.


No. Although that and which can be used in the same restrictive sense in certain circumstances, the sentence would always be written as it appears in (A), denotes the extent to which. We want an answer to what is denoted, so we are looking for a noun to follow: the extent works perfectly; to the extent does not.

I see that AjiteshArun has also weighed in. If you have further questions, though, you know how to reach out.

- Andrew

GMATNinja how is the use of present perfect 'has been' correct when the usage should possibly be a simple present to describe a fact?

Gagan

gagan0303, simple present (Denotes) has been used to state a fact. However, the fact itself is such that the use of present perfect is required to describe the fact. Hope this helps!

We sometimes use the present perfect to describe an action that happened in the past, but whose impact continues to be felt in the present. For instance:

Tim has been fired from 17 jobs in the last three years.

Here, "has been fired" is appropriate. This might be a fact, but it's a fact that describes an action that began in the past and whose consequences continue to be felt into the present.

Same deal here. If we're describing a light shift, that shift must have started at some point before we started talking about it, so it's perfectly reasonable to use the present perfect.

Note also that the only options that don't use the present perfect are (D) and (E), both of which have a glaring meaning issue. It's nonsense to write about the extent "of light" or the extent "of the shift." We're talking about the extent of an action -- how much the light has shifted.

Because we're introducing an action, we need a clause with a verb to follow "extent." (D) and (E) both lack verbs, so if you kill them on this basis, you're stuck with the perfect tense, and you're on to other issues.

I hope that helps!

EducationAisle

What is the difference between the verbs "has been shifted' and 'has shifted'?

Gagan

Hi Gagan, "has been shifted" is passive voice.

Passive voice is more appropriate here because light has not shifted on its own but by something else (by the rapid motion of the galaxy away from the Earth).

Could expert explain why C is wrong? If we use A, does it make the sentence become "light has been shifted to toward the red"?

AndrewN, AjiteshArun sir,

The meaning conveyed in option D is that the light on its own is shifting toward the red end of the spectrum. We need a passive construction.
Is my analysis correct? Are there any other errors in this sentence?
Please share your two cents.

Hello krndatta,

We hope this finds you well.

To answer your query, your analysis here is, indeed, correct.

Kudos.

Further, Option D is also incorrect due to the phrase "extent of light"; the construction of this phrase illogically implies that “red shift” denotes the extent of the light that is shifting; the intended meaning is that “red shift” denotes the extent to which - in other words, how much - the light has shifted.

We hope this helps.
All the best!
Experts' Global Team

Hi krndatta,

That's correct. The nonunderlined portion of the sentence contains the clue that we need here (by the rapid motion).

Hi experts, my doubt is that for stating universal truths aren't we supposed to use simple present tense? Based on this logic i eliminated A & B. Could you please explain why present perfect tense is being accepeted here?

Check out our earlier post to see why the present perfect is logical here.

And you can use either tense to express general truths. It's perfectly reasonable to write "baby raccoons are adorable," or "baby raccoons have always been adorable." Just don't pet them.

MartyTargetTestPrep

When do we use "to which" and why is the construction of extent "that" incorrect?

"That" is incorrect, because "extent that light ... has been shifted" conveys the illogical meaning that light has been shifted an extent. It's not possible to shift light an extent. An extent is not a measure of distance.

Think about it. We don't say, "Jim walked an extent," or "I carried the water for a long extent."

Similarly, we can't say, "light has been shifted an extent." Thus, "the extent that light ... has been shifted" doesn't make sense.

On the other hand, light can be shifted TO an extent. So, it's correct to say, "light has been shifted to an extent."

Thus, the correct version of the sentence makes sense because it uses "to which" in describing "the extent." It correctly describes the extent as "the extent TO which light ... has been shifted."

we need "the extent TO which light ... has been shifted."

Only a small part of the sentence is underlined but before we try to get the correct option, we must look at the meaning of the sentence.
‘Red shift’ is the extent to which light from a distant galaxy gets shifted toward the red end by the rapid motion of the galaxy away from the Earth. So, the rapid motion makes the light from a distant galaxy shift toward the red end of the spectrum.

Note that light does not shift on its own. It gets shifted by the rapid motion.
Hence, we need a passive structure:
Red shift is the extent to which light has been shifted toward A by B.

(A) to which light from a distant galaxy has been shifted
(B) to which light from a distant galaxy has shifted

The only difference between the two is the use of passive vs active voice (has been shifted vs has shifted)
Since we need a passive structure, option (A) is correct and option (B) is not (which uses an active structure).

(C) that light from a distant galaxy has been shifted

In option (C), ‘extent that’ is incorrect usage. We use ‘extent to which A has happened ’ or ‘extent of A’ depending on context. For example, ‘extent to which he can change …’ or ‘extent of his influence…’

(D) of light from a distant galaxy shifting

We need to measure the extent of the shift, not the extent of light and hence, option (D) is not correct. It uses ‘extent of light shifting …’ in which ‘shifting …’ becomes a modifier of light. Then the meaning of measuring the extent of the shift is lost.

(E) of the shift of light from a distant galaxy

This is the structure of option (E):
(E) Red shift denotes the extent of the shift of light from a distant galaxy toward the red end of the light spectrum by the rapid motion.

To say the least, it is confusing. What is done ‘by the rapid motion’? We don’t know. The prepositional modifier needs to have a verb to modify. Option (A) provides that verb ‘has been shifted.’ So in option (A), we know that rapid motion has shifted the light toward the red end of the spectrum. Here, we don’t.
Also, ‘from the distant galaxy toward red end’ sounds as if the shift has happened from the distant galaxy (point A) toward the red end (point B). This we know is not correct. All we are trying to say is that the light comes from the distant galaxy and shifts on the spectrum. Hence, option (E) is not correct.

Answer (A)

Hi,
I think the position of commas is misleading. ‘’By the rapid motion’’ does not seem to directly affect the light action. Maybe it’s because I am a non native speaker but I find the position of commas very misleading

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Can someone explain why c is wrong?