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I found the following article on BBC. Indeed, it is a scientifically proven fact that the speed of the expansion of the universe is accelerating. So, it is something that is happening now. Therefore, I cannot understand that why the writer of the following article used "was" instead of "is". Thus, could someone please let me know what are the reasons that they have used past tense in the following sentence.


For example, the observation that the expansion of the Universe was speeding up was attributed to a mysterious phenomenon known as dark energy. But some researchers have previously suggested it could be evidence of a fifth force.


Reference:-

https://www.bbc.com/news/56643677


Edit: Corrected header. CJ

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dileepaobservation

It is a form of indirect speech.

They observed that the expansion of the universe was accelerating.

Galileo observed that the little stars around Jupiter were moving.

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dileepaI cannot understand that why the writer of the following article used "was" instead of "is".
dileepathe observation [ that the expansion of the Universe was1 speeding up ] was2 attributed to ...

was1 in the subordinate clause matches the tense of was2 in the main clause.

The technical term that some grammarians use for this kind of matching is "modal preterite". It is a past tense in a subordinate clause that refers to present time but which is made past just to match another past tense in the main clause. Native speakers are very familiar with this usage of the past tense, so they automatically adjust the times in their minds so that everything works out just fine.

Everyone in the class knew that the earth went around the sun.

CJ

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Comments  
dileepaSo, it is something that is happening now.

You are right, of course, but we often do that. It is called backshifting. The observation happened in the past, and that is when the universe was speeding up for our purposes in this sentence.

You need to review how to form a question.

ie Why have they use Past Tense . . . ?


Not Why They Have Used Past Tense . . .?

Clive

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 CalifJim's reply was promoted to an answer.

Thank you very much for the answer.