a post says

the photon is a massless particle. According to theory it has energy and momentum but no mass, and this is confirmed by experiment to within strict limits.

Is it grammatically correct to put "to" and "within" together like sentence above? If yes, which part of the sentence does "to" serve with?

1 Answer 1


Yes, as unusual as it is to have two prepositions in a row, this sentence is grammatically correct and natural.

The "to..." in the context of "confirmed by experiment" means "to some degree/precision/etc.", for example:

This result is accurate to five decimal places.

Expressions that describe the degree of accuracy are often not simple nouns:

about/around/within/over/less than... a millimetre

"Within strict limits" is a prepositional phrase, but here it acts as a noun representing the degree of accuracy.

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