Sentence:  Some of the most beautiful and thus appealing physical theories, including quantum electrodynamics and quantum gravity, have been dogged for decades by <WSD>infinities</WSD> that erupt when theorists try to prod their calculations into new domains. Getting rid of these nagging <WSD>infinities</WSD> has probably occupied far more effort than was spent in originating the theories. 
Meaning of the word marked with <WSD> tags:  A number that has an infinite numerical value that cannot be counted.