Hey @steemcleaner I am not the author of the above mentioned link

http://www.plenglish.com/index.php?o=rn&id=20969&SEO=light-always-travels-the-same-distance

and plenglish is neither. I can't tell you the original source, but it must be one of those I did choose for my article. I went through the main source yesterday, but couldn't find the relevant passages.

What I can tell you is that the mentioned site was totally unknown to me before I gave a plagiarize-checker-software a try.

It seems like I did a mistake while composing my article. Anyway, I replaced the content in question.