What does this paragraph mean? I read it somewhere that a relatively newer observation renewed the concept of "cosmological constant", and it was connected with "dark energy", again, can anyone provide detailed information on that? Wasn't "cosmological constant" proved erroneous long ago? Or is it something are now being called "cosmological constant", something other than "cosmological constant" itself? What is it, then? How should I understand the word "economical" here? I know it may be quite difficult to answer my question since I got the experience when trying to explain something to an outsider about the concept withing my speciality, so I start by telling the inquisitor whatever pertinent. I'm not trying to "teach" you how to explain this issue in any fashion (if I did made you feel so, I apologize), rather, this is just a personal suggestion, because I do not even know this question I'm asking is hard to begin with or not. I hope my question is not so valueless. Any help will be appreciated, a paragraph, a link etc. Also, sorry for my english.