an increasing rather than constant energy, a constant is still permitted within the rules of general relativity.
But others are dubious, questioning whether this dark energy would ever truly be a constant, yielding the same force throughout time. Indeed, observational evidence suggests that the repulsive effect has been varying across time, and not constant.
Earth, Wind and Fire… and Quintessence?
Enter the notion of quintessence, named after the ancient Greeks’ notion of an unseen “fifth element” beside earth, air, fire and water. Quintessence is posited as “a dynamic, time-evolving and spatially dependent form of energy with negative pressure sufficient to drive the accelerating expansion,” according to Paul Steinhardt of Princeton University, one of the originators of the inflation theory who predicted an accelerating universe back in 1995.
But whether it’s a constant or quintessence, dark energy most likely exists and has to be accounted for. To the amazement of scientists today, somehow Einstein anticipated this energy nearly a century ago. Yet he went to his grave thinking that including that factor was his greatest error. In a twist of irony, it now seems that something close to what Einstein described belongs in that equation, though not for the reason he thought. One hundred years after his great equations were published, Einstein continues to demonstrate his uncanny genius. Some now note that Einstein’s too-hasty removal of this repulsive energy “fudge factor” actually may have been his “greatest blunder.”