Changes

==Historical background==

==Historical background==

In 1915 Einstein introduced the field equation that placed into balance and found equal the curvature at one side and mass on the other. He hoped that the equations of [[general relativity]] would determine a single universe model without any beginning or end. For reasons he could never make clear, he found universe so conceived particulary satisfying and he managed to find a solution to his own equations that specified universe of that sort, static and unchanged forever. A.G. Riess declares that Einstein's original idea was to have constant amount of energy in the space.<ref name="RiessNobel"/> When in 1920s Russian mathematician A.Friedman (1924)<ref name="Friedman">{{cite web

In 1915 Einstein introduced the field equation that placed into balance and found equal the [[Curvature of space|curvature]] at one side and mass on the other. He hoped that the equations of [[general relativity]] would determine a single universe model without any beginning or end. For reasons he could never make clear, he found universe so conceived particulary satisfying and he managed to find a solution to his own equations that specified universe of that sort, static and unchanged forever. A.G. Riess declares that Einstein's original idea was to have constant amount of energy in the space.<ref name="RiessNobel"/> When in 1920s Russian mathematician A.Friedman (1924)<ref name="Friedman">{{cite web

|author=Alexander Friedmann

|author=Alexander Friedmann

|title=Über die Möglichkeit einer Welt mit konstanter negativer Krümmung des Raumes

|title=Über die Möglichkeit einer Welt mit konstanter negativer Krümmung des Raumes