Variants: "... is man’s greatest invention" and "... is the eighth wonder of the world".
May add: "He who understands it, earns it; he who doesn’t, pays it."
This Snopes article http://www.snopes.com/quotes/einstein/interest.asp concluded that its status was uncertain, while this post from The Quote Investigator http://quoteinvestigator.com/2011/10/31/compound-interest/ concludes it is most likely a false attribution, since variants of the quote date back to at least 1916, with the early variants not being attributed to Einstein.
Disputed
The Complete Neurotic's Notebook (1981), Unclassified
“In established interests are the most powerful force of resistance to good.”
Letter to James Lloyd (1 October 1822)
Interview with Rynn Berry in The Vegetarians https://books.google.it/books?id=vK_uAAAAMAAJ (1979), p. 64<!-- Brookline, MA: Autumn Press -->
Context: Man is innately a creature of love. That love is the most powerful force in the universe, and eventually — it's a very slow process — it will conquer. I think there will come a time, and this is down the road a great many years, when civilized people will look back in horror on our generation and the ones that have preceded it: the idea that we should eat other living things running around on four legs, that we should raise them just for the purpose of killing them! The people of the future will say “meat-eaters!” in disgust and regard us in the same way that we regard cannibals and cannibalism.
“Habits are the compound interest of self-improvement.”
Source: https://twitter.com/JamesClear/status/1059504530130395136
Banquet speech http://nobelprize.org/nobel_prizes/physics/laureates/1927/compton-speech.html for his Nobel Prize, 1927.
“Who are we? We are the life force power of the universe.”
Ted Talks http://www.byronkatie.com/newsletter_april_08.html
The Keys to Well-being in Students, Presentation to the X NIS International Conference, Astana, Kazakhstan, 26 October 2017 (https://www.youtube.com/watch?v=d8hG_p7sujU)
“It's the most powerful stuff in the universe.”
North and South Trilogy (1982-1987), Answer the Drum
Context: "Iron can destroy anything: families, fortunes, governments, whole countries. It's the most powerful stuff in the universe."
"Oh?" Orry's skeptical glance fell down on the Plain below. "You really think it's more powerful than a big army?"
"Without weapons - without this - there are no big armies."
