Detailed Instructions: You need to read the given passage and construct a question about the information present in the passage. The question should be answerable from the passage. Most importantly, only those questions are allowed whose answers cannot be determined from a single sentence. Do not generate questions that require only a single sentence to answer. Instead, try to combine two sentences and create a question from that combination. Do not create open-ended questions, i.e., the answers to them cannot be found precisely from the information provided in the passage.
Q: Paragraph- Sent 1: In 1917, Einstein applied the general theory of relativity to model the structure of the universe as a whole.
Sent 2: He apprehended that his equations predicted the universe to be either contracting or expanding.
Sent 3: He wanted the universe to be eternal and unchanging, but this type of universe is not consistent with relativity.
Sent 4: To fix this, Einstein modified the general theory by introducing a new notion, the cosmological constant, which he called ''Lambda''.
Sent 5: The purpose of Lambda was to rectify the effects of gravity and allow the whole system to stay balanced.
Sent 6: With a positive cosmological constant, the universe could be an eternal static sphere.
Sent 7: However, in 1929, Edwin Hubble confirmed that the universe is expanding, Einstein exclaimed after his Mount Wilson visit with Hubble: "If there is no quasi-static world, then away with the cosmological term!"Sent 8: and Einstein supposedly discarded the cosmological constant.
Sent 9: Einstein believed a spherical static universe is philosophically preferred, because it would obey Mach's principle.
Sent 10: He had shown that general relativity incorporates Mach's principle to a certain extent in frame dragging by gravitomagnetic fields, but he knew that Mach's idea would not work if space goes on forever.
Sent 11: In a closed universe, he believed that Mach's principle would hold.
Sent 12: Mach's principle has generated much controversy over the years.
Sent 13: In many of Einstein biographies, writers claim that he called the creation of Lambda his "biggest blunder".
Sent 14: Recently, astrophysicist Mario Livio showed that Einstein possibly never said that.
Sent 15: Instead of discarding Lambda, Einstein was continually experimenting with it.
Sent 16: In late 2013, Irish physicist Cormac O'Raifeartaigh, happened to discover a handwritten manuscript by Einstein which was since then overlooked by other scientists.
Sent 17: The research paper was titled ''"Zum kosmologischen Problem"'' ("About the Cosmological Problem").
Sent 18: And Einstein proposed a revision of his model, still with a cosmological constant, but now the constant was responsible for the creation of new matter as the universe expanded.
A:
What did Einstein use as his "cosmological constant" and what was its purpose?