a model of the universe in which the universe expands forever because there is not enough mass to counteract the expansion by means of gravitational attraction.
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Compare closed universe.
Origin of open universe
First recorded in 1975–80
Words nearby open universe
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021
Scientific definitions for open universe
Model of the universe in which the curvature of space is flat or curved away from itself, entailing that the size of the universe is infinite. According to this model, gravity between objects is not able to stop or reverse the expansion of the universe, thus objects continue to move farther and farther apart as space moves outward. An object moving in a straight line in an open universe would never return to its starting point. According to current cosmological theories, the universe is open if it is insufficiently dense. Such a universe will never end, but will eventually become very cold and dark because stars gradually lose all of their energy. Compare closed universe. See Note at big bang.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Cultural definitions for open universe
If there is not enough matter in the universe to exert a strong enough gravitational force to stop the universal expansion associated with the big bang, the universe is said to be open. (Compare closed universe and flat universe.)
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.