Universes, Baby

The term baby universe can be applied to any newly formed universe, including the initial stages of our own universe. More commonly, the term has been applied in speculation about the existence of other universes that could have developed before or after our own universe came into being—universes that have existed, are existing, or will exist outside of the framework of our own cosmos. Since such universes would inhabit a different time and space, we are unable to verify or observe them.

The popularization of the term baby universe apparently had its genesis in astrophysicist Stephen Hawking's lecture “Black Holes and Baby Universes,” presented at the University of [Page 1400]California, Berkeley, in 1988. The contents of that lecture were later included in a collection of his essays with the same name.

A black hole has generally been defined as a region in space and time with such a strong gravitational field that nothing can escape from it. Hawking, however, speculated that there could be an exception because the uncertainty principle would allow particles and radiation to travel faster than light for a very short distance. These emissions would eventually result in the loss of mass, with the black hole completely disappearing. Nothing coming out of a black hole would resemble what fell into it, though it would retain the same energy. A separate intriguing question is what would happen to the objects that fell into the black hole. Hawking suggested that they might enter a baby universe of their own that would branch off from our own part of the universe. If the baby universe was ever able to rejoin our region, it would appear as another black hole.

The idea of the existence of other universes has led to some speculation in the past about time travel. But Hawking added the important qualification that the baby universes would occur in imaginary time, defined as existing at right angles to real time. Though imaginary time is a well-established scientific concept and an important one for the understanding of quantum mechanics and the uncertainty principle, it in no way resembles our own subjective view of time. If human beings fell into a black hole, their history in real time would come to an end, and they would be torn apart by gravitational forces. In imaginary time, the changed particles would enter a baby universe and come out again from another black hole. Because of the small size of baby universes, we are unable to observe them or to predict their numbers or patterns. However, Hawking thought that their existence might help explain such values as the cosmological constant, which gives the universe its natural tendency to expand or contract.

In 2004, Hawking surprised some cosmologists by stating that he now considered himself wrong about the existence of baby universes that branched off from our own. He now claims that as a black hole begins to die it simply sends its contents back out into the universe in a transformed state. Other cosmologists, however, continue to speculate about the possible existence of baby universes and/or multiple universes, sometimes referred to as the multiverse.

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