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The work suggests the parallel universes proposed by some quantum theorists may not actually be parallel but could interact – and with disastrous consequences.

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Quantum theory states that all universes are not created equal – each “parent” universe is much larger according to a particular quantum measure than its later descendants.

Quantum interactions between the universes were thought to be too small to really affect them, but Hanson says the interactions can be significant between universes of vastly different size.
Boiled worlds

The interactions can “smash or mangle the small worlds”, says Hanson. He has not worked out exactly what happens, but he believes the small universes would be either destroyed or assimilated by the large universes, like specks of dust colliding with a planet.