I think you mean Einstein-Rosen Bridges, which are a kind of wormhole geometry. You'll find them discussed here...
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The Einstein-Rosen Bridge[/URL]
...if you want a more advanced presentation then I'm sure there's plenty of notes to be found on the web now you know what it's called.
John Wheeler demonstrated in the early 1960s that such simple wormholes were unstable to collapse and they shut before anything can pass through them, even light. Stable wormholes require "exotic matter" to keep open.