Como Lyra vai de Svalbard a Oxford?

A explicação é dada em uma frase descartável perto do final de A luneta âmbar (Ch. 38):

Xaphania had told Serafina Pekkala that when all the openings were closed, then the worlds would all be restored to their proper relations with one another, and Lyra’s Oxford and Will’s would lie over each other again, like transparent images on two sheets of film being moved closer and closer until they merged—although they would never truly touch.

At the moment, however, they were a long way apart—as far as Lyra had had to travel from her Oxford to Cittàgazze.

Então, os mundos se desviaram do alinhamento por causa das janelas cortadas entre eles.

No final de Aurora boreal/A Bússola de Ouro, Lord Asriel abre um caminho entre o mundo de Lyra e o mundo de Cittàgazze (que implica a cidade vista dentro da Aurora). Os detalhes que temos sobre como Lyra fez uso desse caminho estão no início do capítulo 3 de A faca sutil:

He carried the bowl outside and said, "If you don't come from this world, where's your world? How did you get here?"

"Over a bridge. My father made this bridge, and ... I followed him across. But he's gone somewhere else, I don't know where. I don't care. But while I was walking across there was so much fog, and I got lost, I think. I walked around in the fog for days just eating berries and stuff I found. Then one day the fog cleared and we was up on that cliff back there —"

She gestured behind her. Will looked along the shore, past the lighthouse, and saw the coast rising in a great series of cliffs that disappeared into the haze of the distance.

"And we saw the town here, and came down, but there was no one here."

É em Cittàgazze que Lyra encontra Will, que entrou por uma janela em seu Oxford, e é depois por essa janela que Lyra chega ao outro Oxford.