The Rituals of Infinity

From the back cover:
It is nearly three decades since the discovery of the sub-spacial alternatives - twenty-four lumps of matter hanging in a limbo outside of space and time, each sharing the name of Earth.
Now there are only fifteen of them - the rest blown to extinction by the ruthless attacks of the D-squads. Even the surviving planets are doomed to a cruel, mutilated existence.
Standing between them and their final destruction at the hands of the merciless demolition teams is Michael Moorcock's zaniest hero - the brilliant, offbeat physicist Professor Faustaff.