Bring a large saucepan full of water to a boil; submerge peaches in boiling water with a slotted spoon for 45 seconds.
Drain peaches in a colander; refresh under cold running water.
Remove peach skins.
Halve peaches; remove pits.
Combine sugar and water in a deep saucepan and bring to a boil, stirring to dissolve sugar.
Add ginger, cardamom, vanilla bean seeds and pod, cinnamon stick, and thyme sprigs; cover and simmer mixture 5 minutes.
Remove from heat; let syrup cool to room temperature for flavors to develop.
Strain out solids from syrup.
Return syrup to saucepan; add peaches and bring to a boil.
Lower heat to low, cover, and simmer until peaches are just tender when pierced with the tip of a knife, about 4 minutes.
Remove from heat; let peaches cool in syrup to room temperature (peaches can be made up to 8 hours ahead and refrigerated, and served chilled, if desired).
To serve, with slotted spoon, place 2 peach halves, cut sides up, into each of four dessert bowls.
Top with a scoop of sorbet; scatter fresh raspberries over top.
Spoon some of the poaching syrup over each serving and garnish with a thyme sprig.