Isso é explicado com muito mais detalhes na novela oficial do filme ; Em suma, o "aperto de mão" foi de fato causado por Coop quando ele foi enviado de volta através do buraco de minhoca pelos "alienígenas" depois de ter cumprido sua missão principal ...
...to send the secrets of gravity manipulation to his daughter and the coordinates of NASA to his former self.
...
He wondered where Brand was, how she was doing. He wished he could
explain to her why he’d had to leave her alone. Ahead he saw a glassy,
golden distortion, and in it the Endurance, and for a split second he
thought his wish had brought him to her—but then he saw that this
Endurance was like new, undamaged, just entering the wormhole. He
drifted through the bulkhead and saw Brand and Romilly there, both
strapped in.
Brand, he thought, reaching toward her. In a way, he had gotten his
wish. Could he communicate with her? Probably not, or at least nothing
important, since this was the past, and she hadn’t known that any of
this was going to happen.
To his surprise, she saw him. She reached her hand up to his, and he
realized there was something he could communicate. Something that
maybe was important. So he reached back, hoping to feel the warmth of
her hand, give it an affectionate squeeze. But when their fingers came
together they mingled, distorting each other but not really touching.
A quiet moment in the chaos.
Não há indicação específica de que o aperto de mão tenha sido intencional ou desejado pelos alienígenas. A probabilidade parece ser que foi apenas um artefato não intencional da função do buraco de minhoca como um canal de viagem (capaz de viajar no tempo).
Você pode ver essa mesma cena no próprio filme
E na descrição da cena no rascunho final do roteiro
Cooper FLIES through the EXPANDING COSMOS, past PLANETS ORBITING
STARS, WHICH BECOME ATOMIC PARTICLES, WHICH BECOME MATTER, BECOMING
STARS ...
Cooper APPROACHES A GLASSY TUBE. Inside is the OLD, UNDAMAGED
ENDURANCE. As Cooper looks in from the bulk he sees: Brand, strapped
in, Doyle opposite, traversing the wormhole for the first time ...
Cooper REACHES for Brand ... She sees something, reaches up
- their hands would touch if they weren’t in different dimensions, her fingers distorting the space of his fingers
-
WHAM! She, and the Endurance, are SWEPT PAST - Cooper is SMASHED into
the spacetime of the wormhole - he SCREAMS AND
WE -