If it's just us, it seems like an awful waste of space.
Why it is hard sci-fi
Carl Sagan wrote the novel and the film follows the real workflow of radio astronomy. SETI surveys, hydrogen line targeting, signal verification across multiple sites, peer review, and political control of the discovery. The transit machine itself is exotic but the path to it is procedural. Most of the film is about how a society would actually receive a message from another civilisation.
Science inside it
Radio astronomy at the Very Large Array, the 1420 MHz hydrogen line as a natural carrier frequency, prime-number transmissions as a signature of intelligence, embedded video in the carrier wave, and a wormhole-style transit using a constructed device. The transit science gets hand-wavy on purpose at the edge.
Spoiler alert
Ellie experiences an eighteen-hour journey through a network of wormholes. From the outside the pod falls through the device in a fraction of a second and her recorder appears blank. The film closes with the disclosure that the recorder captured eighteen hours of static, which neither proves nor disproves her account. That ambiguity is the whole point.