Reply #54: Basically it's the same, but there are some differences. (SPOILER)

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(SPOILER) In the book, five people travel together in the machine, while in the movie, Ellie travels alone. But they come back, after what appears to be 20 minutes to people on Earth, but seemed like many hours to the travelers. In the movie, it is 18 hours for Ellie, but only a few seconds on Earth. In the book, all video footage was erased somehow, so the travelers have no proof that anything happened. In the movie, I don't recall any video footage, but her data instruments did register 18 hours elapsed time - but she is never told this by the government. In the book, the government claims it was all a conspiracy by the world's richest man (Hadden) but I don't think that claim is made in the movie. For the most part, though the movie follows the plot in the book.