Watching Interstellar for free may be possible through some unauthorized websites or torrent sites. Still, it's important to note that these methods are illegal and can expose your device to malware or other security risks. If you want to watch Interstellar legally and without paying, some options include signing up for a free trial of streaming services like Netflix, Amazon Prime Video, or HBO Max. These services typically offer a free trial period of 7 to 30 days, which allows you to watch Interstellar and other movies and TV shows for free.