The song and album title refers to the second law of thermodynamics, which states that because energy is naturally expended and consumed and no new energy produced, unlimited growth is unsustainable. Frontman Matt Bellamy told NME: "I got interested in reading about energy. The second law of thermodynamics is saying that it seems to be gradually decreasing in our bodies, the planet, the sun and so on, but it seems like life, humans or whatever, seem to be going directly against that. So the album is my own internal conflict of celebrating that strength but also saying, 'F---, where do we go from here?'"
The song was inspired by the Dubstep sounds of such electronic artists as Skrillex and was constructed with analog instruments only. Bellamy told NME: "That stuff is capturing the imagination. The mosh pit has moved from guitars and gone towards the laptop. With the song we're trying to see if we can challenge the laptop. We created something that's dubsteppy, but we wanted to see if we could do it with real instruments. We wanted to ask, 'Can rock bands compete with what these guys are doing?"
Drummer Dom Howard added: "We went to see Skrillex in Camden around October. We went, 'F---, it's so heavy,' loved it. It was like a full metal gift, they had the circles of death, people were moshing, I hadn't seen a reaction like that to electronic music before. We took inspiration and came up with 'Unsustainable.'"
Speaking to Classic Rock magazine, Bellamy said that he considered The 2nd Law to be very cinematic, adding that film soundtracks had always been a big influence on the band. "I've always been very influenced by and interested in film music," he commented, "growing up watching Stephen Spielberg films or John Williams' stuff. And I've always been a big fan of Hans Zimmer. He's the greatest film composer of recent times. That song 'The 2nd Law,' you can definitely hear some Hans Zimmer influence."
When news first broke that Muse had recorded a Dubstep track, some doubted if the band could pull it off. However, Bellamy said they've proved skeptics about the track wrong. "The thing about dubstep is it's really heavy," he told The Sun. "When it really kicks and the bass drops, it's like heavy metal with these big build-ups and a big riff that kicks in.For 'Unsustainable' I wanted to write the idea electronically and then when we came to record it we did it with real, organic instruments and we got a real orchestra in. We were trying to see if real instruments could make a sound like electronica. A lot of people were sceptical about it but it works."