The programme begins with the dilemma posed in Liu Cixin's novel The Three-Body Problem: if humanity receives a message from aliens, should we reply?

For the fictional character Ye Wenjie, the answer is 'yes' and Douglas Vakoch who is President of METI International shares the same view.

[18] The search for extraterrestrial intelligence has so far focused primarily on electromagnetic signals in radio or microwave frequencies[19] since this is the form of interstellar communication that human civilisation first became capable of.

[21] But Liu Cixin's novel The Dark Forest explores the possibility of communication based on more exotic physics such as gravitational waves or neutrinos.

[19][22] Scientists at the Advanced Propulsion Laboratory at Applied Physics have argued that LIGO is already capable of detecting artificially generated gravitational wave signals.

[35] Astronomer Jill Tarter describes her involvement in drafting one of the first post-detection protocols, establishing principles for what should be done in the event of the detection of extraterrestrial intelligence.

[36] The discovery of an apparent signal or alien technology is likely to have a high degree of uncertainty and many factors will impact its potential significance.

Scientists such as Stephen Hawking argued that the colonisation of space is necessary to mitigate the risks of human extinction from natural or human-made disasters.

The programme begins with an interview with Dr Dario Izzo of the European Space Agency's Advanced Concepts Team.

He describes the 10th edition of the Global Trajectory Optimisation Competition in which 73 teams[41] from around the world competed to find the most efficient approach for galactic settlement using future hypothetical technology such as Generation Ships.

[44] Physicist Bradley Edwards describes the concept of the space elevator - a system that could transport material from the surface of Earth into geostationary orbit.

For example, the construction of the International Space Station relied on conventional chemical rockets and cost $150 billion (in 2010 dollars) making it one of the most expensive objects ever built.

Jane Poynter describes how Biosphere 2 attempted to create a partially closed system, by duplicating many of Earth's natural processes.

[51] Another proposed solution, widely explored in science fiction, is to extend the human lifespan through artificial hibernation or suspended animation.

Professor Jon Rittenberger describes experimental studies he carried out at the Applied Physiology Laboratory at the University of Pittsburgh in which the core body temperature of nine healthy volunteers was lowered by around 3 °C for 3 hours with medication used to suppress shivering.

[57] Mathematician and philosopher Stuart Armstrong discusses how humanity could become a Type II supercivilisation through the construction of a Dyson Sphere around the Sun.

[60] Liu Cixin's science fiction novel Death's End describes the possibility of an even larger ‘circumsolar’ particle accelerator constructed in orbit around the Sun.

[61] Beacham speculates about how such an experiment might be realised in practice and whether it could ultimately reach the Holy Grail of particle physics - the Planck Energy.

[65] Physicist and historian James Woodward describes another speculative idea: using the principle of inertia to generate thrust through the hypothesied 'Mach Effect'.