While Drake's famous equation is common knowledge among those with any interest in the search for extraterrestrial life, there hasn't been enough focus on why it was an important landmark in the history of humankind. This documentary, commissioned by The Open University and produced by the BBC, goes a long way towards remedying this awkward situation.

The equation itself was a vital step towards wider acceptance of the concept of extraterrestrial life among the scientific community. However, telling the story of an equation poses certain challenges which could have led this TV film to be very bland. This was not the case, and the crew do a wonderful job of bringing the history behind the numbers to life with a sense of true excitement.

Director Tim Usborne does a fantastic job telling the story of this landmark equation through some incredible directorial work. His presence is never felt too overtly, which gives presenter Dallas Campbell a sense of control over the narrative woven through this documentary.

We are thus left with a compelling piece of television that adequately demonstrates why the Drake equation is such an important element of astrobiology.

I think there was too much focus on the equation and too little on the filters. The physical factors aren't really that important--the product of the physical terms will no doubt end up somewhere within a few orders of magnitude of 1. The prevalence of ETs clearly comes down to the biological factors and the filters he was talking about. Unfortunately, I do not feel he handled this well at all.

The thing is, there aren't three filters, there are four. He touched on the L parameter but only in reference to external threats. The really scary threat is internal--there are many ways we could do ourselves in and we've already had multiple close calls. We might not see any ETs out there because L is always very short.