Media playback is unsupported on your device Media caption Experts at the SETI institute are attempting to find funding amid closures of their facilities (video produced by the BBC's Matt Danzico)

The hunt for signals from intelligent extraterrestrials has been in full swing for half a century. But the effort's flagship facility recently came to a grinding halt. The first of a two-part series on the Search for Extraterrestrial Intelligence (Seti) takes a look at the facility and what it means for Seti's future.

"It's never been this bad."

Seth Shostak, principal astronomer for the Seti Institute in Mountain View, California, is trying the door of an outbuilding at the Allen Telescope Array (ATA). Like all the others, it is locked.

"There's always been at least one or two people around who can let you in."

The group of 42 antennas is, as the flyer posted nearby advises, "in the process of being returned to operations". Last April, there wasn't enough money in the Seti coffers to pay the staff, and the facility shut down.

A funding drive raised money from Seti enthusiasts including former astronaut Bill Anders, sci-fi author Larry Niven, and even Hollywood actress Jodie Foster. But it's only enough to keep going for a few months.

"Since 1993, Seti has had to run on private donations from people who think this is an interesting thing to do," Seth tells me.

"I remain confident that we'll find the money to make this a permanent operation. After all, you're not going to find ET unless you have the telescope operational."

Blind valley

But even if the telescope is operational, will the effort find ET? Ask Seth or his colleagues, and you'll get the same answer: it's a long shot. It may take years, or decades, or centuries to pick up a signal.

Image caption The Allen Array is now partly used by the US Air Force, who are helping to financially support it

We humans have only been on the radio for about a century, and listening for cosmic signals for half of that. That is an infinitesimal slice of time in the 13 billion years that our Universe has been around.

Yet, we are probably closer, at least philosophically, than we have ever been to answering the timeless question of whether we are alone.

Fifty years ago, all we had was the Drake equation - a string of factors that, multiplied together, yielded a guess of how many ETs might be out there, phoning our home.

Many of those factors were a matter of complete guesswork in the early 1960s: the rate of star formation in the galaxy, how many stars may host planets, how many of those planets could potentially support life.

Today, some of those factors are being solidly quantified thanks to results from the Kepler space telescope, which is discovering far-flung planets - some potentially hospitable to life - at an astonishing rate.

And where once there were single radio dishes listening in on single frequencies - single radio stations - improvements in the electronics behind the scenes make it possible to sift through literally millions of stations automatically.

If you're the lucky one that finds ET, you get the Nobel prize Dan Werthimer, UC Berkeley and Seti@home

So Frank Drake, the originator of the equation, says it is a terrible time for Seti and the ATA to be experiencing what he calls a "valley".

"After many years of quite a lot of action, the economic troubles of the world have had a great impact," he told BBC News.

"There are very few searches going on in the world, despite the fact that at the present time we have far better equipment than we've ever had."

Seti does have its economical ways and means, however. As with other areas of science that require vast computing power, there is the Seti@home screen saver - which sends signals from the Arecibo radio telescope to millions of volunteers around the world.

"Everybody gets a different part of the sky to analyse, and it wakes up like any other screen saver when you go out for a cup of coffee," says Dan Werthimer, director of the Seti programme at the University of California Berkeley and a Seti@home pioneer.

"It goes through the [Arecibo data] looking for all kinds of possible radio signals. Any strong signals it finds, it sends back to our server at Berkeley. Your name is attached to that data, so if you're the lucky one that finds ET, you get the Nobel prize."

Other things are changing the nature of the hunt, too.

Radio is one good way to squash energy into a signal carried across the cosmos. But another is the laser, which can focus a lot of energy, or information, into a lighthouse-like beam.

Enter "optical Seti" - a hunt using good old-fashioned optical telescopes to look for laser lighthouses in the cosmos - one of the eight types of Seti searches that Berkeley carries out.

"We think the best strategy is a variety of strategies," Dan tells me. "It's really hard to guess what an advanced civilisation might do."

DNA message

Back at the ATA, we find a technician who lives nearby to drop off the keys so we can head inside the control room.

Seth tells me that his take is that we should be looking for signs of artificial intelligence, as well as squishy "biological" aliens.

The autonomous robotic vacuum cleaners we have now are just a harbinger of the truly advanced intelligence he thinks will soon be developed.

Image caption The Arecibo radio telescope sends millions of signals to Seti@home volunteers worldwide

And if any advanced civilisation can invent its technological successor, these "thinking machines" could carry on searching the cosmos long after their biological forebears are gone.

But it gets even more intriguing. Paul Davies of the Beyond Center at Arizona State University has proposed looking not for aliens but for footprints of alien technology, such as waste from their nuclear energy technology. And he has other ideas.

"The one that most intrigues me is the possibility that the aliens may have engaged in some kind of biotechnology - if they had come to Earth and tinkered with terrestrial micro-organisms, or even made their own from scratch, the products of that could still be around."

In other words, if aliens came through our neck of the woods long before we were here to see them, they may have left deliberate clues tucked in the DNA of microbes that have faithfully copied the message for millions of years.

Prof Davies reckons that, since we're sequencing the DNA of life of all sorts anyway, we should keep an eye out for this kind of "message in a bottle".

Powerful question

But as the locked doors of the Allen Telescope Array remind me, all of this does take money.

Those at the Seti Institute argue that the $2m (£1.3m) a year or so that the wider Seti effort requires is a drop in the ocean compared to, for example, military spending.

Jill tells me that she spends a lot of her time trying to organise a foundation that can fund the effort far into the future - not just money to keep telescopes turning, but also to pay the next generation of Seti scientists.

What is clear, though, is that the Seti effort speaks to something far deeper than the politics and the money issues that occasionally put it in the spotlight.

"Calibrating our place in the cosmos is something that's important for humans to do, to really get a better sense of where we came from and where we're going, and I think that's part of the Seti story," she tells me.

"That question 'are we alone?' hasn't lost any of its impact and its emotive power, even though it's been asked for millennia."

The first of a two-part BBC World Service Discovery series, "Seti: the past, present and future", will be first broadcast at 19:32 Monday 9 January and the podcast can be found here.