The search for extraterrestrial intelligence has had a frustrating first 100 years searching for ET (extra terrestrials), and is facing a crisis of confidence despite being bankrolled in July 2015 to the tune of $100 million by Russian billionaire Yuri Milner as part of an effort called "Breakthrough Listen."

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One of the main causes of pessimism: ET might not exist in this universe or even if it does, might be lower on the evolutionary scale than humans. And there's the fact SETI, or the search for extraterrestrial intelligence, has so far only investigated a very small slice of sky.

But the most demoralizing reality staring SETI in the face it we human are all alone as an intelligent species -- in this universe at least.

SETI is a collective term for the scientific search for intelligent extraterrestrial life by monitoring electromagnetic radiation for signs of transmissions from civilizations on other worlds, for example.

"Maybe they're waiting for us to stop killing each other," said Dan Werthimer, SETI's chief scientist and an astronomer at University of California at Berkeley, referring to the aliens and why they haven't revealed themselves to us.

He surmised aliens might be lower than us on the evolutionary and technological scale.

"We don't know how to find them if they are more primitive than we are," Werthimer said.

"What's the chance we can find a civilization that's just invented radio? It's kind of small in the 4 billion years of life on this planet."

There's also the chance we're more primitive than them, in which case why should they bother to contact an inferior race.

"There (are) a lot of different scenarios but the other possibility is that we really are alone and that's why we don't see them zooming around the galaxy," said Werthimer.

"We've only had 100 years, but we'd be kind of lucky to find (alien life) now because we don't know what frequency to look at, we don't know if they're broadcasting radio and we can't cover the whole spectrum. But I'm optimistic because the technology is changing so fast."

Despite this bleak scenario, Werthimer believes extraterrestrial life will eventually be found since we're still in the early stages in the hunt for ET.

"I think it's not going to be in my lifetime [that we find aliens], I think it's going to be my students or my students students...it will take a couple of generations," said Werthimer.

"It's hard to predict but my guess is that it's going to be a generation or two" before we find them or they find us.

SETI, however, has the funding to keep on looking. Milner's Breakthrough Listen project with its $100 million warchest is one of the biggest investments in SETI. It will allow astronomers to use more modern radars to scan any of the 1,000 closest stars, and to detect an alien laser with the power output of a common 100 watt light bulb from the distance of the nearest stars some four light-years away.

It also guarantees more observing time on some of the world's biggest radio telescopes, which SETI astronomers receive only one night a year.

"This is beyond my wildest dreams," said Werthimer.

"It's just a miracle," said Frank Drake, an emeritus professor at the University of California, Santa Cruz.

Tagssearch for extraterrestrial intelligence, SETI, extraterrestrial life, Dan Werthimer, Yuri Milner, Breakthrough Listen