Australia's star astronomer has debunked a Harvard professor's theory that we're not alone.

Harvard University astronomy department chair Avi Loeb believes there could be so many civilisations out there that "as soon as we leave the solar system, we will see a great deal of traffic out there".

But Associate Professor Alan Duffy is among critics who has shot down Professor Loeb's out-there claims, reports news.com.au.

Prof Loeb believes an interstellar object that passed through our solar system in late October 2017 could have been an alien probe.

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He's talking about "Oumuamua", which translated from Hawaiian means "messenger sent from the distant past".

The scientist who discovered the object dismissed the theory as "wild speculation".

But Prof Loeb came out swinging this week, defending his controversial claim to an Israeli newspaper, saying the search for extraterrestrial life was not mere speculation.

He went on to describe what would happen when we left the solar system.

"Possibly we'll get a message that says, 'Welcome to the interstellar club.' Or we'll discover multiple dead civilisations — that is, we'll find their remains."

Professor Duffy, an astrophysicist at Swinburne University of Technology, explained the amazing discovery as something exploding in the sky thousands of times a day.

"It has the energy of the sun over the course of an entire day and all of that explodes in the blink of an eye," he said.

"Australia has seen it with the Parkes telescope and now Canadians have."

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Associate Professor Alan Duffy is one of Australia's leading science communicators. Photo / Supplied
Associate Professor Alan Duffy is one of Australia's leading science communicators. Photo / Supplied

Prof Duffy said there was no way the alien theory could be right. "It's a real thing, we just don't know what it is and unfortunately someone has gone down the alien explanation route which is pretty bad," he said.

"If it was alien, there's so many of these things exploding that there would be aliens everywhere, which is a big problem because we have never seen them anywhere, so that theory is a bust."

Prof Duffy said the Parkes telescope had been capable of impressive feats over the last 50 years, since 1969 when it was a prime receiving station for the Apollo 11 mission to the moon.

Aussie movie The Dish was based on the real role the telescope played in receiving video footage of the first moon walk by the Apollo 11 crew.

And in First Man, starring Ryan Gosling as Neil Armstrong, Prof Duffy said we are reminded of Australia's longstanding space capabilities again. "This was into the unknown every step of the way," he said.

"Everything about Apollo was an adventure, and Australia was a part of that."

This story was originally from news.com.au and republished here with permission