If aliens really do exist, why haven’t they already tried to contact us?

The idea of intelligent extraterrestrial life has long gripped scientists and the public alike, with a multitude of theories about what may or may not be out there in the depths of space.

A recent study has now put forward a new explanation for why aliens haven’t visited our planet – because there is no sign of intelligence here.

In essence, they mean that we have only been sending out signals detectable from space since the 1930s, so extraterrestrials haven’t really had that long to receive the message or reply to it.

The radio waves have reached about 15,000 stars and their orbiting planets out of up to 400 billion stars in the Milky Way, the researchers said.

On top of that, the study’s author Amri Wandel, an astrophysicist at The Hebrew University of Jerusalem, wrote in the paper that it takes time for any return message from aliens to travel back.

Essentially, only stars within 50 light-years have had time to respond since Earth started broadcasting deep into space.

Not only that, but Earth’s first radio signals weren’t deliberately sent into the cosmos, meaning it would be difficult for aliens to distinguish them because of how jumbled they would be after reaching one light-year into space.

It wasn’t until 1974 that we sent the first deliberate high-power broadcast to aliens with the Arecibo message.

However, there have since been plans to send another in the form of the Beacon in the Galaxy (BITG) message.

It will include a drawing of DNA, the solar system and a diagram of the male and female form, but it also contains a lot more information about basic mathematics and science than the Arecibo message did.

All of this is evidence that extraterrestrial life just hasn’t had enough time to respond to us, the researchers say, with Wandel writing that there would have to be more than 100 million technologically advanced planets in the Milky Way for a civilisation to have even received one of them.

He believes his theory suggests there are no intelligent aliens within about 50 light-years of Earth, but that doesn’t rule out them existing somewhere in the Universe.

It may be that they’re waiting for Earth’s technological signals to reach them, or their reply is still on the way.

‘The contact probability is defined as the chance to find a nearby civilisation located close enough so that it could have detected the earliest radio emissions (the radiosphere) and sent a probe that would reach the Solar System at present,’ Wandel wrote.

‘It is found that the current contact probability for Earth is very low unless civilisations are extremely abundant.

‘Since the radiosphere expands with time, so does the contact probability.’

He added: ‘The Contact Era is defined as the time (since the onset of radio transmissions) at which the contact probability becomes of order unity. At that time alien probes (or messages) become more likely.

‘Unless civilisations are highly abundant, the Contact Era is shown to be of the order of a few hundred to a few thousand years and may be applied not only to physical probes but also to transmissions (i.e. SETI).

‘Consequently, it is shown that civilisations are unlikely to be able to inter-communicate unless their communicative lifetime is at least a few thousand years.’

The new preprint paper has been published to the arXiv database.

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