Gap Fill - Level 4


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   billion      billions      contact      extraterrestrials      galaxy      galaxy      humans      languages      life      one      other      place      possibility      should      signals      space      stars      theories      there      yet  
It could be 1,500 years before make with aliens. Astronomers joined two about the of life on planets. One theory is the Fermi Paradox. This states that while of Earth-like planets exist in our , not has made contact . The other is the mediocrity principle. This suggests that because there is on Earth, it will exist on Earth-like planets in the universe.

Researcher Evan Solomonides said: "We haven't heard from aliens yet, as is a big , but that doesn't mean no one is out ." He said may not have decoded the we sent. They would also need to decode 3,000 human . Signals from Earth have reached 8,500 ; our Milky Way has 200 stars. Solomonides said: "If we stop listening or looking, we may miss the signals, so we keep looking."

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