The scientists performed a calculation based on the likelihood of technological civilisations arising among the stars, and the probable length of time they had been transmitting signals across space.
They concluded that while there was no reason to think we are alone in the universe, getting in contact may take some time.
US researcher Evan Solomonides, a PhD student from Cornell University, said: "We haven't heard from aliens yet, as space is a big place – but that doesn't mean no one is out there.
"It's possible to hear any time at all, but it becomes likely we will have heard around 1,500 years from now.
"Until then, it is possible that we appear to be alone, even if we are not. But if we stop listening or looking, we may miss the signals. So we should keep looking."
Astronomers have long pondered why, given the number of stars in our galaxy, the Milky Way, there has been such...