It means that at this point, ground based detectors probably won&#x27;t work due to the massive amount of background noise (activities from people, geological activity, etc). There are plans for detectors in space that would not suffer the same problems.<p>There&#x27;s little reason, almost none at all, to think they don&#x27;t exist. The standard model clearly predicts they should exist, and non-direct evidence has been seen already.