During density switching, which alien visitors and their ships and even their contactees are doing regularly, the mass being switched is relatively small. The switch, as we have explained, is done by making a reservation in the density receiving the mass, so a collision is avoided. But during massive switching, as will occur during the Earth's Transformation to 4th Density, other procedures are involved. There is, at the present time, nothing in 4th Density in the Solar System except alien visitors and their paraphernalia. This is moved aside. Then the switch will be made, and then the alien visitors will migrate back, setting up housekeeping in different places.