Almost all computers in the Physics and Astronomy department are using internal IP addresses. This means that unless someone is connected to the BYU internal network (on campus, ResNet, etc) then they will not be able to access most computers in the department from home or anywhere outside of BYU campus.
However, there are some options for accessing on-campus resources from an off-campus location.
Remote Desktop Gateway should work for any remote desktop connections and the RD Gateway Instructions on OIT's page can help you get connected.
If you ever want to map network drives or access any other campus resources rather than just establish a remote desktop session, you'll need VPN access which can be requested through OIT. Then you'll connect your computer's network to the campus network with OIT's provided Cisco client.
Go to OIT's page about VPN and click the order button in the top right while logged in with your BYU account. Usually within a day or less they should be able to grant your VPN access. Then download the client and follow the instructions on their VPN page for connecting to the campus network.