First of all, thanks for a very interesting question, even without the possibility of a poltergeist.
Let me summarise my understanding of your situation (please correct me if I'm wrong) before I offer some suggestions to isolate the cause (I can't be sure, without having physically looked at your setup, that something strange isn't going on).
In your room (the blue room) you have a wifi router connected to a broadband modem ("the one that connects us all to the internet") which establishes the internet connection from your internet service provider (ISP) via a cable connected to your telephone socket. The router is connected to the modem, presumably, via a cable running from its (the router's) WAN port to the modem's LAN port, and also presumably the router contains the access point (AP) that broadcasts the wifi radio signal for the wireless network that you and your roommates connect to when online (this signal is actually picked up by an embedded device in your laptop's motherboard called a network interface card (NIC, or wireless adapter) - it acts as a wireless receiver of the radio signals.
You are saying that when the room 1 occupant walks out of their room (do they leave their door open or closed?) you have wifi loss on your laptop and also your Android phone, and generally the room 2 occupant is not affected. You also say that when they walk back in and close the door your wifi connection is fine again (does this happen always when they do this, or most of the time, or only some times?)
You haven't given enough details, like what kind of modem you have (DSL, ADSL, cable?) and whether the modem is in the same room as the router (this is not indicated on your apartment plan, but I assuming this is the case), the position of the router in your room and in relation to the modem (which part of the room is it in, is the wireless antenna properly extended up or blocked by something else), whether the router antenna is omni-directional (the radio signal propagates in all directions from the source) or not, what kind of wifi software you have (Airport for Macs, or something else) and how old your NIC is, and whether the person occupying room 1 also has connection issues when they temporarily leave the room and come back. With regards to the last question, it may be important for you and the room 1 occupant to find out what happens to their connection when they leave the room and come back (with and without closing the door). Another question is whether the room 1 door is closed or open when its occupant walks out of or into the room and you have wifi loss.
The first link in the chain of your laptop's internet connection is provided by the router in your rooom, so I would focus on this first. Don't worry about the modem, try and work backwards to the source (modem) from the router. Presumably you are not connected to the router by an Ethernet cable (if you were connected by Ethernet then I don't think this could happen, at least not in the way you are describing) but only wirelessly.
- First, use an Ethernet cable to physically connect your laptop to the router. Provided your base internet connection via the modem is up you should be able to connect without any problems regardless of what the occupant of room 1 is doing - that should not affect a working Ethernet connection with your laptop and the router. If you can do this, then you know it is the router and/or something related to the router link with your laptop.
I will assume that this test will be successful (since your room mate in room 2 seems to be unaffected by the issue and therefore there must be a stable internet connection coming from the modem to the router, otherwise you would all have connection issues). If the test fails then it may be more serious and you may need to look at the router-modem-telephone socket link.
If the Ethernet test is successful then you can rule out the modem and focus on the router and the router-laptop link. In this case, the fact that you can't ping the router during your connection loss indicates a potentially faulty NIC (the wireless receiver in your laptop). You should always be able to ping your router when it's on even when there the modem connection is down. Check the NIC, do a diagnostics test via the OS (if you are using OS X you can use the Network Utility tool from /Applications/Utilities or via the Assist Me button on the Network panel from System Preferences. Why are you pinging 8.8.8.8? You should ping the router's private IP address (the default gateway), which is something like 192.168.0.3 - if you are using OS X or a Unix like OS you can find this out by running the terminal command ifconfig en0 or ipconfig ifaddr en0 ) in OS X you can also find this out by looking at your wifi connection properties on the Network panel from System Preferences or using the Network Utility app from /Applications/Utilities). While doing all of this make sure that you have the room 1 occupant out of the room, which you say is the cause.
If none of the above, check that the router antenna is properly extended vertically and is at a right angle to the floor, not facing horizontally or downwards at the floor. Standard consumer WRs have antennae which are not omni-directional but one-dimensional, i.e. they propagate the signal in one diretction or plane from the side of the antenna. If your antenna is not properly vertical or is directed at a certain acute angle towards room 1, say the room 1 door, then the signal from the router to your laptop bounces off from the parts of the wall and corridor near the room 1 door and isn't properly picked up by your laptop's NIC. By moving the router and pointing its antenna closer to your laptop, and trying different positions, you can figure out whether it's this or something else causing the problem.
Otherwise, check the signal strength of your wifi (you can do this by using the wifi's and/or the router's configuration/admin utility, ask your provider, they will guide you), and/or change the wifi channel. Increase the wifi signal strength and/or the channel, and test this with the room 1 occupant walking out of and into their room, while online.
There is a strong possibility that network hardware is the problem here. I attempted some of the troubleshooting suggestions given by Journeyman Geek in the comments above. In addition:
The Windows computer was set to have a static IP address (rather than obtaining a dynamic IP from a DHCP server on the network).
In the network adapter properties, I de-selected the option "Allow the computer to turn off this device to save power" so that the WiFi adapter would not go to sleep.
The scan valid interval for the network adapter was set to 120, a higher value that increases the interval for the computer to scan for another access point.
After these changes, the computer has been paired with the WiFi network for more than 8 days (longer than before). It appears that more than one action had to be performed to allow the computer to remain on the network. In the past, even if the network adapter powersave option was turned off, the computer would still drop off the WiFi network. A combination of approaches might have been necessary.
Best Answer
Try downgrading (rolling back) Wi-Fi driver as well. If it won't help, try connecting via cable (if you have an Ethernet NIC) or USB Ethernet NIC. If your connection is lost even when you're on the cable, try these steps. If you're experiencing problems only with Wi-Fi, try another Wi-Fi adapter (USB Wi-Fi for example) and see what happens.