Falling In

Test Chamber 13: Place portals as shown in the image to redirect the laser. Use a time portal to move the laser into the future. You may take some damage from the laser to enter the future. Once in the future, rearrange portals without affecting the present. Position portals so the laser hits the target directly, then proceed through the exit door.

Test Chamber 14: First, travel to the present using a time portal. Summon a reflector cube from the central switch and position it in the present as indicated. Use a portal to direct a laser through the first node, then use the reflector cube to guide the laser into the next two nodes. Travel to the future. Use portals to bring a laser into the present through the time portal, ensuring it passes through the node. Retrieve the reflector cube from the future and bring it to the present via a time portal. Adjust the present reflector cube to hit all three nodes. If necessary, return to the future to retrieve the future reflector cube again if you moved it. Finally, place the future reflector cube at the end of the nodes to reflect the laser into the receiver, completing the chamber.

Test Chamber 15: Start by passing through the particle field to the left. Place a portal where the laser hits the wall and a time portal on the opposite wall. Travel through the time portal to reach the future, bypassing the particle field. Proceed to the other side of the room and use another time portal to return to the present, now on the far side of the particle field. Place a new portal on the upper wall above the laser room so the laser hits the first receiver. Travel back to the future and place a portal on the small wall in the laser room to aim at the receiver. Return to the present; the laser should still be hitting the first receiver, powering an elevating platform. Stand on this platform and place a time portal behind the node to raise the platform further, allowing you to summon a reflector cube. Place this reflector cube on the lip above the second receiver. Travel to the future by placing your time portal conveniently. Retrieve the future reflector cube and enter the laser room. Place another time portal in the laser room to bring the future reflector cube to the present. Position it to reflect the laser into the second receiver through the node. To reach the other side of the particle field without going through it, use an existing portal or a time portal. Once in the present on the other side of the particle field, climb the stairs and use a portal on the upper wall to hit the third receiver. Move the reflector cube onto the switch to complete the test chamber.