The Variable — LASERS Walkthrough

Test Chamber 13: Place portals as shown in the image. Use a portal to move the laser sideways and a time portal to move it into the future. You can take some damage from the laser to travel into the future. Once in the future, rearrange portals without affecting the present ones. Position portals so the laser goes directly into the target, then proceed through the door.

Test Chamber 14: First, travel to the present using a time portal. Summon a reflector cube from the center switch and position it in the present as shown. Use a portal to bring a laser through the first node, then use the reflector cube to direct it 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. 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 other 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 shoot at the receiver. Return to the present; the laser should now be hitting the first receiver, powering an elevating platform. Stand on the 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. Retrieve the future reflector cube and bring it back to the present via a time portal placed in the laser room. Position it to reflect the laser into the second receiver through the node. To get to the other side of the particle field without going through it, use a portal on the other side or a time portal. Once in the present on the other side, climb the stairs and place a portal on the upper wall to hit the third receiver. Move the reflector cube onto the switch to complete the chamber.