Final answer:
Mrs. Whatsit made the characters watch an empty space to disconnect them from a virtual reality room and encourage them to engage in the real world.
Step-by-step explanation:
Mrs. Whatsit made the characters watch an empty space in the story because the empty space represented a nursery room. In the story, the nursery room was a high-tech virtual reality room that could create realistic environments, such as an African veldt with lions. However, Mrs. Whatsit believed that the children were using the room too much and becoming too attached to it, so she made them watch an empty space to disconnect them from the virtual reality and encourage them to engage in the real world.