Ask a question in the box below, or search using the box above.

As you enter your question, our massive, TARDIS-sized computers will search out other similar questions. So be sure to check the list that pops up before asking your question. Once you've decided that your question has not been asked before, push the not-so-threatening blue button below.

If you want to ask questions needing speculation or people's opinions, please do it in our Watercooler forum, not here. The main Q&A space is for questions with definitive factual answers. Thanks!

To avoid spoilers in the main Q&A section, please do to not post information about stories that have not been released in the UK, or ask for information about stories that have not yet aired there.

These are two different kinds of universes. The one that Rose is in is called a "parallel" or "alternate" universe, and was said to be of the kind of universes that branch off from another universe whenever a decision is made or an action is taken, forming an alternative universe in which a different action or decision took place and thus set history on a different course ("Doomsday"). These universes are separated from each other by the "walls of reality," which were sealed after the Time Lords were put in a time lock. Because the walls of reality are closed, the Doctor cannot cross over into these kinds of parallel universes.

The universe in "the Doctor's Wife" was described as a "bubble universe," or another pocket of space that is connected to the universe by a time rift (like a small soap bubble forming on the skin of a larger soap bubble, hence the term "bubble universe"). The Doctor is able to enter bubble universes because they are connected to the primary universe by a time rift, which can be easily traversed - there are no "walls of reality" dividing the universe from any smaller "bubble universes."