SG Atlantis #2

If you are not familiar with the science fiction series Stargate Atlantis, it involves a group of people from earth who have managed to travel to another galaxy, the Pegasus Galaxy, by means of a "Stargate". There they encounter a race of life-sucking aliens referred to as the Wraith who just love to "feed" on human beings by sucking the life out of them, leaving a shriveled corpse behind.

The following question doesn't require any specific knowledge, but does require a general awareness of the reality how things are in space.

In one episode of SG Atlantis, "Intruder", our heroes are onboard a newly designed spaceship that is capable of travelling between galaxies. At the beginning of the show two of our people are seen aboard the spaceship complaining that it takes 18 days to travel the distance to Atlantis in the Pegasus Galaxy, instead of 3 or 4 days as it previously took, because they no longer have a "Zero Point Module" to power the spaceship.

During the trip they discover that the ship's computers have a virus, and it is suggested that they stop and remove the virus before completing their trip. The captain of the ship says that they have less than two days to reach Atlantis and he would prefer not to stop and drop out of "hyperspace", and thereby risk being detected by the Wraith, because they are now in the edge of the Pegasus Galaxy, where the Wraith inhabit.

However, the scientists on board convince him to do so. In attempting to remove the virus, they discover that it is an intelligent virus that is able to observe them, predict their responses, and take steps to protect itself from being destroyed, including killing people who get close to discovering its secrets. The virus directs the spaceship toward a nearby sun to destroy everyone. It takes several attempts to get the virus out of the computers, but they finally do so and regain control of the spaceship (just in the "nick of time" to avoid all being killed, of course).

What is wrong with the above scenario?

Answer:

With almost two days to go they would still not be near the Pegasus Galaxy. As with most things in space, galaxies are very tiny compared to the distance between them. The Milky Way Galaxy is between 100,000 to 180,000 light-years in diameter (50,000 to 90,000 light-years in radius) and the Pegasus Galaxy, a "dwarf" galaxy, is about 2,000 light-years in diameter (1,000 light-years in radius), whereas the distance between them is about 3 million light-years. The radius of the Pegasus Galaxy is thus 1,000/3,000,000 or 0.03% of the whole journey. If they were travelling at a rate of speed to travel the entire distance in 18 days it would only take only about 8 1/2 minutes to travel from the edge to the center of the Pegasus Galaxy or 17 minutes to completely cross the Pegasus Galaxy, not nearly 2 days.

Below is a more-or-less scale drawing of the trip. (Actually if the Pegasus Galaxy were drawn to perfect scale it would be a dot rather than a circle.) The arrow points to the location of the ship with two days left to travel -- nowhere near being inside the Pegasus Galaxy yet.

Of course, being between galaxies, this also means that there would not likely be any nearby stars for the virus to fly the spaceship toward.