When you are put into the Vortex you are given just one momentary glimpse of the entire unimaginable infinity of creation, and somewhere in it a tiny little mark, a microscopic dot on a microscopic dot, which says, "You are here."Zaphod is able to survive the Vortex with his sanity intact because his ego is robust enough to conclude that the "You are here" marker means that he is the most important thing in the universe, the whole vastness of which was made specially for him.
The American Museum of Natural History has produced a video that, while not having the intended impact of the Vortex, nevertheless gives a sense of the immensity of the known universe (double click twice on the video to bring it to full screen size for maximal effect):
As the text on the video notes, our view of the known universe has a temporal as well as a spatial dimension. Because light travels at a finite speed, light from distant objects reaches us some time after it originated. When we look at Alpha Centauri, the nearest star, we are seeing it as it was about four and a half years ago. As we've developed more powerful telescopes, we've expanded our temporal as well as our spatial horizon, looking farther and farther back in time. Below is an image taken by the Hubble Space Telescope, in which the circled objects are the most distant galaxies yet detected.
NASA web page, the faint galaxies in this image are about 13 billion light years away, which means we are seeing them as they were six to eight hundred million years after the Big Bang.
Thanks to Geoff Abrams for forwarding the AMNH video.