Mapping the World
Maps are everywhere: from pirate novels to car GPSs. But what does it actually take to make them? For centuries cartographers used all available sources of information to accurately craft the first maps. However, as few as a couple hundred years ago, no complete geographical map of the Earth existed.
A so-called “Birth certificate of America”, the first map that outlined America as a separate continent was made only in 16th century (Figure 1). Australia was discovered by the Western world in 1630s and Antarctica in 1820s.
During the past few centuries the geographical maps have improved dramatically and nowadays nobody expects to discover a new continent or even a tiny island (however, some deepest regions of the oceans remain unvisited). Does it mean that the whole mystery of exploration and pioneering is gone? Does the World map end here? Let us look around. The closest object to the Earth is its moon — the Moon. You can see the craters on it with your naked eye. It may look like nothing intriguing is happening over there. However, the humanity has been staring only at one side of the Moon, because its orbital and axial rotations are synchronized, until 1950s, when the opposite — “dark” — side was revealed (Figure 2).
Since then, numerous spacecrafts explored the Solar system, taking a closer look at each of the planets and even asteroids (Figure 3). Most recently NASA’s spacecraft New Horizons captured a photo of Pluto, revealing its landscape.
Even though the map of the Solar system still has unexplored corners, its mechanics is well understood. So what is beyond it? The night sky was a source of inspiration for many cultures (Figure 4). Human can see up to a few thousand stars by a naked eye. A thought that those tiny dots are similar to our Sun came relatively early — in Ancient Greece (Anaxagoras, 450 BC). Most recent surveys include up to billions of stars (about 1% of all stars in Milky Way) and allow to arrange a three dimensional map of local stars (Figure 5).
Of course the Milky Way is not the limit. The past few decades have seen many experiments devoted to exploring the Universe beyond the Milky Way. Most recent studies allow scientists to assemble the three dimensional map of galaxies for up to few billion of light years across (Figure 6).
Can we expand our World map even further? Easily. When we look deep into the sky between galaxies we see darkness. Nothing. Almost: there is dim glow, which is called the Cosmic Microwave Background (CMB). It is the echo of the Big Bang, which was predicted and measured in 20th century. The CMB is nothing else but the map of the primordial quantum fluctuations from which the galaxies and everything in them originated. It is the furthest thing we can potentially observe given our current understanding of the physics of our Universe (Figure 7).
Since we cannot see anything else, the mapping the world could be assumed to be complete. It may seem that the science of the last century answered all our questions about the Universe. But is it really the end of the story? If everything is mapped out what would be our next steps?
Mapping the World is far from complete. However, our further exploration of the Universe might not be about traveling like it was in the 15–18 centuries, or about sending out robots to planets and asteroids, or about taking pictures and observing with telescopes. Current science leads us to questions of a different sort. We know where Black Holes are, but we do not know how they work and what is inside. We know that Dark Matter exists, but we do not know what is it and how to detect it. We know that many species of elementary particles exist, but we do not know why we ended up with exactly this set of particles. These are the problems that will be the focus of science in the 21st century.