It is believed that Vikings had a piece of advanced technology in their possession which enabled them to sail to America.
Legends speak of a strange “solar stone”, used by Vikings in the distant past, a device that acted as an ancestral GPS-like device.
In 1967 Danish archeologist Thorkild Ramskou launched a bold hypothesis: the Vikings used the polarization of light scattered by clouds using cordierite crystals in order to navigate. Only a few believed him because most people did not see how this theory was possible.
Almost half a century ago, a book called Waves, from a series of textbooks from the Berkeley Physics Course mentioned in an exercise the use of birefringence crystals as navigation instruments, something that would have allowed the Vikings to navigate and orient themselves even when the sun was obscured by clouds.
The Cern magazine, on the other hand, published an article where experts discuss a research done by Hungarian researchers. In the study, experts argued that the Vikings used Iceland spar, a clear variety of calcite common in Iceland and parts of Scandinavia. This incredible crystal has a very interesting property called birefringence: when light rays fall on calcite they will divide into two, forming a double image on its far side.
Also, Iceland space is considered as a polarizing crystal, meaning that the two images would consequently have different brightness’s, all depending on the polarization of light. However, the study proposed had two setbacks. The first is there were no medieval books that speak about the possible use of solar stones in navigation, and the second is that this crystal can only be found in Iceland. This mineral is not found in Norway, Sweden, and Denmark.
In any case, the theory proposed by Thorkil Ramskou is more plausible since the Vikings could have used cordierite to orient themselves while navigating, and this mineral is found in Norway and Sweden, unlike Iceland spar.