To measure their quantities and properties should be studied volume, temperature and pressure.
A group of scientists from Harvard University have decided to challenge natural laws by creating a new matter on our planet.
It is a creation similar to the lasers we usually see in animated action movies.
What we have done is to create a special kind of medium in which the photons interact with each other so strongly that they begin to act as if they had mass, and they come together to form molecules.
This type of united state of photons has been discussed strongly in theory for quite some time, but until now it has not been observed, "explained Mikhail Lukin, a professor at the prestigious university.
Outside the Earth there is a fourth state, known as plasma, which abounds in places like the Sun and the stars.