Welcome to EF, Cla! Grammatically both are possible in English. Obviously, there's nothing wrong with the genitive version
Einstein's equations as he is the father of his equatuions and nothing in English grammar prevents us from using the genitive. However, it is also possible to use a proper noun (Einstein) before another noun in its basic form. This usage makes the proper noun adjectival and is especially common in place names:
a London night club
Waterloo Bridge
Gatwick AirportOf course
Einstein isn't a place but I see nothing wrong with
the Einstein equations. In the realm of science, there is sometimes vacillation in the use of such phrases owing to the fact that English is the leading language of science and therefore scientists from about 200 countries write theses in English. Their command of the language may vary considerably, which results in errors now and then. I think in this case both are correct, though.
CB