Not without big compromises and a lot of extra work. If you want a truly horizontally scaling database, and not just multi-master for the purpose of availability, a good example solution is Spanner. You have to lay your data out differently, you're very restricted in what kinds of queries you can make, etc.
Clarification, you can make unoptimized queries on Spanner with a great degree of freedom when you're doing offline analysis, but even then it's easy to hit something that's too slow to work at all, whereas in Postgres I know it'd not be a problem.
