Let's suppose there is only one object in this universe. May that be a quark, an atom, etc. What will be the consequences? I'm not a physics expert, but this question really intrigued me, so I thought "why not ask those who are"!

Let's suppose there is only one object in this universe. May that be a quark, an atom, etc. What will be the consequences?

In terms relating to, Gravitational force, Electrical force, etc. individually, and in terms of Grand Unified Theory.
And also in terms of Quantum Mechanics. I'm assuming there will be no Quantum Mechanics, but correct me if i'm wrong.
 A: An atom and a quark are very different objects. A quark is a fundamental particle, whereas an atom is a made up of many fundamental particles (quarks and electrons) which are continually exchanging other fundamental particles such as photons and gluons.
To keep things simple, let's suppose your hypothetical universe just contains one quark. As far as we know, quantum physics will still apply in your one-particle universe, and in particular the uncertainty principle will apply. This means that your single fundamental particle will be surrounded by a sea of virtual particles, and the more precisely you try to describe it, the more complicated it will appear. In simple terms, quantum physics tells us that the model of a single, isolated particle is only a very rough approximation to reality.
A: With Quantum Mechanics (actually quantum field theory) there is no single elementary particle, but "the electron field", the "quark field" etc and their excitations (little waves in the field that we call elementary particles). OK, you can remove the "quantum fluctuations" (namely the broth of particles generated by the quantum field) and think about a theory where there is gravity (classical General Relativity) and a single classical field (e.g. the quark field or the electron field, or the photon field...). This is already a complex system which dynamics is governed by non-trivial equations. On the other hand, maybe you are asking about a single point particle (that you call "quark" or "atom") that is not the by-product of a field (i.e. it's existence is not related to the fact that it is an elementary wave propagating in a more fundamental entity called "field"). In this case my feeling is that the situation is more boring and nothing happens: the particle (supposed space exist or makes sense when there is a single point object) moves with  uniform linear motion forever.
