How to stop thinking about metaphysical questions?
Practice Vipassana meditation using breath or walking. This will help you to contemplate on wholesome thought. If you want to stop Vitakka and Vicara you have to practice Samatha meditation. Vitakka and Vicara stop at second Jhana which is I have not experienced myself. Being aware that your mind is unrest alone is meditation. If you can increase this awareness, you will improve your meditation eventually.