Yes, there are big T truths.
They are layers this universe is built upon.
They are all extremely metaphysical, because the physical stems out of them.
They are the building blocks, or first layers of this universe.
And there are truths which are outside of human's ability to think currently.
Gravity and all the other physics phenomena (like space and time) are subservient to these truths.
As you seek, so shall yee find. Enjoy your journey.
How do you know?
From direct knowing.
But you can also come about it from the angle of they can't be disproven. So, you can chip away all else and be left with the Truth.
Many people are ego-invested in not knowing these truths, and so you get a lot of flack for writing them out.