What is spacetime made of?
>>1
Still unsolved. You could easily have searched it yourself.
In reality, nobody knows.
Matter?
If such a fundamental question is not answered,how much can we rely on science?
>>8
Nope it doesn't tells a thing about what is spacetime made of.
Spacetime is made from space and time.
Pancakes are made out of pancakes and maple syrup.
If you don't understand how to derive algebra from Zermelo–Fraenkel set theory, how much can I rely on you giving me correct change at the supermarket checkout?
For physical reasons, a space-time continuum is mathematically defined as a four-dimensional, smooth, connected pseudo-Riemannian manifold together with a smooth Lorentz metric of signature \left(3,1\right). The metric determines the geometry of spacetime, as well as determining the geodesics of particles and light beams. About each point (event) on this manifold, coordinate charts are used to represent observers in reference frames. Usually, Cartesian coordinates \left(x, y, z, t\right) are used. Moreover, for simplicity's sake, the speed of light 'c' is usually assumed to be unity.
A reference frame (observer) can be identified with one of these coordinate charts; any such observer can describe any event p. Another reference frame may be identified by a second coordinate chart about p. Two observers (one in each reference frame) may describe the same event p but obtain different descriptions.
>>1
If I answer that you'll ask Well?? What's THAT made out of???!?.
It's stuff all the way down, young man.
Time and space are relational concepts. They are meaningless outside the context of events and objects in them.