Does gravity affect the past?

At the quantum level, yes. Quantum uncertainty applies as much to time as to space. You are strictly forbidden from knowing the absolute position of any graviton in spacetime.If you hold Superstrings to be real and the Copenhagen interpretation to be correct, there is

How is it that NASA astronaut, Scott Kelly's historic one-year mission aboard the International Space Station (ISS), made his identical twin Mark an even older brother? Does it mean that time and space have an effect on our body?

It didn't. That's just silly Michio Kaku hoohah.The time dilation attributable to being in orbit around the Earth is utterly, utterly insignificant to human experience. So far, in the lifetime of the ISS, the total time dilation is less than one-tenth of one second. A watch would have to be onboard ISS for 140

In layman's terms, what is spacetime in string theory?

You ask for an explanation in layman's terms but in the question details you talk about QFT, GR and position operators. So I'll give you an explanation that assumes basic knowledge of QFT and GR; it might not be suitable for an actual "layman".We only know how to describe string theory perturbatively. What this means is

Does anxiousness cause time to slow down?

There's this funny thing about time, that we only have moments. Moments are infinitely small.The sense of a flow of time that we experience inside every single isolated moment is based on memory. No memory, no experience of a flow of time.For instance, there's a condition where people