The block theory of time is flawed because it depends on an unstated assumption: proper time.
Proper time is what we describe as our experience of time in our immediate environment. It’s what we think time is as we go about our daily business. When people talk about the block theory of time, they claim that all time exists, it’s just that you have the past and the future, and the immediate now.
That’s where people are wrong. When they take a “slice” out of the block of time and call it “now”, that slice is like a Polaroid snapshot of the entire universe. And that any slice of time is infinitesimally short/thin, and no different than any other slice of time.
But proper time does not exist. It’s the immediate illusion that we create in our minds to make sense of the world. The reality, according to the general and special theories of relativity, is that every particle, indeed, every speck or “pixel” of spacetime, has its own “clock”. The follicles on your head age faster than the cells that create your toenails. Yet we ignore this fact of relativity and lump everything together, and call it proper time.
Proper time can’t exist. The ancient Greeks argued that time couldn’t exist. The past is over and done with, the future has yet to be. So what is “now”, and how does change occur in the world? Change could NOT occur in a world where proper time existed. The fact that every particle and every pixel of spacetime has its own “clock”, and is racing to be where it’s “supposed” to be, means that change is the true nature of things. Nothing is ever static so that you could carve out a slice out of a block of time. What we call the past is not true of every particle in the universe, and what we call the future has happened for some particles, but not others, in our reality. There is no “now” because, to be so, every particle would have to share the same clock. And that cannot be.
If every particle had the same clock, we’d be frozen in time. NOTHING would happen.
Any slice of time in a block of time is rather like a chocolate bar that has almonds in it. Some almond pieces stick out to the left, some to the right. It’s not a single uniform slice of chocolate bar. And this is because different particles have different clocks.