Isn't the amount of matter in the universe the same, no less, nor
more, because nothing is ever lost, nor created, everything causes
everything, and thus fixated and permanent?
If this is true, then how would that be possible if Dhammas are always
changing, impermanent according to the Venerable Buddha?
All conditioned and/or compounded things are impermanent, in the sense that they would arise and cease, and also change. Only Nibbana is not impermanent. Everything else, including space, time, matter and energy are subject to arising, ceasing and changing.
Take gold for example. Gold atoms initially arose out of nuclear reactions in stars. Gold can be melted and molded using heat. Gold in its solid form can be dissolved in acid. This shows that gold is impermanent, arising, ceasing and changing. It is also compounded, in the sense that it is composed of subatomic particles like protons, electrons and neutrons. When gold is used to conduct electricity, it constantly replaces its electrons.
The total amount of matter is also constantly changing. Think about nuclear reactions in stars, radioactively decaying matter and nuclear reactors. Think of the burning of flammable objects. Think about decaying or digesting biological matter. Think about matter entering a black hole.
What about energy? Kinetic energy in a moving turbine of a windmill arose conditioned by another movement like wind. But then it ceases due to friction, and conditions the arising of other forms of energy like heat due to friction, and electricity due to electromagnetic induction. So, forms of energy too are impermanent, because they are arising, ceasing and changing. Forms of energy are also conditioned.
What about space? If you have 1 m3 of vacuumed empty space, is it permanent? If air or matter gets into it, then it's not empty anymore. According to quantum field theory, empty space is never truly empty, because quantum particles appear and disappear constantly. In cosmology, space in the universe is said to be expanding, causing galaxies to become further apart as time goes by.
What about time? Have you heard about time dilation? Time moves relatively a lot slower for an object that is moving closer to the speed of light. Therefore, time is conditioned.
The more we understand science, the more we understand that everything in the physical realm is impermanent, arising, ceasing and changing.
What about the laws of physics? Is that permanent? There is speculation among cosmologists that our universe may be one of many universes in a multiverse. They speculate that universes may be arising and ceasing like bubbles emerging and popping from a boiling soup. In each of these universes, the laws of physics may be different. So, even this could be impermanent.
Apart from Nibbana, it's almost impossible to find anything that is truly impermanent and unchanging for eternity.