Not so. You're right that it is an assumption that the 'laws of nature' were the same in the past, but it is an assumption that has been questioned by scientists, resulting in some detailed modeling of what kind of universe we would expect to see around us if various laws were different in the past.
So you concede the main point, OK. As for so called modelling to see if the laws were different, that is not true at all. One cannot use our time and laws today on and near earth as a basis to determine what they will be or were! ALL we see has to be in the fishbowl of our time, and our laws, and our reality. In the fishbowl earth, manscience cannot even so much as detect the spiritual! It is rather comical when they make grand pronouncements about creation based on a beggarly little limited scope of perception. Actually, when the results are taught to man and child as gospel truth, overriding the truth revealed to man by God, then it is tragic.
It turns out that although some of the fundamental constants governing the physical laws we see today could have been slightly different in the distant past, the differences would only be significant on cosmological scales and would not have significantly affected the small-scale behaviour of matter (e.g. chemistry).
That could never be determined from a fishbowl perspective! Fishbowl science and rules and methods all make that impossible. They look through a fishbowl filter and try to reinvent the spiritual created universe accordingly. Since it all seems to fit our reality here and current laws, and comes down
in our time, man has assumed this means all creation is under the same limits! That is the great mistake of science, and the Achilles heel of the scientific method.
Any changes sufficient to change the chemistry of the elements would preclude the development of the kind of universe we see today, particularly the elemental composition of stars and planetary systems.
NO! Changes from something else to what we have could not be detected
from the vantage point of where we are today!
Astronomical observations of the spectral emissions of the most distant galaxies shows that their stars are consistent with the composition we would expect from first and second-generation stars under the same physical laws as we see today.
The basics like size and distance cannot be known unless we know time exists out there and exists just as it does here! (Time is used in all measures of distance such as parallax) Furthermore, the light carrying info that streams into fishbowl earth is under our time! You cannot do something like look at a light curve, and how
much time it takes to decay or whatever, and then assume that the time we see and experience it take is universal.
The light from these distant galaxies has taken so long to reach us that what we see was emitted in the first stages of galaxy formation in the early universe, so we have independent corroboration of the relative constancy of the relevant physical laws billions of years before Earth even formed.
That is a good illustration of limited thinking. You determine how much time light takes to
move only
here where there IS time! Then you arbitrarily and without logic or reason, superimpose that time (I won't bring up space here, to keep it simple) onto the whole of the universe!!!
So the best fit to explain the observations we have made is that the physical laws determining chemistry have been unchanged at least since stars began condensing out of the primordial hydrogen clouds in the early universe.
That is one of the worst fits actually. A better fit might even be to assume that Creation Background Remnants (including gases) might exist...rather than assuming the 'gas' created all things. Chemistry in the fishbowl, is only see here. How much time any given reaction takes, for example would depend on where the reaction takes place. ( or where the light was seen and interpreted)
Have you not heard? Jesus created all things. The little baby born today (or whose birth is celebrated today) created all the stars and man, and ....everything.