Which underlying assumption is made when creating models for the universe?

The laws of physics are the same everywhere in the universe

Explanation:

The underlying assumption made when creating models for the universe is that, the laws of physics are the same everywhere in the universe.

answer and explanation;

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =