B Understanding randomness in universe

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In a one-particle universe, the concept of randomness is limited as the evolution of the particle is governed by its Hamiltonian without any meaningful measurement. Introducing additional particles complicates the scenario, as their interactions lead to more complex dynamics. However, without a macroscopic measuring device, the notion of measurement remains ambiguous, suggesting that randomness may not truly exist. This discussion highlights a variation of the measurement problem in quantum mechanics. Understanding these principles is essential for exploring the nature of randomness in the universe.
shivakumar
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TL;DR
finding randomness in single particle universe and understand randomness in nature
how will randomness of particle be in one particle universe? how will it evolve with two, three or four particle based universe?
 
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shivakumar said:
TL;DR Summary: finding randomness in single particle universe and understand randomness in nature

how will randomness of particle be in one particle universe? how will it evolve with two, three or four particle based universe?
As far as QM is concerned, a universe with a small number of particles will evolve under the Hamiltonian associated with their mutual interaction. Without a macroscopic measuring device, the question of a measurement of the particles is meaningless. In that sense there is no randomness.

That is one variation of the so-called measurement problem.
 
For fun I was trying to use energy considerations to determine the depth to which a solid object will sink in a fluid to reach equilibrium. The first approach that I tried was just to consider the change in potential energy of the block and the fluid as the block is lowered some unknown distance d into the fluid similar to what is shown in the answer to this post. Upon taking the limit as the vessel's cross sectional area approaches infinity I have an extra factor of 2 in the equilibrium...
Some physics textbook writer told me that Newton's first law applies only on bodies that feel no interactions at all. He said that if a body is on rest or moves in constant velocity, there is no external force acting on it. But I have heard another form of the law that says the net force acting on a body must be zero. This means there is interactions involved after all. So which one is correct?