How does the Universe's expansion relate to Newton's 1st law

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SUMMARY

The expansion of the universe does not relate to Newton's 1st law of motion. Instead, General Relativity (GR) and Quantum Mechanics provide the framework for understanding cosmic expansion, which is governed by the Einstein equations. Newton's 1st law is superseded in GR by the concept that point particles follow geodesics, the straightest paths in spacetime. Therefore, the expansion of space is not a force in the traditional sense, and Newton's laws do not apply to this phenomenon.

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  • General Relativity (GR) principles
  • Einstein equations
  • Quantum Mechanics fundamentals
  • Concept of geodesics in spacetime
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  • Study the Einstein equations in detail
  • Explore the implications of General Relativity on cosmology
  • Investigate the role of Quantum Mechanics in early universe models
  • Learn about geodesics and their significance in spacetime physics
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Astronomers, physicists, and students of cosmology seeking to understand the relationship between cosmic expansion and classical mechanics.

Pjpic
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How does the universe's expansion relate to Newton's 1st law.

In other words, is all the expansion due to an unknown cause at the big bang and the 4 forces now act on it? Or maybe is the expansion not really due to a force (as is gravity) so the 1st law doesn't apply?
 
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Pjpic said:
How does the universe's expansion relate to Newton's 1st law.

In other words, is all the expansion due to an unknown cause at the big bang and the 4 forces now act on it? Or maybe is the expansion not really due to a force (as is gravity) so the 1st law doesn't apply?
It really doesn't apply. General Relativity and Quantum Mechanics are both important for understanding the behavior of the very early universe, neither of which were conceived of when Newton wrote that law.
 
Hi,

Newtons 1st law is in GR replaced by the 'law' that point particles follow geodesics, the straighest possible paths in spacetime. However, this is a statement about stuff in spacetime, not about spacetime itself. Spacetime itself obeys in GR the Einstein equations. The expansion of space is perfectly described by these Einstein equations.

So, short answer: it does not.
 
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