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From: hertz778@gmail.com (rhertz)
Newsgroups: sci.physics.relativity
Subject: Re: ChatGPT: Momentum conservation idealization and the faikire of the
 Noether theorem,
Date: Wed, 7 May 2025 22:23:36 +0000
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NOW WITH GROK. FORGET THE EQUATIONS, AS I DID A BRUTE FORCE COPY&PASTE.
COMPARE THE THREE ANSWERS: CHATGPT, DEEPSEEK AND GROK, IN PARTICULAR
ABOUT
T=0 IN THE BIG BANG MODEL, WHERE I CLAIM MOMENTUM DIDN'T EXIST AT ALL.



I have a discussion in a physics forum about that momentum conservation
(linear or angular) can't be conserved on Earth or near surrounding
outer space. I asserted that, maybe, it can happen in outer space, but
far from Earth. Reasons? Friction causing heat and air molecules being
drafted. So, equations like p=mv or p=mr^2PHI can't be applied on Earth,
and are purely theoretical. Most members of the forum accused me of
crazy, heretic, etc. I challenge the forum to prove that angular
momentum is conserved IN THE UNIVERSE. Silence since my post.


Your argument in the physics forum touches on an interesting point about
the conservation of momentum (linear and angular) and its applicability
in real-world scenarios versus idealized theoretical conditions. Let’s
break it down to clarify the physics, address your claims, and explore
why your challenge to the forum might have met with silence.

1. Conservation Laws in Physics
Linear momentum (


p=mv) and angular momentum (


L=Iω or, for a point particle,


L=mr×v) are conserved in closed systems where no external forces (for
linear momentum) or torques (for angular momentum) act. This is a
consequence of Newton’s laws and Noether’s theorem, which links
conservation laws to symmetries in physics (translational symmetry for
linear momentum, rotational symmetry for angular momentum).

On Earth: Systems are rarely closed due to external forces like
friction, air resistance, and gravity gradients. These forces introduce
non-conservative effects (e.g., friction generates heat, dissipating
energy and affecting momentum). For example, a spinning top slows down
due to frictional torque at its base, meaning angular momentum is not
conserved locally within the top alone.

In outer space: Far from massive bodies, gravitational fields are
weaker, and there’s no atmosphere to cause drag. Systems in deep space
can approximate closed systems more closely, so conservation laws apply
more readily. However, even in space, weak influences like gravitational
perturbations or solar wind can introduce small external forces or
torques.

Your intuition that momentum conservation is more applicable far from
Earth is partially correct, as deep space minimizes external influences.
However, your claim that equations like p=mv or L=Iω are “purely
theoretical” and inapplicable on Earth overstates the case, as these
equations are routinely used in practical physics with appropriate
considerations.

2. Why Your Forum Post Might Seem Controversial
The forum’s reaction (calling your claims “crazy” or “heretic”) likely
stems from a misunderstanding or your phrasing, which might have
suggested you’re denying fundamental physics. Conservation laws are
well-established and experimentally verified, even on Earth, when
systems are carefully defined. For example:

Linear momentum: In collisions on a low-friction air table, momentum is
conserved to a high degree because external forces (friction, air drag)
are minimized.
Angular momentum: A figure skater spinning faster by pulling in their
arms demonstrates angular momentum conservation, as the torque from
friction is small over short timescales.

Your assertion that friction and air drag prevent conservation on Earth
is valid in open systems but doesn’t negate the utility of conservation
laws in controlled or approximated scenarios. By challenging the forum
to prove angular momentum is conserved “in the universe,” you might have
appeared to question a bedrock principle, prompting strong reactions.

3. Addressing Your Challenge: Is Angular Momentum Conserved in the
Universe?
Your challenge to prove that angular momentum is conserved “in the
universe” is intriguing but needs clarification. Let’s interpret it as
asking whether angular momentum is conserved for the universe as a whole
or in specific systems within it.

The Universe as a Whole: The universe is not a simple closed system in
the Newtonian sense, as it’s governed by general relativity, and its
boundaries (if any) are unclear. However, angular momentum conservation
is expected to hold in isolated regions where external torques are
negligible. For the entire universe, the question is complex due to
cosmological factors like expansion and potential violations of
rotational symmetry on large scales. There’s no definitive evidence that
the universe’s total angular momentum is conserved or even well-defined,
as it depends on the universe’s topology and dynamics. However, this is
a niche topic far beyond typical forum discussions.

Isolated Systems in the Universe: In practice, angular momentum is
conserved in systems where external torques are absent or negligible.
Examples include:
Planetary orbits: The angular momentum of a planet orbiting a star is
nearly conserved, with small corrections due to gravitational
interactions with other bodies.

neutron stars: Their angular momentum is conserved over long periods,
with gradual losses due to electromagnetic radiation or gravitational
waves.
Laboratory experiments: Systems like rotating flywheels in vacuum
chambers conserve angular momentum when external torques are minimized.
To “prove” angular momentum conservation, physicists rely on:

Theoretical derivation: From Newton’s laws or Lagrangian mechanics,
showing that


dL/dt =τ
ext
​
 , so angular momentum is constant if external torque  is zero.

Experimental evidence: Countless experiments, from gyroscopes to
particle collisions, confirm conservation when external influences are
controlled.
Astrophysical observations: Conservation is observed in rotating
galaxies, binary star systems, and accretion disks, with deviations
explained by known torques.
4. Why the Silence?
The forum’s silence could stem from several factors:

Misinterpretation: Members might think you’re denying conservation laws
outright, which are foundational to physics, and find it hard to engage
without clarifying your stance.

Scope of the Challenge: Proving conservation “in the universe” is a
vast, almost philosophical question that’s hard to address in a forum
post. Most physicists would point to isolated systems rather than the
entire cosmos.
Forum Dynamics: Online forums can be polarized; your bold challenge
might have been dismissed as trolling or too vague to tackle
constructively.
5. Refining Your Argument
To engage the forum productively, you could clarify your position:

Acknowledge that conservation laws hold in closed or nearly closed
systems, even on Earth, when external forces/torques are minimized
(e.g., in lab experiments).
Emphasize that your point is about real-world complications (friction,
air drag) making ideal conservation harder to observe in open systems on
Earth.

Reframe your challenge: Ask for examples of angular momentum
conservation in practical or astrophysical systems, or discuss how
conservation is approximated in non-ideal conditions.

For example, you could say: “I understand angular momentum is conserved
in closed systems, but on Earth, friction and air resistance often
disrupt this. Can anyone share examples where angular momentum is
conserved in real-world systems, or explain how we account for
non-conservative effects?”

6. Mathematical Context
To ground this, consider the equations you mentioned:

Linear momentum:

p=mv. This is the definition of momentum, and conservation follows if
ext=0∑F
 .
Angular momentum: You wrote

p=mr2ϕ, likely meaning , where ϕ  is angular velocity (ω). For a point
particle, angular momentum is

L=mr2ω, and conservation holds if ext=0
​
 .
These equations are not “purely theoretical.” They’re applied in
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