Why Is Universal Attraction Used If Galaxies Accelerate Apart?

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Discussion Overview

The discussion centers around the terminology of "universal attraction" in the context of galaxies accelerating apart from each other. Participants explore the implications of this terminology in relation to gravitational forces, cosmological expansion, and the effects of dark energy.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants question why "universal attraction" is used when galaxies are observed to be accelerating away from each other, suggesting it might be more appropriate to describe this as "universal repulsion."
  • One participant draws an analogy with a rock thrown upwards, questioning whether it is attracted or repelled by Earth and discussing the forces acting on it.
  • Another participant emphasizes that mutual gravitational attraction is evident in the case of the Milky Way and Andromeda galaxies, which are on a collision course.
  • Some participants mention dark energy as a dominant factor at cosmological scales, which contributes to the accelerating expansion of the universe.
  • There is a challenge regarding the possibility of two objects attracting each other while one accelerates away, with references to rockets leaving Earth.
  • One participant expresses skepticism about the use of the term "universal attraction," asking for specific references that utilize this terminology and suggesting that Newtonian gravity may not apply at cosmological scales.
  • Another participant asserts that the force pushing the universe is a force of universal repulsion, prompting disagreement from others.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the terminology of "universal attraction" versus "universal repulsion." Multiple competing views remain regarding the nature of gravitational forces and the implications of dark energy.

Contextual Notes

Some statements rely on specific interpretations of gravitational forces and cosmological phenomena, which may not be universally accepted. The discussion includes references to both classical mechanics and cosmological theories, indicating a potential divergence in applicability.

Zerger
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If galaxies fly apart from each other with ACCELERATION, why is the term "universal attraction" used and not "universal repulsion"?
 
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Throw a rock staright up in the air. While it's moving up, is it attracted or repelled by the Earth? Is it accelerating? How many forces, do you think, are acting on the rock on its way up?
 
The object of the question is the universe. Maybe the rock is pushing in.
 
Zerger said:
If galaxies fly apart from each other with ACCELERATION, why is the term "universal attraction" used and not "universal repulsion"?
To expand on @kuruman's question, why do you think it is not possible for two things to attract each other even while one accelerates away from the other? How do rockets leaving Earth act?
 
Zerger said:
If galaxies fly apart from each other with ACCELERATION, why is the term "universal attraction" used and not "universal repulsion"?
The Milky Way and Andromeda galaxies are on a collision course, due to their mutual gravitational attraction. See, for example:

https://en.wikipedia.org/wiki/Andromeda–Milky_Way_collision

At the largest cosmological scales, so-called dark energy (energy of the vacuum) dominates gravitational attraction and results in an accelerating expansion of the universe.
 
PeroK said:
The Milky Way and Andromeda galaxies are on a collision course, due to their mutual gravitational attraction. See, for example:

https://en.wikipedia.org/wiki/Andromeda–Milky_Way_collision

At the largest cosmological scales, so-called dark energy (energy of the vacuum) dominates gravitational attraction and results in an accelerating expansion of the universe.
And ... so much for the Socratic Method.
 
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phinds said:
To expand on @kuruman's question, why do you think it is not possible for two things to attract each other even while one accelerates away from the other? How do rockets leaving Earth act?
Why do you think that two objects cannot repel each other, even if one is accelerating toward the other?Which should be exemplified - all rocks or all galaxies?
 
Zerger said:
Why do you think that two objects cannot repel each other, even if one is accelerating toward the other?Which should be exemplified - all rocks or all galaxies?
Answering my question with a strawman does not answer my question, even though you seem to think that it does.

To specifically answer your question, I do NOT think that two objects cannot repel each other even if one is accelerating toward the other, since they clearly can. Think magnets.
 
Can we focus on cosmology?
 
  • #10
PeroK said:
The Milky Way and Andromeda galaxies are on a collision course, due to their mutual gravitational attraction. See, for example:

https://en.wikipedia.org/wiki/Andromeda–Milky_Way_collision

At the largest cosmological scales, so-called dark energy (energy of the vacuum) dominates gravitational attraction and results in an accelerating expansion of the universe.
The force pushing the entire universe is the force of universal repulsion. Ok?
 
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  • #11
Zerger said:
why is the term "universal attraction" used
Where is the term "universal attraction" used? Please provide some specific references that use that term. Two words taken out of context are not particularly meaningful.

My guess is that those specific references are describing the Newtonian law of gravity. This law does not apply at cosmological scales.
 
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  • #12
Zerger said:
The force pushing the entire universe is the force of universal repulsion. Ok?
Not OK!
 
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  • #13
PeroK said:
Not OK!
Ok.
 

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