Why Is Universal Attraction Used If Galaxies Accelerate Apart?

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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?
 
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The object of the question is the universe. Maybe the rock is pushing in.
 
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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?
 
  • #5
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.
 
  • #6
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?
 
  • #8
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.
 
  • #9
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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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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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.
 

FAQ: Why Is Universal Attraction Used If Galaxies Accelerate Apart?

What causes objects moving away from each other with acceleration to experience attraction or repulsion?

The primary cause of attraction or repulsion between objects moving away from each other with acceleration is the nature of the forces acting upon them. These forces can include gravitational forces, electromagnetic forces, or other types of interactions depending on the context. For instance, gravitational forces would typically cause attraction, while like charges in an electromagnetic field would cause repulsion.

How does Newton's third law apply to objects moving away from each other with acceleration?

Newton's third law states that for every action, there is an equal and opposite reaction. When objects move away from each other with acceleration, the forces they exert on each other are equal in magnitude but opposite in direction. This principle helps explain the dynamics of their motion, whether it results in attraction or repulsion.

Can two objects accelerating away from each other still be attracted to each other?

Yes, two objects can still be attracted to each other even if they are accelerating away from each other. For example, if two objects are initially moving apart due to an external force but are gravitationally attracted to each other, the gravitational force will act to pull them together, even if their initial motion is away from each other.

How does the concept of relative motion affect the perception of attraction or repulsion?

Relative motion plays a significant role in the perception of attraction or repulsion. If two objects are moving away from each other, an observer might perceive repulsion. However, if the objects are under the influence of an attractive force, such as gravity, their relative acceleration might eventually decrease, and they could start moving towards each other, altering the initial perception.

What are some real-world examples of attraction or repulsion in objects moving away from each other with acceleration?

Real-world examples include celestial bodies such as stars or planets. For instance, two stars initially moving apart due to a supernova explosion might still be gravitationally attracted to each other. Another example is charged particles in a magnetic field; like charges will repel each other while opposite charges will attract, even if they are initially moving away from each other due to an external force.

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