Why is gravity a weak force at the atomic scale?

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Discussion Overview

The discussion revolves around the nature of gravity at the atomic scale, specifically questioning why gravity appears to be a weak force compared to other fundamental interactions, such as electromagnetism. Participants explore the implications of quantum mechanics on gravitational effects and the potential mechanisms that might explain the perceived weakness of gravity in quantum contexts.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that classical mechanics indicates gravity should be strong at quantum distances, raising questions about the quantum mechanisms that might suppress gravitational effects.
  • Others argue that the gravitational force between elementary particles, such as electrons, is significantly weaker than the electrostatic force, even when applying classical formulas at Planck distances.
  • A participant points out that while classical expressions may suggest infinite gravitational fields for point masses, they also imply unbounded electrostatic forces, which are always greater.
  • There is a suggestion that the gravitational field may have limitations due to the quantum environment, particularly in the context of non-charged particles like neutrinos.
  • Some participants note that Newton's law of gravity is not considered a fundamental law and that the fundamental nature of quantum gravity remains unknown.
  • It is mentioned that the gravitational coupling in quantum field theory is weak compared to other fundamental interactions, and that the classical limit of a massless spin-2 field aligns with General Relativity.
  • One participant emphasizes that gravity does not "vanish" at the subatomic scale but is overwhelmed by other forces, maintaining that every subatomic particle's gravity affects others across vast distances.

Areas of Agreement / Disagreement

Participants express differing views on the nature and strength of gravity at the atomic scale. While there is some consensus that gravity is weaker than other forces, the reasons for this and the implications of quantum mechanics remain contested and unresolved.

Contextual Notes

Participants highlight the limitations of classical gravitational models when applied to quantum scales and the unresolved nature of quantum gravity theories. There is also an acknowledgment of the practical difficulties in conducting gravitational experiments with subatomic particles.

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TL;DR
Following the classical mech. g=-GM/R^2, for quantum distances the gravity force would be strong. What are the quantum mechanisms that cause the effects of gravity to vanish?
Hi. Following the classical mech. g=-GM/R^2, for quantum distances the gravity force would be strong. What are the quantum mechanisms that cause the effects of gravity to vanish? The position uncertainty or the probabilistic wave function can be a justification for suppressing strong gravitational coupling?
Thank you,
Arend
 
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Arend said:
TL;DR Summary: Following the classical mech. g=-GM/R^2, for quantum distances the gravity force would be strong. What are the quantum mechanisms that cause the effects of gravity to vanish?

Hi. Following the classical mech. g=-GM/R^2, for quantum distances the gravity force would be strong. What are the quantum mechanisms that cause the effects of gravity to vanish? The position uncertainty or the probabilistic wave function can be a justification for suppressing strong gravitational coupling?
Thank you,
Arend
Do the mathematics. The gravitational force between two electrons, say, is very weak compared to the electrostatic force.
 
PeroK said:
Do the mathematics. The gravitational force between two electrons, say, is very weak compared to the electrostatic force.
Sorry, incomplete question. For example, applying the classical gravitational force between two electrons at Planck distance results in a strong force (~1.35 x 10^20 N). I know, that the "size" of the electron is bigger, but could be the case for other scenario. The point is, the classical expression allows infinite gravitational field for a "point". tks
 
Arend said:
Sorry, incomplete question. For example, applying the classical gravitational force between two electrons at Planck distance results in a strong force (~1.35 x 10^20 N). I know, that the "size" of the electron is bigger, but could be the case for other scenario. The point is, the classical expression allows infinite gravitational field for a "point". tks
It allows an unbounded gravitational force, but also an unbounded electrostatic force, which is always much greater.

The electrostatic force between two electrons is much greater than the gravitational force. Do the maths!
 
PeroK said:
It allows an unbounded gravitational force, but also an unbounded electrostatic force, which is always much greater.

The electrostatic force between two electrons is much greater than the gravitational force. Do the maths!
For example, a not charged particle, such as a neutrino, even a very small mass would generate a huge gravitational field closer to such "point" mass. Changing the question, would the gravitational field have a limitation due to the quantum environment?
 
Arend said:
For example, a not charged particle, such as a neutrino, even a very small mass would generate a huge gravitational field closer to such "point" mass. Changing the question, would the gravitational field have a limitation due to the quantum environment?
Newton's law of gravity isn't a fundamental law. No one knows what is the fundamental law of quantum gravity.

Nevertheless, one problem is that the gravitational force is so much weaker than the electrostatic force for elementary particles.

Someone got a Nobel Prize simply for detecting a neutrino. Doing a gravitational experiment with neutrinos would be great - but the practical difficulties are immense.
 
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Understood. tks!
 
Arend said:
What are the quantum mechanisms that cause the effects of gravity to vanish?
We don't know that they do. All we know is, as @PeroK said, the effects of gravity are many, many orders of magnitude smaller than the effects of any other interaction.

Arend said:
strong gravitational coupling?
The gravitational coupling, as far as quantum field theory is concerned, is not strong. It's weak--much weaker than any of the other fundamental interactions.

Note that this is a quantum question you're asking, so the Newtonian gravitational force formula is irrelevant. We don't have a good comprehensive quantum theory of gravity, but in the 1960s and early 1970s, the quantum field theory of a massless spin-2 field was investigated, and it was found that its classical limit is General Relativity, so that QFT is at least a plausible effective theory of gravity's quantum properties. The coupling in that theory is weak, much weaker than any of the other couplings in the Standard Model.
 
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As others are telling you, the gravitational effect does not "vanish" at subatomic scale. What makes you think it does?

It certainly is overwhelmed by larger forces, but gravity is still there. In principle, the gravity of every subatomic particle affects every other particle in the universe, across vast distances.
 

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