A question from hawking's grand design

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Discussion Overview

The discussion revolves around a statement made by Stephen Hawking in his book "The Grand Design" regarding the nature of electromagnetism and its interaction with particles, specifically questioning whether photons can interact with neutrons.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions Hawking's assertion that electromagnetism acts only on charged particles, specifically asking about the interaction of photons with neutrons.
  • Another participant agrees with the initial claim, stating that electromagnetism primarily interacts with charge and not with neutrons.
  • A different participant argues that Hawking's statement is incorrect, noting that while neutrons have no total charge, they possess electromagnetic properties such as a magnetic dipole moment and are made of charged quarks, suggesting that photons do interact with neutrons.
  • One participant mentions that photons have momentum, which can affect neutrons without requiring electromagnetic interactions.
  • A later reply reiterates that the interaction between photons and neutrons, which results in energy transfer, is indeed an electromagnetic interaction.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the interaction between photons and neutrons, with some asserting that photons do not interact electromagnetically with neutrons, while others argue that they do due to the underlying properties of neutrons.

Contextual Notes

The discussion highlights the complexity of particle interactions, particularly at different energy levels, and the nuances of electromagnetic properties of particles like neutrons.

jnorman
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a question from hawking's "grand design"

in hawking's new book, the grand design, he states, in his discussion of the four known forces, "electromagentism - ...acts only on particles with an electric charge..."

is this correct? do photons not interact with neutrons? can i not fire photons at a free neutrons and knock them around? what exactly is he saying here? thanks.
 
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It gets more complicated at very high energies, but for the most part: yes. Electromagnetism only interacts with charge. I.e. not with neutrons.
 


You are correct, and Hawking misspoke. While neutrons have zero total charge, they have other electromagnetic properties, for example a magnetic dipole moment. On a more fundamental level, they are composed of quarks which themselves carry a charge. So yes, photons and neutrons do interact.
 


I don't claim any high energy physics expertise, but photons have momentum, which is enough to "knock neutrons around" without any need for electromagnetic interactions.
 


AlephZero said:
I don't claim any high energy physics expertise, but photons have momentum, which is enough to "knock neutrons around" without any need for electromagnetic interactions.

The interaction that results in the transfer of energy from the photon to the neutron IS an electromagnetic interaction.
 

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