A question from hawking's grand design

[jnorman]

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.

 

[zhermes]

It gets more complicated at very high energies, but for the most part: yes. Electromagnetism only interacts with charge. I.e. not with neutrons.

 

[Bill_K]

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.

 

[AlephZero]

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.

 

[Drakkith]

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.