Activity for dmckee
| Type | On... | Excerpt | Status | Date |
|---|---|---|---|---|
| Edit | Post #291482 | Initial revision | — | 6 months ago |
| Answer | — |
A: Why is it forbidden for two photons to turn into one? Olin and Derek have covered the biggest part of this: the combination of energy and momentum conservation rules out the two-into-one combination of photons that are not co-linear. That might leave you optimistic about having a special case, but there is one more rule to respect: conservation of an... (more) |
— | 6 months ago |
| Edit | Post #283616 |
Post edited: |
— | over 3 years ago |
| Comment | Post #283511 |
You have two distinct questions here. I've followed @Olin's lead in answering the electron-proton question, and suggest that the question text be edited to focus on that case alone. (more) |
— | over 3 years ago |
| Edit | Post #283616 |
Post edited: |
— | over 3 years ago |
| Edit | Post #283616 | Initial revision | — | over 3 years ago |
| Answer | — |
A: What happens if an electron collides with a proton? Answering from the point of view of a particle physicist. Meaning we consider an event where and electron and proton approach each other in an initially free condition (not already bound). Electron-Proton scattering Believe it or not, the whole story is >They can scatter elastically or inelas... (more) |
— | over 3 years ago |
| Comment | Post #283293 |
@Istiak There is no need or expectation that you are in school to read a text, but publishing industry pressures drive most texts into those rough categories. The only exceptions that spring to mind are self published online (and so immune to industry pressures). But in order to recommend books to ma... (more) |
— | over 3 years ago |
| Edit | Post #283429 | Initial revision | — | over 3 years ago |
| Answer | — |
A: Book suggestion category proposal The experience we had on the physics site Somewhere Else may be instructive (I've already written a little about it on Software Meta). In short, against my wishes they were allowed but because there was a fairly strong and well enforced notion of what a "good" answer would look like it worked out muc... (more) |
— | over 3 years ago |
| Comment | Post #283293 |
That said, authors don't write down every detail of every development: they expect readers to see some steps. How much they expect depends on the level of the text, the specified mathematical prerequisites, and the author's personality. Some texts are terse and expect a lot of the reader, others are ... (more) |
— | over 3 years ago |
| Comment | Post #283293 |
What level are you interested in. In the US (at least) it is typical to talk about "introductory", "upper-division", and "graduate" level texts. Introductory texts represent the first year of college instruction in physics and survey mechanics, thermal physics, and E&M in brief (the mechanics section... (more) |
— | over 3 years ago |
| Comment | Post #283046 |
While one can find an historical origin for the units in modern system they won’t be the original origin. Organized systems of units go back a long time. I’d guess they date back to roughly the origin of writing (because both relate to trade) with refinements piled on as necessary. We know a lot, for... (more) |
— | over 3 years ago |
| Comment | Post #280916 |
It’s worth noting that there is no direct relationship between indexes of refraction (at the top of the post) and corrective diopters (at the end). The closest you come is the lens-makers formula which tells you how to take those two numbers and build a suitable lens. (more) |
— | over 3 years ago |
| Comment | Post #280385 |
@celtschk "Natural units" is a broader term—it can refers to any scheme where you drop constants—and I was educated before "Planck units" had become popular. For instance I took general relativity from James Hartle (while he was developing his textbook on the subject) and he described the units he us... (more) |
— | almost 4 years ago |
| Edit | Post #280385 |
Post edited: |
— | almost 4 years ago |
| Edit | Post #280385 | Initial revision | — | almost 4 years ago |
| Answer | — |
A: Unusual way to write spacetime coordinates/metric: Is there any downside? There is no problem with the approach you suggest: it's equivalent to deciding to use seconds and light-seconds as your units for space-time four vectors instead of light-meters and meters. (I actually prefer that when I want to connect to human scaled measurements.) But ... most professionals who... (more) |
— | almost 4 years ago |