42,634 reputation
458136
bio website inspirehep.net/…
location Duchy of Grand Fenwick
age 44
visits member for 4 years, 9 months
seen 6 hours ago

Experimental nuclear and particle physicist. These days I'm teaching, but I've spent a lot of time on nucleon structure in fixed target electron scattering and neutrino oscillations using reactors and beam sources.

Been reading Zemansky & Dittman's book on thermodynamics recently. Quote: ``The concept of temperature is rich in interpretations and levels of abstraction.'' Nice.


9h
comment How to determine the observables rigorously?
"I know that this works, but how can one justify that?" Not to poo-poo the possibility that there might be deeper mathematical structure at work here, but ... this is science "it works" is the ultimate justification. If someone shows you a deeper mathematical structure, the reason you should use it is because "it works", not because it is math or even because it is rigorous.
9h
comment Does nitrogen have the strongest bond in chemistry. If so, could a nitrogen-based material be stronger than graphene or carbyne?
Anyone know if [chemisty.se] like being used as an alternative to google? There is a flag for migration to that site, but I want to follow the "don't migrate poor quality questions" guideline and this would seem to qualify (for the reason Floris outlines) unless chemistry specifically accepts such questions.
9h
comment The History of Dark Matter
If I may say so (without moderator's hat), from your earlier comments I assume have a alternate theory in mind. In that case I would suggest that the details of why equilibrium is understood to exist may be important to you, but focusing on the history of how it came to be believed is not a road you want to go down. A myopic focus on the lines of "but [originator] should never have thought [idea, now perhaps even outmoded] in [long ago year] because..." is the hallmark of one kind of crank. Keep the focus on the arguments used by today's scientists to present a credible alternative.
15h
comment Why do so many galaxies in clusters have a near zero velocity?
I'm with Kyle. Better to edit slightly and preserve the good than to toss out the effort.
1d
comment Do individual rays of light lose energy via the inverse square law?
I like your comment about the meaning of an isolated ray. We don't generally draw just one so I hadn't thought about it, but it is clear that just one can only convey direction and should be taken to stand for a plane wave.
1d
comment Why do so many galaxies in clusters have a near zero velocity?
@KyleOman I have to say that I think this answer covers an important notion that may not be clear to Donald. That many objects in an extended bound system should have small relative velocities is not always obvious.
1d
comment Do individual rays of light lose energy via the inverse square law?
I don't know that "it represents a plane wave" is really applicable in many situation introduced to students in a intro course. When you are doing the unit on image creation be mirrors and lenses most rays diverse from nearby objects. In that case the ray has to be taken as standing in for all the rays in a region which are, in general diverging slightly. Under those assumptions the intensity associated with any given ray is falling as it propagates.
2d
comment Best twin paradox trajectory for constant acceleration rocket?
Of some possible interest here: Elisha Huggins' article "Gravity, Time, and Lagrangians" in The Physics Teacher vol 48.
2d
comment Why are neutrinos ruled out as a major (or even sole) component of dark matter?
This answer might be slightly improved by being specific that it refers to know neutrino flavors, and that there is still speculation about possible heavy, sterile flavors as a possible dark matter component.
2d
comment What all has intrinsic spin?
Spin anugular momentum takes on values that are forbidden to $\mathbf{r}\times\mathbf{p}$ angular momentum (i.e. the stuff involving extended matter actually whirling around). So it is "of the same nature" (i.e. angular momentum), but not generated by extended matter in rotational motion. So, yeah. Pretty much wrong.
2d
comment Is there a difference between 0.18 and 0.180 seconds?
This. Following (correctly) the conventions about recording numbers can make the difference significant, but reading the difference as significant when the writer wasn't following them is an error. It's about communication.
2d
comment What all has intrinsic spin?
@SebastianRiese A number of people have been throwing that link around a lot lately and trying to imply that it proves something that it doesn't. All that the Einstein-de Haas effect tells you is that spin is angular momentum. But we knew that. It doesn't address why spin can take on values that are forbidden by the quantization of $\mathbf{r}\times\mathbf{p}$, and that is why it doesn't prove that electrons are little whirling balls.
2d
comment Why can gold be drawn out finer than light?
Meh. It takes a strained interpretation to allow that phase to be true. In a natural interpretation it's nonsense because light doesn't have a limiting transverse extent. The "sizes" you've quoted for light are wavelengths (which are longitudinal.) and they also require that "light" be interpreted to mean "visible light". Crappy writing that favors drama over accuracy.
Aug
31
comment Intuitive definition of electromagnetic field
Textbooks aren't interactive. They can't do the demo, so those that take that approach describe some situations. Often one they hope the students will be familiar with. But most of the recent texts I've looked at for intro electrostatics use a fairly definition driven style. The thing is that you don't have to see the demos to understand that the purpose of all this mucking around with abstract concepts is to describe nature; of course if you don't it really helps to have someone put the abstractions in context for you.
Aug
31
comment Intuitive definition of electromagnetic field
Presentation in terms of a formal system or by leading with a bunch of demos is a implementation detail of a particular teaching strategy. I strongly prefer demo-led for introductory courses, but rather like the formal approach for some advanced subjects.
Aug
31
comment Is Wikipedia's definition of angular velocity incorrect?
A common first counter-example is a massless bar with two point masses on the ends rotating about a axis through its center that is neither co-linear with nor perpendicular to the bar.
Aug
31
comment Is Wikipedia's definition of angular velocity incorrect?
@0celo7 Watch out for with the claim that the angular momentum is parallel to angular velocity. In general $I$ is a second rank tensor and they are not guaranteed parallel.
Aug
31
comment Shouldn't dark matter distort light and there for be directly detectable?
The word you want is "microlensing", and it is a minor industry these days though it does not distinguish between baryonic and dark matter.
Aug
30
comment Will a string always be tangent to a pulley at 45 degrees above the horizontal?
Grab a pulley (or wheel, or pipe) wrap some string around it and play with it. A taunt string will always be tangent to the object, but can take on any angle.
Aug
30
comment Is displacement in circular motion a chord or an arc?
Instantaneous speed is the magnitude of instantaneous velocity, but that does not mean that average speed is the magnitude of average velocity.