35,901 reputation
350122
bio website inspirehep.net/…
location Duchy of Grand Fenwick
age 43
visits member for 4 years, 1 month
seen 13 mins 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.


Mar
16
comment Must the Lagrangian always be known for the Euler-Lagrange equations to be of any use?
The Euler-Lagrange equation were originally derived without an extremum principle at all. You can see a modern version of that derivation in Goldstein.
Mar
16
comment How is parity relevant to determining angular momentum?
The parity quantum number is defined if the the state is (anti-)symmetric under reflection: that is $\psi(\vec{x}) = \pm \psi(-\vec{x})$. If parity is defined it is $\pm1$ according to the sign of the first relationship. You are probably expected to know that even orbital angular momentum states have parity +1 and odd orbital angular momentum states have parity -1.
Mar
16
comment Why do far away objects appear to move slowly in comparison to nearby objects?
Welcome to Physics.SE, kiranadhikari. Like the rest of the Stack Exchange network we use a questions and answer model here, not a threaded conversation model and there is not fixed ordering of posts. That means that phrases like "I also think the same.." are not very useful because the antecedent is not clear. On top of that "The basic definition of relative velocity must be wrong.." is a very strong claim as physicists and engineers have been using those definitions successfully for centuries. The concept that you may be looking for, "angular velocity", has also been known for centuries.
Mar
16
comment Can negative energy explain black holes?
You do realize that we haven't study any black holes in an experimental way, and that they are known entirely from some limited observational evidence and the existence of a theoretical explanation, right? Is there a particular reason you think that they need a new explanation? Any particular reason you think that objects which are observed to curve space with very high positive energy density should be explained by negative energy? I'm tempted to close this as so speculative as to be off-topic until someone explains to me that I'm off base here. Using small words, please.
Mar
16
comment What is the path integral exactly?
John, you can merge this account with you others at physics.stackexchange.com/help/user-merge. Of course, using a registered account will reduce the likelihood of that happening at all.
Mar
16
comment What does the quantification of causes and effect look like, for clouds in offshore wind turbine wakes?
Link only answers are strongly discouraged. Look how Martin's answer has included some text from the papers abstract that provides an outline of the argument. That is enormously more useful than just "here is a link".
Mar
16
comment Nuclear reaction: creation of deuterium
Yep. For myself I would usual say one equation but it is one for equality of four-vectors. Or you are welcome to think of it as one for energy and one for the vector momentum. Or you can rip them apart and count them individually. In this case there is a rotational symmetry, but pick one plane (say, x--z) and work it that way.
Mar
16
comment Nuclear reaction: creation of deuterium
"So seems im supposed to set up two equations: energy- and momentum-balance." Yep. Except that you have three equation: one for energy, one for momentum along the protons initial momentum and one for transverse momentum. The problem is highly constrained: there is only one free parameter which can be the angle they've asked about. Do it using $E^2 = m^2 + p^2$ (in $c = 1$ units or the expanded version if you prefer) and do not muck about with factors of $\gamma$: just momentum, energy and mass.
Mar
16
comment Number of configurations of the universe
John, you have the power to delete question with no upvoted answers, but you should not remove the content from posts and leave it on the site. Posts here are not ephemeral, they are expected to last delete it if you must but do not erase it that way.
Mar
16
revised Number of configurations of the universe
rolled back to a previous revision
Mar
15
comment Electric field outside nonconducting sphere
We strongly discourage re-asking questions here. There are some other strategies that you can employ. The other thing that you can do is focus on the physics that you.re tripping on. You presumably saw a Gauss' law based derivation for the region outside a charged sphere at some point. You can use the same set of arguments to solve you problem here. You need (1) the system has spherical symmetry and (2) how much charge is at lower radius that the point you are trying to find the field for.
Mar
15
comment Going through a ring of black holes
I'm way way out of my depth here, but I think there has been some work on extremal Kerr black holes that heads in the same direction. Of course, that also leads into the question whether naked singularities can occur or not, but that is also outside my ken.
Mar
15
comment Going through a ring of black holes
"Suppose moreover that the event horizons of neighboring holes overlap" You're going to run into real trouble here ... I believe, that there is no such stable relationship, though I'd have to ask one of our theorists for a reference.
Mar
15
revised Electric field due to nonconducting sphere
deleted 5 characters in body
Mar
15
comment Electric field outside nonconducting sphere
The string of question you've asked look a lot like you are trying to get physics.se to work your problem for you by iteration. We've not going to do that. If you have questions about physics not about a question you are facing we'd be happy to help you understand whatever it is that is troubling you.
Mar
15
comment Should the electric potential of a positively charged sphere be negative?
It is, of course, vitally important to get the sign of $d\vec{r}$ right, but do not neglect that you can make a gauge transformation to get any particular point at any potential you care to name.
Mar
15
comment If we are using [eV] as a unit for energy, what, then, should the unit for mass and distance be?
Wadda ya mean "if"? //particle physicist who knows that $c = 1$ so that mass is in units of $\text{eV}$ and length is in units of $\text{eV}^{-1}$ like God and Leon Lederman intended
Mar
15
revised Should the electric potential of a positively charged sphere be negative?
fix latex; strip sighn off
Mar
14
reviewed Approve Potential of particle exchange
Mar
14
comment Ion Drive Propulsion Top Speed
Well, this is true, but for long journeys the top speed is usually given by the mass-fraction of fuel available (because you generally can not carry enough fuel to burn all the way to a space-patrol style flip-turn at the middle of the trip and that is, in any case, an inefficient way to use your fuel) and the specific impulse of your drive. Ion drives have very high specific impulse by comparison to chemical rockets.