35,901 reputation
350122
bio website inspirehep.net/…
location Duchy of Grand Fenwick
age 43
visits member for 4 years, 1 month
seen 8 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.


1h
comment How do we find the accuracy of atomic clocks?
The fundamental reason that atomic clocks are so accurate is that they are just counting devices. You count cycles. And when you count enough of them the bits that you may have missed at the beginning and the end get too small (fractionally) to care about. Then the problem becomes one of checking that you don't miss some as you go along and that is easier to do in comparison mode.
1h
comment Why is Larry Niven's Ringworld Unstable?
@JamesBowery No. For the same reason that gravity isn't a restoring force. Both fall by $1/r^2$, so both are subject to the same math.
20h
comment Why do physics students find vectors so difficult to deal with?
I would hesitate to use the word "component" in that way for fear of students conflating it with the use of the same word meaning the inner-products with the basis vectors of our coordinate space. Students sufficiently confused without adding any ambiguous vocabulary to their difficulties. Perhaps "two properties" would be better.
21h
comment Elastic scaterring of neutrinos - Why does the electron neutrino dominate this channel
The speed of the electron needs to be about 3/4 of c for that to happen. That means a kinetic energy of about 270 keV = 0.27 MeV. Solar neutrinos have energies of about 1 to 10 MeV. In general there is more than sufficient energy.
1d
comment What is the temperature of the clear night sky from the surface of Earth?
Mind you "clear" to the mark 1 eyeball means a wide range of absorbtivity as measured by sensitive instruments.
1d
comment Can Einstein's 'Theory of General Relativity' exist in Harmony with 'Quantum Mechanics'?
Also related: physics.stackexchange.com/q/71568. You seem to be asking a lot of questions in a hurry without even researching them on this site. Seriously, don't expect us to do your work for you.
1d
comment Why can't dark matter be baryonic?
Duplicate of physics.stackexchange.com/q/26778
1d
comment At what point do researchers in physics make the leap from wild theoretical ideas to physical experiments?
To be blunt, dark matter only appears wild if you don't know the history of what was carefully considered and ruled out before this hypothesis came to the fore nor what evidence accumulated in favor of the idea while other--less unusual--ideas were considered more plausible. In other words dark matter as a serious candidate hypothesis didn't spring fully formed from anyones forehead, it was reluctantly admitted through the servants entrance when nothing more respectable could be found to do the job.
2d
comment Relativistic Kill Vehicle
The drag at those speeds isn't well treated by a viscous parameterization like that. The forces are essentially all inertial.
2d
comment How possible is it that the Large Hadron Collider (LHC) on its second try, could disrupt the gravity of Earth?
As with all these (pop-sci plausible) suggestions, if there was any truth to it the Big Particle Accelerator in the Sky would have done this to us long, long ago. SO relax.
Dec
12
comment Can antimatter-matter collisions generate heat?
"usually high energy gamma radiation" Er ... if hadrons are involved there are a lot of pions which means that a lot of the energy ends up as neutrinos.
Dec
11
comment Do the fields exist without electric charges?
I'm with @John here. The only fundamental neutral fermion is the neutrino and $\nu + \bar\nu$ goes only to $Z^0$ which does not couple directly to photons.
Dec
11
comment What is meant by the temperature of the CMB?
"Temperature usually means the jiggling about of atoms" In an very introductory treatment it does, but that is just to give you a starting place. Serious treatments of temperature are not linked to any given system.
Dec
10
comment What's the difference between centre of mass & centre of gravity for massive bodies?
Mark, well at least where I see people make a distinction this is the one they make. There are texts that do not distinguish at all.
Dec
10
comment What is meant by the “intensity” of light?
Intensity is usually power per unit area (i.e. energy per unit area per unit time) so $\mathrm{W/m^2} = \mathrm{J/(s\,m^2)}$.
Dec
9
comment Does infinity really exist?
As usual you should define what it would mean for a mathematical concept to "actually exist". How would that be different from it's not actually existing?
Dec
7
comment From escape velocity to gravitational acceleration
Strictly speaking you also know need to know that the mass distribution is (a) spherically symmetric and (b) confined to smaller radii than your current position. Obviously that is reasonably true "at the surface of a planet", but I thought I'd throw it out there.
Dec
7
comment Has the speed of the higgs boson been measured yet?
Particle with non-zero mass can take on any speed below the speed of light (given sufficient energy). Particles with zero mass are the only ones that have a fixed speed and they all have the same speed: $c$.
Dec
6
comment If we increase the aperture of a telescope and decrease its magnification, can it be harmful to the eyes?
See also exocomics.com/352
Dec
6
comment Can matter be annihilated to form kinetic energy
Kinetic energy isn't a "stuff", it is a property of an object or system. I know, I know. We talk about energy using language that treats it as a thing, but you have to keep in mind that it is not something that you can isolate and say "Ta da! I have a beaker of energy!".