33,147 reputation
344108
bio website inspirehep.net/…
location Duchy of Grand Fenwick
age 43
visits member for 3 years, 9 months
seen 5 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.


7h
revised What are the quantum numbers of an exchange particle in the t channel?
deleted 335 characters in body
7h
comment What are the quantum numbers of an exchange particle in the t channel?
@Jupith I have not been able to get is squared away in my head, so I'm going to strip the offending paragraphs for now. You have to conserve momentum between the initial and final states, and when the spin math lets you down that requires the addition of a change in orbital state as well.
8h
comment How far has a black hole to be in order for its tidal forces to disintegrate earth?
As Indicated by @Bitrex's link the search term you are looking for is "Roche Limit". Mind you the atmosphere is pulled off first because it can be treated as having slightly negative tensile strength. Quick, someone switch MegaMaid to the other mode.
9h
comment Is the Big Bang defined as before or after Inflation?
The statement of the questions seems to boil down to "The experts are divided about Proposition X. What is the expert consensus on Proposition X?"
9h
comment How do you add temperatures?
The scenarios that I'm dreaming up that involve adding temperature (other than the averaging all ready notes for which you convert to like units first and then just proceed) involve a temperature and a change-in-temperature. The distinction is important because $\Delta T_1 = 50\,^\circ\mathrm{C}$ and \Delta T_2 = 50\,\mathrm{K}$ are the same while $T_3 = 50\,^\circ\mathrm{C}$ and $T_4 = 50 \,\mathrm{K}$ are different.
9h
comment Metaphysics and spacial dimensions
Perhaps it is unfortunate that philosophers often receive a curt reception in physics circles, but my (personal, not diamond powered) observation is that it usually follows from a impedance mismatch in in style and vocabulary. This post is stated in terms that can't be matched up to a set of related physics concepts. Just to pick an example, the use of the word "dimension" has no relationship whatsoever to the way physicists use the word. The result is that we haven't a clue what this is suppose to mean.
9h
comment What forces determine the distance of the electron from the proton in a hydrogen atom?
@ACuriousMind's comment is bang on. These things are quantum mechanical objects and in this context they expresses that completely. Thinking that a "little billiard balls"-particle picture is going to have a correct answer is an error. (At the QFT level you can talk about particles, but those don't act anything like little billiard balls and you have to really "get" quantum mechanics in order to appreciate that.)
11h
answered What moves an object? Momentum or Kinetic Energy?
13h
comment Why should any physicist know, to some degree, experimental physics?
@Aaron Those pre-existing symmetries are tested. Fine. No one is arguing about that. But re-writing them doesn't add anything new to the sum of human knowledge. The math itself adds something to mathematics, but at this point there is no experimental reason to prefer string theory to the jumble of existing theories. There are philosophical reasons: the theory is gorgeous and unified. But that's not data. And the new prediction have not been tested. Or rather the theory has failed the test over the accessible energy ranges.
13h
comment Conservation of energy in a different frame of reference
@JanHudec The usual way. Find the path $s$ that the object takes down the slope in each frame and compute $W = \int ( \vec{F}_n - mg\hat{y} ) \cdot \mathrm{d}\vec{s}$, where $\vec{F}_n$ is the normal force.
13h
comment Why should any physicist know, to some degree, experimental physics?
@Aaron String theory is falsifiable in principle, but it has not yet faced a experimental test which could have falsified it. Lorentz invariance, and the symmetries of the electro-weak and strong interactions were already well established as features of the universe when string theory was brought together so no theory that didn't include them could have gotten off the ground. Sting theory's new prediction have not been observed, but that is not probative because we may not have reached the necessary energy scale. String theory is testable, but not tested.
1d
comment Conservation of energy in a different frame of reference
To understand BMS's interest in work here, it's probably worth recalling that in intro mechanics the conservation of energy is developed starting with the work-energy theorem: $W = \Delta T$.
1d
comment Is there a quantity measured in kilogram seconds?
In science the kilogram is defined by the International Bureau of Weights and Measures.
1d
comment Is there a quantity measured in kilogram seconds?
The scale is calibrated to read one $\mathrm{kg}$ for every $9.8\,\mathrm{N}$ actually measured, but that does not change the fact that kilograms are units of mass. By definition.
1d
comment What is the relationship between radation intensity and count rate?
I interpreted the question to be about counting and answered it that way as well as adding the appropriate tags, but the clearly draw distinction between energy and activity here is important as the OP's text is ambiguous.
1d
revised What is the relationship between radation intensity and count rate?
edited tags
1d
answered What is the relationship between radation intensity and count rate?
1d
comment Amplitude of an electromagnetic wave containing a single photon
You may be making a mistake relying on a 1936, experimental paper as your source for the semantics of photons. Firstly the paper predates QED and therefore misses out on a lot of important work on how a photon should be understood and secondly experimental papers tend to give only as much theory as needed for that measurement and only in the interpretation in which the measurement is clearest (I speak as an experimenter). All the qualified theorists I've talked to about this subject suggest caution in trying to impose a simple wave-packet interpretation on a photon.
1d
comment Why should any physicist know, to some degree, experimental physics?
@annav All the "predictions" (really postdictions) of string theory that can be validated now are inherited from its predecessors. Getting that right is a minimum requirement for a candidate new theory, and it is a mathematical triumph not yet accomplished by any other candidate theory, but it doesn't make string theory experimentally validated. String theory is a scientific theory because it could be falsified if wrong, but as yet it hasn't faced a test in which a negative result can't be written off by saying "Well, we haven't gotten to the scale where that appears yet".
2d
comment The need for a 'particle description' of electrons
"The fact that we experience the electron to hit just one point, that is the wave function appears to collapse, is an effect of entanglement." I think you have misunderstood what entanglement means. Perhaps you had decoherence in mind? Even so the claim that you are then allowed to dismiss the particle-like properties of the electron misses the point.