136,117 reputation
9228377
bio website ratsauce.co.uk
location Chester, United Kingdom
age 54
visits member for 4 years, 4 months
seen 11 hours ago

Semi retired old time computer nerd who started programming on a Commodore Pet.

Since I'm also active in the Physics forum I should add that I started as a theoretical chemist, moved into solid state photochemistry and finally worked in industry as a colloid scientist. I only became a full time computer nerd in 1997.


Nov
19
comment What's the escape velocity of Naked Singularities?
@BenCrowell and others: I assume Sachin meant escape velocity from black hole with a naked singularity rather than the escape velocity from the singularity itself. The latter is of course undefined.
Nov
19
comment What's the escape velocity of Naked Singularities?
@BenCrowell: I've been scratching my head trying to work out if the imaginary escape velocity has any physical meaning. I suspect it means nothing can approach the singularity closer than the point where $v^2 = 0$ i.e. beyond that point the gravity from electric field outside is too strong. If you can shine any light on this I'd be very interested.
Nov
18
comment How do blankets keep you warm?
@Geremia: There have been attempts to make flexible aerogels. See for example this article. If you Google aerogel clothing there are lots of hits, but how successful it is I'm not sure ...
Nov
18
comment What's the escape velocity of Naked Singularities?
@BenCrowell: all your comments would make a good answer. Given the vagueness of the question I think an answer that discusses the issues, rather than just give a formula, is entirely reasonable. I'd upvote it :-)
Nov
18
comment Reason behind formation of doublets in diffraction spectrum
See also: The energy level of electrons in an atom depend on l?
Nov
18
comment Reason behind formation of doublets in diffraction spectrum
In the case of the sodium D lines it's spin-orbit coupling. If you want more details you really need to read the article I've linked and formulate your question more precisely.
Nov
18
comment Why is the color of fire is yellow or blue sometimes?
Related (though not a duplicate): Possible colors of fire?
Nov
18
comment Is metric tensor invariant under rotation?
The representation of the metric tensor will depend on the coordinate system. For example the Schwarzschild, Gullstrand-Painlevé, Eddington-Finkelstein and Kruskal-Szekeres metrics all look very different, but they are all the same metric describing the same spacetime. Is this what your question is getting at? If not, can you clarify exactly what you're asking?
Nov
17
comment How do photons know they can or can't excite electrons?
@AfrishKhan: you calculate the transition probability using Fermi's golden rule. If you do the maths you'll find you only get a high probability when the photon frequency matches the difference in the energy levels.
Nov
17
comment Photon absorption by a hydrogen atom :
possible duplicate of How do photons know they can or can't excite electrons?
Nov
17
comment How many grams of anthracite coal is needed to convert to steam?
@AlmondBaby: $L$ is the latent heat of the water i.e. it is the heat required to convert 1kg of water at 100°C to 1kg of steam at 100°C.
Nov
17
comment Time Dilation Experiment
See also Where are the time dilatational effects of orbital motion and gravitational acceleration equal?
Nov
17
comment Why isn't our universe symmetric?
@asperanz: oops, yes. Thanks :-)
Nov
17
comment Why isn't our universe symmetric?
@zibadawatimmy: see this Wikipedia page in the Low multipoles and other anomalies section. There may be anomalies in the CMB on such a large scale that they threaten the concept of large scale homogeneity. However I must stress that this is still very much an open question.
Nov
15
comment Effect of Earth's rotation on apparent weight (acceleration due to gravity)
possible duplicate of how apparent weight varies due to the rotational motion of earth
Nov
15
comment What happens to the energy of photons when two light waves with plane wavefront interferes destructively?
See also Where does energy go in destructive interference?
Nov
15
comment why a engine convert all of its heat into work?
possible duplicate of Energy density and Carnot cycle
Nov
14
comment Direction of gravitational field in Hemisphere
You're assuming that the direction of the gravitational acceleration always points towards the centre of mass, and in general this is not true.
Nov
14
comment What is the smallest length scale ever measured?
@BrandonEnright: that's why I included the weasel words directly measured. I think that the IceCube measurements are really an indirect measurement. There are all sorts of indirect measurements because energies higer than 1TeV may have to be included when calculating scattering cross sections i.e. very high energy physics will affect probabilities at lower (observable) energies. As a result arguably we have probed energies far higher than 1TeV.
Nov
14
comment Is it really possible to create some mass only from equivalent energy?
Likewise in beta decay neutrons turn into lighter particles and the missing mass turns into kinetic energy. The key thing to understand about all this is that matter is an excitation in a quantum field, as I discuss in the linked question. However I concede that the linked question doesn't directly answer what you've asked here.