117,027 reputation
5183312
bio website ratsauce.co.uk
location Chester, United Kingdom
age 53
visits member for 3 years, 11 months
seen 1 hour 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.


Aug
12
comment A clock in freefall
@aepryus: if you measure $r$ in a coordinate system and $t$ in the same coordinate system then by definition $v = dr/dt$ in that coordinate system.
Aug
12
comment A clock in freefall
... a very important point. Beginners to SR tend to think of time dilstion as a simple thing with a simple formula. Then they get massively confused about the twin paradox. It's important to understand that time dilation comes from the metric, and I think you question neatly illustrates how the metric can be used to calculate it.
Aug
12
comment A clock in freefall
@aepryus: the homework tag is meant to indicate that the working is straightforward for any reasonably experienced physicist. For example we get endless questions about blocks sliding down slopes etc, and solving these is just routine mechanics. The point is not that the question really was homework, but that the working is routine and therefore uninteresting. In this case I suspect the VTCers underestimated the subtlety of the question. Even though I've done this sort of thing before it took me a day to realise how it could be answered. I also think the question helps illustrate ...
Aug
12
comment Assuming that the Cosmological Principle is correct, does this imply that the universe possess an empirically privileged reference frame?
@CuriousOne: by symmetry I guess you're referring to the FRW assumptions of isotropy and homogeneity. I'm not sure the breaking of these symmetries in a frame with a non-zero peculiar velocity is anything very significant.
Aug
12
comment A clock in freefall
@ja72: in the above $v$ is the velocity measured by the Schwarzschild observer, and $v \rightarrow 0$ as $r \rightarrow r_s$. So you will indeed never cross the event horizon. This is a well known result and discussed in many, many questions on this site.
Aug
11
comment A clock in freefall
@JerrySchirmer: since you're around - is my equation (3) really correct? It seems suspiciously simple. The working looks fine though ...
Aug
11
revised A clock in freefall
Another rewrite
Aug
11
comment A clock in freefall
@aepryus: I realised the calculation was easier than I thought, so I've completely rewritten my answer to do it.
Aug
11
revised A clock in freefall
Add link
Aug
11
comment Spectral series' formula of a given atom (other than hydrogen-like)?
@SébastienPalcoux: in principle the spectrum is zero between peaks. In practice spectra always contain background light e.g. from black body radiation.
Aug
11
comment Can an electron make a transition between sub energy states of the same energy level?
@RadhaKrishna: a quick Google suggests lines are observed for such transitions. There is no selection rule that forbids them.
Aug
11
reviewed Looks OK Would a 9v battery be able to produce gas bubbles by water electrolysis at 1000 meters?
Aug
11
reviewed Looks OK Is 'amp' a technically invalid term?
Aug
11
comment Spectral series' formula of a given atom (other than hydrogen-like)?
@SébastienPalcoux: there is no formula for the spectral series in multielectron atoms. The transition energies can only be calculated numerically.
Aug
11
answered Can an electron make a transition between sub energy states of the same energy level?
Aug
11
comment Confusion about proper time
This difference in the proper times is of course the origin of the twin paradox - not that it's a paradox to anyone who knows how to integrate a line element.
Aug
11
comment Spectral series' formula of a given atom (other than hydrogen-like)?
@SébastienPalcoux: not even the Schrodinger equation is soluble for atoms with more than one electron. However we can use numerical methods to construct very accurate approximations. CuriousOne mentions QFT because for heavy atoms the energy of the inner shell electrons is so high that their velocity becomes relativistic. Since Schrodinger's equation is non-relativistic it no longer gives an accurate description of the atom. Actually we can use relativistic QM, so strictly speaking QFT isn't needed.
Aug
11
answered Conductivity of Aqueous Ionic Solutions as a Function of Time
Aug
11
comment Does pulling or pushing take more effort?
Can you clarify what question you're asking about physics? At the momnt the question seems to be about human psychology.
Aug
11
comment Must length equal distance?
Can you clarify what you are asking?