100,646 reputation
4146258
bio website ratsauce.co.uk
location Chester, United Kingdom
age 53
visits member for 3 years, 7 months
seen 41 mins 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
21
comment Am I right in saying that $gmm/r$ is motion due to potential energy?
@StanLiou: the $F$ I'm using is the norm of the four acceleration multiplied by the mass, so it's the Newtonian force multiplied by $1/\sqrt{1-r_s/r}$ and this diverges at $r = r_s$. You're now going to say this isn't particularly meaningful, and I agree - that's my point.
Aug
21
comment Interaction Between Two Bar Magnets
Anthony, Googling the title of your question returns the Wikipedia article BMS links as the very first hit. This comes awfully close to qualifying as insufficient effort.
Aug
21
comment Why exactly is it that light cannot escape a black hole?
Re the last question, see the Pound-Rebka experiment.
Aug
21
comment Why exactly is it that light cannot escape a black hole?
Also see the question If you shoot a light beam behind the event horizon of a black hole, what happens to the light?. This is the same calculation as the one I linked, but phrased in a slightly more user friendly way (still not especially non-nerd friendly though!).
Aug
21
comment Why exactly is it that light cannot escape a black hole?
possible duplicate of Why is a black hole black?
Aug
20
comment Angular acceleration
Radial accn is $a_r = r\omega^2$, and $\omega = \alpha t$ so $a_r = r\alpha^2t^2$. Tangential velocity is $v_t = r\omega = r\alpha t$, and tangential accn is $dv_t/dt$ so $a_t = r\alpha$. Set $a_r = a_t$ and you get your answer.
Aug
20
comment Angular acceleration
Actually, though this is a gratuitous homework question it does nicely illustrate how useful a tool dimensional analysis is.
Aug
20
comment Angular acceleration
@Gummybears: you're asked for a time, and that has units of $T$. If you feed in $\alpha$ as $T^{-2}$ into the four equations which one returns a value that has units of $T$?
Aug
20
comment What makes us move in time?
A footnote: It turns out from the chat that the question is really about the cause of the arrow of time.
Aug
20
comment How does the gravity well change as space expands?
Not true. For example in a de Sitter background the Schwarzschild metric becomes the de Sitter-Schwarzschild metric.
Aug
20
comment What makes us move in time?
@LIUFA: yes, if you want to nip over to the h bar (chat.stackexchange.com/rooms/71/the-h-bar) I'm there now.
Aug
20
comment Question about supercooling
Experience of putting things in the freezer tells us that we quite often get systems that are half frozen and appear to be stable in the half frozen state. Typically this is because the composition changes with freezing e.g. as you freeze a bottle of salt water the remaining water gets saltier so its freezing point changes. In effect your phase boundaries move as the system freezes.
Aug
20
comment Question about supercooling
@KelvinS: If you're precisely at the equilibrium temperature then the system will not change. If you're slightly on the solid side then the whole system will (eventually) freeze, and if you're slightly on the liquid side then the whole system will (eventually) melt.
Aug
20
comment What makes us move in time?
@LIUFA: the title to the question i linked is a bit misleading. If you read my answer to it you'll see I specifically address the question of the flow of time, which is what (I think) your question is about.
Aug
20
comment Alcubierre drive and inertia.
@MichaelGantz: I suspect that the reason no-one has put in the effort to publish such an analysis is because no-one takes the Alcubierre drive seriously enough to make it worth the (considerable) effort involved. This sort of physics is good fun, but there is little chance it corresponds to anything in the real universe.
Aug
20
comment Alcubierre drive and inertia.
I have to say I agree with Void on this one. You could argue that the question should be migrated to MathSE on the grounds that it's mathematics with no physical relevance, but it's a perfectly sensible question and I don't think you should write sneering comments to it.
Aug
20
comment Pushing a crate on a friction floor
The $\theta$ you have is the limit of $\theta$ when the mass of the crate is zero. So I guess it's the maximum value of $\theta$ for any crate of any mass. For crates with $m > 0$ the value of $\theta$ will be less than this limiting value.
Aug
20
comment How exactly and WHY does matter affect space-time?
The equivalence principle is an assumption rather than something that is derived. Are you asking why it seems a physically reasonable assumption?
Aug
20
comment How can one explain gravitational time dilation in non-rotating bodies?
Are you asking how your equation is derived, or are you asking what the physicial origin of the time dilation is?
Aug
20
comment How can I boost the FM reception of a smartphone?
This question appears to be off-topic because it is about Nokia mobile phones. Possibly move to the Windows phones SE