# sethoflagos

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1. ## CMB - TV aerial handshake?

I was musing on the life experience of a CMB photon travelling from its source emitter - perhaps some excited hydrogen atom at recombination - to it's absorber which for sake of argument might be a TV aerial. Am I right in thinking that the spacetime interval between these events is zero? And in particular that the photon 'travels' zero spatial distance in zero time (due to Lorentz contraction)? Is there a sense that the photon is sitting for an instant inside some weird tiny spherical(?) surface, in intimate contact with all its possible futures (one of which is said TV aerial), a myriad of even tinier exits to all available absorbers peppered within a matrix of paths forbidden by destructive interference, and/or routes to some eternal void? Because if source and destination are touching perhaps there's no need for any significant energy investment in filling up its light cone with .... stuff (insert correct jargon). Just pick a destination that matches up and hey presto it happens instantaneously (give or take 13-odd billion years).
2. ## Residual terms in numerical integration of ODEs - normal error or reality?

I set up an excel spreadsheet to integrate the following system by first order forward difference equations: 2/(k-1)*dc/dt + du/dt = 0 in direction dr/dt = u + c 2/(k-1)*dc/dt - du/dt = 0 in direction dr/dt = u - c With r=0 boundary conditions u=Asin(wt), c = c0, I got a solution that was a very good fit to u=Asin(wt)cos(wr/c0) which is the expected result for a standing wave in a cylinder. How good a fit? Well the integration yielded maximum variance values of 0.5 in both r and t trends over one wavelength, and subtracting the above expression reduced this by 99.9954% in the r trends, 99.99902% in the t trends. A pretty good fit. However, looking at the residual and experimenting a little, I found that adding a further term wr(A/c0)^2/pi*sin(2wt)cos(2wr/c0) removed 99.75% of the r, and 98.97% of the t remaining residual max variances. This term may have a very small value over one wavelength, but the proportionality to r means that eventually the second harmonic will dominate the waveform, and the proportionality with A^2 means that it's proportional significance increases with input amplitude. Any suggestions as to how I might go about determining whether this term is no more than an artifact of non-linearities in the forward difference method, or if it really is a true component of the system? In passing, the small residual that remains is almost equal to a simple product of sin(2wt)sin(2wr/c0), leaving something closely proportional to r^2sin(3wt)cos(3wr/c0). And still, little sign of randomicity. Many thanks in advance for your time, Seth
3. ## The Big Bangy Field Equation

We're getting too hung up on t=0 here. Question 1) is really a general question about whether the quantum fields for a finite system at any particular instant extend throughout spacetime (even if the precise future geometry of spacetime were somewhat indeterminate).
4. ## The Big Bangy Field Equation

The Big Bang says nothing about T=0. It only describes what happens once expansion begins. I don't know what your first statement means, maybe you could re-frame it ? Difficult to rephrase it without presupposing part of the answer. As I picture it, it's a Schrödinger equation describing the time evolution of the universe (or all possible universes courtesy of the superposition principle of quantum mechanics) in some kind of primordial Hilbert space. Don't know where 'preferable' came from, Your invention not mine. The 2nd Law of Thermodynamics favours such outcomes. I guess I'm looking for some parallel between the 2nd Law and the time evolution of superimposed quantum states. They are both essentially statistical in behaviour after all,
5. ## The Big Bangy Field Equation

Three questions have recently been bothering me. If the universe originated (as I read on a lavatory wall somewhere) as a field of superimposed probabilities of all possible futures: 1) Would that field be necessarily bounded in any dimension before any 'actual' future began to unfold? 2) Is there any damning reason why the fundamental constants of our universe could not be quantum variables, initially indeterminate? 3) Would combinations of fundamental constants that led to eternally expanding, species diverse universes have more 'quantum votes' (ie a higher probability of manifesting themselves) due to their greater number of permutations than those combinations that led to finite universes supporting a low diversity of elemental species? Many thanks in advance for your considered points of view.
6. ## Water dissociation

Dissociating water requires an energy source. A block of tungsten heated to say 3,000K, will cause water molecules at and around its surface to dissociate until the system comes to thermal equilibrium and rates of dissociation/recombination equalise. The choice of tungsten is purely to meet your requirement for the agent to be a solid at temperatures where the degree of water dissociation is significant. EDIT: Okay reread the OP. Looking for ionic dissociation rather than H2 and O2. Hence off-topic (I think).
7. ## Neanderthal!!!???!!!

Okay. How would a Neanderthal react to you informing him that he appeared archaic? Would he have you before, after or with the wild garlic and chives? Yes, I'm bored at last, No sign of any counter-argument worth thinking about.
8. ## Neanderthal!!!???!!!

Grow a spine and answer for the consequences of your stated beliefs. Or retract them. Simples!
9. ## Neanderthal!!!???!!!

I'm happy to accept the moderators considered opinion on this. Either way. Feel free to report. The verdict would be interesting. I look, but I see no empirical evidence to support these claims. Quite the opposite.
10. ## Neanderthal!!!???!!!

Like it or not, these are the logical consequences that must be taken on board if we were to accept the speculations that you have been bombarding us with lately. So either present us with a convincing dataset demonstrating that extant basal lineages such as those occurring in high frequency amongst the Khoisan and Nilotic populations, for example, can be characterised by a suite of 'archaic' physical characteristics (such as heavy brow ridges, receding chin, sloping forehead, occipital bun, supraoccipital crest or whatever) that average so far beyond the phenotypic range of all other extant human lineages that they should be considered as taxonomically distinct: ...or Accept that any reasonable estimate for the appearance of 'anatomically modern humans' must predate any significant isolation or divergence of those lineages and withdraw your uncorroborated contrary assertions without reservation. There is no option 3)
11. ## Neanderthal!!!???!!!

No. But I was watching most intently for what you didn't say (which I often find to be more informative). In particular, it was your deliberate sidestep of this key question. I even gave you two further chances to declare that your (apparently arbitrary) choice of N-MtDNA Cro-Magnon as the common ancestor of all modern humans, excluded the vast majority of extant sub-saharan Africans from that category (not to mention M Haplogroup Indians etc etc). You chose not take those opportunities either. I take your silence as strong indication that this is indeed what you believe, coupled with insufficient spine to admit it explicitly. The final straw was your derisory hand-waving dismissal of the recent MSA advanced culture evidence from Blombos Cave, Still Bay etc. strongly indicating that you hadn't the slightest interest in counter-evidence to your speculations. I see no science in what you write. But I do detect an attempt to abuse taxonomic classification for purposes of racial discrimination. At which point it ceases to be a scientific argument, and becomes an ethical one.
12. ## Neanderthal!!!???!!!

So everything and everybody was archaic until one small, select band left the dark continent, and in a sudden blinding flash turned spontaneously into modern 'Cro-Magnons'. Smacks rather of divine intervention, doesn't it? I guess it's clear that we both find each others point of view morally repulsive. Sleep well.
13. ## Neanderthal!!!???!!!

So a 28,000 year old skull from France appears to be a little more modern than a 160,000 year old skull from Ethiopia. This is hardly earth-shattering news is it? Maybe greater insight can be gained from evidence lying between those dates, Are you referring to http://adsabs.harvard.edu/abs/2010Sci...330..659M? Very exciting stuff going on at Blombos Cave. A benchmark technology of undisputably modern human behaviour at 75,000 years BP. That puts your 'cultural revolution' back 30,000 years, deep into the Middle Stone Age and most definitely in sub-saharan Africa. (Incidently, rather early for the birth of Haplogroup N to have any conceivable involvement). I don't believe any reputable scientist would dream of calling this a Cro-Magnon site, though. Way too eurocentric a concept. But I'm quite comfortable to see sites such as this as indicative of the activities of the common ancestors of all of us. Besides which, it places my wife and I back in the same taxon. Which is nice
14. ## Neanderthal!!!???!!!

Cro-Magnon1 is only 28,000 years old - it is not especially representative of our species at that time. Haplogroup N pretty well excludes all Africans. Just where exactly are you setting the boundaries for our species? And I do not need you to tell me what I mean by the first arrival of early moderns into Australia (ca. 50,000 +/- 10ka BP).
15. ## Neanderthal!!!???!!!

Cro-Magnon isn't even a taxon. It's a somewhat mixed bag of exclusively European early modern human fossils. You cannot reasonably propose them as a credible common ancestor of all extant members of our species. We were in Australia even, long before the earliest Cro-Magnon date. And to suggest that BB King is even slightly more distantly related to our common ancestor would put him into an outgroup would it not? Is this really what you wanted to say? I really do hope not.
16. ## Neanderthal!!!???!!!

Cro-magnon? Really? Well, that blows the 'out of Africa' theories right out of the water, doesn't it. Trailer parks across the US will be rejoicing at that astonishing revelation! PS George Dubya was renowned for his distinctly simian facial expressions when faced with a difficult question. Wonder how the trailer trash school of anthropology explain that little factoid
17. ## How does this pump work without moving parts?

I did my apprenticeship in a paper mill laboratory that had a small liquid eductor we could rig up to one of the water taps with rubber tube to create a partial vacuum. It was good enough to boil water at room temperature (not that high in the hills outside Halifax), which was moderately entertaining. Or maybe indicative of how fulfilling a paper mill job in the Yorkshire pennines was in those days
18. ## How does this pump work without moving parts?

+1 The 'big daddies' of these, much used in the process industries, are steam ejectors (see http://croll.com/vacuum-systems/applications/chemical-processing/24-2/). There are subtle differences in the equations for liquid and gas driven eductors, but the basic idea is the same. Those born before the widespread use of fuel injection systems may remember that carburettors use a similar principle to 'suck' fuel through atomising jets into the inlet airstream.
19. ## Fluid flow through square or rectangular passageways.

Aha! I wish you'd yelled 'Prandtl!' at me after post #2 ;-) This must be the effect the OP has seen. But the question is where? Years of weekly air flow measurements inside paper machine drying hoods; working with gas ducting up to 27 feet square section; and not to mention countless ciggies smoked in draughty passageways; and the effect has always been swamped by bulk flow.
20. ## Fluid flow through square or rectangular passageways.

This clip seems to get across the key ideas quite clearly. What catches most people out is the deep contrast between steady state flow and unsteady (or dynamic) flow. This is not synonymous with laminar vs turbulent. Laminar flow can be dynamic without being turbulent. And despite laminar often being described as streamline flow, streamlines exist in turbulent flow too. Other than maybe some extreme situations such as a shock wave front, there is always an instantaneous velocity vector field with no discontinuities between the vectors (thanks to the continuity equation), so streamlines can be drawn.
21. ## Fluid flow through square or rectangular passageways.

studiot's usage of the 'streamline' terminology is absolutely correct. Any other related term (pathline, streakline, timeline) would not be consistent with his explanation of it's relationship to the instantaneous flow velocity vector field. Perhaps you should be asking questions rather than trying to rubbish other people's answers........?
22. ## Fluid flow through square or rectangular passageways.

Nothing against aeronautics engineers btw. It's simply that flow of air around various solid body sections within very restricted ranges of pressure and temperature corresponds to an extremely narrow band of interest within the vast, rich universe of Navier-Stokes. Is it more efficient to stir coffee with a teaspoon or a fork? Strangely, I've found Wikipedia unusually silent on this commonplace, everyday dilemma.
23. ## Fluid flow through square or rectangular passageways.

Strangely enough.....He's presenting a simplistic model for students in a discipline that rarely need worry itself with the full picture. I guess by 'particles' he means what we usually describe as 'fluid parcels' in the literature, and, yes, in pure laminar flow, fluid parcels are constrained to simple streamlines, and eddy diffusivity is zero. But you cannot extend this reasoning down to the molecular scale because individual fluid molecules move in anything but a straight line. So at the boundaries of fluid parcels and streamlines there is constant material (and momentum, and thermal) flux across those boundaries. If there is a higher concentration of dye in one streamline, there may be no convective mixing, but there is definitely nett movement of dye in the direction of negative concentration gradient into adjacent streamlines of lower dye concentration through the mechanism of molecular diffusion. To paraphrase an ancient and not particularly good engineering joke, one may in certain instances quite reasonably commence an analysis with the phrase 'assume spherical chicken'. Even if this analysis proceeded to provide an excellent fit with experimental data, it would take a particular kind of fool to conclude from this that all chickens were indeed spherical. Beware simplifying assumptions. They are only useful approximations; they are not fact.
24. ## Fluid flow through square or rectangular passageways.

Please don't quote Wikipedia at me. Most of the fluid flow entries seem to have been written by aeronautical engineers, and they tend to have very limited bandwidth in the field. My comments stand,
25. ## Fluid flow through square or rectangular passageways.

I recall neither the OP nor myself mentioning laminar flow. 'Churn flow' has a very specific understanding in fluid mechanics, which is not relevant here, If you intended 'formation of vortices' then you are incorrect: vortices can and must occur in general regimes of laminar flow to account for conservation of angular momentum. 'Mixing' also occurs in laminar flow whether by means of convection or molecular diffusion.
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