41

Just Chat! / Re: What is the difference between Beer, Lager and Ale?

« on: 26/02/2024 22:29:07 »

Beer is the common term. Ale and Lager are more specific.
From what little I know, Lager is cold brewed, with most of the fermentation going on at the bottom of the batch. Ale is the other way around: warmer and top fermenting.

Not sure if the ingredient list is necessarily different. Sounds like a different process more than a different recipe.

42

Just Chat! / Re: What is the difference between Beer, Lager and Ale?

« on: 26/02/2024 22:16:23 »

In general there are 2 main types of beer, lagers and ales.  The difference is the kind of yeast that is used.  Ales have a stronger flavor and usually more hops (bitterness).  Lagers have a lighter crisp flavor.  Lagers are also usually served colder than ales.
Lagers yeast thrives in a cool environment as low as 40F.  Ale yeast thrives in around 70F.

43

Physics, Astronomy & Cosmology / Re: Can plutonium exist naturally in the universe?

« on: 25/02/2024 18:32:08 »

The half life of the longest lived plutonium isotope is too short for any substantial quantities to exist given the age of the earth. As 0rigin has pointed it is found in trace amounts.

44

Technology / Re: What are the assumptions of the hydrogenic model in semiconductors?

« on: 25/02/2024 18:08:35 »

In full pedant mode, I now wonder if the question is correct?

You take a mathematical (not physical) model of a hydrogen atom (though it happens that solving the Schrodinger equations gives you the same answer), plug it into a non-vacuum environment, and add appropriate experimental values to get an answer for electron mobility that once again gives you a result close to experiment . I don't see any assumptions there, just a few inspired Ave Marias and the mystical transubstantiation of m to m*. 

More articles of faith than assumptions, I think. But at least the dictatus ex cathedra survives experimental test! 

45

Physics, Astronomy & Cosmology / Re: Can plutonium exist naturally in the universe?

« on: 25/02/2024 15:39:17 »

Or is it pretty clear that it can only exist through the intervention of an illegent specie?

An illegent specie is not required since trace amounts of naturally occurring Plutonium can be found in uranium deposits.

46

Technology / Re: What are the assumptions of the hydrogenic model in semiconductors?

« on: 25/02/2024 09:56:38 »

Hi ES, I read your post yesterday around midday but I was rather busy at the time so I did not reply. I certainly agree that Alan is an excellent contributor. However I doubt if I can be of any value as my semiconductor theory(50 years ago) was extremely rudimentary as opposed to semiconductor application. I have a query peripheral to yours and I hope I am not digressing too much: the permittivity of a material is a bulk property that is due to polarisation of charges within that material--does this have a real meaning at the atomic scale?,  ie  is it not just a case of vacuum permittivity+ whatever electrostatic effects are occurring locally?  Another conundrum for me is why electron and hole mobility varies when a hole is effectively an electron moving in the opposite direction, step by step. Apologies if this is too much off topic. 

47

Technology / Re: What are the assumptions of the hydrogenic model in semiconductors?

« on: 25/02/2024 09:42:24 »

I read it.

How is this making explanation of the low temperature state? I am assuming that the free electron is loosed at low temperature?

48

Technology / Re: What are the assumptions of the hydrogenic model in semiconductors?

« on: 25/02/2024 08:17:06 »

Always a pleasure to blow half a century of dust off the textbooks, my friend. Hopefully I'll have time to read the multi page proof before they nail the lid down.

You need some justification to make the change ε0  →  ε   to begin with.

The Bohr atom assumes (as do all other sensible models) that a hydrogen atom consists of charged particles in a vacuum, so whatever is happening between them is normalised to practical units by introducing a factor of ε₀ (hence my reference to electrostatics).

Once you have delocalised the electron into a real material, its behavior is going to be modified by the bulk properties of that material, so ε_vacuum must be replaced by ε_material - electrostatics again.

It's very satisfying that an ab initio calculation aligns closely with experiment*, but a mathematician or theoretical physicist might argue that whilst ε₀ is a legitimate scaling factor, ε_r is always an experimental fudge factor to make the numbers fit the theory!

* Or does it? Suddenly we have to introduce another concept m_e*, with orders of magnitude variance between materials, to make it fit.  A number that can vary between 0 and 1000 "depending on the circumstances" exceeds even the wildest dreams of aether/phlogiston/pseudoscience/politics and looks more like religion to me. But then so does the Bohr atom. 

49

Technology / Re: What are the assumptions of the hydrogenic model in semiconductors?

« on: 24/02/2024 22:50:50 »

I hadn't come across the first equation previously (must have been asleep in one of the solid state physics lectures!) but it does look like a statement of electrostatics. The neat thing is that the answer matches the highest energy of the absorption line spectrum, so we do at least know it is correct!

We have experimental methods for estimating effective mass and permittivity so it could be said that no assumptions are required to propose the hydrogenic model, it just happens to work. Or you could argue that it is actually a circular argument because m_e* is derived from a knowledge of electron resonance and ε, which makes it a somewhat fictitious interpretation of "mass" with an apparently enormous range for 0 to 1000 m_e or more!

 

50

Physics, Astronomy & Cosmology / Re: Would a gigantic stick out of neutronium bend around the Sun?

« on: 21/02/2024 20:16:08 »

Thanks all for commenting, be it a witty reply, because of the healing power of laughter, or a concrete answer. Yes, that is very interesting, Eternal Student and others. I see I'll have to do my homework or be more specific.

My mind turned to clay, and all I that can't think of at the moment would be some other alloy (of the stick), steel or another material, other than neutronium, perhaps an alloy of neutronium, something similar and not so similar, seen in some science fiction shows, no matter how unrealistic that may well be, with EM shields or not. Is it then possible for this stick, enormously long, to, somehow, become the 'darn' ring around the Sun, perfectly symmetrical, considering the space around the Sun that's bent by its immense gravity, or it must be crushed, ripped apart to pieces?

I offer ten thousand apologies for being clueless, again. But at the very least I'm not alienated as long as Zer0 is Clueless too. Join the club! Perhaps not. No need to strive to provide a perfect answer, just if You have an additional idea, that is very welcome, even if it is fantastic, yet possible in SF, regarding the Sun's future ring. I've other stories as well, and not necessarily SF, so this one, no matter how intriguing, is not the only one. Thanks for your efforts. You've already answered quite a bit.

Usually we consider an object being ripped apart as it approaches the sun (because the sun is the more massive thing)...

Must this very long stick, out of a certain other alloy, be ripped apart for sure? Is it at all likely for the stick to get not too close or too far from the Sun, just the right distance, so that it wouldn't be ripped apart, rather form a stable ring (which You call a sphere, perhaps a Dyson sphere, even if the stick, rather than a wall, is no more than, say, 20 cm wide)?

Presumably that force-field along the edges of the stick is also sufficient to keep it long and straight rather than collapsing together to form a sphere.

This part I don't get (science is not my strong suit). I thought that space is bent around the star, so how can this stick defy space that is bent, even if equipped with EM field? Isn't the stick, well, inside this space that is bent around the Star - where else could it be? - so no matter how strong or resistant the stick is, it ought to bend, at the very least, just like the space it occupies? I guess I'm talking nonsense to You, neither do I completely comprehend gravity, being a bit more confused than usual. Perhaps this story is too ambitious for me. Aw.

Later.

51

Physics, Astronomy & Cosmology / Re: Would a gigantic stick out of neutronium bend around the Sun?

« on: 21/02/2024 16:36:47 »

The neutronium would collapse into a sphere (or almost a a sphere if it was rotating)

52

Chemistry / Re: Is halogenation of alkynes with propylene glycol possible?

« on: 09/02/2024 13:45:41 »

You really need to understand some basic chemistry first. I have no idea what is meant by "halogenation causes anaesthesia". Inorganic fluoride is extremely stable and non-reactive: to introduce fluorine into a molecule an activated reagent is needed such as a fluoro-sulphur compound, fluoride will not do it. Enol tautomers occur in ketones with an alpha hydrogen: acetone will exhibit keto enol tautomerism while benzophenone will not. There is no such thing as an enol tautomer of fluoride. Where did you get the idea that 1, 3 dichloropropanol would be an anaesthetic?, I very much doubt it. 

53

New Theories / Re: If there was one Big Bang event, why not multiple big bangs?

« on: 05/02/2024 21:31:42 »

Hi.

    I've only glanced at some of the more recent posts, sorry,  I hope I've got the gist of it.

Bogie_smiles said:    It could be a flat Universe (Euclidean; zero curvature)
Halc replied:   It has been measured to not be flat.

    I'd just like to remind both parties that "curvature" can mean different things.   There may be some confusion between a spacetime curvature and a purely spatial curvature.

    Space-time is a 4 dimensional object (3 from space + 1 from time) and we can construct a  4-indexed  Riemann Curvature Tensor for spacetime.   (The details aren't too important, it's a 4x4 matrix of values).   The Riemann curvature tensor for Minkowski space is "0" (all entries R^ρ_σμν = 0 for all ρ,σ, μ, ν).
    You (Halc ) are correct in that the Riemann curvature of a spacetime manifold in which space is expanding is not "0".  So that no transformation of co-ordiantes exists which would reduce the metric on that spacetime to the metric of plain old flat Minkowski space   <=> "our spacetime cannot be Minkowskian".

    However when "the curvature of space" is discussed it is the convention to understand that we are ONLY talking about the curvature of space   (a 3 dimensional object) and not the curvature of spacetime (a 4 dimensional object).

    Thus, we live in a universe where the Riemann tensor is not "0", there is definitely some difference from Minkowski space.   However, if we confine our attention to just the 3-dimensions of space then we do have (almost exactly) 0 spatial curvature.    So we say that our space is flat.  Indeed, geometry that operates only in 3 dimensions should work exactly as it would in Minkowski space (and that is just plain old Euclidean space since we are only considering the 3 dimensions of space, so we could also say our space is Euclidean).   The difference between the curvature of our space and that of Minkowski space is only exhibited when time is also included and we examine the full Riemann curvature tensor R^ρ_σμν.

     I hope that makes some sense:   "Flat" does not exclude the possibility of space expanding,   by convention "flat" is only a description of the spatial part of our 4-dimensional spacetime.

When it comes to possible universe types, there are different shapes and structures our observable universe could be part of. It could be a flat Universe (Euclidean; zero curvature), a spherical or closed Universe (positive curvature) or open (negative curvature). I'm no expert, but I think that if it is infinite and eternal, that translates to "flat" with no curvature.

    The curvature terminology you have used is correct.   Since we assume space is isotropic and homogenous its spatial curvature is extremely limited and we don't need a multi-indexed tensor (or matrix of values) to describe it.   It can be described by just a single Real number, k.   As regards a purely spatial curvature,  the universe  has curvature k=0  and is said to be "Flat" ;      positive curvature k>0 ("Closed")  ;   or  negative curvature k<0 ("Open").
    A few years ago,  this spatial curvature also determined the ultimate fate of the universe and you can still find plenty of textbooks, articles and You Tube videos that continue with this tradition.     An open universe would continue expanding forever,  a flat universe also exists forever but settles down asymptotically to a constant scale factor.   A closed universe must collapse  (the scale factor starts to reduce).   One thing (spatial curvature) was synonymous with the other thing (ultimate fate of the universe).   You need to watch out for this, a lot of articles still assume that the geometry of space determines the long-term expansion (or vice versa:  Eternal expansion forces an open geoemtry etc).

     The more modern understanding has considered dark energy or vaccum energy more carefully and it appears that you can pick certain ratios of ordinary matter to dark energy  so that  ALL combinations of spatial curvature and long term expansion can be exhibited.   I don't seem to be able to find an online version of the diagram  but  fig. 8.4  in Chapt. 8 of  Spacetime and Geometry,  Sean  Carroll    has an excellent diagram.
   As of the time that book went to print (2020),  the astronomical data we have suggests our universe is spatially flat and under the old view that would mean expansion slows and eventually stops so that we end up with a static universe (neither expanding or contracting).   Under the new understanding of cosmology, the current data suggests we have the right mixture of dark energy to matter so that it will continue expanding forever and not settle down to a constant scale factor.

Best Wishes.

I always try to take caution when making my assertions/dissertations about the nature of some aspect of the universe, because most of my rants are only my opinions, and often are lonely points of view.

Referring to the universe, neither flat nor curved are words that come to me naturally when I consider and discuss my own ideas; infinite and eternal are words I use, and I mean them in their common context. I struggle to reconcile my views with the consensus from the scientific community, and I'm short on proofs or justification for my views on cosmology of the universe. I often post in hopes of getting learned responses that point me in the right direction on one subject or another. Thenakedscientists forum is a good place for my kind of activity because of the "on the lighter side/New Theories" sub-forum, where I can air some of my fanciful views without upsetting the mods or the community, and in return receive helpful and cordial responses from which I learn, and my thanks to the community for all of the helpful responses.


248792,249319,

54

New Theories / Re: If there was one Big Bang event, why not multiple big bangs?

« on: 05/02/2024 17:57:40 »

@Bogie

Here is the Original Source link for that short BBC snippet i posted before.

https://www.uclan.ac.uk/news/big-ring-in-the-sky

ps - Welcome@Eternal@l.S.U.
: )

55

Just Chat! / Re: Is there a change afoot?

« on: 03/02/2024 08:50:06 »

It's happening on practically all websites and will eventually kill the "free" internet if everyone turns off all the cookies.

56

Just Chat! / Re: Is there a change afoot?

« on: 02/02/2024 12:18:03 »

Yep, me too, on the cookie selection, that is. Never seen that before today. I wanted to select chocolate chip but alas that option does not exist.

57

Just Chat! / Re: Is there a change afoot?

« on: 02/02/2024 02:37:18 »

This is supposed to be the sum of n terms in a geometric progression:

Ah, getting tex to work again. We seem to have lost that permanently with the changeover to the private server. A science site kind of depends on it, else we're reduced to an offsite formula generator and then screen-shot the output of that.

The greek letters from above the edit box seem to work, but other stuff (the whole bottom line?) don't work.

Why are spades, club, and heart the same color, but diamond is light color? Who thought of that?

[Spoiler:]

58

Just Chat! / Re: Short puzzle, just for fun.

« on: 28/01/2024 21:05:45 »

Now allow circle A to roll around the perimeter of circle B and return to where it started.    How many times will circle A have rotated?

Spoiler: show

5, 8 for the mobius

This one is super easy because it's been in the news. It (not the mobius variant) appeared on an SAT question that everybody gets wrong because the correct answer wasn't one of the options.
That seems impossible. Surely the test had one of the 4-5 multiple choices as the desired answer, even if incorrect. A percentage of people must have guessed it by accident, so the article title saying that everybody gets it wrong was, well, gotten wrong.

And no, I've yet to look at the hints


My favorite puzzles have often been just geometric.
My fave 5 piece puzzle: Arrange the 5 pieces into a square.
I also have a 'worlds hardest' 4 piece puzzle, both easily cut out of a piece of cardstock.


5piece.png (6.32 kB . 338x228 - viewed 285 times)

Yay Microsoft paint, crude, but it let me draw that in under 2 minutes.

59

Physics, Astronomy & Cosmology / Re: Can Planck's law curve be matched to Rayleigh-Jean's law curve like this?

« on: 22/01/2024 14:59:03 »

I have looked up the derivation of the wave equation via the Laplacian of the E or H field in phasor form and it is completely symmetric: a time variation in either produces an em wave.

60

Physics, Astronomy & Cosmology / Re: Can Planck's law curve be matched to Rayleigh-Jean's law curve like this?

« on: 22/01/2024 14:18:08 »

I also am fairly sure a rotating magnet would radiate em. It would have to rotate at quite a high speed to generate easily detectable radiation. I have been trying for several hours to mentally model the maths involved but I have failed so far. We normally look at charge acceleration to produce em as it is the most convenient method but one has to remember that the magnetic field is simply the electric field as seen from a different frame of reference.

I never could do the maths, but I don't care.

I can get a toy magnet and put it on the turntable of a record player.

I can put a compass near it.
And I can watch the compass needle move.
If I'm lucky it will even rotate in synchrony with the turntable.

The force acting on the needle is electromagnetic.

The carrier of the EM force is the photon.
So, in this case, I know that a rotating magnet emits EM radiation. That force is periodic and thus there must be a component of the EM radiation with the same period.So it must have photons with energies corresponding to the frequency of rotation of the record player.


Re. "but a magnet in an infinite vacuum won't. "
If the magnet falls over in a non-existent forest with no observers, does it matter?

I contend that it will still emit EM radiation.
Imagine that we somehow have a magnet in an infinite empty universe.
We set it spinning (We know it is spinning, because an ant who happens to be standing on it notices the centrifugal effect).

After a while, and at some distance from the magnet, we magically call a compass needle into being.

Does the needle have to "wait" for EM radiation from the magnet to reach it, or is that changing field already there?

I can't see how it would so I think the magnet must have been emitting EM radiation all along.

But... if there's EM radiation, then there are photons.
And, if there are photons, the universe isn't empty.
So the solution may be that you can't have a rotating magnet in an empty universe.

All seems a bit esoteric..
But let's ignore nearly the whole of the universe and consider some hydrogen atoms.
Some of them have the magnetic dipoles of the electron and the proton aligned parallel, and in others it's antiparallel.
And if one happens to flip from the first state to the second, it emits a photon of about 21 cm wavelength.

That photon crosses space and is picked up many years later by a detector here on earth.

But we have only been constructing such detectors for about 100 years.
So, for a source more than 100 light years away, the detector had not been built when the photon was emitted.

I think that's close enough to " we magically call a compass needle into being." for the analogy to work.

An electron- with a magnetic diploe moment- was flipped and sent out EM radiation. It did so in a universe in which the detector did not exist.
You may say that, without the proton of the hydrogen atom, the energy of the photon would be undefined. Which is a fair point
But, at that point, I think you need to be able to do Laplace transforms and, as I said, I can't do the maths.