1

Just Chat! / Re: On Gender Reassignment...

« on: 11/03/2023 17:52:33 »

I'm all for people doing whatever they want as long as (a) it doesn't harm or disadvantage anyone else and (b) I don't have to pay for it. But (a) isn't satisfied when a male rapist or professional athlete says he is a woman.

[Spoiler:]

2

That CAN'T be true! / Re: How can academia tolerate such error?

« on: 28/02/2023 02:59:16 »

Hi.

He then states that the term grad div E represents the "scalar wave"

   Grad  (of a thing) is always a vector not a scalar.   So on the face of it I would be concerned about it being called the "scalar wave"  - but I haven't looked at exactly what this professor did.

PS I apologise for alternating between the del operator and grad, div as I cannot get consistent use of symbols on this computer/operating system.

   Obviously what you have done is OK anyway.    However, if you ever really wanted some mathematical notation then it can be done on any computer with any keyboard (e.g. a mobile phone)  if you use  LaTeX coding.   I'll put all of this under a pull-down spoiler, since it's not essential for the original post or reply.

Spoiler: show

You have probably noticed already that this forum software places something you want to appear in BOLD  inside  tags.   One very useful set of tags is the start and end     tex    tags because everything between those will be processed as LaTex.

This code produces  some usefull stuff:

Code: [Select]

"Del" or "nabla"  symbols are called with a "backslash" \  and the text "nabla" written straight after it   like this   [tex]  \nabla    [/tex]
Most special LaTex sybols are called with the backslash \ in front but note that a forward slash / MUST be used in the end tex tag.

Vectors with the arrow over the top   [tex] \vec{A}   [/tex].      Vectors as underlined characters    [tex] \underline{A}  [/tex]

The times symbol [tex] \times [/tex]  looks neater than using a letter  [tex] X [/tex]  for multiplication or vector cross products.

Write the curl of a vector like this  [tex] \nabla \times \vec{A}  [/tex]    but I prefer underlined vectors [tex] \nabla \times \underline{A} [/tex]

Exponentials can be done with the ^ character. So the Laplacian operator is written as   [tex] \nabla^2  [/tex]   
Just type that directly into the forum reply box and you will get this produced when you hit  "preview" or "post":

                - - - - - - - - - -
"Del" or "nabla"  symbols are called with a "backslash" \  and the text "nabla" written straight after it   like this   
Most special LaTex sybols are called with the backslash \ in front but note that a forward slash / MUST be used in the end tex tag.

Vectors with the arrow over the top   .      Vectors as underlined characters   

The times symbol   looks neater than using a letter    for multiplication or vector cross products.

Write the curl of a vector like this      but I prefer underlined vectors

Exponentials can be done with the ^ character. So the Laplacian operator is written as   
 - - - - - - -  - -  -

   Back to your original post:

   The identity         will hold for any sensible  vector  E.
   See half-way down the page here:   https://en.wikipedia.org/wiki/Vector_calculus_identities#Second_derivative_identities

By sensible vector, I mean it's smooth enough - all the derivatives you would want actually do exist.   You could have deliberately chosen a vector that had some discontinuity in some first derivatives if you wanted to invalidate that identity.
Note also that the operator ∇² on the right hand side is understood to be the vector Laplacian  (it acts on a vector to produce another vector).   Assuming E is the electric field and satisfies Maxwell's equations then you automatically have most of what you'll need to be confident the vector function is smooth enough for that identity to hold.   I haven't spent too long looking at it but it seems you would have to be deliberately trying hard to find a most unusual E field if you wanted to defeat that vector identity - so we'll just go along with the assumption the vector identity will hold.

   So nothing much is wrong with what that professor said to this point.   The only bit, as I said previously, that concerns me is the terminology "scalar wave".   That's not terminology I'm familiar with and the thing isn't a scalar, it would be a vector.

   Just from Maxwell's equations,  we have Grad(E) = 0 in free space without any charges exactly as you stated,  so yes  all of what he/she is calling the "scalar wave" would become a 0 vector there.    I'm going to assume the professor knows that and their  "scalar wave" idea is only interesting in regions where there are charges.   Overall impression  --->  I wouldn't be rushing off to find out what the professor was trying to say (or sell) based on what you have written.   

    As regards the fuel thing.   "An ice" can have a meaning other than the usual solid water ice.   Here's an example:
     In astrophysics and planetary science the term "ices" refers to volatile chemical compounds with freezing points above about 100 K, such as water, ammonia, or methane, with freezing points of 273 K (0°C), 195 K (−78°C), and 91 K (−182°C), respectively (see Volatiles).           [Extract from Wikipedia:     https://en.wikipedia.org/wiki/Ice_giant ]
     Without reading the full details,  maybe their ice thing could work.

Best Wishes.

3

That CAN'T be true! / Re: Can I get infinite "green" heat from my barn?

« on: 22/02/2023 16:48:51 »

That gives ~2.7A. The expression "tens of amps" is what I queried. I am going to do a test on this, a thermocouple in a flame, short circuited and current measured with a dc clamp meter( hall sensor ). Also can we assume that the source of emf has no resistance, neglecting the leads involved?

You probably can't neglect the leads here.
But you might be able to measure the hold-in current of the electromagnet when the valve is open.

Tens of amps might be optimistic. But it's a much bigger current than people usually consider.

4

New Theories / Re: Biblical Flood

« on: 01/02/2023 19:00:35 »

Object B at close proximity to object A has a strong charge polarization and is pushed towards object A more strongly than is pushed away from object A. Object C at longer distance from object A has a weak charge polarization and is pushed away from object A more strongly than pushed towards object A, accounting for the attractive force of gravity at shorter and repulsive force of gravity at longer astronomical distances.

https://twitter.com/Yaniv_Stern/status/1620730118980395012/photo/1

Bollocks.

5

New Theories / Re: What is the Biological Combination Theory?

« on: 27/01/2023 22:46:33 »

WHAT IS THE BIOLOGICAL COMBINATION THEORY?
Biological Combination Theory is a great advance in science.  While the Earth was formed in the black hole, the biological elements (coal dust) were randomly scatter to earth surface and to the lower layers of the earth. Living Things have formed on the earth's surface and in the soil close to the earth's surface. The biological elements that are far below the earth's crust remained as coal dust because they could not form living thing. Viruses have formed from the elements in coal dust. Viruses caused the formation of bacteria. Viruses and bacteria caused the formation of the cell of living things.

Formation stages of the first living things
According to the research, it is understood that human DNA consists of 5-8% Endogenous retro viruses. There are 20 bacteria in a human cell. In these research, he proved the accuracy of the Biological Combination Theory.

Coal Elements => Virus => Bacterium & Virus => Cell => Living Thing

- Viruses are about 100 times smaller than bacteria. Bacteria are about 1000 times smaller than living cells. All living things, including plants, contain DNA and RNA. Viruses contain DNA or RNA nucleic acid. Bacteria are made up of endless combinations of viruses. Living cells, on the other hand, consist of an infinite combination of bacteria and viruses.
- The first living things were formed in this way as a result of biological combinations, each separately. They reproduced by reproduction after the formation of the first living things. After the first living things were completed separately, they did not turn into a different living things. The theory of evolution is also invalid in this respect. Today, living things formations in the ocean and sea bottoms continue.
ORIGIN OF HUMANS
- Coals are not the old living remains, but the seeds of living creatures that have no chance to live.
- Coals are the seeds of the first life in the world. It is therefore the ancestor of all living things.
- During the formation of the Earth in the black hole, the biological elements were randomly scattered on the earth and near the earth's crust. The biological elements scattered on the earth have created living things.
- The biological elements that are well below the earth's crust do not form alive, but remain as coal dust.
- The deeper coal came into contact with the leaked gas from the center of the earth and turned into crude oil.
- The chemical composition of the coals varies according to their location and atmospheric effects. Coals consist of two parts, organic and inorganic.
- These examinations clearly show that the origin of all living things, including humans, is coal.
- These examinations show that coal is exposed to various gases and converted to oil.
- According to recent researches, chlorophyll derivatives and hemoglobin were found in the content of oil. Chlorophyll is found in plants. Hemoglobin gives blood color.
- This research proves that oil is the first source of living things.
For detailed information, you can visit my youtube, instagram and pinterest channels.

Even by the standards of new theories, this barking mad nonsense is a new low.

6

New Theories / Re: How did life begin? Viruses and bacteria. Biological Combination Theory?

« on: 27/01/2023 16:02:51 »

Bacteria are made up of endless combinations of viruses.

This is not true.

Living cells, on the other hand, consist of an infinite combination of bacteria and viruses.

This is not true.

The first living things were formed in this way as a result of biological combinations, each separately

This makes no sense at all.  How can the first living things be a combination of viruses and bacteria when bacteria are already alive?  The first life was made up of things already alive??  Huh?

The theory of evolution is also invalid in this respect.

Well, since this is mostly nonsense, I think evolution is not going to be overturned anytime soon.

Coronavirus is the most primitive, oldest and unknown virus.

Not true.

If it is not known how a virus originated and how it first got infected, it is very difficult to find the vaccine and control the virus. For this reason, scientists should consider The Biological Combination Theory to find the vaccine and control the corona virus.

Apparently you haven't heard that there is already a vaccine.

Biological Combination Theory is a great advance in science.

This also is untrue.

7

Technology / Re: Is solar energy the same as light energy?

« on: 27/01/2023 00:00:13 »

but at the heart of every photon is a magnon

You should stop posting this bull.

8

Just Chat! / Re: Why was society more vapid and conformist during the 2010-2015 time period?

« on: 25/01/2023 16:14:39 »

Interesting to note that the Big Brother franchise is owned by Bazalgette. Why does the name seem familiar? Sir Joseph Bazalgette was the Victorian engineer charged with the task of rebuilding London's sewage system, taking sh1t out of people's houses . Same family (great grandson), same business, just reversing the flow and piping it into their living rooms.   

9

Physics, Astronomy & Cosmology / Re: Why do my Christmas lights give such a nice ambience?

« on: 04/01/2023 16:28:42 »

Cataract rarely mists the entire lens at once - it tends to form in small nuclei which spread out with time. If all the n nuclei have radius r and the lens aperture is R, then the proportion of light not passing through the cataract is
(R²-nr²)/R²
 which clearly increases rapidly with R for any fixed value of r. I first made this diagnosis when a friend remarked that she couldn't read the signs in a brightly-lit supermarket but had no problem driving at night, and an optician confirmed it a few days layer.

Image "sharpness" increases with decreasing aperture either because the lens is distorted or because you define sharpness as depth of focus. An animal eye, unlike a camera, doesn't really rely on d.o.f. but tends to focus sharply on the object of interest*, so only the first condition applies: the infinitesimal segment of any convex surface approximates to spherical!


*serious problem for sailors and aviators! Thanks to lots of evolution the relaxed "normal" human eye doesn't focus at infinity but at around 20m - where you might find a natural predator or prey that you can do something about. Not a lot of use if you are trying to spot a hostile or converging aircraft in the "blue bowl".

   

 

10

New Theories / Re: Is remote neural monitoring possible?

« on: 31/12/2022 14:01:38 »

They remotely raped me, followed me, sold me to someone for electronic harassment 24/7, have been mentally (and later physically) destroying me. 

You should discuss this with your doctor if you have not already done so.  Good luck.

11

Physiology & Medicine / Re: Quantum Manifestation Code Review

« on: 30/12/2022 14:23:04 »

And the quantum bit?

12

Physics, Astronomy & Cosmology / Re: why do a lot of people confuse between interference and diffraction?

« on: 28/12/2022 15:59:52 »

Hi.
   Now just some basic tests to see if everyone really has thought this through:

When monochromatic light passes through a single slit and produces a pattern on a screen.  What do you call that pattern on the screen?
   (a)   A diffraction pattern.    (Note that Feynmann suggested diffraction applies only for multiple sources interacting.  However, light does spread out when passing through a slit, I mean this single slit thing is the text-book example of a diffraction process isn't it?).
   (b)   An interference pattern.   (Can you have interference with one source of light?  Yes you can and you do @alancalverd  whenever that light passes through an aperture).

When monochromatic light passes through two slits and produces a pattern.... What do you call that?
   (a)  A diffraction pattern.
   (b)  An interference pattern.

When ...light  ... passes.... diffraction grating... screen.  What do you call that?
    (a)  A diffraction pattern.   (I mean, it had the name "diffraction" in "diffraction grating" didn't it?)
    (b)  An interference pattern.    (Feynmann suggestion is that you really should be calling this diffraction by now).

   I think common usage of the terms would have the answers   a (for 1 slit),  b (for 2)  then back to a (for diffraction grating).  @hamdani yusuf  asked about school pupils and what they are taught in schools.  I've just spent 20 minutes going through the AQA syllabus for physics at "A" level.  They do describe the patterns with these terms.

   Meanwhile the Feynmann suggestion should give   b, b, a.

    If I've got the gist of what @hamdani yusuf  wants the definitions of diffraction and interference to be.   (One is about bending light, the other includes producing bright and dark bands in a pattern)  then the answers   are  b, b, b.

    My view is... what the figgy pudding does it matter?

Best Wishes.

13

Physics, Astronomy & Cosmology / Re: why do a lot of people confuse between interference and diffraction?

« on: 27/12/2022 18:24:54 »

Hi.

    Yes, OK, it's possible to try and keep diffraction and interference separate.
However,   is it necessary to try and do so    and    is it accidentally concealing the possibility that they are both due to the same underlying phenomena?

    Let's take an example and consider Huygens principle of secondary wavelets.   It's not the best ever explanation of how or why em radiation travels and exhibits certain phenomena,  for example you can always ask why the secondary wavelets only travel forward,  however it is one reasonable model that can be used.
    Let's just assume that something like Huygens principle is happening.   According to many references (e.g. see any reference provided below), the continued propagation of a plane wave or spherical wave can be explained just by using Huygens principle.   Specifically, once a wavefront has travelled away from it's original source (any tiny distance) then it is possible to forget about that source entirely.   The next position of the wavefront at a later time, t+δt, can be determined just by considering every point on the wavefront at time t to act as a new spherical source.   This is an important point so it's worth saying it again in a slightly different way...
    Nature does not need to know or be concerned about what the original source of the wave might have been.   It is not trying to keep the wave progressing or propagating away from that original source.  As far as Nature is concerned there is now a set of sources (one new source at every point on the wavefront) and the new position of the wavefront will be determined just by propagating each of those spherical waves away from those sources.
   A simple version of Huygens principle is provided by reference [2],  where it is stated that the new wavefront would be on the surface which is tangential to all the spherical wavelets.   Other references (e.g. [3] ) make the situation more easily expressed by referring to "the envelope" of the spherical wavelets but this is the same surface.  I think - but I'm not certain - that the original statement by Christiaan Huygens used the concept of an envelope but it probably wasn't in English and the translation is subject to some interpretation.
   Now, most versions of Huygens principle suggest that the secondary sources do behave like genuine sources of a new wave in most respects.   In particular there will be some superposition and interference.   It is very possible that the placement of the new wavefront on the envelope of the set of spherical wavelets is just a simplification of the underlying process that is actually happening.  Examples:
a)    From reference [1]:   ...every point on a wavefront is itself the source of spherical wavelets, and the secondary wavelets emanating from different points mutually interfere. The sum of these spherical wavelets forms a new wavefront.
b)    From reference [4]:   Wave propagation is linear so superposition holds: it should be possible to decompose an impulsive propagating wave front into its constituent points, then consider the impulsive wavelets radiating from each of those points at a future time, and combine those wavelets in a simple direct geometric manner to obtain the progressing wave front at that future time.

    I have included reference [4] just because it's one of the few articles I've seen where a very direct attempt is made to remove the notion of placing the new wave front "on the envelope" and there is an attempt to show that the new wavefront could just be a result of something like conventional superposition and interference.   There is a different type of wave generated by Huygens secondary sources (a Dirac delta function) but with that assumption you no longer need to exclude a backward propagation, there is just an automatic cancellation when a sum of all the waves is computed.  In a similar way, there is no effect often described as a "wake" left behind.   What remains from the superposition is precisely the same as putting the new wavefront right on the envelope (i.e. a lot of the problems and apparently arbitary rules for Huygens principle have been resolved).
   Anyway the key issue is that what is seen as a conventional straight line or spherical propagation of a wave could actually be the result of interference from many secondary wave sources on the wavefront.

Let's take this point mentioned in one of the much earlier posts:

I don't think that diffraction is a subset of interference. We can produce diffraction without interference pattern.

   
   It is quite possible that you are seeing the results of interference.  The propagation of those waves just doesn't look like a typical interference pattern but wherever there is straight line or spherical propagation of a wave then this has been the result of interference from Huygens secondary spherical wavelets.   More-over the "diffraction" effect from the knife edge on the mountain is entirely due to the phenomena of Huygens secondary wavelets.   The radio waves are entering the geometric shadow only because there were no wavelets below them that were able to provide the interference necessary to keep the radio wave progressing in a straight line from the original transmission aerial.

Summary:
   This is NOT an attempt to state that the propagation of an e-m wave has to be this way.  I have provided reference [4] because it's an article in a respected publication ("Nature", see * LATE EDITING) and it simply suggests that Huygens principle and ideas along the lines of conventional superposition and interference could play an important role in all wave propagation phenomena.
   As such what we call "diffraction" could very well be just an "interference" effect.  When light seems to bend around an obstacle, that could just be due to the lack of the interference required to keep it going in a straight line from the original source.  The opening sentence of this post can be re-stated:   Is it necessary to keep the terms "diffraction" and "interference" entirely separate    and    is it accidentally concealing the possibility that they are both due to the same underlying phenomena?


Best Wishes.

References:
    1.    Wikipedia:    https://en.wikipedia.org/wiki/Huygens%E2%80%93Fresnel_principle
    2.   Byjus:    https://byjus.com/physics/the-huygens-principle-and-the-principle-of-a-wave-front/
    3.   University of New Mexico, physics course:   https://physics.unm.edu/Courses/Fields/Phys2310/Lectures/lecture16.pdf
    4.   Nature*:   https://www.nature.com/articles/s41598-021-99049-7

* LATE EDITING:   On closer inspection, reference [4] is properly an article from "Scientific Reports" which is a sub-journal affiliated to "Nature".   It still has a peer review process but the readership and general academic reference value is not the same as the major journal "Nature".

14

New Theories / Re: "New" theory of human movement as described by Tesla

« on: 23/12/2022 14:44:54 »

Nikola Tesla, the prominent 20th century inventor, stated in his book "My Inventions" that all human movements appear to come from the will but are are actually generated from the outside.

Tesla was very smart and an excellent inventor, but let's not forget that he was a bit of a lunatic and came up with many crazy ideas.

15

Physics, Astronomy & Cosmology / Re: Is there an experiment that shows the oscillation in the E field of light?

« on: 21/12/2022 10:38:04 »

There is an underlying misunderstanding here.

The wavelength of visible light is orders of magnitude larger than an atom or molecule. When you walk on sand your speed depends on its bulk properties (wet, dry, compacted...) not the interaction of your foot with each individual grain, though the inter-grain mechanics (sharp, soft....) actually determine the bulk property. 

The fact that for instance μ_iron is sometimes enormously greater than most other materials is clearly a function of group (domain) behavior rather than that of a single atom.

As the wavelength of EMR approaches atomic dimensions so we need to model the interaction by quantum rather than wave mechanics, as I stated several posts ago.   At the other end of the scale we can measure μ and ε statically for any substance, and as we can see with the dispersion of white light in glass, these parameters vary with wavelength and with the nature of the transmitting medium, since bulk properties ultimately depend on atomic properties. 

So to address HY's problem: Maxwell's equations describe wave propagation. The wave model works well when considering propagation at wavelengths greater than an atom or molecule diameter and also describes diffraction from a crystal lattice (a bulk property), but does not describe the interaction of EMR with individual atoms, for which we have a particle model. 

Maxwell's equations don't "break down" any more than a train timetable "breaks down" when you want to catch a bus - they predict only and exactly what they say they predict.

16

Physics, Astronomy & Cosmology / Re: How dense is neutronium and how many stars are in the Milky Way?

« on: 21/12/2022 05:28:08 »

Hi again.
    Looks like everyone was writing a post at the same time.
Somehow everyone forgot to mention the important point about degeneracy pressures.

From one of the very early posts:

There is space between the particles, held at distance by the nuclear strong force which is strong enough to resist the pressure due to the gravity.

   Which is not entirely true and also uses the term "pressure" in a very informal way (I think "compression due the gravity" might have been better.  You can see that calling it pressure instead of compression has started a bad trend because @evan_au has gone right down the same road).

(i)  To keep it simple, gravity produces a net inward force, pressure does not.  Pressure is a force in all directions and the gradient in pressure is what can give rise to an outward force that can help to fight against gravity and prevent further collapse.
(ii)   It isn't just the strong nuclear force that stops the collapse.   The degeneracy pressure is a significant contributor.   Just to be clear then for anyone else reading, the collapse of the star is not caused by pressure, quite the opposite, pressure is on our side fighting against the collapse.

   What is degeneracy pressure and why would it form a gradient (With P decreasing from the centre to the outer edge of the star)?
[LATE EDITING - surplus discussion removed]  ...Well no-one asked and it's not entirely relevant to the OP, so I won't bore everyone with that.

If the electrons could get to the protons, they'd likely be turned into neutrons as had occurred to most of the proton/electron matter, but the picture below has electrons quite deep where the protons are, so go figure.

     The Chandrasekhar limit describes the point where the density of electrons would exceed that permitted by the Pauli exclusion principle.  If the star has mass above the Chandrasekhar mass, then gravity is too strong and the pressure due to electron degeneracy is insufficient to stop it.  At that point, either the temperature has to increase, so that the degeneracy of the electron gas is lifted and higher energy states are available to the electrons  (which doesn't happen*)  OR ELSE  the usual thing happens.
   *I'm going to pause here and just mention that there really was a good way out of the problem - electrons could have just occupied ever-higher energy states (which is just saying they could have higher momenta).   However, there was already high enough temperatures and pressures so that electrons and protons can fuse and that is the escape route from the Pauli exclusion principle that will be taken.   Pop Sci articles often skip that and just imply that violating the Pauli exclusion principle was inevitable at this point.
   As the star continues to collapse (and since promoting electrons to even higher energy states isn't done) the Pauli exclusion principle is about to be violated and that just cannot happen,  that number density of electrons has to be brought down somehow.   What seems to happen is that protons in the region pick up some electrons and form neutrons.  This is where or why we get a Neutron star,  the electrons are being depleted and only Neutrons tend to persist.   However, there is no need to deplete ALL the electrons,  Pauli is quite happy with their being some density of electrons,  it just can't exceed a certain density.
   In a simple model we have:    At any place in the universe,
n_e(p) dp  ≤     
  where n_e(p) dp =  number density of electrons (number per unit volume) with momentum between p and p+dp.
   There's nothing really special about a Neutron star in this respect, it abides by the same limits imposed by the Pauli exclusion principle.   It's just that the density can be so high that the limit of n_e(p) dp  was reached.
   To say this another way,  an ordinary lump of iron on your desk at home can have a free electron density of about 10²⁸  electrons per cubic metre.   So a Neutron star can also have an electron density of 10²⁸ electrons per cubic metre anywhere in it, even right at the centre.   
    Actually the momentum distribution of the free electrons in the lump of iron on your desk followed a Maxwell-Boltzmann distribution (more or less) which meant that the temperature had to be quite high to support that density (room temperature say, otherwise at some value of momentum p, the quantity  n_e(p) dp  would have exceeded the limit).  Meanwhile the electron gas in a Neutron star is almost fully degenerate (which means all of the lower energy states are filled only) and so that has a very different probability distribution for momenta.  Being fully degenerate is the optimum way to accomodate all of the electrons while having the lowest total energy.  This means, a degenerate gas of electrons would support a total electron density of 10²⁸ at a much lower temperature  (an equivalent way of saying this is that an electron gas with that total number density of electrons would not be fully degenerate unless the temperature is close to 0 kelvin).  I'm mentioning this because a simple model would treat the electrons in a Neutron star as an electron gas which is assumed to be fully degenerate - and yet the temperature is many thosuands of kelvin.  So that the total number density of electrons is necessarily way above 10²⁸ electrons/m³ everywhere.

There is another limit: If the total mass of the neutron star exceeds about 2.5 times the mass of the Sun (in a ball only 10km across!), it is thought that even the Strong Nuclear Force will not be able to withstand the pressure, and it will collapse into a black hole.

   That comment from evan_au was just another example where it reads as if "pressure" is what was causing the inward collapse and not the thing opposing it.  Additionally, degeneracy pressure has to be mentioned again.  It's not just the strong force that is keeping the Neutrons apart.  Neutrons are also fermions - they behave much like electrons and must comply with the Pauli exclusion principle.  The degeneracy pressure of the Neutron soup is the last bastion that gravity has to overwhelm.   This one is a much more genuine last great barrier where degeneracy pressure and the Pauli exclusion principle really is everything because there is no alternative this time.  The electrons could combine with protons and be removed.  The neutrons don't seem to fuse with anything and be removed.

Best Wishes.

LATE EDITING:  Changed notation   n(e) dp   to    n_e(p) dp     which is more sensible to describe the number density of electrons at a given momentum p.

17

Physics, Astronomy & Cosmology / Re: How dense is neutronium and how many stars are in the Milky Way?

« on: 20/12/2022 21:08:42 »

How dense is neutronium?

Neutron star material is remarkably dense: a normal-sized matchbox containing neutron-star material would have a weight of approximately 3 billion tonnes, the same weight as a 0.5 cubic kilometre chunk of the Earth (a cube with edges of about 800 metres) from Earth's surface

https://en.wikipedia.org/wiki/Neutron_star

how many stars are in the Milky Way?

It is estimated to contain 100–400 billion stars and at least that number of planets

https://en.wikipedia.org/wiki/Milky_Way

But no fundamental particle has a meaningful volume

Just expanding on Halc's comment a little...
- All subatomic particles (and even atom and molecule-sized objects) are not hard little balls with a definite radius
- In quantum theory, all subatomic particles (like neutrons and protons) are a little "fuzzy" or "blurry", meaning that there is no definite boundary. There are just regions where they are very likely to be found, fading off into regions where they are less likely to be found.
- You can still talk about the "average distance between protons & neutrons in a Uranium nucleus", as the uncertainty in the size of a Uranium nucleus is smaller than the uncertainty in the size of an individual neutron (relatively speaking)
- The strong atomic force between neutrons becomes repulsive at shorter distances, as if they were bumping into each other; but applying more force (eg the gravitational field of a collapsed star) will push them a bit closer together
See the graph here: https://en.wikipedia.org/wiki/Nuclear_force#Description
- Neutron stars start off extremely hot (like 10¹¹ °C), but cool down in a few years to something more like 10⁶ °C.
- Like the temperatures we are more familiar with, things at a higher temperature "jiggle" more, and the average distance between particles is greater than between cooler things, which vibrate less. This leads to the general rule that things shrink as they cool (freezing water being one notable exception). I expect that this would also apply to neutron stars, too.
https://en.wikipedia.org/wiki/Neutron_star#Mass_and_temperature

so there is in theory no limit to how far it can be compressed given enough pressure

There is another limit: If the total mass of the neutron star exceeds about 2.5 times the mass of the Sun (in a ball only 10km across!), it is thought that even the Strong Nuclear Force will not be able to withstand the pressure, and it will collapse into a black hole.

There are various theories about other subatomic particles (like the "Strange" particles and "Quarks") that are denser than neutrons, and may be able to withstand slightly higher pressures than neutrons.
- Evidence for this is being collected by the NICER X-Ray telescope mounted on the ISS, which is trying to measure the mass, size and density of neutron stars. This will give some clues about the density of neutron stars, and whether "Strange stars" or "Quark Stars" exist.
https://en.wikipedia.org/wiki/Neutron_Star_Interior_Composition_Explorer

Oops! Overlap with Halc's latest post. One comment:

otherwise heavily positively charged star.

I expect that a neutron star would be electrically neutral, overall. Electrons will be attracted into regions with protons by the electric force. Due to the size and temperature of the neutron star, I expect that atomic orbitals will not exclude electrons from proton-rich regions.

PS: In our normal experience, the electric attraction between electrons and protons is far greater than the gravitational attraction of electrons and protons. But in the extreme environment of a neutron star, the gravitational force is more comparable to the electric force.

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Physics, Astronomy & Cosmology / Re: How dense is neutronium and how many stars are in the Milky Way?

« on: 20/12/2022 21:05:21 »

Hi.

Just thought I'd mention a couple of minor points, relating to the original questions in the first post.

1.   You can Google to get estimates of the number of stars in the Milky Way.  Estimates are between 1~4  x10¹¹ stars     (checked several references for consistency:   https://en.wikipedia.org/wiki/Milky_Way   ;
    https://earthhow.com/milky-way-galaxy/          and     https://asd.gsfc.nasa.gov/blueshift/index.php/2015/07/22/how-many-stars-in-the-milky-way/  ).
   The NASA reference describes in more detail precisely where some of the problems are and why this is JUST AN ESTIMATE and provides another 3 references with more discussion of the problem.
    Note that we do sometimes "un-discover" a star.  For example, a black hole can distort space and create a lensing effect.  What can happen is that you see two points of light on each side of the black hole which you may have thought were two stars in different places but they were actually light from just the one star that has been bent around both sides of the black hole.    Meanwhile, we also frequently discover two stars where we thought there was only one.  Two close stars forming a binary system can look like just one point of light until you get a better resolution image of the region of space.
   The key point then is that this is a very rough estimate, don't be surprised if it's an order of ten bigger or smaller.   If we do revise our estimate then your book can start to look quite dated.

2.  "Neutronium" seems to be a term used mainly in Science Fiction and some Pop Sci articles.  It's not really used in more formal scientific literature.  It can mean the material a Neutron star is made of,  it could mean something else.  Historically it was a hypothetical element on the periodic table with 0 protons in the nucleus.

...I take it from what you (Halc) are saying that the strong force is repulsive at very short ranges?

   It can be desirable to try and keep two terms slightly separate.  The strong interaction or "strong force" is a fundamentally quantum mechanical interaction between quarks.   The nuclear force or "strong nuclear force" is a residual effect from that,  where a classical Newtonian force is identified as something that exists between any two nucleons  (which, as I'm sure you know, is a collection of quarks).   All too frequently the terms are used differently and often interchangeably, which is just a shame.  Just go about reading an article with the idea that they are different, one acts only on quarks, the other acts on whole nucleons.   If you were trying to consider all things in a very Newtonian way (which isn't always a great idea) then the Strong force always acts so as to keep some quarks bound together.   However, the residual strong nuclear force is different.   There can be an attractive force between nucleons at large distance and a repulsive force at small distances.
   
   See this description and diagram in Wikipedia for a discussion of the nuclear force between nucleons.   (Especially the sub-section titled "The nuclear force as a residual of the strong force")

   image taken from  https://en.wikipedia.org/wiki/Nuclear_force

  That "force" is, of course, just treating the nucleons as particles and the interaction between them in a very mechanical or classical Newtonian way.  A fully quantum theory just has some other mathematics describing the more fundamental strong interaction and there is no need to assign a mechanical force or assume the nucleons were ordinary solid particles on which a classical Newtonian force can act.

   I hope that helps a bit.

Best Wishes.

(Another post has just been added by @Halc before I completed this.   I'll read that next and hope this isn't repeating anything).

19

Physics, Astronomy & Cosmology / Re: How dense is neutronium and how many stars are in the Milky Way?

« on: 20/12/2022 20:38:17 »

I take it from what you are saying that the strong force is repulsive at very short ranges?

It is, and it is quite attractive at the normal separation between protons (only way to keep them together), so the packing in neutronium is going to be tighter to a point. I don't know the percentage density difference of each of the layers.

I had assumed( naively ) that a neutron star was one big "macro" neutron. Also, if there is a lot of proton matter at the centre there must be a collection of electron somewhere.

There's been a bunch of newer models that show different stuff at different layers, starting with hydrogen/helium/carbon atoms in the 'atmosphere'. Yes, the low-mass free electrons remain with some still-atomic nuclei ions in the outer crust of the otherwise heavily positively charged star. This is followed by inner crust of neutron superfluid where most of the neutrons are (and some electrons), and which insulates the negative particles above from the positive ones below. The outer core is superconducting protons and a sort of neutron-rich quantum liquid, and the inner core is still kind of a mystery exotic substance, perhaps a degenerate quark soup of some kind. The amazing part is how they've measured it all enough to know this stuff.
If the electrons could get to the protons, they'd likely be turned into neutrons as had occurred to most of the proton/electron matter, but the picture below has electrons quite deep where the protons are, so go figure.



Google says density varies from a billion kg/m³ (1e9) at the surface to perhaps 700 million times that at the core (7e17)
Mind you, the former figure (at the crust) is waaay below the density of an atomic nucleus, which is about 2.3e17. So most of the neutron star is less dense than any ordinary atomic nucleus, but near the middle it gets about thrice the density.
The picture above shows inner density at only 4e14 g/cm³ which is 4e17 kg/m³, which is a bit lower than the one google gives me..

20

Physics, Astronomy & Cosmology / Re: Is there an experiment that shows the oscillation in the E field of light?

« on: 20/12/2022 18:42:48 »

I understand what Hamdani is alluding to and it is something I have often thought about-permeability and permittivity are macroscopic properties derived fundamentally from the presence of charges in said material. Do they have a meaning at the atomic level?

You can calculate a refractive index from the relative permeability and permittivity.
That's a measure of how much light slows down as it passes through the material.
But light doesn't actually slow down,  simplistically, it gets "stuck" to the particles
So, on the microscopic level, a refractive index isn't well defined and thus nor is the permeability or permittivity.

On the other hand, I can say the plastic they make thin spectacle lenses from has a high refractive index because it's full of sulphur compounds and the sulphur is big and polarisable- the nuclei don't keep a very tight grip on the electrons so, a passing ray of light interacts strongly with the electrons and thus with the plastic.
That's a good enough model down to the atomic level or thereabouts

It's not a clear cut issue.