1

Physics, Astronomy & Cosmology / Re: Is the inverse square law only approximately correct in general relativity?

« on: 25/06/2022 10:08:47 »

The reasoning about Event Horizons is almost backward.

I was not thinking about a horizon at a fixed distance.
- After all, the size of our observable universe is not at a fixed distance - it expands at the speed of c.
- But space can expand faster than c, so (in principle) there are distant galaxies that people on Earth could see today, but
 which will not be visible in 10 billion years, because the expansion of space has carried them outside our visible universe.
- If you posit some particle that travelled at c/10 (and didn't slow down), there would be regions of our visible universe that could never detect these particles, because the space in between is/will be expanding faster than c/10.

Usual disclaimer: Ignoring intergalactic medium, electrostatic forces, magnetic fields, etc which will change the velocity and/or direction of real beta particles.

2

Physics, Astronomy & Cosmology / Re: Is the inverse square law only approximately correct in general relativity?

« on: 24/06/2022 22:52:52 »

Suppose it was something else like Beta particles being emitted isotropically by the source.

If we assume that the particles are traveling at (say) c/10, then there will be an event horizon beyond which these particles will not pass, because space will be expanding faster than c/10 by the time they got there.
- This event horizon will be much smaller than the event horizon for light (which defines the limits of our observable universe).

3

Just Chat! / Re: Test of the Poll system

« on: 22/06/2022 23:44:38 »

I do now...

4

Physics, Astronomy & Cosmology / Re: Does The Gravity Of A Black Hole Travel Faster Than The Speed Of Light ?

« on: 15/06/2022 10:24:53 »

About 75% of the mass of the star is ejected into space in the supernova.

That is the case for visible supernovas.

However, the observed rate of supernovas in our galaxy is lower than calculated by astrophysicists
- This may be due to mundane reasons like the large amount of dust in the plane of the Milky Way
- But some speculate that there may be "dark" supernovas or "failed" supernovas, where the black hole eats the star from the inside, and doesn't blast most of the star's envelope into space.
- Astronomers are hopeful that  the next supernova in our galaxy will leave an imprint in neutrinos and/or gravitational waves, even if it is not visible in electromagnetic radiation.
See: https://en.wikipedia.org/wiki/Failed_supernova

5

Just Chat! / Re: how can intelligent people be trump supporters?

« on: 15/06/2022 00:59:05 »

quite low intelligence

There are many kinds of intelligence (according to some theories).

One is called "Emotional Intelligence Quotient": "EI" or "EQ".
- It is what allows counselors to empathize and assist people suffering trauma
- It is what allows fraudsters and sociopaths to see what motivates others, and to manipulate others to their own ends, sometimes without feeling a shred of empathy.

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

6

Physics, Astronomy & Cosmology / Re: Does The Gravity Of A Black Hole Travel Faster Than The Speed Of Light ?

« on: 15/06/2022 00:48:42 »

Is gravity...travelling then ?

A Gravitational Field can be viewed as a distortion in spacetime (thanks to Einstein).

Stellar-mass black holes typically start off as a massive star.
- This star bends spacetime around the star
- At the end of its life, after it has burnt all the fuel in the core to iron, the star explodes/implodes as a supernova, forming a black hole, with almost the same the same order of magnitude as the mass of the star before it imploded.
- Before the supernova, the distortion of spacetime outside the surface of the star emulates the distortion as if all the mass of the star existed at a single point at its center (thanks to Newton's shell theorem)
- After the supernova, the distortion of spacetime outside the (original) surface of the star shell of ejected material emulates the distortion as if all the mass of the star existed at a single point at its center (thanks to Newton's shell theorem). This point is now at the center of the newly-formed black hole.
- So the gravitational field outside of the star does not really change before and after the supernova, so the gravitational field does not need to "travel" for light-years.
- There are major changes in the gravitational field between (the original surface of the star) and (the surface of the new black hole). Changes in the shape of spacetime/Gravitational Field would propagate within this zone, but this is typically within a radius of a few light-seconds.

If the implosion of the supernova were completely symmetrical, no gravitational waves would be emitted outside the star
- However, computer simulations (and some recent observations) suggest that a supernova implosion is a very chaotic process, and often very asymmetrical, meaning that gravitational waves may be detectable from a nearby supernova (and neutrinos too - but astronomers have been waiting since 1987).

https://en.wikipedia.org/wiki/SN_1987A#Neutrino_emissions

Update: Corrected to account for visible supernovae ejecting 75% of their mass

7

That CAN'T be true! / Re: hydrinos!

« on: 11/06/2022 02:06:57 »

If you produced energy by lowering the ground state of hydrogen, this would produce a nasty waste stream: Toxic hydrogen.

Hydrogen is very useful in our bodies because:
-  it engages in reactions at specific energies: If you change that energy, enzymes won't work, and metabolism would stop
- Hydrogen takes up a certain amount of volume, which determines the shape of biological molecules. Change this, and you have a toxic product.

Or is he proposing a form of "Hydrino capture and restoration", where you generate energy from the Hydrogen atoms, then capture the Hydrinos and put the energy back so it is now safe Hydrogen (but losing some energy in the process)?
- Hydrinos would be very difficult to store, because they would be even harder to contain than Hydrogen

8

Physics, Astronomy & Cosmology / Re: What is the mechanism of Hawking radiation?

« on: 08/06/2022 23:29:47 »

I consider a statement that infinity+x to be greater than infinity undermines the basic consistency of mathematics

Mathematicians prefer to speak of limits as quantities "approach infinity".

An example (without TeX):
- The limit of a=1/x²→∞ as as x→0
- The limit of b=(1+1/x²)→∞ as as x→0
- I have no problems with the statement that b > a for all real values of x
- b > a, even though a→∞ and b→∞ when x→0
- In common parlance, we might even dare to say: b > a, even though a and b "are" infinite when x=0

Dealing with infinities is hard, and requires more information than comparing finite numbers
- Limits are one way of providing the necessary additional information
- But provided the additional information is obtained and properly analyzed by someone who knows what they are doing, I don't have a problem comparing infinities.

After all, some fundamental mathematical operations depend on dealing with infinities, for example:
      - differentiation ultimately comes down to calculating a limit approaching 0/0
      - and integration ultimately comes down to calculating a limit approaching 0*∞
      - Newton got correct answers for differentiation & integration, but apparently he used a bit of hand-waving in his proof that this was a valid thing to do.

9

Just Chat! / Re: Titles

« on: 04/06/2022 22:30:03 »

I don't feel particularly god-like...

10

Physiology & Medicine / Re: Link between supercentenarians and smoking?

« on: 31/05/2022 10:51:08 »

a good deal of supercentenarian individuals happen to be lifelong smokers

This probably reflects the prevalence of smoking 100 years ago, rather than any health-promoting characteristics of cigarettes.
- Most of the people who were smoking 100 years ago have died
- A tiny fraction who have more efficient DNA auditing capability (or are just plain lucky) have managed to dodge the cancer bullet.

non-smokers could break the record for longest lifespan?

Average life expectancies have increased significantly over the past couple of decades
- Partly due to reduced smoking, enforced seatbelts, pollution regulation, etc
- But maximum life expectancy is not increasing nearly as much as average life expectancy - by age 120, there are so many organ systems wearing out simultaneously that one of them is going to kill you.

There are suggestions that due to over-nutrition, increases in life expectancy may plateau, and perhaps fall, due to increases in diabetes and heart disease.

https://en.wikipedia.org/wiki/Life_expectancy#Life_expectancy_vs._maximum_life_span

11

Plant Sciences, Zoology & Evolution / Re: Why Are There No Freshwater Cephalopods?

« on: 29/05/2022 08:45:41 »

According to this article, cephalopods lack the sodium pump that is required to prevent them turning into an osmotic balloon in fresh water.
https://www.abc.net.au/science/articles/2013/01/16/3670198.htm

the brief squid, Lolliguncula brevis, found in Chesapeake Bay, is a notable partial exception in that it tolerates brackish water.

So, to maintain their trim, jet-propelled, ocean-going shape, they have to stay in salty water.

12

General Science / Re: Are Black Holes The Blackest Things Ever ?

« on: 28/05/2022 02:39:42 »

Apparently, the current record-holder for blackest materials (as of 2019) is a forest of carbon nanotubes grown on aluminium, claimed to absorb 99.995% of incoming light.
- Ultrablack materials are very useful in construction of telescopes, as they reduce those annoying lines radiating from bright stars, and other optical defects.
See: https://sitn.hms.harvard.edu/flash/2019/back-black-new-blackest-material/

But black holes are far blacker: Despite the accretion disk of a black hole getting hot enough to emit X-Rays, the event horizon of a solar-mass black hole has an effective surface temperature of around 60 nanoKelvins, due to Hawking radiation.
See: https://en.wikipedia.org/wiki/Hawking_radiation#Overview

13

Physics, Astronomy & Cosmology / Re: Why does The Sun's Polarity Change Every 11 years and Earth's is so unreliable ?

« on: 28/05/2022 02:28:59 »

A magnetic field is generated by the movement of conductive fluids inside the Earth and the Sun.
- In the case of the Earth, this is liquid iron/nickel alloy in the outer core
- For the Sun, it is Hydrogen/Helium plasma in the core
- Laboratory studies have used liquid sodium, and produced magnetic field reversals on timescales that are feasible in a laboratory experiment (ie much less than years)
- As you could imagine, there is a very different viscosity and inertia (and temperature) between these different fluids
- So it is not surprising that magnetic field reversals happen on very different timescales in these different environments.

Fluid flow is often a chaotic process, as we see with the Earth's magnetic field, and laboratory studies.
- The Sun's magnetic field is not exactly a model of regularity, since sunspots virtually disappeared for 70 years during the Maunder minimum (ironically, this started not long after Galileo brought them to the attention of European scientists - the Chinese had been studying them for centuries).

See: https://en.wikipedia.org/wiki/Maunder_Minimum

14

Physiology & Medicine / Re: Can JUST a head survive ?

« on: 28/05/2022 02:13:50 »

It's already been done, on Futurama... 

15

Physics, Astronomy & Cosmology / Re: Correlation vs association

« on: 24/05/2022 23:35:29 »

a is the independent variable, b is the dependent variable

I know that this is normal terminology, but it implies a causal direction.
- If there is some variable in your experiment that you can easily control, and another variable that you can easily measure, then it is fair to say that "when I changed variable x, variable y changed in a (linear/parabolic/exponential) manner"

However, when it comes to complex things like the impact of obesity in a human population on heart attacks:
- There is no easy way to control obesity in a whole population
- There is no easy way to control heart attacks in a whole population
- There are many factors which can cause heart attacks (eg genetics, congenital problems, education on exercise, stress)
- There are many factors which can cause obesity (eg genetics, income, education on healthy diet, stress)
- So the easiest thing to do is to do some sort of scatterplot of obesity vs age of first heart attack
- Then do a regression line through it, to conclude that  "with increased variable x, variable y changes in a (linear/parabolic/exponential) manner"
- You could hypothesize that obesity contributes to heart attacks (since the obesity was present before the first heart attack), but it's not guaranteed: Someone who has an underlying heart condition may be predisposed to a sedentary lifestyle, which may make them obese.
- You could make comments like "For patients with BMI > 30, a weight reduction of 1 kg is associated with a delay of z years in age of first heart attack."

16

Just Chat! / Re: a suitable pseudonym

« on: 22/05/2022 01:03:17 »

I've never met a scientist who I would call remotely autistic.

Until around the 1980s (perhaps, until the release of Rainman, in 1988), autism was commonly seen as a development problem of infants, who were often locked up in institutions. Since virtually all scientists are adults, they could not be autistic, by definition.

Now it is recognised as:
- occurring in adults too (usually children who grew up outside an institution, and learned to adapt)
- occurring in a spectrum, from very mild to very severe
- more severe cases often being seen as children of parents with mildly autistic tendencies (ie a strong genetic contribution) - with Silicon Valley being a particularly intense hotspot

We can now look back and see scientists who were almost certainly autistic, eg
- Cavendish, who was brilliant, but could never talk directly to people, but used correspondence.
- Mendel, who spent years breeding peas
- Darwin, with his intense childhood focus on collecting bugs
- Even many of the early researchers into childhood autism! (in one case, because they had an autistic child themselves)
- It is that often-introverted focus on collecting information in some specific area, often with a numeric focus that means someone with autistic tendencies is more likely to become a scientist, engineer, musician or perhaps an artist (in contrast to movie star or a socialite, for example).
- A text-based forum like this one is likely to attract people with some of these characteristics...

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

You spend your whole life trying to find something you enjoy, and then everyone tells you to shut up about it.

17

Chemistry / Re: How well understood is the Chemistry of the trans-uranic elements?

« on: 17/05/2022 11:46:54 »

I wonder if Schrodinger's cat thought experiment needs to be re-written.

Sean Carrol is a cat-lover, and has rewritten the Schrodinger's cat thought experiment: Instead of a radioactive decay releasing a poison gas, it releases an anesthetic gas.
- So the question becomes: "Is the cat awake or asleep?".

18

COVID-19 / Re: Can covid tests also detect common colds?

« on: 13/05/2022 00:20:04 »

There are around 150-200 viruses that we classify as "the common cold". Only 4 of them are coronaviruses, so it's not really accurate to say "a cold is a Coronavirus".

You could produce a RAT test that detected one or a couple of the common cold viruses (eg adenoviruses), but it is unlikely that a single RAT test could detect all of them.

I am sure that one of the criteria for a successful COVID-19 RAT is that it did not react to the 4 "Common Cold" coronaviruses.

There are hints that people who have recently suffered from a "Common Cold" coronavirus are slightly protected from COVID-19, as their immune system responds to the family resemblance.
- This may be why children under 2 years old show some benefit from a COVID vaccine, while those 3-5 do not
- Children under 2 have lived during some form of lockdown, and may have had less exposure to the 4 "Common Cold" coronaviruses, and so may have less protection against COVID-19 than slightly older children.

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

19

Just Chat! / Re: What is your main area of interest or expertise?

« on: 03/05/2022 23:22:08 »

Philosophy should be the basis of our biggest and most influential decisions.

It has been noted that if you recursively trace the first significant word in a Wikipedia article back to its Wikipedia article, you get back to the Wikipedia entry on Philosophy (in about 95% of cases).

So perhaps Philosophy is the basis of our biggest and most influential Wikipedia articles? (in a roundabout sort of way...)
See: https://en.wikipedia.org/wiki/Wikipedia:Getting_to_Philosophy

20

General Science / Re: spherical implosions

« on: 03/05/2022 22:37:56 »

The Trinity test didn't need a perfectly spherical implosion - just good enough.
- And it worked - but they needed a much more compact arrangement if they were to fit it into a plane.
https://en.wikipedia.org/wiki/Trinity_(nuclear_test)

Another area trying to do spherical implosions today is the US National Ignition Facility, which is trying to initiate nuclear fusion with a spherically symmetrical arrangement of 192 lasers.
See: https://en.wikipedia.org/wiki/National_Ignition_Facility#Tests_and_construction_completion