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Physics, Astronomy & Cosmology / Re: How much precession is observed in Parker Solar Probe's orbit?

« on: 15/09/2022 22:46:49 »

Parker Solar Probe's orbital period is similar to Mercury's

NASA planned the orbit of the Parker Probe so that it will periodically meet up with Venus.
- That means the aphelion is just outside the orbit of Venus (allowing 2 potential encounters)
- They ensure that the orbital period of the probe is a simple fraction of the orbital period of Venus (but this fraction changes on every encounter).
- This is so they can use a gravitational slingshot from Venus to reduce the perihelion of the Parker probe.
- It takes a huge delta-V to bring the orbit close to the Sun, and it is impractical to provide this much delta-V with chemical propellants

How does it affect its precession?

It would be interesting if NASA used Einstein's corrections to Newton's equations in planning the orbit of this space probe.
- For trips to Mercury, Venus, the Moon and farther out, Newton's equations are fine.
- Einstein's corrections apply on the order of centuries, while the planned lifetime of this space probe is just 7 years

https://en.wikipedia.org/wiki/Parker_Solar_Probe#Mission

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Technology / Re: Shower Chairs

« on: 14/09/2022 00:38:49 »

Because if you aren't very stable on your feet at the best of times, adding a slippery floor is a recipe for disaster!
- Osteoporosis (weak bones) is common in older people, and in people who don't get enough exercise
- A broken hip is a common trigger for people to move from independent living into a nursing home
- And months of confinement to bed only causes weaker bones - leading to a downward spiral

On the other hand, being seated frees up your hands for showering, instead of supporting yourself (eg on a Zimmer frame).

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Plant Sciences, Zoology & Evolution / Re: Evolutionary DNA Leaps in Chromosome counts?

« on: 06/08/2022 01:42:49 »

Chromosomes can merge (reducing the count of chromosomes) or split (increasing the number of chromosomes).
- Recent research has found that use of CRISPR can chop up a chromosome, leaving a "spare" bit floating around in a cell nucleus
- Neither of these processes need be immediately fatal to a cell, since you still have the same number of genes
- The problem comes when the cell divides - does each "daughter" cell still have a full set of genes?
- And in the next generation of organism - do they still have a full set of genes?

The centromere is a structure in the center of each chromosome that plays a vital role in duplicating DNA into each daughter cell.
- A split-off portion of a chromosome may lack a centromere, inhibiting gene replication (or sometimes, a new centromere may appear)
- Two joined chromosomes may have two centromeres, which leads to chromosome breakage
- So most cases of chromosome splitting or joining are bad for the individual organism (often leading to cancer) and the descendents (who will suffer high rates of genetic disease and infertility with the parent species)
- But in rare cases, a descendent will receive two copies of the same mutation, allowing speciation
- Gene sequencing can identify cases where chromosomes have split or joined, since biologists can compare which genes occur on which chromosome.
See: https://en.wikipedia.org/wiki/Centromere

The leap from 46 or 44 Chromosomes to a working group of 48 chromosomes in the new species to be Gorillas

The human genome appears to be the result of the fusion of two chromosomes that remained separate in other primates (ie humans went from 48 to 46, while gorillas & chimpanzees remained at 48).
- So "progress" (new species) do not always come from splitting chromosomes (fission).
- New species can come from fusion, too.
https://www.mun.ca/biology/scarr/Human_Ape_chromosomes.htm

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Physics, Astronomy & Cosmology / Re: What images do you most want to see from JWST?

« on: 04/08/2022 22:54:04 »

I would like to see stars circling the supermassive black hole at the center of our galaxy.
- At infra-red wavelengths, it should be possible to see more stars than we can see with ground-based telescopes
- and see how active the accretion disk is now
- By watching nearby stars move over a period of years, we should be able to predict when the accretion disk might fire up again.

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Physics, Astronomy & Cosmology / Re: How many levels of orbit can a planetary system sustain?

« on: 31/07/2022 22:08:05 »

Could we have something orbit the moon that is 1/(1.2x10^2) the mass of the moon?

The Moon/Earth system is very "similar" in size: The Moon is 1/80 the mass of the Earth. Some have called it a "twin planet"
- Probably due to the method of formation: The current popular theory is a Mars-sized body smashing into the Earth.
- But other ratios in our Solar system are more extreme:
- Mars has the tiny Phobos & Deimos
- Jupiter & Saturn have significant sized moons, but the planet is huge.

When we come to smaller objects:
- Pluto & Charon are fairly similar in size
- There are a number of double asteroids
- Some comets look like they were originally two objects which stuck together, with descriptions like "duck" and "snowman"

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Cells, Microbes & Viruses / Re: 'When' would you use nucleotides to construct phylogenetic trees?

« on: 30/07/2022 02:01:06 »

You might use protein amino-acid sequences when:
- Temperatures are so high that fossil DNA has been corrupted beyond our ability to read, but there is some intact protein available.
- When you are looking for functional changes in a protein, rather than non-functional genetic changes in the protein.
- But untangling and reading the sequence of a protein is not easy, and different techniques need to be developed for every different protein

In most cases, if you can recover intact DNA, you would use it, because:
- You can read the sequence of every protein in the same way, without having to develop a new technique for every protein
- You can read changes in "non-protein-coding" DNA, which often changes more rapidly than protein-coding segments, allowing the researcher to chart even very close family relationships
- Techniques for reading DNA have accelerated exponentially over the past few decades, making it the cheapest and fastest method available
- COVID-19 has resulted in the deployment of far more PCR machines and DNA sequencers than ever before...
- If you can't read nuclear DNA, mitochondrial DNA will also give some clues (there are more copies of mitochondrial DNA in each cell than nuclear DNA)

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New Theories / Re: What makes Riemann's Hypothesis Hard to Prove?

« on: 23/07/2022 23:53:27 »

the thing about Mathematics:   It often looks easy when you know how to do it

I have heard that the mathematician Gauss had a reputation for working on a mathematical problem until he solved it. And then, knowing it was true, he looked for the most elegant way of showing that it was true - but in a way that made it difficult for other mathematicians to use the learnings he had gained in discovering the result.
https://mathworld.wolfram.com/NonconstructiveProof.html

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Physics, Astronomy & Cosmology / Re: Star distance appearences

« on: 20/07/2022 00:26:16 »

It is a well known fact that stars that we see don't exist anymore

It is a well known expectation that most of the stars we see with our eyes do still exist.
- There are a few exceptions, such as a few stars that are thought to be nearing the end of their lives, and displaying some instability. They are very bright, so we see them from far away, and it is possible that they have already gone supernova.
- But most of the stars we can see have life expectancies far in excess of the light-travel time.

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Physics, Astronomy & Cosmology / Re: Star distance appearences

« on: 13/07/2022 02:27:00 »

You have to admit - the constellations do not look much like their names, at first glance.

I heard that some researchers had extrapolated stellar proper motions backward in time to see what the constellations would have looked like thousands of years ago. They came up with some date that they thought the familiar Ancient Greek constellations looked "most like" their name. From this they deduced a date when these constellations may have been originally named.
- I've not heard of the same thing being done for Australian Aboriginal constellations, which are apparently more about galactic dust clouds, and it would be much harder to measure a proper motion (compared to an individual star)..

Of course there is another explanation that I heard, about some Ancient Greek astronomers spending the night outside, with a very large amphora of ouzo...

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New Theories / Re: What makes Riemann's Hypothesis Hard to Prove?

« on: 03/07/2022 10:45:45 »

some problems are impossible to solve- That's the incompleteness theorem

The Incompleteness Theorem applies within a specific domain of mathematics - it may be impossible to prove some true statements within the axioms of that system.

However, some mathematical breakthroughs occur when applying results from a quite different domain of mathematics.
- Effectively, this extends the original set of axioms with an additional set of axioms over a different domain
- There may be additional true statements within the new, extended set of axioms that are unproveable within that extended set of axioms.

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General Science / Re: How much of me is original?

« on: 29/06/2022 22:53:11 »

Some cells are not replaced during your lifetime. This applies to the lens of your eye, and brain cells.
- Most parts of the cell are generated from instructions in the DNA, using new raw materials from your diet
- But if the cell does not divide after birth (eg brain), it can continue to use the same DNA with which you were born
- Some parts of the brain do generate new cells (eg hippocampus), but this does not apply to most of the brain
- There will be spot repairs to DNA when it is damaged by natural radioactivity or metabolic stress, and these repairs would be made from "new" atoms in your diet.

I understand that some of these DNA ages were determined by measuring the radioactive content of DNA from different tissues. The isotopic mix in the diet changed noticeably in the years that atmospheric nuclear testing was underway.
https://www.sciencefocus.com/the-human-body/what-cells-in-the-human-body-live-the-longest/

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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.

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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).

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Just Chat! / Re: Test of the Poll system

« on: 22/06/2022 23:44:38 »

I do now...

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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

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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

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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

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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

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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.

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Just Chat! / Re: Titles

« on: 04/06/2022 22:30:03 »

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