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Question of the Week / Re: QotW - 23.12.08 What are black holes made of?

« on: 03/12/2023 20:14:13 »

Mass and/or energy (any kind): but concentrated into such a small radius that the escape velocity exceeds the speed of light.

The most common way that black holes form today is when a massive star (>10 times the mass of the Sun) explodes as a supernova. The remnant left behind will be a black hole.

Less massive stars can form a dense neutron star; if two neutron stars later collide, they could also turn into a black hole.

The James Webb Space Telescope has revealed large active galaxies, soon after the Big Bang. These are believed to have supermassive black holes at the centre. Theoreticians are inventing new mechanisms that would allow these supermassive black holes to form in the hot, dense early universe, without first forming stars.

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COVID-19 / Re: What is "long covid" and what different types are there?

« on: 28/11/2023 09:39:29 »

Chronic Fatigue Syndrome is a well-known condition that can last for months after an infection of mononucleosis or some viruses.
- The causes are not well understood
- Some COVID patients seem to suffer something similar.
https://en.wikipedia.org/wiki/Chronic_fatigue_syndrome

COVID attacks cells via the ACE2 receptor on their surface. This receptor is involved in regulating blood pressure.
- This receptor appears on many cell types including lungs (the normal route of infection), lining of blood vessels, kidneys, and nerve-supporting cells.
- Loss of nerve-supporting cells can kill nerve cells, resulting in COVID's most distinctive symptom: Loss of taste and smell.
- If this spreads into the brain, it could be responsible for the death of brain cells - a study of patient MRIs before and after COVID showed a reduction in brain volume (faster than normal shrinkage). This could be responsible for the "brain fog" symptom which is often reported by long COVID sufferers.
- Since every organ depends on a flow of oxygen and glucose, inflammation of the blood vessels (and resulting blood clots) could damage every organ in the body (depending on where the blood clots occur), resulting in a wide array of medical conditions.

Probably, Long COVID symptoms will eventually be grouped into 5 or more clusters of symptoms - where one person may be suffering from 1 or more of these clusters.
https://en.wikipedia.org/wiki/Long_COVID

(Overlap with Paul)

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Plant Sciences, Zoology & Evolution / Re: Can Animals Appreciate Beauty ?

« on: 15/11/2023 20:34:20 »

Humans are very visually-oriented.

Other animals rely more on other senses.

I can imagine a dog appreciating a beautiful scent that would be lost on a human.

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Physics, Astronomy & Cosmology / Re: Are All The Planets Moving Away From The Sun Due To Sun Losing Mass ?

« on: 15/11/2023 09:13:18 »

In about 500 million-1 billion years (please correct  if inaccurate)

The estimate from Wikipedia is that the Sun will turn into a Red Giant in about 5 billion years.
https://en.wikipedia.org/wiki/Red_giant#The_Sun_as_a_red_giant

Either way, I will be gone by then...

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Physiology & Medicine / Re: How Does The Placebo Effect Work ?

« on: 14/11/2023 20:32:05 »

The mind does have considerable control over your body, and how you feel about your body (eg pain sensitivity).
- So telling your mind that someone you trust has prescribed this medication will probably make you feel better, even if it does nothing for an underlying biological problem.
- We saw this during the COVID pandemic, where a significant fraction of the US population believed that Ivermectin had protected them from COVID and/or cured them - because Donald Trump told them (with no clinical evidence at all, initially).

That's why the gold standard for clinical trials is to test a proposed medication/treatment against an identical-looking placebo.
- That tells you (and anyone funding your health) that paying for this medication is better than doing nothing (for free).
- Often, the placebo effect is bigger than the effect of the proposed medication! But the small effect of the medication is visible because you can "subtract out" the placebo effect.
- However, large studies have shown that Ivermectin is no better than placebo at treating COVID (with the possible exception of trials in some 2/3 world countries, where the proven de-worming effect of Ivermectin may have reduced the known immune-suppressing effects of parasitic worms, allowing a more robust immune response to COVID).

I have heard of a 2010 study that demonstrated that the placebo effect really makes people feel better, even if they know they are taking an inert substance!.
See: https://en.wikipedia.org/wiki/Placebo#Mechanisms

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New Theories / Re: How Jupiter magnetic fields is created?

« on: 11/11/2023 21:34:53 »

Re "there are at least two magnetic dipoles": The correct term is "quadrupole". 2, 4, 6, 8 or more poles are also possible.

Re "1. random activities as swirling mass of hydrogen deep within the planet": Chaotic motion of conducting fluids has been observed in the lab to create a magnetic field, which also has chaotic characteristics (including periods of oscillation).
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.98.044502

The Earth's magnetic field is currently mainly a dipole, but during magnetic field reversals, it may pass through a quadrupole (or higher-order) phase.

Hydrogen's position on the periodic table places it near the metallic elements. There have been multiple experiments showing that hydrogen becomes metallic at very high pressures (such as occur in the centre of Jupiter).
https://en.wikipedia.org/wiki/Metallic_hydrogen#Experimental_pursuit

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Question of the Week / Re: QotW - 23.11.17 Why can't things travel faster than light?

« on: 11/11/2023 00:09:44 »

As Paul says, you can't accelerate an object to the speed of light (or beyond) using a finite amount of energy.

With Dark Energy, it is spacetime itself which is expanding. There is no known limit to how fast space-time can expand.
- So some distant objects which are visible to us today (relative speed < speed of light) will one GigaYear not be visible to us (relative speed > speed of light), and no photons will reach us from those objects.

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Technology / Re: Why Don't Smartphones Have Antennae?

« on: 10/11/2023 23:50:14 »

If you have an old 4G iPhone like mine, there is a metallic pattern in the case, visible from the outside, with gaps in-between. Mine has:
- One metal stripe along the top (above where you hold it)
- One metal stripe along the bottom (below where you hold it)
- A large metal area across the back and sides (where you hold it)
- These metal stripes (antennas) are linked to internal circuitry, which can pick up signals from 2 antennas (or, in more recent models, more than 2 antennas), for transmission and reception.

When the original iPhone was introduced, reception was horrible. It turns out that your hand covered the antennas, attenuating the signals.
- People complained that it was a design flaw, and wanted their money back
- Apple retorted that people were holding it all wrong
- But when you look at the Apple iPhone ads, all the advertising models were holding it wrong, too.

Lesson: Don't just test it in a lab, test it in the real world, too!

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Chemistry / Re: What acid mixture can dissolve plastic

« on: 10/11/2023 23:37:43 »

The best way to soften plastics, and then later have them harden again is to melt them.
- Mild heat leaves the polymer chains intact, but temporarily mobilises them.
- Only works for thermoplastics...

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That CAN'T be true! / Re: What is "four times less"?

« on: 02/11/2023 20:43:35 »

I think it is shorthand for "one quarter of"
- But understandable by people who are comfortable with the counting numbers, but uncomfortable with fractions...

I suspect that the quantity that is reduced to a quarter is the mechanical energy of scrubbing - perhaps this new product chemically reacts or dissolves the dirt, much better than (say) water.

It is possible that "one quarter of the energy expended in scrubbing" translates into "one quarter of the time spent scrubbing"
- However, I am sure that it does not mean that it removes dirt, three-quarters of which has not yet been generated

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Plant Sciences, Zoology & Evolution / Re: Can an arctic polar bear survive in Antartica?

« on: 30/10/2023 05:59:11 »

One won't survive very long.
But two or more have a chance of severely depleting the penguin and seal population...

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Technology / Re: Why is my sattellite receiver behaving oddly?

« on: 30/10/2023 05:54:54 »

Perhaps your satellite receiver had been preconfigured to use certain transponders?
- If a channel was shuffled to a different transponder, it would no longer be found.
- The blind scan checks all the transponders it can find.

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Physics, Astronomy & Cosmology / Re: Why isn't my salt water evaporating?

« on: 15/09/2023 09:09:02 »

May be hygroscopic salts in there - they absorb moisture from the atmosphere (which BC was alluding to).
https://en.wikipedia.org/wiki/Hygroscopy

In extreme cases, this becomes "deliquescence" - these compounds absorb water from the atmosphere, and dissolve in the extracted water.
https://en.wikipedia.org/wiki/Hygroscopy#Deliquescence

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Physics, Astronomy & Cosmology / Re: Does helium make all sounds higher pitched?

« on: 06/09/2023 22:10:18 »

a plastic saxophone

Some researchers are 3D-printing plastic violins. They model the structure on computers, so the sound is very much like a professional wood violin.

Unfortunately, you can't use a 3D-printer to turn  yourself into a professional violin player!
https://www.sciencefriday.com/segments/3d-printed-violin-song/

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Physics, Astronomy & Cosmology / Re: Does helium make all sounds higher pitched?

« on: 05/09/2023 11:41:54 »

A tone played through a loudspeaker will have the same pitch in air or helium.

If it is a bass reflex loudspeaker, the higher speed of sound in helium will make the bass response tail off at a higher frequency than in air. So the frequency of the tone will be unchanged, but lower frequencies will be less loud.
https://en.wikipedia.org/wiki/Bass_reflex

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Physics, Astronomy & Cosmology / Re: Could the James Webb telescope had saved NASA hundreds of millions?

« on: 29/08/2023 22:16:29 »

The James Webb Space Telescope cost $US10 billion. It was a gross budget blow-out!
- They considered canceling it several times, but then it became "too big to fail"

The JWST cannot take pictures of Pluto/Charon in anywhere near the same detail as an up-close fly-by.
- And it cannot take pictures of farther objects, either, like Arrakoth in the Kuiper Belt
- JWST is an infra-red telescope, and you need a much larger dish to get the same resolution as a visible-light telescope like Hubble. JWST has similar resolution to Hubble.
- Hubble was used in selecting Arrakoth as a target to visit beyond Pluto. Hubble can only see it as a faint dot of light, which moves against the background stars as Earth goes around its orbit.
- But New Horizons took high-resolution images of Arrakoth from up-close. Not possible with Hubble.

https://en.wikipedia.org/wiki/486958_Arrokoth

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General Science / Re: Pneumatics Question

« on: 19/08/2023 22:50:17 »

due to wind speed, as in 'windchill'

I thought 'windchill' (as used on the nightly weather forecast in some countries) refers to the fact that wind makes water evaporate faster from human skin, making the weather feel colder than if the air were still.

However, a plastic and brass pump does not evaporate water from its surface, so 'windchill' would not have an effect like on humans (or at least, not the same effect).

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Physics, Astronomy & Cosmology / Re: Why Is The Oooooooort Cloud Spherical ? ..and Not an Accretion Disc

« on: 16/08/2023 09:57:30 »

Why is there an asteroid belt rather than being consolidated?

One suggestion I heard was that the gravitational tug of Jupiter was greater than the self-gravitation of the asteroid belt, so it prevented the asteroid belt from coalescing into a single body.
...But that was before the more recent theories about planetary orbits migrating around.

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Physiology & Medicine / Re: How dangerous is it for someone to wean themself off paroxetine?

« on: 10/08/2023 10:34:44 »

cessation of antidepressant medication is associated with unpleasant symptoms ... Is it dangerous?, I would say no

That is talking about the pharmacological side-effects.

However, anti-depressants also have psychological effects.

I heard one comment about a particular anti-dpressant that going off it resulted in more suicides. According to my vague recollection:
- Depression sometimes results in suicidal thoughts
- But severe depression often prevents the sufferer doing anything about it
- One scenario presented was that when going off the medication, the depression and suicidal thoughts started to return, but the sufferer was still well enough to act on them
- Result: an increase in suicides amongst people ceasing this anti-depressant
- I guess changes in medication should always be supervised by a trained professional.

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Physiology & Medicine / Re: Why Does Almost Everyone Seem To Hold On To Their Ability To Speak?

« on: 10/08/2023 10:25:25 »

Some forms of dementia render people unable to speak (or do other complex functions).

In these cases, the brain fails before the body.