1

Physics, Astronomy & Cosmology / Re: What happens when photons leave the sun?

« on: Today at 00:39:01 »

how much Doppler shift is there?

Each year, around 3-4th January (perihelion, closest to the Sun) and 3-4th July (aphelion, farthest from the Sun), the Earth is neither moving towards or away from the Sun, and there is no Doppler shift. Around October there is a maximum Doppler blue shift (Earth moving towards the Sun) and around May there is a maximum Doppler red shift (Earth moving away from the Sun).

As others have pointed out, all year long there is a gravitational red shift (or "Einstein shift"), as photons "climb out" of the Sun's gravitational well. Depending on your frame of reference, you could say some of the following things:
- Photons don't lose speed as they always travel at c
- Photons don't lose kinetic energy, since the photon is massless
- Photons do lose momentum
- The photon frequency does decrease

One way of looking at this frequency decrease is to consider Einstein's time dilation.
- Deep in a gravitational well (eg the surface of the Sun), time moves more slowly, compared to an observer on the surface of the Earth
- So a Hydrogen atom emitting a spectral line on the surface of the Sun will do so more slowly than a Hydrogen atom emitting the same spectral line on the surface of the Earth
- So when you compare the frequency of the light from the Sun with the frequency of light generated here on Earth, you will find the light from the Sun has a lower frequency.

Einstein shift will be a maximum at aphelion, and minimum at perihelion.

photons are on their 1,000,000 year journey out of our sun

Under the extreme conditions of a supernova, energy from the core of a star can reach the surface much more quickly - just 3 to 4 hours.

But neutrinos don't interact much with matter; traveling at (pretty much) the speed of light, they can reach the surface of the star in just 1 second.
- To date, such a "race" has only been observed once, when a supernova occurred in the nearby Large Magellanic Cloud (a dwarf galaxy orbiting our Milky Way galaxy).

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

2

Chemistry / Re: What colour is paint before the colour is added?

« on: Today at 00:10:29 »

'White' paint is a base with a bright white pigment, probably titanium dioxide, added.

Before titanium dioxide, lead oxide was often used as the base. Lead is a neurotoxin, and children sometimes picked up lead from flaking paint, or even lead paint on kid's toys. Thankfully, lead paint (and leaded petrol) is now banned.

Even farther back in time, lead oxide was used in makeup.

There have also been cases where arsenic was used as a green tint...

3

Plant Sciences, Zoology & Evolution / Re: Why doesn't evolution revert when environments change back?

« on: Yesterday at 23:17:15 »

Ecosystems can revert back when conditions change: In the exclusion zone around the abandoned Chernobyl reactor (in Ukraine), many native animals have returned.
- But this only happens if those species (and their genes) haven't been driven into extinction.

A similar thing happens with individual species: There are different variants of genes, and these gene variants can come back - provided they haven't been driven to extinction.
- An often-quoted (but somewhat controversial) example is the peppered moth, which developed a dark color in polluted city areas during the industrial revolution, but the original light color persisted in less-polluted rural areas. As pollution levels decreased in cities, the light colored variant spread back into previously polluted areas.
See: https://en.wikipedia.org/wiki/Peppered_moth#Evolution

If you take something like the dinosaurs, so many genetic variants went extinct during the meteor impact that these variants can't come back. Another group of animals (the mammals) eventually filled the newly vacated ecological niche, and now those dinosaur variants can't come back, because there is no ecological niche for them (except in Jurassic Park).

4

Physiology & Medicine / Re: CKD-EPI equation for eGFR

« on: 17/05/2022 22:19:52 »

2021 CKD-EPI in european units

That is an oxymoron.

If it uses different units for inputs and/or outputs, then the equation will be different, and it is no longer the 2021 CKD-EPI equation.

It is now the jinjon  equation, and since jinjon  does not have the reputation (or published, peer-reviewed papers) of the National Kidney Foundation, no-one will know what that is, and no-one will use it.
So stick to the 2021 CKD-EPI equation, in its original units.

See, for example: https://academic.oup.com/clinchem/article-abstract/68/4/534/6509513?redirectedFrom=fulltext

5

Physiology & Medicine / Re: What is the CKD-EPI equation for eGFR?

« on: 17/05/2022 12:07:05 »

It looks like this 2021 CKD-EPI equation was developed by the National Kidney Foundation, based in New York. So it would make sense that it uses measures common in the USA.
https://www.kidney.org/

They provide the equation here: https://www.kidney.org/professionals/kdoqi/gfr_calculator/formula
- Some of the units are metric, eg ml,  mg and m²
- Some of the units are semi metric, eg dl
- Some of the metric units are mis-spelled, eg mL & dL
- Some of the units are "convenient" units, like kidney filtration time in minutes and patient age in years
- Some of them are constants which appear to have been derived from some regression analysis, like 142 and 0.9938

So if you want the results in "European" units, you will have to define what those "non-American" units are.
- For example, you could easily calculate patient age in seconds, if you think that is more European/Metric, but I don't think that is a good idea; age in years is a convenient measure
- If you arbitrarily change the units, that may change the constants in non-obvious ways
- So I suggest that if you are quoting a measurement of 2021 CKD-EPI, I suggest that you use the standard units, as that allows you to compare results between countries.

The following website shows the "normal" range, and even lets you compare with earlier versions of the formula:
https://www.mdcalc.com/ckd-epi-equations-glomerular-filtration-rate-gfr#pearls-pitfalls

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Question of the Week / Re: QotW: 16.05.22 Can we generate electricity through the spinning of the Earth?

« on: 17/05/2022 11:48:16 »

This has already been discussed, here: https://www.thenakedscientists.com/forum/index.php?topic=84653.0
Please add any additional comments there...

7

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?".

8

Technology / Re: Should games be used to train the military?

« on: 16/05/2022 10:05:51 »

On the weekend, I went to an airshow, and the Army was letting members of the public try out their VR helicopter flight simulators - effectively a video game with realistic hand/foot controls.

Judging by the number of people ahead of me in the line who crashed and burned, it's much cheaper to use a game than a real helicopter. (In one case, the apprentice pilot flew straight through a dozen residential homes...)

I was able to take off, fly around a bit, and land (with a lot of help!).

VR_Helicopter_simulator_cropped.jpg (91.38 kB . 720x493 - viewed 151 times)

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General Science / Re: Is it safe to transport hydrogen gas compressed into a water tank?

« on: 15/05/2022 22:53:19 »

The idea to compress hydrogen into water

Solubility of Hydrogen in water at normal room conditions is about 0.00016, which sounds rather low.
- Compared to Carbon dioxide at 0.169, which is 1000x higher
- You would get somewhat more dissolved under pressure (just like a soda siphon), but it's not very effective.

Or do you mean that water is a very compact (denser) way of transporting Hydrogen?
- Unfortunately, once Hydrogen is combined with Oxygen to make water, it is useless as a fuel.

10

General Science / Re: How to prove scientifically if someone is addicted to cocaine?

« on: 15/05/2022 22:36:57 »

If there is no physical addiction, then any addiction will be psychological.

Interviewing an actor will be a battle of wills between the interviewer and interviewee.

To bypass the acting skills, it may be possible to put the subject in a FMRI scanner (Functional Magnetic Resonance Imaging), and show them a series of pictures of various items including typical cocaine scenes.
- A psychological addiction may be visible in the patterns of brain region activation.


All of this assumes that said person is willing to comply with the process at all - they may just not turn up!
- So the judge would need to determine that this finding would materially affect the outcome of the trial (which would be preceded by much argumentation from highly-paid lawyers)
- And the judge would need to order that the investigation be done
- In which case, failure to comply would be considered contempt of court
See: https://en.wikipedia.org/wiki/Functional_magnetic_resonance_imaging

11

New Theories / Re: What is the real meaning of the most-distant-quasar/galaxy?

« on: 15/05/2022 09:45:11 »

A theory is ...like a family tree of COVID-19

There is a significant difference here between scientific theories and COVID-19:
- COVID-19 continually adds new mutations on top of its "parent" virus, resulting in a divergent evolution. Some similar mutations are seen, but they are outnumbered by the dissimilar mutations
- Scientific theories can "cross-breed", taking the best parts of other theories, and mixing in the a particular researcher's theoretical tweaks or experimental results. This will result in a degree of convergence over time which is not seen in COVID-19.

But the overall result may look similar, with one theory slowly taking over, and then being supplanted by an even more successful theory. A high-level graph of this process with COVID-19 is as follows:

COVID_Variant_Frequencies.jpg (73.1 kB . 1624x409 - viewed 532 times)
See: https://nextstrain.org/ncov/gisaid/global/all-time

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New Theories / Re: What is the real meaning of the most-distant-quasar/galaxy?

« on: 14/05/2022 23:12:50 »

Why the same process (which formed SMBH) can't form less massive black hole seeds?

Physicists are still open to the idea that there may be black holes of many sizes formed in the Big Bang.
- These might have formed when the universe was itself very dense (even denser than quark soup), so it wouldn't have taken so much of a density fluctuation to produce a black hole.
- These would have formed much earlier in the Big Bang timeline than the black holes implied by the Direct Collapse scenario, which operates on neutral atoms

The really tiny black holes won't be around today, because they would have evaporated long ago by Hawking radiation.
- However, ones that started out merely small could still be around today (just a bit smaller)
- Indeed, black holes were an early contender for "Dark Matter", but stellar-mass black holes were ruled out by the low rate of microlensing events
- Micro black holes are still theoretically possible - we just don't have any confirmed sightings (yet)
- Experimental scientists are still actively searching for primordial black holes (which then places limits on how many there might be in the universe today)

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

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New Theories / Re: What is the real meaning of the most-distant-quasar/galaxy?

« on: 14/05/2022 11:18:40 »

Based on the BBT, the first atom had been only created 380,000 My after the bang.

You are off by a factor of 10⁶.

According to BBT, the plasma cooled enough to form atoms around 380,000 years after the Big Bang (not 380,000 My).
- This is the era from which we see the CMBR.

14

New Theories / Re: What is the real meaning of the most-distant-quasar/galaxy?

« on: 13/05/2022 10:41:38 »

I compare a theory to a software.
Software must come with "version".

Software that is released a single organisation may have a single version number.
- But science is not a single organisation
- A theory is more like an open-source software project, where everyone who is interested gets their own copy, and make their own favorite tweaks, which others may or may not adopt, and which may or may not get merged into the "main line". Such software does not have a single version, but has many variants circulating independently (like a family tree of COVID-19, from https://nextstrain.org/ncov/gisaid/global/6m !)

COVID_Family_Tree_May-2022.jpg (183.71 kB . 949x928 - viewed 411 times)
- So a theory cannot have a single version number (Although Einstein's Relativity comes close, with a Special and a General version)

Please be aware that the "direct collapse scenario"  is based on dark matter idea.

Dark Matter would have contributed considerably to the gravitational attraction in the early universe. But it's not central to the theory.
https://en.wikipedia.org/wiki/Direct_collapse_black_hole

However, do we know how the that dark matter & dark energy in the Universe had been created by the BBT so early?
So, how can we call a theory for just 5% of the matter in the universe as a theory for the Universe?

Current computer models of the Big Bang have shown that Dark Matter and Dark Energy are required for the universe to form in the manner we observe. These models have informed deductions about what are the percentages of each.
- So actually, these computer simulations of the BBT account for all of the (known) mass-energy of the universe.

Description of the video: https://esahubble.org/videos/heic1005a/

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New Theories / Re: What is the real meaning of the most-distant-quasar/galaxy?

« on: 13/05/2022 04:09:07 »

there is a Super-Massive Black Hole at the center of our galaxy (even though we can't see it, as yet)

I spoke too soon. Today, the Event Horizon Telescope collaboration released it's image of the "shadow" of Sgr A*, seen against the glow of its accretion disk.

See: https://astronomy.com/news/2022/05/black-hole-at-heart-of-milky-way-imaged-for-first-time

16

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

« on: 13/05/2022 04:02:13 »

can a Covid lateral flow test give a positive result for the common cold?

This would be called a "False Positive": Indicating that you have COVID, when in fact you have something much milder.
- The antibodies used in these tests are quite specific, so provided you use an antibody target that is absent on the "Common Cold" coronaviruses, you should get a low False Positive level
- Providing that the test isn't too old, hasn't been exposed to high temperatures, etc

It is harder to control how well people do their swab, whether they do it 1, 3 or 5 days after they are infected, whether they have just drunk coffee, etc. So False Negatives are more of a problem: Indicating that you don't have COVID when in fact you do have it.

Lateral Flow Tests are generally considered to be 80% - 90% accurate, which is enough to indicate that you are infectious today. Taking one of these every 2 days gives a pretty good detection rate.
See: https://en.wikipedia.org/wiki/False_positives_and_false_negatives

17

New Theories / Re: What is the real meaning of the most-distant-quasar/galaxy?

« on: 13/05/2022 01:04:24 »

Sorry, there are only two options:
Fit or not fit.

There is another (more common) option: Evolve.
- Tweak the theory to account for the new observations, making it an even more successful theory, but keeping the name the same.
- In Evolutionary terms, this makes the theory even more fit!

It's only when someone discovers a major new mechanism that the theory might be given a new name.
- CMBR was a major new source of data, but the theory retained the same name: BBT
- Cosmic Inflation was a major new mechanism, but the theory retained the same name: BBT

For example: gravity theory.
Based on the mechanism of this theory the sun completes one galactic circuit in about 220 million to 250 million years.
Therefore, if we observe a star (with the same size/radius as the sun) that completes one galactic circuit in just one earth year then we should understand that there is a severe mistake in our theory.

We already know of one star that completes a galactic orbit in 16 years.
- With the James Webb telescope, we should be able to see smaller stars making faster galactic circuits.
- But this doesn't imply that there is a problem with the current theory of gravity.
- It just tells us that there is a Super-Massive Black Hole at the center of our galaxy (and allows us to estimate its mass, even though we can't see it, as yet).
https://en.wikipedia.org/wiki/S2_(star)

So do you agree that "we don't know the exact process" for the origin of the heaviest elements?

Astrophysicists expect that a number of processes will contribute to each of the heavy elements. There is no single "exact process"
- This periodic table even gives the current best guess about the mix of processes by which different elements were formed.
https://en.wikipedia.org/wiki/Stellar_nucleosynthesis#Key_reactions

18

Cells, Microbes & Viruses / Re: How long do unicellular bacteria live for?

« on: 13/05/2022 00:39:15 »

Unicellular bacteria are effectively immortal. Provided they have food and a suitable environment, they can continue to divide forever (provided they don't get too overcrowded).
- When they get overcrowded, evolution takes over; some strains survive better in crowded conditions, and outcompete those that are less fit for these resource-limited conditions.

In one sense, cancer cells have almost reverted to a unicellular state, where it is "every cell for itself", to the detriment of the body in which they originated. Most cancers are limited to one individual - any cancer cells that transfer to another individual are recognized as "alien" and destroyed by the recipient's immune system.
- However, in inbred populations, transmissible tumors can be transferred from one individual to another, without being destroyed by the other individual's immune system.
- Examples of this are the Tasmanian Devil facial tumor, Canine sexually-transmitted cancer, and a cancer of shellfish.
https://en.wikipedia.org/wiki/Clonally_transmissible_cancer

Can they persist without reproducing?

Some unicellular organisms discovered deep in a gold mine have a very low metabolic rate, and it is thought that individual may go many decades between divisions.

Unicellular organisms engage in "Horizontal gene transfer", which is a way to share useful snippets of DNA, which introduces more genetic variability than the usual cellular division. This helps them cope with extreme conditions.

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

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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

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Chemistry / Re: Can we make a microwave that cools down food?

« on: 12/05/2022 22:56:17 »

The James Webb Space Telescope has to operate at very low temperatures (like 50 degrees on the Kelvin temperature scale).

There is a very big sunshade on one side. The telescope is on the other side, exposed to open space.
The Cosmic Microwave Background Radiation will effectively heat the telescope to 2.7K.
The telescope uses microwave radiation from the telescope itself to cool down from room temperature on Earth (around 300K) to around 30K. But this is a slow process that took a month or so.

The Mid Infra-Rad Instrument needed to get down to 7K, so they had to use a refrigerator mechanism to get the rest of the way.

See: https://webb.nasa.gov/content/webbLaunch/whereIsWebb.html   and click on "Temperature Plots"