41

Physics, Astronomy & Cosmology / Re: How Do We Know The Universe is 13.8B yrs Old If We Can Only See The Observable ?

« on: 26/02/2023 10:02:43 »

This recent release from the James Webb Space Telescope identified some galaxies that seem to be as big as the Milky Way, but with red shifts that suggest that they reached this size only 500-800 million years after the Big Bang.
- Current theories of galaxy formation can't account for how a galaxy would grow so big, so fast.

https://www.popularmechanics.com/space/deep-space/a43026293/jwst-discovers-impossible-galaxies/

42

Physics, Astronomy & Cosmology / Re: How Do We Know The Universe is 13.8B yrs Old If We Can Only See The Observable ?

« on: 26/02/2023 09:58:11 »

even though we have no idea how large the unobservable Universe is, we can still take an educated guess and infer its existence , age and properties through indirect observations.

We can't infer whether the unobservable universe is finite or infinite by what we can observe.
- But we do know that there are parts of the universe that we cannot see (and will never see from here)
- We can make an educated guess that an observer in the unobservable universe will see something like what we see from here

...unless some of the more radical aspects of string theory are true, and different parts of the universe adopt different parameters for their strings, which could produce radically different types of physics.

43

Physics, Astronomy & Cosmology / Re: Is it possible for a planet to be highly-highly abundant in magnesium?

« on: 25/02/2023 06:44:33 »

Magnesium is believed to be distributed into space primarily by the explosion of massive stars.
- So if you had a star that is massive enough to burn three Helium-4 nuclei to Magnesium-24...
- But not massive enough to burn Magnesium-24 to Silicon-28...
- Then, when this massive star exploded, it would distribute Magnesium-rich material into the interstellar medium
- From which magnesium-rich planets could form (in theory, if stars of this mass were the major contributor to the material in the subsequent protoplanetary disk).

https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Universe
https://en.wikipedia.org/wiki/Nuclear_binding_energy#Nuclear_binding_energy_curve

44

Physics, Astronomy & Cosmology / Re: Distribution of Earth's mass?

« on: 25/02/2023 06:25:20 »

The NASA GRACE gravity map of the Earth (link from Kryptid above) shows deviations from an ideal Earth ellipsoid.
- They expect the equator to be farther from the axis of rotation (and it is, as surmised in the OP)
- They have subtracted that out, leaving only the deviations from a perfect ellipsoid.

However, because water flows downwards, the gravitational acceleration felt at mean sea level is fairly uniform around the world.
- Although there is more mass between the Sri Lanka and the center of the Earth than beneath Oslo...
- Sri Lanka gets a lift from Centrifugal force
- And Sri Lanka is farther from Earth's dense iron center

If there was some place in the ocean with higher surface gravity, the water would flow from there to a place with lower surface gravity (if you ignore things like ocean density differences and the effect of ocean gyres)...

45

Geology, Palaeontology & Archaeology / Re: Why do insects fly?

« on: 20/02/2023 20:24:49 »

Apparently, flowering plants evolved about 130 million years ago.

But flying insects reached their maximum size about 300 million years ago, supported by higher oxygen levels than today.
Some had wingspan of up to 70cm. Some were insectivores (like dragonflies today), but there was obviously something nutritious at the base of the food pyramid...
https://news.ucsc.edu/2012/06/giant-insects.html

Maybe your hydrogen car economy could be supported by solar-powered home electrolysis, storing hydrogen and driving fuel cells in the evening?

46

General Science / Re: Good examples of contemporary computational/theoretical engineering/physics rese

« on: 20/02/2023 09:36:48 »

both computational as well as experimental in every paper

Computation has become such a common way of studying phenomena that there is even a name for it: in silico

Traditionally, biology experiments have been done:
- in vivo: in living organisms
- in vitro: in a glass dish (eg Petri dish)
- in situ: as found in nature

We now have:
- in silico: Done in a computer (silicon chips being the basis of today's computer hardware)

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

47

General Science / Re: Good examples of contemporary computational/theoretical engineering/physics rese

« on: 19/02/2023 09:17:18 »

That question is so broad that it is hard to give a meaningful response.

For a starter, the title mentions engineering/physics research
- While the body of the question only mentions computational research
- The title only mentions theoretical research, while the body adds experimental research
- Most theoretical research in any field involves computation
- Most experimental research (including in computation) involves building things

Some extreme examples:
- Manipulating real stars and galaxies is far beyond our capabilities, so cosmology is one area of research which is dominated by theoretical & computational methods.
See: https://en.wikipedia.org/wiki/Illustris_project
- Manipulating real protons and lead ions has become more effective over the past 50 years. So the Large Hadron Collider at CERN does experiments in nuclear physics. Processing and storing and analysing the results involves lots of computation, which is why CERN originated the concepts between today's World Wide Web, and Cloud Computing.
See: https://en.wikipedia.org/wiki/CERN

48

Technology / Re: Does wi-fi harm the environment?

« on: 15/02/2023 20:21:47 »

electromagnetic radiation.... damages DNA

It is true that electromagnetic radiation at UV and higher frequencies does damage DNA by breaking the chemical bonds; sometimes that damage cannot be repaired by your cells. That's why you should use sunscreen if you are going to spend a long time in bright sunlight.

However, visible and Infra-Red radiation have too low energy per photon to break DNA bonds.
- The frequencies used by WiFi and 5G cellular towers are much lower again, and cannot break bonds in DNA
- Your phone can get hot, and the radiation can also heat the skin; if you feel your ears burning, it's time to switch to hands-free.

49

Plant Sciences, Zoology & Evolution / Re: Is eugenics possible?

« on: 13/02/2023 20:18:20 »

Eugenics is performed all the time as part of mate selection. Darwin saw that.

There are some areas where eugenics is carried out voluntarily, assisted by technology - in the case of families with genetic diseases:
- If the parents are known to be carrying a genetic disease, pre-implantation genetic diagnosis can be used to select embryos which do not carry the disease. But it is a difficult process for the parents. https://en.wikipedia.org/wiki/Preimplantation_genetic_diagnosis
- Amongst certain populations with a high level of dangerous recessive genes, an anonymous teenage genetic profiling service is available. Teens interested in a relationship can anonymously check if their genes are compatible (a baby with 2 recessive genes could suffer from a severe genetic disease),  and genetic counseling is available if they don't like the answer.
https://en.wikipedia.org/wiki/Dor_Yeshorim
- But some particularly biased and brutal attempts have certainly given eugenics a bad name!

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

50

Plant Sciences, Zoology & Evolution / Re: The Speed of Life

« on: 10/02/2023 19:58:14 »

ionising radiation can induce defects in nucleic acids

There are some very hardy critters which can stand high levels of radiation.

Deinococcus survives 5,000 Greys (5 Greys will kill a human)
https://en.wikipedia.org/wiki/Deinococcus_radiodurans#Ionizing-radiation_resistance

5,000 Greys will kill half of tardigrades:
https://en.wikipedia.org/wiki/Tardigrade#Physiology

One reason elephants don't die of cancer at a young age is because they have 20 copies of the P53 gene that detects and destroys cells with DNA damage (compared to 1 in humans).
https://en.wikipedia.org/wiki/Peto%27s_paradox#Evolutionary_considerations

51

Just Chat! / Re: What is your theodicy?

« on: 07/02/2023 19:25:32 »

theodicies  from ChatGPT

...and what is ChatGPT's theodicy?

52

General Science / Re: Why Does Making A Sandwich Enable Ewe To Cut Anything?

« on: 02/02/2023 20:11:00 »

What a great inventor, from a distinguished line!
https://en.wikipedia.org/wiki/Earl_of_Sandwich

53

Geek Speak / Re: Should you secure erase an SSD before giving it away, like you should an HDD?

« on: 01/02/2023 20:50:38 »

There are legends about spooks who could read the data previously stored on a hard-disk, by reading the stray data "between" the tracks.
- Hence the idea of overwriting every sector with random data, multiple times, approaching from multiple directions, to also overwrite the "stray" data between the tracks.

I do not know whether the spook art has progressed to the point of sawing open the chips and counting the electrons on an EEPROM NAND gate, and determining whether that cell previously contained a 0, 1, 2, 3, 4, 5, 6 or 7 before it was overwritten
- I am sure that spooks would attempt this procedure if they had the opportunity to read the guidance software of a missile - before it has been erased.

Overwriting the every sector multiple times will cause wear on the SSD - but apparently they are rated at 100,000 write cycles, so not too much wear.
- As sectors wear out, they are put on a "do not use" list, and the result is that the disk capacity slowly decreases (and you might lose an occasional file which suddenly couldn't be recovered)
- I suggest that for an SSD, it is sufficient to use a tool which overwrites every sector once

See (other brands are available): https://www.kingston.com/en/blog/pc-performance/nand-flash-technology-and-ssd

54

Just Chat! / Re: Is it half full or half empty?

« on: 30/01/2023 01:20:14 »

I like this one...

glass_half_full.jpg (17.96 kB . 235x283 - viewed 1018 times)
See more at: https://www.pinterest.com.au/joanthuffman/cup-half-full-half-empty/

55

Physics, Astronomy & Cosmology / Re: Does anyone understand Roger Penose's view of cyclic universe?

« on: 20/01/2023 20:15:40 »

I stand corrected.
Penrose does talk about a continuously expanding universe, but assumes that by changing the coordinates of the universe, the near-zero density and near-zero temperature at the end of one universe becomes the near-infinite-density singularity and near-infinite temperatures at the start of the next universe.
https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology

56

Physics, Astronomy & Cosmology / Re: Has the speed of light been tested in a vacuum?

« on: 05/01/2023 20:38:30 »

Has the speed of light been tested in a vacuum?

When it comes to the speed of light, air at sea level is a pretty good vacuum.

Light slows down in a medium, compared to its speed in a vacuum
- For example, in glass, light is slowed by a factor of about 1.5
- In air at sea level, light is slowed by a factor of 1.0003
- The amount of slowing is measured by the "Refractive Index"
- See the Refractive Index list at: https://en.wikipedia.org/wiki/List_of_refractive_indices#List

For non-magnetic materials, you can calculate the amount of slowing from the measured relative permittivity of the medium.
- For air at sea level, the relative permittivity is already close to 1 (almost the same as a vacuum)
- For achievable vacuums (eg at LHC), the relative permittivity is immeasurably close to 1
- See the list at https://en.wikipedia.org/wiki/Relative_permittivity

From a totally different viewpoint, gravitational waves also travel at "c" (commonly called "the speed of light in a vacuum", but its more fundamental than that).
- Gravitational waves travel almost unaffected through the high density of the Earth, the Sun and neutron stars
- The LIGO observatory observed a neutron star merger, which was accompanied by a gamma-ray burst starting 1.7 seconds later. The source was in a galaxy 130 million light years away.
- This suggests that light travels at a speed through intergalactic space at a speed that is reduced by at most 1.7 seconds in 130 million years, ie pretty much the speed of light in a vacuum.
- See description at: https://en.wikipedia.org/wiki/Neutron_star_merger#Observed_mergers

57

Chemistry / Re: Strange aroma off smokeless fuel or has covid ruined my snout?

« on: 04/01/2023 22:01:48 »

Is Covid never ever gonna go away?

Probably not.

We will just need to learn to live with it (and some people will continue to die from it...).

The best parallel is OC43 (another coronavirus) which is probably to blame for the 1889 "Russian flu" pandemic.
- This had continuing waves for about 6 years.
- Today, it is treated as a "Common Cold", with outbreaks mostly in the winter months.
- It can still be severe in babies, the elderly and immune-compromised individuals, but the death rate is much lower than for the early outbreaks

The early outbreaks of "Russian flu" were not aligned with the usual winter colds
- This is roughly where we are with COVID-19 now
- But we can hope that it later becomes a seasonal cold
- There is one significant difference: Anyone with a genetic susceptibility to OC43 died in the early outbreaks, so today's survivors are less susceptible
- Through masks, testing, lockdowns and now vaccines & anti-virals, we have managed to reduce the number of people who died from COVID-19. But these people (and their descendants) will still potentially have a genetic susceptibility to COVID-19, which may cause ongoing deaths in later years and decades.

https://en.wikipedia.org/wiki/Human_coronavirus_OC43
https://en.wikipedia.org/wiki/1889%E2%80%931890_pandemic

58

Physics, Astronomy & Cosmology / Re: Has the speed of light been tested in a vacuum?

« on: 04/01/2023 21:20:34 »

I always thought a vacuum was a process of extracting the air from a containment . Are you saying the universe is contained or something similar ?

Actually, while it was forming, the baby Earth extracted any nearby atoms out of space by its gravitational field, interacting with the protoplanetary disk
- The same goes even more so for the Sun (mostly hydrogen and helium) and the large planets (Jupiter, Saturn, etc)

The Sun blows out a high-speed Solar Wind, but its density is far less than the density at the surface of the Sun.
- Since the surface of the Sun is strongly compressed by gravity into the sphere we see in the sky
- By the time this Solar Wind reaches the Voyager spacecraft, its density and speed have dropped enormously. In this region, the extremely low density of the interstellar medium dominates.

CERN uses very fancy vacuum pumps, but for most of space, gravity is the invisible "pump" which keeps the air out of space.

https://voyager.jpl.nasa.gov/mission/status/

59

Physiology & Medicine / Re: Why is stroke induced paralysis sometimes temporary or sometimes permanent?

« on: 30/12/2022 22:14:34 »

It depends on how extensive the damage is, and whether there are nearby areas of the brain that can take over the damaged areas (when given suitable training).
- A major factor in the extent of the damage is how quickly the patient can be taken to hospital, diagnosed and given suitable treatment. The brain is very oxygen-hungry, and an hour can make a big difference to the amount of damage.
- Physiotherapy and similar rehabilitation can help with recovery, if the damage is not too extensive, and the rehabilitation is affordable
https://en.wikipedia.org/wiki/Stroke#Prognosis

60

General Science / Re: How would you explain or define calculus in a sentence or two?

« on: 27/12/2022 20:23:41 »

Historical answer: "calculus" originally comes from the Latin, and means a small stone or pebble. These were used in an abacus for calculations.