1

Technology / Re: How did they make the first screw?

« on: 19/03/2023 19:52:09 »

You have just invented CNC machining.

North Korea discovered CNC machining - and wax lyrical about it (the chorus is recognizable by English-speakers, and starts at 24 seconds).
- A decade ago, this was one of their most popular songs...

2

Technology / Re: Are solar panels worthwhile?

« on: 16/03/2023 09:00:13 »

I had a look at my electricity bill recently...
- The amount of kWh I export to the grid..
- Is roughly the same as the amount of kWh I import from the grid (but at different hours)
- The bill doesn't tell me how much I consume onsite, without exporting to the grid

I installed the solar panels 2 years ago, by which time all the really attractive sell deals had been scrapped.
- So I get paid a lot less for electricity exported to the grid than the electricity consumed from the grid
- But I'm happy that my electricity consumption is now fairly much carbon-neutral (averaged over a week or so)

...now all we need is a good grid-scale battery technology to align peak production (around midday) with peak consumption (around 7am/7pm).

3

Chemistry / Re: Can glucose be synthesized without organic inputs as sources?

« on: 13/03/2023 09:16:57 »

There is apparently quite a lot of Ethanol in molecular dust clouds...
https://en.wikipedia.org/wiki/List_of_interstellar_and_circumstellar_molecules#Nine_atoms_(10)

4

Chemistry / Re: Can glucose be synthesized without organic inputs as sources?

« on: 12/03/2023 07:29:37 »

A wide variety of organic chemicals have been discovered in space, presumably formed in dust clouds from inorganic sources.

Glucose (C₆H₁₂O₆) is a fairly complex molecule; to date detection has not been reported in space, but a number of other molecules with 6 or more carbons have been discovered.
https://en.wikipedia.org/wiki/List_of_interstellar_and_circumstellar_molecules#Ten_or_more_atoms_(21)

5

Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: 10/03/2023 21:57:51 »

Multiple modes can be put to good use by making the second cavity tunable.
- This allows selection of one mode amongst many possibilities
- By selecting different modes in different devices, you can have many different devices transmitting on the same optical fiber, increasing the fiber capacity by a factor of 10 to 100: "Wavelength Division Multiplexing"
- If the independent wavelengths are closer together, then better control over wavelength accuracy and stability is needed (ie more cost)
https://en.wikipedia.org/wiki/Wavelength-division_multiplexing

Today, Erbium-Doped Fiber Amplifiers (EDFA) are used to amplify a wide range of wavelengths (other exotic elements like Thulium, Praseodymium and Ytterbium are also usable).
- This is effectively a laser without a cavity, and it is able to amplify all wavelengths in a Wavelength Division Multiplexing system.
- See EDFA at https://en.wikipedia.org/wiki/Optical_amplifier

6

Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: 10/03/2023 08:04:10 »

Lasers have a 1-dimensional cavity, for which there are several modes.
- Cheap semiconductor laser pointers continually jump between these modes
- More expensive lasers for telecommunications often have a second optical cavity coupled to the first; only one mode is able to resonate in both cavities, reducing interference due to the different speed of light of different modes when traversing an optical fiber.

This video shows mode changes every few seconds in a green laser.

This page shows a typical laser spectrum, averaged over time - but in practice, not all of these resonances are there at the same time.
https://www.researchgate.net/figure/The-laser-spectrum-at-t-6-nsec-Axial-cavity-modes-are-visible-in-the-laser-spectrum_fig4_321257044

7

Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: 10/03/2023 06:51:48 »

The only way radiation of those frequencies could have got into the cavity would be when the oven door was opened

If you are looking at the spectrum excited by the cavity magnetron, it spans a range of about 10MHz (it jumps around between different modes inside the magnetron).
- So there are a number of modes that might be excited by the magnetron
- To minimise uneven heating due to standing waves, microwave ovens often have a rotating platform for the food, or else a mode stirrer (like a metal fan, but usually out of sight)

https://www.researchgate.net/figure/Magnetron-spectrum-without-PLL-control-and-with-full-heater-power-68-W_fig4_3074637

8

Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: 09/03/2023 07:15:45 »

One of the boundary conditions that must be satisfied is that ψ = 0 at the walls of the oven  ...since these waves do not continue through the walls

I understand that historically, black body radiation was calibrated with a block of graphite (already pretty black, visually), with a sphere carved out in the center, and a hole bored through from the outside, so you could observe the radiation inside the cavity.
- You heat up the graphite block to a certain temperature (presumably with no oxygen present), and measure the spectrum of the radiation visible at the small hole.

Because graphite is a fairly effective black body, it actually absorbs any radiation impinging on the surface of the sphere
- getting hotter in the process
- and generating black-body radiation back into the cavity
- You measure the spectrum after this has settled down to an equilibrium

Because the graphite is absorptive, you don't need "ψ = 0 at the walls", since the radiation acts as if it is propagating off to infinity
- When in fact it gets absorbed within a few mm of the wall
- So there are no standing waves in the cavity
- This is quite unlike a metal-walled microwave oven, where the E field is zero at the conductive walls, and standing waves are definitely present (causing uneven heating of the food)

So I suggest that a reflective metal oven is a much worse representation of black body radiation than a cavity carved in graphite.

See the diagram here:
https://www.physics.utoronto.ca/~phy293lab/experiments/blackbody.pdf

9

Physiology & Medicine / Re: Why do some people not get hangovers?

« on: 07/03/2023 08:46:08 »

Alcohol tolerance increases with alcohol consumption (ie your body adapts) - until the point where the liver is badly damaged, and alcohol tolerance decreases.

Some individuals (and racial groups) have differing levels of alcohol dehydrogenase, which breaks down ethanol into acetaldehyde (which is even more toxic).
- Depending on how rapidly your body breaks down acetaldehyde, drinking alcohol may make you feel more or less "hung over".
https://en.wikipedia.org/wiki/Alcohol_tolerance

10

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

« on: 04/03/2023 11:13:41 »

How far can We go, before it starts getting Harmful?
10G?
100G?
1000G?

Around 7x10¹⁴ Hz. which is about 70,000GHz.
Above that, the photons have enough energy to disrupt chemical bonds, including DNA.

11

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/

12

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.

13

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

14

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)...

15

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?

16

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

17

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

18

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.

19

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

20

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