21

Physics, Astronomy & Cosmology / Re: BLC 1 Signal from Proxima Centauri?

« on: 17/05/2023 22:45:07 »

Radio Telescopes in Deep space?
Or on the ' Other ' side of the Moon?

If you put a radiotelescope on the other side of the Moon, there is no line-of-sight back to Earth, so no easy way to relay back results for detailed analysis.

In practise, various countries are putting relay satellites in orbit around the Moon, so they can relay messages from experiments on the other side of the Moon back to Earth (eg China's Yutu-2 rover). If it is simultaneously visible from Earth and the Far side of the Moon, then it is in view of a conceptual radiotelescope there.

But perhaps technology will come to our aid - various satellite operators are using optical communications to carry the increasing flood of data collected from space, including LEO broadband satellite constellations, NASA missions, and military satellites.

22

Physics, Astronomy & Cosmology / Re: Can Light Experience 'Time'

« on: 15/05/2023 09:56:05 »

in an expanding universe, light will be redshifted...a photon experiences time because it does have a property that can change

That is a fairly slow rate of change, not easily observable within a lab.

Another property that can change more rapidly with time is the amplitude of the electric and magnetic fields of a coherent light beam. In the absence of any measurable expansion of the local universe in the time that light takes to cross the lab, a light beam in a vacuum will keep the same amplitude, frequency and direction (ok - you need to ignore Earth's gravity too!). Since these are the main characteristics of light, the light itself is not changed by the passage of time.

Similarly, if you slow down light by putting it through glass or water, any light that managed to avoid absorption, scattering or reflection will be effectively identical to what went in, so they are unchanged by the "experience". Since there is no change, there is no experience of time (for the light itself).

23

Question of the Week / QotW - 23.05.05 - How fast does evolution happen?

« on: 06/05/2023 03:43:41 »

On today's podcast, a listener asked how long does it take a mutation to spread through a population?
In summary, the answer was: Evolution can be very fast or very slow.

24

Physics, Astronomy & Cosmology / Re: Forgotten vocabulary - a thing being pulled apart by tidal forces.

« on: 09/04/2023 10:00:27 »

A month ago, I had the privilege of seeing 47 Tucanae (in the Toucan constellation) from a dark-sky park - it's a spectacular globular cluster.
- It's about 7% of the distance to the small Magellenic Cloud, which means that tidal effects from the Milky Way will be around 3,000 times stronger.
- However, this very dense concentration of stars has (so far) resisted tidal disruption, perhaps aided by the presence of a central black hole (not yet firmly established).
- It is possible that this is the core of a small galaxy, and that all of the outer stars have already been stripped off.
- The Gaia satellite has been able to spot stellar streams from other torn-apart globular clusters, but to date none have been detected from 47 Tucanae

This video from ESA starts with the Small Magellanic Cloud, and then zooms in on 47 Tucanae

25

Physics, Astronomy & Cosmology / Re: Forgotten vocabulary - a thing being pulled apart by tidal forces.

« on: 07/04/2023 11:25:29 »

Roche Limit.

There is a series of science fiction stories set on "Rocheworld" - a double planet which almost at the point of being torn apart, set against the very peculiar geography that might result...

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

26

General Science / Re: [Asking ChatGPT] Why would LED ligths in cargo ship is a good idea?

« on: 28/03/2023 09:49:54 »

Today I heard a story about someone who became an editor at a major newspaper, just 2 years after graduation...
- She was editor of AI
- It turns out that the AI was writing the news stories, and her editors job was to detect and correct (or delete) the AI hallucinations...

The story is here: https://www.scientificamerican.com/podcast/episode/if-ai-starts-making-music-on-its-own-what-happens-to-musicians/#transcripts-body

27

Physiology & Medicine / Re: Marburg?

« on: 27/03/2023 20:33:01 »

Monkeys are closely related to humans, so whatever infects monkeys can easily infect us (especially if humans eat the monkeys!).

Among mammals, bats have a very unusual immune system - perhaps tied to their very high metabolic rate (needed for flight).
- They harbour a lot of viruses (eg coronaviruses), but they don't seem to be severely affected.
- Bats are not closely related to humans, so these viruses are less likely to infect humans (or be transmitted amongst humans)
- But humans in rural areas of Asia do go into bat caves to collect guano as fertiliser (and often don't wear masks) - antibody testing have shown that many villagers  have antibodies against coronaviruses - even before COVID!
- Humans also eat bats

28

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...

29

The Environment / Re: Is it not time to question pet ownership?

« on: 19/03/2023 01:20:07 »

During Wilson’s testimony, senator John Pastore bluntly asked, "Is there anything connected with the hopes of this accelerator that in any way involves the security of the country?"

"No, sir, I don’t believe so," Wilson replied.

"It has no value in that respect?"

"It has only to do with the respect with which we regard one another, the dignity of man, our love of culture. It has to do with: Are we good painters, good sculptors, great poets? I mean all the things we really venerate in our country and are patriotic about. It has nothing to do directly with defending our country except to make it worth defending."

From: https://www.aps.org/publications/apsnews/201804/history.cfm

30

COVID-19 / Re: can i have a full run down on spike protiens please?

« on: 18/03/2023 20:53:04 »

I think that "spike protein" only hit the public press since COVID hit the public press in early 2020.

Google ngram says discussion about "spike protein" has been around a lot longer:

ngram_Spike_protein.png (13.15 kB . 1076x378 - viewed 1829 times)
 https://books.google.com/ngrams/graph?content=spike+protein&year_start=1800&year_end=2019&corpus=en-2019&smoothing=3

The Coronavirus family of viruses is notable for their crown-shaped appearance under an electron microscope, with spikes sticking out, like a jewelled crown ("corona" comes from Latin, and means "crown"). These spikes are how coronaviruses mate with cells, and then enter them to infect them. The proteins which make up these spike are called Spike (S) proteins.

Other viruses have a variety of different shapes, and different mechanisms for entering a cell.
- Tobacco Mosaic Virus (one of the first to have its structure deduced, using X-Ray crystallography). It looks like a packet of cigarettes (no spike), when crystallised.
- Ebola looks like a bowl of spaghetti (no visible spike)
- Influenza virus does have projecting proteins, but they are described as hemagglutinin (H) and neuraminidase (N) proteins, hence variants of influenza are described like H5N1.

>correction from bored chemist

31

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).

32

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)

33

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)

34

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

35

Just Chat! / Re: How Human Morality 'Evolves'...

« on: 10/03/2023 21:12:57 »

diversity, which is counter-evolutionary.

Isn't diversity the basis of new species?
- In this case, we are talking about "cultural species", rather than the more biological genetic species..

How we can have multiple cultural species coexisting in the same country or city is a challenge, which is where the tolerance for "diversity" comes in.
- The government is likely to be less tolerant of diversity when it comes to paying taxes
- Otherwise there will be a rapid and overwhelming evolutionary pressure for people to join the "no taxes" sect
- Soon after which, the government bureaucracy and social infrastructure will crumble and chaos ensue...

There is still opportunity for diversity between countries, eg:
- High-taxing Scandinavian countries
- Medium-taxing Australia & UK
- Low tax USA
- Near-zero tax in some Caribbean tax havens (but near-zero services, too)

36

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

37

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

38

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

39

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

40

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.