1

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

« on: Yesterday at 20:11:00 »

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

2

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

3

New Theories / Re: What is the real readshift in the Cosmic Microwave Background (CMB)

« on: 31/01/2023 08:01:50 »

CMBR data it doesn't carry any redshift.

The CMBR exhibits a dipole, suggesting a motion of our star in our galaxy of about 600km/sec, relative to the CMBR. https://astronomy.swin.edu.au/cosmos/c/Cosmic+Microwave+Background+Dipole

BBT calculation/Theory?

If this is a subtle way to sneak a New Theory into a mainstream thread, it will be demoted quickly...

4

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 98 times)
See more at: https://www.pinterest.com.au/joanthuffman/cup-half-full-half-empty/

5

Just Chat! / Re: Middle English Variations of 'You'...

« on: 28/01/2023 21:05:13 »

if you don't get this information here, where will you?

I've been following "the History of English" podcast.
- It is the history of the English language (including the many admixtures), intertwined with the more traditional history of invaders and kings and plagues.
- It is just reaching the point where English gained loan words from the Americas, and started diversifying into today's national accents

1 hour per month, currently up to episode 164.
https://historyofenglishpodcast.com/

6

Plant Sciences, Zoology & Evolution / Re: Why haven't birds (such as wrens) evolved to eat more sufficiently?

« on: 28/01/2023 20:48:29 »

Birds do evolve to eat more efficiently.

Darwin noticed groups of finches in the Galapagos islands that had slightly different beaks, depending on their environment and diet.
- It is thought that these subspecies diversified from a single finch species that arrived in the Galagos about 1 million years ago.
https://en.wikipedia.org/wiki/Darwin%27s_finches

7

Just Chat! / Re: Why was society more vapid and conformist during the 2010-2015 time period?

« on: 25/01/2023 20:03:44 »

complete cynicism in politics

Australia had this well before 2,000.

As a colony of convicts exiled on the other side of the world in 1788 (many for just being Irish), Australia has long had a cynicism of politics and politicians.
- Being ruled from the far side of the world until 1900 did not help, either
- Until the international undersea telegraph was deployed, instructions from the government in UK were always 6-12 months out of date...

Someone once contrasted Australian & US politics as follows:
- In the USA, the president is trusted until he proves that he can't be trusted.
- In Australia, the prime minister is not trusted until he proves that he can be trusted
- Note; "He" is an historical dominance, in both countries...

8

Just Chat! / Re: When was the first time you recall hearing about and/or using the internet?

« on: 21/01/2023 19:36:32 »

In the 1980s I visited Bolt, Beranek & Newman (BBN) in Cambridge Massachusetts (now part of Raytheon). This was the company which managed the early ARPANET, linking 4 universities on the other side of the USA, in California.

They had some interesting stories to tell...
- They had set up remote maintenance, so they could measure error rates on all of the individual links between sites.
- It had automatic re-routing, so that if any link failed, it would take an alternate path
- When they detected excess error rates on one of the links, they would ring up "Ma Bell" (the telephone company) and say you have this error rate on this link (quoting the specific link reference in the internal Bell reference system).
- The technical people in the telephone company would be astonished that BBN could tell this specific information from the other side of the country...

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

9

Just Chat! / Re: When was the first time you recall hearing about and/or using the internet?

« on: 20/01/2023 20:28:21 »

When I was at university in 1976, the university was connected to the internet, and some people were using email and receiving feeds from various interest groups over the internet.
- The internet connection was hosted on a PDP-11 mini-computer with 128kBytes of RAM, running UNIX*

Around 1995 I loaded Gopher on my Macintosh computer (also with 128 kBytes of RAM); Gopher was an early internet index system. My wife's reaction was "It's just like a library catalogue - it will never catch on"
- Soon after that, web browsers became available, and it did catch on!

*I took the Operating Systems course; it was about UNIX. At the start of the course, they provided the source code for the entire operating system kernel, and warned that in the final exam they would pull out a line of code, and expect you to write about it. Surprisingly, it was actually possible. It's been quite a while since operating systems were that small!

10

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

11

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

« on: 20/01/2023 10:41:56 »

Penrose's theory assumes that the universe has enough mass to slow down the expansion of the universe, so that it eventually contracts into a "Big Crunch" (or "Gnab Gib", as some palindromically express it).

This theory took a (possibly fatal) beating in the 1990s, when it was discovered that the universe is expanding at an accelerating rate.
- This suggests that Penrose's proposed contraction does not seem possible.
https://www.scientificamerican.com/article/the-2011-nobel-prize-in-prize-physics/

12

Science Experiments / Re: Looking for investors

« on: 19/01/2023 20:53:47 »

DC to AC using electrical transformers. Without help of semiconductors

Transformers only produce an output current while the input current is changing.
- If you apply DC to a transformer, the current will initially increase, producing a blip of output current. After that:
        1. The input current will grow to exceed the circuit breaker limit, it will trip, producing another blip of current (of opposite polarity). This seems to be what you describe.
        2. The input current will grow to exceed the maximum continuous current on the transformer primary, causing a meltdown of the transformer.
        3. The input current will grow until it is limited by circuit resistance to below the maximum continuous current on the transformer primary. The falling current will produce another blip of current (of opposite polarity).

Two blips of current of opposite polarity does not make a continuous supply of AC (that you could use to power a toaster, for example).

The usual way of doing DC to AC today is with a semiconductor "inverter" circuit.
- When I was a kid I converted DC to AC using the "Extra High Tension" transformer that originally powered the CRT tube of an old black-and-white TV, in series with an electromechanical buzzer. The whole thing was powered by a pair of AA batteries.
- It could produce respectable sparks - but the batteries did not last very long.

13

General Science / Re: Why are code makers and code breakers obsessed with prime numbers?

« on: 19/01/2023 09:54:46 »

Prime numbers have many neat mathematical properties which do not apply to other "composite" numbers.

One of the simplest pseudo-random number generators is x_n+1 = (a*x_n + c) mod m
- It is important that constants a, b and c be relatively prime, otherwise the sequence will repeat long before it has generated all m values.
- Using prime numbers for m has the advantage that all bits of the generated sequence have a long period before they repeat
https://en.wikipedia.org/wiki/Linear_congruential_generator

Another application for prime numbers depends on the fact that for conventional computers, it is hard to factor large numbers
- If the number has just 2 large prime factors
- If the number has smaller factors, it is much easier to factorise (especially if there are many factors)
- In theory, a quantum computer may be able to factor large numbers much more quickly than a classical computer - but it will need a few thousand qubits.
https://en.wikipedia.org/wiki/RSA_(cryptosystem)

Another role that prime numbers play here is that raising a number to a high power modulo a prime number generates a unique value.

Note that some of these algorithms use the weaker requirement of being relatively prime, not specifically a prime.

It is hard to prove that a number is prime, but there are practical tests for pseudoprimes, which can determine that a number is prime for all practical purposes.
- These tests are useful for generating public/private key pairs.
https://en.wikipedia.org/wiki/Pseudoprime

14

Physics, Astronomy & Cosmology / Re: why do a lot of people confuse between interference and diffraction?

« on: 19/01/2023 09:19:49 »

half sphere, instead of full sphere, for no clear reason.

This accounts for the direction of propagation.

Huygens didn't know about electromagnetic waves, where the interaction of electric and magnetic fields produces a direction of propagation. So he represented the direction of propagation geometrically.

15

Plant Sciences, Zoology & Evolution / Re: How do carnivorous animals eat bones without harming themselves?

« on: 18/01/2023 20:20:18 »

Hyenas are renowned for their ability to crunch bones (ie anything left after the lions have finished with their prey).

Some ancient species are thought to have been strong enough to crunch elephant bones...
https://en.wikipedia.org/wiki/Hyena#Bone-crushing_hyenas

16

Chemistry / Re: Which radioactive elements have the longest and shortest half lives?

« on: 17/01/2023 20:12:09 »

From the link provided by Bored Chemist:

Bureaucratium. A commonly heard description describes it as "having a negative half-life". In other words, the more time passes, the more massive "Bureaucratium" becomes; it only grows larger and more sluggish.

I guess a negative half-life beats a half-life of 10^-6 seconds?

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

17

Chemistry / Re: Which radioactive elements have the longest and shortest half lives?

« on: 17/01/2023 20:06:03 »

xenon 124

I assume that Xenon has been studied quite extensively, since it is at the heart of some Dark Matter experiments.
- Increasingly large vats of liquid xenon studded with photomultiplier tubes have been studied carefully to find the tiniest glimmer of the merest brush with a hypothetical Dark Matter particle.
- The largest current experiment at Gran Sasso in Italy has over 3 tonnes of liquid Xenon, and larger ones are planned
- The decay of Xenon would be one form of "false positive" that they would need to detect (and find some way to distinguish from a potential Dark Matter particle).

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

18

Physics, Astronomy & Cosmology / Re: Are red dwarf stars red?

« on: 17/01/2023 19:53:03 »

Astronomers have discovered 131 objects within 20 light-years of the Sun. 80 of them are red dwarf stars, and another 22 are even smaller and dimmer.
- Of the 131, only 22 are bright enough to be visible to the naked eye (in a dark-sky location)
- More distant red-dwarf stars (>20 light-years) would be very hard to spot with the naked eye
- It is thought that throughout the galaxy, red-dwarf stars far outnumber stars like the Sun.
- It's hard to know if brown-dwarf stars are even more numerous, because they are so hard to spot (maybe James Webb can help us, here?)

So in general, red dwarf stars would look red, if you could get close enough to see them with your colour vision.

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

19

Just Chat! / Re: What happened to QotW?

« on: 16/01/2023 20:58:41 »

Umm...can i start posting QotM in that Section?

I don't know if this segment will be resurrected.

Best if you don't post your own questions in there - that is reserved for questions that made it onto the radio/podcast show.

You are welcome to post interesting and amusing questions in other sections of the forum....

20

Physics, Astronomy & Cosmology / Re: Are red dwarf stars red?

« on: 16/01/2023 07:27:31 »

The retinal "rod" cells that operate at night are not colour-sensitive.
- To see star colours, use a camera.
- In the "old" days with chemical film, leaving the shutter open for a few hours creates streaks of many different colours.

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