1

Chemistry / Re: What is the most and least metallic metals?

« on: 04/02/2025 23:35:54 »

This is what 1 gram of cesium looks like in water, from the Periodic Table of Elements series of videos:

The action starts at 3:45 (the rest is chemistry and engineering)

Potassium is more spectacular:

The action starts at 0:45

There is a video about Francium

They showed some pictures that purported to be Francium in water, but I suspect were relabeled atomic bomb tests.
The longest-lived isotope of Francium has a half-life of 20 minutes, which prevents accumulating any significant amount of Francium to drop it in water.
However, measurements show that Francium is slightly less reactive than Cesium, due to relativistic effects (mentioned around timestamp 12:30)
https://en.wikipedia.org/wiki/Isotopes_of_francium

2

Physiology & Medicine / Re: How Does Belly Differentiate Between Recently Eaten Food & Earlier Eaten Food ?

« on: 04/02/2025 23:10:18 »

For us humans, the intestinal tract is rather linear, so it deals with food in a first-in/first-out sequence, with various nutrients being drawn off at various stages along the way.
- In some cases, our digestive system can temporarily operate in reverse, such as after over-imbibing

For you and your bovine friends in the next field, food needs a bit more processing through 4 stomachs,
- Once the rumen starts getting full, it's time to have a rest and chew over the cud...
- This requires the esophagus to routinely operate in bidirectional mode
- As in all animals, the brain and nervous system around the gut put a lot of priority on processing food efficiently and safely (and animals which fail to do this tend to die out...)

https://en.wikipedia.org/wiki/Ruminant#Digestive_system_of_ruminants

3

Physiology & Medicine / Re: How Do We Know we know Something Without Recalling It ?

« on: 04/02/2025 22:53:58 »

The brain stores different types of information in different places - and the hippocampus is the master directory that pulls all the pieces together.
- So the hippocampus may have a directory entry for the information you seek, but the part of the brain which actually knows it takes a while to respond.
- or you may remember when or where you learned it (or from whom), but not what you learned
- Much of what we know is not stored explicitly, but is mashed together with other similar information from other sources (and updated with context of the last time you recalled it). So it might take a while to untangle the specific piece of information you need now from all the similar information that is stored with it over many years.

4

Plant Sciences, Zoology & Evolution / Re: Why do we have synchronised urination?

« on: 04/02/2025 09:21:08 »

How is the contagion spread?

It's a common saying that if you want a child to pee, run some water in the basin - the tinkle of running water seems to encourage urination. I've heard adults say that this sound also makes them want to pee.

So could the sound of urination (the tinkle of running water) encourage nearby individuals to also feel like urinating?

What is the benefit of contagious urination?
If you have a group of 20-100 individuals on the move, if you had to stop every time one of them wanted to pee, you couldn't move very far or fast.
- But if urination is contagious, they would all pee at the same time, meaning they could travel a fair distance before they all had to pee again.
- Is an army pausing for 5 minutes in every hour of marching an example of synchronised urination?

5

Plant Sciences, Zoology & Evolution / Why do we have synchronised urination?

« on: 04/02/2025 09:12:56 »

A recent episode of The Naked Scientists podcast discussed a finding that chimpanzees seemed to exhibit "contagious urination".
https://www.thenakedscientists.com/articles/interviews/weeing-contagious-chimpanzees

What is the benefit of contagious urination? How is the contagion spread?

6

Question of the Week / Re: QotW - 24.01.31 - Can you separate crude oil without making petrol?

« on: 04/02/2025 09:08:54 »

crude oil

Fossil fuels come in many different flavours in different places, ranging from coal (almost pure carbon), bituminous tar (long chains, solid at room temperature). heavy oil (medium chain). light oil (short chains) and natural gas (mostly methane).

It's slightly cheaper if you start with a feedstock that is closer to the final product you want, but the chemical processes in a petrochemical plant can change the nature of the feedstock closer to what you want (eg cracking shortens organic chains).. .

But petrol for cars is not the only useful product:
- coal (almost pure carbon): usable in coal-fired power stations, and used for steel production
- bituminous tar (long chains, solid at room temperature): Used to produce road surfaces, and power many container ships
- heavy oil (medium chain):  lubricants
- light oil (short chains): fuel for cars, trucks, airplanes and plastics
- natural gas (mostly methane): Used directly for domestic and industrial cooking, heating and powering vehicles with Liquid Natural Gas. Used in fast-response gas turbine power generators and space rockets.

As we incrementally displace various fossil fuel applications and replace them by cleaner renewable sources, we can change the mix of raw materials we use to produce the remaining products required, or chemically modify them to meet the current demands.

7

Physics, Astronomy & Cosmology / Re: Is The Surface of a Neutron Star The Smoothest Thing Ever ?

« on: 04/02/2025 06:44:03 »

I expect the event horizon of a black hole is smoother, as it doesn't have the tiny mountains which form on the surface of a neutron star
- These hills form as the neutron star cools and shrinks, and also as it reduces its spin rate due to magnetic fields interacting with the environment.

Both a neutron star and an event horizon are oblate due to their spin.

...but then, the surface of a neutron star is a physical thing, while the Event Horizon of a black hole is a virtual boundary in spacetime, whose perceived location depends on your position and velocity.

8

Technology / Re: Whatever Happened To Antennae?

« on: 04/02/2025 06:37:56 »

An anecdote: When Apple introduced the original iPhone back in 2007, they built the antennae into the slimline case.
- It had to overcome many technical challenges to fit so much computer circuitry in close proximity to a sensitive radio receiver.
- Early users found that it had poor reception, and sued Apple
- Apparently, the way users held the phone "shorted out" the different segments of the built-in antenna
- Steve Jobs said "You shouldn't hold it like that"
- But images from the early ads showed models also holding the phone in the "wrong" way.

To bring it up-to-date: Modern smartphones have become much more sophisticated; they typically have several antennae which can radiate in different directions, and work together to "beamform" the radiation pattern for best reception (and also work around whatever way you are holding the phone).

9

Chemistry / Re: What is the most and least metallic metals?

« on: 04/02/2025 06:18:01 »

is there a borderline metal/non metal ?

In the periodic table shown here ( https://en.wikipedia.org/wiki/Periodic_table ), there is a dotted line showing the approximate border between metal and non-metal.

One of the characteristics of a metal is that it tends to give up an electron in a chemical reaction.
- In the elements down the bottom rows of the periodic table, the outer electrons are shielded by many shells of inner electrons, so they are more "willing" to give up an outer electron
- This is why the fuzzy borderline extends farther to the right in the lower rows of the periodic table.
- Conversely, in the top row/upper left, Hydrogen is close to the border. It is able to give up its sole electron in an acidic water solution. Under immense pressure (eg deep inside Jupiter), it is able to conduct electricity.

10

Physics, Astronomy & Cosmology / Re: Did the Sun take 100000 years to shine ?

« on: 03/02/2025 09:00:21 »

"Brown Dwarf" stars >13 times the mass of Jupiter will start deuterium fusion, at a slow rate.
https://en.wikipedia.org/wiki/Brown_dwarf

So the Sun could have started to heat up long before it reached its current mass.
- But this slow fusion would have been lost in the heat of the friction and infalling matter which formed the star out of the protoplanetary disk.
https://en.wikipedia.org/wiki/Protoplanetary_disk

Fusion of normal hydrogen starts when a star is the size of a red dwarf (10% of the mass of the Sun), using the proton-proton chain.
- For stars larger than the Sun, fusion via the CNO process dominates
- The Sun itself uses both processes to generate heat
https://en.wikipedia.org/wiki/Stellar_nucleosynthesis

It seems to me that as a star gains mass, it's temperature increases. When fusion starts (long before the Sun reached its current mass), the temperature increased more rapidly. One way to tell when fusion starts is to detect neutrinos (and measure their energy to determine what reactions are producing the neutrinos).

11

Physics, Astronomy & Cosmology / Re: Why Does Light NOT Experience Time When It Slows Down ?

« on: 03/02/2025 08:39:06 »

Why Does Light NOT Experience Time?

On a sidenote...  I heard an interesting podcast from Sean Carrol on "Does Time Exist?" (2 hours).

the ordinary Schrodinger equation says Hamiltonian acting on quantum state is the time derivative of the quantum state.
The Wheeler-DeWitt equation says, Hamiltonian acting on the quantum state equal zero. So, there is no time variable in the Wheeler-DeWitt equation. ... So, time has disappeared

Sean Carrol does not resolve this apparent contradiction in the podcast; it is a paradox of modern physics.

I don't pretend to understand much of it, but my primitive summary is:
- The Schrodinger equation is a local measure of a wavefunction (eg of an isolated electron or a photon) and has a time-dependent component, so wave-functions change with time in a local sense
- The Wheeler-DeWitt equation when applied to the entire universe is not time-dependent
     - But the particles in the universe are entangled by their past set of interactions with other particles
     - So the local changes in one particle are canceled by changes in some other particle with which it has become entangled in the past
     - Leaving not net change with time at the scale of the universe

I am sure that others here can make more sense of it than I can!
https://www.preposterousuniverse.com/podcast/2025/01/06/300-solo-does-time-exist/

12

General Science / Re: Bitcoin

« on: 23/01/2025 08:05:46 »

Bitcoin uses the SHA-256 hash algorithm to map ("Hash") from the user's private key to the public identifier on the blockchain.
- If you lose the private key, you have to guess a 256-bit number, which will take about 10⁷⁷ hashes, far beyond the capability of today's computers.
- But if you could do that, you could steal anyone's Bitcoins.
- Wikipedia gives a few examples of people losing their private key.
https://en.wikipedia.org/wiki/Bitcoin#Addresses_and_transactions

The world workforce of Bitcoin miners is currently increasing the rate of hashes, at an exponential rate. Back in 2017, they were doing 10¹⁹ hashes per second. Now it looks like 10²¹, see graph here:
https://www.blockchain.com/explorer/charts/hash-rate

13

Physics, Astronomy & Cosmology / Re: What Is The Final Parsec Problem ?

« on: 19/01/2025 10:55:18 »

Unfortunately, the length of current gravitational wave detectors does not allow us to detect the very low frequencies/long wavelengths of merging supermassive black holes. So we can't directly measure the rate of such events*.

There is an indirect indication that such mergers might occur, in the form of "X-shaped" radio galaxies; one theory suggests that a supermassive black hole was emitting a jet of matter from the poles of the accretion disk - and then it suddenly gets hit by another massive impactor, which changes the axis of rotation, and the direction of the polar jet.

In the images I have seen of these objects, there does not seem to be a large gap in the polar jets, suggesting no final parsec pause.
https://en.wikipedia.org/wiki/X-shaped_radio_galaxy

PS: This next paper suggests that the X-shaped radio galaxies might occur due to interactions between the jet and the accretion disk, which does not turn off the jet:
https://www.space.com/black-hole-feeding-x-shaped-galaxies

*Perhaps the proposed LISA space-based gravitational wave observatory will give a better idea of how common these are
https://en.wikipedia.org/wiki/Laser_Interferometer_Space_Antenna

14

Technology / Re: Does cold weather damage the batteries used in an EV?

« on: 13/01/2025 05:21:15 »

I ran across this comment from Blair Korchinski on Qora, comparing petrol and electric cars in the Canadian cold... (he obviously likes EVs)
https://www.quora.com/If-electric-cars-are-not-good-in-extreme-cold-then-why-do-people-keep-buying-Teslas-in-Canada


Q: If electric cars are not good in extreme cold, then why do people keep buying Teslas in Canada?
A: As the owner of two gasoline-powered pick-ups and the driver of a diesel at work, questions like this always make me laugh.
In the cold an EV (Electric Vehicle) loses 40% of its capacity. In the best conditions, the very best ICE vehicle reaches 40% efficiency [loses 60%].
When it?s cold here in Canada we plug in our ICE vehicles so they will start. Double block heaters, like in my 2004 Chevrolet Silverado, suck about as much electricity as the average commute uses in an EV.
Gas mileage goes way down in the winter in ICE vehicles. Most of us warm up our cars for 10?15 minutes twice a day. The engines don?t run as efficiently, so even warmed up fuel mileage suffers. Then there are problems with fuel lines freezing, cars not starting. Then there?s extra wear and tear caused by thick oil not lubricating properly until the oil warms up. Catalytic converters don?t get hot enough to do their jobs, so we pollute even more.
Diesels, well diesels suck in the cold. The fuel doesn?t atomize properly, the batteries get so weak they won?t run the glow plugs or engine heater, and in the bad cold, the fuel gels up. DEF (Diesel Exhaust Fluid) tanks freeze solid and the little heater in there can?t keep up, so you get emissions alarms. The heaters don?t put out enough heat, you have to leave them idling for extended periods. Stop for fuel and the damned pumps freeze up so it takes forever to fill the tanks.
Go to an area where there are lots of diesels when it?s -30 ?C and you can smell the half-burnt diesel in the air. That?s how inefficient they become in the cold.
All of that is just an average winter day for guys like me. We?re so used to it, we barely think about it as we stand out there in the cold with our booster cables.
So the question shouldn?t be why we buy EVs, but why we don?t buy more of them. The modern technology makes way more sense here than ICE vehicles do.

15

General Science / Re: Can Human Consciousness Be Uploaded?

« on: 06/01/2025 08:43:26 »

It must ... be working now in order for a copy of it (to work)

Our conscious minds are able to reboot after anesthetic.
- That includes some subconscious functions like breathing, which are suppressed during heavy sedation

Is it possible that our brains could reboot after being copied?

16

Physics, Astronomy & Cosmology / Re: Am I safer on Mars?

« on: 06/01/2025 08:37:48 »

At present, there are estimates about the quantity of meteors hitting the Earth's atmosphere, but only a small fraction of them (larger than 1 kg) actually survive to hit the ground.
- Smaller ones are more frequent than more massive ones, but we don't have good statistics on them

The LUMIO space probe (planned launch in 2027 or 2028) will study meteorite impacts on the far side of the Moon (but only while it is also the dark side of the Moon).
- It will look for flashes as meteorites strike the Moon, vaporising the lunar rock
- They expect to detect meteorites as small as 1 gram
- This will give a better idea of the size distribution of meteorites - even a 1g meteorite could destroy an above-ground lunar habitat.

https://www.sciencedirect.com/science/article/pii/S0094576522001424

17

Geology, Palaeontology & Archaeology / Re: Why does Earth have tectonic plates?

« on: 04/01/2025 10:04:52 »

To add to the comment by Diverjohn...
During the expected glancing blow between Thea and Earth, it was mostly lighter crustal material that was thrown out to make the Moon.
- This meant that the floating crustal material no longer covered the whole Earth in a solid thick skin
- So the remaining crustal material was thin enough to be pushed around by convection currents in the mantle beneath, forming continents where convection cells converged, and splitting them apart where convection cells diverged.

Perhaps the lack of a large, low-density moon may explain why neither Mars nor Venus have plate tectonics?

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

18

Physics, Astronomy & Cosmology / Re: What are the physics of brakes?

« on: 04/01/2025 09:48:13 »

Regenerative braking is another form of dynamic brakes, used by say electric locomotives and cars

During braking, my hybrid car puts the car's kinetic energy into the battery (with some losses).
- As Halc noted, this can't bring you to a complete stop - but it works down to quite low speeds
- When you know that you will have to stop (eg because the traffic lights are red), you can take your foot off the accelerator, and "coast" (slowed by air resistance, any uphill slope and gentle regenerative braking), until it is time to pick up the speed again.*
- Fuel efficiency is "gamified" in my car: The car has a little report card at the end of every trip - hard acceleration and hard braking yield a lower score.

This raises a question I had for Chris:
- In one podcast it was mentioned that full-electric cars would cause more wear on brake pads (and particulate pollution) because the battery made the car heavier.
- However, regenerative braking means that the mechanical brakes should be used only rarely, and this should produce less particulate pollution?
- The tyres would still produce particulate pollution for both electric and petrol cars (more for a heavier car)...

*Note that coasting in an electric vehicle is not the same as putting a petrol car into Neutral and coasting; in the electric car, the engine is still engaged with the wheels.

19

Plant Sciences, Zoology & Evolution / Re: Could we eat wood?

« on: 04/01/2025 09:24:35 »

termites have bacteria in their guts that digest the normally indigestible cellulose

Many herbivores have microbes in their guts which digest cellulose.
- But the cellulose must first be crushed very thoroughly to give the microbes free access to the cellulose, which is why cows and sheep spend so much of the day chewing

The cellulose breakdown process is very slow, which is why herbivores have physically large guts, and long transit time
- The energy extracted is relatively low
- Humans have small relatively guts and medium transit time, which is possible because the food is "pre-digested" by external processes like grinding, fermenting and cooking.
- And cooked meat (protein+fat) forms a portion of the diet for many humans.
- So the conditions in our guts are probably not ideal to host cellulose-digesting bacteria
- And the anaerobic conditions in out guts are not suitable for nitrogen fixation.

Maybe we could genetically engineer bacteria that can quickly digest cellulose, and are at home in the human gut?
- But humans prefer to do things externally - in the environment or in domesticated animals
- It means we carry around less "baggage".

20

Plant Sciences, Zoology & Evolution / Re: Could we eat wood?

« on: 04/01/2025 09:11:26 »

a  fungus which fixed nitrogen and produced protein

I see mixed responses on whether this is true.
- In digesting wood, fungi free the protein that was originally in the wood. They incorportae the released protein into the growing fungi.
- Some discussions say that fungi themselves can't fix atmospheric nitrogen - this is only done by prokaryotes
- Some fungi have a symbiotic relationship with bacteria that can fix atmospheric nitrogen.

This paper tested a theory that a particular fungus could fix atmospheric nitrogen by itself - they found that fungus growth was best when the symbiotic bacteria were present; they conclude it is the bacteria which fix nitrogen.
https://pubmed.ncbi.nlm.nih.gov/15381850/