1

Physics, Astronomy & Cosmology / Re: Why do we see any stars at all?

« on: 10/04/2018 21:06:47 »

A testament to the awesome emptiness of space.

There are parts where there is enough junk in the way to occlude the stars (the dark patches in our own milky way are due to large dust clouds which scatter the light).

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

2

That CAN'T be true! / Re: What is a manchurian candidate?

« on: 28/02/2018 22:43:27 »

School is definitely not a place to put guns.

I will agree with you there!

3

Physics, Astronomy & Cosmology / Re: Why do clouds go red at sunset? Why not green, or some other colour?

« on: 28/02/2018 20:07:02 »

Excellent, context is always useful.
Although lead oxide is red I’m not sure that the tetraethyllead used in fuel produces a particulate which would reflect red, perhaps @chiralSPO  could help here. I suspect that the haze is from other pollutants and lead is an indirect cause. As you know particulates are removed from car exhaust by the catalytic converter, unfortunately lead deposits stop the catalyst working so they can’t be used in cars using leaded fuel, hence greater pollution.

I would bet that the red color from old cars is probaby due to NO_x emissions. NO₂ has a brownish-red hue, and it also reacts with volatile organics to form photochemical smog https://en.wikipedia.org/wiki/Smog#Photochemical_smog

4

Chemistry / Re: Does one invent or discover new synthetic compounds?

« on: 28/02/2018 19:46:43 »

What if another species elsewhere has already made said compound. In which case it does already exist somewhere in the universe.

This is something I often consider when preparing a "novel" compound. I find it very pleasing that for compounds not previously made by humans (not the same as not previously disclosed by humans), the following statement must be true: "Either I am the first to behold this compound, or there must be intelligent life elsewhere." Either way, I am happy.

If you have discovered the steps required to produce the compound then is it an invention? In the right circumstances and with the same steps the compound would occur without intervention. This is not true of say an internal combustion engine.

I am not so sure that an internal combustion engine is less likely to occur by random accident than a synthetic compound such as 3^rd generation Grubbs' catalyst (https://en.wikipedia.org/wiki/Grubbs%27_catalyst). The probability of any of the multiple reactions required to produce such a structure occurring is quite small, let alone all of them, in the correct order, at the right intervals and proportions. Especially given the wide variety of temperatures, pressures, and chemical environments involved--it would be just as ridiculous for a hot spring to distill out a pure organophosphine ligand directly into a dry-ice-cooled and highly alkaline solution of ruthenium as it would for a meteorite impact to produce a twisted metal working 4-cylinder engine.

5

Just Chat! / Re: I might be gone for some time...

« on: 28/02/2018 14:09:10 »

You will be missed. Best of luck until we hear from you again.
 

6

Chemistry / Re: Is there an easy (cheap) way to identify aluminium alloys?

« on: 21/02/2018 16:19:45 »

I agree with ↑. Often the cheapest, simplest way to answer such a question, is to pay someone who has the means to answer it!

However, I will also recommend some simple chemical tests, for the sake of DIY folks. NOTE: While "simple" these methods are NOT SAFE unless proper precautions are taken. I will be discussing the use of some highly corrosive and some mildly toxic substances. Eye protection and gloves are a must! The reactions will also release heat and flammable gasses (also possibly splashing the corrosive contents, so use vessels > 5x bigger than the solutions they contain).

By dissolving known quantities of the metal in question in either acid or base you can learn a fair amount about what's in it (I would recommend a gram or two of metal to begin with--larger quantities will give more precision in determining the composition, but danger scales non-linearly with size--if you double the size of your reaction, it is wise to treat it as 4x as dangerous etc.)

Aluminum will react with concentrated solutions of sodium hydroxide in water (20 grams of NaOH dissolved in 80 mL water), as will zinc, and probably silicon. Magnesium, nickel, copper and iron will not react with this alkaline solution, and will remain as solid precipitates (note, these precipitates may be quite flammable, even pyrophoric, when dry KEEP THEM WET--see Raney nickel: https://en.wikipedia.org/wiki/Raney_nickel)

Aluminum, zinc, magnesium and iron will all react with concentrated solutions of hydrochloric acid (add 30 mL of concentrated HCl, sometimes called muriatic acid, to 70 mL water). This will leave nickel, copper, and silicon behind.

In each case you can separate out the precipitates (by filtration or centrifugation, or just decanting.) KEEP THEM WET! They can then be dissolved using nitric acid. The species in solutions (original and dissolved precipitates) can be determined by reaction with chemical indicators (such as 2,10-phenanthroline) or by using solubility profiles to selectively precipitate out salts of each metal.

Neutralize all acid and base solutions before discarding them. Never mix nitric acid with organic compounds.

AGAIN: DON'T TRY any of this until you have done your research, figure out how to protect yourself (and your friends, family, pets, neighbors etc.) and have a plan for executing the experiments, as well as contingency plans for spills and fires (be prepared!)

7

Physics, Astronomy & Cosmology / Re: Why must c be an absolute "speed limit"?

« on: 20/02/2018 18:36:15 »

I have heard the fact that there is a "speed limit" invoked as evidence supporting the Simulated Universe theory (the idea that are universe is actually a complex simulation--I am not a big fan of this idea, because I am not sure if it is falsifiable, but at any rate, I don't think we have any evidence either way, so I am willing to entertain the notion periodically...)

If I were the Programmer, I would probably have (or need) a maximum speed at which simulated information could move about. That the universe appears to expanding at superluminal speeds at the edges of our observable universe could also be a nice trick invoked to prevent the Processor from needing to crunch infinitely many operations per unit time (of course, once we start thinking about the universe in which our universe exists, who knows if "time" is meaningful.)

Problems with this theory include, "well this doesn't answer anything, it just puts the 'real' universe beyond our observation," and "wouldn't a Simulator need some sort of universal frame of reference?"

(these are the sorts of ridiculous answers that can come up when "why" questions are posed)

8

General Science / Re: Could we hack humans genetically to eat less?

« on: 20/02/2018 14:21:33 »

It is probably possible scientifically and technologically, but there will be major political/social/religious obstacles to any research, let alone implementation.

It might be easier (politically and maybe scientifically) to genetically engineer the bacteria that live in our GI tracts. We have a symbiotic relationship with many different types of bacteria, and there is a fair amount of research suggesting that some strains of bacteria are linked to obesity (and even some linked to depression). It makes sense that they would have significant control over how much of which nutrients get absorbed.

This might be an interesting read (and without a paywall!!! Trigger warning: poop)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5479392/

9

General Science / Re: Why are some stains more stubborn / harder to remove than others?

« on: 19/02/2018 01:48:32 »

(from the top of my head)

There are multiple types of stains, each of which have fairly different chemical explanations:

1) A strongly colored compound (like a pigment) gets on the article (for now lets just say it's cloth, though anything can get stained...), and stays there because of non-covalent bonds.

These stains can be removed by washing the pigment away using solvents with or without surfactants, or they can be degraded into less-colorful compounds, which is what bleach does, and either left in place or washed away.

2) A strongly colored compound becomes covalently attached.

This will not allow simple rinsing away of the stain. Chemical modification of the pigment, or cleavage of the attaching bonds would be required.

3) The original pigment (or actual material itself) undergoes a chemical reaction that produces a change in color. (ever notice how blue fabric often turns bright orange if you get some bleach on it?)

In this case there is no residue to be washed away. The article itself is fundamentally changed. Either find a way to reverse the reaction (this is not very common, but some color-changing chemical reactions are quite reversible, for instance pH-sensitive pigments aka indicators), or re-dye the article.

4) Colorless compounds that do not react with the item chemically, but still change how it interacts with light because of refractive index, which will change the way light scatters, like oil stains. Or there can even be "solvatochromic" effects on the dyes if you spill something more exotic on your clothes. (many dyes have a very significant change in dipole moment when they absorb light, so being in environments with different dielectric constants can have noticeable effects on the energy of the light absorbed.)

Here you just have to wash the offending liquid away, or wait for it to evaporate...

10

Physics, Astronomy & Cosmology / Re: Is the Planck scale accurate according to the photo-electric effect?

« on: 16/02/2018 16:19:53 »

Correct me if I am wrong, the distance of the energy jump is indicative of the wavelength of jump, and thus inversely proportional to the frequency?

This is wrong, you stand corrected

I think you may be confusing the "distance" between energy levels with an actual spatial distance. An electron doesn't have to to move physically through space to change energy levels. The Bohr model of the atom shows electrons as distinct particles moving in circular orbits around the nucleus like a mini solar system, but this model is a dramatic oversimplification which is in many ways misleading. If instead we think about orbitals (not orbits), in which electrons are behaving as waves in a spherical distribution about the nucleus, it can be seen that there is no strict relationship between where the electron is in the atom and how much energy it has (you can think of electrons in high energy levels as either having more potential energy than their lower-energy counterparts, which would place them farther from the nucleus, or having more kinetic energy, but actually being as close or closer.

It is fairly easy to prove that red light has longer wavelength than green light, which is still longer than the wavelengths for blue light. All you need is a diffraction grating and some monochromatic lasers, or just white light (and the equation which relates diffraction patterns to wavelength, found here: https://en.wikipedia.org/wiki/Diffraction_grating#Theory_of_operation )

That the energy of shorter (bluer) light is higher than for others can be demonstrated through the photoelectric effect or by looking up (or testing) the voltages required for monochromatic LEDs to emit light. I can easily power a red LED with 2 V, but need at least 3 to get my blue LED to function.

11

Physics, Astronomy & Cosmology / Re: Does a field require a source?

« on: 15/02/2018 20:58:26 »

As I understand it, a field needs no source. A field just is. It's a sort of accounting or mapping tool that we can use to describe the universe. Every field exists everywhere, even if it has zero amplitude at specific places, or even everywhere.

We base our understanding on experience, so we tend to think in terms of things and actions, but "things" or "actions" can be equally well (or better) described as perturbations in the field.

To continue this thought slightly differently: The gravitational field is all around us, whether or not the is a planet nearby. Whether a planet moves here or even just randomly appears here, there will be a change in the local amplitudes of the gravitational field, but the field itself has not gone from "nonexistance" to "existence."

Put yet another way: we get lazy and talk about the forcefield of an object as if it were the universal field, when in fact it is just a part of the universal field. When I turn on an electromagnet, I haven't created any new field, just changed how the electromagnetic field is.

12

Physics, Astronomy & Cosmology / Re: Does a field require a source?

« on: 15/02/2018 20:56:53 »

As I understand it, a field needs no source. A field just is. It's a sort of accounting or mapping tool that we can use to describe the universe. Every field exists everywhere, even if it has zero amplitude at specific places, or even everywhere.

We base our understanding on experience, so we tend to think in terms of things and actions, but "things" or "actions" can be equally well (or better) described as perturbations in the field.

Let us consider electrons. It is very comforting to think of electrons as point-like particles. But even though this works well sometimes, it becomes apparent that this is an oversimplification, because under certain circumstances, they clearly behave as waves (enter the wave-particle duality). But even this is an oversimplification. Electrons are electrons. And it turns out that (as far as we can tell) every electron is identical to every other electron. And because of the wavy aspect of their nature, it doesn't really make any sense to say there is an electron right here. We just know roughly where they are. But since they are all the same, we can just say there is a universal field of electron. The amplitude is higher here and lower there, and is changing like so. This field is related to other fields we can imagine (electric field, magnetic field, gravitational field, proton field etc.).

13

General Science / Re: How does our strength compare with that of other apes?

« on: 15/02/2018 15:00:41 »

I would also add that chimps have much more upper body strength than humans do, but I would not be surprised if we had stronger legs. Chimps not only have more musculature in their upper bodies, they also have longer arms and wider chests, giving them much more leverage. Extreme body builders (human) may be able to bulk up enough muscle to theoretically lift as much as a chimp, but they run the risk of severe injury (like ripping a muscle or a tendon) because there isn't nearly as much support.

On the other hand, chimps have pretty pathetic lower limbs, in comparison, and might face similar challenges when exerting their legs...

14

General Science / Re: Must ∞ monkeys on ∞ typewriters really write everything given ∞ time?

« on: 15/02/2018 14:35:56 »

There is a non zero probability of a monkey pressing the same key an infinite number of times. How meaningful is this?

Actually, I think there is a probability of zero for any infinite string of keys (only finite strings will appear with a nonzero probability).

This can be shown by considering the limit as n approaches ∞ of the probability of a string being generated (typed). If we limit ourselves to 26 letters of the alphabet, then the probability of repeating the same letter every time is (1/26)^n–1 (allowing the first letter to be any of the 26, but then requiring all subsequent letters to be the same as the first.) As n approaches ∞, (1/26)^n–1 definitely approaches 0. (even by the 10th repitition, we are down to 7x10^–15)

An interesting paradox arises here: If a random string of numbers is generated, and is infinitely long (countably infinite), the probability of any specific infinite string is 0. Every infinitely long string has a 0 probability of being generated randomly. But, if you consider all of the uncountably infinitely many "possible" strings, there is still a probability of 1, that the string generated is contained within that set.

For example, if we consider selecting a single number from a uniform distribution of the continuous number line between 0 and 1 (including all rational and irrational numbers), it's guaranteed that the number selected had a 0% chance of being selected!

I think many of these apparent paradoxes come up because people are playing fast and loose with the concept of infinity, trying to plug it in as a number and do arithmetic, rather than solving for the limits in each case....

15

Physiology & Medicine / Re: Why do I lose weight when I sleep?

« on: 14/02/2018 16:00:39 »

Besides watching my diet and calorie intake, I have dropped nearly 70 pounds since the end of August.  I feel great.  It's just weird.

Losing 70 pounds in six months without trying sounds somewhat alarming to me. You may want to get your thyroid checked. My father in law felt "great" and "energized" for a year, and lost nearly 100 pounds in that year without making an effort. It turned out his thyroid was way out of whack, producing too much thyroxine, and he needed to get it killed with radioactive iodine because it was also affecting his heart.

Don't freak out, but also don't ignore sudden changes in your body.

Regarding the timing of the weight loss:

For example, last night I went to bed weighing 244.8 pounds, and this morning I rose, relieved, and then weighed in at 241.2.

Are you weighing yourself right after "relieving" yourself in the evening too? If not, that is almost certainly the culprit. 2 lbs sounds about right for "a tinkle and a plop" (that's very specific scientific terminology, right there!)  or just a tinkle after a night of drinking...

Even if you are weighing yourself immediately after having made your sacrifice to the porcelain alter in both the evening and morning weigh-ins, the difference may also lie in the fact that presumably you are weighing yourself after dinner and before breakfast?

16

Physics, Astronomy & Cosmology / Re: What are the radioactive decay products of uranium?

« on: 12/02/2018 14:47:51 »

According to this decay chain presented on wikipedia, a very small fraction of nuclei from the ²³⁸U decay chain become mercury nuclei, but this is only transient (half life of minutes), and ultimately lead is the only stable product.

https://upload.wikimedia.org/wikipedia/commons/4/4e/Uranium_series.gif

17

Plant Sciences, Zoology & Evolution / Re: What is the current distinction between man and animal?

« on: 11/02/2018 20:50:54 »

As has been pointed out, humans are a subset of animals. Tool making and use has been observed in many different animal species, notably primates, birds (ravens and magpies), and octopuses. Several types of birds, and possibly cetaceans, also have very complex languages. Even some types of ants have mastered agriculture!

I would argue that there is not a clear line of only we do x, and they don't. It's really an issue of degree. And after all, many early hominids had fairly advanced tool-making, language, and abstract thought. None of them were human yet.

18

Physics, Astronomy & Cosmology / Re: Can macroscopic objects be considered quantum objects?

« on: 11/02/2018 18:49:39 »

It looks like people have been addressing this question in two different valid ways. There are macroscopic objects or devices that have properties that can only be explained using quantum mechanics, but most of these phenomena occur at a very small scale (subatomic to dozens of atoms), and only the concerted action of many small regions behaving in quantum "oddness" delivers the macroscopically observed phenomenon. Actually, in addition to all of the exciting examples provided, like lasers and superconductors and superfluids, basically every boring attribute of a material we can think of can be traced to quantum effects. Why is iron magnetic? Why is copper conductive? Why doesn't helium form stable compounds? Why is water colorless? Why is potassium permanganate intensely purple? Why does propane burn in oxygen? etc. etc. etc.

All chemical and electronic properties, and all the interactions between light and matter ultimately require a QM treatment of the components of species involved at a subatomic level.

Then there are those who have offered examples of ensembles of atoms of ever-increasing size that still behave as a system in a way that we could treat as a "particle" with QM properties. I think the largest claim I say in this thread concerns the wave-particle duality of buckyballs (C₆₀  molecules). This has been experimentally verified, and has even been extended to much larger molecules, over ten times as big (https://medium.com/the-physics-arxiv-blog/physicists-smash-record-for-wave-particle-duality-462c39db8e7b).

I will also add that in addition to the de Broglie wavelength, which contracts with "particles" having greater momentum, there is a purely probabilistic reason that we do not see macroscopic versions of QM like lab rats "tunneling" through walls. Let us imagine for a moment, that there is a small flea pressed right up against a 1 mm-thick piece of glass, and that each atom in the flea has a one in a billion chance (10^–9 of "tunneling" through the glass in a given second (the chances are actually much smaller, but still nonzero). The flea is composed of about 10¹⁹ atoms, so even though the chances are so small for any given atom to appear on the other side of the glass for a moment, because of the large number of atoms, we would expect (again, in this unrealistic scenario) about one billionth of the atoms to be on the other side of the glass at any point in time, which is still about 10 billion atoms! (10¹⁹ Χ 10^–9 = 10¹⁰ atoms). But, if we want to know what are the chances of the whole flea appearing on the other side of the glass, we find that number to be so vanishingly close to zero, that we can even discount it from ever happening in the ridiculously inflated example. (1–10^–9)⁽¹⁰¹⁹⁾ < 10^–40 The universe is only about 10¹⁷ seconds old, so you would expect to wait 10²³ times the age of the universe before the flea could escape.

19

Physics, Astronomy & Cosmology / Re: Could we make solidified electricity?

« on: 09/02/2018 17:42:31 »

Back in the days when Wimshurst machines and electrostatics were all the rage I think they used to melt something like pitch and induce a charge into it that it retained when it solidified.

This sounds like a type of "electret," the electrostatic equivalent of a magnet. Essentially a macroscopic object with a large permanet dipole. see more here: https://en.wikipedia.org/wiki/Electret

20

Physics, Astronomy & Cosmology / Re: Could we make solidified electricity?

« on: 09/02/2018 15:25:09 »

Yes, I have also heard of aluminum referred to as "congealed electricity," but despite the name, and the significant number of available electrons per unit mass in Al,  I don't think it would actually qualify as "solidified electricity."

I'm not really sure what "solidified electricity" would even be. I have only heard the word "electricity" used when referring to a flow of electric charge (AC, DC, or whatever waveform you want, but there must be current involved). So "solidified electricity" is kind of like "a molten song," there are certainly significant poetic meaning in the phrases, but nouns like song and electricity can't be described as being in one state of matter or another.