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Physics, Astronomy & Cosmology / Re: The most advanced space craft of the recent time that impressed you the most

« on: 06/01/2021 15:40:25 »

https://solarsystem.nasa.gov/missions/dawn/overview/

I would say the Dawn Probe. It uses an advanced ion thruster, allowing it to be the first (man-made) spacecraft to orbit multiple non-terrestrial bodies (Vesta and Ceres). This feat would not be possible (practical) using conventional chemical thrusters, which have too low of a specific impulse.

This mission also gathered reams of data regarding the composition and history of the asteroid belt. I don't think we're ready to be a space-faring civilization yet, but I think the first step along that way is likely to involve the asteroid belt (or one of the Martian moons), rather than colonization of our own moon or planetary bodies like Mars or Venus (ick!).

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Plant Sciences, Zoology & Evolution / Re: Why is compost black?

« on: 04/01/2021 16:13:33 »

From an electronic structure perspective, carbohydrates are essentially made only of sigma bonding and sigma antibonding orbitals (and some nonbonding orbitals, as lone pairs on oxygen). These are highly localized orbitals, and have very large energy gaps between occupied and unoccupied orbitals, so they will absorb very far into the UV, and are therefore colorless in the visible part of the spectrum.

As the carbohydrates decompose, many of the reactions involve eliminations to form water and pi bonds. The difference in energy between occupied and empty pi bonding and pi antibonding orbitals is much smaller (still well in the UV for single isolated pi bonds). As more water is eliminated, forming additional pi bonds, the molecules can start forming conjugated systems, where pi bonds extend over several atoms. This allows the energy levels to come still closer. At this point the color might start turning yellowish or brownish (think honey, syrup, molasses etc.) As the mixture continues to change, the light absorbed will also change, with growing conjugated systems absorbing longer and longer wavelengths, and more and more pi systems coming into being (so the a greater range and greater proportion of photons can be absorbed). Eventually, the mixture looks black because it absorbs essentially all visible light that lands on it!

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That CAN'T be true! / Re: I don’t understand physics: does anyone understand physics these days?

« on: 02/01/2021 16:26:21 »

@charles1948

I think the aspect of science that appears to be eluding you is that scientists, above all else, want to be right. Yes, I want the answer that I found to be the right one, because it is important to my ego and career to be the one who found it. But I would much rather use someone else's better answer than my own worse one!

Because of this, often scientists are their own most dogged critics. We test, and double test, and triple test. Concerned about false wiring? I'm sure the guy who did the wiring spent more time checking it than actually setting it up. And then come the control experiments!

The nifty thing about control experiments is that they very unambiguously allay "what if it's just ___" questions. Because you can set up thee experiment exactly the same way many times, and then verify that the results are X. Over and over and over: always X. Then you change something about the experiment, and the result is Y. Try it the first way again, X. New method? Y. Back and forth a few times, two experiments simultaneously in neighboring setups. Multiple experiments done on different parts of the planet! etc. If what you change about the experiment doesn't change the result, then you have "controlled for" that variable.

So a control experiment is not a guarantee that the experiment is valid, but it can guarantee that whatever factor is being "controlled for" is not causing the results (or it can identify that it is). We only say A causes B when we have ruled out C causes B, D causes B, C and D cause B... etc.

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General Science / Re: Is Mathematics Falsified?

« on: 20/12/2020 21:05:30 »

There is no number that can be expressed in base 2, which also cannot be expressed in base 10. There are some inherent mathematical advantages to using base e, but really the only special thing about base 2 is that it is easiest to compute using base two and two-state 0/1 switches.

But there is no difference between any base when discussing infinity.

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General Science / Re: Is Mathematics Falsified?

« on: 11/12/2020 19:56:08 »

There is no shortage of apparent contradictions and paradoxes when dealing with infinity. Many times these can be resolved by making sure that the question and context are properly defined.

For instance, with no context, ∞ – ∞/2 is undefinable. But if we give some context, the answer can be defined in a way that is both meaningful and unambiguously provable to be true.

Imagine a farmer planting a row of seeds, and never stopping. There is a crow that follows behind him and eats the seeds at precisely half the rate that the farmer is planting them.

At any given finite value of time, there will be a non-zero number of seeds in the ground. But if we want to know what the "final" result is, we run into problems without knowing more.

If the crow eats every other seed (let's say it eats the odd ones: 1, 3, 5, 7, 9....), then there will be infinitely many seeds in the ground after infinite time passes, and we can say exactly where they will all be (holes 2, 4, 6, 8, 10....). For any hole, if you know whether it is even or odd, you will know whether there is a seed in it or not.

On the other hand, if the crow eats each seed in sequence (at half the rate that the farmer plants them), then there will be no seeds that can be found in the ground. How can I prove this? Pick a hole, any hole. Did the farmer put a seed in it? yes, at time = t. Did the crow eat the seed? yes, at time = 2t. So there are no holes that you can find a seed in.

Is this useful? It can be if you ask the right questions.

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Physiology & Medicine / Re: Novel treatment

« on: 08/12/2020 18:48:03 »

If said family member has a doctor already monitoring their condition, then this doctor would be the place to start. They would know how to verify improvement, and possibly what sort of side effects to look out for.

You. can also try a google scholar search for the condition, and. limit to articles published in the last 5 years. Contact info for the "corresponding author" is typically available, even if the content is behind as pay wall. Email them and ask.

Be aware that your results are likely to be falsified, or found to have other problems by serious study (most treatments are ultimately not FDA approvable, even those generated by teams of professionals).

Good luck!

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Chemistry / Re: Can Sulphites be removed from wine other than by adding hydrogen peroxide?

« on: 02/10/2020 15:17:27 »

sulfites (sulphites) are unlikely to volatilize--you can get rid of them by oxidation, but why do you want to? They are protecting the wine by essentially serving as sacrificial reducing agents (oxygen in the air will react with sulfite before it oxidizes components of the wine)

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Physiology & Medicine / Re: Where are the major 5 senses inside a human brain?

« on: 10/09/2020 16:40:30 »

Clearly there are some ways of messing with how time is perceived (adrenaline and hallucinogens such as LSD being obvious examples of chemicals that can influence time perception), but I don't know if a person can be made to experience a day in an hour...

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Physiology & Medicine / Re: Where are the major 5 senses inside a human brain?

« on: 10/09/2020 16:37:56 »

It's hard to say precisely *where* a sense is located. But there are specific regions of the brain that are associated with processing the various senses at different levels.

Vision is processed first in the eye itself, and then signals are sent via the optic nerve to the visual cortex in the occipital lobe:
https://en.wikipedia.org/wiki/Optic_nerve
https://en.wikipedia.org/wiki/Visual_cortex
https://en.wikipedia.org/wiki/Occipital_lobe#Function
(one could imagine hacking in at any point in this process)

For touch, you might be interested in the cortical homunculus:
https://en.wikipedia.org/wiki/Cortical_homunculus

There are also structures known for processing sound, smell, and other senses.

As far as putting our own signals in, I think there is some work that has been done using implanted electrodes (fairly crude), as well as use of microwaves, which can apparently cause people to perceive sounds.
https://onlinelibrary.wiley.com/doi/pdf/10.1002/bem.10163

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Physics, Astronomy & Cosmology / Re: Does spacetime bend only locally around objects?

« on: 20/08/2020 15:30:17 »

Great answer from Colin2B!

I will also add: we can detect gravitational waves from stellar (black hole and neutron star) collisions from billions of light years away!! It takes the most sensitive instruments on the planet to detect the motions of the most massive bodies in the universe—but it clearly demonstrates that massive bodies can distort space (space-time) across cosmic distances.

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COVID-19 / Re: Could asymptomatic people have invisible organ damage?

« on: 04/08/2020 19:37:57 »

My understanding is that this may be possible. "asymptomatic" unfortunately doesn't strictly mean "no symptoms of the disease occurred," it means "no symptoms of the disease were recognized."

It took many weeks before people realized that "asymptomatic" individuals could be diagnosed by looking for loss of smell/taste, or "covid toes." (new symptoms were discovered)

There are anecdotes of individuals who are (otherwise) "asymptomatic," but developed blot clots, which then caused stroke. So I would imagine that there could be cases of individuals who are infected, don't present the "standard" fever/cough/malaise but could still sustain significant damage to liver or kidneys or what have you...

There is still so much we don't understand about this disease...

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Physics, Astronomy & Cosmology / Re: How Do We Know Absolute Zero Is The Temperature It Is If It's Unattainable ?

« on: 02/08/2020 13:17:33 »

Extrapolation!

If you put a gas in a sealed piston (which will keep the internal pressure constant by allowing the volume to change), and start cooling it down (and/or heating it up) you will notice that the volume varies with temperature. After collection of much data it will become apparent that the volume is proportional to temperature, but only if you use a really odd temperature scale, that has a zero point at –273.15 °C.

There are other ways to get there, but I believe that historically, this is how it came about.

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Question of the Week / Re: QotW - 20.06.29 - Why does instant coffee dissolve so well?

« on: 30/06/2020 03:56:00 »

I have a question as to how coffee granules dissolve so well compared to soup-in-a-pack, for example. The difference is amazing, coffee dissolves with minimal or no stirring!

There are a few factors involved:

The inherent solubility of thee compounds in instant coffee is relatively high (compared to the amounts of stuff). Soup mixes will contain significant amounts of fats and other lipophilic/hydrophobic compounds (which melt and float in the soup, rather than dissolving).

The instant coffee grounds have quite a bit of exposed surface area, and I would guess that there might even have been a significant investment in engineering the particles to dissolve just so.  (if you could invest $5M once to figure out how to make your coffee dissolve 20% faster than your competitors' for only a 0.2% increase in production cost, it could well be worth it!)

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Chemistry / Re: Why don't electrons crash into the nucleus?

« on: 02/06/2020 15:52:35 »

It is entirely reasonable to say that an electron in an atomic orbital *has* fallen all the way to the central nucleus. It just so happens that electrons are effectively fluffy, and spread out over a volume 100,000 times larger that that occupied by the nucleus. Similar to how the atmosphere on Earth has fallen all the way down to the ground, but still measurably extends more than 100 km from the surface.

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Geology, Palaeontology & Archaeology / Re: Can Google Earth provide detailed images of caves in the Grand Canyon?

« on: 25/05/2020 02:06:33 »

The National Parks Service has virtual tours of many of the parks, including the Grand Canyon, which may be useful: https://www.nps.gov/grca/learn/photosmultimedia/virtualtour.htm

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Technology / Re: Is there commercially available gas centrifuge to filter out SO2?

« on: 16/04/2020 03:35:49 »

Even in  a sealed container with no temperature gradient, you won't get a useful degree of separation.

What do you think will happen if I put a mixture of Helium, Nitrogen, and SO2 with equal volume and pressure inside a 10 meters vertical pipe. Will we get the same composition between top and bottom part?

That will depend on the temperature, pressure, and gravity.

But assuming that you mean Earth gravity (9.8 m•s^–2), 1 atm, and 300 K (27 °C), then the difference in gravitational potential energy between having 1 mole of He at the very top of the 10 m tube and 1 mole of SO₂ at the very bottom, and having 1 mole of He at the very bottom of the 10 m tube and 1 mole of SO₂ at the very top is 9.8•10•(0.064–0.04) = 5.88 J/mol. This could be viewed as the maximal enthalpy of gravitational un-mixing in a 10 m column (being favorable by 5.88 J/mol, so ΔH > –5.88 J/mol).

But there is also an entropic cost. http://hyperphysics.phy-astr.gsu.edu/hbase/Therm/entropgas.html
The change of entropy of an ideal monoatomic gas with change in volume is (ideal gas is a good model for He, not so great for SO₂, but doesn't really matter here... the errors will cancel):

ΔS = N•k*ln(V_f/V_i)

so if we had 1 mole of each gas being restricted to 1/2 the volume of the tube (from having had the whole tube), then for each mole of gas we would have:
ΔS = N•k*ln(1/2) = –5.76 J•K^–1•mol^–1
and therefore ΔS = –11.52 J•K^–1•mol^–1 (because we are restricting two moles of gas, the He and the SO₂)

thus at 300 K:

ΔG_un-mixing = –5.88 J•mol^–1 – (300 K)(–11.52 J•K^–1•mol^–1 ) = +3450 J/mol

(recall that ΔG must be negative for a process to be spontaneous)

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COVID-19 / Re: What test were Chinese officials applying to the forehead to diagnose Covid?

« on: 14/04/2020 16:08:18 »

I think they were infrared thermometers looking for people with fevers. A cheap and quick test that identifies people in need of more testing (many causes of fever), or at least greater extent of isolation/restriction based on being more likely to be infected/infectious.

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Physics, Astronomy & Cosmology / Re: What difference does this make to our understanding of infinity?

« on: 14/04/2020 15:36:45 »

A nice way of showing this 1-1 correspondence of the uncountably infinite reals between 0 and 1 (or any finite distance) and all the reals is to imagine an arc (semicircle) connecting the two endpoints. Every point on that arc corresponds to a point on the line beneath it (we can define every point on the semicircle uniquely using only the x coordinate, so if the diameter of the circle is 1, this is the continuum from 0 to 1. Every point on this arc also has a slope (slope of the tangent line), and it contains all real numbers, from arbitrarily large negative slopes to arbitrarily large positive slopes. Therefore there is a 1:1 correspondence between the continuum from –∞ to +∞ and the continuum between 0 and 1.

Screen Shot 2020-04-14 at 10.42.13 AM.png (15.17 kB . 394x306 - viewed 2692 times)
In other words: if you think there are more slopes than x values in the setup described above, choose any real slope, and I will find you the only x value that gives it. Likewise, if for some bizarre reason you think that there should be more x values than slopes, I challenge you to find an x value in the domain that does not uniquely correspond to a slope.

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COVID-19 / Re: Is Lockdown Cost Effective?

« on: 14/04/2020 02:59:27 »

This gif uses data for USA specifically, but is likely reasonably extended to most industrialized nations. It is a fascinating and horrifying graphical progression:

https://public.flourish.studio/visualisation/1727839/

It indicates that in the order of a few weeks, deaths directly attributable to COVID-19 has eclipsed even heart disease as the leading cause of death (who knows how many otherwise preventable deaths will result from the flooding of hospitals and the exhaustion of physical and human resources associated with outbreaks).

That said, the value of human life is not infinite. The United States Department of Transportation defines the value of a statistical human life as about $10,000,000. So the difference between 100,000 deaths (locked down) vs 2,000,000 deaths (not locked down) is on the order of (1.9x10⁶)(10⁷) = $1.9x10¹³

Add to that lost wages assuming that everybody was still working, and it looks like without the lockdowns ~80% of people would contract the disease, of which about 50% would have no symptoms. So if 40% of the US working population were out sick for 2 weeks, with US median pay, that's about $1800x1.56x10⁸x0.4 = $1.1x10¹¹. Not so big compared to all the dying, but also not great.

It's hard to know what "would" have happened without lockdowns, but we can see example after example of places that "should" have locked down earlier (from a casualty perspective). But if we really want an "economical" strategy. Aggressive testing and tracking will be able to ensure that populations with low enough infection rates can return to business "as usual" while those with problematic infection rates can shelter in place for a few weeks at a time. (the more people self-isolate, the less time is required to strangle the infection: if only 10% of people isolate, there's no point at all)

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Cells, Microbes & Viruses / Re: Are 85 Covid-19 deaths ON AVERAGE a day per 60 milllion a reason to PANIC?

« on: 02/04/2020 04:00:05 »

with respect to the original question:
https://public.flourish.studio/visualisation/1727839/