The dumb questions thread

[Jokodo]

So here is my dumb question:

According to everything I find on the webs, the caloric value of sugar is roughly 400 kcal/ 100g, while for alcohol (ethanol) I find 700kcal/100g.

What's confusing me is that ethanol is the product of fermenting sugars in what I must assume is an exothermic reaction. I mean, it's what yeasts live of, right? I'm aware that this reaction produces carbon dioxide as a side product, but I still can't seem to get the math to work. 1 mol of glucose (180g) produces 2 mol of carbon dioxide (44g each) and 2 mol of ethanol (46g each), so the resulting 82 grams of ethanol must have very nearly the same caloric value as the original glucose (692 for 100g of ethanol vs 757 for the sugar required to obtain those 100g if I plug in concrete figures I find). Is alcoholic fermentation really that marginally exothermic?

Yes, it is. But a little is infinitely better than nothing, and when you have no source of additional oxygen, you have to make do with what you've got.

That's why yeast goes with aerobic respiration rather than anaerobic fermentation, if you don't restrict its access to oxygen.

I guess my original confusion stemmed mostly from the fact that I would never have guessed that CO2 is almost half of the mass. I guess I could have ballparked it, as in "both have three medium sized (C/N/O range) nuclei, one of them has extra hydrogen but we can ignore hydrogen in a first approximation", but it didn't even come to me that this volatile gas could be anywhere near as massive as that complex organic molecule.

Without that information, the math *really* didn't work. With it, it kind of does. 757>692 after all, though the margin still felt smaller than what I would have expected.

 

[bilby]

So here is my dumb question:

According to everything I find on the webs, the caloric value of sugar is roughly 400 kcal/ 100g, while for alcohol (ethanol) I find 700kcal/100g.

What's confusing me is that ethanol is the product of fermenting sugars in what I must assume is an exothermic reaction. I mean, it's what yeasts live of, right? I'm aware that this reaction produces carbon dioxide as a side product, but I still can't seem to get the math to work. 1 mol of glucose (180g) produces 2 mol of carbon dioxide (44g each) and 2 mol of ethanol (46g each), so the resulting 82 grams of ethanol must have very nearly the same caloric value as the original glucose (692 for 100g of ethanol vs 757 for the sugar required to obtain those 100g if I plug in concrete figures I find). Is alcoholic fermentation really that marginally exothermic?

Yes, it is. But a little is infinitely better than nothing, and when you have no source of additional oxygen, you have to make do with what you've got.

That's why yeast goes with aerobic respiration rather than anaerobic fermentation, if you don't restrict its access to oxygen.

I guess my original confusion stemmed mostly from the fact that I would never have guessed that CO2 is almost half of the mass. I guess I could have ballparked it, as in "both have three medium sized (C/N/O range) nuclei, one of them has extra hydrogen but we can ignore hydrogen in a first approximation", but it didn't even come to me that this volatile gas could be anywhere near as massive as that complex organic molecule.

Without that information, the math *really* didn't work. With it, it kind of does. 757>692 after all, though the margin still felt smaller than what I would have expected.

Very few people understand that when they lose weight, the mass mostly exits their body via the lungs.

It's one of those counterintuitive truths that is rarely grasped, or even considered.

Similarly, the majority of the mass of a tree came from the air. If it came out of the soil, trees would all be growing in deep depressions.

 

[Jokodo]

So here is my dumb question:

According to everything I find on the webs, the caloric value of sugar is roughly 400 kcal/ 100g, while for alcohol (ethanol) I find 700kcal/100g.

What's confusing me is that ethanol is the product of fermenting sugars in what I must assume is an exothermic reaction. I mean, it's what yeasts live of, right? I'm aware that this reaction produces carbon dioxide as a side product, but I still can't seem to get the math to work. 1 mol of glucose (180g) produces 2 mol of carbon dioxide (44g each) and 2 mol of ethanol (46g each), so the resulting 82 grams of ethanol must have very nearly the same caloric value as the original glucose (692 for 100g of ethanol vs 757 for the sugar required to obtain those 100g if I plug in concrete figures I find). Is alcoholic fermentation really that marginally exothermic?

Yes, it is. But a little is infinitely better than nothing, and when you have no source of additional oxygen, you have to make do with what you've got.

That's why yeast goes with aerobic respiration rather than anaerobic fermentation, if you don't restrict its access to oxygen.

I guess my original confusion stemmed mostly from the fact that I would never have guessed that CO2 is almost half of the mass. I guess I could have ballparked it, as in "both have three medium sized (C/N/O range) nuclei, one of them has extra hydrogen but we can ignore hydrogen in a first approximation", but it didn't even come to me that this volatile gas could be anywhere near as massive as that complex organic molecule.

Without that information, the math *really* didn't work. With it, it kind of does. 757>692 after all, though the margin still felt smaller than what I would have expected.

Very few people understand that when they lose weight, the mass mostly exits their body via the lungs.

It's one of those counterintuitive truths that is rarely grasped, or even considered.

Similarly, the majority of the mass of a tree came from the air. If it came out of the soil, trees would all be growing in deep depressions.

And the majority of the remainder came from groundwater.

 

[steve_bank]

If yu go by relativity then there is no possible absolute reference point to deduce a rotating universe.

 

[Bomb#20]

If yu go by relativity then there is no possible absolute reference point to deduce a rotating universe.

That depends on whose relativity principle you're applying. You're assuming Mach's interpretation of relativity. If we assume Galileo's or Einstein's relativity then rotation is absolute.

 

[steve_bank]

I think it is mor basic.

Altitude has meaning relative to an arbitrary deference point. As does mass and distance.

In the BB theorit does not matter what observational point you take, everything is moving away. There is no discernible center.
If there is we have no absolute reference point to measure from, only relative motions.

If you are on street corner the position of buildings relative to where you stand does not change as the Earth rotates and moves through the unverse.

Pick a reference point on an airplane or the surface of Mars and poistion of buildings on EWrath chnge.


AE's example I think.


You stand on a flat railroad car at constant velocity with a wind screen, and drop a ball. To you in your frame the ball goes straight down.

To an observer on the ground the ball traces a parabolic arc.

Which observation is correct?

 

[Bomb#20]

But those are examples of how we can't tell which unaccelerated reference frame is "correct". Rotation isn't like that. A rotating reference frame is accelerated. You can detect acceleration using internal measurements, without comparing to a reference point outside the system. Imagine a universe consisting only of an inner ring and an outer ring, with the same center, one spinning relative to the other. Release a particle from the inner ring. If it's the inner ring spinning, the particle moves out toward the outer ring. If it's the outer ring spinning, the particle stays put. Observers on both rings can observe the particle and will agree on which ring is spinning.

 

[steve_bank]

Even if the rail car is accelerating the falling ball trajectory appear different to the two observers.

Conceptually to me a rotating universe has problems. If the universe is infinite in extents as I think it may be, how can it rotate about a point?

If the inverse has a finite boundary how can it rotate? What is e boundary?

Same with an expanding inverse.

Any number of consistent theories and speculations can be constructed mathematically, but observationaly you still have to have a reference point that can be identified.

Looking up at clear night skies it is obvious the universe revolves around the Earth, which is a stationary point.

 

[Shadowy Man]

The right scientific questions are: how would you modify the GR metric for a rotating universe? What observable consequences would this modification have? What techniques and accuracies do we need to observe them?

Anything else is mostly just fun speculation.

 

[Loren Pechtel]

But those are examples of how we can't tell which unaccelerated reference frame is "correct". Rotation isn't like that. A rotating reference frame is accelerated. You can detect acceleration using internal measurements, without comparing to a reference point outside the system. Imagine a universe consisting only of an inner ring and an outer ring, with the same center, one spinning relative to the other. Release a particle from the inner ring. If it's the inner ring spinning, the particle moves out toward the outer ring. If it's the outer ring spinning, the particle stays put. Observers on both rings can observe the particle and will agree on which ring is spinning.

Internal measurements won't reveal rotation due to curved spacetime. However, you can detect that because the curvature isn't the same at different locations. Make a 4 pointed object that would be circumscribed by a tetrahedron and if you're in a curved spacetime you will see forces other than the mutual gravity.

 

[Jokodo]

So here is my dumb question:

According to everything I find on the webs, the caloric value of sugar is roughly 400 kcal/ 100g, while for alcohol (ethanol) I find 700kcal/100g.

What's confusing me is that ethanol is the product of fermenting sugars in what I must assume is an exothermic reaction. I mean, it's what yeasts live of, right? I'm aware that this reaction produces carbon dioxide as a side product, but I still can't seem to get the math to work. 1 mol of glucose (180g) produces 2 mol of carbon dioxide (44g each) and 2 mol of ethanol (46g each), so the resulting 82 grams of ethanol must have very nearly the same caloric value as the original glucose (692 for 100g of ethanol vs 757 for the sugar required to obtain those 100g if I plug in concrete figures I find). Is alcoholic fermentation really that marginally exothermic?

Yes, it is. But a little is infinitely better than nothing, and when you have no source of additional oxygen, you have to make do with what you've got.

That's why yeast goes with aerobic respiration rather than anaerobic fermentation, if you don't restrict its access to oxygen.

I guess my original confusion stemmed mostly from the fact that I would never have guessed that CO2 is almost half of the mass. I guess I could have ballparked it, as in "both have three medium sized (C/N/O range) nuclei, one of them has extra hydrogen but we can ignore hydrogen in a first approximation", but it didn't even come to me that this volatile gas could be anywhere near as massive as that complex organic molecule.

Without that information, the math *really* didn't work. With it, it kind of does. 757>692 after all, though the margin still felt smaller than what I would have expected.

Very few people understand that when they lose weight, the mass mostly exits their body via the lungs.

It's one of those counterintuitive truths that is rarely grasped, or even considered.

Similarly, the majority of the mass of a tree came from the air. If it came out of the soil, trees would all be growing in deep depressions.

Another example for a counterintuitive truth that is rarely grasped, or even considered, for residents of the Northern hemisphere at least, is that Earth reaches its perihelion, the closest point to Sun in its orbit, around January 4. This also marks the longest day of the year (solar noon to solar noon, not sunrise to sunset, of course).

 

[Swammerdami]

Another example for a counterintuitive truth that is rarely grasped, or even considered, for residents of the Northern hemisphere at least, is that Earth reaches its perihelion, the closest point to Sun in its orbit, around January 4. This also marks the longest day of the year (solar noon to solar noon, not sunrise to sunset, of course).

Another common error, I think, is the idea that the  Milankovitch cycles affect the average energy Earth receives from the Sun.

Earth gets the most total sunlight on January 4 but due to axial tilt the Southern hemisphere gets the bigger share. Given R, the ratio of aphelion and perihelion distances, the Earth gets R² more sunlight at perihelion than aphelion but is only moving at R times the speed (cf Kepler's 2nd Law). This leads to the conclusion that, over the course of a year, the Southern hemisphere (SH) receives more sunlight than the Northern hemisphere (NH).

But the TOTAL sunlight received by BOTH hemispheres in a year is almost constant; it does NOT depend on the  Milankovitch cycles. Instead it is the split BETWEEN hemispheres that is affected by those Cycles and which leads to glaciation cycling. And that split is important because the hemispheres are so different (NH is 40% land compared with 20% SH). For example, when the Earth is closer to the Sun during the Southern hemisphere winter, the Antarctic will be colder, more sea ice will form, the ice will reflect sunlight and cool the planet. With more land in the NH, less ice forms during Northern hemisphere winters.

 

[Jokodo]

Given R, the ratio of aphelion and perihelion distances, the Earth gets R² more sunlight at perihelion than aphelion but is only moving at R times the speed (cf Kepler's 2nd Law). This leads to the conclusion that, over the course of a year, the Southern hemisphere (SH) receives more sunlight than the Northern hemisphere (NH).

I may well be missing something, but I don't think that's correct. While it moves at R times the velocity, measured in millions of km/day, the path along which it moves approximates a circle with radius 1/R compared to aphelion, so it also covers R times the arc minutes per million km. The time it stays within a given angular distance from perihelion should thus be 1/R², and the total sunlight identical even per hemisphere.

Either way, I find it surprising that the SH boasts glaciers that reach the ocean an 48°+ small change in the Chilean Andes, while the Champagne region in France grows some of the world's most famous sparkling wines between 48° and 49° North.

 

[Cheerful Charlie]

Dumb question:

Is the only reason we think humans originated in Africa is because we find remains there that date back millions of years? And the reason we still find those is because they were preserved because the area dried up and became arid?

Suppose humans evolved elsewhere outside of Africa, but the environment remained well watered and fertile and destroyed any remains before they could become fossilized?

Many were preserved because volcanic ash covered them and preserved them.

 

[Gospel]

How do we know for certain there isn't life on other planets when even in our own galaxy it takes 10,000 to 100,000 years for light (the fastest bit of info from them) to reach us? What if 300,000 planets just reached the means to leave a detectable footprint around the same time we have, we wouldn't even detect them until the year 11900 or some such no?

 

[Wiploc]

How do we know for certain there isn't life on other planets

We don't know for certain.


Here's Terry Bisson's fabulous explanation for why we haven't found anybody else: "They're Made out of Meat" by Terry Bisson


Here's a couple of relevant XKCDs:

 

[bilby]

How do we know for certain there isn't life on other planets when even in our own galaxy it takes 10,000 to 100,000 years for light (the fastest bit of info from them) to reach us? What if 300,000 planets just reached the means to leave a detectable footprint around the same time we have, we wouldn't even detect them until the year 11900 or some such no?

It takes between 4.3 and 100,000 years - the closest known exoplanet is Proxima Centauri b, which is about 4.3 lightyears away. It's orbiting a Red Dwarf though.

There are about 500 type G stars (the same class as our Sun) within 100 lightyears of us, so any civilisation in one of those systems could, hypothetically, detect our radio emissions, assuming that they are able to detect the fairly weak transmissions made by our earliest radio broadcasts.

Only around 64 such stars are within 50ly, and would be able to pick up our most powerful transmissions that were beamed into space - the Cold War Distant Early Warning radars of the mid-20th century.

Of course, some of those type G stars could easily be twice as old as our Sun, giving any potential civilisation several billion years head start on us. Realistically, that seems likely to vastly exceed the average lifespan of a civilised species (or indeed any species of complex life); Sufficient to say that if there's other intelligent life in our galaxy, it's quite likely that at least some of it is far ahead of us technologically.

Which could very much limit our ability to detect them - our own radio signature rose from nothing to its peak in about half a century, and is well on its way to becoming either too weak to detect (due to improvements in efficiency that see less power radiated into space where no advertisers expect to find paying customers); or too highly encrypted to recognise as a product of intelligence; Or both.

Most information flow between continents is now done at ground level via cables - reducing still further our detectable radio signature.

If a technological civilisation lasts only a couple of centuries as a detectable radio broadcaster, even if it still persists as a high tech civilisation thereafter for millennia, it gives other such civilisations a very narrow window to detect them.

The galaxy could be teeming with highly advanced alien life, and we would not reasonably be expected to be able to both detect and recognise it.

And of course, the nearest one could be similarly advanced to us, but located a couple of thousand lightyears away, leaving us listening out for radio signals from a civilisation like that of Ancient Rome. Good luck with that.

 

[Loren Pechtel]

How do we know for certain there isn't life on other planets when even in our own galaxy it takes 10,000 to 100,000 years for light (the fastest bit of info from them) to reach us? What if 300,000 planets just reached the means to leave a detectable footprint around the same time we have, we wouldn't even detect them until the year 11900 or some such no?

The thing is why would they all reach that point at the same time? There are a lot of random processes in the path of reaching intelligence, even if there was a trigger event that wiped out all higher life at some point in the past different planets would climb back up at different rates. It was the better part of a billion years to go from simple life to technological civilization, a planet that did it even 1% faster or slower would be millions of years ahead/behind us.

Yes, interstellar travel is hard. Interstellar colonization is even harder. Unless there's some plateau there is no reason think it's a showstopper. 70 years ago space flight was a dream. Then it was the realm of major nations. Now it's in the realm of smaller first world nations and the most prolific launcher in the world is a private company, not a government at all. At some point the ability to do an interstellar colony will become within reach of a group of dissidents.

Taking very pessimistic views of what it will take to go to the stars (lightsail without laser pumping, 1000 years before a colony sends out colonies of it's own) a simplistic answer gives colonizing the galaxy in 100 million years, in reality it will go faster because of the rotation of the galaxy. That's 1% of the existence of the galaxy. Nobody was 1% faster than us?!

The Drake equation has already been posted but we have learned more since then and I do not believe it gives a good picture anymore. From what we have seen:

Planets are common. We haven't found anything terrestrial yet but our detection techniques are very skewed towards the sort of planets we have been finding--there are lots of others that we simply can't see.

Life on Earth arose basically as soon as it was possible. (Or perhaps arose even earlier on Mars and traveled here by meteorite--we might actually be Martians.) Is Earth ridiculously lucky or does life arise easily? The latter is an easier assumption. Thus there should be a lot of life-bearing worlds out there. Yet we don't see aliens everywhere, why??

Instead, lets look at the things that history shows aren't so easy:

1) Simple life -> Complex life. On Earth this took something like 2 billion years.
2) Complex life -> Civilization. Again, in the ballpark of 2 billion years.

If we figure Earth isn't abnormal we get a range of 200 million to 20 billion years for each of these.

And the L from the Drake equation--do we survive?

Of these three things, one or more must impose billions-to-one odds against becoming starfaring. Fortunately, both #1 and #2 have the potential for being the stumbling block. We have already used 99% of Earth's habitable time (Earth's ability to compensate for the sun warming as it ages is going to peg in 50 million years and we will see warming with a vengence--not conductive to the development of a long-lived species) to get where we are. Are we the lucky one that got past the fence (long odds where can be explained by the observer effect) or is the fence in the future? Is it impossible to develop without developing some sort of suicide tech? (Suicide tech either is something we don't know will kill us until it's too late, or something that can be used by some sort of suicide cult to destroy us.)

 

[Loren Pechtel]

Of course, some of those type G stars could easily be twice as old as our Sun, giving any potential civilisation several billion years head start on us. Realistically, that seems likely to vastly exceed the average lifespan of a civilised species (or indeed any species of complex life); Sufficient to say that if there's other intelligent life in our galaxy, it's quite likely that at least some of it is far ahead of us technologically.

A G type star of that age isn't going to have suitable planets.

 

[bilby]

Of course, some of those type G stars could easily be twice as old as our Sun, giving any potential civilisation several billion years head start on us. Realistically, that seems likely to vastly exceed the average lifespan of a civilised species (or indeed any species of complex life); Sufficient to say that if there's other intelligent life in our galaxy, it's quite likely that at least some of it is far ahead of us technologically.

A G type star of that age isn't going to have suitable planets.

Probably not.

Seven out of eight of the planets of the nearest G type star aren't suitable, for that matter.

And I strongly suspect that you're missing something vital in your assessment of how hard interstellar colonisation is - even generalist species like ours struggles to survive on most of our planet's surface, and on a large fraction of its land surface as well - Antarctica is essentially uninhabitable, as are big chunks of Africa, Asia, and both Americas. And these places are on the planet we evolved with.

The probability that we could survive and thrive, even with some pretty high technology, as a colony on any part of any exoplanet, is pretty small.

And of course, that's likely also true for any aliens. Any planet other than the one on which they evolved would be a massive struggle to survive on - atmospheres with toxic components, and/or lacking needed components; painful gravitational conditions; too much (or to little) of any of dozens (maybe hundreds) of trace compounds that they (or we) either cannot tolerate, or desperately need; unsurvivable or highly problematic weather and climate; and that's all assuming that the places were pre-selected based on having suitable temperature ranges and adequate water availability.

Technologically advanced life is clearly very rare in the immediate vicinity (say 50ly radius); But that shouldn't really be a surprise, given that it's very rare right here where we know conditions are suitable.

Earth has broadcast radio signals from intelligent life for about 0.2% of the existence of our species, and about one part in 30,000 of the existence of complex life forms.

We have had radio for only about one part in sixty of our having civilisation (defined using the etymological root that says we are civilised if some of us inhabit cities).

It seems that even when a species with all the characteristics needed for civilisation exists, it can take several thousand years to stumble across radio, and they may only then employ it for a few centuries in a manner easily detectable across interstellar space.

And that's starting on a planet that had a Carboniferous Era long enough ago for abundant fuel to be lying about waiting for them to have an industrial revolution. If Earth had no coal, it probably wouldn't have much by way of technology either.

Perhaps coal forming eras are uncommon. Or some other essential element of our progress that we barely notice is found only rarely in other star systems, or on other planets.