6 ms·

Knowing very little about chemistry and physics, I always enjoy learning the names of new measurements. Milliangstroms? Lmao great name.

nayuki 4y ago
Yes, it's a great name like millimetres of mercury (mmHg), kilotons of TNT, light-years, etc. /s But seriously, SI already has appropriate units for these quantities. Milliangstroms should be converted to picometres, millimetres of mercury should be converted to kilopascals, kilotons of TNT should be converted to terajoules, and light-years should be converted to petametres.
- idiotsecant 4y ago
  'everyone should use the units I want them to use and not the commonly used ones'
  - hypertele-Xii 4y ago
    That's how we get standards.
  - nayuki 4y ago
    This is a disingenuous argument. Do you not see the problems with using application-specific units? They are jargon and don't form a coherent system. When you have a jumble of units, it is hard to relate them. If an acre of land gets an inch of rain, how many gallons of water is that? If you did this in millimetres, metres, and cubic metres, it is easy. If your car's motor is rated in horsepower but electricity is measured in kilowatts, how do you compare those? What about fitting copies of a product measured in ounces in a shipping container measured in short tons? Typesetting measured in points, but paper measured in inches? Fitting metalwork done in mils but woodwork done in binary-fraction inches in a house measured in feet? The list goes on and on. It's easy to say "but my domain is special and deserves its own units". It's much harder to resist and say no, there is a perfectly suitable unit with power-of-1000 prefixes to use in your application.
    - blix 4y ago
      There are an infinite number of possible coherent unit systems, all of them totally arbitrary. Why should any system be preferred over the rest?
      - saimiam 4y ago
        Because mathing in one is much easier by orders of magnitude (pun intended) in one system.
        blix 4y ago
        OK, but why choose any one system over any others? Why chose base 10 over base 2? Why choose the current definition of the meter as opposed to some other length?
- namanyayg 4y ago
  How is 1 light year = 1 petameter?
  - drekk 4y ago
    They're not. We're saying the non-SI unit of light years shouldn't be used over something like petameter. Just multiply the "light year" measurement by .9461 and you're set. Or, ideally, just measure in SI units to begin with? The US is the holdout here and for no good reason
    - dylan604 4y ago
      How long does it take for light to travel petameter vs how long did it take to travel that light year? The light year is something people can relate to
      - 12ian34 4y ago
        I for one welcome the idea of measuring time in lightpetametres ;) (that's about 38.6 days for the curious)
      - Maursault 4y ago
        The problem is with what a year is, which is arbitrary to begin with, but worse still, a year is not constant. The momentum of every planet is affected by the gravity of every other planet, leading to fluctuations in solar orbital speed, which means a full orbit is likely never the same period as the previous or subsequent orbit. Maybe these fluctuations are small, but light travels so fast that over long distances it is sure to be significant. Thus the definition of a light year is defined as the distance light travels in a Julian year, 365.25 days, but this just pushes the error down to a different measure, because days are not constant either. Since the speed of light actually is constant, maybe we should define years and days by the speed of light instead of vice versa.
        dylan604 4y ago
        Of course, there's also the problem that a light year is only relevant to someone from Earth. A light year for a Neptunian would be drastically longer, let alone someone extra-solar system to us
- dylan604 4y ago
  >kilotons of TNT should be converted to terajoules I disagree with this one. A ton of TNT is much more easily understood vs some measurement of energy that no normal human has any capacity of understanding. Also, milliangstroms vs picometers. if you are already using angstroms, then dividing it by milli makes sense.
  - aaronax 4y ago
    I doubt a typical person can describe the effect of one ton of TNT with any accuracy. I'll give it a try though: 2 meter deep and 6 meter wide crater in typical soil, death due to shockwave out to 150m, death likely due to shrapnel out to 300m, buildings destroyed out to 300m, audible from 10 km. From here: https://unsaferguard.org/un-saferguard/blast-damage-estimation https://unsaferguard.org/un-saferguard/blast-damage-estimati... 26 meters fatal distance, 83 or 142 meters buildings destroyed My estimates are more appropriate for a 20-30 ton explosion, it seems.
    - dylan604 4y ago
      You think the typical person can tell the effect of whatever value in terajoules would be? At least the typical person would know that dynamite/TNT is an explosive causing damage and that can be extrapolated in one's mind the effect of 1000 tons of TNT would be much larger and so forth.
      - rcxdude 4y ago
        No, the point is can't do it with kilotons otherwise. but at least terajoules are consistent with other units of energy. If there's no familiar reference point then why use random units?
- dotnet00 4y ago
  This is a bad argument. Units exist to make things easier to communicate, using lightyears or kilotons makes perfect sense for contexts where they convey more information directly than petameters or terajoules. Especially since the conversions aren't exactly difficult to remember for anyone who needs them. Here the use of milliangstroms easily conveys the information that bond lengths are measured in angstroms and thus this is a very small correction, picometers would not convey that to anyone not already familiar with typical bond lengths.
  - nayuki 4y ago
    Turn this around: How many people have seen the speed of light, even for a second? How many people have seen a kiloton of TNT being blasted? You're only advocating for these units because they are commonly reported in the media and are thus familiar - at least in print, not in physical experience. Angstroms are needless jargon because nanometres already cover roughly the same scale. Do you want to go back to the bad old days when every town had its own definition of feet and pounds, and consumers were routinely cheated through the use of confusing and obfuscated units?
    - dotnet00 4y ago
      People haven't seen the speed of light, but they have an understanding of the fact that it's the maximum possible speed. Similarly, while people haven't seen a kiloton of TNT being blasted, they can easily visualize what a kiloton of TNT is and understand what that means. Your claim that I'm only advocating these units because they're common in media is ignoring the fact that these are also very common as formal units in their respective fields. Another great example is AU, no one has seen what 1AU exactly is, but everyone can intuitively understand that 5AU means 5x further from the Sun than the Earth is, 0.74 terameters conveys absolutely nothing on its own and even for someone who is aware that 1AU=0.15 terameters, it takes a bit of extra mental effort to obtain the same information while not really adding anything because '1AU=0.15 terameters' is fundamental knowledge in the field anyway. This is not going back to the old days of units for two big reasons, they have important meaning within their field and there is widespread knowledge of conversion factors. Normalized units are also very popular in physics as they simplify the math and are more intuitive due to being directly tied to physical properties. Hell, even going back to the old metric vs imperial debate, there were very good benefits to the imperial system back when calculators were rare as multiples of 12s were more convenient to divide in the most common fractions (2, 3, 4, 6). Even now our clocks are based on those multiples due to their convenience for general use.
- sidlls 4y ago
  Except for kilopascals, sometimes, none of the other things is even something physicists (or chemists or engineers) use regularly. Nanometers, angstroms, and femtometers are much more commonly found in the jargon. You’re being pedantic, and incorrectly so at that.
- rsfern 4y ago
  Ångström is currently approved by NIST for use with the SI, so I don’t think it’s quite in the same category as mmHg and hogs heads and pound force. I agree pm is a better choice than mÅ, but I’m not positive mÅ wouldn’t pass NIST internal review, especially if it’s in common use in the field. https://physics.nist.gov/cuu/Units/outside.html https://physics.nist.gov/cuu/Units/outside.html
chasil 4y ago
If you want to know a little more about benzene, it is also known as a "Kekule Structure." It is also called a "resonant structure" as the double bonds are said to flip in the ring of carbon atoms. ...or, at least, that was what I heard in high school organic chemistry. That was a very long time ago, and interpretations might have changed. https://en.m.wikipedia.org/wiki/Benzene https://en.m.wikipedia.org/wiki/Benzene
- infinite8s 4y ago
  They don't exactly flip. It's more like each bond is on average 1.5 electrons. You'll often see it drawn as a hexagon with a small circle in the middle.
- jcranmer 4y ago
  It's not that the bonds are flipping, but rather that each bond is kind of half a C-C single bond and half a C=C double bond--more of an average 1½ bond. This makes a lot more sense when you start getting into full-blown molecular orbital theory.
  - absolutelynobo 4y ago
    aka superposition?
    - moring 4y ago
      That's something I wondered too, but I doubt it. The model used to explain benzene's bonds superficially sounds like superposition, and I can't really speak about the electrons involved (way too complex for me to even imagine), but when you look at the nuclei involved, it sounds implausible that the superposition of irregularly-positioned nuclei results in regularly-positioned nuclei. Implausible because they are too heavy and therefore localized. But that's my layman's knowledge. I'd like to be corrected!
    - jcranmer 4y ago
      I can see why you might think this. It is a quantum mechanical effect, but it has nothing to do with the main quantum mechanical effect everyone knows about (superposition). Superposition of two states is not preserved by measurement: it's more akin to a (complex, not real) probability you'll find the system of one of the states. By contrast, resonant bonds are a real mixing of the two states: you don't observe the carbon-carbon bonds in a benzene molecule as either being a single bond or a double bond, you observe them as a uniform bond that's somewhere between a single bond and a double bond (e.g., bond length). Treating such things as a weighted average of various resonance structures is a usable approximation that allows you to predict the structure of more molecules without having to dive deep into molecular orbital theory.

nayuki 4y ago

Yes, it's a great name like millimetres of mercury (mmHg), kilotons of TNT, light-years, etc. /s But seriously, SI already has appropriate units for these quantities. Milliangstroms should be converted to picometres, millimetres of mercury should be converted to kilopascals, kilotons of TNT should be converted to terajoules, and light-years should be converted to petametres.

idiotsecant 4y ago
'everyone should use the units I want them to use and not the commonly used ones'
- hypertele-Xii 4y ago
  That's how we get standards.
- nayuki 4y ago
  This is a disingenuous argument. Do you not see the problems with using application-specific units? They are jargon and don't form a coherent system. When you have a jumble of units, it is hard to relate them. If an acre of land gets an inch of rain, how many gallons of water is that? If you did this in millimetres, metres, and cubic metres, it is easy. If your car's motor is rated in horsepower but electricity is measured in kilowatts, how do you compare those? What about fitting copies of a product measured in ounces in a shipping container measured in short tons? Typesetting measured in points, but paper measured in inches? Fitting metalwork done in mils but woodwork done in binary-fraction inches in a house measured in feet? The list goes on and on. It's easy to say "but my domain is special and deserves its own units". It's much harder to resist and say no, there is a perfectly suitable unit with power-of-1000 prefixes to use in your application.
  - blix 4y ago
    There are an infinite number of possible coherent unit systems, all of them totally arbitrary. Why should any system be preferred over the rest?
    - saimiam 4y ago
      Because mathing in one is much easier by orders of magnitude (pun intended) in one system.
      - blix 4y ago
        OK, but why choose any one system over any others? Why chose base 10 over base 2? Why choose the current definition of the meter as opposed to some other length?
namanyayg 4y ago
How is 1 light year = 1 petameter?
- drekk 4y ago
  They're not. We're saying the non-SI unit of light years shouldn't be used over something like petameter. Just multiply the "light year" measurement by .9461 and you're set. Or, ideally, just measure in SI units to begin with? The US is the holdout here and for no good reason
  - dylan604 4y ago
    How long does it take for light to travel petameter vs how long did it take to travel that light year? The light year is something people can relate to
    - 12ian34 4y ago
      I for one welcome the idea of measuring time in lightpetametres ;) (that's about 38.6 days for the curious)
    - Maursault 4y ago
      The problem is with what a year is, which is arbitrary to begin with, but worse still, a year is not constant. The momentum of every planet is affected by the gravity of every other planet, leading to fluctuations in solar orbital speed, which means a full orbit is likely never the same period as the previous or subsequent orbit. Maybe these fluctuations are small, but light travels so fast that over long distances it is sure to be significant. Thus the definition of a light year is defined as the distance light travels in a Julian year, 365.25 days, but this just pushes the error down to a different measure, because days are not constant either. Since the speed of light actually is constant, maybe we should define years and days by the speed of light instead of vice versa.
      - dylan604 4y ago
        Of course, there's also the problem that a light year is only relevant to someone from Earth. A light year for a Neptunian would be drastically longer, let alone someone extra-solar system to us
dylan604 4y ago
>kilotons of TNT should be converted to terajoules I disagree with this one. A ton of TNT is much more easily understood vs some measurement of energy that no normal human has any capacity of understanding. Also, milliangstroms vs picometers. if you are already using angstroms, then dividing it by milli makes sense.
- aaronax 4y ago
  I doubt a typical person can describe the effect of one ton of TNT with any accuracy. I'll give it a try though: 2 meter deep and 6 meter wide crater in typical soil, death due to shockwave out to 150m, death likely due to shrapnel out to 300m, buildings destroyed out to 300m, audible from 10 km. From here: https://unsaferguard.org/un-saferguard/blast-damage-estimation https://unsaferguard.org/un-saferguard/blast-damage-estimati... 26 meters fatal distance, 83 or 142 meters buildings destroyed My estimates are more appropriate for a 20-30 ton explosion, it seems.
  - dylan604 4y ago
    You think the typical person can tell the effect of whatever value in terajoules would be? At least the typical person would know that dynamite/TNT is an explosive causing damage and that can be extrapolated in one's mind the effect of 1000 tons of TNT would be much larger and so forth.
    - rcxdude 4y ago
      No, the point is can't do it with kilotons otherwise. but at least terajoules are consistent with other units of energy. If there's no familiar reference point then why use random units?
dotnet00 4y ago
This is a bad argument. Units exist to make things easier to communicate, using lightyears or kilotons makes perfect sense for contexts where they convey more information directly than petameters or terajoules. Especially since the conversions aren't exactly difficult to remember for anyone who needs them. Here the use of milliangstroms easily conveys the information that bond lengths are measured in angstroms and thus this is a very small correction, picometers would not convey that to anyone not already familiar with typical bond lengths.
- nayuki 4y ago
  Turn this around: How many people have seen the speed of light, even for a second? How many people have seen a kiloton of TNT being blasted? You're only advocating for these units because they are commonly reported in the media and are thus familiar - at least in print, not in physical experience. Angstroms are needless jargon because nanometres already cover roughly the same scale. Do you want to go back to the bad old days when every town had its own definition of feet and pounds, and consumers were routinely cheated through the use of confusing and obfuscated units?
  - dotnet00 4y ago
    People haven't seen the speed of light, but they have an understanding of the fact that it's the maximum possible speed. Similarly, while people haven't seen a kiloton of TNT being blasted, they can easily visualize what a kiloton of TNT is and understand what that means. Your claim that I'm only advocating these units because they're common in media is ignoring the fact that these are also very common as formal units in their respective fields. Another great example is AU, no one has seen what 1AU exactly is, but everyone can intuitively understand that 5AU means 5x further from the Sun than the Earth is, 0.74 terameters conveys absolutely nothing on its own and even for someone who is aware that 1AU=0.15 terameters, it takes a bit of extra mental effort to obtain the same information while not really adding anything because '1AU=0.15 terameters' is fundamental knowledge in the field anyway. This is not going back to the old days of units for two big reasons, they have important meaning within their field and there is widespread knowledge of conversion factors. Normalized units are also very popular in physics as they simplify the math and are more intuitive due to being directly tied to physical properties. Hell, even going back to the old metric vs imperial debate, there were very good benefits to the imperial system back when calculators were rare as multiples of 12s were more convenient to divide in the most common fractions (2, 3, 4, 6). Even now our clocks are based on those multiples due to their convenience for general use.
sidlls 4y ago
Except for kilopascals, sometimes, none of the other things is even something physicists (or chemists or engineers) use regularly. Nanometers, angstroms, and femtometers are much more commonly found in the jargon. You’re being pedantic, and incorrectly so at that.
rsfern 4y ago
Ångström is currently approved by NIST for use with the SI, so I don’t think it’s quite in the same category as mmHg and hogs heads and pound force. I agree pm is a better choice than mÅ, but I’m not positive mÅ wouldn’t pass NIST internal review, especially if it’s in common use in the field. https://physics.nist.gov/cuu/Units/outside.html https://physics.nist.gov/cuu/Units/outside.html

chasil 4y ago

If you want to know a little more about benzene, it is also known as a "Kekule Structure." It is also called a "resonant structure" as the double bonds are said to flip in the ring of carbon atoms. ...or, at least, that was what I heard in high school organic chemistry. That was a very long time ago, and interpretations might have changed. https://en.m.wikipedia.org/wiki/Benzene https://en.m.wikipedia.org/wiki/Benzene

infinite8s 4y ago
They don't exactly flip. It's more like each bond is on average 1.5 electrons. You'll often see it drawn as a hexagon with a small circle in the middle.
jcranmer 4y ago
It's not that the bonds are flipping, but rather that each bond is kind of half a C-C single bond and half a C=C double bond--more of an average 1½ bond. This makes a lot more sense when you start getting into full-blown molecular orbital theory.
- absolutelynobo 4y ago
  aka superposition?
  - moring 4y ago
    That's something I wondered too, but I doubt it. The model used to explain benzene's bonds superficially sounds like superposition, and I can't really speak about the electrons involved (way too complex for me to even imagine), but when you look at the nuclei involved, it sounds implausible that the superposition of irregularly-positioned nuclei results in regularly-positioned nuclei. Implausible because they are too heavy and therefore localized. But that's my layman's knowledge. I'd like to be corrected!
  - jcranmer 4y ago
    I can see why you might think this. It is a quantum mechanical effect, but it has nothing to do with the main quantum mechanical effect everyone knows about (superposition). Superposition of two states is not preserved by measurement: it's more akin to a (complex, not real) probability you'll find the system of one of the states. By contrast, resonant bonds are a real mixing of the two states: you don't observe the carbon-carbon bonds in a benzene molecule as either being a single bond or a double bond, you observe them as a uniform bond that's somewhere between a single bond and a double bond (e.g., bond length). Treating such things as a weighted average of various resonance structures is a usable approximation that allows you to predict the structure of more molecules without having to dive deep into molecular orbital theory.