Atomic Weight Not So Constant 147
DangerousBeauty writes "Yahoo has a Canadian Press story up about new changes to the periodic table of elements concerning the weights of specific elements — it seems that the weights fluctuate based on where they are found in nature. Quoting: '"People are probably comfortable with having a single value for the atomic weight, but that is not the reality for our natural world," says University of Calgary associate professor Michael Wieser.' He is is secretary of the International Union of Pure and Applied Chemistry's Commission on Isotopic Abundances and Weights."
You know the cliché (Score:2, Funny)
American atoms are fat.
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It's global warming, it causes everything to rise.
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You mean you actually *have* an economy, these days ?
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http://www.iaso.org/site_media/uploads/Global_Prevalence_of_Adult_ObesityMay__2010_revised_with_headings.pdf [iaso.org]
(from the association quoted by the Guardian article)
The only stat that is lower than average in US by EU standards is, surprisingly, the one of males less than 30. The one that is suprisingly high is the number of obese women of more than 30 years. I guess that is why there are so "yo mama" jokes on the other side of the Atlantic... As the article pointed, you can find some categories in
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Well, first of all, you're completely misreading the stats. There is no breakdown by years. The numbers at the top indicated the BMI percentage, not the age.
So, with that in mind, looking at the stats tells us that the US has the highest percentage of males with a 30+% BMI. On the other hand, MANY European nations have a higher percentage of males who are obese, but under the 30% mark. What that seems to indicate is that they have a roughly equivalent prevalence of overall male obesity, but fat men in t
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If the definition of obesity is simply "more than 30 of BMI", USA really wins the contest in the males category.
If you consider the definition to be 25 or more (what the table calls "overweight"), the gap is closer but neither Germany nor Greece mentioned in the article manages to top the 72% of overweight of USA. The only way for them to do so is to compare the 25-29.5 category while dismissing the 30+, which is a kind of silly way to measure don't you think ?
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Yeah, I agree that comparing these measurements in general is a bit ridiculous. It's much more interesting (and useful) to look at how various societal factors correlate to the change in BMI over time.
On the other hand, I think these stats can be quite valuable for dispelling myths. For instance, I don't think anyone pictures Greeks as particularly obese (quite the opposite, actually), while Americans have a reputation for being a nation of gluttons. Looking at some of these figures has changed some of m
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Yeah, I agree that comparing these measurements in general is a bit ridiculous. It's much more interesting (and useful) to look at how various societal factors correlate to the change in BMI over time.
Yes, there is much to be learned looking at the increases in obesity over time. The U.S. corn subsidies, lower-protein corn engineered for the production of high fructose corn syrup, and the widespread use of corn syrup directly and indirectly in foods has been shown to have had a major impact. (An example of a harmful indirect use is for feeding cattle. They're higher fat and harbor more-harmful strains of E-coli due to the higher acidity the diet causes)
A long list of related links is available from the
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The U.S. corn subsidies, lower-protein corn engineered for the production of high fructose corn syrup, and the widespread use of corn syrup directly and indirectly in foods has been shown to have had a major impact.
Lets just say I find the data unconvincing. It's been repeatedly shown that, as far as weight-loss/gain is concerned, the only thing that matters is calories in and calories out. You can eat a balanced diet of 4,000 calories a day and you'll gain weight, or drink 2,000 calories of pure fructose corn syrup a day and you'll lose weight. Professor Haub provided the most recent example of that principle, when he pulled his little Twinkie Diet [cnn.com] stunt. People who tell you otherwise are generally trying to sell
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I was 5'10" and 180 lbs. I could pump out 100+ pushups, 40+ chinups,
that makes you not fit the "profile" to begin with. Generic BMI is only supposed to be used for people with "average" physique. "average" people cant do half of that.
Obviously, you have/had way more muscle than the average.
I'd like to see body-fat percentage measurements replace BMI as a standard measurement of obesity
well of course that would be better... but most people dont have an accurate "body fat measurement device".
They DO, however, have a scale and a tape measure.
(it's odd, though, that even hospitals dont normally measure body fat%: just "height and weight")
Your post made me look around to s
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Then our profile of an "average" person is someone who has never seen the inside of a gym. I only work around twice a week these days, and can still crank out 100+ push-ups (in sets of ~40, not all at once) if I have to.
Much like GP, my BMI is just edging into the "overweight" category at 6'2" and 200 lbs.
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The calories in, calories out myth has be thoroughly debunked. It is a good premise for life forms that do not have anuses, and that have 100% matter/energy conversion digestive systems, but that does describe humans. Can you really say that you have never met someone who worked out a lot, and watched what the
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The calories matter, but very little fructose can be used by the body directly compared to glucose. It gets converted to fat. If you're pretty active, you can burn that fat. But for things like providing the energy your brain needs, it isn't metabolized well. You can actually feel short on energy at the same time you're converting fructose to fat. The liver has to work harder to process it too. Most of the time what people perceive as energy from a soda is actually the caffeine.
And with fructose, your
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I call shenanigans. I have offered many a bet that I can put on weight eating a 2500 calorie a day diet, and lose weight at a 4000 calorie a day diet. This with absolutely no change in exercise.
I would gladly take your bet, if I could monitor you 24/7 for the duration of the experiment. If I lost - which is unlikely - we'd have learned something useful about human metabolism. If I won ... well, I don't mind taking your money :)
The calories in, calories out myth has be thoroughly debunked.
Riiiiight. Feel free to follow the link I posted. The "calories in calories out myth" is pretty much the accepted standard in the scientific community. It's only been "debunked" by protein-powder-pushing muscle-heads with a 6th grade education.
(ok, I'm exaggerating a bi
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One woman on Science Friday interview said something that throws it off is that when the US collects its numbers, it weighs the people sampled. In other countries, often they just ask, and people tend to give a number that's probably off by several percent. This might have changed in the last year or so, I don't know.
Actual Link to Document (Score:5, Informative)
link [iupac.org]
Re:Actual Link to Document (Score:5, Informative)
Yes. thank you for that link. Anybody with minimal knowledge of how atomic weights are computed (i.e. a weighted average of the atomic masses of the various isotopes) can guess that if the concentrations of isotopes are different in different samples, the "atomic weight" will be different.
I went and read the famous abstract anyway. quote: "This fundamental change in the presentation of the atomic weights represents an important advance in our knowledge of the natural world and underscores the significance and contributions of chemistry to the well-being of humankind in the International Year of Chemistry 2011."
This article is just about the results of some measurements. ok, useful measurements, but NOT an important advance in our knowledge of the natural world.
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the value of the findings vary depending on the observer.
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mebbe for you they don't
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The important advance is in the presentation of weighted atomic masses as ranges with context, rather than the wet chemistry behind the changed numbers. At the very least, presenting a range of masses reminds us to think about the sources of the atoms analysed and variations in their collective attributes.
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Atomic weights based on accepted isotope distributions have always been somewhat approximate. That accepted weights would be revised should have been expected.
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Yup - this is also one of the reasons why the mass of a liter of water/etc was avoided as the basis for the kilogram. It is almost impossible to obtain water of any particular isotopic composition, and it varies around the world. Water is also non-ideal for other reasons as well which I won't get into...
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Yeah; my first reaction was "WTF? Archaeologists have been using variations in isotope ratios for decades as a way of learning about the diet of the people and other critters who left remains." This works (sort of) because different plant species have different isotope ratios for many of their constituent elements. Isotope ratios are also used to do things like locate the source of plant, mineral and metallic objects. Anyone who knows about this understands that the published "atomic weight" numbers are
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I was a little surprised by the summary, as I don't recall ever seeing atomic weight on the periodic table. The only number I recall seeing as a constant was the only constant that can be used; the number of protons.
http://en.wikipedia.org/wiki/Periodic_table [wikipedia.org]
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I've always been bothered by the fact that no standard deviation is ever given. Of course, there's not much room on there for that info on a periodic table, but I don't even see it when the full properties are listed.
TFA presents the value as a range ([1.007 84; 1.008 11] for Hydrogen). Why not say 1.00798 +/- 0.014%. IANAC (chemist), but that seems to give the same information, but in a way that's more natural to the way people will use the value. Unless I know what the correct average weight is where
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nothing new here, it was know from ages that isotopes have a different weight.
nothing is changing, especially not the atomic weight of atoms.
their value is revised, but the value all by itself is as constant as it ever was.
I can see some changes in that it seems like one might be able to find the average atomic weight of some Al and make an educated guess at where it was mined, It also means that if you are looking for a particular isotope, it might be worthwhile to start with ore from one location rather than another.
While I agree that they seem to be overstating the significance, this may have real world effects, so it is at least a small advance.
Re:Actual Link to Document (Score:5, Informative)
Thanks. The article makes it clear that the major change here is that the way in which atomic weights will be presented is changing. It's not just that they're being updated to reflect a more complete measurement, it's that atomic weights will now be represented as a range of possible values rather than a single value. It's not every day that the way in which information is presented in the periodic table changes.
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Actually, from the Slashdot front page you can tell everything you need to know about the differences between the article and the summary: It was posted by kdawson, and therefore the differences are fundamental in nature.
Has it ever been explained why kdawson posts usually have titles that are flat-out contradicted by the article in question? Perhaps another study is in order...
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But the range of possible values for the atomic weight is already represented by the number of decimal places displayed. For example, compare the the number of decimal places for F (18.9984032) and Pb (207.2).
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How does that work ? Does that mean Pb can vary between 207.20 and 207.29... ? How about when the weight of an element could vary between, say, 200.45 and 200.47 ?
I don't get it (Score:4, Insightful)
Isotopes exist, right. And by definition, different isotopes of the same element have different mass. I'd take it as a given that the distribution of certain isotopes are different in different places.
But what is this article actually saying? The atomic mass number is meant to be the universal average ... now they may have got that slightly wrong, but why exactly do we need a range of universal averages for each isotope? That's surely some sort of misnomer.
Re:I don't get it (Score:5, Informative)
They're recalculating the average atomic weight, the one on the periodic table, based on the abundances of the different isotopes in nature. If you're trying to calculate the mass of, say, 300,000 molecules of something, you use the average atomic weight and don't try to figure out what isotope each atom is.
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The atomic weight has always been a weighted average that isn't new. What is new is that they are no longer going to print that average as the singular atomic weight. Now they are going to print a range because the abundance of a given isotope varies based on where a sample is gathered.
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What I do not get is, of course weight will be different in nature. Weight is dependant on acceleration due to gravity and mass. An atom would weigh more on Earth than it would on the moon.
I think these chemists mean 'atomic mass'? I'm an engineer so correct me if I'm wrong.
Re:I don't get it (Score:5, Informative)
What I do not get is, of course weight will be different in nature. Weight is dependant on acceleration due to gravity and mass. An atom would weigh more on Earth than it would on the moon.
I think these chemists mean 'atomic mass'? I'm an engineer so correct me if I'm wrong.
Atomic weight is a dimensionless quantity (ratio of the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12).
I think the convention in chemistry is to call the absolute mass of an isotope (in kg or whatever) "atomic mass", and to call its relative mass (dimensionless) "atomic weight".
Comment removed (Score:5, Informative)
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Well, IUPAC can't be right all the time - they standardised on "Sulfur" for goodness sake! ;)
I just got used to hydrogen being 1.0079, now I'm going to have to memorise the table all over again.
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What I do not get is, of course weight will be different in nature. Weight is dependant on acceleration due to gravity and mass. An atom would weigh more on Earth than it would on the moon.
I think these chemists mean 'atomic mass'? I'm an engineer so correct me if I'm wrong.
You aren't alone in that opinion - there is some controversy [wikipedia.org] over the name, simply because it is *not* a "weight" in any sense of the word.
The most popular suggested replacement is "relative atomic mass" (the base unit is 1/12 the mass of a carbon 12 atom), but even that is somewhat misleading since it's actually intended to be relative to the average atomic mass of a sample of the element as found "in nature".
The change is a result of them realizing that that there is actually some variation in the proport
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it is *not* a "weight" in any sense of the word.
Yes it is. It is a weight in the sense meant by the term "atomic weight."
But if you really want change for change's sake (it's not like this leads to confusion among chemists), let's call it atomic mojo. How about that?
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Weight is dependant on acceleration due to gravity and mass. An atom would weigh more on Earth than it would on the moon.
Not relevant. Theres nothing chemists love more than STP standard temperature and pressure. Extending that to "we're going to define all our weights as being in a 9.81 m/s2 grav field" is to be expected from that crowd (which I was/are almost a part of)
Wait until you learn about the various gas laws, and start posting to slashdot that they are all wrong because a mole of gas "on the moon" would take up a heck of a lot more than 22.4 liters.
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Well from reading the link what I am getting is that they are changing how it is listed and calculated. It does make sense in away since the variablity in atomic weight of hydrogen is much higher than say uranium when looking at it as a percentages. So they are going to show Hydrogen as a range instead of a fixed number.
Isotopes (Score:5, Insightful)
Atomic weight is calculated based on the number of isotopes of any given element. A handful have only one isotope and therefore a stable atomic weight, but most elements have more than one isotope, carbon 12, 13 or 14, for example.
Makes much more sense than weights fluctuate based on where they are found in nature. Its why centrifuges can be used to separate uranium 235 from uranium 238.
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weights fluctuate based on where they are found in nature
But it's the truth. When we discovered some silicon on the moon, man, did that have a different weight.
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Next up on Brainiac:
Silicone breast, will they float or will they sink?
And are they really the best thing to grab hold of in case of office flood thanks to global warming?
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Next up on Brainiac:
Silicone breast, will they float or will they sink?
And are they really the best thing to grab hold of in case of office flood thanks to global warming?
Well, for the record, silicone is typically slightly denser than water [answers.com] so that'd make for a less-than-excellent flotation device.
And, as a strange aside, newly-filled saline implants sometimes have a bit of air in them, and they can audibly slosh, which is a bit weird.
Atomic Weights were never constant (Score:5, Insightful)
The Atomic Weight is only an average of the isotopes found in nature divided by some constant mass unit.
How could they be constant if "they vary from sample to sample" [wikipedia.org] as even Wikipedia knows?
Somebody seemed to have failed his physics or chemistry classes.
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Somebody seemed to have failed his physics or chemistry classes
That's a little harsh. Yes, it's been known for quite some time that average atomic weights vary from sample to sample, and the information content of the paper may not seem fundamentally novel. However, this is a paper where scientists are recommending a change in IUPAC's policy. For these standards boards, this is a fundamental issue. Think of it as similar to the "Pluto is/isn't a planet" debate. It seems like it's just semantics they're arguing (and I'm inclined to think that, in either case, it i
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Somebody seemed to have failed his physics or chemistry classes
That's a little harsh. Yes, it's been known for quite some time that average atomic weights vary from sample to sample, and the information content of the paper may not seem fundamentally novel. However, this is a paper where scientists are recommending a change in IUPAC's policy. For these standards boards, this is a fundamental issue.
I didn't really mean the scientists in question. But as is usual nowadays, ./ headlines and summaries are often quite incorrect.
Even though the stories are seen by several people before the hit the front page.
Think of it as similar to the "Pluto is/isn't a planet" debate. It seems like it's just semantics they're arguing (and I'm inclined to think that, in either case, it is. Funny story: I had to correct some kid in a museum recently because he was telling his little brother that Pluto no longer existed.), but passions can still become pretty inflamed.
Anyway, just thought I'd try to put the whole thing in perspective.
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Meh (Score:4, Insightful)
Looking at the title of the story I thought it would be something funky, but the entire story is just that they want to make the periodic table slightly more accurate for atoms that have isotopes. Everyone that has gone through high school chemistry should already know that that for unstable elements the table reference is an average at best.
This story is basically "ZOMG, it turns out that the weight of my mac and cheese isn't constant because the ratio of cheese to mac can vary!!!"
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Not just unstable elements. Plenty of stable elements have more than one, sometimes multiple isotopes. boron, chlorine, bromine, tin to name just a couple off the top of my head.
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Everything stable that isn't one of the monoisotopic elements
http://en.wikipedia.org/wiki/Monoisotopic_element [wikipedia.org]
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I agree. People who work with the atomic weights are aware that they are averages of multiple isotopes. Mass spec folks never use the average values. The 35.453 of Chlorine may change from region to region on Earth by a fraction of a percent, but the problem is that if you're doing something that needs the rough average value (e.g. calculating the mass of HCl in a lecture bottle), you now can't just look at the periodic table and get the atomic weight. You have to look up the local ratio and then calcula
Masses not changing; only ratio of isotopes. (Score:4, Informative)
The scientific paper can be found here [doi.org].
In Section 1.1 the weight is defined as the weighted mean over all the isotopes. Caesium 135 still has atomic mass 134.9059770(11) and caesium 137 still has mass 136.9070895(5); the way in which the relative abundances of isotopes is measured - that is all.
Not surprising (Score:2)
Acronym of union (Score:1)
mass vs weight (Score:1)
Why not look in Wikipedia first? (Score:1)
Useful info for Mars terraformers (Score:1)
But other than some intergalactic engineers, and of course astronomers, I don't think that any engineer will care. The earth was so properly blended when it was made that it's safe to assume that the isotope mixtures are a constant.
Wrong assumption (Score:2)
The earth was so properly blended when it was made that it's safe to assume that the isotope mixtures are a constant.
Your assumption is actually wrong and that's why the values are updated. For instance, if you get a metal, from different mines around the world, the relative abundances of each of the isotopes vary slightly and this leads to different atomic weights for the same metal. This is why the atomic weights are updated. You can read about it in wikipedia [wikipedia.org].
Indeed, this won't matter much (even for a chemist), but this is not a problem just for intergalactic engineers (and please do remember the fact that it is the In
Holy crap (Score:2)
Next they'll be telling us their weight depends on their energy too.
Proper summary: (Score:2)
Elements have isotopes, different isotopes have different atomic weights, the proportion of isotopes present differs from sample to sample, the standard periodic table reports an average atomic weight that may or may not be appropriate to the sample you're considering at the moment. Way to report the scientific news of 70 years ago.
Location of nuke material (Score:2)
Hasnt this always been known that even different mines from the same countries produce isotope "fingerprints" that let the 3 letter agencies identify where nuke material come from? This is simply making it more obvious to those who use the reference for the range of values found so far ?
The consequences for Carbon Dating... (Score:1, Insightful)
...are that it's proved to be a completely inappropriate way of measuring the age of a sample, particularly for older samples.
In fact for any sample over 2000 years old the errors are absolute.
So in fact, this is big, big news.
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We know that the isotope concentration of C14 changes in the atmosphere, and we think we know why. That's why the dates are calibrated against other ways of estimation (dendrochronology, ice cores, varves, etc). We also know that C14 is not uniformly distributed because there are carbon sinks (oceans, rivers from ice melt, etc.), so that is taken into account as well. The referenced paper has no bearing on this at all, and radioca
Re:The consequences for Carbon Dating... (Score:4, Informative)
...are that it's proved to be a completely inappropriate way of measuring the age of a sample, particularly for older samples.
In fact for any sample over 2000 years old the errors are absolute.
So in fact, this is big, big news.
I'd be curious to see where it's been "proved" to be an inappropriate way of age measuring, since carbon-14 dating closely correlates with tree ring data [wikipedia.org] out to 26,000 years back, using the INTCAL04 data group, which is internationally recognized as valid, and likewise it correlates well with deep ocean sediments, coral, cave rock formations, and other sources [wikipedia.org], all of which give similar age data to radiocarbon dating, which is currently using the INTCAL09 data for correction, that is internationally recognized as valid out to 50,000 years [qub.ac.uk]. So, if there's a problem with radiocarbon dating, the same problem is also affecting how fast sediments accumulate, coral grow, and stalactites form, and I've never heard of anyone suggesting anything that can affect all those, at the same time, and alter them all in a proportional manner. If you've any suggestions for something that could do that, I'd love to hear about it.
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Keep guessing, coward.
Not that surprising (Score:2)
In other news (Score:2)
This sounded like it might be a fundamental change in something big, but it isn't. As many have already said, anyone with a passing knowledge of chemistry - even misremembered over 19 years like mine - is aware of the underlying reasons and the implications!
It's presented as sensational but it's really not news in any way, shape or form.
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The pope has been found to be catholic, birds fly, fish swim and bears defecate in woods.
quote>
While I don't know about the pope, but there's birds that swim, fish that fly, bears that defecate outside the woods and other things that defecate in the woods...
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The pope has been found to be catholic, birds fly, fish swim and bears defecate in woods.
I'm an ostrich you insensitive clod.
Weight vs mass (Score:2)
Reality? (Score:1)
"People are probably comfortable with having a single value for the atomic weight, but that is not the reality for our natural world"
They didn't consult Karl Rove [wikipedia.org] for this, did they?
Somehow this make sense (Score:2)
Trying to discuss theoretical physics with a skilled theoretical physicist is like playing card with someone who plays by changing the rules when they are losing. So long as you're not betting much on it, what the heck. And when they go all in, well, we know they must not be playing with their own money.
Time for a new periodic table! (Score:2)
You heathens just keep screwing things up worse and worse. Everybody knows that there is only one true periodic table: Fire Earth Air Water [jumbojoke.com]
This has been known since 1972 (Score:1)
Not News (Score:2)
WORST TFA EVVAR! (Score:2)
I feel dumber for having clicked that link:
Newfoundland comedian wha?
Bane of high school students everywhere huh?
Stupid jokey crap that never ends?!
Shit, if I want god-knows-how-many-paragraphs of lead-in followed by a bunch of handwavy bullshit seemingly intended for people that enjoy feeling smart without having to think or understand things, I'd get a subscription to People magazine.
While the underlying news is definitely for nerds, THIS was not the link we're looking for.
Score one for general semantics (Score:1)
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*cough* speed of light/red shift *cough*
(I know it's not apparent, but I'm not disagreeing... but I'm totally expecting to be jumped by a million and a half people claiming how ignorant I am for defying conventional physics theory.)
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Okay yes constants, but as you know this is only known really well for our light cone and epoch, and even then many caveats.. speed of light changes when traveling through different substances / states of matter. Red shift changes depending on gravitational potential relative to the source, or to expanding spacetime, etc. as wikipedia tells us..
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Where can I find a perfect vacuum? Nowhere. So never in the universe is light traveling at exactly c - there are always tiny variations. So yeah, in practice, it's not really a constant.
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Photons, like any other massless particle, always travel at exactly c. It is a constant.
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You mean just like atomic weight is a constant?
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This article isn't about atomic weights changing. It's about estimates of isotopic ratios found in nature changing.
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Re:Natural constants? (Score:5, Insightful)
I don't think there are any constants in nature.
We humans just like to perceive them as such, so it makes our calculations a whole lot easier.
Also, those same calculations show that some things, like proton mass, speed of light, gravitational constant, a couple others, have to have remained constant within a very large number of decimal places in order for old stuff to have changed the same way new stuff changes. More decimal places that we usually have sig figs to measure stuff, so by sig figs rules, have to treat them as constant, its not just an "easier" thing.
For your average chemical engineer bucket chemist, small changes in atomic weight are going to be statistical noise.
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I don't think there are any constants in nature.
Pi would like a word with you.