With , what is the most recent date which can be accurately determined, and why?   Is there an accepted time range, within which, accurate results can be attained using carbon-14 dating? I understand that the method can provide dating up to ca. 50,000 years into the past, but I'm interested in the other end of the time range: is there a point in time when younger (recent) specimens can no longer be dated with accepted accuracy?   I have read sources that place this limit anywhere between 50 and 500 years. I have read that this difficulty in the young-sample range is due to the fact that not enough material has been depleted to calculate accurately. I also understand the concerns with carbon-14 dating regarding the impact of fossil fuels / atomic activity in recent dating attempts. I also am aware of new carbon contamination when sampling.  I am a paintings conservator and have been requested to examine a panel painting from approximately 1550 A.D., and I have  evidence which supports this date. Would a carbon-14 analysis be of equal accuracy in this case?
124154
A friend and I recently discussed the idea that radioactive decay rates are constant over geological times, something upon which dating methods are based.  A large number of experiments seem to have shown that decay rate is largely uninfluenced by the environment (temperature, solar activity, etc.). But how do we know that decay rates are constant over billions of years? What if some property of the universe has remained the same over the one hundred years since radioactivity was discovered and measured, but was different one billion years ago?  An unsourced statement on the Wikipedia page on radioactive decay reads:     [A]strophysical observations of the luminosity decays of distant   supernovae (which occurred far away so the light has taken a great   deal of time to reach us) strongly indicate that   unperturbed decay rates have been constant.   Is this true?  I'm interested in verifying constancy of decay rates over very long periods of time (millions and billions of years). Specifically, I'm not interested in radiocarbon dating or other methods for dating things in the thousands-of-years range. Radiocarbon dates, used for dating organic material younger than 50,000 years, are  and crossed-checked with non-radioactive data  of millennial trees and similarly countable yearly deposits in marine , a method of verification that I find convincing and that I am here not challenging.
113904
I've been seeing arguments of this form for awhile:   (agreed true premise) Some predicate P was applicable to behavior/event/thing A in the past. Variations: P(A) may have been true at some particular past time t, or over all past time T. (fallacious consequence) Therefore P(A) is true now. Variations: P(A) must be true now and all futures.   But I haven't known what to call them (e.g., when "calling out" their utterers). The problem seems to me to be due to ignoring (empirical) context and quantity (but has nothing to do with logical quantification). Some examples:   Mass immigration was "good for America" in its (past) history. Therefore mass immigration must be "good for America" now. (P=good for America, A=mass immigration) (even more logically problematic) Humans have been burning fossil fuels for centuries, and "there was no crisis then." Therefore, to claim that fossil fuel combustion is "a crisis now, one must believe that we've been in crisis for centuries." (P=not crisis-producing, A=fossil fuel combustion)   Does this fallacy (or cognitive bias, but this failure "feels logical" to me--ICBW) have a widely-accepted name? Given the extensive and systematic attention to logic and rhetoric over millenia, I suspect this has been previously taxonomized.
97189
I'm having a discussion with someone. I said that it is -even theoretically- impossible to reach $0$ K, because that would imply that all molecules in the substance would stand perfectly still.  He said that this isn't true, because my theory violates energy-time uncertainty principle. He also told me to look up the Schrödinger equation and solve it for an oscillator approximating a molecule. See that it's lowest energy state is still non-zero.  Is he right in saying this and if so, can you explain me a bit better what he is talking about.
55408
I think I know the answer to this, but I'm not sure, and it's a good question, so I'll ask:  What is the accepted/proper way to correct a mistake made on a check?  For instance, I imagine that in any given January, some people accidentally date a check in the previous year.  Is there a way to correct such a mistake, or must a check be voided (and wasted)?  Pointers to definitive information (U.S., Canada, and elsewhere) are helpful.
70199
It is on the need of accuracy assessment of classification product.  Land cover/use classification is a prominent analysis in remote sensing. Now the question is if I generate a landcover from LANDSAT, do not perform ground survey for cross-checking and want to do a scientific analysis with this classification, is it scientifically invalid?  If I do this cross-checking with some very high-resolution image (5m) and Google Earth, is it robust method to fit scientific standards, if yes then how much.  Now my question is can anyone list some articles link that used their research based on un-ground-truthed image classification data or at least guide me on how to find those type of article    By ground survey, I mean field survey in body with some instruments like dgps, densitometer etc.  I asked  that has some tone matches with this question but still feeling unhelped. I emailed Mr. Hansen about a month ago but no response yet.
70792
Take as an example the well-known . In the original paper, the regression model was used to model the amount people were willing to pay for improved air quality.  But the 'people' whose behaviour was being modelled was never specified. Presumably, it was not limited to 'residents of Greater Boston'. Only implausibly would it be 'humans anywhere on the planet'. Nor, 'all US residents'.   So what inference are we invited by the authors to draw about the scope they intend for their theory? Perhaps 'all residents of large US metro areas'. But - what about other First World metro areas? The first two sections of the Boston paper scrupulously avoid any reference which might suggest that they had a particular 'population' to which their 'sample' was to apply.  There is also the dimension of time - the data came from the 70s, whereas the theory is has no time limitations spelt out.  Plus - going back to first principles - how could the Boston data be treated as a sample of a population including, say, the Chicago metro area when no data from the Chicago area was considered?   Besides, lots of the covariates in the Boston regression weren't samples at all, but totals - so, for example, the proportion of blacks was supplied from census stats.  My question: how can we conceive the Boston data as supporting the geographically unlimited propositions in the paper? Is there a mathematical way of showing equivalence or approximation of the Boston data analysis to other cities? Or is it just assumed as a matter of common sense - such that the paper's authors would be amazed to think anyone could have any doubts on the matter?
45818
In , temperatures of millions of degrees (Celsius, Kelvin, it doesn't really matter at that point) are mentioned. But, what does it mean exactly? What is measured, and how? As I more or less expected,  the  mentions that the official definition  (the one I was told in elementary school, either between freezing and boiling points of water for Celsius, or between absolute zero and triple point of water for Kelvin) doesn't really work above 1300K. So, questions:   For &quot;earthly temperatures&quot;, how is temperature measured consistently? Why would linearity of the measuring device be assumed, in particular to extrapolate beyond the initial (0-100, or 0-273.16) range? What guarantees that two thermometers, working under different principles (say, mercury and electricity), that agree at 0C and 100C, will agree at 50C?  What do statements like &quot;the temperature in the Sun's core is $1.5\times10^7K$ mean? Or, even, what do the &quot;7000K&quot; in the Earth's core mean?
2451
What minimum half-life an isotope should have to be considered stable?
97254
As short as possible: From what I understand the Cosmic Microwave Background was predicted by multiple people as a theoretical consequence of the Big Bang theory, and hence today, is evidence for the Big Bang. So of course there was also a prediction of the age of the CMB, because it was predicted to have occurred at a certain point in time.  Now, is that the only reason cosmology dates the CMB to 13.8 billion years ago, i.e. is the dating inferred by the theory? I assume there must be many types of measurements that somehow connect to this so as to infer the exact age of what we are seeing there.
87816
If a radioactive material takes a very long time to decay, how is its half life measured or calculated? Do we have to actually observe the radioactive material for a very long time to extrapolate its half life?
68116
A friend of mine just found 3 rolls of exposed 135 (i.e. 35mm) film. They are at least 10 years old. He'd like to know if it is even worth taking them to the local hour photo lab but also if he should give them any special instructions.
50322
Carbon-14 has a half-life of 5,730 years.  That means that after 5,730 years, half of that sample decays.  After another 5,730 years, a quarter of the original sample decays (and the cycle goes on and on, and one could use virtually any radioactive isotope).  Why is this so?  Logically, shouldn't it take 2,865 years for the quarter to decay, rather than 5,730?
91496
Something's been bugging me about SO for a while now, that is the inaccuracy of "length of time" strings.  The best example I can give at the moment is .  If you look at the length of time he's been registered, it says 1 year.  He joined the site September 2008, which is only 3 months off two years.  It's the same with answers - you can give an answer 50 seconds before anyone else, but at certain times page views will show both as "5 minutes ago" or whatever.  That's not quite as bad, but with answers being sorted "randomly by votes" by default you could lose out on votes or being marked as the correct answer to the slower answer even if they're both the same.  There's probably a better method amongst these, IMO:   "Vulgar fraction" unicode characters     Member for 1½ years   answered 5¼ minutes ago asked 3⅓ hours ago  Different units   Member for 21 months (at least it's better than "1 year") Answered 306 seconds ago (ugly, I know) Asked 64 minutes ago (also ugly)  Combining units   Member for 1 year 9 months (fits easily on the profile screen) Answered 5 minutes 6 seconds ago (probably too long) Asked 3 hours 20 minutes ago (also long)  Rounding up   I personally prefer option 1, unicode fraction characters.  "Member for 21 months" is pretty good too because it's easy to quickly work out.  "Asked 452 seconds" ago is horrible though.  EDIT: I'm completely aware of the timestamp hover because I am forced into using it so much. It's a great feature, but it's not really in your face so not everyone knows about it. I still think there's a better "glancing" solution than having to hover over the time string.
22155
Is there any way to predict the half-lives of radioactive isotopes from theory (that is, using only theoretical considerations, without using data about the decay)? For example, could we predict that the half life of Carbon-14 is roughly 5700 years?
75961
I have an ancestor for whom I have very little information for.  I am trying to identify the exact birth date for this person.  I have a death certificate which lists the birth date as "May 1st", however the gravestone for this person lists "May 4".  I am certain that the numbers were readable, so there is definitely a discrepancy in the dates.  Which record should be trusted more?  I know that the family supplies the date for both the death certificate and the gravestone, however I would suggest the family would be more concerned that it be correct on the gravestone, as the death certificate might be created in haste.  Is there general guidance for this?  For those who may be curious, attached below are the records.  I missed it before, but the year of the birthdate is actually different by 1 as well. (1962 on the gravestone and 1961 on the death certificate)  I am actually more concerned about the year than the actual date, of course.
64325
So, as I understand it, in a substance that is made of radioactive elements, the half-life tells us how long until the half of those atoms decay into their next atom [is there a name for that: the element or isotope that is the result of a prior radioactive decay?]. My question is, is there some sort of pattern to which atoms decay at which time, or is it some miraculous property of quantum mechanics that somehow each atom knows when to decay? or do I just understand radioactive decay incorrectly?   Are the particles entangled or in some otherway attached (aside from their molecular bonds)? If there is no known answers, I would prefer any serious, leading theories.
108658
13.2 billion years ago the universe was rather small, having started only half a billion years ago. Today, with the help of Hubble Space Telescope, we are able to capture the light of galaxies emitted at that time.  The point at which Earth exists now must have been quite close to those galaxies back then. If so, why is it that it is only now, after 13.2 billion years later the light from those galaxies has reached us? Or in other words, are we sure that the light we are seeing from those galaxies indeed travelled for 13.2 billion years?  It looks like as if there was a race between our point running away from those galaxies (with the expansion of universe and space) and the light that was emitted at that time. And only now that light has reached and overtaken us. But if that is so, then wouldn't it put a limit on the oldest light we can see, no matter how powerful the telescope is (even it is more powerful than the James Webb Space Telescope)? This should be expected, because at the time just after the Big Bang, the light emitted by all objects must have already overtaken all other objects, including the location of earth. Therefore we will never see the light that old (close to the time of Big Bang) no matter how powerful the telescope. If this is so, what is the theoretical limit we can see far back in the past?