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Such short news he brought them, too! "It's 5σ at .2" His wife, also a theoretical physicist - blank stare "Discovery?" - immediately melts into a hug. What

by skore 13y ago

Such short news he brought them, too! "It's 5σ at .2" His wife, also a theoretical physicist - blank stare "Discovery?" - immediately melts into a hug. What a great thing, to be able to see the human side, makes you all warm and fuzzy for human progress.

eranation 13y ago
Any chance a non physicist / scientist can understand in a nutshell what it means? (5σ at .2) it has been a long time since college. Is that a statistical notation? or something specific to physics? Googling it (or even using symbolhound) didn't render good results for me.
- tshadwell 13y ago
  https://en.wikipedia.org/wiki/Uncertainty#Measurements https://en.wikipedia.org/wiki/Uncertainty#Measurements "When the uncertainty represents the standard error of the measurement, then about 68.2% of the time, the true value of the measured quantity falls within the stated uncertainty range. For example, it is likely that for 31.8% of the atomic mass values given on the list of elements by atomic mass, the true value lies outside of the stated range. If the width of the interval is doubled, then probably only 4.6% of the true values lie outside the doubled interval, and if the width is tripled, probably only 0.3% lie outside. These values follow from the properties of the normal distribution, and they apply only if the measurement process produces normally distributed errors. In that case, the quoted standard errors are easily converted to 68.3% ("one sigma"), 95.4% ("two sigma"), or 99.7% ("three sigma") confidence intervals."
- sorenvrist 13y ago
  http://en.wikipedia.org/wiki/Standard_deviation#cite_ref-4 http://en.wikipedia.org/wiki/Standard_deviation#cite_ref-4 "Particle physics uses a standard of "5 sigma" for the declaration of a discovery. At five-sigma there is only one chance in nearly two million that a random fluctuation would yield the result. This level of certainty prompted the announcement that a particle consistent with the Higgs boson has been discovered in two independent experiments at CERN."
- wpears 13y ago
  r is a model parameter that affects the strength of gravity waves. r=0.2 was much higher than expected. See http://www.reddit.com/r/science/comments/20mrz4/cosmic_inflation_spectacular_discovery_hailed/cg4u10g http://www.reddit.com/r/science/comments/20mrz4/cosmic_infla...
- lutusp 13y ago
  Each experimental outcome has an associated probability that the outcome resulted from chance, not the thing being measured. This arises from the default scientific precept that is called the "null hypothesis", the assumption that a given measurement was produced by chance, not nature. Scientists use a value designated by p to describe the probability that a result arose by chance rather than design. In the social sciences, a p value of 0.01 - 0.05 is common, which means a result can be explained by chance with a 1% to 5% probability. As one moves through fields of greater rigor and seriousness, the p value required to declare a discovery becomes smaller. In experimental physics, 5σ (five sigma) has become the standard. In statistics, σ refers to an area under the normal distribution defined in terms of standard deviations (1σ = 1 standard deviation). Experimental physics uses a one-tailed 5σ value, which is quite strict -- it has a numerical value of about 3×10-7. What this means is that an experimental result must be solid enough (and/or be repeated often enough) that the probability that it arose from chance is equal to or less than 5σ. More here: http://blogs.scientificamerican.com/observations/2012/07/17/five-sigmawhats-that/ http://blogs.scientificamerican.com/observations/2012/07/17/...
  - graycat 13y ago
    > In statistics, σ refers to an area under the normal distribution defined in terms of standard deviations (1σ = 1 standard deviation). No. The Gaussian (normal distribution) is not involved. Sigma is just the symbol for standard deviation, that is, the square root of the variance. So, for random variable X where with expectation E[X] that exists and is finite (in practice a weak assumption), the standard deviation is square root of E[(X - E[X])^2]. So, the standard deviation is just a number, a measure of how 'spread out' the distribution is, and not an "area". Then 5σ is just 5 times the standard deviation.
    - sigterm 13y ago
      Are you sure? I'm pretty confident in this case the assumption is that the distribution is normal. With no knowledge of the shape of distribution, the 5 sigma bound is extremely weak (one given by Chebyshev's inequality [0], in this case, ~4%). Prove me wrong though, as I'm not a physicist or mathematician. [0] http://en.wikipedia.org/wiki/Chebyshev's_inequality#Sharpness_of_bounds http://en.wikipedia.org/wiki/Chebyshev's_inequality#Sharpnes...
- ngoldbaum 13y ago
  They measured the tensor-to-scalar ratio of the inflation field, r, to be nonzero at 5 sigma significance. The measured value is 0.2.

by skore 13y ago

eranation 13y ago

Any chance a non physicist / scientist can understand in a nutshell what it means? (5σ at .2) it has been a long time since college. Is that a statistical notation? or something specific to physics? Googling it (or even using symbolhound) didn't render good results for me.

tshadwell 13y ago
https://en.wikipedia.org/wiki/Uncertainty#Measurements https://en.wikipedia.org/wiki/Uncertainty#Measurements "When the uncertainty represents the standard error of the measurement, then about 68.2% of the time, the true value of the measured quantity falls within the stated uncertainty range. For example, it is likely that for 31.8% of the atomic mass values given on the list of elements by atomic mass, the true value lies outside of the stated range. If the width of the interval is doubled, then probably only 4.6% of the true values lie outside the doubled interval, and if the width is tripled, probably only 0.3% lie outside. These values follow from the properties of the normal distribution, and they apply only if the measurement process produces normally distributed errors. In that case, the quoted standard errors are easily converted to 68.3% ("one sigma"), 95.4% ("two sigma"), or 99.7% ("three sigma") confidence intervals."
sorenvrist 13y ago
http://en.wikipedia.org/wiki/Standard_deviation#cite_ref-4 http://en.wikipedia.org/wiki/Standard_deviation#cite_ref-4 "Particle physics uses a standard of "5 sigma" for the declaration of a discovery. At five-sigma there is only one chance in nearly two million that a random fluctuation would yield the result. This level of certainty prompted the announcement that a particle consistent with the Higgs boson has been discovered in two independent experiments at CERN."
wpears 13y ago
r is a model parameter that affects the strength of gravity waves. r=0.2 was much higher than expected. See http://www.reddit.com/r/science/comments/20mrz4/cosmic_inflation_spectacular_discovery_hailed/cg4u10g http://www.reddit.com/r/science/comments/20mrz4/cosmic_infla...
lutusp 13y ago
Each experimental outcome has an associated probability that the outcome resulted from chance, not the thing being measured. This arises from the default scientific precept that is called the "null hypothesis", the assumption that a given measurement was produced by chance, not nature. Scientists use a value designated by p to describe the probability that a result arose by chance rather than design. In the social sciences, a p value of 0.01 - 0.05 is common, which means a result can be explained by chance with a 1% to 5% probability. As one moves through fields of greater rigor and seriousness, the p value required to declare a discovery becomes smaller. In experimental physics, 5σ (five sigma) has become the standard. In statistics, σ refers to an area under the normal distribution defined in terms of standard deviations (1σ = 1 standard deviation). Experimental physics uses a one-tailed 5σ value, which is quite strict -- it has a numerical value of about 3×10-7. What this means is that an experimental result must be solid enough (and/or be repeated often enough) that the probability that it arose from chance is equal to or less than 5σ. More here: http://blogs.scientificamerican.com/observations/2012/07/17/five-sigmawhats-that/ http://blogs.scientificamerican.com/observations/2012/07/17/...
- graycat 13y ago
  > In statistics, σ refers to an area under the normal distribution defined in terms of standard deviations (1σ = 1 standard deviation). No. The Gaussian (normal distribution) is not involved. Sigma is just the symbol for standard deviation, that is, the square root of the variance. So, for random variable X where with expectation E[X] that exists and is finite (in practice a weak assumption), the standard deviation is square root of E[(X - E[X])^2]. So, the standard deviation is just a number, a measure of how 'spread out' the distribution is, and not an "area". Then 5σ is just 5 times the standard deviation.
  - sigterm 13y ago
    Are you sure? I'm pretty confident in this case the assumption is that the distribution is normal. With no knowledge of the shape of distribution, the 5 sigma bound is extremely weak (one given by Chebyshev's inequality [0], in this case, ~4%). Prove me wrong though, as I'm not a physicist or mathematician. [0] http://en.wikipedia.org/wiki/Chebyshev's_inequality#Sharpness_of_bounds http://en.wikipedia.org/wiki/Chebyshev's_inequality#Sharpnes...
ngoldbaum 13y ago
They measured the tensor-to-scalar ratio of the inflation field, r, to be nonzero at 5 sigma significance. The measured value is 0.2.