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Hi everybody !
I don't understand the formula on the page about the proper distance along a path P :
where gμν is the metric tensor, and dxμ is the coordinate separation between neighboring events along the path P.
To me, it seems that this is the square root of an interval which already has the dimension of a lenght. So I don't understand the factor in front of the integral. Where am I wrong ?
Thanks for your reply (
DVdm ?).
Observateur01 (
talk) 16:14, 13 February 2019 (UTC)
I've been wondering, for years, if the Southern Hemisphere ever had the kind of boreal forest/taiga present across large swathes of the Southern Hemisphere, like Canada, Russia, and Scandinavia. The closest things that I have found in doing some research, is that there are some alpine forests consisting of Eucalyptus in Australia, some Nothofagus species in New Zealand and southern South America (Chile and Argentina), and a lowland type of "sub polar" forest in Patagonia and Tierra del Fuego consisting of a few NOthofagus species. However, none of these are coniferous proper boreal forests. Digging into research done into the last tree species and forest types in Antarctica itself, I've found that several million years ago, before the continent turned completely to ice, the last forest consisted of scraggly, low growing Nothofagus trees and Podocarpus. However, still no evidence that there was actual boreal forest in the Southern Hemisphere, only ecosystems roughly approximating a boreal forest in the conditions that were present. I ask this question because, I believe, Antarctica itself once had the climatic conditions equivalent to where boreal forests grow today, and presently the alpine environments of New Zealand and southern South America have the right climate to support an alpine conifer forest equivalent to the alpine conifer forests of the northern hemisphere. So we can rule out that climate isn't necessarily an issue, but the right flora to constitute a cold climate conifer forest in the southern hemisphere is instead what is lacking. Thanks in advance if you can point me in the right direction! — Preceding unsigned comment added by 2600:1702:4000:5D40:F446:7F82:C6A9:B110 ( talk) 16:45, 13 February 2019 (UTC)
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The above discussion is very interesting and I particularly enjoyed @ Dragons flight:'s response and would love to see a link to the thought experiment @ Count Iblis: mentioned, but we need a new topic, having strayed too far from the old one. What I'm wondering is whether there have been proposals for any device capable of mapping the source of a wave function collapse. Warning: the following probably contains dozens of grievous errors...
For example, I'm daydreaming of a rudimentary quantum computer that takes a |0> state, implements the Hadamard quantum logic gate (turns it to a 50-50 superposition), then "measures" the result in a way that is questionably a measurement, before doing another Hadamard operation and seeing if the result is reliably 1. What I want is a "measurement" that stores the result in a pair of entangled photons of opposite circular polarization, so that if they both impinge on the same target at the same time, the angular momentum cancels out, the information is lost and no "measurement" occurs ... I think. If they strike near each other then maybe no information is retained?
I'm not sure if this would violate the no-cloning theorem. The photons would have probability according to the quantum state, however it would be according to the real number probability only, not the complex value of the state, so I'm thinking not. Yet if it were permissible, would it permit backward communication in time, since who knows if the photons' data will be lost? (The processor counting the |1>'s...) But if it doesn't work then why not, what are the limits? What makes a measurement a measurement? Wnt ( talk) 23:58, 13 February 2019 (UTC)
Web searches on "speed of decoherence" might cast some light (or more confusion) on this question. 173.228.123.166 ( talk) 09:43, 19 February 2019 (UTC)
Science desk | ||
---|---|---|
< February 12 | << Jan | February | Mar >> | February 14 > |
Welcome to the Wikipedia Science Reference Desk Archives |
---|
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages. |
Hi everybody !
I don't understand the formula on the page about the proper distance along a path P :
where gμν is the metric tensor, and dxμ is the coordinate separation between neighboring events along the path P.
To me, it seems that this is the square root of an interval which already has the dimension of a lenght. So I don't understand the factor in front of the integral. Where am I wrong ?
Thanks for your reply (
DVdm ?).
Observateur01 (
talk) 16:14, 13 February 2019 (UTC)
I've been wondering, for years, if the Southern Hemisphere ever had the kind of boreal forest/taiga present across large swathes of the Southern Hemisphere, like Canada, Russia, and Scandinavia. The closest things that I have found in doing some research, is that there are some alpine forests consisting of Eucalyptus in Australia, some Nothofagus species in New Zealand and southern South America (Chile and Argentina), and a lowland type of "sub polar" forest in Patagonia and Tierra del Fuego consisting of a few NOthofagus species. However, none of these are coniferous proper boreal forests. Digging into research done into the last tree species and forest types in Antarctica itself, I've found that several million years ago, before the continent turned completely to ice, the last forest consisted of scraggly, low growing Nothofagus trees and Podocarpus. However, still no evidence that there was actual boreal forest in the Southern Hemisphere, only ecosystems roughly approximating a boreal forest in the conditions that were present. I ask this question because, I believe, Antarctica itself once had the climatic conditions equivalent to where boreal forests grow today, and presently the alpine environments of New Zealand and southern South America have the right climate to support an alpine conifer forest equivalent to the alpine conifer forests of the northern hemisphere. So we can rule out that climate isn't necessarily an issue, but the right flora to constitute a cold climate conifer forest in the southern hemisphere is instead what is lacking. Thanks in advance if you can point me in the right direction! — Preceding unsigned comment added by 2600:1702:4000:5D40:F446:7F82:C6A9:B110 ( talk) 16:45, 13 February 2019 (UTC)
|
|
The above discussion is very interesting and I particularly enjoyed @ Dragons flight:'s response and would love to see a link to the thought experiment @ Count Iblis: mentioned, but we need a new topic, having strayed too far from the old one. What I'm wondering is whether there have been proposals for any device capable of mapping the source of a wave function collapse. Warning: the following probably contains dozens of grievous errors...
For example, I'm daydreaming of a rudimentary quantum computer that takes a |0> state, implements the Hadamard quantum logic gate (turns it to a 50-50 superposition), then "measures" the result in a way that is questionably a measurement, before doing another Hadamard operation and seeing if the result is reliably 1. What I want is a "measurement" that stores the result in a pair of entangled photons of opposite circular polarization, so that if they both impinge on the same target at the same time, the angular momentum cancels out, the information is lost and no "measurement" occurs ... I think. If they strike near each other then maybe no information is retained?
I'm not sure if this would violate the no-cloning theorem. The photons would have probability according to the quantum state, however it would be according to the real number probability only, not the complex value of the state, so I'm thinking not. Yet if it were permissible, would it permit backward communication in time, since who knows if the photons' data will be lost? (The processor counting the |1>'s...) But if it doesn't work then why not, what are the limits? What makes a measurement a measurement? Wnt ( talk) 23:58, 13 February 2019 (UTC)
Web searches on "speed of decoherence" might cast some light (or more confusion) on this question. 173.228.123.166 ( talk) 09:43, 19 February 2019 (UTC)