I'm still holding out for 1-way glass/mirrors that actually WORK AS EXPECTED. An ex-gf's father, who is an architect, told me about this super-modern house in the town where he studied that was clad with one-way mirrors. However, after dark, the inside lights would turn them quite see-through. Favourite hang-out for students was by the bedroom wall, no x-ray glasses needed.
I said something similar to my undergrad physics advisor while working in experimental optics. He said that "true" one-way glass would probably break the laws of thermodynamics. Imagine a box filled with light, and split it in half with a pane of one-way glass. One side would become dark and the other would become twice as bright. It would have to act like Maxwell's demon, which isn't physically possible without energy input.
All "one-way mirrors" in the world are actually just windows with partial mirroring in both directions. The "one-way" part is determined entirely by which side has brighter ambient light. That's why interrogation rooms have bright lights, whereas the viewing room for cops and witnesses is usually very dimly lit.
Oops. That first paragraph should end like this.... directly under/opposite the Moon. In this case, the Moon's distance to the Earth wouldn't change with time.
ready up on it some.. the moon's moving away from us is the transfer of energy from the rotation of the earth slowing down into potential energy of the moon in earths gravity well. if we are to siphon off energy some/all/maybe more.. then we would be slowing/stopping/reversing the moon's accent from earth
No, he's right. Consider an Earth that's a perfect, frictionless sphere covered in a superfluid ocean. This idealized scenario has no friction, and the resulting tidal bulges would be directly under/opposite the Moon.
In reality, the coastlines and bathymetry of the liquid water oceans exert a drag on the tidal bulge. Because the Earth spins in the same direction as the Moon orbits, the tidal bulge is dragged ahead of the Moon. This asymmetry exerts a torque on the Moon which speeds it up and thus moves the Moon away from the Earth. This drag also slows down the Earth's rotation which preserves conservation of energy, as you correctly say.
But harnessing tidal energy is equivalent to increasing drag on the tidal bulge, which will imperceptibly move the tidal bulges farther away from the line connecting the Earth and Moon. This will increase the torque on the Moon and hasten its rise, exactly as PMBjornerud said.
PE = m x g x h ; m = 7.3477 × 10^22 kg ; g = 9.8 m/s2 ; h = 363,104,000 m
No. PE=m*g*h is only an approximation to be used when g is approximately constant. This is useful if you're puttering around on the surface of the earth where g really IS 9.8 m/s^2, but you're applying it to a situation where g changes enormously. Try PE = -Gm1m2/r instead.
Because I understand the need for initial condition ensembles, tend to agree with Nature's response to that tabloid nonsense, and have noted the decrease in stratospheric water vapor since 2000 (all these points have already been explained in that link).
It is a little know fact that, given the uncertainties of what is happening in our climate system, the warming seen over the last few decades is entirely attributable to the reduction in aerosols in recent years. This is mentioned in WGI chapter 2 of the IPCC report. Of course, that fact didn't make it into the "Summary for Policy Makers." In fairness I should mention that the chances of the temperature change being entirely attributable to the change in aerosols is actually quite low, but it's still something worth considering.
Yeah, it's odd that an ~18 page summary for nonscientists doesn't include all the nuances in a ~1000 page report filled with scientific jargon.
The summary's forcing chart clearly shows a huge, lopsided error bar on the cloud albedo effect, and lists the Level Of Scientific Understanding as "low". This is a copy of figure 2.20 on page 203 of chapter 2. In both charts, notice that the CO2 forcing is very large and known far more precisely.
The particular statement you found, that "the warming seen over the last few decades is entirely attributable to the reduction in aerosols in recent years" isn't something I've seen in chapter 2. The bottom panel of figure 2.22 on page 206 seems like the closest match to your statement, but it's a projection based on emissions over 20 years in the future. Could you specify the page number where you found your statement?
I'll note that your claim isn't necessarily contradicted by figure 2.20 because that's the radiative forcing integrated from 1750-2005, whereas you're referring to something like 1985-2005... right?
Dear Science Community... after arguing myself blue in the face with my right-wing relatives that environmentalism transcends politics and just because I like clean air and a healthy earth, doesn't make me a commie, publishing a single report that wildly contradict previous findings makes it practically impossible to defend you.... Simply leaving the conclusion of the report at "Sorry guys, you know how we told you that we were all going to die if we don't outlaw sulfate aerosols? Yeah, well, we were wrong, and it turns out now we're really fucked up" is just like throwing handfuls of painkillers at Rush Limbaugh's mouth.
Dear BonquiquiShiquavius,
The LA Times and NPR aren't part of the scientific community. They reported on a book written by Eli Kintisch who is a journalist who writes about science. Also not really part of the scientific community.
I don't think geoengineering is a viable solution, so I don't care to read Kintisch's book. But in the article he seems to be repeating the well known facts that aerosols cool Earth's surface and have a shorter lifetime in the atmosphere than CO2. This doesn't "wildly contradict previous findings"-- I've been explaining for years that these nuances are described in detail by the IPCC AR4 WG1 report.
Yes, I agree. But there are many people who won't want to live like that, and even I would want to keep backups of Earth's biosphere (for nostalgia or the possibility that we still have things to learn from studying it). So biological life probably isn't going away. I tend to agree with Greg Egan when he suggests that this diversity within each species is greater than the differences between species. That is, each species likely has some members (individuals, or sub-hive minds, or whatever) who are willing to download into a computer, and some who wish to live in their ancestral forms.
The fact is, though, that making giant tin-cans in the sky is more expensive than finding viable hunks of rock with usable resourses already present.... It really all comes down to value. The value of a cylinder, more or less, is just habitable space. The value of a planet includes large volumes of otherwise rare elements or chemicals, biological materials, etc... all conveniently sitting there for the taking, and all of which would be needed to make cylinders anyway.
Rare elements on planets aren't conveniently placed; they're at the bottom of a gravity well. For this reason, elements in asteroids are more easily exploited by any civilization with sufficient experience in spaceflight. It's cheaper for us to mine the dirt under our feet because our space program is in its infancy (so just getting to an asteroid is hard), and because ~99.999% of mined minerals are used to build devices for use at the bottom of this gravity well anyway. But any civilization with a "mature" spaceflight capability would mine asteroids in order to construct spacecraft. In addition to not being trapped in a gravity well, asteroids are already in a zero-g vacuum which is a superior environment for fabricating devices with nanometer-scale features.
Mining a planet only seems cost-effective if you're building items to be used on that planet, or unless it has elements which aren't found in asteroids. Planets are useful heat sinks, though. Industrial processes that generate a lot of heat would benefit from being able to dump that heat into a planet rather than building liquid droplet radiators which seem like the most efficient theoretical radiators at the moment.
Spending some hundred years taking out all major forms of life and terraforming it to spec hardly seems impossible or unreasonable for an alien race of sufficient technological capability.
It seems like an alien race with "sufficient technological capability" that evolved on a terrestrial planet would probably prefer to build swarms of O'Neill cylinders rather than nuking and terraforming terrestrial planets. Consider that:
Building O'Neill cylinders could provide living space even in star systems without planets in the habitable zone.
Materials science appears to allow cylinders several kilometers in diameter to rotate fast enough to impart 1g of "apparent" gravity. Rotational effects are indistinguishable at these large radii, so life inside a cylinder could be made nearly identical to life on the surface of a terrestrial planet.
A civilization spread among 10,000 cylinders is more robust than one concentrated onto 1 (or even 10) planets.
Planets provide a certain amount of surface area for a given mass. The same mass converted to cylinders would provide much more surface area. Planets are the least efficient way of using matter to provide habitable surface area, by many orders of magnitude.
A civilization on the surface of a planet is at the bottom of a gravity well which is expensive and dangerous to traverse. A civilization on a network of cylinders has no such handicap, and can actually use the rotation of the cylinders to facilitate cheap travel.
Suppose the cylinders use artificial lighting powered by external solar cells. While less efficient than reflecting sunlight directly into the interior, this approach would allow cylinders to be built around red dwarfs, which don't have the right spectra to support Earth life. Considering the abundance of red dwarfs, this significantly expands the range of potential colony stars.
Nuking and terraforming a planet with life destroys invaluable sources of information about evolution and alternative forms of biology.
Nuking and terraforming a planet with intelligent life is genocide.
Sounds like the dark galaxy called VIRGOHI 21 which might have ~1000x as much dark matter as visible matter (compare to ~10-20x for the Milky Way's ratio).
... Everyone seems to be skipping step 2, especially when professing to "believe" in evolution and what that supposedly means (you know the "evolution means jesus doesn't exist, but has nothing to do with children or death" crowd. Hell I've actually heard one person claim that genes were unfair and that "therefore" evolution cannot have anything to do with genes. Although I must agree with the part that genes are VERY unfair things indeed)
No, I don't know that crowd. Are there any links showing this crowd's arguments?
I simply asked you a polite question.... a simple question is a "nonsensical outburst"? That's interesting. I wonder how you would judge an actual rant....
No, you didn't "simply ask a polite question." You went on a rude, nonsensical rant. Let's review:
This comment is similar to all the other crackpots in this thread who dispute modern physics which clearly shows that some amount of somekind of dark matter exists.
Abcd1234 clearly assumed you were expressing support for MOND, and helpfully linked impressive evidence which convinced many physicists that dark matter explains the evidence better than MOND. Then I chimed in:
... Measurements of galactic rotational velocities conflict with expected velocities based on the amount of matter observed to be present.... At this point, dark matter was simply an hypothesis. MOdified Newtonian Dynamics (MOND [umd.edu]) was another hypothesis with equal weight. But then in 2006 measurements of the Bullet Cluster supported the dark matter hypothesis over the MOND hypothesis... [Dumb Scientist, Sunday March 28, @07:57PM]
The next day:
... There are alternative theories, such as MoND, that might explain this (since it explains the apparent gravitational anomalies in spiral galaxies, it is possible that it could explain this kind of gravitational anomaly equally as well). Most "evidence" I have seen that is supposed to support the Dark Matter theory tends to also support the alternative theories.... [Jane Q. Public, Monday March 29, @12:28PM]
You present as evidence exactly the same sort of imaging techniques that were used to make the image in question? That's really lame.... You offered the wikipedia link as evidence that OP's picture is correct... yet they used exactly the same techniques (having to do with gravitational lensing) to produce the pictures. Therefore you can't use one as evidence of the veracity of the other. [Jane Q. Public]
Nonsense. You made what sounded like a general statement about dark matter "very possibly" not even existing, which implies that physicists who overwhelmingly do think it exists are either incompetent or suffering from frequent hallucinations. The only reasonable objection to dark matter was MOND, and the Bullet Cluster presented very strong evidence that seems to rule out MOND with no dark matter. It's not "exactly the same technique" as the current survey because the main point of the Bullet Clust
I finished undergrad in 2004, and my experience was similar to yours. I was being overly conciliatory to MOND because in my experience non-physicists aren't swayed by issues of elegance and simplicity.
As you say, unidentified gamma ray sources aren't relevant to the galaxy collision observations or dark energy acceleration observations in question. You've demonstrated true scientific spirit here by admitting a mistake. Kudos.
The only other person to respond to you was too harsh. Your idea is "out there" and probably wrong, but it's not obviously wrong. It's even an interesting thought experiment. The same thing occurred to me during my undergrad in 2004, and the story is here. Long story short: normal matter in parallel universes wouldn't explain the Bullet cluster observations mentioned elsewhere on this page.
Keeping stuff in separate files and including them is a good organization technique...
Why? That just means I have to open more files when I want to perform extensive maintenance on the program.
Compiling is definitely faster if you only change 1 out of 100 similarly sized files, but I've chosen to create two main source files: the first is infrequently edited and large (30k lines), while the second is edited dozens of times a day and only has 1k lines. The Makefile compiles the large file into object code which is then linked to the object code from the small file. The large file is thereafter only compiled if the revision date of the large source file is newer than the large object file. Even the compiles for the large file are just ~10 seconds on a netbook if optimization is disabled, and it's not clear that my compile times will grow faster than CPU speeds will. (Especially if parallel g++ ever gets decent.)
I suppose one could say that code segmentation helps to enforce the "few interconnections between functions" principle. (Or whatever it's formally called- the notion that functions should interact in only a few well-defined ways.) This ideal is theoretically attractive, but seems annoying to implement without allowing for occasional exceptions. I don't want to change a useful guideline to a rigid law that will probably just slow me down.
I also write code by myself, so reasons involving programming teams aren't really relevant. A good version control system like Mercurial should minimize these issues anyway.
Are there any real (i.e. productivity, scalability) reasons to abandon this approach and start putting new functions in separate files? I'm not a professional programmer, so I may have missed something that a computer science PhD would consider obvious and compelling...
Working group 2 of the IPCC seems to have made some embarrassing mistakes. Upon seeing the letter in Science, I wondered why I'd never noticed these ludicrous statements before. Then I realized that the mistakes weren't in working group 1 report, which is all I'd ever bothered to read. Here's what each working group does:
The IPCC Working Group I (WG I) assesses the physical scientific aspects of the climate system and climate change.
The main topics assessed by WG I include: changes in greenhouse gases and aerosols in the atmosphere; observed changes in air, land and ocean temperatures, rainfall, glaciers and ice sheets, oceans and sea level; historical and paleoclimatic perspective on climate change; biogeochemistry, carbon cycle, gases and aerosols; satellite data and other data; climate models; climate projections, causes and attribution of climate change.
The IPCC Working Group II (WG II) assesses the vulnerability of socio-economic and natural systems to climate change, negative and positive consequences of climate change, and options for adapting to it.
It also takes into consideration the inter-relationship between vulnerability, adaptation and sustainable development. The assessed information is considered by sectors (water resources; ecosystems; food & forests; coastal systems; industry; human health) and regions (Africa; Asia; Australia & New Zealand; Europe; Latin America; North America; Polar Regions; Small Islands).
The wild claim that "glaciers in the Himalaya are receding faster than in any other part of the world", the 2350/2035 typo, confusion of Himalayan glacier area with the worldwide total, and reliance on non-peer-reviewed source material all occurred in a single paragraph(!) in the WG2 report (section 10.6.2, paragraph 2).
Statements in the WG1 report regarding glaciers, on the other hand, accurately reflect conclusions in the peer-reviewed literature.
Due to my obsession with the physical sciences, I'd never even realized that other working group reports existed. Perhaps other scientists reacted in a similar fashion, which might be why such an absurd cluster of errors went undetected for so long...
Thanks for that comment. It inspired me to post a snippet of a similar conversation I had months ago, with your links and some others added:
Is it right, however, to lump together those who are skeptical of evolution with those who are skeptical of AGW, particularly CO2-driven AGW ?
Creationists confuse religious faith with falsifiable science. Among the general public, climate-change contrarians (and your average Greenpeace/PETA loony) confuse political affiliation with falsifiable science. In both cases, scientists are much less likely to agree with either claim, and that likelihood decreases with increasing relevance of the scientist'sfield. That's probably why both groups tend to accuse the scientific community of conspiracy and/or widespread incompetence.
At my blog, the following statement is both legible and has popup titles describing why that link was chosen. Here it is without the links first: "And, in my experience there's a significant overlap between the two groups. Most of their arguments seem to be at similar intellectual and educational levels."
Slashdot Mirror
I said something similar to my undergrad physics advisor while working in experimental optics. He said that "true" one-way glass would probably break the laws of thermodynamics. Imagine a box filled with light, and split it in half with a pane of one-way glass. One side would become dark and the other would become twice as bright. It would have to act like Maxwell's demon, which isn't physically possible without energy input.
All "one-way mirrors" in the world are actually just windows with partial mirroring in both directions. The "one-way" part is determined entirely by which side has brighter ambient light. That's why interrogation rooms have bright lights, whereas the viewing room for cops and witnesses is usually very dimly lit.
grr.. average distance
Oops. That first paragraph should end like this. ... directly under/opposite the Moon. In this case, the Moon's distance to the Earth wouldn't change with time.
No, he's right. Consider an Earth that's a perfect, frictionless sphere covered in a superfluid ocean. This idealized scenario has no friction, and the resulting tidal bulges would be directly under/opposite the Moon.
In reality, the coastlines and bathymetry of the liquid water oceans exert a drag on the tidal bulge. Because the Earth spins in the same direction as the Moon orbits, the tidal bulge is dragged ahead of the Moon. This asymmetry exerts a torque on the Moon which speeds it up and thus moves the Moon away from the Earth. This drag also slows down the Earth's rotation which preserves conservation of energy, as you correctly say.
But harnessing tidal energy is equivalent to increasing drag on the tidal bulge, which will imperceptibly move the tidal bulges farther away from the line connecting the Earth and Moon. This will increase the torque on the Moon and hasten its rise, exactly as PMBjornerud said.
No. PE=m*g*h is only an approximation to be used when g is approximately constant. This is useful if you're puttering around on the surface of the earth where g really IS 9.8 m/s^2, but you're applying it to a situation where g changes enormously. Try PE = -Gm1m2/r instead.
Because I understand the need for initial condition ensembles, tend to agree with Nature's response to that tabloid nonsense, and have noted the decrease in stratospheric water vapor since 2000 (all these points have already been explained in that link).
MOD PARENT UP!
Yeah, it's odd that an ~18 page summary for nonscientists doesn't include all the nuances in a ~1000 page report filled with scientific jargon.
The summary's forcing chart clearly shows a huge, lopsided error bar on the cloud albedo effect, and lists the Level Of Scientific Understanding as "low". This is a copy of figure 2.20 on page 203 of chapter 2. In both charts, notice that the CO2 forcing is very large and known far more precisely.
The particular statement you found, that "the warming seen over the last few decades is entirely attributable to the reduction in aerosols in recent years" isn't something I've seen in chapter 2. The bottom panel of figure 2.22 on page 206 seems like the closest match to your statement, but it's a projection based on emissions over 20 years in the future. Could you specify the page number where you found your statement?
I'll note that your claim isn't necessarily contradicted by figure 2.20 because that's the radiative forcing integrated from 1750-2005, whereas you're referring to something like 1985-2005... right?
Dear BonquiquiShiquavius,
The LA Times and NPR aren't part of the scientific community. They reported on a book written by Eli Kintisch who is a journalist who writes about science. Also not really part of the scientific community.
I don't think geoengineering is a viable solution, so I don't care to read Kintisch's book. But in the article he seems to be repeating the well known facts that aerosols cool Earth's surface and have a shorter lifetime in the atmosphere than CO2. This doesn't "wildly contradict previous findings"-- I've been explaining for years that these nuances are described in detail by the IPCC AR4 WG1 report.
Sincerely,
A dumb member of the scientific community
Yes, I agree. But there are many people who won't want to live like that, and even I would want to keep backups of Earth's biosphere (for nostalgia or the possibility that we still have things to learn from studying it). So biological life probably isn't going away. I tend to agree with Greg Egan when he suggests that this diversity within each species is greater than the differences between species. That is, each species likely has some members (individuals, or sub-hive minds, or whatever) who are willing to download into a computer, and some who wish to live in their ancestral forms.
Rare elements on planets aren't conveniently placed; they're at the bottom of a gravity well. For this reason, elements in asteroids are more easily exploited by any civilization with sufficient experience in spaceflight. It's cheaper for us to mine the dirt under our feet because our space program is in its infancy (so just getting to an asteroid is hard), and because ~99.999% of mined minerals are used to build devices for use at the bottom of this gravity well anyway. But any civilization with a "mature" spaceflight capability would mine asteroids in order to construct spacecraft. In addition to not being trapped in a gravity well, asteroids are already in a zero-g vacuum which is a superior environment for fabricating devices with nanometer-scale features.
Mining a planet only seems cost-effective if you're building items to be used on that planet, or unless it has elements which aren't found in asteroids. Planets are useful heat sinks, though. Industrial processes that generate a lot of heat would benefit from being able to dump that heat into a planet rather than building liquid droplet radiators which seem like the most efficient theoretical radiators at the moment.
It seems like an alien race with "sufficient technological capability" that evolved on a terrestrial planet would probably prefer to build swarms of O'Neill cylinders rather than nuking and terraforming terrestrial planets. Consider that:
Sounds like the dark galaxy called VIRGOHI 21 which might have ~1000x as much dark matter as visible matter (compare to ~10-20x for the Milky Way's ratio).
No, I don't know that crowd. Are there any links showing this crowd's arguments?
Ditto.
No, you didn't "simply ask a polite question." You went on a rude, nonsensical rant. Let's review:
This comment is similar to all the other crackpots in this thread who dispute modern physics which clearly shows that some amount of some kind of dark matter exists.
Abcd1234 clearly assumed you were expressing support for MOND, and helpfully linked impressive evidence which convinced many physicists that dark matter explains the evidence better than MOND. Then I chimed in:
The next day:
Nonsense. You made what sounded like a general statement about dark matter "very possibly" not even existing, which implies that physicists who overwhelmingly do think it exists are either incompetent or suffering from frequent hallucinations. The only reasonable objection to dark matter was MOND, and the Bullet Cluster presented very strong evidence that seems to rule out MOND with no dark matter. It's not "exactly the same technique" as the current survey because the main point of the Bullet Clust
I finished undergrad in 2004, and my experience was similar to yours. I was being overly conciliatory to MOND because in my experience non-physicists aren't swayed by issues of elegance and simplicity.
As you say, unidentified gamma ray sources aren't relevant to the galaxy collision observations or dark energy acceleration observations in question. You've demonstrated true scientific spirit here by admitting a mistake. Kudos.
Thanks. I think this would've been impossible if I'd logged in.
It wasn't. Starting scores for users and ACs are different.
The only other person to respond to you was too harsh. Your idea is "out there" and probably wrong, but it's not obviously wrong. It's even an interesting thought experiment. The same thing occurred to me during my undergrad in 2004, and the story is here. Long story short: normal matter in parallel universes wouldn't explain the Bullet cluster observations mentioned elsewhere on this page.
Why? That just means I have to open more files when I want to perform extensive maintenance on the program.
Compiling is definitely faster if you only change 1 out of 100 similarly sized files, but I've chosen to create two main source files: the first is infrequently edited and large (30k lines), while the second is edited dozens of times a day and only has 1k lines. The Makefile compiles the large file into object code which is then linked to the object code from the small file. The large file is thereafter only compiled if the revision date of the large source file is newer than the large object file. Even the compiles for the large file are just ~10 seconds on a netbook if optimization is disabled, and it's not clear that my compile times will grow faster than CPU speeds will. (Especially if parallel g++ ever gets decent.)
I suppose one could say that code segmentation helps to enforce the "few interconnections between functions" principle. (Or whatever it's formally called- the notion that functions should interact in only a few well-defined ways.) This ideal is theoretically attractive, but seems annoying to implement without allowing for occasional exceptions. I don't want to change a useful guideline to a rigid law that will probably just slow me down.
I also write code by myself, so reasons involving programming teams aren't really relevant. A good version control system like Mercurial should minimize these issues anyway.
Are there any real (i.e. productivity, scalability) reasons to abandon this approach and start putting new functions in separate files? I'm not a professional programmer, so I may have missed something that a computer science PhD would consider obvious and compelling...
Ha! That was easy...
I love how this is modded Score:3, Informative.
... and I hate how my lack of mod points is keeping it from being Score:4, Insightful.
Working group 2 of the IPCC seems to have made some embarrassing mistakes. Upon seeing the letter in Science, I wondered why I'd never noticed these ludicrous statements before. Then I realized that the mistakes weren't in working group 1 report, which is all I'd ever bothered to read. Here's what each working group does:
The wild claim that "glaciers in the Himalaya are receding faster than in any other part of the world", the 2350/2035 typo, confusion of Himalayan glacier area with the worldwide total, and reliance on non-peer-reviewed source material all occurred in a single paragraph(!) in the WG2 report (section 10.6.2, paragraph 2).
Statements in the WG1 report regarding glaciers, on the other hand, accurately reflect conclusions in the peer-reviewed literature.
Due to my obsession with the physical sciences, I'd never even realized that other working group reports existed. Perhaps other scientists reacted in a similar fashion, which might be why such an absurd cluster of errors went undetected for so long...
The futility of these conversations is depressing and frustrating.
Thanks for that comment. It inspired me to post a snippet of a similar conversation I had months ago, with your links and some others added:
Creationists confuse religious faith with falsifiable science. Among the general public, climate-change contrarians (and your average Greenpeace/PETA loony) confuse political affiliation with falsifiable science. In both cases, scientists are much less likely to agree with either claim, and that likelihood decreases with increasing relevance of the scientist's field. That's probably why both groups tend to accuse the scientific community of conspiracy and/or widespread incompetence.
At my blog, the following statement is both legible and has popup titles describing why that link was chosen. Here it is without the links first: "And, in my experience there's a significant overlap between the two groups. Most of their arguments seem to be at similar intellectual and educational levels."
And, in my experience there's a significant overlap between the two groups. Most of their arguments seem to be at similar intellectual and educational lev els.