There appears to be a consensus that a "significant fraction" of climate change is the result of human activities. How much is significant (10%?, 50%?, 90%?) isn't specified.
And what "climate change" means isn't specified.
I think getting bogged down in a discussion of semantics is beside the point; most climate scientists think that humans are playing a significant role in changing the climate. Most agree that that change is much more rapid than ever before, and most agree that that will cause harm to humans in several ways (from increased storms to agricultural disruption). Hence most climate scientists (e.g. as represented by statements from various national academies, and the IPCC among others) think that significant action is warranted.
Meanwhile, our lakes and air are getting polluted with things that have immediate and significant impact on our lives now. We have a throw-away culture...[] Why are we distracting ourselves with trivialities as CO2?
Pollution is a problem, too. I'm not happy about the fact that my wife can't eat tuna because the mercury levels in it would damage our children.
But that doesn't mean that CO2 increases aren't also a serious problem. Tens of meters of sea level rise, or incresed hurricane frequency, or the shutdown of the ocean conveyor aren't "trivialities". The latest mirco$oft story IS a triviality in comparison.
I've read reports that the sun is getting warmer and is causing the global warming.
As near as the best science can tell (hence the "consensus"), the Sun is not causing the observed levels of global warming. For a full discussion, check out
this link.
t's just not true - the belief that the majority of climate researchers agree that humanity is to blame for the rise in global temperatures is also 'hotly' debated.
So a joint statment by 11 national academies of science (including the U.S.), or the IPCC doesn't represent a consensus? It's not just a matter of counting abstracts.
Keep in mind you can never get every self-proclaimed scientist to agree on everything - so there will always be a few contrarian voices that you can dig up (with enough money), but the overwhelming majority of climate scientists hold the view that human greenhouse gas emissions are causing climate change.
I thought I'd never say that. It's interesting how mainstream media has declared that a majority of scientists say global warming is real and directly tied into carbon emissions.
It's pretty clear that the evidence is there - if you have an open mind.
I have no trouble accepting that carbon emissions could cause warming, however the evidence isn't there yet.
Just what would you require as evidence - a personal note from God? I can list some of the studies indicating a link, but I honestly doubt I could ever convince you...
I have several friends in climatology, geology and astronomy who shake their heads everytime a new panic prediction is released.
And I have many friends in geology and climatology, and I am an astronomer, and I have to say that while the "panic announcements" may not be very likely, I think some of them are more likely than the scenarios presented by the contrarians. Case in point - the West Antarctic ice sheet may not melt this decade, but some time in the next century (given no limits on CO2) it will melt. When it does, that's 10 meters of sea level rise right there. I'll probably be dead, but my children might not be.
They're scientists who see multiple cause for global warming, man being only one of them.
Man being the one we can control, and the largest one, at the present time.
The "better something than nothing" crowd loses traction with me when it comes to Kyoto. It's just a bad plan.
No, be honest. You just spent most of your post arguing against human responsibility for GW; you can't seriously claim that you just have a problem with how Kyoto implements greenhouse reductions, and that you'd support some other mechanism. I didn't hear you say "GW is real, but we should go with voluntary reductions" or something to that effect. You claim that GW is either due to natural causes, or just not real.
this sounds like a mixed blessing, and brings about visions of some sterile, Spandex-jumpsuit future where food production is controlled by some central authority, and real, hoof-grown meat is a rare delicacy
Jeez, lighten up. There are plenty of technologically-induced distopias to worry about. This one ranks near the bottom of the list. First of all, food is pretty much already controlled by a central authority (ADM anyone?). Besides, have you ever been inside an abattoir, or within 5 miles of an industrial hog farm? The idea of eating meat without killing cows (and mad cow disease!) seems pretty good to me.
If you absolutely must freak about technology, worry about what happens when your health insurance company can do genetic screening on you. The go watch GATTACA.
It's nevered happened like that in the past. Short-sighted legislation leads to unintended negative consequences.
And short-sighted profit motive has never led to negative consequences?
Instead, if we had a good idea of the external cost (ie, the cost imposed on everyone else) of producing one extra ton of CO2, then we could impose that cost (as a tax) on the producer. And distribute the payment appropriately to those effected by global warming. But the science isn't to that point.
So you acknowledge that there is a cost associated with GW? But then you say we don't know enough to try and correct for the "inefficiency" that comes from not accounting for the cost properly... But isn't it worse to do nothing instead of trying to maximize efficiency based on the best available knowledge? "Perfect" is the enemy of better, after all.
Even the experts don't really know what the hell is going on, and why should we expect them to? [...]
I have a huge problem with passing seat-of-the-pants legislation which will have real, measurable, enormous effects on our standard of living.
You overestimate the uncertainties. If you read things like the IPCC report you will see that there is actually a fairly strong consensus on the amount of warming (they give confidence limits); and fairly good models for the impact. Scientists always admit uncertainty - but uncertainty isn't synonymous with having no clue...
You then state that the economic impact will be devastating. That statment is probably fraught with more uncertainty than any of the climate change predictions. How do you know that the effect of limit greenhouse emissions won't actually improve our economy by stimulating greater efficiency and innovation?
Throatless rockets aren't new... they've been around for awhile. They aren't as efficient as a throated rocket but they offer some operational advantages
How much loss of efficiency are we talking? (presumably Isp). Would that pretty much kill any chance if using them for space launch vehicles?
Is the whole design of the shuttle overly fragile?
It's not so much that the Shuttle is fragile, it's that getting to space is a rough ride. Shuttle hardware is pretty solid stuff - but those solid rocket boosters are more like semi-controlled detonantions than anything else. If you've ever heard a launch, that "ripping" sound you hear are shockwaves from the solids. They will pretty much shake the sh*t out of anything. In this case, they rattle the tiles in the heat shield to the point where it opened up a small temporary gap long enough for the gapfiller to shake partway out.
I've flown experiments on the Shuttle and when we qualify payloads for spaceflight we have to run them through qualification tests that include shake tests. Let me tell you, that can be rough.
A more general point to remember about any space launcher is that due to simple physics ( the rocket equation) any launcher has to be more than 90% pure fuel. The mental image I like is: is take a gasoline tank truck, get rid of the tractor part, and strap a lawn chair to the end. Now imagine riding that to 17,000 mph. It's hard to make a rugged vehicle that is mostly fuel tank - you have to try and make things both lightweight and strong. In the case of the Shuttle it also has to be reuseable. That last part is what is turning out not to be possible with the technology of the 70's and 80's.
I understand that there are some sizable forces acting on the launch vehicle, but how can insulating foam do so much damage?
You will notice that this time the foam didn't do any substantial damage. Last time it may have been ice, or ice-filled foam that hit the wing (remember the tank wall is at liquid hydrogen temperatures). In any case, the foam is hitting the heat shield going several hundred mph with respect to the Shuttle (even though it only fell off a second earlier, the relative acceleration is substantial). Think of the heat shield as tiles made out of pumice - very light, very resistant to heat, but relatively fragile to hard impact. "Why not use steel?" you might ask - but the problem is again physics. At the temperatures the shield gets to it will simply melt. "Why not cover the shield until it' needed?" - too heavy for anything other than a small capsule. So now that NASA has gven up on re-useable spacecraft, that's what we'll see. But make no mistake - capsules mean the complete end to any dream of space becoming affordable, routine, or accessible to anyone other than goverments or those with as much money as a government. Kiss your idea of a vacation in space goodbye forever.
And, if insulating foam can damage the tiles, what about micro meteors or drifting debris from previous flights?
Absolutely. Micrometeroid damage is definitely a risk. That's why the Shuttle always flies payload bay first when in orbit - to minimize the chance of damaging the heat shield. But there is always a risk of something going wrong in space. That's why its rare and expensive.
I politely disagree with RayBender's simplification of the issue. I would frame the question thus: do we want time to represent a digital or analog concept?
I think that is such an oversimplification as to be wrong. Remember that even "atomic time" is defined in relation to an arbitrary physical world. In this case, some arbitrary number of oscillations in the radiation emitted by an atom undergoing a particular transition (definition here). I don't see this as a digital vs. analog thing at all.
Where in the Bible does it say that life begins at conception? Is the current position of most conservative churches therefore not something adopted by later theologians? Is it therefore not subject to error, or revision? (whether or not the Bible is subject to error is something that I will leave to the Alabama legislative subcommittee on mathematical definitions.)
I understand that in the past masturbation and birth control were both considered sins (in Christianity at least) because (to paraphrase) "every sperm is sacred". The potential of the sperm and egg were considered such that it was murder to ehh...release them without a chance of conception.
Then why do most U.S. Christians now accept birth control? What changed in the last 100 years to move the line of where life begins to conception?
There is a related point for the more cynical - many of those who oppose stem cell research would probably in their heart of hearts like to outlaw birth control if given half a chance. (Yes, I know what the Pope says, but I also know that something like 80% of american catholics practice artificial birth control, Pope or no Pope.)
Of course, "conception" is not so black and white as many claim. A single fertilized egg can split into a pair of identical twins. Or it may never implant, or it may not be viable. So strictly speaking, a fertilized egg has the potential to be zero, one, or two human beings.
What if you modified the genome of the fertilized egg to inhibit, say, implantation? Then there would never be "potential" for human life. Would that be acceptable?
Potential is a tricky thing - and not a great way to set policy. What if the potential life was Adolf Hitlers? For every potential saint you have a potential serial killer (or corporate lawyer - you decide which is worse). Potential is by definition a gray area...
On the other hand you might say that the moment when a sperm meets an egg is of special metaphysical importance ("ensoulment"?), and that is the reason that a fertilized egg is sacred.
I could then argue that cloning is therefore acceptable - when you create a clone you are never mixing sperm and egg, never creating a new genetic sequence. So no new soul - hence nothing special, no new rights.
It seems to come down to this; you cannot arrive at any particular moment in the continuum of life as being the "beginning" just by logic alone. At some point people choose to plant a flag and prove by assertion that that particular moment is when life begins. But that's what it is - proof by assertion (or proof by intimidation).
I think we'd be better off to move the flag a bit and say that life (and individual rights) begin slowly and grow as the individual develops; coupled with the idea that all sentient beings should be treated "as an end" rather than a "means to an end". Before neurons there can be no pain or suffering, so perhaps that is a good place to start. But I make no claim that this position is the only logically acceptable one. Merely that it seems to allow for the greatest good for the greatest number of sentient humans, while limiting the potential for abuse.
Doing away with leap seconds has the effect of breaking the connection between the rotation of the Earth and time. The point of a leap second was to compensate for the fact that the Earth changes its rotation rate by very small amounts (due to changes in mass distribution).
It will make it harder to run telescopes, but also a number of navigational devices. The mention of the Glonass screwup is actually misleading - even if you abolish the leap second, you still have to have software in your satellites compensate for changes in Earth rotation rates - abolishing the leap second will not change that at all.
Probably the worst argument for getting rid of leap seconds is "they are rare anomalous events that cause potential danger for systems like ATC that are tightly coupled to time". That's misleading, though, because the proposal is actually to replace leap seconds with leap hours every 500 years. Which means that you replace a small, bi-annual anomaly with a gigantic one 500 years from now (on a scale larger than the Y2K bug, for sure.) Kicking the problem down the road so to speak - I'm not surprised it was originally suggested by a bunch of lazy programmers. Not to mention that that practice would mean that 400 years from now solar noon would be almost an hour away from actual noon (not that big a deal, of course, but annoying).
The argment for keeping the leap second is more than just tradition - it has practical value too.
Re: Your sig, not to crap on it, but the human genome is 3 Gigabytes according to the project page.
"Since the human genome is 3 billion base pairs long, 3 gigabytes of computer data storage space are needed to store the entire genome."
3 billion bases long. There are 4 bases (ATCG). Hence you can use 2 bits to store the base. Hence 6 billion bits. I think the ORNL page is wrong, or written by someone who doesn't understand the difference between a bit and a byte.
What am I missing? Even if I were wrong, isn't it pretty impressive that you can fit all the instructions to make a human into a couple of CDROMs, while the last time I installed XP+Office it took more than that?
I wondered how long it would take someone to bite on that. Look at the history - Triana ran into political opposition from Republicans in the House who thought of it as "Al Gores" mission. It's technically in storage, but realistically it's deader than a doornail. Check out this article or this one. It was Republicans who opposed it.
I for one would go out and finally buy an HD TV and subscribe to a channel that consisted solely of Earth views from an HD-capable camera placed in orbit permanently. Or you could just bolt this on to the side of the ISS. How hard could this be?
Not hard at all, in a world without Republicans. Check out the history of the Triana mission. Among many other things it would have provided just the HDTV image you mentioned. It was killed for essentially political reasons.
What they're saying is that this is BETTER THAN Hubble at MANY THINGS at 1/10th the cost. [...] But ten times the resolution of Hubble is nothing to sneeze at.
And I'm saying that in one area where it is often claimed to be better (angular resolution), it isn't actually better. Adaptive optcs doesn't correct for all the atmospheric blurring, and it only works well in the near-IR. Even there is doesn't recover more than about 70% of the light compared to a perfect image. GMT would only have ten times the resolution of HST if adaptive optics worked at visible wavelengths. And again, the real metric isn't just resolution, it's "Strehl ratio", which is basically the fraction of light recovered into a perfect image.
Where GMT is unquestionably better is in collecting area - but no-one has argued that some projects don't need light-buckets. They clearly do. But not every project needs a light bucket - hence the need for HST.
People keep comparing this large ground-based telescope to Hubble, and invariably say seomthing like "we can do just as good as Hubble at 1/10th the price". Nonsense, for three reasons:
1) Absorption. The atmosphere absorbs in many wavelengths of interest, including the UV and parts of the IR.
There are some projects that can never be done on the ground.
2) Background emission. The atmosphere "glows" at a number of wavelengths; this acts as a source of background contamination and reduces your sensitivity.
3) Blurring. The stars twinkle. This reduces the sharpness of ground-based images by an enormous factor (for GMT in the optical, excluding AO, by a factor of about 200).
People keep mentioning "adaptive optics" as a way to overcome the blurring from the atmosphere. But the harsh truth is that AO doesn't work all that well, for situations where you actually need to get rid of the effects of the atmosphere. Sure, it sharpens up pictures of binary stars pretty well, but it leaves a bunch of uncalibrated "scruff" near the star that e.g. makes it impossible to look for planets near that star. Another limitation of AO is that it requires a bright star to guide on - although lasers are becoming available. Mind you, the laser stuff seems to have even worse issues with calibration. Finally, AO has a very limited effective field of view; you can only correct over a small patch at a time. It makes it hard to do wide-field surveys that way.
Sooo, the upshot is that you need both, and will continue to need bothy for a long time. That being said, I wish the GMT guys lots of luck.
We request the same infomation from politicians to make sure they don't have conflicts of interest.
Should scientists who's reports can have a very real effect on policy be so diffrent?
Small difference; the request was intended mostly as harassment. The raw data used always was publicly available at a number of websites (including nature.com). The list of grants received is something that every scientist who submits a grant proposal has to compile. The NSF has said as a matter of policy that source codes are the intellectual property of a scientist and don't have to be disclosed. He did disclose the code voluntarily, however.
Look, what the Congressman is doing is basically the same thing SCO is trying. It's a legal fishing expedition, intended to tie up the scientists in endless amounts of paperwork. The hope is that maybe they'll get lucky and find some mistake that they can use, but in any case, it keeps the scientists distracted.
It also sends a clear message to everyone else - work on global warming and you'll spend the rest of your career defending every approximation, typo and mistake in every lab notebook you or your grad student ever made. To young faculty looking for tenure projects, such considerations make a difference. To grad students, it makes that job offer from Schlumberger look that much better.
Finally, Bartons tactics indicate a fundamental misunderstanding of how science operates. Science of this kind isn't a matter of one guy achieving something once and everyone else having to take his word for it. It's a matter of doing something, explaining what you did (hence the "methods" section in every paper), then having others go out and reproducing the results independently. This is what has happened - the "hockey stick" has been reproduced a bunch of times. I've even done it (as a grad student I did a project on coral temperature records and showed that the late 20th centrury temperature rise was statistically significant and unprecedented in the last several centuries).
The upshot is that if you want to critique the hockey stick paper, you should go out and try to process publicly availbe temperature records for yourself, not harass the scientists.
What Barton et al are trying is more like what lawyers do - attack the oppoenent by any means available. If you can't get them for the original thing, subpoena every document they've ever touched and see if you can't get them for tax evasion, or see if they're cheating on their spouse, or whatever. It's good ol' hardball, not science.
I must admit I'm not a nuclear engineer - I just play one on slashdot. But I've studied the physics a fair bit and do research in a related area. I was actually thinking of putting the uranium down the center of the tokamak. The neutron field is pretty intense there...
The other thing to remember is that if you don't need the fusion to be at break-even, you can make the tokamak smaller. That makes it easier to get a good value for k, I'd imagine. Should also allow you to get away from superconducting magnets.
Your point about the U238 cross section vs 14 MeV neutrons is interesting. How about moderating them somewaht, say using the Lithium blanket that has to be there anyway?
I'm not so sure what is meant by a hybrid though. If you mean using a simple neutron source as a supplement to the neutron economy within the commercial reactor, then I'd say that you'd be wasting your time.
No. Make a tokamak that runs at 0.1 of breakeven. Surround it with a blanket of U238 at k=0.99 (gives a gain factor of 100). The net result is a plant gain of 10, which is reasonable for a power plant. The fission supplies most of the energy, and the fusion most of the neutrons. Since the blanket is sub-critical it can be made safer than a standard fission reactor, and/or can use fuels that you couldn't otherwise use (i.e. an actinide burner, to get rid of the waste products). You don't have to bust your a** building a tokamak that does breakeven, that way.
It seems something like that would be the only way to get anything fusion-related actually producing power any time before my kids go to college... Think of it as an approach to getting fusion seen as an actual, viable choice to replace coal, and not just pie-in-the-sky.
The running joke of fusion is that it's always 30-50 years away. This is more due to meager funding levels than anything else..[] ITER will be a very large-scale test device. Some of the phenomena that we see disrupting our current experiments are related to physical device size.
I hear it's ~10 $G for iter. That's not exactly chump-change. Especially since we're not actually sure that even after ITER we'll have a working plant or a path to one. In addition, your scaling arguments (I've heard elsewhere that the minimum size of a plant would have to be ~10 GW)
imply very very large plants. That may be to large to be feasible - a 10GW plant is a pretty big investment.
One problem with very large tokamaks is that although they are above breakeven, it's not by much - which means that you have to recirculate large amounts of power. That makes for a very large and expensive generator facility.
I also understand that the amount of tritum circulating in a working plant would be enormous; much, much larger than ever used before. Tritium is notoriously hard to keep contained - so it's not obvious that a fusion plant wouldn't have issues with radioactivity releases...
My personal opinion is that it is best to stick with our Gen-IV nuclear plants when it comes to fission.
(Actually, I wasn't thinking of a hybrid based on tabletop fusors, but rather tokamaks).
Wouldn't a hybrid allow you to use a smaller (and presumably more feasible) tokamak as a neutron source, while at the same time the sub-critical fission blanket could be designed very safe, since neutron economy isn't such a driving concern?
You can imagine a blanket that gives a gain factor of 100, and a tokamak at 0.1 of breakeven, and you still have a feasible plant.
In addition, it would allow you to burn U238 or even nuclear waste instead of just U235. Seems like a win-win-win to me. Fusion gets operational experience and increased development funding, the country gets a good nuclear energy source, we're no longer oil-dependent or dependent on limited amounts of U235, and it reduces the waste issue (which is what is going to kill even the Gen IV plants).
As an aside, it's interesting to note that even nuclear weapons are fission/fusion hybrids... we've never extracted pure fusion energy in any quantities, controlled or not.
I wouldn't toss ITER aside before I get to at least read the journal article on a few of these desktop setups.
You have dropped enough acronyms and jargon to make me assume that you know something more about the details of tokamaks than the average Slashdotter, so I have a couple of questions for you:
1) Why is it said to take "50 years" for fusion to be developed? Whats the freaking hangup? I learned a long time ago that if something is expected to take more than 5 years to develop, it means that the technology is so immature that we don't even know what we don't know (with a nod to Rummy for that one). Hence we don't really know if "50 years" is 10, 20 or 500 years. You can't seriously tell me it'll take 50 years to find a suitable diverter material, or to design a cooling system for the magnets. So what is the real problem?
2) What about hybrids? A small fusion reactor to act as a neutron source, irradiating a sub-critical fission blanket that would provide an energy gain factor of 50-100. That seems like it would work really well in the near term. Why not?
WTF do you know that Elon Musk and his team of highly skilled (and so far thoroughly successful) engineers don't?
Not that thoroughly successful yet. Talk to me when they've flown. Not to mention that even they don't claim their vehicle will be that much cheaper (the cheap flights are supposedly the Falcon V, which is pretty far from ready as far as I can tell).
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I think getting bogged down in a discussion of semantics is beside the point; most climate scientists think that humans are playing a significant role in changing the climate. Most agree that that change is much more rapid than ever before, and most agree that that will cause harm to humans in several ways (from increased storms to agricultural disruption). Hence most climate scientists (e.g. as represented by statements from various national academies, and the IPCC among others) think that significant action is warranted.
Meanwhile, our lakes and air are getting polluted with things that have immediate and significant impact on our lives now. We have a throw-away culture...[] Why are we distracting ourselves with trivialities as CO2?
Pollution is a problem, too. I'm not happy about the fact that my wife can't eat tuna because the mercury levels in it would damage our children. But that doesn't mean that CO2 increases aren't also a serious problem. Tens of meters of sea level rise, or incresed hurricane frequency, or the shutdown of the ocean conveyor aren't "trivialities". The latest mirco$oft story IS a triviality in comparison.
As near as the best science can tell (hence the "consensus"), the Sun is not causing the observed levels of global warming. For a full discussion, check out this link.
So a joint statment by 11 national academies of science (including the U.S.), or the IPCC doesn't represent a consensus? It's not just a matter of counting abstracts. Keep in mind you can never get every self-proclaimed scientist to agree on everything - so there will always be a few contrarian voices that you can dig up (with enough money), but the overwhelming majority of climate scientists hold the view that human greenhouse gas emissions are causing climate change.
That might be because that is in fact the consesnus of a majority of published peer reviewed papers in the ltterature.
It's pretty clear that the evidence is there - if you have an open mind.
I have no trouble accepting that carbon emissions could cause warming, however the evidence isn't there yet.
Just what would you require as evidence - a personal note from God? I can list some of the studies indicating a link, but I honestly doubt I could ever convince you...
I have several friends in climatology, geology and astronomy who shake their heads everytime a new panic prediction is released.
And I have many friends in geology and climatology, and I am an astronomer, and I have to say that while the "panic announcements" may not be very likely, I think some of them are more likely than the scenarios presented by the contrarians. Case in point - the West Antarctic ice sheet may not melt this decade, but some time in the next century (given no limits on CO2) it will melt. When it does, that's 10 meters of sea level rise right there. I'll probably be dead, but my children might not be.
They're scientists who see multiple cause for global warming, man being only one of them.
Man being the one we can control, and the largest one, at the present time.
The "better something than nothing" crowd loses traction with me when it comes to Kyoto. It's just a bad plan.
No, be honest. You just spent most of your post arguing against human responsibility for GW; you can't seriously claim that you just have a problem with how Kyoto implements greenhouse reductions, and that you'd support some other mechanism. I didn't hear you say "GW is real, but we should go with voluntary reductions" or something to that effect. You claim that GW is either due to natural causes, or just not real.
Jeez, lighten up. There are plenty of technologically-induced distopias to worry about. This one ranks near the bottom of the list. First of all, food is pretty much already controlled by a central authority (ADM anyone?). Besides, have you ever been inside an abattoir, or within 5 miles of an industrial hog farm? The idea of eating meat without killing cows (and mad cow disease!) seems pretty good to me.
If you absolutely must freak about technology, worry about what happens when your health insurance company can do genetic screening on you. The go watch GATTACA.
And short-sighted profit motive has never led to negative consequences?
Instead, if we had a good idea of the external cost (ie, the cost imposed on everyone else) of producing one extra ton of CO2, then we could impose that cost (as a tax) on the producer. And distribute the payment appropriately to those effected by global warming. But the science isn't to that point.
So you acknowledge that there is a cost associated with GW? But then you say we don't know enough to try and correct for the "inefficiency" that comes from not accounting for the cost properly... But isn't it worse to do nothing instead of trying to maximize efficiency based on the best available knowledge? "Perfect" is the enemy of better, after all.
You overestimate the uncertainties. If you read things like the IPCC report you will see that there is actually a fairly strong consensus on the amount of warming (they give confidence limits); and fairly good models for the impact. Scientists always admit uncertainty - but uncertainty isn't synonymous with having no clue...
You then state that the economic impact will be devastating. That statment is probably fraught with more uncertainty than any of the climate change predictions. How do you know that the effect of limit greenhouse emissions won't actually improve our economy by stimulating greater efficiency and innovation?
How much loss of efficiency are we talking? (presumably Isp). Would that pretty much kill any chance if using them for space launch vehicles?
Is the whole design of the shuttle overly fragile?
It's not so much that the Shuttle is fragile, it's that getting to space is a rough ride. Shuttle hardware is pretty solid stuff - but those solid rocket boosters are more like semi-controlled detonantions than anything else. If you've ever heard a launch, that "ripping" sound you hear are shockwaves from the solids. They will pretty much shake the sh*t out of anything. In this case, they rattle the tiles in the heat shield to the point where it opened up a small temporary gap long enough for the gapfiller to shake partway out.
I've flown experiments on the Shuttle and when we qualify payloads for spaceflight we have to run them through qualification tests that include shake tests. Let me tell you, that can be rough.
A more general point to remember about any space launcher is that due to simple physics ( the rocket equation) any launcher has to be more than 90% pure fuel. The mental image I like is: is take a gasoline tank truck, get rid of the tractor part, and strap a lawn chair to the end. Now imagine riding that to 17,000 mph. It's hard to make a rugged vehicle that is mostly fuel tank - you have to try and make things both lightweight and strong. In the case of the Shuttle it also has to be reuseable. That last part is what is turning out not to be possible with the technology of the 70's and 80's.
I understand that there are some sizable forces acting on the launch vehicle, but how can insulating foam do so much damage?
You will notice that this time the foam didn't do any substantial damage. Last time it may have been ice, or ice-filled foam that hit the wing (remember the tank wall is at liquid hydrogen temperatures). In any case, the foam is hitting the heat shield going several hundred mph with respect to the Shuttle (even though it only fell off a second earlier, the relative acceleration is substantial). Think of the heat shield as tiles made out of pumice - very light, very resistant to heat, but relatively fragile to hard impact. "Why not use steel?" you might ask - but the problem is again physics. At the temperatures the shield gets to it will simply melt. "Why not cover the shield until it' needed?" - too heavy for anything other than a small capsule. So now that NASA has gven up on re-useable spacecraft, that's what we'll see. But make no mistake - capsules mean the complete end to any dream of space becoming affordable, routine, or accessible to anyone other than goverments or those with as much money as a government. Kiss your idea of a vacation in space goodbye forever.
And, if insulating foam can damage the tiles, what about micro meteors or drifting debris from previous flights?
Absolutely. Micrometeroid damage is definitely a risk. That's why the Shuttle always flies payload bay first when in orbit - to minimize the chance of damaging the heat shield. But there is always a risk of something going wrong in space. That's why its rare and expensive.
I think that is such an oversimplification as to be wrong. Remember that even "atomic time" is defined in relation to an arbitrary physical world. In this case, some arbitrary number of oscillations in the radiation emitted by an atom undergoing a particular transition (definition here). I don't see this as a digital vs. analog thing at all.
I understand that in the past masturbation and birth control were both considered sins (in Christianity at least) because (to paraphrase) "every sperm is sacred". The potential of the sperm and egg were considered such that it was murder to ehh...release them without a chance of conception. Then why do most U.S. Christians now accept birth control? What changed in the last 100 years to move the line of where life begins to conception? There is a related point for the more cynical - many of those who oppose stem cell research would probably in their heart of hearts like to outlaw birth control if given half a chance. (Yes, I know what the Pope says, but I also know that something like 80% of american catholics practice artificial birth control, Pope or no Pope.)
Of course, "conception" is not so black and white as many claim. A single fertilized egg can split into a pair of identical twins. Or it may never implant, or it may not be viable. So strictly speaking, a fertilized egg has the potential to be zero, one, or two human beings. What if you modified the genome of the fertilized egg to inhibit, say, implantation? Then there would never be "potential" for human life. Would that be acceptable?
Potential is a tricky thing - and not a great way to set policy. What if the potential life was Adolf Hitlers? For every potential saint you have a potential serial killer (or corporate lawyer - you decide which is worse). Potential is by definition a gray area...
On the other hand you might say that the moment when a sperm meets an egg is of special metaphysical importance ("ensoulment"?), and that is the reason that a fertilized egg is sacred. I could then argue that cloning is therefore acceptable - when you create a clone you are never mixing sperm and egg, never creating a new genetic sequence. So no new soul - hence nothing special, no new rights.
It seems to come down to this; you cannot arrive at any particular moment in the continuum of life as being the "beginning" just by logic alone. At some point people choose to plant a flag and prove by assertion that that particular moment is when life begins. But that's what it is - proof by assertion (or proof by intimidation).
I think we'd be better off to move the flag a bit and say that life (and individual rights) begin slowly and grow as the individual develops; coupled with the idea that all sentient beings should be treated "as an end" rather than a "means to an end". Before neurons there can be no pain or suffering, so perhaps that is a good place to start. But I make no claim that this position is the only logically acceptable one. Merely that it seems to allow for the greatest good for the greatest number of sentient humans, while limiting the potential for abuse.
It will make it harder to run telescopes, but also a number of navigational devices. The mention of the Glonass screwup is actually misleading - even if you abolish the leap second, you still have to have software in your satellites compensate for changes in Earth rotation rates - abolishing the leap second will not change that at all.
Probably the worst argument for getting rid of leap seconds is "they are rare anomalous events that cause potential danger for systems like ATC that are tightly coupled to time". That's misleading, though, because the proposal is actually to replace leap seconds with leap hours every 500 years. Which means that you replace a small, bi-annual anomaly with a gigantic one 500 years from now (on a scale larger than the Y2K bug, for sure.) Kicking the problem down the road so to speak - I'm not surprised it was originally suggested by a bunch of lazy programmers. Not to mention that that practice would mean that 400 years from now solar noon would be almost an hour away from actual noon (not that big a deal, of course, but annoying).
The argment for keeping the leap second is more than just tradition - it has practical value too.
Indeed. Someday it will no doubt be required ID.
3 billion bases long. There are 4 bases (ATCG). Hence you can use 2 bits to store the base. Hence 6 billion bits. I think the ORNL page is wrong, or written by someone who doesn't understand the difference between a bit and a byte.
What am I missing? Even if I were wrong, isn't it pretty impressive that you can fit all the instructions to make a human into a couple of CDROMs, while the last time I installed XP+Office it took more than that?
Not hard at all, in a world without Republicans. Check out the history of the Triana mission. Among many other things it would have provided just the HDTV image you mentioned. It was killed for essentially political reasons.
And I'm saying that in one area where it is often claimed to be better (angular resolution), it isn't actually better. Adaptive optcs doesn't correct for all the atmospheric blurring, and it only works well in the near-IR. Even there is doesn't recover more than about 70% of the light compared to a perfect image. GMT would only have ten times the resolution of HST if adaptive optics worked at visible wavelengths. And again, the real metric isn't just resolution, it's "Strehl ratio", which is basically the fraction of light recovered into a perfect image.
Where GMT is unquestionably better is in collecting area - but no-one has argued that some projects don't need light-buckets. They clearly do. But not every project needs a light bucket - hence the need for HST.
1) Absorption. The atmosphere absorbs in many wavelengths of interest, including the UV and parts of the IR. There are some projects that can never be done on the ground.
2) Background emission. The atmosphere "glows" at a number of wavelengths; this acts as a source of background contamination and reduces your sensitivity.
3) Blurring. The stars twinkle. This reduces the sharpness of ground-based images by an enormous factor (for GMT in the optical, excluding AO, by a factor of about 200).
People keep mentioning "adaptive optics" as a way to overcome the blurring from the atmosphere. But the harsh truth is that AO doesn't work all that well, for situations where you actually need to get rid of the effects of the atmosphere. Sure, it sharpens up pictures of binary stars pretty well, but it leaves a bunch of uncalibrated "scruff" near the star that e.g. makes it impossible to look for planets near that star. Another limitation of AO is that it requires a bright star to guide on - although lasers are becoming available. Mind you, the laser stuff seems to have even worse issues with calibration. Finally, AO has a very limited effective field of view; you can only correct over a small patch at a time. It makes it hard to do wide-field surveys that way.
Sooo, the upshot is that you need both, and will continue to need bothy for a long time. That being said, I wish the GMT guys lots of luck.
Small difference; the request was intended mostly as harassment. The raw data used always was publicly available at a number of websites (including nature.com). The list of grants received is something that every scientist who submits a grant proposal has to compile. The NSF has said as a matter of policy that source codes are the intellectual property of a scientist and don't have to be disclosed. He did disclose the code voluntarily, however.
Look, what the Congressman is doing is basically the same thing SCO is trying. It's a legal fishing expedition, intended to tie up the scientists in endless amounts of paperwork. The hope is that maybe they'll get lucky and find some mistake that they can use, but in any case, it keeps the scientists distracted.
It also sends a clear message to everyone else - work on global warming and you'll spend the rest of your career defending every approximation, typo and mistake in every lab notebook you or your grad student ever made. To young faculty looking for tenure projects, such considerations make a difference. To grad students, it makes that job offer from Schlumberger look that much better.
Finally, Bartons tactics indicate a fundamental misunderstanding of how science operates. Science of this kind isn't a matter of one guy achieving something once and everyone else having to take his word for it. It's a matter of doing something, explaining what you did (hence the "methods" section in every paper), then having others go out and reproducing the results independently. This is what has happened - the "hockey stick" has been reproduced a bunch of times. I've even done it (as a grad student I did a project on coral temperature records and showed that the late 20th centrury temperature rise was statistically significant and unprecedented in the last several centuries).
The upshot is that if you want to critique the hockey stick paper, you should go out and try to process publicly availbe temperature records for yourself, not harass the scientists. What Barton et al are trying is more like what lawyers do - attack the oppoenent by any means available. If you can't get them for the original thing, subpoena every document they've ever touched and see if you can't get them for tax evasion, or see if they're cheating on their spouse, or whatever. It's good ol' hardball, not science.
The other thing to remember is that if you don't need the fusion to be at break-even, you can make the tokamak smaller. That makes it easier to get a good value for k, I'd imagine. Should also allow you to get away from superconducting magnets.
Your point about the U238 cross section vs 14 MeV neutrons is interesting. How about moderating them somewaht, say using the Lithium blanket that has to be there anyway?
No. Make a tokamak that runs at 0.1 of breakeven. Surround it with a blanket of U238 at k=0.99 (gives a gain factor of 100). The net result is a plant gain of 10, which is reasonable for a power plant. The fission supplies most of the energy, and the fusion most of the neutrons. Since the blanket is sub-critical it can be made safer than a standard fission reactor, and/or can use fuels that you couldn't otherwise use (i.e. an actinide burner, to get rid of the waste products). You don't have to bust your a** building a tokamak that does breakeven, that way.
It seems something like that would be the only way to get anything fusion-related actually producing power any time before my kids go to college... Think of it as an approach to getting fusion seen as an actual, viable choice to replace coal, and not just pie-in-the-sky.
I hear it's ~10 $G for iter. That's not exactly chump-change. Especially since we're not actually sure that even after ITER we'll have a working plant or a path to one. In addition, your scaling arguments (I've heard elsewhere that the minimum size of a plant would have to be ~10 GW) imply very very large plants. That may be to large to be feasible - a 10GW plant is a pretty big investment.
One problem with very large tokamaks is that although they are above breakeven, it's not by much - which means that you have to recirculate large amounts of power. That makes for a very large and expensive generator facility.
I also understand that the amount of tritum circulating in a working plant would be enormous; much, much larger than ever used before. Tritium is notoriously hard to keep contained - so it's not obvious that a fusion plant wouldn't have issues with radioactivity releases...
My personal opinion is that it is best to stick with our Gen-IV nuclear plants when it comes to fission.
(Actually, I wasn't thinking of a hybrid based on tabletop fusors, but rather tokamaks). Wouldn't a hybrid allow you to use a smaller (and presumably more feasible) tokamak as a neutron source, while at the same time the sub-critical fission blanket could be designed very safe, since neutron economy isn't such a driving concern? You can imagine a blanket that gives a gain factor of 100, and a tokamak at 0.1 of breakeven, and you still have a feasible plant.
In addition, it would allow you to burn U238 or even nuclear waste instead of just U235. Seems like a win-win-win to me. Fusion gets operational experience and increased development funding, the country gets a good nuclear energy source, we're no longer oil-dependent or dependent on limited amounts of U235, and it reduces the waste issue (which is what is going to kill even the Gen IV plants). As an aside, it's interesting to note that even nuclear weapons are fission/fusion hybrids... we've never extracted pure fusion energy in any quantities, controlled or not.
You have dropped enough acronyms and jargon to make me assume that you know something more about the details of tokamaks than the average Slashdotter, so I have a couple of questions for you:
1) Why is it said to take "50 years" for fusion to be developed? Whats the freaking hangup? I learned a long time ago that if something is expected to take more than 5 years to develop, it means that the technology is so immature that we don't even know what we don't know (with a nod to Rummy for that one). Hence we don't really know if "50 years" is 10, 20 or 500 years. You can't seriously tell me it'll take 50 years to find a suitable diverter material, or to design a cooling system for the magnets. So what is the real problem?
2) What about hybrids? A small fusion reactor to act as a neutron source, irradiating a sub-critical fission blanket that would provide an energy gain factor of 50-100. That seems like it would work really well in the near term. Why not?
You obviously have enough time to be posting on Slashdot... Or is that a shell-script, too?
Not that thoroughly successful yet. Talk to me when they've flown. Not to mention that even they don't claim their vehicle will be that much cheaper (the cheap flights are supposedly the Falcon V, which is pretty far from ready as far as I can tell).