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http://hyperphysics.phy-astr.gsu.edu/hbase/icyl.html#icyl2

It depends on what values you consider constant. If you consider mass as a constant then moment of inertia is proportional to the square of the radius but if you consider density and thickness to be constants then moment of inertia is proportional to the fourth power of the radius.

IMO when talking about platters considering thickness and density as constants is more sensible than considering mass as a constant.

In clarification, don't confuse work with energy. They aren't quite exactly the same thing. What is correct to say, is a force does no work if it does not cause a displacement of the object along the vector of the force. This says nothing about the expense of energy though other than to say, an appropriate amount of energy expended will accounted for in the work done. It does not mean that that is the only energy expense nor that for energy to be expended work must be done.

It's a long time since I was really up on physics and maths and I may have been imprecise with terminology etc. I agree that the vector components of the force need to be considered - particularly important for the string-rock system under discussion where the force on the rock along the tangent is 0, hence the KE does not change (assuming string is attached to a fixed point, frictionless system etc). I'm not sure I understand your last sentence - are you thinking about systems with friction etc?

I've enjoyed reading these posts - it's good to get back up to speed with some of the basic concepts I used to be familiar with as a student. I've found a couple of the links here useful.

there is this farsical disscuion that always gets recycled about uranium, that there is only 50 years supply left. yes, there is 50 years of KNOWN AND DEFINED ore body. there has been almost zero exploration done in the last 40 years due to hard campgaining against uranium mining and nuclear power. it's dishonest of the green lobby to succeed in banning uranium mining in most countries then claim short supply as a problem for nuclear power. In australia alone we have massive deposits that aren't properly explored, and there's no doubt there are more deposits we don't even know about.

It could work for one vuvuzela, but not for a bunch of them. Destructive interference with a bunch of sources all out of phase with each other.
Kind of like an incandescent light bulb (many vuvuzelas) vs. a laser (one vuvuzela). The other problem would be location. The interference would be alternating between constructive and destructive, unless the "anti-sound" were located in the exact same place as the vuvuzela.
In short, it would not work.

See this for some background: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/interf.html
especially the part about interference with a tuning fork.

That's the current estimate, yes (ozone layer destruction from supernova within 26 LY).

Also, supernovae output a lot of energy (equivalent to the lifetime energy output of our sun over 10 billion years in one massive explosion).

Even though many nearby wavelengths trigger a particular cone, that doesn't mean the cone sends a range of colours to the brain. I still think that each cone represents and sends a pure primary colour, specifically red, green and blue for L, M and S. I'm talking about the final sensation here, rather than any intermediate signals such as preliminary wavelengths.

Cones don't send colors, they send activation levels. Each cone is activated in proportion to all the differently-colored photons that hit it, weighted by frequency. While photons of a given frequency are most efficient at generating an activation response, the activation level does not correspond to any particular spectral color. The colors come in when the visual system takes the activation levels of the cones and maps them to two internal color axes: the red/green axis and the blue/yellow axis. These, plus black and white, are the brain's primary colors — the ones that are perceptually pure. This is called the opponent process model.

The mapping process uses some sort of antagonistic weighting. The different cone types are not evenly distributed across the retina (the M and L cones are mostly in the fovea, while the S cones are scattered more widely), so the weightings must vary across the retina, or some sort of correction must be applied downstream after the color axis mapping.

A candle that burns twice as bright, burns half as long.

Inverse Square Law of Light

Twice the light at a given distance requires four times the energy to produce so that should be, "A candle that burns twice as bright, burns one-quarter as long." [/pedant]

A car going 30 mph travels 44 feet per second. (5,280 / 120 = 44). The stopping distance of a vehicle is a function of friction, speed, and mass. One of the calculators is here: http://hyperphysics.phy-astr.gsu.edu/HBASE/crstp.html. Just google 'vehicle stopping distance' and you have a choice of several calculators and you can look at the full formula, which is impossible to write correctly here. Assuming you have good tires, and all other things being equal, the stopping distance from 30 mph is 37 feet. Most studies on this issue assume it is fair to give a driver one second to determine whether to stop. First, you must recognize the yellow light, then assess the situation. Are you going downhill? Are the streets wet? Do you have a bowl of goldfish on the seat beside you? This is not trivial. Stopping on wet pavement requires twice the distance. Here's an article that says more or less the same thing: http://www.driveandstayalive.com/info%20section/stopping-distances.htm.

The basic issue here is that it will take you at least two seconds to stop from 30 mph on dry pavement, four seconds if it is wet. It takes one second to react and one second to stop (though deceleration throws a curve on time here). But in terms of distance this means you absolutely must be MORE than 81 feet away from the stop light to stop at all. My car is 16 feet long. If mine is average, that means five car lengths are required to stop. If that yellow light is less than two seconds long and you are within 81 feet of the light, you will go through on red. You have no choice; the laws of physics dictate it.

The last time I was stopped by the State Patrol for this I said, "Look. It was pretty close. I was doing 40 mph on a hill and the streets were wet. Plus, I thought about it. If I had just slammed on the brakes, I might have been able to stop, but the extra half second cost me." He let me go.

The idea expressed here that you just 'stop on yellow' is ridiculous. If your vehicle is within that window close to the light, you cannot stop, ever. Adjust for wind speed. If you are ever given a ticket for this, vidceotape the intersection to prove tghe length of the yellow light, compute the calculations, and take it to the judge.

In our area, they can ticket you, but it does not appear as a moving violation on your driver's record so your insurance will not go up. There is also some sentiment that putting in these cameras results in more rear-end accidents because drivers become hypersensitive. It's definitely a money-making issue.

Sigh.

Trying to convince yourself you didn't get ripped off? Don't let me stop you with those inconvenient facts.

Inverse Square Law applies.

A good upsampling DVD player - functionally, giving you 720p quality on a "50 1080p" screen - at a normal couch distance of 10 feet will be nearly indistinguishable from putting the blu-ray disc in. That's reality.

Add on to that the crappy "own but don't really own" DRM attached to this, and the fact that it will only play on your PS3 and can't be traded/gifted/loaned to anyone else? Fuck it, just buy the goddamn movie on a real disc.

It is right to be skeptical, but the theoretical efficiency of a typical Diesel is in the 50% range.

http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/diesel.html

This thing is not a Diesel engine, but it looks like it might be similar to one.

I think my AIP Handbook may have a typo. It gives 15 mbarns for the 2200 km/s neutron absorption cross section for Pb-208 but it is doubly magic so 1.5 mbarns might be a better guess. http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/shell2.html If so, 100 m of travel gives a probability of 0.5 of absorption so our reactor might need a large diameter (20 m or more) to avoid losing too many neutrons. In this situation, neutrons may recross the proton/deuterium target region to a significant degree and so we should think about how the proton/deuterium target may act as a poison if it absorbs neutrons. Indeed, we might prefer deuterium as the projectile because it is less likely to absorb a neutron than a proton is.

Having a liquid catalyst should keep the lead and bismuth isotopes well mixed.

So the idea here is apparently that the energy itself can be transmitted instantly, but you can't actually transmit information this way. Just energy

... which would immediately violate the principle of the conservation of energy.

The problem here is that energy == matter (via e=mc^2) and the system of matter/energy together in space-time yields information. Beckenstein shows that the total information in a volume of space is described by the area of the volume which encloses it. See "Bekenstein Bound" http://en.wikipedia.org/wiki/Bekenstein_bound/
    So in order for this new theory to work, the energy that is instantly transfered to another point in space-time must not be useful until we know what we can do with it through the classical channel. Otherwise you violate the conservation of energy.

Consider for example a mass at height in a gravitational field. To hold the mass stationary at height without any means of support other than using some of the mass itself for the creation of thrust, you would neccessarily run out of mass eventually (time). But if this theory were true, you'd have a loophole where you could take the energy expended for thrust and send it instantaneously back to the point in space above the mass where it could thusly be re-utilized. You would then have your first anti-gravity machine, which can't exist. A mass at height can be used to create energy in free-fall, and which is only equal to the potential difference in height. See http://hyperphysics.phy-astr.gsu.edu/HBASE/gpot.html

Btw, this is why theoretical wormholes can only exist along gravitationally equal field vectors. If a wormhole were to connect two different locations in space that don't exist with the same gravitational potential, you could generate an almost infinite amount of energy. Consider two ends of a wormhole, one end at 1000 meters height above the earth, the other at the ground. Throw a very large mass in at the ground hole. The mass then appears at 1000 meters, and starts falling. You could then make energy from it indefinitely. (What's that video game? Portal?) I would assume, in such a scenario, that the two ends of the wormhole would neccessarily begin to edge closer and closer to each other until they "evaporate" from existance altogether. This might be similar to black hole evaporation.

My question is, what actually is the total amount of energy required to actually hold any object at height, indefinitely, in a gravitational field?

This year's challenge: write a luggage routing program that mysteriously misroutes a customer's bag if a check-in clerk places just the right kind of text in a comment field

As opposed to the current system that does it at random? If you come up with a system that ONLY does it when malicious text is written in the comment field, the government wants to talk with you. They paid $500 per LINE for a baggage-routing system that never worked. It was finally abandoned after half a billion was sunk into it.

Just a minor correction. the scientists did use interferometry but it was not "very long baseline interferometry". The "very long" term applies to the telescopes being separated by extreme distances, say over the entire United States as is the case of the VLBA. Also, the VLBA can only function in radio wavelengths because the data can be taken at the individual telescopes an recombined later. With near-infrared interferometry, what the authors of this study were using, requires that the light from each telescope be sent down an optical tube with mirrors and recombined at a central location which constrains the IOTA telescopes to be close together.

IOTA was dismantled a few years ago, geiven that a new optical/near-infrared interferometry was coming online, CHARA http://www.chara.gsu.edu/CHARA/

The short answer is yes, and GP's "empty space" model never really holds any water, but the analogies all get fuzzy here. The real variable of merit is the "cross-section", which is a probability of a given interaction taking place in units of certain accelerator collision parameters.

At low energy, the cross-section for "elastic" (traditional photon exchange with the proton) scattering is very high, and inelastic (probing the quark substructure) is very low. At high energy, the elastic cross-section falls off sharply (you're "missing"), and inelastic remains near its small, but now comparatively bigger, number. When these inelastic collisions do occur, instead of hitting one of the three "constituent quarks", you have to apply a parton distribution function (the odds of interacting with a particular flavor of quark or gluon) to see what element of the "sea" you hit, and how much momentum it's carrying away from the proton. And then the rest will fly off to form color-neutral debris

http://hyperphysics.phy-astr.gsu.edu/HBASE/nuclear/scatele.html
http://en.wikipedia.org/wiki/Parton_(particle_physics)

No, you don't get annihilation from electrons and protons.

You do get radiation, if things are energetic enough. If the electron becomes bound to the proton, you get emissions at one of the Hydrogen lines.

If, for example, the electron went all the way to the Hydrogen ground state, you would have emissions at the limit of the Lyman Series, up in the hard UV at 91 nanometers.

If things are more energetic, you will get electrons and protons combining to form free neutrons. These will decay (this decay is called beta decay) and release gamma rays at 782 KeV, but since the half life of free neutrons is 10.3 minutes, this will be really spread out in time and hard to see. Free neutrons have been directly detected from lightning strikes, so some of this is presumably going on.

I think this is better than the wikipedia intro:
http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/phonon.html

The vibrational energies of molecules, e.g., a diatomic molecule, are quantized and treated as quantum harmonic oscillators. Quantum harmonic oscillators have equally spaced energy levels with separation DE = hu. So the oscillators can accept or lose energy only in discrete units of energy hu.

The evidence on the behavior of vibrational energy in periodic solids is that the collective vibrational modes can accept energy only in discrete amounts, and these quanta of energy have been labeled "phonons". Like the photons of electromagnetic energy, they obey Bose-Einstein statistics.

-l

I can't help but remember all the talk about nuclear fission doing the same thing- energy too cheap to meter and all. Fusion as it is currently is dependant on Deuterium and Tritium fuel for the most part and Tritium is mostly produced from the Li6+n => He4+T and Li7+n => He4+T+2n reactions both of which must occur in a high neutron flux environment (conventional fission reactor) which makes the first fusion plants very dependant on fission reactors for fuel production. What is worse is that you'd have to produce about a dozen Tritium nuclei for every Uranium atom fissioned just to make fusion produce as much energy as the fission reaction that was used to synthesize the fusion fuel in the first place. The future of fusion that *may* approach what you're expecting of it will likely involve aneutronic fusion reactions such as the B11+H1 => 3He4 reaction among several others. THe problem is that they are much more difficult to get working than D+T fusion. The B11+H1 reaction requires a roughly 10^9 degree core to work which is nearly ten times what D/T does.

You can read more about what's required here:
Fusion

> No, "high temperature" superconductors cannot be used in magnets.

[citation needed]

Hmm, after looking it up, I apparently misremembered slightly. Materials with higher critical temperatures do tend to have higher critical fields, so you would want to use the high-temperature materials to make magnets. But, you can have either high temperatures or strong magnetic fields, but not both.

So you can use "high temperature" superconductors to make magnets, but the mangnets will still only work at low temperatures.

someone do some analysis on the statistics and tell us all something and get +5

Sure. It's Poisson statistics, so the standard deviation is the square root of the count.
placebo: 74 plus or minus 8.6
vaccine: 51 plus or minus 7.1

The statistical significance of the difference (23) is equal to the standard deviation of the sum (not the difference!) of the counts, so:

difference between placebo and vaccine:
23 (=31%) plus or minus 11
= (2.06 standard deviations)

Assuming they set their criteria for statistical significance at two standard deviations, then they are significant.

So, even with this fundamentally implausible drive method, we still need to carry nearly 7 times as much fuel as mass of the rest of the ship.

Is that necessarily a big issue?

If we go back to matter+anti-matter reactions, you'd need some matter to annihilate. Any human expedition will have to carry food and water in large quantities, and if we can annihilate the human waste directly, we can save weight on toilet facilities. If we use large amounts of water as a shield against radiation, we get "free" radiation shielding and drinking water in one, and our fuel store just ended up having two extra functions = more weight reduction. Well, water used as radiation shielding is probably a lot heavier than something like lead.

At decent temperatures (the ones we'd need for human habitation in the ship) water is very easy to transport as well, so there are no need for highly complicated fuel pipelines. Can be done with very lightweight plastics built directly into the plumbing systems.

I'm sure there are lots of other ways you could cut down on the weight requirements as well.

One thing that confuses me a little bit, is that if you reduce the acceleration to 50g and up the travel time to 12 days you still end up with a delta_v of 5.1 e8. That way we can keep halving and doubling and ending up with constantly having that much energy.

Using the Motion Example from Hyper Physics, I get some rather different numbers:
Halfway distance (where you need to turn around) is 2,143,589,742,000 meters.
Initial velocity: 0 m/s
Acceleration: 982 m/s^2
That solves for time = 66,073.92 seconds (18 hours, 21 minutes, 13.92 seconds)
Final velocity: 64,884,591.80 m/s (21.64% of the speed of light)

If we change it to 30 m/s^2 (just over 3 g) we solve for v_max = 11,340,872.3 m/s (3.78% of c) and time 4 days, 9 hours, 1 minute.

At 9.82 m/s^2 we get 7 days, 15 hours, 32 minutes and v_max = 660,739.2 m/s (0.22% of c).

At those speeds even 1 g would be sufficient. We can easily pack enough food etc. to last for a 3 month expedition into space. How Stuff Works says ~400 kg food and 1,500 litres of water per person for a 2 year expedition. If we're doing 3 months total (2 months on Pluto, 14 days out, 14 days back) you'd only need about 250 kg of food per person. That's a tiny amount.

If we use your formulas again:
I = Isp*Mr = 3e8*Mr kg m/s

3e8*Mr = (0.5*Mr + Ms)*660,739.2*2 (*2 as we have to slow down again)
Mr = (0.5*Mr + Ms)*660,739.2 m/s*2/c
Mr = (0.5*Mr + Ms)*0.0044
907.44 Mr = 0.5 Mr + Ms
907 Mr = Ms

Now we're down to carrying 1.2 kg of fuel for every ton of spaceship for the improbable type of drive. Up that to a 1:1 ratio and I think something like fusion becomes readily attainable? 2 tonne of fuel to 1 ton of spaceship would probably considered an insane leap forward.

But, again, this is something I only have very little knowledge about, and I know that most of that is probably incorrect. And I wouldn't be at all surprised if I screwed up the calculations. I'm just a very curious kind of guy :D

Thank you Chris,
I deleted my initial response to this as I took a rather insulting tone towards his EE degrees. I'm having enough problems with him thinking I'm insulting his intelligence.

Though I got my information from a electrical engineering site, not wiki. It explained inductive and impedance losses.
A power factor of one or "unity power factor" is the goal of any electric utility company since if the power factor is less than one, they have to supply more current to the user for a given amount of power use. In so doing, they incur more line losses. They also must have larger capacity equipment in place than would be otherwise necessary. - Note they don't say MORE FUEL would have to be burned, other than to presumably offset the increased line losses.
For two systems transmitting the same amount of real power, the system with the lower power factor will have higher circulating currents due to energy that returns to the source from energy storage in the load. These higher currents in a practical system may produce higher losses and reduce overall transmission efficiency.

Speaking as a chemist, could you explain what exactly this means? Up until this very moment I have been under the misguided notion that the nucleus of an atom was orbited by electrons within groups called "shells", and these worked very similarly to satellites around a planet.

You're thinking of the Bohr model.

So, could you in any way explain how we get from "think of it as a planet with many moons" to this or more importantly, what gives orbitals this shape?

It's because the Schrodinger equation is a Laplacian, and the hydrogen atom is a spherically symmetric problem. The natural basis for the Laplacian in spherical coordinates is spherical harmonics. The shape you are seeing is the characteristic shape of different spherical harmonics, corresponding to the angular momentum of the electron.

The observatory's going to be fine according to some of the people who work there.

I guess there's no such thing as a 100% guarantee, but the observatory appears to be very well protected.

There is a link to a blog on the Webcam page:

http://joy.chara.gsu.edu/CHARA/fire.php

Chief Powers expressed his absolute confidence that they will save the Observatory. He said that while it may have appeared over the last day or so that the Observatory was being neglected, that they never lost sight of the importance of Mount Wilson's preservation and it is now their highest priority.

The article presents a very interesting possibility of transferring genetic capabilities of other species into humans. There are several areas where essential metabolic functions are not available to humans.

If you do not have a regular supply of fruits and vegetables that contain Vitamin C (ascorbic acid) you will develop scurvy. This was the leading cause of deaths on oceangoing voyages up until the early 20th century. (it is also why British sailors were called "limeys" because of the storage and consumption of limes while at sea). Humans lack one enzyme L-gulonolactone oxidase that would allow the liver to convert glucose into ascorbic acid and give an humans back an evolutionary edge that was lost to our species.

http://www.seanet.com/~alexs/ascorbate/196x/stone-i-acta_genet_med_et_gemell-1966-v15-p345.htm

There are at least 10 essential amino acids that are not produced in the human body. In many other organisms genetics has provided the "key" to unlocking amino acid production.

http://hyperphysics.phy-astr.gsu.edu/HBASE/Organic/essam.html

Further research into what biochemical processes that can be incorporated either as a treatment regimen or as a modification to the human genome can greatly expand our adaptability as a species. Could the ability of the wood frog to survive being frozen solid enable us to travel to distant stars through hibernation?

http://www.blurtit.com/q476575.html

Here's a crazy idea: how about nuclear power? Oh, that's right, the word "nuclear" is too super-scary for the science-based environmentalists. Never mind that they actually are better for the environment than anything else.

I would agree with you if, by "actually," you really mean "not actually." Many opponents of nuclear power, myself included, are not so much bothered by radioactive waste disposal issues. We are much more concerned about the high cost of system failures.

Everyone here is familiar with how difficult it is to keep defect rates in the 5 sigma region, let alone the 6 sigma region. Even with a spectacular 6 sigma failure rate, that means some failures _will_still_happen_. The longer a plant operates, the more likely a problem with occur. The more plants the operate, the greater the number of towns and cities that will be contaminated.

No control system is fool-proof, as students of the nuclear power industry know. What is most dangerous to safe reactor operation is the idea that a system, or one (or more) engineer(s), is fool-proof. Chernobyl and Three Mile Island should cure anyone of that attitude. The reality is, reactor contamination "events" are much more common that industry advocates would like you to believe (see below).

Remember, nuclear power in some places is a for-profit industry. Nuclear power industry CEO's have the same short-term incentives to minimize labor costs, keeping reactors online, and minimizing maintenance costs that AIG, Comcast, AOL, Best Buy, McDonalds, and every other for-profit company has. In other places, it's run by the incumbent utility company. With threats of budget reductions due to economic trends, political decisions (tax cuts anyone?), etc., event public and quasi-public utilities experience many of these pressures.

So, before portraying opponents of the nuclear power industry as milksops (or whatever you were insinuating), educate yourself a bit.

I prefer no to have a few hundred MBA's riding shotgun on doomsday machines. It's bad enough as it is already.

See also:

• http://news.google.com/news?q=nuclear%20reactor%20leak (way too many results show up)
• http://www.nytimes.com/2006/03/17/national/17nuke.html
• http://www.miamiherald.com/982/story/1035992.html
• http://www.physorg.com/news162708897.html
• http://bristol.indymedia.org/article/18446
• https://secure.wikileaks.org/wiki/The_Monju_nuclear_reactor_leak
• http://hyperphysics.phy-astr.gsu.edu/HBASE/nucene/nucacc.html

You get the point. You don't want one of these in your backyard. Nobody does. So let's not build any more of 'em.

Here's a crazy idea: how about nuclear power? Oh, that's right, the word "nuclear" is too super-scary for the science-based environmentalists. Never mind that they actually are better for the environment than anything else.

I would agree with you if, by "actually," you really mean "not actually." Many opponents of nuclear power, myself included, are not so much bothered by radioactive waste disposal issues. We are much more concerned about the high cost of system failures.

Everyone here is familiar with how difficult it is to keep defect rates in the 5 sigma region, let alone the 6 sigma region. Even with a spectacular 6 sigma failure rate, that means some failures _will_still_happen_. The longer a plant operates, the more likely a problem with occur. The more plants the operate, the greater the number of towns and cities that will be contaminated.

No control system is fool-proof, as students of the nuclear power industry know. What is most dangerous to safe reactor operation is the idea that a system, or one (or more) engineer(s), is fool-proof. Chernobyl and Three Mile Island should cure anyone of that attitude. The reality is, reactor contamination "events" are much more common that industry advocates would like you to believe (see below).

Remember, nuclear power in some places is a for-profit industry. Nuclear power industry CEO's have the same short-term incentives to minimize labor costs, keeping reactors online, and minimizing maintenance costs that AIG, Comcast, AOL, Best Buy, McDonalds, and every other for-profit company has. In other places, it's run by the incumbent utility company. With threats of budget reductions due to economic trends, political decisions (tax cuts anyone?), etc., event public and quasi-public utilities experience many of these pressures.

So, before portraying opponents of the nuclear power industry as milksops (or whatever you were insinuating), educate yourself a bit.

I prefer no to have a few hundred MBA's riding shotgun on doomsday machines. It's bad enough as it is already.

See also:

• http://news.google.com/news?q=nuclear%20reactor%20leak (way too many results show up)
• http://www.nytimes.com/2006/03/17/national/17nuke.html
• http://www.miamiherald.com/982/story/1035992.html
• http://www.physorg.com/news162708897.html
• http://bristol.indymedia.org/article/18446
• https://secure.wikileaks.org/wiki/The_Monju_nuclear_reactor_leak
• http://hyperphysics.phy-astr.gsu.edu/HBASE/nucene/nucacc.html

You get the point. You don't want one of these in your backyard. Nobody does. So let's not build any more of 'em.

The real question is "how plentiful is ANYTHING relative to silicon?"

The answer: really, really, goddamned scarce, unless you're oxygen.

http://hyperphysics.phy-astr.gsu.edu/Hbase/tables/elabund.html

Actually the efficiency of a diesel engine has more to do with the greater compression ratio rather than density of diesel fuel

You probably mean these fellas

Forgive me for responding based on reality, rather than nonsense.

Anyway, even in the nonsense-verse, the pressure required to pump blood up 15 feet is quite likely to exceed the difference in atmospheric pressure over those 15 feet (the important part here is that only the delta can help push the blood up, the air at the top is pushing down...); animals don't maintain a vacuum in their brains and diffuse oxygen up a column of liquid, so a barometer is pretty much a useless analogy.

In our present day atmosphere, 15 feet of altitude provides a pressure difference of less than 1 mmHG (and that is starting at sea level, start higher and you will get less of a drop), about 1% of the pressure required to circulate blood through our puny human bodies. I used this widget to make that calculation:

http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/barfor.html

That's using 760 mmHg as ground pressure, 30 degC as a temperature (using a lower temperature doesn't change it much), and 15 feet as an altitude.

I'm pretty sure the formula is an approximation, so just plugging in huge numbers won't be real accurate, but plugging in a pressure of 282,000 mmHg (that's 370 atmospheres) does give 150mmHg of difference, enough to have a real impact, even for a huge creature. A 15 foot neck means that the blood pressure needs to be able to push, roughly, a 15 foot column of water, which is equivalent to about 350 mmHg. So an ultra-thick (probably to the point of absurdity) atmosphere could certainly help, but that is all it is going to do, the creatures are still going to face an interesting problem.

"... does a light dimmer use something like a potentiometer?"

A light dimmer uses a Triac, a semiconductor device that can be turned on at some point during one half-cycle of alternating current. If it is turned on late, the light is dim. If it is turned on earlier, the light is brighter. When the alternating current passes through zero voltage, the device turns itself off.

A Triac is a kind of Thyristor.

1. All work requires energy. Energy is the capacity for doing work.
2. Oil and gas production is at or near peak, and we get 85% of our energy from it, and Coal is not a "good idea".
3. Therefore: our capacity to do work will decline if efficiency doesn't meet decline rates, and work can't grow if the efficiencies don't exceed decline rates.
4. decline rates in major oil fields are extreme - The North Sea, Mexico's Cantarell, are both in double digit decline rates. The USA has been declining since 1970. The only places left are mostly i nthe middle east, and some of them are at or near peak, and their production cannot be increased to match the declines elsewhere.

Therefore, a loan, which is a claim on future labour, is not a "great idea" when we know that the sum total of work can only decline from present levels, if efficiencies are not implemented immediately, and decisively.

From this, and the excesses of the system at the peak of energy development, the logical direction of survival would be for the USA to:

1. Nationalise the banks, immediately.

2. By nationalising the banks the USgov repudiates the bank debt.

3. Disband the Federal Reserve. The USgov will be responsible for its money supply.

4. Nationalise USA Health Care. Face facts: This whole nonsense about âoeyour health care decisions should be between you and your doctorâ is BS. You know who makes your health care decisions? The insurance company. The USgov should eat the health care industry directly (on the one end) and get really pretty damn stiff with fat ass Americans on the other end.

5. Gas should be USD$5 gallon. Minimum. If gas is cheaper than that due to over production or demand destruction, then the remainder goes directly into alternative energy systems.

6. Car makers should go chap 11, and restructure under strict supervision. There should a be a refocusing of vehicles away from the armoured chariat and more towards the beefed up bicycle/tricycle. 7. The USA must abandon its Empire. The Pentagon must cut its budget by 50% a year until it is the size of the Chinese rate, or less, of spending. American Troops must be brought home, decomissioned, and retrained for the powerdown.

8. Crash Infrastructure improvements geared around livable homes and communities worth caring about. LOTS of insulation. Lots of geothermal, etc..

Now if you see an opening for financial mathematics in that, you're better than I am.

I don't think "financial mathematics" has much of a future. Any more than public relations or drama therapy.

a traveler at a velocity 0.9 times the speed of light will make the trip in only a few years

A speck of paint put a nearly quarter inch wide pit in the window of the space shuttle.

http://www.space.com/spacewatch/space_junk.html

Bear in mind as the article mentions orbital velocities are as slow as 17,500 mph. The speed of light is approx. 670,000,000 mph.

http://en.wikipedia.org/wiki/Speed_of_light

If you're going at 0.9c, hitting anything the size of a golf is going to end your trip real quick!

A golf ball has the mass of about 0.046kg.

http://hypertextbook.com/facts/1999/ImranArif.shtml

At 0.9c it would have about 5.4*10^15 J of KE.

http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/releng.html

In contrast, a 20 kiloton fission bomb has about 8.4*10^13 J.

http://www.chemcases.com/nuclear/nc-09.htm

Another way to look at it is this... you're not going towards Alpha Centauri at 0.9c ... Alpha Centauri is coming towards you at 0.9c.

Granted the space between here and Alpha Centauri is mostly empty, but what are the chances of hitting anything within a couple of orders of magnitude of the mass of a golf ball b/w here and Alpha Centauri? Even hitting something 1/100 its mass at that speed is going to be like a small nuke going off.

That definition of heat which you have given is commonly stated in physics or thermodynamics textbooks, and for most things, it's perfectly correct. I really should not have used the words "basic thermodynamics" in the grandparent post, because, yes, as you've stated, photons are a form of heat as the word "heat" is used in thermodynamics. I should have made much more clear the context of my pedantry. ;) I'm just tired of all the people who have the misconception that the molecules in a solid object at room temperature are sitting still, and that there's this magical thing called "IR light" that hot things are somehow full of.

However, you don't hear the term "heat" used unqualified very often in academic literature without some sort of meaningful context. In the English language, heat has dozens of definitions, and you can guarantee that your research will be misunderstood if you say something that might have slightly different meanings to chemists, mechanical engineers, cosmologists, particle physicists, solid-state electronics designers, etc. That's why it's almost always given with a certain context and is typically found in a phrase such as "heat transfer," "heat capacity," "specific heat," etc., which all have very explicit usage and meaning. When most people casually refer to heat, they are referring to the internal energy, a sum of the kinetic energy (actually a very complex thing; the simple water molecule has six vibrational modes) and latent energy from the arrangement state and material phase (again, water has more fun behavior to offer). When most people refer to light, they are referring to a collection of photons. The energy associated with the process of heat transfer is a quantity, whereas photons are a physical object. Quantities and physical objects are not interchangeable in language.

(This whole problem of communication is made even worse by adjectives like "hot," which often refers to temperature, a quantity with a distinctly different nature and meaning than "heat.")

This is really a question of usage and semantics. I would say that light can impart heat to a substance, but photons themselves are transfer particles. Heat transfer is known through three processes, conduction, convection, and radiation; in a specific temperature range, the energies of most photons radiated from an object with perfect emissivity (a black-body) fall into the FIR range. I think conceptually, though, it's a lot better for someone to think of heat as molecular movement and light as electromagnetic particles with a definite energy corresponding to their frequency; explaining to most people that one mechanism of heat transfer that brings bodies into equilibrium is the exchange of photons with energies corresponding to the absorption spectra (ignoring fluorescence and similar phenomena here) of said bodies--but that heat on a molecular level is typically considered a function of particulate motive behavior--only seems to confuse many people, reinforcing the misperception that hot things are hot because they're full of infrared light that slowly leaks out. You would not BELIEVE how many people think something like this.

you want to double our NG production, taking us from about ~50 years of capacity to less than 25.

Currently LNG generates 20% of the electricity in the US, that should be enough for the baseload.

With breeder reactors or proper reprocessing, we reduce the amount of waste by something like 90%

My memory may be wrong but I think you said you had worked at the Monju reactor in Japan. According to wiki, which I'll grant may be wrong, the only breeder reactors that were commercially operating was Monju and the BN-600 reactor in Russia. Monju was closed though and BN-600 has had a number of leaks. Every other breeder reactor I could find is only in the test stage, such as those in France and Japan. Are there any commercially operating breeder reactors actually other than the two above? Or is more research needed before they are put into production? If there are any in production can use the waste sitting in casks and cooling ponds at operating power plants be used as fuel for them?

What I'm puzzled about is I found this webpage that says BN-600 is France's. It also mentions France's Super-Phenix but it doesn't say whether it's in commercial operation or if it is a test reactor.

Falcon

Chernobyl didn't have a containment dome. It suffered Xenon poisoning because of the low power levels the test demanded, the technicians turned all the safety measures off to run their test, they pulled the control rods out, and it had a positive void coefficient so that the process fed back on itself. See the Hyperphysics page here. To quote from that page: "It was like airplane pilots experimenting with the engines in flight" (Legasov).

Okay, so human error will always happen, right? That's why newer plants fail safe. All western plants have containment domes, and newer plant types (such as pebble bed reactors or Generation III reactors like the AP1000) are passively safe, which means that even if all the coolant is removed, nothing happens. Also, most plants automatically scram (insert control rods to maximum positions) on error.

Now let's look at Three Mile Island. A problem in an unrelated system caused the primary feedwater pump to fail. The reactor automatically went to scram as designed (thus showing what I said in the last paragraph). However, a valve that would vent steam caused by heating the water by decay heat (since radioactive decay still happens even when no fission is going on), failed to close, and the monitoring systems did not show clearly enough that it was indeed open long after it should be.
The result was that the reactor in question (TMI-2) was severely damaged and some radioactive Krypton was released. What danger did this entail? To quote the Merck manual, "the Three Mile Island accident did not result in major radiation exposure; in fact, anyone living within 1 mile of the plant received only about 0.08 mSv additional radiation". As a comparison, a chest x-ray is between 0.05 and 0.1 mSv.

Solar might be more safe, but it also occupies a great deal of space and is much more expensive. Fossil fuel plants pollute and for coal in particular, there are mining accidents; since a given amount of coal provides much less energy than a given amount of uranium, a lot more has to be mined for the same amount of energy. Chernobyl was the Bhopal of nuclear power, but we don't stop making pesticides just because of Bhopal, and so we shouldn't stop nuclear power just because of Chernobyl either, but instead take the proper precautions and engineer the systems to be safe.

Except that the interaction cross-section of something like this is so low that the density of the core of the earth might as well be zero. Even were it to fall into the center of the Earth and were it to have an infinite lifetime, it would fall there without colliding with anything and remain there for billions of years, still without interacting.

A solar-massed singularity would have a SC radius of 3km. The Schwarzchild radius (event horizon) for a black hole with the mass of the Earth has been calculated to be about 9mm. Therefore, any singularity created out of LHC experiments will be far tinier than 9mm, very likely microscopic in fact.

Something that dense and that tiny will fall to the center of the earth at near-freefall speeds, and nothing would be able to stop it.

If the hole were to fall down to the center of Earth's mass the way I describe, it would have picked up some mass as it descended, due to the "snowball effect", but it would not be a terribly large amount relative to Earth's overall mass. So its event horizon would still be considerably tinier than 9mm.

If we can estimate how much mass the hole would pick up via the snowball effect, we can get a decent estimate of its Schwartzchild radius. To make a wild guess, I'd speculate perhaps it would be measured in micrometers or nanometers.

The Schwartzchild radius and gravitational mass of the hole is irrelevant if the hole sits at the bottom of a larger mass's gravity well, and all of that mass is pressing down into it.

It's true, but irrelevant that the Earth's core's density might as well be zero compared to the density of the microsingularity. The singularity's density is infinite; anything non-infinite might as well be zero in comparison. This does nothing to protect the earth, however.

However tiny the singularity is, any mass that crosses its event horizon adds to the mass of the hole, and increases its lifespan, and increases its gravitational strength, and increases its event horizon.

As the very center of the core falls into the hole, the material above will fall in to replace the void left by the compression of the material that just fell into the hole. It's not that the singularity's gravity well will be causing the earth to be eaten; it's that the earth's own mass will continue to press inward, where it will be eaten by the microsingularity, adding to it, and increasing its lifespan. The mass more falls into it, the more the surrounding outer mass will tend to collapse inward.

Interaction will accelerate, just as a falling body accelerates in Earth's gravity well, which is indeed what would be happening. The entire Earth would be falling into its own gravity well, disappearing behind the event horizon of the singularity at the center.

One of the important factors that was overlooked other than the inefficiency of DC over large distances is the risk of electric shock. DC is unforgiving and anyone who receives a shock at the higher voltage levels will have very little to no chance of survival as DC current polarizes the blood and there is no way to reverse that effect in time to save that person.

See the following for a basic description of what this is about.

http://www.cdc.gov/eLCOSH/docs/d0500/d000543/section2.html

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/shock.html

The difference between direct and alternating voltages and currents is that one swings negative to positive thereby reversing the polarity of the potential while with dc everything is a constant supply and thus more harmful.

=Smidge=

Iron is unlikely to be depleted any time soon

There's no such thing as -20 K

Depending on who you talk to, that's not strictly true.

It is possible to have a negative Kelvin temperature, you can approach absolute zero asymptotically from either direction, you just can't reach 0 K.

The most common example is the laser. When the active layer is excited, there is a population inversion where there are more excited states than ground states (in this case electrons sitting on higher energy levels). This is reversed on the emission of coherent photons, which brings the electrons back down to their ground state.

Note: This ground state is still higher than that at 0 K, thermal energy excites some of the electrons, just not the majority.

Another way of looking at it, is that something with a negative temperature is hotter than anything with a positive temperature. This is because energy will flow from the unstable negative temperature to the positive temperature.

1) 20 picoseconds is a half life (so it has a 50% chance of decaying every 20 picoseconds).

2) Time slows down for a fast moving particle. This was one of the first pieces of evidence for special relativity:
http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/muon.html

I would not call it radioactive - I would say that it emits radiation. Radioactivity is a property of an atomic nucleus see here and here. If you are generous you could extend it to decays of subatomic particles but it does not really stretch to radiation produced by interacting subatomic particles!

No, he is not wasting away his life, he is trying to join dreamers who are trying to change Second Law of Thermodynamics. When he understood that unfortunately, that was just a dream, -sorry R.E.M. was on the radio :)- it will be long past the point of no return....

It's not misspelled.

http://www2.gsu.edu/~wwwesl/egw/jones/differences.htm

In the late 1960s, I was taught high-school physics from the PSSC (Physical Science Study Committee) Physics textbook. The curriculum and textbook were put together by an NSF-convened panel. All the curriculum materials (textbook, supplementary readings, teacher's guides, experimental equipment) were made freely available. I still have two copies of the textbook produced by different publishers and with different covers but identical inside.

Although it was demonstrably superior to other physics curricula, the PSSC program was ultimately a failure because publishers, who couldn't make much money selling the PSSC textbook due to competition, eventually dropped the book and pushed hard to get their proprietary, therefore more heavily marked-up, textbooks adopted by school boards.

Since water is much more reflective to infrared and ultraviolet than visible light, ocean plants should be unaffected.

If petroleum companies want to fund such a project all by themselves, fine, but no taxes should be spent treating their pollution one symptom at a time. Instead, governments should fund replacements: solar, wind, cellulosic ethanol and maybe nuclear power.

I'm guessing: E=mc^2.
See for instance here

It literally is a rule of the universe.

Entropy