Economics 101: if the economy does badly, it's the fault of unions
It is arguable whether the unions were to blame for the state of the UK economy in the 1980s but they certainly were not helping it recover. The reforms she introduced included things like requiring a vote of members before a strike could be called, limiting the terms of union leaders (before her some unions elected leaders like popes - they were elected for life), requiring one vote per member - no massive block votes. Effectively she required the unions to actually pay attention to their members - I don't see anyway that these reforms can be seen as anything but a good thing. It stopped union bosses making decisions in their own best interests rather than the interests of the workers they were supposed to be representing.
Had she stopped there she would have been remembered as a truly great prime minister. Unfortunately having fixed the economy by making the unions function properly again she then went a lot, lot further and did a lot of damage. Her legacy would have been far greater had she been a one term prime minister.
Like air travel? Coupled with a higher population density I'm not convinved the net affect of breakthroughs has made containment easier. Again, sticking to real events as a guideline, containment did not work with swine flu did it?
Yes but with the Spanish flu as much as 50% of the world's population was infected so, while a nuclear weapon is limited to killing the people in one city a biological weapon can reach into practically every home on the planet. Those "some people" will include your friends and family so again I would say it seems just as terrible as a nuclear weapon but in a different way.
Speaking of naive. You're sure of this. Just a 'few sequences' and poof, the end of life as we know it?
Obviously that seems exceedingly unlikely so to try to cut through irrational fears lets try looking at a real disease. The Spanish flu of 1918 killed 50-100 million people world wide. If we scale that as a percentage of the population today that number would be 180-300 million and that is for a disease which 80-90% of the people who caught it survived. This is clearly comparable to several, powerful nuclear weapons and for something as infectious as flu it is unlikely that you could stop it once it got out e.g. the recent swine flu outbreak.
So for those involved in researching viruses with the same, or worse, potential as the spanish flu why shouldn't there be similar safe guards to nuclear weapons researchers? The consequences of material getting out is similar in both cases and, in a world with suicide bombers, I'm not sure I'd rely on the fact that a biological weapon may well kill the one who releases it to stop if from happening.
So you're saying it's impossible that science will ever be able to create the conditions to cause dark matter to come into being?
No, I'm personally working on a large, international experiment which hopes to do exactly that and we certainly aren't using chemistry! Once DM is made it is stable and does not interact easily with matter and we know this from astronomy.
Twice as many would be needed because you have to slow down too.
Please, please, please take a high school physics course - you seem to be very interested in physics but also seem to lack even the most basic understanding of it and I can't correct that in a few posts. However in this case after you have fallen into the planetoids gravity well and zoomed by the surface at 10% fo c you will then start to move away from it on the other side and slow down automatically due to the gravitational field.
Wouldn't these "clumps" of Dark Matter suck in regular matter too?
Yes they would...and in fact did: this is how galaxies formed! Dark Matter far outweighs normal matter the gravitational field of its clumps pulled in normal matter which then formed the galaxies we see today.
Wouldn't all of these particles keep piling up at the same point and eventually become black holes?
No because for particles to "pile up at a point" they all have to have the same position AND velocity. If they have the same position but different velocities then they just move apart - like two water waves travelling in different directions they would just pass through each other. To get particles to pile up should have to have an interaction when they get close which will cause them to exchange momentum so that, given time, all the particles end up with the same velocity. Whether they can have the same position depends on what type of particle they are. Particles called "bosons" (which give us forces) can pile up in the same position and velocity state. Particles called "fermions" (which give us matter) cannot. So overall, while it is possible, I would say it is unlikely that you would get a dense enough collection of Dark Matter to make a black hole without normal matter helping out...but I'm a particle physicist not an astronomer!
How can Dark Matter be a particle if the particles do not interact except through gravity?
Neutrinos are particles even though they are electrically neutral and so not feel the EM force. Electrons are particles even though they do not feel the strong (nuclear binding) force. If DM particles only interact through gravity it just means that they carry no charge of any of the other forces of nature (weak, strong or EM). However it is possible that they do carry a weak charge and so will feel the weak force...we just don't yet know.
Yes - the Moodle algebra question plugin was written by me and has been ported to newer Moodle versions by others (one of the things I love about Open Source!). However I've now teamed up with others around our campus and we are putting together a more math-capable engine with far better SAGE integration. Thanks for the links to your projects - they look interesting!
People are good at taking otherwise inoffensive substances and concentrating them into all sorts of volatile configurations.
Dark Matter is not made of atoms nor does it have any electrical charges. You cannot do chemistry with it - it is fundamentally different from any normal form of matter. What you propose is in direct contradiction to the know properties of Dark Matter.
Gravity gets stronger the closer you are to its source. A chain of dark matter 'planetoids'...
Take a high school physics course and then do the maths. To get up to 10% of light speed (30,000 km/s), assuming your planetoid was Earth-sized and neglecting relativistic effects you would need a mass 22 times that of the sun. Now explain to me again how sticking a mass 22 times larger than the sun anywhere near our solar system would not severely impair the orbits of the planets?
If you include relativity the mass you need will increase and, even if you get to 10% of c we are still talking 30-40 years to get to the nearest star. Although this travel time will soon decrease as the line of 22 solar mass planetoids you'll need to sustain this speed will rapidly collapse into a blackhole with a mass so large that us and all the nearby stars will get pulled into it. Technically at this point travel to the matter which used to be Alpha Centauri might be possible but since we will all be being ripped to shreds by the tidal forces in the black hole's accretion disc I doubt anyone will appreciate it.
So, as I said, please don't try this anywhere near out solar system.
Yes...but it is not neutrinos. Neutrinos have tiny masses - so low in fact that we have not been able to measure them yet but we know that they are not zero because the oscillate which means there are mass differences between them. This means that when they were created they were moving at close to the speed of light so they would travel a huge distance before gravity would pull them back into the clump.
This would result in huge sized, very diffuse clumps of Dark Matter. However all the data suggest that Dark Matter is more clumped than that i.e. the clumps are far smaller than they would be for a particle travelling nearly at the speed of light. So the result is that we need something that interacts somewhat like a neutrino but which has a huge mass - probably heavier than any particle we have yet discovered. If we can find it then this would be a bigger discovery than even the Higgs!
Grading is not, or should not be, about the grade, it should be about the feedback that the lecturer gives to the student.
Not always: there are two types of assessment. Formative assessment where the aim is to let the student know what they understand and what they need to work on. This is what you describe. There is also Summative Assessment where the aim to to assess what the student actually knows. Usually I try to get some of both - for example although a midterm is mainly aimed and finding out how much the students have learnt I'll also spend a lecture to go through the exam to give detailed solutions and feedback to students so they know what they did not understand and can learn from the experience. However since final exams occur after the end of the course these are pretty much entirely assessing a student's knowledge and have little educational value (although I post usually solutions online and will explain things to students if they come and ask).
It sounds reasonable in the abstract, but in practice it was utterly wretched.
No, the abstract does not sound reasonable: as with most things online you can always find bad ways to do it. I'm a physics prof working as part of a team to develop an open source, algebra capable question and content system. However even the current capabilities of something like Moodle (which is Open Source) is far in excess of what you describe. You can type in multiple "answers" to a problem and have the student get feedback and a partial grade if they get the problem wrong in a way that you managed to guess. Obviously if they find a new way to get it wrong then they will not get feedback though.
Commercial systems go even further with the student having the option to click on a help button which can break the question into steps for the student to complete in rder to guide them through to the right answer. This can be configured to give a grade penalty at the choice of the instructor - this is one of the features we want to add to an Open Source solution.
However even with current Moodle capabilities you can build a system that, I would argue, is better pedagogically for many physics problems (those with numerical or symbolic responses) than paper-graded assignments because, with an online system with some feedback and multiple attempts the student is encouraged to keep trying until they figure out how to get it right. This encourages them to think out the solution themselves whereas with a paper assignment they get one try and are then given the answer. To make this work though you need some means for students to come and talk to you and/or TAs to provide some help towards getting the right method. So you still need the student-teacher interaction but computers can provide a first line of contact and so let a teacher help more students.
That being said I find it exceedingly unlikely that this EdX system can work for written responses beyond checking that their english is good. For physics how can it possibly know that the statement "the Higgs boson has a mass of 140 GeV/c2" is wrong and "Dark Matter does not interact with photons" is correct? To be able to grade it will have to know a huge amount of information about a massive range of topics - and looking this stuff up on Google is not an option given all the crazy people and their wacky physics theories which they stick on a web page.
It has a mass because it exerts a gravitational field and the distribution of the mass is non-uniform. This means it is a particle, unlike Dark Energy which is the energy of the vacuum.
I'm sorry that I cannot distinguish the finer details between the US American and the British English
Sorry but if you've been to London and still don't know that it's called the tube, or at least the underground, then you can't blame a reader for having doubts - the first being whether you've ever actually visited London and the second why someone from a land of people brave enough to ride the Chicago 'L' would have any concerns about the London Underground.
Why would Dark Matter be more diffuse? If it only interacts via gravity, shouldn't it be more compact than ordinary matter
That's a very intelligent question! That's exactly what you might expect but you need to go a little deeper. Think about a planet forming from a cloud of dust and rocks. Once a clump of a few rocks has formed it starts to pull in more dust and rocks from the surrounding cloud and a planet starts to form because rocks in the cloud are pulled in my the gravitational field of the clump until they smash into it and stop. This increases the mass of the clump so it pulls in more rocks and grows.
The critical part is that the only reason that the rocks stop when they hit the clump of material is because of the electromagnetic repulsion between the atoms in the rock and the atoms in the clump. This is the same reason that you do not fall to the centre of the Earth - the atoms on the soles of your feet are repelled by the atoms of whatever you are standing on.
Now lets think about Dark Matter. It has no electrical charge and so feels no electromagnetic force. So when a Dark Matter particle is attracted towards a clump of other Dark Matter particles it simply passes right through them without any interaction! It then starts to slow down under their gravitational field until it, eventually, turns around and flies back through the centre. Effectively all a "clump" of Dark Matter is is a group of particles oscillating back and forth in their shared gravitational well. This is why Dark Matter is so diffuse - it can form structures but only on a very large scale.
This is not quite the entire picture - there may be a very small chance of an interaction when Dark Matter particles pass by each other. This will help the particles to clump more but it will be a very, very slow process - and this is only the case if Dark Matter feels the weak force which is not certain. These interactions might also involve two Dark Matter particles annihilating which, if true, may give the positron signal which AMS sees. However to confirm this they need to look at a sightly higher energy which they claim they already have the data for.
It does form structures, so I'd say it's too early to make definitive statements about what can and can't be done with it.
That it does - huge, massive structures on a galactic and cosmic scale. The reason for this is that it interacts via gravity and, perhaps, the weak force. I agree that we can say very little about it at all at the moment but I do think that we can say that it will not form structures on a stellar scale which can generate a large enough gravitational field to accelerate an object to close to light speed in a reasonable length of time.
Yes, if you read the rest of the comments the concept isn't within the solar system nor is it a single large gravitational field.
You cannot stop a gravitational field at the edge of the solar system - gravitational fields are infinite in extent. In order to have feasible interstellar travel you would need to have a reasonably rapid acceleration. Any gravitational field capable of generating that would disrupt planetary orbits.
First the energy limit on interstellar travel is not getting out of the gravitational well of the sun it is getting up to a large fraction of the speed of light. If your intention was achieve that sort of velocity with a gravitational field then please try this is someone else's solar system because a gravitational field of that magnitude - think black hole - will do nasty things to planetary orbits.
Second Dark Matter is incredibly diffuse, far more so than normal matter because it only interacts via gravity and - possibly - the weak force. So there it no way to make small, dense concentrations of it like you can with normal matter.
Finally, the AMS results does not yet show any evidence for Dark Matter. They need to extend their energy by a few bins to see whether the spectrum starts to drop - the current spectrum could be explained by pulsars - the positron excess has been known to be there for some years already thanks to PAMELA and Fermi/Glast(for a slightly more technical announcement with plots see here). So it is a very interesting result but not yet evidence of Dark Matter. However, if it is Dark Matter, it should have a low enough mass to be created in the LHC so we may get a shot at finding whatever it is in 2015 when we turn back on with ~twice the energy. In fact my grad student and I worked on the ATLAS search for Dark Matter models associated with this type of positron-only signature but found no evidence. It's now being repeated with the 2012 data so stay tuned...
I was especially appalled by the famous London subways (and took a double take when I saw what they wanted from me to ride on it).
I'm not surprised you were shocked if you were trying to ride on something you found in a London subway. Next time I'd suggest you take the London Underground, usually referred to as the tube.
well, it's a no brainer if you have the option for a 300km/h line. but for a route like that, it's likely a bus would get you there in half a day anyhow
Clearly you have not seen the traffic in Europe. You cannot generally calculate travel time by taking the distance and dividing by ~100 km/h for motorway speeds like you can in Canada and the US. I knew an American postdoc who planned to drive his family from Cambridge to Hadrian's wall (~200 km) for a day trip because he thought it would just be a 2 hour drive each way - he did not have a good weekend!
A higher population density helps trains more than just by making the lines more economical: it makes driving far less attractive!
Does anyone know of a flight search engine that allows you to do this ?
While it will not specifically filter out transfers through a particular country it lets you manually select individual flight legs and you can filter via airline (there are a lot of other options too) so just do not use a US airline and you should be good. I use it regularly to get from Canada to CERN avoiding the US and the multi-transfer, large lay over option via Montreal that the Air Canada site will invariably pick out purely for their benefit so you fly on an Air Canada flight all the way to Geneva rather than use Swiss or Lufthansa in Europe. You may have to try a few options before you find one with a reasonable price but I've found it to be the most flexible of all the travel sites I've used (and in case you were wondering I am not in anyway associated with it!).
Its only downside is that you cannot book through their site - they just provide a link to a travel site like Travelocity or Expedia with the options to book the exact flight schedule. So you usually end up having to pay in US dollars even though you never go through the US!
It might be a joke but it raises the question: whose dollar? As a virtual currency whose regulations will apply to a transaction when, for example, one person is in Europe and another in the US?
The most unethical people through history has been highly educated.
Even if true that does not make them scientists. For example Hitler wanted to be an arts student (but was rejected), Stalin studied at a theological school and seminary and, if we switch to financial ethics, Kenneth Lay (CEO of Enron) had a PhD in economics. So, based on a sample of these three I would argue that your hypothesis looks to be on shaky ground and, even if it is true in general, does not seem to contradict the claim that _scientists_ are more ethical.
If you look at cases of scientific fraud then of course this has to be committed by highly educated scientists. I would argue that this is probably a far lower level than the rate of financial fraud among economists and other business types because scientific fraud is counter-productive and rarely results in a benefit for the perpetrator because the very nature of science requires that claims be independently verified. Financial fraud can have huge benefits for the individual can be significantly harder to detect - did a CEO choose to do X because they thought it best or because they were bribed to do it? Without clear evidence of a bribe you cannot be certain. In science the evidence of the misdeed is inherent in the claim - the best you could hope for is to make it appear as an honest mistake and even then you incompetent.
I'm saying it's wrong, and I'm not going to play the game.
That's your choice but unusually given modern business practices I actually don't see a lot wrong with this one. Apple are selling a popular phone and frankly the reason it is popular has more to do with fashion than functionality. So to keep it popular it needs to be in adverts for the carriers which have it. Assuming the minimum numbers are not punitive all this contract does is ensure that a carrier is making a major commitment to sell the phone. They don't want iPhones sitting on some carrier's shelf and getting sold almost by accident - they need to have it pushed to keep its fashionable appeal.
Yes but that is not the way that it worked. ATLAS PhD students worked on a piece of the detector which did not, and could not, deliver physics results before there was beam in the LHC. Their "physics" was simulation studies about what they would be able to do once the LHC was turned on. This is why special permissions and understandings had to be obtained for them to submit their theses because there were no real physics results in them only simulations of what those results might be.
Even after paying the shipping container and the VAT, it is still significantly cheaper than buying in Australia.
So why is there no business which buys goods in the US, ships them to Australia and undercuts the prices there then? That's not illegal, they could do it for a lot less than a commercial plane ticket and private shipping and you would not need to get felt up or irradiated by US security.
It's because it is what the patient expects and not delivering that is damaging to the doctor/patient relationship. In the long run that damage can have a catastrophic impact on the patient's health.
That's incredibly short sighted. By prescribing unneeded anti-biotics you are encouraging anti-biotic resistance which in the long term can damage the health not only your patient but also of millions of others. Not only that but you risk damaging the doctor-patient relationship irretrievably because you are effectively lying to the patient that they need a treatment which they do not. If they ever find out not only have you destroyed that relationship but, if I was the patient, I'd report you to the relevant authorities.
I know that patients can be a really insistent at times - my dad was a GP - but his attitude was that he would never prescribe unneeded anti-biotics and if the patient didn't like that they could find another doctor. Speaking as a patient I'd much, much rather have a competent doctor who's primary concern is my health and not whether he might hurt my feelings by telling me I don't need a treatment. It might be irritating at the time but, as long as the decision is correct, over time those correct decisions will build trust which is a far stronger foundation for a relationship than unnecessary treatments.
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Economics 101: if the economy does badly, it's the fault of unions
It is arguable whether the unions were to blame for the state of the UK economy in the 1980s but they certainly were not helping it recover. The reforms she introduced included things like requiring a vote of members before a strike could be called, limiting the terms of union leaders (before her some unions elected leaders like popes - they were elected for life), requiring one vote per member - no massive block votes. Effectively she required the unions to actually pay attention to their members - I don't see anyway that these reforms can be seen as anything but a good thing. It stopped union bosses making decisions in their own best interests rather than the interests of the workers they were supposed to be representing.
Had she stopped there she would have been remembered as a truly great prime minister. Unfortunately having fixed the economy by making the unions function properly again she then went a lot, lot further and did a lot of damage. Her legacy would have been far greater had she been a one term prime minister.
No big breakthroughs since then.
Like air travel? Coupled with a higher population density I'm not convinved the net affect of breakthroughs has made containment easier. Again, sticking to real events as a guideline, containment did not work with swine flu did it?
Yes but with the Spanish flu as much as 50% of the world's population was infected so, while a nuclear weapon is limited to killing the people in one city a biological weapon can reach into practically every home on the planet. Those "some people" will include your friends and family so again I would say it seems just as terrible as a nuclear weapon but in a different way.
Speaking of naive. You're sure of this. Just a 'few sequences' and poof, the end of life as we know it?
Obviously that seems exceedingly unlikely so to try to cut through irrational fears lets try looking at a real disease. The Spanish flu of 1918 killed 50-100 million people world wide. If we scale that as a percentage of the population today that number would be 180-300 million and that is for a disease which 80-90% of the people who caught it survived. This is clearly comparable to several, powerful nuclear weapons and for something as infectious as flu it is unlikely that you could stop it once it got out e.g. the recent swine flu outbreak.
So for those involved in researching viruses with the same, or worse, potential as the spanish flu why shouldn't there be similar safe guards to nuclear weapons researchers? The consequences of material getting out is similar in both cases and, in a world with suicide bombers, I'm not sure I'd rely on the fact that a biological weapon may well kill the one who releases it to stop if from happening.
So you're saying it's impossible that science will ever be able to create the conditions to cause dark matter to come into being?
No, I'm personally working on a large, international experiment which hopes to do exactly that and we certainly aren't using chemistry! Once DM is made it is stable and does not interact easily with matter and we know this from astronomy.
Twice as many would be needed because you have to slow down too.
Please, please, please take a high school physics course - you seem to be very interested in physics but also seem to lack even the most basic understanding of it and I can't correct that in a few posts. However in this case after you have fallen into the planetoids gravity well and zoomed by the surface at 10% fo c you will then start to move away from it on the other side and slow down automatically due to the gravitational field.
Wouldn't these "clumps" of Dark Matter suck in regular matter too?
Yes they would...and in fact did: this is how galaxies formed! Dark Matter far outweighs normal matter the gravitational field of its clumps pulled in normal matter which then formed the galaxies we see today.
Wouldn't all of these particles keep piling up at the same point and eventually become black holes?
No because for particles to "pile up at a point" they all have to have the same position AND velocity. If they have the same position but different velocities then they just move apart - like two water waves travelling in different directions they would just pass through each other. To get particles to pile up should have to have an interaction when they get close which will cause them to exchange momentum so that, given time, all the particles end up with the same velocity. Whether they can have the same position depends on what type of particle they are. Particles called "bosons" (which give us forces) can pile up in the same position and velocity state. Particles called "fermions" (which give us matter) cannot. So overall, while it is possible, I would say it is unlikely that you would get a dense enough collection of Dark Matter to make a black hole without normal matter helping out...but I'm a particle physicist not an astronomer!
How can Dark Matter be a particle if the particles do not interact except through gravity?
Neutrinos are particles even though they are electrically neutral and so not feel the EM force. Electrons are particles even though they do not feel the strong (nuclear binding) force. If DM particles only interact through gravity it just means that they carry no charge of any of the other forces of nature (weak, strong or EM). However it is possible that they do carry a weak charge and so will feel the weak force...we just don't yet know.
Yes - the Moodle algebra question plugin was written by me and has been ported to newer Moodle versions by others (one of the things I love about Open Source!). However I've now teamed up with others around our campus and we are putting together a more math-capable engine with far better SAGE integration. Thanks for the links to your projects - they look interesting!
People are good at taking otherwise inoffensive substances and concentrating them into all sorts of volatile configurations.
Dark Matter is not made of atoms nor does it have any electrical charges. You cannot do chemistry with it - it is fundamentally different from any normal form of matter. What you propose is in direct contradiction to the know properties of Dark Matter.
Gravity gets stronger the closer you are to its source. A chain of dark matter 'planetoids' ...
Take a high school physics course and then do the maths. To get up to 10% of light speed (30,000 km/s), assuming your planetoid was Earth-sized and neglecting relativistic effects you would need a mass 22 times that of the sun. Now explain to me again how sticking a mass 22 times larger than the sun anywhere near our solar system would not severely impair the orbits of the planets?
If you include relativity the mass you need will increase and, even if you get to 10% of c we are still talking 30-40 years to get to the nearest star. Although this travel time will soon decrease as the line of 22 solar mass planetoids you'll need to sustain this speed will rapidly collapse into a blackhole with a mass so large that us and all the nearby stars will get pulled into it. Technically at this point travel to the matter which used to be Alpha Centauri might be possible but since we will all be being ripped to shreds by the tidal forces in the black hole's accretion disc I doubt anyone will appreciate it.
So, as I said, please don't try this anywhere near out solar system.
Yes...but it is not neutrinos. Neutrinos have tiny masses - so low in fact that we have not been able to measure them yet but we know that they are not zero because the oscillate which means there are mass differences between them. This means that when they were created they were moving at close to the speed of light so they would travel a huge distance before gravity would pull them back into the clump.
This would result in huge sized, very diffuse clumps of Dark Matter. However all the data suggest that Dark Matter is more clumped than that i.e. the clumps are far smaller than they would be for a particle travelling nearly at the speed of light. So the result is that we need something that interacts somewhat like a neutrino but which has a huge mass - probably heavier than any particle we have yet discovered. If we can find it then this would be a bigger discovery than even the Higgs!
Grading is not, or should not be, about the grade, it should be about the feedback that the lecturer gives to the student.
Not always: there are two types of assessment. Formative assessment where the aim is to let the student know what they understand and what they need to work on. This is what you describe. There is also Summative Assessment where the aim to to assess what the student actually knows. Usually I try to get some of both - for example although a midterm is mainly aimed and finding out how much the students have learnt I'll also spend a lecture to go through the exam to give detailed solutions and feedback to students so they know what they did not understand and can learn from the experience. However since final exams occur after the end of the course these are pretty much entirely assessing a student's knowledge and have little educational value (although I post usually solutions online and will explain things to students if they come and ask).
It sounds reasonable in the abstract, but in practice it was utterly wretched.
No, the abstract does not sound reasonable: as with most things online you can always find bad ways to do it. I'm a physics prof working as part of a team to develop an open source, algebra capable question and content system. However even the current capabilities of something like Moodle (which is Open Source) is far in excess of what you describe. You can type in multiple "answers" to a problem and have the student get feedback and a partial grade if they get the problem wrong in a way that you managed to guess. Obviously if they find a new way to get it wrong then they will not get feedback though.
Commercial systems go even further with the student having the option to click on a help button which can break the question into steps for the student to complete in rder to guide them through to the right answer. This can be configured to give a grade penalty at the choice of the instructor - this is one of the features we want to add to an Open Source solution.
However even with current Moodle capabilities you can build a system that, I would argue, is better pedagogically for many physics problems (those with numerical or symbolic responses) than paper-graded assignments because, with an online system with some feedback and multiple attempts the student is encouraged to keep trying until they figure out how to get it right. This encourages them to think out the solution themselves whereas with a paper assignment they get one try and are then given the answer. To make this work though you need some means for students to come and talk to you and/or TAs to provide some help towards getting the right method. So you still need the student-teacher interaction but computers can provide a first line of contact and so let a teacher help more students.
That being said I find it exceedingly unlikely that this EdX system can work for written responses beyond checking that their english is good. For physics how can it possibly know that the statement "the Higgs boson has a mass of 140 GeV/c2" is wrong and "Dark Matter does not interact with photons" is correct? To be able to grade it will have to know a huge amount of information about a massive range of topics - and looking this stuff up on Google is not an option given all the crazy people and their wacky physics theories which they stick on a web page.
What makes us believe dark matter is particulate?
It has a mass because it exerts a gravitational field and the distribution of the mass is non-uniform. This means it is a particle, unlike Dark Energy which is the energy of the vacuum.
I'm sorry that I cannot distinguish the finer details between the US American and the British English
Sorry but if you've been to London and still don't know that it's called the tube, or at least the underground, then you can't blame a reader for having doubts - the first being whether you've ever actually visited London and the second why someone from a land of people brave enough to ride the Chicago 'L' would have any concerns about the London Underground.
Why would Dark Matter be more diffuse? If it only interacts via gravity, shouldn't it be more compact than ordinary matter
That's a very intelligent question! That's exactly what you might expect but you need to go a little deeper. Think about a planet forming from a cloud of dust and rocks. Once a clump of a few rocks has formed it starts to pull in more dust and rocks from the surrounding cloud and a planet starts to form because rocks in the cloud are pulled in my the gravitational field of the clump until they smash into it and stop. This increases the mass of the clump so it pulls in more rocks and grows.
The critical part is that the only reason that the rocks stop when they hit the clump of material is because of the electromagnetic repulsion between the atoms in the rock and the atoms in the clump. This is the same reason that you do not fall to the centre of the Earth - the atoms on the soles of your feet are repelled by the atoms of whatever you are standing on.
Now lets think about Dark Matter. It has no electrical charge and so feels no electromagnetic force. So when a Dark Matter particle is attracted towards a clump of other Dark Matter particles it simply passes right through them without any interaction! It then starts to slow down under their gravitational field until it, eventually, turns around and flies back through the centre. Effectively all a "clump" of Dark Matter is is a group of particles oscillating back and forth in their shared gravitational well. This is why Dark Matter is so diffuse - it can form structures but only on a very large scale.
This is not quite the entire picture - there may be a very small chance of an interaction when Dark Matter particles pass by each other. This will help the particles to clump more but it will be a very, very slow process - and this is only the case if Dark Matter feels the weak force which is not certain. These interactions might also involve two Dark Matter particles annihilating which, if true, may give the positron signal which AMS sees. However to confirm this they need to look at a sightly higher energy which they claim they already have the data for.
It does form structures, so I'd say it's too early to make definitive statements about what can and can't be done with it.
That it does - huge, massive structures on a galactic and cosmic scale. The reason for this is that it interacts via gravity and, perhaps, the weak force. I agree that we can say very little about it at all at the moment but I do think that we can say that it will not form structures on a stellar scale which can generate a large enough gravitational field to accelerate an object to close to light speed in a reasonable length of time.
Yes, if you read the rest of the comments the concept isn't within the solar system nor is it a single large gravitational field.
You cannot stop a gravitational field at the edge of the solar system - gravitational fields are infinite in extent. In order to have feasible interstellar travel you would need to have a reasonably rapid acceleration. Any gravitational field capable of generating that would disrupt planetary orbits.
First the energy limit on interstellar travel is not getting out of the gravitational well of the sun it is getting up to a large fraction of the speed of light. If your intention was achieve that sort of velocity with a gravitational field then please try this is someone else's solar system because a gravitational field of that magnitude - think black hole - will do nasty things to planetary orbits.
Second Dark Matter is incredibly diffuse, far more so than normal matter because it only interacts via gravity and - possibly - the weak force. So there it no way to make small, dense concentrations of it like you can with normal matter.
Finally, the AMS results does not yet show any evidence for Dark Matter. They need to extend their energy by a few bins to see whether the spectrum starts to drop - the current spectrum could be explained by pulsars - the positron excess has been known to be there for some years already thanks to PAMELA and Fermi/Glast(for a slightly more technical announcement with plots see here). So it is a very interesting result but not yet evidence of Dark Matter. However, if it is Dark Matter, it should have a low enough mass to be created in the LHC so we may get a shot at finding whatever it is in 2015 when we turn back on with ~twice the energy. In fact my grad student and I worked on the ATLAS search for Dark Matter models associated with this type of positron-only signature but found no evidence. It's now being repeated with the 2012 data so stay tuned...
I was especially appalled by the famous London subways (and took a double take when I saw what they wanted from me to ride on it).
I'm not surprised you were shocked if you were trying to ride on something you found in a London subway. Next time I'd suggest you take the London Underground, usually referred to as the tube.
well, it's a no brainer if you have the option for a 300km/h line. but for a route like that, it's likely a bus would get you there in half a day anyhow
Clearly you have not seen the traffic in Europe. You cannot generally calculate travel time by taking the distance and dividing by ~100 km/h for motorway speeds like you can in Canada and the US. I knew an American postdoc who planned to drive his family from Cambridge to Hadrian's wall (~200 km) for a day trip because he thought it would just be a 2 hour drive each way - he did not have a good weekend!
A higher population density helps trains more than just by making the lines more economical: it makes driving far less attractive!
Does anyone know of a flight search engine that allows you to do this ?
While it will not specifically filter out transfers through a particular country it lets you manually select individual flight legs and you can filter via airline (there are a lot of other options too) so just do not use a US airline and you should be good. I use it regularly to get from Canada to CERN avoiding the US and the multi-transfer, large lay over option via Montreal that the Air Canada site will invariably pick out purely for their benefit so you fly on an Air Canada flight all the way to Geneva rather than use Swiss or Lufthansa in Europe. You may have to try a few options before you find one with a reasonable price but I've found it to be the most flexible of all the travel sites I've used (and in case you were wondering I am not in anyway associated with it!).
Its only downside is that you cannot book through their site - they just provide a link to a travel site like Travelocity or Expedia with the options to book the exact flight schedule. So you usually end up having to pay in US dollars even though you never go through the US!
It might be a joke but it raises the question: whose dollar? As a virtual currency whose regulations will apply to a transaction when, for example, one person is in Europe and another in the US?
The most unethical people through history has been highly educated.
Even if true that does not make them scientists. For example Hitler wanted to be an arts student (but was rejected), Stalin studied at a theological school and seminary and, if we switch to financial ethics, Kenneth Lay (CEO of Enron) had a PhD in economics. So, based on a sample of these three I would argue that your hypothesis looks to be on shaky ground and, even if it is true in general, does not seem to contradict the claim that _scientists_ are more ethical.
If you look at cases of scientific fraud then of course this has to be committed by highly educated scientists. I would argue that this is probably a far lower level than the rate of financial fraud among economists and other business types because scientific fraud is counter-productive and rarely results in a benefit for the perpetrator because the very nature of science requires that claims be independently verified. Financial fraud can have huge benefits for the individual can be significantly harder to detect - did a CEO choose to do X because they thought it best or because they were bribed to do it? Without clear evidence of a bribe you cannot be certain. In science the evidence of the misdeed is inherent in the claim - the best you could hope for is to make it appear as an honest mistake and even then you incompetent.
I'm saying it's wrong, and I'm not going to play the game.
That's your choice but unusually given modern business practices I actually don't see a lot wrong with this one. Apple are selling a popular phone and frankly the reason it is popular has more to do with fashion than functionality. So to keep it popular it needs to be in adverts for the carriers which have it. Assuming the minimum numbers are not punitive all this contract does is ensure that a carrier is making a major commitment to sell the phone. They don't want iPhones sitting on some carrier's shelf and getting sold almost by accident - they need to have it pushed to keep its fashionable appeal.
Yes but that is not the way that it worked. ATLAS PhD students worked on a piece of the detector which did not, and could not, deliver physics results before there was beam in the LHC. Their "physics" was simulation studies about what they would be able to do once the LHC was turned on. This is why special permissions and understandings had to be obtained for them to submit their theses because there were no real physics results in them only simulations of what those results might be.
Even after paying the shipping container and the VAT, it is still significantly cheaper than buying in Australia.
So why is there no business which buys goods in the US, ships them to Australia and undercuts the prices there then? That's not illegal, they could do it for a lot less than a commercial plane ticket and private shipping and you would not need to get felt up or irradiated by US security.
It's because it is what the patient expects and not delivering that is damaging to the doctor/patient relationship. In the long run that damage can have a catastrophic impact on the patient's health.
That's incredibly short sighted. By prescribing unneeded anti-biotics you are encouraging anti-biotic resistance which in the long term can damage the health not only your patient but also of millions of others. Not only that but you risk damaging the doctor-patient relationship irretrievably because you are effectively lying to the patient that they need a treatment which they do not. If they ever find out not only have you destroyed that relationship but, if I was the patient, I'd report you to the relevant authorities.
I know that patients can be a really insistent at times - my dad was a GP - but his attitude was that he would never prescribe unneeded anti-biotics and if the patient didn't like that they could find another doctor. Speaking as a patient I'd much, much rather have a competent doctor who's primary concern is my health and not whether he might hurt my feelings by telling me I don't need a treatment. It might be irritating at the time but, as long as the decision is correct, over time those correct decisions will build trust which is a far stronger foundation for a relationship than unnecessary treatments.