timo

That was, of course, what I kind of tried to suggest with my statement. But still I cannot really put a finger on what the translation back from the example into the real world would be. Media campaigns and paid "smoking is not bad for your health" studies would come to my mind, but they don't fit the topic here. "Not playing by the rules" could be denying the off-side rule (not what I meant, but also interesting). A suitable analogy would be to demand to be considered for the team instead of Beckham, because there is the -admittedly small- possibility that you perform better in the next match. That also captures one of the more under-appreciated issues: Just like the number of slots in a team, attention is a finite resource. A very memorable econophysics talk I attended a few years ago even went as far as to claim it was the most valuable resource of our century. But the foul statement is more catchy @Overtone: I am not convinced about your statement about more physicists being crackpots. What I do believe is that incorrectly extrapolating from being used to be the smartest guy in your peer group to being the smartest person in another group occurs and leads to irritation. The teenager whose friends are impressed with their pop-sci knowledge that come up with their idea of [relativity is wrong, maybe gravity is magnetism in reality, maybe everything is just energy, I think I found a key stone to the world formula] fall into this category. I am not sure if that effect explains resistance to correction, which seems to be what most people find annoying in people they call "crackpots".

Or you could brutally foul him to get a draw.

Not sure about the situation in the US (where judging from "4th year PhD student" I assume you are located at). But from my experience (Germany): It is perfectly normal for PhD students to realize they do not want to follow the university research path at some point. It does feel weird at first, because almost all people you know do not know any other life than that - and that also includes your advisor, for example. But as a matter of fact, all the top people in my undergrad, masters and PhD peer group left academia (top people being measured by academic performance). And none of them regretted it. There is a lot that could be said about weirdness/wrongs of academia, the ridiculous trend to publish papers for the sake of getting a paper published being only one of them. But such weirdness exists in every place, so that should not be what turns you off (I have enough stories from my current workplace that people would not believe, like the expert for the analysis of a 20 million Euro research project not being able to attend the meetings because being an undergrad he had to attend lectures ...). My recommendation would be to realize that there is a huge range of interesting opportunities of what one can do in life, and that a university career is only one of them. So open up your mind what you find interesting. And if you do not find anything better you can still go for the post-doc - which should be an interesting one, not merely one you happened to get offered.

I did a lot of programming in my free time in a time and hang around a programming forum a lot. Turned out I almost exclusively explained solutions or possible solutions to physics and math problems there. So one day when someone replied to such a question with "such a question is better asked at sfn", I had a look at this forum and ended up posting here more than on the programming forum - and eventually got stuck here. I am probably much less active than the average "resident" here, since my activity subsequently declined over the years. I'd still count myself as a "resident". The reasons I still sneak around here are: 1) seeing "familiar faces" (even though I neither see the faces nor am personally familiar with the people), that is people whose posts I have been reading for many years now (For example Klaynos, whom I know from sfn since he was an "academic child" ). 2) In my early times what kept me here was the occasional interesting question that I felt challenge to understand myself and put it into a format that others could understand. I remember having spent a 5-hour train ride plus some hours at work to write an article about gravitational time dilatation for the sfn wiki from which I myself learned a lot about the effect. Particularly about the implicit assumptions and conditions that you read over when reading about it and only start to worry about once you go down as deep as trying to write up a solid explanation for others. I did, however, move on to the German Wikipedia with time-consuming high-quality texts, because the impact of a good article there is much higher than that of a good post here. So for the last, ... oh my god ... eight years or so being around sfn has been a bit more intellectually casual for me, which brings me to ... 3) the intellectual level which is not so high that reading posts turns into actual work, in which case I'd rather spend the time doing something with more impact than posting on a forum. But which is way above e.g. the average comments below newspaper articles (which is abysmal, but you still need to prevent your forum going down there). This mixes very well with the mix of different sciences/fields here. Something that is casual knowledge for a biologist, a computer science veteran or an engineer can still be interesting news to me. Related to this I also do like the level of moderation here a lot, which to a large degree sets this environment. And if I finally got my request for the option of setting complete sub-forum on ignore fulfilled, that would be awesome

Just to be sure: You are aware that S is a linear operator so that from the matrix elements in any basis you can calculate the <i|S|f> for any states |i> and |f>, even if they are not elements of your basis, right? Irrespective of this, I agree that many QFT courses are lousy exercises of tedious calculations.

It's funny that yesterday my though was "if they give the Nobel prize for blue LEDs they could as well have awarded it for STED".

Troll vs. Thread: 1:0

(I wrote this 12 hours ago but somehow couldn't send it. So apologies for not taking the previous comments into account. From skimming them my thoughts go in a slightly different direction, anyways) While other fields have their weirdos, I do believe that physics has some aspects that make it suitable for crackpots. I do not know for sure, but I would expect that chemistry, a very related subject with a lot of overlap, would have less, for example. There are two reasons that come to my mind: First is Albert Einstein. To many outsiders it looks like he is the prophet of physics who descended from the havens of intellectual ingenuity to bring enlightenment to the mortals. A similar even though arguably less well-known figure would be Charles Darwin. Needless to say, similar effects as denial of relativity hold true for Darwin (except that in this case religious aspects play a large role, too). Lots of contact points for crackpottery, be it disenchanting the holy being or striving to be the next avatar of human intellectual evolution. The wording i have chosen so far already hints at a second effect, that I believe may be the most important one: Common understanding of physics often has a spiritual touch (and I probably don't have to tell you how many people you'd consider crackpots run around in the esoteric and spiritual community). Notions like physics giving you insight to "the true nature of the universe" are very common. Not only in the widest general public and among crackpots. You fill find a lot of physicists, especially younger ones and physics students, who believe the same.

It is not quite clear to me what a simulation of an atom is supposed to be. For the hydrogen atom, reasonably good analytical approximations exist that give you the energy eigenstates (Wikipedia should have then, if not they can be googled). More complicated atoms, particularly with multiple electrons are more complicated. To give an approximate order of complication: the hydrogen atom is taught to every physics or chemistry student in their 2nd year in 1-3 weeks as part of the QM introduction lecture. I took multi-electron systems as a half-year specialization course in theoretical physics in 3rd or 4th year. So I will assume the standard hydrogen atom: What you could simulate is the time-development of a given initial state. The way to go forward with this is as follows: First, you find the basis of energy eigenstates. Then, you transform the original state in a superposition of these basis states. The time-evolution for the Schrödinger equation for these basis states is trivial, so expressed in this basis the time-evolution of your initial state becomes straightforward (more or less - it certainly helps having done it once). That is what you could simulate, and the probability density of the electron location is something you could visualize. That should already be quite a project. There are a few details why I am not sure if it will actually work: You might have to take into account the "continuum states" in addition to the bound states. And I am not sure that something interesting will be seen (but if you are interested in the Schrödinger equation chances are you are interested in research, so maybe just try it). A related project I did in a "Computational Physics" course was a simulation of a harmonic oscillator. Same idea as with the hydrogen atom, but not plagued by potentially-relevant continuum states and guaranteed (by my experience of having done it) to have some visual effect: If you start with a wave packet around some location you will see it oscillate around. If you are not tied to the atom and just want to play around with quantum mechanics, programming and visualization I suggest starting with the harmonic oscillator, even if it sounds less interesting. Once you leave the situation where a teacher gives you homework that is guaranteed to have a simple solution, even seemingly trivial tasks can turn out to be huge amount of work (e.g.: do not underestimate the effort to debug simulation code, especially if you are not very familiar with the system you simulate). For particular reference material, I think it would help if you can be more specific about what you want to do - and maybe share your progress with us, later. I just read a book claiming that some personal consultants are paid a lot of money to tell people to break down their idea in 20-40 well-defined sub-steps

Makes me wonder why Royost thinks he doesn't have to convince the experimentalists. One would imagine that they are much more bull headed and exclusive that the theory guys. If I can vote for a prediction I'd prefer the calculation of the light density over the dark matter distribution one. Reason is that I feel that if you accept the dark matter distribution you could just as well accept that dark matter is not hot (i.e. the ratio of momentum to invariant mass is small) which would rule out photons in the first place. Light density sounds much more interesting, because one can have some fun thoughts about it (e.g. an upper level of possible wavelengths due to lack of detection), and because I have no feeling about what would come out of it.

I'd go as far as to claim that 0.0000... equals zero. So it simply doesn't matter, as long as nothing special happens at the interval borders (e.g. if you have discrete possible outcomes that happen to lie exactly on the interval borders). Note that this is only the statement of someone with a little background in mathematics and statistics. I cannot tell you about conventions in fields that use this Chebyshev's rule that I never heard about.

What difference do you think including the boundaries of the interval makes? Assuming a continuous underlying distribution, what percentage of events lies exactly on the boundary?

I wasn't even aware that you are talking about technology use in the classroom. I thought you were asking if it is okay to have a private conversation during a lecture, and if it is still okay after fellow students complained about it. A lot of the other posters might have also gotten than impression. So maybe that is why you are so confused about our strange posts ... Btw.: Lecturers being annoyed about students having laptops or smart phones should be happy that they were never forced to leave the ivory tower of university research and have to take part in real-world meetings.

But you have to admit that experimental evidence suggests it was disruptive to at least one student. To the point that he even bothered to complain (most people will just remain silent despite being annoyed). I wouldn't say that there has to be complete silence all the time - some level of interaction may indeed be appropriate. But I do not quite see how the amount of fellow students disturbed should play a role, except that "zero" would of course be an acceptable number.

Not going into details of my cultural prejudices: I am indeed surprised that it is Ireland that declared war on Denmark. I though the Irish were either too polite to declare war on others (if sober) or too busy fighting each other (if not sober) to declare war on Denmark.

Of course we all know that there is only one country in the world whose residents think that everyone on the Internet speaking English is from their country. But one day those arrogant Indians will learn that just because they are the largest English-speaking country in the world, not everyone comes from there

Oh, those good old times when wars were declared instead of "military interventions" being undertaken, and where you could see the guy you just stabbed bleed to death live instead of only having a screenshot of it. Sounds like an opportunity for a PR coup for politicians that need attentions: Negotiating a peace treaty between Denmark and whomever they may be at war with.

Not new or not trash? I might agree on the majority of "new ideas" being presented not being new at all. Not sure if I agree that they are not trash, at least for the many of those sold on sfn as "new thoughts". The few interesting new thoughts I see here are usually not labelled as such, but tend to come along in more modest clothing. Reasons for self-proclaimed "new thoughts" being forum-trash usually are: - arrogance (being certain that an idea is new because it is new to me) - ignorance to the fact that a lot of other people spend a lot of time working on scientific ideas - delusions of grandeur ("... but those other people are not as smart as me") - being a social asshole (pretending humility despite actually being arrogant, ignorant and delusional) - a qualitative understanding of probabilities (requesting for my ideas to be taken seriously because the chance of it being valuable is not mathematically zero) - and possibly most importantly a lack of a scientific background, implying (a) not knowing the actual state of the field I talk about and (b) not having been trained to be critical towards my own ideas/results Luckily, this was a general question by a new member not relating to any specific post. If someone feels offended by this: Don't worry, I did not mean you. Your new ideas posted here are different, of course

You cannot boost to a frame in which the photon has zero energy (EDIT to be precise: at least that is what I would imagine from physical intuition, if you want to verify it then look up redshift formulas explicitly). Maybe I should have phrased "energy as low as you want" explicitly as "non-zero energy as low as you want". Also note that in my initial post I was explicitly referring to a limit process. This implies that for any positive "minimum energy" you would impose you can find a case in which the photon energy would be lower than this minimum. It is common practice to refer to this as the minimum being zero, even if no such state actually exists. EDIT: Since I just ranted about "new theories" somewhere else, I feel that a clarification is in order for this post: The bold part was not written as a reference to the thread title, and technically you did not claim something like being up to revolutionize physics anywhere. The reason I wrote it was much simpler: While writing I realized that going into more details would get me on a slippery slope where one could get lost in a lot of, in my opinion ultimately irrelevant, details. So I wrote this to jump off the slope

Interestingly, in that case you kind of gave a reasoning against that statement yourself: Assuming a flat gravitational background: If you move in the direction of the photon fast enough, you can get the photon energy as low as you want. And if you move towards it you can get its energy as high as you want. If the statement about high-energy photons being black holes was correct, every free photon would be a black hole and not a black hole at the same time. Before you get excited about having found a new groundbreaking result in physics, the black hole duality: The simple solution is that photons are not black holes.

In the simplest case there would be a lower limit of zero in the limit of an infinite wavelength and no upper bound ("upper limit of infinite energy") in the limit of zero wavelength. ... and now it's showtime for the people telling you about pair production and Planck lengths ...

Maybe the OP was considering a photon gas

There are three main examples of energy at 0 K: 1) Often you are free to chose the zero-level of energy yourself, which obviously makes it possible. 2) Mass is often considered a form of energy and does not vanish at zero temperature. 3) most relevant to the question: Many systems will have kinetic energy at zero temperature, e.g. a set of many independent atoms (the atoms do not move, but the electrons orbiting the nucleus have a certain amount of kinetic energy). Your 2nd part of the question is a bit tricky, going into some subtleties of thermodynamics. The simple answers would be a mix of yes and no: Thermodynamics states that zero Kelvin cannot be reached by thermodynamics processes. But apart from that there is nothing too special about zero temperature, at least in theoretical models. The mainstream answer would probably be "no" due to the well-known statement about thermodynamic processes (combined with an incomplete understanding of the concept of the thermodynamic limit). The formally more correct -but completely useless- statement would be that thermodynamics cannot exist.

@Fiveworlds: You are correct that bias (or correlations) are important for practical work. However, complicating the picture will probably not help the OP understanding the original question. So I recommend against expanding on this point, even if it may be interesting/fun for you. Also note that the web-page you used as a source has terms and conditions that explicitly state that you need a written permit to distribute the contents.

I'm not sure to what extend it is really true that teaching at non-university hurts academic career. But there are two thoughts that come to my mind: 1) Maybe research experience is worth more for a career in university/research than teaching experience. 2) If you have troubles finding a research position directly after your PhD, that may be a bad sign for your chances to get a much more competitive faculty position later on.