timo

I doubt anyone here could give a spontaneous explanation to such a wide question that is better than the Wikipedia article on the topic. Yes. Think of it as "statistical physics". Because different physical systems have different behaviors. Also, it's not considered as different statistical physics, but really just as different classes of systems/behaviors/statistics. As a not-100% fitting analogy: Normal probability theory has different probability distributions, too: Gaussian distributions, Poissonian distributions, binominial distributions, ... Probably "yes", if you stretch your understanding of "related" sufficiently.

Is AB from a subset of the real numbers and smaller than +1, by chance? In that case, the two expressions are equivalent. Hope that helps. But if you don't even know what A and B is yourself, then I believe you still have very fundamental problems to solve in your work.

Right. Forgot about that. Makes one feel better due to it Sci-Fi touch and is actually used.

Higher-dimensional volumes are also called "volume", usually. Perhaps also 4D volume or 4-volume. But you can also call it "xurbit", if that makes you feel better. EDIT: It's amazing that Google returns 2000 hits for a term I just made up.

Interesting observation. My Internet activities underwent a sudden drop when I hit PhD level and for the first time in my life actually liked physics. Which leads me to the recommendation I would offer: Get a job you enjoy. Not in the sense that you find molecular biochemistry an amazing topic, but in the sense that mixing together your reagents, diligently typing your result into an Excel sheet or improving the colors of your plot for the talk next week (or whatever molecular biochemists may actually do) is more interesting than collecting the next 50 gold pieces from Orc raiding or trying to preach to "relativity is wrong" ignorants on a webpage. Making a written plan, as CharonY points out, also works well for me. Not only with the huge "do not forget" lists I carry around nowadays. Also as a PhD student the difference between scribbling the three points "add errobars to plot, restart simulation with higher temperature, reply to mail from X" on the piece of paper and not doing so made a surprisingly large difference for me (if only for realizing that starting the simulations should probably be moved to the top of the list). And if we are honest: despite all the complaints and horror stories about long working hours these three points roughly correspond to the daily workload of a PhD student in academia . For the record: it's 21:15 on a Friday evening in Germany right now, and I brought some work home for the weekend. I have the right to post here now

Yes. In the Standard Model, the Higgs Boson originates from adding extra field content (think of "particles", if you don't understand "field") with interaction with other particles and interactions with itself to the model. This causes the emergence of a single new particle, the Higgs Boson, as well as effective masses for all the particles it interacts with. In principle, one can add even more extra fields. In fact, in popular extensions of the Standard Model this is required (but no direct experimental evidence for these models exists). This gives rise to even more Higgs Bosons. They primarily differ from the Higgs Boson (which then is often called the "Standard Model like Higgs Boson") in mass and couplings to the other particles. More dramatic differences to Higgs Bosons are also possible in priniciple (parity, spin, electric charge).

Straightforward plugging into the equation will show you that your result is a correct solution (it doesn't show that it is the only solution, though): [math]ACA - AB \stackrel{C=BA^{-1}}{=} AB\underbrace{A^{-1}A}_{=1} - AB = AB - AB = 0[/math]

There is no clear rule about it, in your example. The original expression obviously does not apply for v=0. In all other cases, the 2nd expression is equal to the first one. So in all cases where the 1st expression applies (*), the 2nd expression is identical, and therefore a valid simplification. On the purely mathematical level, the only difference is that the 2nd expression doesn't explicitly show that the equation isn't supposed to hold true for v=0. If you switch from this out-of-context view of your example to real physics, then things get even more interesting: Assuming that the physical quantity the term represents does not run into some magical undefinedness at v=0 but is somewhat continuous there (**), then the 2nd expression already includes the limit that gives a proper description of what happens at v=0. In this case, the 2nd term may be more appropriate than the 1st. Bottom line: Contrary to widespread public opinion, physics is not math. (*) Strictly speaking: where it formally applies. Physics equations usually come with a lot more restrictions about the applicability, that are usually not mentioned explicitly but assumed to be understood by the reader (who usually is assumed to be a proper physicist or engineer). (**) Note that a physical observable with a discontinuity at v=0 but well-defined behaviour arbitrary close to v=0 would be a strange beast: If an infinitely small deviation from v=0 leads to a completely different behaviour of the variable, then considering you cannot measure anything to an arbitrary degree of accuracy your model to describe nature may be useless, anyway - depending on the context.

I'd also take your money.

For simplicity, let's assume that "carrying a gravitational field" is caused by mass of an object. In that respect, it is remarkable, that while a photon does not have mass, a system to two photons usually does. As a matter of fact, pair production from two photons can only happen for two-photon systems that have a mass at least twice the mass of an electron (due to conservation of energy). Mass is a special form/share/aspect of energy, that does not always equate to what one would expect from it from everyday life. That said, no model for gravitational effects of an on elementary particles exists, anyhow.

I am suggesting that bound states are what this thread is about.

A neutron lives 10 minutes. But that does not stop atoms from being stable. I also don't see where the "no way to connect the two" statement comes from. With its high mass, the Higgs boson has a relatively strong interaction with Gravitons (meaning stronger than most elementary particles - the absolute strength would probably still be negligible). ... or by the weak force. "No way" is a strong statement. In this case, based on little. You are of course right that "something that only weakly interacts" is not exactly the thing you expect to form atomic-scale structures (galaxy-scale structures of dark matter have been found, afaik). But there is a large gap between "would not expect X" and "X is not true".

You shouldn't worry about the first question until you get accepted by both institutions.

Chances are, the people who proposed it put some faith into it. The vast majority of scientists will simply not care at all. The majority of Cosmologists will probably not have an opinion about it, owing to lack of evidence for anything. On the "plus" side, it's not exactly ridiculed, either. The Big Bang as the beginning of time and space is a result of a non quantum-mechanical model. There is no guarantee that in a model taking into account Quantum Mechanics, this still holds true. In fact, from the very few LQG talks I attended I got the impression that at least in their world the Big Bang is indeed not the kind of singularity you have in classical models. No one really expects the classical model to be the last word or the ultimate truth, by the way. It's just that questions about the very moment of the Big Bang are so inconsequential to anything that few scientists really care.

I guess the "how to react to crackpots guide" reads something in the lines of Give them as much attention as possible. Be sure to make those threads the longest and most active in the forum. This will attract even more interesting discussion partners. Discard paying attention to proper and interesting scientific questions over them, if necessary. Those proper questions would take too much time, anyways - might force you to think and possibly even speculate, rather than safely repeating the same stuff that the rest of the forum agreed upon the last times. Always remember that you are the last bastion that stands between modern society and a breakdown of civilization. If you do not react of an incorrect idea, the streets will be roaming with mindless Zombies, soon. Even worse: your post count won't grow.

Glad to hear this. Enjoy Warsaw.

The Drake Equation in your avatar may be a more suitable topic for a high-school newsletter, anyway. Easier to explain and potentially interesting to more people.

He didn't really predict much (he had part in proposing a mechanism; the actual predictions like "the Higgs Boson has to lie in the LHC range for the Standard Model to make sense" were made by other people), and the whole Higgs Boson thing is not exactly cutting-edge quantum physics, anyways. So no. Generally, being a physicist that is mentioned in newspapers does not make one an expert in Quantum Physics (and vice-versa). My bet is that if one was able to compile the list of "top 100 experts on quantum physics worldwide" (definition issues apart), no one on this forum (with the possible exception of the professional physicists - one attends many talks over the course of the years) would know a single name from this list.

So who is supposed to care? And why?

Velocity and acceleration can indeed be in different directions. If they are in opposite directions, the process is usually called "deceleration" or "breaking". The meaning of an acceleration (or a velocity) to be negative is the following: Acceleration (and velocity) have a direction. In many cases, the direction, that in principle can point anywhere, is simplified to "forwards" and "backwards", where the exact meaning of the two terms usually is clear from the context (think of a car, for example). Usually, positive values of acceleration/velocity mean that it is into the "forward" direction. Negative values mean that the direction is into the "backwards" direction. In textbooks, when you learn about velocity and acceleration you usually also have a position x. There, "forwards" usually means "towards increasing x", whereas "backwards" means "towards smaller x".

They indeed are at the same position at time zero. And they will be at the same position at one later time, too - the one that is asked for. The physical reason is that the bike initially moves aways from P faster than the car (admittedly not what one would expect if one only heard the terms "bike" and "car"), but the car keeps on increasing its speed (accelerate) and will catch up and overtake.

The big step in the right direction is realizing that what is asked for is the time when the positions of the car front and the bicycle back are the same. That said, the idea of the homework is that people asking for help first present their ideas and what they already tried to solve the question (the tradition is that new members ignore or don't know of this rule: Welcome to SFN).

I recommend the use of this forum's "ignore list" feature. Many people first have to become accustomed to letting the "opponent" having the "last word", especially on the Internet. But with some time distance from the post, one starts to realize that readers of a thread may have brains of their own, and form their opinion based on what's been written, not on its order. And once you realize this it actually becomes kind of fun to let someone else have a stupid "last word" in a debate (though posting solely for this fun would probably quality as trolling by itself).

Reading this I re-read the OP, that I may in fact have misunderstood. I understood that Sam wanted to increase post quality by attracting more experts (by some magical means). As I said, I see the main problem in the minimum standards that I believe to be too low (and for which I have no proposal how to improve it). I don't think that the so-called experts here lack the competence to provide interesting posts, and in particular I do not think this impact the overall forum quality. In fact, contrary to a few years ago I even begin to see a point in the tag (whereas beforehand my attitude was that people who cannot tell a competent statement from nonsense are not harmed by believing in nonsense).

I believe pretty much everyone would agree with you that a higher standard in this forum would be highly welcome. Also, surprisingly many people would agree that more forum-designated experts would be much welcome, be it for being able to identify credible sources or simply as a result of a higher standard. I can also faintly remember times when we more or less officially said that an expert should roughly have the equivalent knowledge of a PhD in the respective field. So some of the negative comments you got for being concrete (Masters degree) rather than avoid-a-real-statement-that-people-could-call-you-to vague seem a bit lame to me. That said, you have to admit the question: What's your point? You obviously don't propose to randomly push a few people into the "experts" user category to have more experts. And as Swansont correctly says, professional scientists rarely feel the urge to invest their free time in an internet forum which is intellectually less stimulating than their work routine. After the 5th thread where someone demands his superiority to be acknowledged because he found out that gravity in reality is magnetism, even the morbid curiosity that initially makes you bother turns into annoyance. I see two options for improving the quality of posts here: 1) Everyone attempts to improve the quality of their contributions (e.g. not picking up any detail offering the option to prove someone wrong, but trying to overall add something substantial to the discussion). 2) The staff improves average quality by more rigorous selection at the post-intensive quality bottom, which may arguably even lead to some quality in-flux from above (lately, I often felt and followed the urge not to continue posting in a thread after having read the other posts). Both options are not easy to implement, both are unlikely to happen. Your call for improving post quality is not the fist one by far - I would already be happy if threads started by people on my ignore list were not displayed to me, but even this has not been realized. And I can fully understand why the staff is reluctant to kick people out - I wouldn't want to do that, either. So what you are left with is improving the quality of your own posts. That you can influence. In fact, I sometimes decide to try that, myself.