timo

While this is probably true, I´d think that if he made this website without any other interest than providing a forum for scientifically interested people it might in fact be a good idea to let those scientifically interested people have a voice even when it comes to distributing moderator posts (not that I think the majority would have voted agains Mokele - I barely perceived him up to today). But then, there is that very interesting quote (which I think was from a former US president*): "The best argument againt democracy is a 5 minute discussion with the average voter". So far, I had no complaints about the mods here. Most are rather inconspicuous, some are outstandigly friendly and helpful (dave). I don´t really expect any change in that, now. *EDIT: Seems I was wrong: The quote is from Winston Churchill (http://en.wikipedia.org/wiki/Churchill), see: http://www.brainyquote.com/quotes/quotes/w/winstonchu105424.html

Your own firewall? Configure it to your needs. Someone else´s firewall? Go to http://www.e-are-T3h-l33t-hackers.0rg and ask there. My stepfather said a few weeks ago that he can´t understand why people need a driver's licence to drive a car but yet any idiot is allowed to use a computer on the internet. And as the result he demanded a psychological test before someone is allowed to use a computer. From reading several threads like this one, I´m beginning to think that maybe he wasn´t just joking. Sry if you really only wanted to know how to configure your firewall. It´s nothing personal. But I´ve seen several "how do I bypass someone else´s system security"-threads lately and it really makes me think about how irresponsible some people act (starting denial of service attacks without even having the slightest clue about the damage being caused by that and such).

The Particle Data Group (=PDG, see http://pdg.lbl.gov/index.html) is possibly THE resource in high energy physics. Of, course, I don´t have a clue which website you visited (@Locrian) or which website elas meant. Afaik, there actually has been experiments to determine the radius of an electron. Those experiments gave an upper limit so they don´t actually contradict the current theory of an electron without an internal structure. Letting aside the fact that the electron radius is assumed to be zero: How do you go from "nuclei have a radius" to "their constituents have a radius"? Do you even know what "the radius of a particle" means in respect to quantum mechanics? Actually, I´d like to know the same thing because it certainly is a groundbreaking read if there´s anything to it. But "it has been under review for 14 weeks to date" strongly sounds like "it has been ignored for 14 weeks to date" so you´d better not hope on getting to read it. And to say at least a bit on topic (even if it´s not too serious): Yes, especially about you units .

I enjoyed reading it, too. But it´s as much a book on QM as your local newspaper is a book on economy. I don´t know the book by Brian Greene but if it´s anything like these (http://www.pbs.org/wgbh/nova/elegant/program.html), then the same applies there. Simply no substance. On topic: Sadly, I´ve never been the person who is able to learn from books. For me, they´re a great tool to look things up but not one to learn a certain topic. However, there are some really good lecture notes available for free download (or as html sites). Take a look around in the web. If it´s a page of a univerisite´s physics department you can be rather sure that at least you´re not presented complete crap.

The interaction terms in the lagrangian. What do you call "know"? A physicists "know" is "have a mathematical description". Yes. Due to relativity you know how to transfrom back and forth between the system of rest and a moving system. Do the calc in the system of rest and transform. Unless one knows the basics of relativity. Severian mixed up his times a bit. That´s not uncommon since physicists tend to talk to and write for people who can tell out of context which time is meant. The "they decay very fast"-part was about eigentime, the "live long enough to reach us"-part was about coordinate time. Sadly, I do not understand what you want to vibrate.

The time passed measured by a particle itself. This stands in contrast to the "coordinate time" which is ... well, the time value of your coordinate system. Both "times" do not have to coincide. For a particle travelling at a very high velocity from point A to point B you´ll measure larger time (coordinate time) than the particle does (eigentime). Seems like it´s called "proper time" on wikipedia: http://en.wikipedia.org/wiki/Proper_time

A simplified answer: No. The only time you could measure is eigentime. Eigentime does not need to be equal for different objects even if they were created in the same event. The "twins paradoxon" would be an analogy.

You are talking about f(x) = x² for x irrational, are you? If I remember it correctly, convergation lim(x->0) f(x) = 0 demands that for all e>0, there is a d so that for all x in (-d, d) : |f(x)|<e. Splitting up the reals into rationals and irrationals you see that this is trivially true for all rationals as 0<(e>0). For the irrationals in (-d, d) you have f(x) < d². Therefore you get the condition d²<e => d < sqrt(e). Since for all sqrt(e>0) there exists a d that satisfies this condition, your convergation criterion is fullfilled.

Given the picture above: In which direction do I have to look for that the distance between the points decreases?

What are you trying to do?

Afaik, dark matter is supposed to reside within or at the edges of galaxies to describe their internal movement (rotation of spiral galaxies). The stuff nessecary for the theoretic models to fit the observations on the cosmic expansion is called dark energy. This, however, has very exotic properties (negative energy density ... or was it negative pressure?) and is therefore not likely to be explained by chunks of regular matter like black holes. Disclaimer: I´m not an astrophysicist. Above is only what I think to remember from hearing a few talks about that topic.

The uncertainty principle does not (only) state that dE*dt >= hbar. In fact, the dE*dt thing is one that does actually not follow directly from the uncertainty principle, at least in classical QM. The question to what extend it still is correct and how it might actually do derive in relativistic QM aside, I think that the "it [a singularity] somehow violates the uncertainty principle" rather relates to dp*dx >= hbar. So given you have something in a fixed position (dx=0) it can have any momentum. You´d need a mechanism that lets all possible momenta lead to the same velocity for the particle to remain at a fixed location. I don´t really understand what you´re talking about because I neither know what you call a singularity (a point in spacetime with infinite energy density?) nor what the "it´s impossible" argument relates to or how it really works. I hope that my above statement still helps you.

I´m actually still not following you. When you say "everything converges to a point" I read it as "the distance between those objects will decrease". So why doesn´t that apply to the distance between any object and earth? Of course it is possible that earth takes a position in the universe that is qualitatively different from that of the other stars. But this kind of thinking is not very modern since the end of the middle-ages.

Sry that I didn´t want to read up the Hodge star operator (already didn´t understand that one some time ago) so I couldn´t understand your argument, Matt. However, back when I studied math I did one of my seminar talks about a "generalization" of the cross product: From [math] v_i = \epsilon_{ijk} v^j v^k [/math] you simply generalize to: [math] v_i = \epsilon_{i j1 \dots jm} v^{j1} \dots v^{jm} [/math] EDIT: ^^ the v´s with different indices are of course supposed to be different vectors. Attributes like perpendicularity, multiliniearity and an alternating sign are directly inherited from the antisymmetric pseudotensor (didn´t realize that back then, that´s why i had enough stuff for a talk ). Like i said, I didn´t understand why the cross product cannot be generalized to an alternating map (R^n)^n-1 -> R^n in above way for any finite dimension n. Above generalization was good enought for a seminar talk in university, at least (ok, it was only 2nd semester, but the Prof was quite happy that I came up with a topic myself). If fact, you can generalize above further so that on the left side you do not have a vector but an object with any number of indices. All vectors extracted from this object by taking all but one of those indices constant will also be perpendicular to the vectors on the right-hand side.

No. If all the matter is converging to a point then why does all matter (stars) tend to get aways from us?

My favorite experiment is still: Take a walk from the canteen to your lab with a cup of coffee in your hand. How much coffee is spilled on the floor? - Plot the coffee loss over the distance travelled. - Discuss the dependency on your speed. - How does nonuniform walking affect the outcome? Is there a lower/higher likelyness of resonance catastrophe? - What is the influence of the cup´s geometry? Due to the famous "wet trouser"-theorem by A. T. Heist there will always be a resonance frequency available in a spherical cup so it´s impossible to transport coffee in a spherical cup without spilling it when one walks uniformly. - How does the usage of another fluid with a different damping constant for the oscillations affect the outcome of the experiments? - Assuming sensible numbers for the cost of coffee and coffee automats: From the results gathered above, what´s the economically best densitiy for coffee automats in an average university? That should keep you occupied for quite some time.

Perphaps. But I somehow don´t like to see my work reduced to that. Consider it a fact that I disagree with this statement. Now, by definition, you can prove this. How? sounds like "true proof" is smiliar to true belief. I don´t understand that part. What´s "omniscience" ? I don´t understand that, either I think he wanted to say something like "scientific claims contradict themselves". If not, that statement is utter nonsense. It´s certainly not a "true proof" since I doubt it

No. There are two different "times" in SR. Eigentime, which is a scalar (=a real number which remains invariant under coordinate transformations) and coordinate time which is the first entry of a four-vector (also a real number but not invariant under coordinate transformations).

No.

That is of course a very good idea. Initially, "dark matter" stands for nothing more than regular matter we simply cannot see (as it doesn´t emmit light as in stars). But of course, the idea of "perhaps it´s black holes" comes to ones mind so naturally that this idea is far from new. I´m neither an experimentalist nor working in the field of cosmology but I think to remember that there were some experiments looking for massive non light-emmiting objects called "machos" (or at least I think that´s what they´re called). I think some were found but it was way too little to obtain the needed mass. As far as I´m aware there are a few candidates for dark matter but I can´t remember them all (machos were one, neutrinos another, dunno what else). About two months ago Prof. Wim de Boer from the University of Karlsruhe held quite an interesting talk at our university. He was rather convinced that they had found dark matter by analyzing radiation data collected by a satelite. They were even able to determine the density distribution of the radiation´s source. Also, he released a paper about this topic this week (didn´t read the paper, yet). You might want to google for his talk; it´s available on his homepage. Don´t know how easy/hard it is to understand without the explanations given but the talk was probably the most interesting one I heard, lately. EDIT: Deleted my previous "off-topic" paragraph.

I don´t completely understand why the speed of gravity (what is this to you, btw?) had to be greater than the speed of light in order to trap it in a black hole. Prison walls are very good at keeping people inside that move much faster than the walls.

I was hoping to find a more detailed explanation but in the end I didn´t want to keep looking any longer and this short text has all the information needed: http://hands-on-cern.physto.se/hoc_v21en/page_text/sm_paty5.html To sum it up: Considering radioactive decays as a test for time dilatation is not only a very good but also a very old idea.

I didn´t write "you´re an extremist if you phrase something in familiar terms". Furthermore, I didn´t get pissy - you just don´t seem to have the same sense of humor as I do. EDIT: But this was a good one: probably applies to both of us a bit

- You assume non-US citizens know all those people mentioned.