timo

Pretty much every particle accelerator experiment conducted since, I guess. Not sure about other experiments, but I could imagine something in the direction of quark-gluon plasma experiments and primordial nucleosynthesis.

The extent of a space into some dimension can have a size. Take a rectangle. It's a two dimensional object. It is characterized by two lengths, one for each direction/dimension. In that sense, the "height" dimension of the rectangle has a size.

I cannot see where in chapter 2.5 "a high negative pressure condition results in a negative energy/gravity condition". It is true that the negative so-called pressure component of the cosmological constant drives the expansion of the universe. I agree that this is not what one naively expects gravity to do, so I would also agree that one may loosely think of it as "negative gravity" - it's most certainly not what it would be called in a professional environment, though. However, if I understand you and the Kinney text correctly, then you seem to equate your already dubious "negative gravity" with "negative energy". That I object to. I assume the reason is that you heard statements like "in general relativity, the source of gravity is energy": This is not fully correct. In fact the first equation in chapter 2.5 may be a good counter example, as it gives the reaction of spacetime [math]\ddot a / a[/math] (i.e. some gravitational effect) depending energy density [math]\rho[/math] and so-called pressure contribution [math]3w\rho[/math].

You presumably talk about this: http://arxiv.org/abs/astro-ph/0301448 . It's not a book but a script for a mini lecture series. Being on arXiv, everyone has access to it - including me. I do see the mainstream calculation for the vacuum energy in naive QFT in section 2.4. But that's not what I asked for - you can find that in pretty much every intro text on QFT. The statement I wondered about is the claim that high pressure can result in negative gravity or negative energy. I searched the text for the keyword "negative", and all I could find was "negative curvature" and "negative pressure". Have you possibly been confused by dark energy's weird property of having negative pressure?

The combination of two (transformation-) group elements again yields a group element (by definition of a "group"). One usually doesn't call that "superposition", though.

Dark energy has a negative pressure but positive energy component. In fact, it makes up the most of the (positive) energy in the universe. Calling it "vacuum energy" is problematic, btw (for the reason that it doesn't fit to QFT vacuum energy expectations, as you already mentioned). Got a reference on that? I don't even understand what that is supposed to mean. I'm not completely convinced that electrodynamics in a static spacetime is the proper approach for general relativity on scales of the universe. In fact, adding a link to a Wikipedia article saying "in general relativity gravitational energy is extremely complex, and there is no single agreed upon definition of the concept" makes your statement somewhat dubious. EDIT: Oh, and you haven't answered the question whether the thing with the gravitational energy is a well known fact or just a random guess of yours.

As I said previously, I don't know which contituents enter into the energy density calculations fitted on the WMAP results. So is your statement a guess of yours or a fact? And in either case, how is the potential energy calculated?

Radical atheist attitudes have risen by 67% within the last 12 years! If this trend continues the US will be void of honest religious people within ~50 years (and also of dishonest religious people). Might this extrapolation foretell the date of Armageddon? Sinners repent! (brainfucked by trying to sell similarly convincing data to a bunch of referees)

What would that argument be? Which guesstimates? And what are the inaccuracies?

I have no idea what you are trying to say there, Klaynos. Surely, putting some anti-matter in the universe in addition to the matter that already is there would merely increase the energy density some more.

I don't know exactly all the contributions that are taken into account, but I was under the impression that the mainstream view is that the average energy density of the universe (and therefore the total energy) is distinctively non-zero. From the first random Google hit (http://map.gsfc.nasa.gov/universe/uni_matter.html) This critical energy density is roughly one Joule per cubic kilometer, i.e. distinctively non-zero.

To highlight phi's statement: I have no clue who you are, but I find it strange and inappropriate that someone who joined this forum only two months ago makes a drama out of leaving it. If I would really be bothered by that, I might be clicking the red minus - as some people obviously did. Not because I judge you personally, but to express my dislike for drama queen posts from strangers. In other words: me rating posts is about me, not about you. And I am pretty certain that it's the same for other people: them rating posts is about them, not about you.

Depends what you mean exactly. The formulations used to describe modern physics are Lagrangian Mechanics and Hamiltonian Mechanic, which both do not (bother to) explicitly contain forces. Explaining those would be a bit beyond the scope of a forum thread, though - it's more on like the scope of a 2nd or 3rd semester university lecture. However, if you believe the relation Swansont gave, then it's straightforward to formally eliminate forces in the physics you presumably know: 1) an object at position [math]\bf x[/math] experiences a force [math]{\bf F}({\bf x})[/math] that can be expressed by a suitable derivative of a potential energy U via [math] {\bf F}({\bf x}) = - \frac{\partial}{\partial {\bf x}} U({\bf x})[/math] (where [math]\partial/ \partial {\bf x}[/math] is to be understood as the gradient). 2) The change of the object's motion as a function of force is given by the relation [math]\frac{d^2}{dt^2}{\bf x} = {\bf F}({\bf x}) / m[/math], where m is the mass of the object, and [math]{d^2}/{dt^2}[/math] denotes the 2nd derivative with respect to time t (note that the 2nd derivative of the location with respect to time is the acceleration). 3) Combining 2) and 1) the law describing the motion of an object can be expressed as a relation that depends only on the structure of the potential energy in space, i.e. [math]\frac{d^2}{dt^2}{\bf x} = - \frac{\partial}{\partial {\bf x}} U({\bf x})/m[/math]. Given an initial position and an initial velocity (and the value of the potential energy for all times and all locations), this yields a unique result for the motion of the object, just as a=F/m does (if you know the force F). That may merely look like a bookkeeping trick. In fact, it merely is a bookkeeping trick. But it is the way that most modern physics is formulated in: Rather than thinking in terms of "a given charge configuration generates a force fields for some charged particle flying through it" one usually thinks and works in terms of "a given charge configuration generates a potential energy/voltage field for ...". Explaining what "force" in the sense of "four fundamental forces" means is a bit beyond what I can explain at the moment. Simply put, it is the mechanism that dictates what the [math]U({\bf x})[/math] looks like. Note that formally eliminating the "F=ma"-force is of course not sufficient to understand modern physics. To go all the way down to particle physics, there are other and more severe deviation from school physics that one encounters, namely the huge fields of relativity and quantum mechanics and the rather abstract issue of representations of symmetry groups.

Because neither requires it to have mass. The equation of motion in general relativity, the most up-to-date mainstream theory of gravity, does not (explicitly) contain a mass-dependence. How do you produce the question marks with a broken shift key, btw?

That I, too, consider useful ideas in general. Not to mention that even in that case the only "factish" about the thing is the fact that it is claimed in the reference you have - which doesn't necessarily make it true, either. ... oh, and of course you may have misunderstood the reference, too ... Why not? I wholeheartedly agree with that. But I am realistic enough that it takes a certain level of education/experience/scientific training to be accurate. So I do have some sympathy for being lax with expressions (despite complaining about it all the time ).

What I meant by the first sentence is that the term "force" can be considered to have two meanings: On the one side there is the colloquial term rather vaguely meaning "strength", "source of an effect" , "compulsion", ... and not physically precise (think "air force", "brute force", "forcing something", ...). On the other hand, classical mechanics offers a very precise meaning of a physical force, the one you presumably know from the famous relation "F=ma". Type #2 is arguably one of the most fundamental concepts in school physics. And there comes the problem: Particle physics does not work the same way as school physics. The term "forces" in "four fundamental forces" is better to be understood in the vague 1st interpretation (the colloquial usage of the term) as a source of an effect, not as a force in the sense "F=ma". That's why I believe it's better to call it "four fundamental interactions" in the first place. Not because it has any different meaning, but merely because it avoids a potential pitfall for laymen interested in modern physics.

Dunno. It's your equation and your simplification, and most particularly you haven't bothered properly describing the physical process you talk about.

p -> 0.

The "four fundamental forces" are better thought of as "four fundamental interactions". The term "force" is misleading in the sense that none of them is commonly described in a framework footing on the concept of "force" that you are familiar with from classical physics. It is not unambiguously true that "it takes energy to move things". For example, if you drop an object from some height the speed it has upon impact on the floor is usually evaluated from assuming that the total energy is constant.

That's presumably been it (I did check if I still find the thread, but apparently didn't go down far enough). Thanks. Happens that my reply was still my current paste element, so I didn't even have to rewrite it.

It's hard to define what "was supposed to be referenced in another paper" means. If you mean that I (as the author of the not-citing paper) really wanted to refer the respective work but forgot it due to carelessness, then I think the answer is "very seldom". If you interpret it more like the author realizing "well, in hindsight I could have also cited X", then I think we already approach a two-digit percentage - perhaps 50% if you include papers that the author only became aware of after publications. If you mean work that could have been referenced in principle, then we surely talk about almost 100% of the papers published. Actually, it sometimes happens that after publication you get a mail by someone (not a crackpot but a proper university researcher) kindly asking you to also consider a particular related paper of theirs. I've still not met anyone who could make real sense of such mails, though (do they ask to be cited? are they interested in a discussion of the topic? are they just trying to be helpful?). Citing papers and attributing ideas is not an exact thing - I think anyone writing scientific publications will agree with this. There are weird rumors about non-existing papers having hundreds of citations because the authors of some influential paper made a typo in their citations and everyone just copied that citation without looking it up or even reading it. Also, scientific publication is not the only way that people get their ideas across (and also not the best). Scientists talk a lot to other colleagues, and speaking for me I learned much more about current research from a live discussion with visiting scientists, attending talks, and chatting with colleagues met at a conference than I did from reading research papers. This may in some cases lead to the effect that public referencing may not always be what a pure look at published material may indicate.

Oh, and what also is annoying is when you spend 20 minutes writing a reply, and upon submitting the system tells you that the thread no longer exists (as just happened).

Almost all of your questions seem to heavily depend on where you want to go and on personal details. Exceptions are "what are the best places/universities", that strongly depends on how you define "best", and the time a PhD takes, which is in the order of 3-6 years for biology (on average and depending where you go). My advice to get started with collection of information (which is just an advice, not the only possible way to go) would be the following: Take your favorite papers (assuming Indian master's students do read research papers - otherwise just google up some that sound interesting). Look up the academic affiliation of the authors. Check the PhD program requirements of their universities and the countries they lie in. From there on, search paths for further information should become obvious.

The first error is in the statement "If you divide a number by 0 your answer would be infinity". You're welcome.

Running an Internet forum. Capn hasn't given up, yet.