   Some thoughts on gravitons and the relationship between the fundamental forces
  This topic in general has probably been discussed to the brink of dislodging the brain, but unfortuantely that's irrelevant.Having read up on anything from Novikov's princliple to black holes to string theory to special relativity to unification to Calabi-Yau spaces on this beautiful afternoon (okay - morning), I find myself pondering three things - the first one most likely out of insight and the second one out of... well, probably insight.Fistly, string theory proposes the hypothetical existence of gravitons - a special kind of (massless?) subatomic particle - to be used for interdimensional communications much in the same way as gravitons act when fulfilling their normal functions. This idea is based on the simple presumption that gravitons, in fact, are interdimensionally traveling "particles" that we perceive as gravity. The concept I'm not clear on is the perceptual link between general relativity ([time-]space curvatures) and the gravitons themselves: when an object curves the space around itself, we perceive it through its gravitational pull because of the slope (or the gravity well) it generates due to its mass. This slope "sends off" gravitons that then have the capability of leaving our brane (going with the string theory for now...) and entering another brane (dimension), thus becoming detectable in ways and places that we cannot really predict. Right? The only proof to support that thus far is from the observations of particle collisions where certain subatomic particles have been witnessed to have gone missing without an apparent explanation after the collision. My question is: how, so, can we be certain that it is gravity that these disappearing particles carry? What are the physical manifestations of the effects of gravitons not from our universe? Why can't we see in a definitive way anomalies due to a flow of gravitons from a parallel universe? Because as far as I see, if a really large black hole sends out a whole bunch of gravitons, then these should wreak havoc in a friendly neighboring dimension.Secondly - I can't seem to be able to grasp the correlation between an increase in mass large enough to cause the eletromagnetic force (that binds atoms together) to break down. Is that even possible? For instance - if I were to stack 10999999 apples in a pile, could I break down the EM force (effectively forcing the pile to collapse into a black hole), or would the apples, not containing any considerable mass in themselves, just fall over (or, when "stacked" in space, just stay stacked?)? Going one step beyond - presuming each apple weighs a whopping 1 kg, how can I know how many I would need to force them to collapse into a black hole?And lastly, we've estabished a common physical denominator, the absolute zero to denote total absence of any interacting matter in a space. At the same time it's not hard to find numbers as zany as 1032 K proposed on the Internet to describe the temperature of the universe 10-43 seconds after the Big Bang. That's a lot of heat, thermodynamically speaking. And also otherwise. I wonder if it's just a coincidence that we happen to live a negligible 280 degrees above the lowest temperature that the Universe has to offer (actually, the real question should be about life as we know it forming so near the minimum) when the range available to us is, from a layman's point of view, nigh unlimited.edit: yes, I do realize that that many apples couldn't possibly fit in the known Universe. But I like abusing HTML.   
  I like grapes.   ;  Well there's some side-stepping when people call the graviton a "particle". Really, what we have is a gravitational field, and in quantum theory fields can be quantized. Think the same about light - it's a propogating electromagnetic wave, but Einstein applied quantum theory to claim that the electromagnetic wave can be quantized (into photons). It merely means that the energy in the wave can only come in discrete steps - same thing with gravity, except it doesn't work in standard quantum theory.Currently held beliefs say that electromagnetic and gravitational fields stay on our "brane" and don't interact with other branes (which is why we don't observe them). However, Lisa Randall has proposed that certain fields can "leak" between branes, so it's all debatable.The crucial thing with black holes is density. Theoretically, you can have atomic scale black holes form easily using just a fraction of a gram of mass - however they would evaporate very quickly.The other problem is that there's little experimental evidence to work from off of general relativity. What evidence we do have, strongly suggests GR is mostly true. However, the situations like supermassive black holes are needless to say difficult to experiment on and so it's difficult to find the cases when GR does not work (suggesting brane leakage or such)Also, there is no confirmed gravitational attraction between microscopic masses. GR says that any two masses (even two protons) will gravitationally attract, but this has only been confirmed with relatively huge masses still on the macroscopic scale.   ;  That's exactly what I'm confused about - is it that the effect of the "graviton field" (I did use the word "particle" in quotes in the OP :) ) simply cannot (even hypothetically) be detected today and is (prsumably) so negligible that we simply cannot perceive it no matter how strong the interaction is between the dimensions? As in the OP, consider the proximity of two of these branes in a superdimension - if these were to drift close enough to each other, the interactions in the form of the amount of gravitons exchanged would (or should - at least according to logic) increase proportionally the proximity. Moreover, the strength of this "graviton field" is not uniform across space - thus there must be possible cases where one dimension influences another one immensely more strongly than in general. As an example, let's take black holes, which not only manage to tear (or at least radically warp) the space-time of our own universe, but should consequentially have a notably stronger effect on parallel universes (well, at least according to what string theory has to offer). I'm just making the assumption that the reverse also holds true - our universe should be susceptible to the effects generated by similar "anomalies" in parallel universes. Correct me if I'm wrong, of course.Hm - I guess I should've picked the physics forums to post this in, though...   ;Quote:Original post by irreversibleSecondly - I can't seem to be able to grasp the correlation between an increase in mass large enough to cause the eletromagnetic force (that binds atoms together) to break down. Is that even possible? For instance - if I were to stack 10999999 apples in a pile, could I break down the EM force (effectively forcing the pile to collapse into a black hole), or would the apples, not containing any considerable mass in themselves, just fall over (or, when "stacked" in space, just stay stacked?)? Going one step beyond - presuming each apple weighs a whopping 1 kg, how can I know how many I would need to force them to collapse into a black hole?That's not quite how black holes (supposedly) form.  It's not even the right "force" being overcome.  And that's not what the elctromagnetic force does.The electromagnetic force is responsible for the attraction/repulsion between charged particles.The atom is held together by the weak nuclear force.  (And the individual nucleons are held together by the strong nuclear force.)Now here's what happens when a star collapses (in a nutshell).  Since the outward pressure generated by nuclear fusion is no longer sufficient to overcome gravitational attraction, the entire mass of the star begins to rapidly fall towards the center of the star.  Eventually the star reaches a sufficently high density that the gravitational forces are balanced by electron degeneracy pressure that arises from the Pauli exclusion principle. (i.e. the inability of electrons to share the same quantum state.)  This is a white dwarf.If the mass of the star is greater than the Chandrasekhar Limit (1.44 solar masses) even electron degeneracy pressure is insufficient to stop gravitational collapse; since electrons cannot share the same quantum state, electron capture starts to occur; protons "absorb" electrons, becoming neutrons and emitting neutrinos.  The matter continues to collapse to the point where gravity is balanced by neutron degeneracy pressure, again generated by the Pauli exclusion principle (this time between neutrons).  This is a neutron star.If the mass of the star is above the Tolman-Oppenheimer-Volkoff Limit (precise value unknown, but between 3 and 5 solar masses) even neutron degeneracy is unable to halt collapse; it's unknown precisely what happens at this point, but if the star collapses to the point that it's radius falls below the Schwarzchild Radius (which varies with mass), a black hole has been formed.  (Incidentally, the Schwarzchild Radius for the Earth is approximately 9mm; if you could compress the entire Earth into a 9mm-radius sphere, it too would be a black hole.  For the moon, it's about 0.1 mm; for the sun, about 3km.)  Incidentally, you'd need something on the order of 1031 of those 1-kg apples to make a black hole.  (Such a pile would be so large that it would be more apropriate to call it a thick shell of apples covering the planet.)Quote:And lastly, we've estabished a common physical denominator, the absolute zero to denote total absence of any interacting matter in a space. At the same time it's not hard to find numbers as zany as 1032 K proposed on the Internet to describe the temperature of the universe 10-43 seconds after the Big Bang. That's a lot of heat, thermodynamically speaking. And also otherwise. I wonder if it's just a coincidence that we happen to live a negligible 280 degrees above the lowest temperature that the Universe has to offer (actually, the real question should be about life as we know it forming so near the minimum) when the range available to us is, from a layman's point of view, nigh unlimited.First off, that's not quite what absolute zero is; it's actually the temperature at which all atomic motion stops.  It is also impossible to reach absolute zero for thermodynamic and quantum mechanical reasons.  In fact, the lowest temperature observed in nature (i.e. space) is 1.15 K, where as here on Earth we've produced temperatures as low as 4.5*10-10 K.There are several reasons why the Earth's average surface temperature is a relatively cool 287 K (cool compared to, say, the early universe or the interior of a star, but very hot compared to the 4 K of most of space) is that it's primarily at low temperatures (and relatively high pressures) that really interesting particle interactions (i.e. Chemistry) can take place.  To high a temperature, and atoms start to move too fast for them to interact chemically, until you reach the point where they have sufficiently high energy to interact nuclearly instead.As far as the graviton, it's really best not to worry too much about it.  It's existence has been proposed, but it is controversial, and to date it has never been observed.   ;  That was a beautiful reply, Anthony. Thank you!To advance on the topic a little... One thing I find fascinating about theoretical physics (as far as black holes, zero-point energy, strings, branes and parallel dimensionality go) is its imporbability of being physically correct - I mean, we are forumlating these truly elegant ways to describe the universe on the most fundamental level as we strive towards the unification of everything that we know. Yet still - then something as simple as sentient life or religion comes along and puts it all at risk by presenting a completely inverse view of the world. I wonder if there will ever be a unification of the philosophical mindset with that of the scientific - maybe not on a global level, but at least on some meta level - to allow for the true grand prize to be claimed - not just those who choose to tag along.