Mordred

Ok lets take the average energy density of the universe, I've worked out a rough calculation at one time by taking the total energy of the universe (including the cosmological constant) and dividing by the total volume. This value worked out to roughly 6.0 *10-10 joules per m3. Though this was done a few years ago. I needed it for the redshift and expansion article I have under my site (see signature) Wiki however has a correlation to the number of particles including dark matter per cubic meter. "Estimates put the average energy density of the Universe at the equivalent of 5.9 protons per cubic meter, including dark energy, dark matter, and baryonic matter (ordinary matter composed of atoms). The atoms account for only 4.6% of the total energy density, or a density of one proton per four cubic meters" http://en.wikipedia.org/wiki/Outer_space so roughly 6 protons per m3 sounds like a whole lot of empty to me lol. now as far as the first value goes there is an easier way to check the average energy density. We know that the total energy density is extremely close to the critical density, (extremely flat universe) so for a close estimate the critical density serves as a cross check. Critical density is given by [latex]\rho_{crit} = \frac{3H^2}{8\pi G}[/latex] taking 70 km/s/Mpc for Ho will give a mass density of roughly 10-26 kg/m3 energy density= [latex]\rho{crit}* c^2[/latex] =9.0*10-10 joules/m3 there is your proof that there is a whole lot of empty space out there between particles here is an article explaining the critical density and universe geometry http://cosmology101.wikidot.com/universe-geometry page 2 for distance measures is http://cosmology101.wikidot.com/geometry-flrw-metric/ or if you prefer here is a nice pdf slide http://star-www.st-and.ac.uk/~hz4/cos/cosLec3to8.pdf see page 13 for a confirmation of my calculation (though if you truly want to understand the mathematics of that slide that site under my signature has numerous cosmology teaching aids, including a free textbook By Liddle (though older its still an excellent resource) here is two other articles with similar values http://wmap.gsfc.nasa.gov/universe/uni_matter.html http://statistics.roma2.infn.it/~morselli/debernardis01.pdf by the way the geometry ie flat compared to the critical density is an extremely studied area in cosmology. The total density is a crucial value in how we measure the universe also if there is more total energy-mass density than the critical density expansion will approach zero then start to collapse

this part is easy to answer, the leading explanation for dark matter is a weakly interactive particle, the neutrino is another example. dark matter is considered to only interact with gravity, and possibly other weakly interactive particles (though the last is only a conjecture that it may interact with itself) particle interactions fall into several categories, covered by the 4 forces so DM, does not interact with the strong force, the weak force, or the electromagnetic force. this isn't too unusual though for example the neutrino only interacts with the weak force and gravity, the photon only interacts with the electromagnetic force (it could be argued that gravity affects the photon but the photon path follows spacetime geometry but is not directly influenced by gravity)(subject for another thread), gluons only interact with the strong force, the w and z bosons interact with the weak force. The ones I mentioned are primarily the force mediator particles the point is there is different particle classifications that depend on their interactions. as dark matter does not interact with the electromagnetic, weak or strong force, we can only measure its indirect influences due to its mass.(gravity) its due to this combination that we cannot identify what particle dark matter is. No other particle doesn't interact with all 3 forces other than gravity.

I've always preferred thinking of energy as the "capacity of a body or system to do work, or change" not sure if that definition would cover all forms of energy though

here is the arxiv paper for that site http://arxiv.org/abs/1406.6586 unfortunately its rather lacking in my opinion of numerous details I would have expected, for one thing he is describing an new form of dark matter called wave dark matter. Instead of cold dark matter of the LCDM model. The paper shows some interesting simulations done by other research, however lacks any details on the FLRW metrics, nor does it even use any thermodynamic formulas or particle physics references. The paper also does not specify which particle physics model he uses. SU(3), SO(10) etc?, nor does it even apply any perturbation metrics For those lacks of details I would say its an interesting idea but does nothing to identify what dark matter would be, instead the article merely describes a possible type of influence. Though lacking in detail. There is numerous models of how dark matter may be involved in early large scale structure formation by causing early anisotropies. If this paper wishes to compete with those papers already present its going to need considerable more detail. The last proposal for what dark matter may be is relic neutrinos (right hand neutrinos=anti neutrino), including a possible direct measurement paper. "Detection of An Unidentified Emission Line in the Stacked X-ray spectrum of Galaxy Clusters" http://arxiv.org/abs/1402.2301 and "An unidentified line in X-ray spectra of the Andromeda galaxy and Perseus galaxy cluster" http://arxiv.org/abs/1402.4119 Next decade of sterile neutrino studies http://arxiv.org/abs/1306.4954 as far as dark Energy the SO(10) Higg's seesaw Mexican hat potential shows some promise, The SO(10) model delves extensively into the Higg's high energy metastability (further TEV physics studies at the LHC is underway to explore this possibility The Standard Model Higgs boson as the inflaton (I particularly like this paper as it covers both inflation and the cosmological constant as one and the same, without including an exotic particle) http://arxiv.org/abs/0710.3755 .Multifield Dynamics of Higg's Inflation http://arxiv.org/abs/1210.8190 the above approaches from my studies of Cosmology and the numerous articles I've read seem to me to be the most promising approaches to the 3 questions in cosmology inflation dark energy dark matter What I particularly find impressive it the SO(10), has the potential of explaining all 3 problems, The arena of what is oft called "New physics" (TEV high energy research is impressive,)(one can only hope were on the edge of finally answering those 3 questions)

unfortunately Otriolet this article has far to many mistakes in it, to describe and correct all the mistakes would take far longer than the article itself. First off I would highly suggest you look up the 4 forces of nature. The strong force, weak force, gravity and electromagnetism. Atoms and matter are not held together by electromagnetism, the strong force does that. for paragraph two I suggest you study rapid oxidization , we already know what fire is in terms of chemical reactions. gravity has nothing to do with electromagnetism, there are plenty of planets and asteroids that do not have an iron core, and have no magnetosphere. the list goes on some of the other posters covered the light and mass issues. trust me you seriously need to pick up a physics textbook. if I was a high school physics teacher grading this paper you would recieve an "F" I was hard pressed to find a single accurate statement throughout this article. edit on further note I couldn't find one

most of the commentary I've read from various sites, mention the guage symmetry arguments and the use of Newtonian gravity. .A couple of the sites also mentioned the redshift as well. I haven't come across an appropriate professional review paper as of yet. As the comments are similar to the blog that Endy0816 posted there is no need to add those sites (though not nearly as harsh) His statement that c=w(k)k and where k is the angular wave function bugs me for some reason though for some reason. momentum is usually defined by p in the Hamilton form. (still thinking this over)

all I can say is roflmao, the extreme tech article doesn't even agree with the paper or rather misrepresents it. considering the paper discusses light propogation due to interactions with a gravitational potential. Though it never once mentions gravitational redshift or the fact that the photons would blueshift as it approaches the gravitational well then redshift as it climbs back out. Wonder why he chose not to include that? but that point aside, I've been doing some digging and I found a better descriptive of the paper bu the way it is on arxiv. https://medium.com/the-physics-arxiv-blog/first-evidence-of-a-correction-to-the-speed-of-light-65c61311b08a http://arxiv.org/abs/1111.6986 its been around at least the original has since 2011, here is the revision history [v1] Mon, 28 Nov 2011 19:40:42 GMT (387kb) [v2] Tue, 13 Dec 2011 18:26:11 GMT (387kb) [v3] Fri, 17 Feb 2012 19:10:22 GMT (391kb) [v4] Mon, 11 Jun 2012 16:51:56 GMT (390kb) [v5] Mon, 23 Dec 2013 15:42:57 GMT (884kb) [v6] Thu, 3 Apr 2014 17:31:55 GMT (941kb)

ok so lets ask one question if gravity is merely an artifact of time dilation, why would the ball accelerate to the BH in the first place? take your balls place both at rest. The BH would exert no force on the balls they will stay at rest. so no time dilation. According to your descriptive also as pointed out time dilation is relative to an outside observer observer A is at rest object b is in motion, observer a looking at the clock at observer B's reference frame will see the time dilation on observer B's clock, observer B looking at his own clock will see none on his own clock. This was already pointed out.

this should be discussed in the relativity forum in regards to the photon, but one quick correction. As pointed out an outside observer A will measure an object traveling at near the speed of light (object B) as having a time dilation and length contraction object B however will neither experience a length contraction or time dilation, everything is normal form object B's reference frame. there is already a reply in another thread for the planck measurement limitation, http://www.scienceforums.net/topic/83896-photon-emission-split-from-length-contraction/?p=813124 this thread should stay on topic so further side track questions should be done in another thread

are you trying to say pressure causes gravity? if so you have that backwards. The energy density of matter exerts no pressure see the equations of state cosmology w=0. However the stress energy tenser due to gravity can. http://en.wikipedia.org/wiki/Equation_of_state_%28cosmology%29 the higher energy-density of mass causes gravity, this increases the stress energy tenser, the fluid influences of the stress energy tenser is covered in this article http://www.blau.itp.unibe.ch/newlecturesGR.pdf "Lecture Notes on General Relativity" Matthias Blau

its an intriguing idea thanks for sharing that link be interesting to see if it bears fruit

correct

"In physics, quasiparticles and collective excitations are emergent phenomena that occur when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in free space." http://en.wikipedia.org/wiki/Quasiparticle list of quasi-particles http://en.wikipedia.org/wiki/List_of_quasiparticle virtual particles though can occur anywhere, and they are identical to a real particles in all aspects except they are too short lived to be considered a real particle. Where quasi particles are convenient descriptive's for particle like collective interactions. think of it this way excitations=particle (either real or virtual) collective excitations= quasi-particle see the above definition here is a brief descriptive from my notes Quasi-particles require the existence of an external medium or fields, whereas elementary particles do not. For example, phonons require a solid or a fluid to exist (they are collective modes of the atomic lattice vibration), likewise pions require a quark-antiquark sea. These are not fundamental particles, in the sense that they need the existence of other particles. the dropleton has the same requirements http://www.scientificamerican.com/article/dropleton-quantum-droplet-quasiparticle/

acronym for laugh out loud and yes I've been studying cosmology since 1987 so I built up a huge collection of textbooks and articles on every related physics aspects. Currently have over 30 textbooks on cosmology astrophysics, QFT,QED,QCD,QM particle physics, differential geometry, GR etc with a personal database of over 200 gig's of pdf files I like to keep on hand. The better teaching aids I post on my website see signature If I do find the neutrino article I'll forward it to you we should keep this thread back on subject of the OP

there is no point, its old news now lol, unfortunately the internet tends to hang onto the older articles as well as the newer ones. One of the many hazards of learning via the internet. this article covers the SN1987a data, this one is a visual pdf see page 11 http://neutrino.fuw.edu.pl/public/wyklad-From-neutrinos/wyklad10-supernova-neutrinos.pdf still hunting for the professional review but I keep hitting controversial articles there is another factor involved in when the supernova emits neutrinos, apparently the core collapse will allow the neutrinos to be sent sooner. I had forgotten about that. Been a few years "Approximately two to three hours before the visible light from SN 1987A reached the Earth, a burst of neutrinos was observed at three separate neutrino observatories. This is likely due to neutrino emission, which occurs simultaneously with core collapse, but preceding the emission of visible light. Transmission of visible light is a slower process which occurs only after the shock wave reaches the stellar surface" http://en.wikipedia.org/wiki/SN_1987A Supernova neutrino observations: What can we learn? http://wwwth.mpp.mpg.de/members/raffelt/mypapers/200702.pdf unfortunately I cannot find better articles, I recall having a copy from on older physics forum I was on but that site also closed down (it was back when space.com used to have a physics forum)

I used to however it got lost on my old laptop when the HD crashed, I'll see if I can get another copy and I'll post it for you

actually that result was shown to be false, so was the CERN tests here is a reference on the CERN test "On June 8, 2012 CERN research director Sergio Bertolucci declared on behalf of the four Gran Sasso teams, including OPERA, that the speed of neutrinos is consistent with that of light. The press release, made from the 25th International Conference on Neutrino Physics and Astrophysics in Kyoto, states that the original OPERA results were wrong, due to equipment failures." http://en.wikipedia.org/wiki/Faster-than-light_neutrino_anomaly "here is the articles covering why neutrinos arrived early from the supernova data The difference of approximately three hours was explained by the circumstance, that the almost noninteracting neutrinos could pass the supernova unhindered while light required a longer time".[7][8][9][10] http://en.wikipedia.org/wiki/Measurements_of_neutrino_speed meaning that light had more interactions in the mean free path, but neutrinos being weakly interactive had no interactions on its mean free path. Light travels at c in a total vacuum however the intergalactic medium isn't a total vacuum. Neutrinos weakly interactive nature can pass through a 1000 light years of lead without interference where light can't http://www.newscientist.com/article/dn21899-neutrinos-dont-outpace-light-but-they-do-shapeshift.html#.U7DSeLHlrQU http://www.theguardian.com/science/2012/jun/08/neutrino-researchers-einstein-right in both cases it was systematic errors in measurements

Ok I hope your aware that the speed of light calculations are used every day in various industries. For example a personal project that required the speed of light was an automated paving application. Take a paving truck, place a series of photoelectric sensors to measure the bumps on the road. Then depending on how long it takes the light to reflect back to the sensor determines the size of the holes. The rest is controlling how much material to place. If light didn't travel at 300,000 km/s the measurements would have been off. Survey equipment also uses the same technique. These are just two simple applications. Now as far as having to know the exact speed of light in Cosmology applications, the speed of light is a foundation of measurements, as such it is constantly tested. Tests include using celestial objects to long range lasers. well as the speed of light is so fundamental to GR and SR this site has a good listing of the various tests, you can go through it to find the various light tests (including the one way and two way light tests etc.) http://www.exphy.uni....prl78_4741.pdf Non-Stationary Optical Cavities : http://www.exphy.uni....xiv0510169.pdf there is even student level projects to measure the speed of light http://twiki.hep.uiuc.edu/pub/Main/TeachersLight2/TOF-SpeedOfLight.pdf in other words its used in our every day existence numerous times every day, it is constantly tested more often than any of us know about. The speed of light is critical in our everyday industry, as well as physics if light didn't travel how would x-rays work in medical equipment? how would laser distancing sensors work? why is is we can measure the time delay in microwave links in communication equipment? I could go on and on but quite frankly it doesn't take a physicist to google his own examples to see how many examples where light travels from a to b. its so fundamental to our everyday lives that its used everyday all over the planet

that's something we don't know yet, We can only theorize the gravitons properties and how it would decay or interact with photons or matter so there is no degree of certainty. So there is numerous speculations etc however it would behave in a similar fashion to the electromagnetic field, however with a spin 2 (possible set of interactions), one conjecture is that there is also virtual gravitons much like virtual photons, mediates the electromagnetic field. The virtual gravitons would mediate the gravitational field. here is one paper that attempts to describe the graviton to photon interactions "Graviton Physics" http://arxiv.org/pdf/gr-qc/0607045.pdf page 10 describes how its possible though its extremely technical (it also shows the metrics for other possible spin values for the graviton) unfortunately the paper is extremely technical, and I've never found a good paper that simply describes the interactions without being highly questionable. probably the easiest way to relate to this is to study the interactions of the electromagnetic field, on how photons travel through a medium, where the momentum and energy is passed from electron to electron via photon exchange. The graviton would act as the mediator exchanging energy from particle to particle. A higher density of matter would result in a higher number of exchanges with a shorter mean free path between particles. Making for a stronger field strength. The further away you get from the mass the greater the mean free path is between particle interactions(fewer interactions) and the weaker the field strength gets.

thought so you'll find the last link handy its a good introductory level article (algebra based)

no problem, always good to see someone interested in learning the mathematics. for differential geometry a good reference is "Elementary differential geometry" by O'Niel http://www.amazon.com/Elementary-Differential-Geometry-Revised-Edition/dp/0120887355 you will find the above references a bit tricky as they both heavily involve differential geometry however they will be good references for later on. Another good textbook aid is "Roads to Reality" by Roger Penrose its not specifically GR but its a good aid in understanding the mathematics of differential geometry in regards to the various physics fields. http://www.goodreads.com/book/show/10638.The_Road_to_Reality an excellent textbook on general relativity is Wald's "General Relativity" http://www.amazon.com/General-Relativity-Robert-M-Wald/dp/0226870332 this is a very basic entry level article its a reprint of Einsteins paper (its metrics are fairly simple so should get you started http://www.gutenberg.org/files/30155/30155-pdf.pdf: "Relativity: The Special and General Theory" by Albert Einstein just in case you can't afford the textbooks here is another useful article (238 pages) free textbook style Lecture Notes on General Relativity Sean M. Carroll http://arxiv.org/pdf/gr-qc/9712019.pdf unfortunately relativity does require decent math skills, so I would look for good textbooks and articles covering differential geometry and be patient (keep at it) forgot to add one of the better low mathematic (to start with) textbooks to understand GR, I've read is "A First Course in General Relativity" by Bernard Schultz http://www.amazon.co.uk/First-Course-General-Relativity/dp/0521887054 here is a good introductory paper much like the last book I mentioned http://www.math.ist.utl.pt/~jnatar/RM-12/Geom_Rel.pdf General Relativity Without Calculus

Then explain electromagnetism it is both particles and it has a field of influence. The Higg's boson also is a particle with a field of influence. a field cannot exist without particle interactions, energy does not exist on its own, energy is transferred through particle to particle interactions. A gravitational field would also have particle to particle interactions. in order to have a field you must have particles interactions so in this case you must have it both ways. QED, is a working field theory, so is QCD. The problem with quantum gravity is the lack of being able to quantize the graviton. This is the underlying problem in unifying quantum gravity and relativity. Relativity does not work at all energy levels it works great in describing gravity in the macroscopic world however it does not work well in describing the microscopic interactions. This is why a complete theory is needed. If you look at the stress energy tenser of the Einstein field equations (oh wow look the term field is used). "the stress–energy tensor (sometimes stress–energy–momentum tensor or energy–momentum tensor) is a tensor quantity in physics that describes the density and flux of energy and momentum in spacetime" http://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor energy and momentum is transferred through particle to particle interactions. please note the stress energy tenser of the Einstein field equations specifically refer to perfect fluid calculations. see the image to the right on that link. spacetime fundamentally is a geometric description of gravitational influences upon matter (particle to particle interactions) in other words its a geometric description of the effective field strength of gravity at a given range. That geometry is essentially a field, hence the term gravitational field I always find it amazing that so many people limit themselves to their favorite pet theory and never study the alternative theories as though they are always in competition with each other. The best policy is to study EVERY theory they can get their hands on. If they did they would realize that the alternate theories are not necessarily in direct competition, but are in fact merely different ways to describe the same interactions through different coordinate systems and differential geometry. some theories are better at describing x influences other theories describe y interactions better. This does not mean one is necessarily better than the other. here is a decent article on what spacetime means in terms of a perfect fluid http://mathreview.uwaterloo.ca/archive/voli/2/olsthoorn.pdf here is a paper that discusses GR and QFT compatibility it also mentions the various issues http://arxiv.org/pdf/1209.3511v1.pdf "effective field theory has shown that general relativity and quantum mechanics do in fact go together fine at ordinary scales where both are valid. GR behaves like an ordinary field theory over those scales. This is important progress. We still have work to do in order to understand gravity and the other interactions at extreme scales" quoted from the above paper.

yes it can according to QFT (assuming the graviton exists, it is after all a hypothetical particle) http://en.wikipedia.org/wiki/Graviton "Unlike the force carriers of the other forces, gravitation plays a special role in general relativity in defining the spacetime in which events take place" in other words it has a geometric influence which is the same as the stress energy tenser (in essence would be the carrier between mass and the stress energy tenser) though that statement may be a bit poor

I answered in terms of the OP for this thread I've already pointed out your mistake in assuming mass means volume in the other thread you posted. The stress energy tenser is the density of mass energy not the volume or space it occupies. http://www.scienceforums.net/topic/52948-why-does-mass-curve-space-time/?p=813626 please read the entire thread before posting .

good article however its too bad you didn't pay attention to the details.... look at equation 1 here is the quote describing equation 1 "where G is the Einstein curvature tensor,T is the stress-energy tensor,G is the gravitational constant, and c is the speed of light. The Einstein tcnsor describes the curvature of space-time; the stress-energy tensor describes the density of mass-energy. This equation therefore concisely describes the curvature of space-time that results from the presence of mass-energy. This curvature in turn determines the motion of freely falling objects" please note the stress energy tensor is the density of mass energy, in other words if you take the mass of the Earth and reduce its volume below its Schwartzchild radius it will become a black hole. Or if you have an object with the same volume as the Earth but higher density it will exert a greater gravitational influence. this wiki page gives the Schwartzchild radius for the Earth roughly the size of a peanut 9 mm http://en.wikipedia.org/wiki/Schwarzschild_radius here is some more information on the stress energy tenser http://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor please note line "In general relativity, the symmetric stress–energy tensor acts as the source of space-time curvature" by the way your fluid analogy isn't a bad idea, its just a bit more complicated than mere volume. (its due to energy-density relations) You will notice the terms perfect fluid being used numerous times on the stress energy tenser page. see the last link for the fluid solutions of the Einstein field equations "In general relativity, a fluid solution is an exact solution of the Einstein field equation in which the gravitational field is produced entirely by the mass, momentum, and stress density of a fluid." http://en.wikipedia.org/wiki/Fluid_solution by the way welcome to the forum here this reference will help you learn GR, careful though its 927 pages long (page 167 covers the fluid dynamics) http://www.blau.itp.unibe.ch/newlecturesGR.pdf here is another reference for GR fluid dynamics http://www.nikhef.nl/~t32/relhyd.pdf Relativistic fluid dynamics