The group should be a platform to discuss recent progress in Gravitational Physics.

• Prakash Kumar

  Can anyone explain the production of gamma rays & X-rays near black holes?

  Recent observations tend to show that dust clouds, particles or bodies in close orbits of a black hole emit high frequency gamma rays and x-rays. Such events require explanation because supernovaRecent observations tend to show that dust clouds, particles or bodies in close orbits of a black hole emit high frequency gamma rays and x-rays. Such events require explanation because supernova explosions are also thought to produce similar radiations.

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    Ana María Sánchez Peralta replied

    ¿Es más afín a la antimateria que a la materia el agujero negro? Tanta materia y energía que puede entrar en él sin dejar rastro en nuestro Universo parece un traslado a otro lugar que desde este¿Es más afín a la antimateria que a la materia el agujero negro? Tanta materia y energía que puede entrar en él sin dejar rastro en nuestro Universo parece un traslado a otro lugar que desde este lado no se puede ver. ¿Es esférico el BH? Is it more akin to the antimatter than the matter a black hole? Much matter and energy that can enter it without a trace in our Universe seems a transfer to another place from this side can not be viewed. Is it spherical the BH?

    1 day ago
• Ana María Sánchez Peralta

  Is the value of gravity both infinite and zero at the center of gravity of a mass?

  When I studied Physics, we viewed that in the center (x/0) the value of gravity was infinite. But now I see that you say it's 0 (null), because all the force vectors cancel each other, in the exactWhen I studied Physics, we viewed that in the center (x/0) the value of gravity was infinite. But now I see that you say it's 0 (null), because all the force vectors cancel each other, in the exact center. Is near the center near infinite?

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    Zafar Turakulov replied

    What I meant exists as an idealization of a point-like mass in Newtonian theory. Of course, besides there exists continuous mass distributions. As far as I understand Dr. Peralta, she started theWhat I meant exists as an idealization of a point-like mass in Newtonian theory. Of course, besides there exists continuous mass distributions. As far as I understand Dr. Peralta, she started the discussion with that idealization.

    4 days ago
• Prakash Kumar

  Can gravitons be discovered?

  It is believed that gravitons are spin 2 particles according to quantum field theory. Its detection is very difficult and both the Standard Model and the String Theory describe these particles inIt is believed that gravitons are spin 2 particles according to quantum field theory. Its detection is very difficult and both the Standard Model and the String Theory describe these particles in different ways.

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    James Arnold replied

    Prakash wrote: "I fail to see as to where Einstein talked about 'inertial acceleration'." Whether or not Einstein talked about inertial acceleration (seems rather likely!), the point is, that wouldPrakash wrote: "I fail to see as to where Einstein talked about 'inertial acceleration'." Whether or not Einstein talked about inertial acceleration (seems rather likely!), the point is, that would be the situation when the geodesics of two bodies conflict as in the thought experiment. An accelerometer would measure a force between them even though they were not gravitating toward each other -- there would be an inertial acceleration. There is nothing in this scenario that's physically inaccurate, and nothing to conflict with GR. "GR does not explain gravitation as 'force' or 'resistance'." Very true. And that's my point. It's only when geodesics conflict (normally at a massive surface) that force and resistance (described as "weight") is observed in conjunction with gravitation. Einstein coined the principle of equivalence before he developed his geometric theory, and he never revisited it. But as I pointed out earlier, if the "equivalence" can only be invoked in a situation which is so restricted that we can't detect it, it's actually a principle of NON-equivalence. It's like saying red and blue are equivalent if it's dark enough. "Nobody associates energy with weight." An accelerometer does. It's hard to argue with an instrument.

    Apr 17, 2012
• Trao Her

  Gravitation & Time. I heard on NPR Startdate news about some of the work done by researchers at UCLA on Supermassive Blackhole in the center of our galaxy. One of the researchers mentioned thatGravitation & Time. I heard on NPR Startdate news about some of the work done by researchers at UCLA on Supermassive Blackhole in the center of our galaxy. One of the researchers mentioned that they observed very young stars around the supermassive blackhole, a contradiction to their expectation. Let me suggest that their observation is correct. We should expect to see mostly young stars around the supermassive blackhole. The reason behind this argument is that time slows down in a higher gravitation field when observed from outside the influence of the field. In fact, if the field strength is infinite, time would be standing still as observed from by an external observer. In other words, nothing would age (no passage of time) as viewed by an external observer. So once those stars fall to within the influence of the gravitation field of the supermassive blackhole, relativistic time has to be applied to get the correct time information. This is similar to trying to determine the initial time of a man who is on a ship moving near the speed of light. Basis of this interpretation. Einstein's relativistic mass equation suggests that an object gets heavier as it is being accelerated toward the speed of light. Now, let's assume that the constituents (protons, neutrons, and electrons) are conserved, then the only thing that can change is the field strength as measured by an external observer. This also suggests that a moving mass produces a gravitation field, the higher the speed, the higher the field strength. This generated gravitation field (as an effect of motion mass) is then responsible for the time dilation effect of a man on a ship moving near the speed of light as predicted by Einstein's equation (similar to that of a blackhole effect). The important things here are: 1. A mass in motion increases its gravitation field 2. Gravitation affects time 3. The passage of time is inversely related to the field strength (as viewed by an external observer). The higher the field, the slower the passage of time inside the field would appear to an external observer. So in an infinite field, light (and the information therein) would be trapped inside the field as there is no passage of time as viewed by an external observed. This is the reason why the UCLA group observed mostly new stars in their data. There are other implications but let's way on that.

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    Rajan Iyer replied

    My calculations show that strong nuclear entity force tensor matter, what I call m*3 structure with micro_black_holes may originate within super_massive black_holes. This may explain absolute genesisMy calculations show that strong nuclear entity force tensor matter, what I call m*3 structure with micro_black_holes may originate within super_massive black_holes. This may explain absolute genesis of universe corroborating general theory of relativity, theory of strings, & quantum gravity generalizing perhaps big bang theory. Also further Hawking radiation with compacting Planck_time may explain electromagnetic radiation. Hence this will provide a method to formulate grand unified theory of everything. At the very future it will be appropriate to have international world physics conference at many countries on the earth globally. I am hoping that I will be able to present in these world physics teams participating with discussions pertaining to all the findings sharing with all physicists scientists, achieving solutions to many problems such as global warming and future of earth beyond. Hope that all these forums here help in setting the physics of the problem. Of key with note include time quantization solution that will shed light about timeline equation providing key to event-time mapping.

    Apr 12, 2012
• Prakash Kumar

  Is it really true that the universe is expanding?

  Red shift may have other causes apart from the expansion of the universe. It may be only a distance indicator. In this situation it is pertinent to ask whether the universe is expanding or not.

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    Marshall Barnes replied

    Dear Prakash: I might point out that objects in space are not always moving away from each other. This is due to their own direction of movement. Things such as comets and even black holes moveDear Prakash: I might point out that objects in space are not always moving away from each other. This is due to their own direction of movement. Things such as comets and even black holes move through space because of their own power and not because of the expansion of space. That would explain why the Milky Way and Andromeda are getting closer, if in fact they are (I don't have time to look it up). In my own work I've seen stars getting sucked into black holes and black holes moving through space toward other stellar objects, or each other, none of which had anything to do with the expansion of the universe...

    Apr 3, 2012
• Prasanta Mahato

  Newtonian Gravity

  Do Newtonian Gravity has an independent existence in General Relativity, other than static weak field approximation of Einstein's gravity?

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    Iresh Ranjan Bhattacharjee replied

    There was a good discussion in "Nature of Reality" group of ResearchGate in this regard recently. Please visitThere was a good discussion in "Nature of Reality" group of ResearchGate in this regard recently. Please visit http://www.researchgate.net/group/Nature_of_Reality/board/thread/15808_Join_Self_Gravitation_Bio_Group_at_ResearchGate?viewLast=1&dbw=true In fact, it transpired that though electromagnetic force and gravity are of same range, but as electromagnetic force are time bound and based of charges, in contrast to constant in gravitational force with the quantity of 'mass', domination of gravity is the corollary in case of biological mass (having phase transition from non-Newtonian to Newtonian materials). "At the same distances, electromagnetic fields are stronger than gravitational fields. However, gravitational fields work with masses and EM fields work with electrical charges. As I said before, these charges tend to compensate each others effect, such that locally the EM field is neutralized. Masses are not compensated. Indeed, in this case the only force resulting might be gravitational"- Hans Van Leunen. In the discussion it was also questioned that how to perceive gravity? similar "to a blind man to perceive photon, light etc. of electromagnetic force". Apart from me, presence of physicists like David Hirst, Sydney Clouston, and Hans Van Leunen made the discussion on gravity humerous and lively, starting from gravity (means rise in personality) versus lavity (downfall in personality) in human affairs.

    Dec 26, 2010
• Prakash Kumar

  Can a theorem of gravity be true which is capable of describing both attraction and repulsion?

  Both the Newtonian and Einsteinian theories of gravitation do not predict or describe anti-gravity. There can be a mathematical theory capable of describing all those things which are in the GRBoth the Newtonian and Einsteinian theories of gravitation do not predict or describe anti-gravity. There can be a mathematical theory capable of describing all those things which are in the GR besides describing and predicting anti-gravity. In that situation, can we accept such a mathematical description (wider theory) as true?

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    Prakash Kumar replied

    Dear Giovanni Acquaviva, I mean what I say. I may be wrong but I am not trolling you or anybody else. By identical bodies, I mean two bodies having the same amount of mass, same spin, same radii andDear Giovanni Acquaviva, I mean what I say. I may be wrong but I am not trolling you or anybody else. By identical bodies, I mean two bodies having the same amount of mass, same spin, same radii and same orientation of spin. If these conditions are fulfilled, it is quite likely that they will repel each other. In other words, all these factors may constitute attraction or repulsion. Surely, it is quite different from what Einstein or Newton maintained.

    Apr 2, 2012
• Raul Alvarez

  How much does the knowledge cost?

  I would like to apologize in advance for using this space for "socio-scientific activism", but i think the discussion (in the link below) is important enough and actually fits perfectly well with theI would like to apologize in advance for using this space for "socio-scientific activism", but i think the discussion (in the link below) is important enough and actually fits perfectly well with the philosophy of this social network . The main site of " The cost of knowledge" http://thecostofknowledge.com/ You can find the general statement of the problem here: http://gowers.files.wordpress.com/2012/02/elsevierstatementfinal.pdf

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    Henk Smid replied

    Hi Brandon Avast Ye Matey !!!

    Mar 28, 2012
• Prakash Kumar

  How is the Doppler red-shift differentiated from gravitational red-shift?

  Doppler red-shift is caused by distance and the separation speed whereas the gravitational red-shift is caused by a body having mass. The gravitational red-shift is an expression of space-timeDoppler red-shift is caused by distance and the separation speed whereas the gravitational red-shift is caused by a body having mass. The gravitational red-shift is an expression of space-time curvature.

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    Giovanni Acquaviva replied

    Dear Prakash, I'm not really inside the topic of operative observational astronomy, so I would wait someone else more expert than me to answer thoroughly to your question. In the meantime, maybeDear Prakash, I'm not really inside the topic of operative observational astronomy, so I would wait someone else more expert than me to answer thoroughly to your question. In the meantime, maybe wikipedia could serve as an appetizer: http://en.wikipedia.org/wiki/Redshift#Distinguishing_between_cosmological_and_local_effects Kind regards, Giovanni

    Mar 27, 2012
• Shirish Phanse

  What is the SI unit of gravitation?

  Please describe

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    Sunil Upadhyay replied

    hi Ahmad ,thanx for supporting my statement.I told several times that gravitation is not a physical quantity so no question of its si unit.

    Mar 21, 2012
• Selva Kumar

  Gravitational force-

  Does really General relativity answer for gravitational force or Gravity. Because i have a serious doubt that if according to General relativity the gravitational attraction is due to space timeDoes really General relativity answer for gravitational force or Gravity. Because i have a serious doubt that if according to General relativity the gravitational attraction is due to space time curvature. If that is true then this Gravitational force should exist even for objects or masses on earth. Then what is the viscinity of masses to be mutally attracted towards each other???

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    Anirudh Kumar Satsangi replied

    Thanks Zhan. If I am correct, at black holes gravitational field has the highest level of energy states.

    Mar 13, 2012
• Prakash Kumar

  Can spin be a fundamental property of both the elementary particles and the large celestial bodies?

  Elementary particles have different values of spin. Similarly, planets and stars are also spinning. It seems that there is something common in both the interactions: nuclear and gravitational.

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    Horacio Dottori replied

    Prakash: I'm sorry. In my previous answer lack the word CONTINUOUSLY. It should read: "In that sense they are related, but the angular momentum of a body can be transferred or dissipatedPrakash: I'm sorry. In my previous answer lack the word CONTINUOUSLY. It should read: "In that sense they are related, but the angular momentum of a body can be transferred or dissipated CONTINUOUSLY. That doesn't happens with the spin of elementary particles."

    Mar 11, 2012
• David Alexander

  What causes the gravitational constant? Is it truly a constant? What makes gravity universal?

  Further, how does the gravitational constant relate to general relativity and the curvature of spacetime? Any input would be useful, thanks.

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    Bill LaPorte-Bryan replied

    I agree with Prakash that your answer is beautiful, Horacio Dottori. The approach you described of setting the value of something in an equation to 1 is a powerful way to understand things. IfI agree with Prakash that your answer is beautiful, Horacio Dottori. The approach you described of setting the value of something in an equation to 1 is a powerful way to understand things. If you're a mathematician think of choosing the right units of measure to do that; or, if you like to think abstractly, think of viewing the system described by the equation from the perspective of the thing you want to give the value of 1 to. For example, consider the equation E=mc^2. If E=1 you have a relation between mass and the speed of light; if m=1 you have a relation between energy and the speed of light; if c^2=1 you have a relation between energy and mass. Thanks again, Horacio Dottori for sharing your insight with us.

    Mar 6, 2012
• Stefano Gusman

  A way to use breaking symmetry concept to explain gravity fields

  Symmetry and gravity.doc.doc

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    Michael Brayer replied

    I think that the problem is an encoding problem, I will see it in your blog, thnk you

    Mar 3, 2012
• Mohd Bilal

  It is the gravitation which is responsible for the curveness of the space. and gravitation means mass and our universe is full of mass (matter) and this matter is responsible for the geodesics.