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Antimatter can be thought of as ordinary matter going backwards in time. Either it is or it isn't, the odds are 50/50. Mainstream science, assumes matter and antimatter to gravitationally attract each other. Why is this assumption so overwhelmingly strong? Does this dogma have any valid scientific reasoning behind it?
Either it is or it isn't, the odds are 50/50.
The arrow of time lets assume for the sake of simplicity can only have two directions and this was the point I was making in saying 50/50. This is self evident.
Physics is almost completely based on this idea, it is so fundamental that it has to be based on something.
If antimatter repels normal matter gravitationally, then that would allow for a violation of the conservation of energy (which is a big no-no).Imagine an electron-positron pair in the gravitational field of the Earth. They both have equal mass, but one is attracted towards the Earth while the other is repelled away from it. In this sense, the pair has no weight, since they cancel out one another's gravitational effects. The net result is that you can change their height above the Earth's surface with no net change in the energy of the system.Now imagine that you put the pair at a high altitude and allow it to self-annihilate to produce a pair of gamma ray photons. Then you move those gamma ray photons down closer to the Earth. When light travels in towards a gravitational source, it's frequency increases and it gains energy (blue-shifting). Think of it as the opposite of what happens when light travels away from a dense object like a neutron star (red-shifting).Once you return to the same height that you originally had the electron-positron pair at (before you moved it up high), you allow the gamma ray photons to create a new electron-positron pair. But wait, this electron-positron pair has a higher energy state than it did before due to the blue-shifting of the gamma rays. You can repeat the process and create a pair with even more energy than that, and so on. Where is this extra energy coming from?If both matter and antimatter are attracted gravitationally, then this problem is avoided.Also, light (which is neither matter nor antimatter) is attracted by gravity (i.e. gravitational lensing). So why would antimatter be different from both matter and light in this sense?
SuperC - nice argument, not entirely convinced, but cannot see the flaw.
"Energy is conserved," is an oversimplefication of the conscept of energy conservation. The energy of a closed system is conserved in any inertial reference frame, but the system has different amounts of energy relative to different reference frames. The photonic energy that is released by annihilation IN THE REFERENCE FRAME OF THE PAIR AT THE TIME AND PLACE WHERE ANNIHILATION OCCURS is equal to the mass of the particle pair, including the mass equivalent of any kinetic energy they had in that reference frame prior to collision. In a different reference frame the mass-energy may vary, but the rest mass is constant. The rest mass of a particle is the mass of the particle in a reference frame which is stationary relative to the particle.
Mike - the upshot of that gedanken is that antimatter is attracted to matter. You will note that this has "kinda" been checked experimentally with the deflection of neutrinos and antineutrinos being the same
Mike I have tried to explain simpler notions to you - you refuse to compromise or see that you could possibly be wrong. The creation of particle pairs will have same amount of excess energy independent of the height above centre of mass of planet - it follows that the two forms you have suggested will have same xs energy, thus if energy is conserved only the attractive model works
Attractive might be the wrong word Mike. You could also think of it as 'gravity' having a 'direction'. That 'direction' gives you a 'up' and a 'down' biologically. Magnets can 'attract' or 'repel'. Gravity just is.
The whole point of the gedanken is to take the antimatter/matter particle pair crunch them together - increase energy of photons produced, remake the pair and the excess energy gained by the photons falling towards earth is matched by the kinetic energy required to move the the particle pair back up to original level. this balance works for attractive.if we assume that antimatter is repulsive of matter then you will get the particles again with enough kinetic energy to get them back to the original higher level BUT now the repulsive antimatter particle gains additional kinetic energy as it accelerates outwards - so instead of having two particle at rest (which is the starting situation) you have the matter at rest and the antimatter with increased velocity and accelerating outwards. So you have gone from two stationary particles at beginning of experiment to one stationary and one fast moving at the end; that is the failure of conservation of energy.
Ordinary gravity, can be thought of as kinetic energy. Repulsive gravity is the opposite, as kinetic energy is gained from acceleration in a gravitational field, so gravitational potential energy is lost. The accelerating antiparticle is gaining kinetic energy at the cost of loosing gravitational potential energy the higher it climbs out of the gravity well. The two cancel and the total energy remains the same. The accelerating antiparticle is not gaining energy.
Quote from: MikeS on 18/06/2011 15:18:22Ordinary gravity, can be thought of as kinetic energy. Repulsive gravity is the opposite, as kinetic energy is gained from acceleration in a gravitational field, so gravitational potential energy is lost. The accelerating antiparticle is gaining kinetic energy at the cost of loosing gravitational potential energy the higher it climbs out of the gravity well. The two cancel and the total energy remains the same. The accelerating antiparticle is not gaining energy.No gravity CANNOT be thought of a kinetic energy - this is just nonsense.Forget Potential Energy. This is why: 1. PE is proportional to distance from centre of mass (CofM) - no matter whether that of antimatter or matter2. Particles are x metres from CofM at begining of experiment3. Particles are x metres from CofM at end of experiment4. Particles mass is same as at beginning and position is same --> PE must be same at beginning and end of experiment.5. There is no change between PE beginning and end whether Anti-M is repulsive or not. But - Kinetic Energy varies. This is why1. There is a FoR in which the two particles start at rest - ie zero kinetic energy2. At the end of the experiment the two particles return to this point3. But by the end the matter particle is at rest - whereas the anti-matter (if repulsive) has a velocity & kinetic energy4. So there is a change in Kinetic Energy iff anti-matter is repulsive under gravityThis is a closed system and you have ended up with more energy than you started with I have laid it bit by bit - Tell me which bit of the above is wrong.
Everywhere in the universe is within a gravitational field, therefore all mass is moving.
Sorry for butting in, but QuoteEverywhere in the universe is within a gravitational field, therefore all mass is moving. does not seem right at all.Just because matter is in a gravitational field, there is no guarantee that it is moving, and matter can be moving regardless of the gravitational field that it is in.
Mike - one last try! Gravitational Potential Energy is proportional to ONLY the masses, the separation and the force.True or False?TrueThe particles are in exactly the same place, have exactly the same mass, and the graviational force is the same at both beginning and end of experiment. True or False?TrueThe particles have the same Potential Energy at beginning and end.True or False?TrueThe fact that the antimatter particle (if g is repulsive) has too much kinetic - does NOT mean that this energy can only have come from lost potential of the same amount! We have shown above that PE remains the same. The fact that KE has increased shows that Energy has not been conserved. if you insist on this form of analysis then you must calculate the PE at the moment of re-creation of the two particles - this is difficult!KE, has either not increased (when the two particles are back at their original starting points KE has not increased) or has increased at the expense of gravitational potential energy GPEWhere I have answered true to the above points, I mean true when the particles are back in their original starting positions.Geezer is correct, I am currently sitting at my desk putting off my phd research, I am in a gravitational field with a force of approx 9.8ms-2, to the best of my knowledge I am not moving
Mike - you keep saying this, it is wrong. PE is ONLY proportional to distance, mass, and gravitational attraction. Either tell me this is wrong, or agree with it.If you give me a straight answer (ie one word) then I can build on that to explain where you are wrong - cos you are wrong. If you insist on long and rambling replies which ignore my posts I am gonna call it quits
I think we both agree that when both particles have returned to their starting points energy has been conserved.
Yes the antimatter particle has velocity and has gained kinetic energy but the kinetic energy gain is at the cost of loosing the equivalent amount of potential energy.
Ah yes! The dreaded PE/KE debate 
Ah yes! The dreaded PE/KE debate At this risk of introducing a gigantic poisson rouge, or at least providing a common target that you might both agree to aim at, a body does not actually have any potential energy because of its position.The "energy" is not in the body at all. It's in the gravitational field.It's not really very different from the situation of a bow and arrow. (I'm sure the clever reference back to the previously mentioned target has not gone unnoticed.) When the archer pulls back the string, the potential energy is stored in the bow, not the arrow.Admittedly it is a bit more complicated than that because the energy stored in the gravitational field is also a consequence of the position of the mass within it, but the energy that is converted into kinetic energy was not stored within the object, so it had to be stored in the field.Exactly what this has to do with antimatter, I do not know, but perhaps it might help.
Hi, I found this discussion really facsinating, thanks. imatfaal, I'm trying to understand your explanation. Please could you help? Firstly, are you suggesting the following, and please could you clarify where I may have mis-understood?
(1) Take a positron and an electron, which are 'stationary'(2) They may combine, and would turn into light(3) The light may move through a gravity field, and then its frequency would change: blue shift if moving towards a (positive?) mass(4) The light can then turn back into a positron and electron, which are now both moving faster than before because the frequency of the light increased. (5) Under the original assumption, the particles may easily be returned to their starting positions without changing the system's kinetic energy
Next, are you saying the following (is this right)? (a) At stage 5 the total gravitational potential energy of the system is the same as at stage 1(b) The particles are moving faster, so Total kinetic energy has increased(c) No other forms of energy would have been changed(d) a b and c would only imply that the total energy of the system has increased, which violates the principle of conservation of energy.
Lastly, may I ask a few questions? These will demonstrate my complete lack of knowledge, sorry! (i) If the pair were to be re-combined and moved back to where they started in the form of light, then would the light start at the higher frequency again (higher because of the additional kinetic energy)? And would the frequency drop this time (as it moved in the opposite direction to before through the field; red shift on the way out instead of blue shift on the way in)? And therefore if they re-appear at the original position by this method would they be 'stationary' again?
(ii) How can we move the pair back to their starting positions, without changing the total kinetic energy of the system? [Edit: I re-read the description by Supercryptid, but I'm still struggling with this bit: "The net result is that you can change their height above the Earth's surface with no net change in the energy of the system."(Should it be re-worded "..kinetic energy of the system."?) How can this be achieved? Does this mean that the energy to move them back out through the field is zero? So they pull against each other in the field, and a small tap sends them off and an equal and opposite one to stop them when they get there? ]
(iii) So to get to (5), have we assumed that both the inertial mass and gravitational mass of the positron are negative? If so, would negative mass affect how the kinetic energy of the system is measured at stages (4) and (5)? May a positron in motion have negative kinetic energy under our assumption, and would this resolve the apparent violation in conservation of energy? Or did we get there without needing negative inertial mass? But then confirming they are still to be treated as the same once again resolves that situation.
(iv) Is it OK to ignore the magnetic potential energy between the positron and the electron? (I think it is, because the electron and positron start and finish the same distance apart - is that right?)
(v) Couldn't half the light go in the wrong direction, and need to be reflected back by a mirror or something? If so, would that move the mirror a bit, or heat it, or change the frequency of the light, and is that relevant when adding up all the energy in the system? Or can all the light go where we want it, without adding components to the system? Can it still do so on a macro scale?
Good luck with ignoring your phd research, perhaps my questions will help with that! I'm busy ignoring a piece of coursework for my accountancy exams right now