interested Posted October 2, 2017 Author Posted October 2, 2017 3 hours ago, swansont said: Dark matter does not interact electromagnetically. It is not made up of e-e+ pairs, or of any other particle we've already detected. That's why we call it dark matter. Thanks for confirming that. I have been googling again and found this also which I think is related. https://arxiv.org/pdf/1612.07698.pdf MeV dark matter (DM) particles annihilating or decaying to electron-positron pairs cannot, in principle, be observed via local cosmic-ray (CR) measurements because of the shielding solar magnetic field. In this letter, we take advantage of spacecraft Voyager 1’s capacity for detecting interstellar CRs since it crossed the heliopause in 2012. This opens up a new avenue to probe DM in the sub-GeV energy/mass range that we exploit here for the first time. From a complete description of the transport of electrons and positrons at low energy, we derive predictions for both the secondary astrophysical background and the pair production mechanisms relevant to DM annihilation or decay down to the MeV mass range. Interestingly, we show that reacceleration may push positrons up to energies larger than the DM particle mass. We combine the constraints from the Voyager and AMS- 02 data to get novel limits covering a very extended DM particle mass range, from MeV to TeV. In the MeV mass range, our limits reach annihilation cross sections of order hσvi ∼ 10−28cm3 /s. An interesting aspect is that these limits barely depend on the details of cosmic-ray propagation in the weak reacceleration case, a configuration which seems to be favored by the most recent boron-tocarbon (B/C) data. Though extracted from a completely different and new probe, these bounds have a strength similar to those obtained with the cosmic microwave background — they are even more stringent for p-wave annihilation 2 hours ago, Strange said: Virtual particle pairs only exist temporarily. Also, they are evenly distributed but dark matter is not. Pair production requires a source of energy. The Big Bang happened because the universe was hot. The universe is cooling. Most models have dark matter appearing in the early universe, like normal matter. We can detect electron-positron pairs. Yes that is why they are called virtual particles. Also at approaching 0 Kelvin they last longer, entropy is seen to be reversed at very low temperatures. The first law of thermodynamics needs to be included in any theory, energy can not be created or destroyed, heat does not come from nowhere. The heat in the big bang was a result of energy that came from some where. The zero energy universe creates matter from nothing ie quantum fluctuations, at around 0 kelvin in space. What models predict what dark matter is? Can electron positron pairs be detected in space a few billion miles away? or would they just appear as a transparent gas, dark matter? with a spin 0, 1/2, or 1. https://arxiv.org/pdf/1612.07698.pdf might be of interest to you. Dark matter may decay to electron positron pairs.
swansont Posted October 2, 2017 Posted October 2, 2017 39 minutes ago, interested said: Thanks for confirming that. I have been googling again and found this also which I think is related. https://arxiv.org/pdf/1612.07698.pdf MeV dark matter (DM) particles annihilating or decaying to electron-positron pairs cannot, in principle, be observed via local cosmic-ray (CR) measurements because of the shielding solar magnetic field. In this letter, we take advantage of spacecraft Voyager 1’s capacity for detecting interstellar CRs since it crossed the heliopause in 2012. This opens up a new avenue to probe DM in the sub-GeV energy/mass range that we exploit here for the first time. From a complete description of the transport of electrons and positrons at low energy, we derive predictions for both the secondary astrophysical background and the pair production mechanisms relevant to DM annihilation or decay down to the MeV mass range. Interestingly, we show that reacceleration may push positrons up to energies larger than the DM particle mass. We combine the constraints from the Voyager and AMS- 02 data to get novel limits covering a very extended DM particle mass range, from MeV to TeV. In the MeV mass range, our limits reach annihilation cross sections of order hσvi ∼ 10−28cm3 /s. An interesting aspect is that these limits barely depend on the details of cosmic-ray propagation in the weak reacceleration case, a configuration which seems to be favored by the most recent boron-tocarbon (B/C) data. Though extracted from a completely different and new probe, these bounds have a strength similar to those obtained with the cosmic microwave background — they are even more stringent for p-wave annihilation That's a description of how, in principle, one could test this particular hypothesis. But the DM itself is not the e-e+ pairs. 39 minutes ago, interested said: Yes that is why they are called virtual particles. Also at approaching 0 Kelvin they last longer, entropy is seen to be reversed at very low temperatures. You've repeated this a number of times. It still has no basis. The work you've cited is not investigating virtual particles. 39 minutes ago, interested said: Can electron positron pairs be detected in space a few billion miles away? or would they just appear as a transparent gas, dark matter? with a spin 0, 1/2, or 1. They would annihilate and give us a characteristic signature we could detect. 39 minutes ago, interested said: https://arxiv.org/pdf/1612.07698.pdf might be of interest to you. Dark matter may decay to electron positron pairs. That's overstating the claims of the paper.
interested Posted October 3, 2017 Author Posted October 3, 2017 (edited) 18 hours ago, swansont said: That's a description of how, in principle, one could test this particular hypothesis. But the DM itself is not the e-e+ pairs. They would annihilate and give us a characteristic signature we could detect. Has anyone written any papers on virtual particle behaviour at or near zero and or compared it with actual particles at the same temperature? What drove the big bang? Could Dark matter be material still existing from the big bang or multiple big bangs or a zero energy universe. If it is entangled particles of matter and antimatter existing in space at near absolute zero, how long would it take for them to annihilate, without any external disturbance. Does dark matter exist in hotter space, near the centre of the domino galaxy for example or does it just exist on the periphery in colder space? What does everyone else think dark matter is????????????????????????????????????? an expert speculation might yield better results than me asking questions in the dark on dark matter. Edited October 3, 2017 by interested
Strange Posted October 3, 2017 Posted October 3, 2017 48 minutes ago, interested said: Does dark matter exist in hotter space, near the centre of the domino galaxy for example or does it just exist on the periphery in colder space? It is distributed throughout galaxies, with the highest density near the centre. (What is the domino galaxy?) 50 minutes ago, interested said: What does everyone else think dark matter is? No one knows.
interested Posted October 3, 2017 Author Posted October 3, 2017 14 minutes ago, Strange said: It is distributed throughout galaxies, with the highest density near the centre. (What is the domino galaxy?) No one knows. I might have got the name wrong, I will check what has been posted but think Beecee may have referenced it. No one knows for sure. If I google it, there are lots of ideas out there, with people speculating. Some say it does not exist others say it does, etc. I am just trying to get an idea of what it may be. Could be primordial matter left over from the early universe or is it evolving in space. As space expands does dark matter increase with it, where did it come from. etc
Strange Posted October 3, 2017 Posted October 3, 2017 1 minute ago, interested said: Could be primordial matter left over from the early universe If it is matter, then it seems like it was created at about the same time as other matter. 1 minute ago, interested said: As space expands does dark matter increase with it No. The amount appears to be constant. 1 minute ago, interested said: No one knows for sure. If I google it, there are lots of ideas out there, with people speculating. Some say it does not exist others say it does, etc. I am just trying to get an idea of what it may be. It could be any of those. Or something else.
interested Posted October 3, 2017 Author Posted October 3, 2017 9 hours ago, Strange said: It could be any of those. Or something else. Please define what you mean by something else.
Strange Posted October 3, 2017 Posted October 3, 2017 1 hour ago, interested said: Please define what you mean by something else. Something not covered by any of the existing theories; something that no one has yet thought of. Something ... you know ... else. (Or maybe, to keep things simple, it is just a form of matter that doesn't interact with electromagnetic forces.)
Mordred Posted October 3, 2017 Posted October 3, 2017 Personally though this is strictly a personal opinion. I feel out of the theories I have studied for DM the most likely contender is right handed neutrinos via Higgs instability. However there is no confirmational evidence, save one possible xray study that I am aware of. 1
MigL Posted October 4, 2017 Posted October 4, 2017 Wild speculation is useless, educated speculation is based on some understanding of the principles involved. Virtual particles exist because they are allowed to. The Heisenberg Uncertainty Principle is what allows them to exist. It says that for non-relativistic treatments the following relation holds... deltaE * deltaT < hbar/2 ( should be less than or equal to, but I don't do LaTex ) so that for a short duration, energy can be 'borrowed', and after that duration, has to be paid back. This is how virtual particle come into existence and annihilate, leaving no residual energy. But because they are popping in and out of existence throughout empty space ( and even about real particles, modifying their fields and properties ), they give empty space a certain vacuum energy: It is this energy, variously called the ( Einstein ) Cosmological Constant, or Dark Energy ( because we don't have a handle on calculating it from first principles yet ) that is driving ( and accelerating ) expansion. Dark matter, on the other hand, is conjectured to exist because the galactic arms are NOT 'winding'. If we consider the mass that is inside the galactic arms, It isn't enough to keep the arms rotating as if the galactic disk was solid; The arms would be winding up, IE the center spinning faster than the edges of the disk. The only way we can get galactic rotation to fit observation is if the sphere inside the galactic arms has fairly even mass distribution, IE extra hemispherical mass distributions above and below the galactic disk. IOW we detect this mass gravitationally ( by its influence ), but not electromagnetically, as it doesn't seem to absorb or radiate EMR ( the other forces are short range and useless in our analysis ). So we call it Dark Matter ( because again, we don't know what it is, NOT because of any relation to Dark Energy ). It could be composed of any particles which have mass, and interact weakly or not at all Elecromagnetically. Mordred's neutrinos fit the bill, although the have very little rest mass, they are extremely numerous, interact via the weak force and so are extremely hard to detect. There are numerous other candidates though.
interested Posted October 4, 2017 Author Posted October 4, 2017 Gravitational wave detectors could shed light on dark matter. https://phys.org/news/2017-10-gravitational-detectors-dark.html?utm_source=nwletter&utm_medium=email&utm_campaign=daily-nwletter http://ruxandrab.blogspot.co.uk/2011/12/luke-warm-dark-matter-bose-condensation.html Ultra light scalar particles, spin 0, could be a candidate for dark matter according to the above links. To have spin 0 could the particles be made of a particle and antiparticle? Or could virtual particles have on average a mass distributed through out a galaxy?
LaurieAG Posted October 4, 2017 Posted October 4, 2017 The Planck 2013 data and Lambda CDM gives a total universal matter which is comprised of 25.8% dark matter and 4.82% ordinary matter leaving us with a ratio of total universal matter to total universal ordinary matter of 30.62/4.82 = 2 * Pi +/- 1.1%.
Strange Posted October 4, 2017 Posted October 4, 2017 1 hour ago, interested said: To have spin 0 could the particles be made of a particle and antiparticle? They could not be particles of anything we know (or they wouldn't be "dark"). Such an arrangement is probably not stable even for unknown particles. Quote Or could virtual particles have on average a mass distributed through out a galaxy? Through all of space - that is the non-zero background energy of the vacuum.
interested Posted October 4, 2017 Author Posted October 4, 2017 9 hours ago, Strange said: Such an arrangement is probably not stable even for unknown particles. Are you talking about virtual particle pairs which are not stable but on average are there.
Strange Posted October 4, 2017 Posted October 4, 2017 3 minutes ago, interested said: Are you talking about virtual particle pairs which are not stable but on average are there. No. A particle-antiparticle pair (like positronium).
interested Posted October 6, 2017 Author Posted October 6, 2017 On 10/3/2017 at 11:49 PM, Mordred said: Personally though this is strictly a personal opinion. I feel out of the theories I have studied for DM the most likely contender is right handed neutrinos via Higgs instability. However there is no confirmational evidence, save one possible xray study that I am aware of. Thanks for the pointer https://en.wikipedia.org/wiki/Neutrino The three known neutrino flavors are the only established elementary particle candidates for dark matter, specifically hot dark matter, although that possibility appears to be largely ruled out by observations of the cosmic microwave background. If heavier sterile neutrinos exist, they might serve as warm dark matter, which still seems plausible.[46]
interested Posted October 10, 2017 Author Posted October 10, 2017 I have managed to confuse my self. Can some one explain spin 0, 1/2, 1, 2 etc. My understanding is fermions have spin 1/2, and mass. Bosons have spin 1 and no mass, gravitons spin 2. Spin 0 is a particle with no spin or a particle antiparticle pair of fermions with total spin 0. Hard to detect. Fermions are normally stationery, and mass increases with speed implying at light speed they would have infinite mass or energy. Bosons are a packet of energy (E=hf) or directional fluctuation (stretch and compress)in space that travels at c. Neutrinos are fermions with spin 1/2, and may produce gravitational lensing and be the source of dark matter, however they can also travel at light speed. Is some dark matter stationery and some moving around? Is dark matter to make the sums work, in individual galaxies. Does dark matter have to be small can it be a mixture of neutrinos and dust particles. Is the graviton best viewed as a fluctuation in space travelling in all directions radiating away from mass, OR towards a mass? I have been thinking of this as a single object like packets of energy, which I suspect is wrong. Rather than a moving fluctuation is it a fixed stretching of space with no frequency unlike photons which are spin 1 and have direction and frequency. Clearly I have managed to confuse myself, not helped by reading neutrinos can and do travel at light speed but may also be stationery dark matter causing the lensing effect thought to be caused by dark matter around some galaxies.
Strange Posted October 10, 2017 Posted October 10, 2017 8 minutes ago, interested said: My understanding is fermions have spin 1/2, and mass. Bosons have spin 1 and no mass, gravitons spin 2. Spin 0 is a particle with no spin or a particle antiparticle pair of fermions with total spin 0. Hard to detect. More generally, fermions have half-integer spin and bosons have integer spin. Some bosons have mass. I don't think there is any reason why spin 0 particles are hard to detect. There is a good summary graphic on this page: https://en.wikipedia.org/wiki/Elementary_particle https://en.wikipedia.org/wiki/Elementary_particle#/media/File:Standard_Model_of_Elementary_Particles.svg 23 minutes ago, interested said: Neutrinos are fermions with spin 1/2, and may produce gravitational lensing and be the source of dark matter, however they can also travel at light speed. Neutrinos travel at less than light speed (they have mass). But because of their low mass, most of them probably move at very, very close to light speed. Slow moving ones are also harder to detects they are even less likely to interact with matter. 25 minutes ago, interested said: Is some dark matter stationery and some moving around? I doubt any is stationary (but I suppose that depends what you are using as a frame of reference). 27 minutes ago, interested said: Is dark matter to make the sums work, in individual galaxies. "To make the sums work" is an odd way of putting it. It is required to explain the orbital speeds around galaxies which don't match those calculated without it. 28 minutes ago, interested said: Does dark matter have to be small can it be a mixture of neutrinos and dust particles. The main constraint is that it only interacts gravitationally. It can't be neutrinos because they move to fast. Unless the hypothetical sterile neutrino exists. https://en.wikipedia.org/wiki/Sterile_neutrino It can't be dust because we would see that blocking light. -1
swansont Posted October 10, 2017 Posted October 10, 2017 2 hours ago, interested said: I have managed to confuse my self. Can some one explain spin 0, 1/2, 1, 2 etc. Spin is intrinsic angular momentum. A fundamental property, like mass and charge. Angular momentum is a vector, so spin adds as vector for composite particles. Two spin 1/2 particles can result in spin 0 or spin 1. We look at the projection of the spin onto one axis of our coordinate system (typically the z axis). A spin 1/2 particle can be spin up (along the +z axis) or spin down (-z) Quote My understanding is fermions have spin 1/2, and mass. Bosons have spin 1 and no mass, gravitons spin 2. Spin 0 is a particle with no spin or a particle antiparticle pair of fermions with total spin 0. Hard to detect. K-38m is spin 0. Not hard to detect at all (it's radioactive). He-4 is spin 0. Ca-40 too, I think. Quote Fermions are normally stationery, and mass increases with speed implying at light speed they would have infinite mass or energy. "Normally stationery" (sic) is, at best, an awkward description, owing to relativity. Quote Bosons are a packet of energy (E=hf) or directional fluctuation (stretch and compress)in space that travels at c. Bosons are particles with integer spin. Full stop. Composites bosons are massive and never travel at c. There is nothing that is a "packet of energy". Energy is a property of particles, as is spin. Quote Neutrinos are fermions with spin 1/2, and may produce gravitational lensing and be the source of dark matter, however they can also travel at light speed. Is some dark matter stationery and some moving around? Is dark matter to make the sums work, in individual galaxies. Does dark matter have to be small can it be a mixture of neutrinos and dust particles. Neutrinos (the ones we've detected) have been ruled out as a source of dark matter. They are known to have a tiny amount of mass, so they do not travel at c, though it was once assumed they did, and were massless. Older texts may reflect that assumption. -1
interested Posted October 10, 2017 Author Posted October 10, 2017 Thanks both for the replies. If neutrinos cant be dark matter, are you assuming dark matter is a new as yet undetected light particle or a form of energy. Since varying degrees of dark matter seem to be randomly ascribed to galaxies to explain the movement of galaxies could dark matter also perhaps be a mix of multiple types of extremely light particles. It appears to clump and not interact with other particles could it be a left over from the big bang. Ref the speed of neutrinos Is wikepedia definately wrong????: qoute from the following link https://en.wikipedia.org/wiki/Neutrino "After the detectors for the project were upgraded in 2012, MINOS refined their initial result and found agreement with the speed of light, with the difference in the arrival time of neutrinos and light of −0.0006% (±0.0012%).[56] A similar observation was made, on a much larger scale, with supernova 1987A (SN 1987A). 10 MeV antineutrinos from the supernova were detected within a time window that was consistent with the speed of light for the neutrinos. So far, all measurements of neutrino speed have been consistent with the speed of light.[57][58]" Is the graviton best viewed as a fluctuation in space travelling in all directions radiating away from mass, OR towards a mass? I have been thinking of this as a single object like packets of energy, which I suspect is wrong. I do not think it is a detectable fluctuation unless there is something like a pair of black holes spinning around each other or a supernovae of some sorts. I suspect Gravity is a fixed stretching of space with no frequency unlike photons which are spin 1 and have direction and frequency. Does spin 2 denote a field in all directions with infinite range, or does spin 2 denote something else. Does other gravitational theories require dark matter, eg modified gravity for instance?. The lensing pointed out by Beecee indicates something is affecting the light passing some galaxies, could a combined modified gravity and a little dark matter explain.
Strange Posted October 10, 2017 Posted October 10, 2017 15 minutes ago, interested said: Thanks both for the replies. If neutrinos cant be dark matter, are you assuming dark matter is a new as yet undetected light particle or a form of energy. Not assuming anything. The answer is we don't know. Among the classes of possibilities are WIMPs and MACHOs: https://en.wikipedia.org/wiki/Weakly_interacting_massive_particles https://en.wikipedia.org/wiki/Massive_compact_halo_object There are many other ideas. Energy is a property of things, so it can't be just energy. 17 minutes ago, interested said: It appears to clump and not interact with other particles could it be a left over from the big bang. Not sure what you mean by a "left over" but I think that in most models dark matter has existed for as long as normal matter. 18 minutes ago, interested said: Ref the speed of neutrinos Is wikepedia definately wrong???? I don't think so. The speed is so close to the speed of light that it is within the error bounds. Or maybe they do travel at the speed of light and this indicates something else wrong with the model. Quote Is the graviton best viewed as a fluctuation in space travelling in all directions radiating away from mass, OR towards a mass? I don't think that either of those is the case. Gravitons would be the quantum of gravitational waves in the same way that photons are the quantum of EM waves. And gravity would be mediated by virtual gravitons in the same way that electromagnetic forces are mediated by virtual photons. Quote Does other gravitational theories require dark matter, eg modified gravity for instance?. The lensing pointed out by Beecee indicates something is affecting the light passing some galaxies, could a combined modified gravity and a little dark matter explain. I think there are models which have both modified gravity plus dark matter. But I don't know any more than that ... -1
interested Posted October 11, 2017 Author Posted October 11, 2017 23 hours ago, Strange said: Not assuming anything. The answer is we don't know. Among the classes of possibilities are WIMPs and MACHOs: https://en.wikipedia.org/wiki/Weakly_interacting_massive_particles https://en.wikipedia.org/wiki/Massive_compact_halo_object There are many other ideas. Energy is a property of things, so it can't be just energy. Not sure what you mean by a "left over" but I think that in most models dark matter has existed for as long as normal matter. I don't think so. The speed is so close to the speed of light that it is within the error bounds. Or maybe they do travel at the speed of light and this indicates something else wrong with the model. I don't think that either of those is the case. Gravitons would be the quantum of gravitational waves in the same way that photons are the quantum of EM waves. And gravity would be mediated by virtual gravitons in the same way that electromagnetic forces are mediated by virtual photons. I think there are models which have both modified gravity plus dark matter. But I don't know any more than that ... Thanks for the response, and links. Is super gravity a viable idea today? Ref energy I have no problems viewing gravity as a result of a the stretching of space, regardless of the existence or not of gravitons. I also see no problem with the concept of photons as stretching and compressing space in the similar way to what gravity does, neither are particles but both transfer energy. Gravity stretching space continuously or photons just causing a fluctuation in space as they move or exist in space do not need to be particles. If gravity can stretch space and transfer energy as detected by ligo , then I assume photons can also. Neither are particles and both transfer energy via the stretching or compression of space. Everything I have found indicate neutrinos can travel at the speed of light, I was seeking clarification. Thank you To stretch space via the movement of virtual gravitons suggests to me a flow of gravitons towards mass, where gravitons must be absorbed or destroyed without increasing the energy of the mass absorbing them. Could gravitons be assumed to be space, or quantum foam? OR are virtual gravitons stationery?
swansont Posted October 11, 2017 Posted October 11, 2017 1 hour ago, interested said: Everything I have found indicate neutrinos can travel at the speed of light, I was seeking clarification. Thank you The mass is small, and the uncertainty in the speed measurement doesn't permit one to determine the speed with sufficient precision. https://en.m.wikipedia.org/wiki/Measurements_of_neutrino_speed On October 10, 2017 at 4:46 PM, interested said: Ref the speed of neutrinos Is wikepedia definately wrong????: qoute from the following link https://en.wikipedia.org/wiki/Neutrino "After the detectors for the project were upgraded in 2012, MINOS refined their initial result and found agreement with the speed of light, with the difference in the arrival time of neutrinos and light of −0.0006% (±0.0012%).[56] A similar observation was made, on a much larger scale, with supernova 1987A (SN 1987A). 10 MeV antineutrinos from the supernova were detected within a time window that was consistent with the speed of light for the neutrinos. So far, all measurements of neutrino speed have been consistent with the speed of light.[57][58]" Consistent with the speed of light is also consistent with a speed just below it.
Strange Posted October 11, 2017 Posted October 11, 2017 1 hour ago, interested said: To stretch space via the movement of virtual gravitons suggests to me a flow of gravitons towards mass, where gravitons must be absorbed or destroyed without increasing the energy of the mass absorbing them. Could gravitons be assumed to be space, or quantum foam? OR are virtual gravitons stationery? This article has a good introduction to the concept of virtual particles: https://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/ 1
Mordred Posted October 12, 2017 Posted October 12, 2017 (edited) Yes super gravity is still viable today. No matter what treatment under physics your working with. Never treat space itself void of all particles as anything other than volume. Space has no particle nor will ever need one. The Prof site Strange linked covers bosons ie VP. Edited October 12, 2017 by Mordred 1
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