Could Dark Matter be composed of Photons?

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barrykirk

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I was rereading one of my physics books where it's explained that the universe is 74% dark energy, 22% dark matter, and 4% regular matter.<br /><br />Now as for the regular matter is concerned it is described as baryonic material which as far as I know consists of mostly protons and neutrons.<br /><br />The Big Bang descriptions describe that initially their was a tremendous amount of matter and antimatter with the tinniest of assymeteries in that their was slightly more matter than antimatter. All of the antimatter is gone when it annihilates with matter leaving a small residue of matter.<br /><br />Now that annihilation process generates a lot of photons which have the same mass as the matter and anitmatter that got annihilated. The mass of those photons should have substantially more mass than the remaining matter.<br /><br />What happened to that mass?<br /><br />Later in the evolution of the universe when things had cooled down to the ponit when atoms formed the photons flying around formed the cosmic background radition. Are those photons drawn from the same mass of photons that came out of the initial annihilation process?<br /><br />Is it possible that the dark matter, at least the hot dark matter is in the form of photons?
 
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yevaud

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Two problems there - interrelated.<br /><br />1. Photons have a rest mass, but that's not a "real" mass.<br /><br />2. With no real mass, they are not a source of gravitation - which was the first clue that Dark Matter might exist - that the rotational velocities of the outer edges of Galaxies were demonstrably wrong, demonstrating that some unseen source of gravity was affecting them. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>
 
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Saiph

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umm...photon's have no rest mass. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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yevaud

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Perhaps you were unaware of this:<br /><br /><i>In 1994, the Charge Composition Explorer spacecraft measured the Earth's magnetic field and physicists used this data to define an upper limit of 0.0000000000000006 electron volts for the mass of photons, with a high certainty in the results.</i> <br /><br />It is very tiny, yes, but it does apparently exist. Of course, it's so tiny that Photons effectively have no mass, for all practical purposes. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>
 
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Saiph

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<img src="/images/icons/smile.gif" /><br /><br /><i>if</i> photons had mass my quantum profs would have an anerysm, as QED wouldn't work so well.<br /><br />Also, that defines an <i>upper</i> limit, stating that if photons have mass, it is no more than that. And they very accurately defined the upper limit. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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yevaud

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Well yes. It's, as they say, "a difference that makes no difference." <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>
 
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Saiph

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it does make a difference though. Such experiments say only that: A photon was found to have no mass, to an accuracy of 0.0...whatever.<br /><br />It's the same thing as experiments that say an electron had no discernable radius, with an upper limit (due to experimental accuracy) of somesuch, or that protons don't decay within 10^30 years. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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yevaud

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Well, yeah. It just seemed germaine to the question, since <insert long and involved username here> mentioned Photons and Mass in the same breath. I suppose, on reflection, it was somewhat confusing to state.<br /><br />My point having done so was that even <i>if</i> there was a tiny but finite measureable mass to a Photon, it is vastly insufficient to cause the rotational velocity anomolies in all the Galaxies we image. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>
 
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Saiph

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right, that, and the fact that it would be classified as hot dark matter, which doesn't really help the models much. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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yevaud

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Well yeah. It would radiate and we therefore could detect it radiometrically; ergo not "dark." <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>
 
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Saiph

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:::grins::: Forgot to mention that.<br /><br />But by "hot" it refers to rapidly moving dark matter, and since dark matter only interacts weakly (another point against photons) it doesn't clump well, and can't cause a lot of what we see. Neutrino's are "hot" dark matter for instance. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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yevaud

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You're a lot closer to recent information than I am by far (many years out of school). Has there been any refinement on what Dark Matter is believed to be? WIMPS, CHAMPS, MACHOS? Cheeze Whiz? <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>
 
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Saiph

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hmmm cheez whiz.<br /><br /><br />Right off hand, i can't remember. I remember chatting with a friend, and I can tell you that cold dark matter models are doing suprising well, and they're ironing out how much of the "other" types is required.<br /><br />But as for what it really is, I can't really say. I'll chat him up here in a day or so and get back to you. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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yevaud

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I appreciate it. Last I'd heard, it looked to be about 20% MACHOs (some detected by microlensing events), and the bulk of the remainder WIMPS as the best bet. But these things can change rapidly, so... <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>
 
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yevaud

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Barry - sorry, this got off on a sort of brief tangent. But I trust you note where I was heading towards, and that it answers your questions.<br /><br /> <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>
 
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barrykirk

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Yes, Yes,<br /><br />Thank you for all of the input. As you can see from my initial post, I was talking about hot dark matter, which doesn't mean much when it comes to holding galaxies together.<br /><br />But, photons have energy and doesn't that correspond to mass?<br /><br />I've heard that gravity itself generates more gravity. Is that the reason that the orbit of Mercury preceses?
 
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alokmohan

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Its for this reason theory of relativity was long overdue.Explains perturbation of planets.
 
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