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Lisa!

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- Thread starter Lisa!
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Lisa!

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Labguy

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If you are talking about something such as http://www.pureenergysystems.com/events/conferences/2004/teslatech_SLC/KonstantinMeyl/NeutrinoPower_ScalarWaves.htm [Broken] , and only photons can be massless and therefore travel at c. Neutrinos are very fast, but do not travel at c nor does any other particle with mass. See:Lisa! said:

http://www.physlink.com/Education/AskExperts/ae476.cfm for the reasons why, and discussion on neutrinos in particular.

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Lisa!

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Thank you very much.

Labguy said:If you are talking about something such as http://www.pureenergysystems.com/events/conferences/2004/teslatech_SLC/KonstantinMeyl/NeutrinoPower_ScalarWaves.htm [Broken]almost nothing relative to my question.

You mean dark matter doesn't consist of neutrino for sure!only photons can be massless and therefore travel at c. Neutrinos are very fast, but do not travel at c

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Labguy

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No, neutrinosLisa! said:You mean dark matter doesn't consist of neutrino for sure!

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ohwilleke

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Lisa!

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I still don't know if neutrino could travel to the past and what does it mean.

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ohwilleke

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This doesn't make sense. Dark matter has to be massive. There are no non-massive dark matter candidates.Lisa! said:I said neutrino couldn't be part of dark matter because it's not massless but well,as you say it's still a good conditate for dark matter.Thanks both of you.

Neutrinos don't behave differently with respect to time than anything else. To the extent that nothing else travels to the past, neutrinos don't either.I still don't know if neutrino could travel to the past and what does it mean.

Existing physics has very weak "arrows of time". There are very few laws of physics that a sensitive to whether you are going forward or backward in time. The second law of thermodynamics and certain CPT violation events are the most significant.

Also, keep in mind that time is not a single absolute coordinate frame. Clocks in coordinate frames which are at motion with respect to each other tick at different rates.

One way of looking at anti-particles, popularized if not invented by Feynman, is that they are ordinary matter moving backward in time. But, normally, we think of all matter, neutrinos included as moving forward in time, and there are no phenomena which we ordinarily think of as having a backwards in time causality.

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Lisa!

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could you please tell me about other condidates?ohwilleke said:This doesn't make sense. Dark matter has to be massive. There are no non-massive dark matter candidates.

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wolram

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Afaik ,The prime candidate is the WIMP, weakly interacting massive particle.Lisa! said:Thank you very much.

could you please tell me about other condidates?

This is from Wikipidia.

Since it cannot be directly detected via optical means, many aspects of dark matter remain speculative. The DAMA/NaI experiment has claimed to directly detect dark matter passing through the Earth, though most scientists remain sceptical since negative results of other experiments are (almost) incompatible with the DAMA results if dark matter consists of neutralinos.

In other words no one can be sure what dark matter is, and to some extent

if it exisists.

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ohwilleke

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The parameters are somewhat defined.Lisa! said:Thank you very much.

could you please tell me about other condidates?

The evidence is pretty clear that dark matter must be non-baryonic. In other words, matter made up of protons, neutrons and similar particles are pretty well ruled out (particles containing quarks other than protons and neutrons are not stable). Thus, very dim stars or large planets (known as MACHOs), interstellar gas, and the like are ruled out. The evidence is also not friendly to black holes as candidates.

The evidence pretty well rules out neutrinos, for reasons discussed before.

There is not evidence that dark matter is electrically charged. Thus, free electrons are ruled out.

We know that dark matter needs to be massive and not emit photons. Gravitons are also not believed to themselves be massive if they exist. Thus, photons themselves are ruled out. Gluons and W/Z particles are either confined to particles composed of quarks or are short lived remnants of them.

This is all rather unfortunate. Because, the evidence has pretty well ruled out all forms of particles known to the standard model.

Also the version of dark matter theory that is the best fit for the evidence is called CDM for Cold Dark Matter. This means that it needs to be relatively slow moving. Basically, we'd like to discover a neutrino-like particle that is massive, electrically neutral and slow moving, that does not interact very strong with anything, just like a neutrino. The acronymn for particles that fit this profile is WIMP for weakly interacting massive particle.

Two of the prime candidates are the proposed "Higgs Boson" a massive particle which mediates a field in the universe that gives rise to inertia, and any of a number of "supersymmetric" particles, such as the neutralino.

Supersymmetry theories are a class of theories which argue for reasons of mathematical symmetry that the world would make more sense if every, or almost every familiar standard model particle had a supersymmetric partner which would be much more massive than the plain vanilla version we see in our particle accellerators, and hence beyond our ability to discover. These would have been common in the early universe and most would have decayed away by now. But, if some kind of supersymmetric particle such as a neutralino (and there are dozens of candidates out there, don't imply consensus from my failure to list them all), that behaved like a WIMP, then this could explain DM.

The big problem with CDM theory is that it requires the bulk of the massive particles in the universe to be made up of some sort of WIMP that isn't made out of anything found in the standard model of particle physics. Thus, while it has the virtue of allowing general relativity's equations to remain essentially unmodified (most CDM theories also require a cosmological constant or some other form of dark energy), we have to go invent some new particle and one can be forgiven for being skeptical of the fact that a ubiquitous constituent of the universe has not yet been encountered. (Have my biases shown here, just a little?)

Now, the trouble is, that if there isn't some new particle, and in fairness, we've discovered all sorts of new particles in the past fifty years, we have to do some major open heart surgery on Einstein's Theory of General Relativity, that remains consistent with all known evidence while modifying those equations in a way that replicates that data currently explained by the majority view in the astrophysical community with dark matter, and has survived nearly a century unmodified, while we've discovered scads of new particles, many of which like the strange and charm and beauty and top quarks, we had no reason to expect existed.

Theoretical physics is in something of a crisis right now, in my view, because the astrophysical data is increasingly suggesting that either the standard model of particle physics, or Einstein's theory of general relativity, which are two of the most fundamental theories of modern physics, must be incomplete (i.e. wrong). Until this is resolved, boards like this one will be interesting places.

The case for the neutralino is made here: http://web.mit.edu/~redingtn/www/netadv/specr/6/node1.html

Several candidates are evaluated here: http://www.amherst.edu/~rloldershaw/TWIN.HTM which also places boundaries on the properties of dark matter given current data.

Links to many journal articles here: http://www.nu.to.infn.it/Dark_Matter/ [Broken]

This article mentions 20 possible candidate, with the axion, a proposed particle related to charge parity law violations, being the most significant non-supersymmetric candidate. http://arxiv.org/PS_cache/hep-ph/pdf/0404/0404175.pdf [Broken]

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There is only one problem,photons do have mass,the mass of the momentum!Labguy said:If you are talking about something such as http://www.pureenergysystems.com/events/conferences/2004/teslatech_SLC/KonstantinMeyl/NeutrinoPower_ScalarWaves.htm [Broken] , and only photons can be massless and therefore travel at c. Neutrinos are very fast, but do not travel at c nor does any other particle with mass. See:

http://www.physlink.com/Education/AskExperts/ae476.cfm for the reasons why, and discussion on neutrinos in particular.

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Labguy

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That is correct, also in that momentum relates to kinetic energy. But, for a photon this does not relate to having "mass" as we generally define it. From a .gov site:No-where-man said:There is only one problem,photons do have mass,the mass of the momentum!

and:It a result of the theory of relativity that a photon has momentum, but have zero mass. One of the worrisome aspects of relativity and quantum mechanics is that we must abandon our graphic notions of Newtonian mechanics, and also some of the notions of classical electromagnetic theory of Maxwell. The problem you are asking about is only one of several notions that has to be abandoned. In addition, there is the "fact" that the photon has angular momentum -- but from the classical picture, "something" has to be spinning. What's spinning? And an electron orbiting a proton in the hydrogen atom should spiral into the proton emitting electromagnetic radiation, but it doesn't. Why not? The "why not" to all the above is that our classical picture just does not correspond to observation, so we are forced to reject our "picture" and adhere to the "observation" and not the other way around.Richard Feynman discusses the momentum of a photon in Vol. I - 34 - 10 of his Lectures on Physics.

Bottom line is we are both right.For most average objects, momentum is truly mass x velocity. When motion gets close to the speed of light, we find that the momentum relation p=mv is only an approximation. It is only correct when speed (v) is much smaller than the speed of light (c). The relation that works for all speeds is E^2= p^2c^2 + m^2c^4. It is much less convenient to use, and doesn't help figure anything out until you reach speeds of perhaps thirty million meters per second. For a particle with no mass, the relation reduces to E=pc. This works for a photon. For very small speeds, the system reduces to E=mc^2 + (1/2)mv^2, and p=mv. This leads to relations with kinetic energy and momentum: much more convenient to work with and just as accurate until you reach speeds close to the speed of light.

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selfAdjoint

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Labguy, No-where-man is NOT right to speak about the "mass of the momentum". The idea of momentum - mass times velocity is simply WRONG for photons. The magnitude of a photon's momentum is given by Einstein's other equation [tex]p = h\nu[/tex] where h is Planck's constant and [tex]\nu[/tex] is the photon's frequency.

And the energy formula you give, [tex]E = \sqrt{p^2c^2 + m^2c^4}[/tex] works easily at slow speeds; massive particles have rest frames (photons don't) and in its rest frame the particle's momentum is zero, so the first term under the square root vanishes and the formula reduces to [tex]E = \sqrt{m^2c^4} = mc^2[/tex], Einstein's famous equation. But note that even for massive bodies, like neutrinos, the formula says part of their energy comes from momentum.

And the energy formula you give, [tex]E = \sqrt{p^2c^2 + m^2c^4}[/tex] works easily at slow speeds; massive particles have rest frames (photons don't) and in its rest frame the particle's momentum is zero, so the first term under the square root vanishes and the formula reduces to [tex]E = \sqrt{m^2c^4} = mc^2[/tex], Einstein's famous equation. But note that even for massive bodies, like neutrinos, the formula says part of their energy comes from momentum.

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selfAdjoint said:Labguy, No-where-man is NOT right to speak about the "mass of the momentum". The idea of momentum - mass times velocity is simply WRONG for photons. The magnitude of a photon's momentum is given by Einstein's other equation [tex]p = h\nu[/tex] where h is Planck's constant and [tex]\nu[/tex] is the photon's frequency.

And the energy formula you give, [tex]E = \sqrt{p^2c^2 + m^2c^4}[/tex] works easily at slow speeds; massive particles have rest frames (photons don't) and in its rest frame the particle's momentum is zero, so the first term under the square root vanishes and the formula reduces to [tex]E = \sqrt{m^2c^4} = mc^2[/tex], Einstein's famous equation. But note that even for massive bodies, like neutrinos, the formula says part of their energy comes from momentum.

One question,first I must warn I'm far from knowing a physics,but I have a question how can a massless particle like photon have energy???Just think about it for a second,mass transforms into energy,when photon travels at the speed of light(and photon always travels at the speed of light),photons must transform some of its momentum mass into kinetic energy,otherwise photons would be unmovable.

If photon doesn't have the mass,than it has the energy of its frequency???

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ohwilleke

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Clearly, photons have energy. Have you have gotten a sunburn or tan? Have you ever owned a solar calculator? Have you ever seen a plant grow?

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Why can't plants live in total darkness,than is because,because they haven't energy,no there is always th energy,it's something else to consider.ohwilleke said:

Clearly, photons have energy. Have you have gotten a sunburn or tan? Have you ever owned a solar calculator? Have you ever seen a plant grow?

Yes,but if they have the energy they have to have mass,too.No particle can exist without energy/mass.And the mass of photon must be equivalent to the photon's energy of momentum.one thing I don't understand.

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ohwilleke

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Lisa; you are probably referring to the speculation that neutrinos may be superluminal. I remember addressing this issue somewhat previously (on a previous thread) and so I've re-printed the post here.Lisa! said:You know I heard "neutrino could travel to the past!" in a lecture I think.so I searched for it and I just found this article!almost nothing relative to my question.

Quote:

Originally Posted by Creator

It is a not-so-commonly realized fact that it is NOT the neutrino mass that is measured experimentally; rather, it is the mass squared term that is measured, and it is turns out almost always to be negative; in other words, negative mass squared. This negative mass squared can be referred to as 'imaginary' and thus can be used to imply superluminal velocity. Thus the supernova 1987A neutrino-preceeding-photon observation can equally be regarded as evidence to support superluminal neutrinos.

http://arxiv.org/PS_cache/hep-ph/pdf/9712/9712265.pdf [Broken]

Just thought you guys ought to know.

Creator

--Give me ambiguity or give me something else.--

Oh yea, and here's another article by Cramer along the same line as my previous post. I always liked his 'alternate view'.

It's a bit less technical for those needing simplicity.

http://www.npl.washington.edu/AV/altvw93.html

(See the very end of the article - last 3 paragraphs)."

Here's another with a bit more info on the implications of the negative mass squared term:

http://www.npl.washington.edu/AV/altvw54.html

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Lisa!

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Thank you very much.You know I'd searched for neutrino and traveling to the past before I started this thread, but I couldn't find what you re-printed here.Creator said:Lisa; you are probably referring to the speculation that neutrinos may be superluminal. I remember addressing this issue somewhat previously (on a previous thread) and so I've re-printed the post here.

Quote:

Originally Posted by Creator

"I thought you were going to bring up the nature of the neutrino measurement which also adds to the speculation.

It is a not-so-commonly realized fact that it is NOT the neutrino mass that is measured experimentally; rather, it is the mass squared term that is measured, and it is turns out almost always to be negative; in other words, negative mass squared. This negative mass squared can be referred to as 'imaginary' and thus can be used to imply superluminal velocity. Thus the supernova 1987A neutrino-preceeding-photon observation can equally be regarded as evidence to support superluminal neutrinos.

http://arxiv.org/PS_cache/hep-ph/pdf/9712/9712265.pdf [Broken]

Just thought you guys ought to know.

Creator

--Give me ambiguity or give me something else.--

Oh yea, and here's another article by Cramer along the same line as my previous post. I always liked his 'alternate view'.

It's a bit less technical for those needing simplicity.

http://www.npl.washington.edu/AV/altvw93.html

(See the very end of the article - last 3 paragraphs)."

Creator

Here's another with a bit more info on the implications of the negative mass squared term:

http://www.npl.washington.edu/AV/altvw54.html

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