Here are a couple of links that discuss possible examples of Dark Matter and Dark Energy, to any who may be interested. These articles also have further links to explore these topics further if you wish.　

http://news.bbc.co.uk/2/hi/science/nature/7977102.stm

　

http://news.bbc.co.uk/2/hi/science/nature/7787461.stm

 Enjoy.

G'day from the land of ozzzz

Thank you dusty for sharing those links.

I will read them.

 

 

Hey thanks!! These links help with a paper I'm writing for an astronomy class. Just what I've been lacking:)

Hey Dusty, I'm new to this site but I,ve been teaching physics for forty years. I think Paul Dirac made an error of judgement seventy years ago, when he dicovered the (then theoretical) existence of antimatter. I think the maths points to matter particles and antimatter particles repelling each other; that antimatter particles, like the positron having normal inertial mass but negative gravitational mass. This concept means a partial rewriting of the description of gravity as a force, and adds a wrinkle into General Relativity. It makes all this dark stuff disappear, or, as Descartes would have it, become unnecessary  hypotheses. There are physicists testing the idea of antimatter repelling matter as we speak, but I would like to raise up those theoretical physicists who want to try the idea in theory. Without the theoreticians giving it a fair go the experimenters will be put off, or worse, denied funding. I see it as a bit like the defrocking of the Phlogiston and ether theories. Always when physicists invent something invisible to solve their problems they take the risk of being completely wrong. As a Kiwi I support Ernest Rutherford: "You don't know it until the experiment makes you know it."

Please explain, Mr. stone What do you mean that by saying that it make's all of this dark stuff disappear? Anti- matter has anti- gravity? From what I've been taught anything that has mass has gravity. Anti matter has mass and therefore in sufficient quantity should have gravity, not anti gravity. Anti matter and matter certainly don't repel each other. They are drawn to each other. Anti gravity as far as I know doesn't exist. Please explain things more clearly to me.

 

HI Dusty,

You might want to check out this site, http://en.wikipedia.org/wiki/Gravitational_interaction_of_antimatter

Dennis

Dear Dusty, The Standard Model in particle physics does indeed give anti-particles like the positron positive mass, just like ordinary particles. But the gravitational force on such particles is negligible in the laboratory, compared to the other forces involved, so the assumption that anti-particles have the same ('normal") mass as ordinary particles caused no embarrassement in the first instance. It also fitted into the bigger picture of general relativity, which is shown by experiment and observations in cosmology to be the correct picture. But Einstein was not clairvoyant. When Paul Dirac, in the 1930's. combined quantum theory with special relativity, the equation he came to for mass was a quadratic, which of course has two solutions. One was negatve (negative energy) and Dirac was distraught and checked with his mates. Was the anti-particle to the electron a proton, a particle with negative mass that repelled the electron gravitationally or what. They made the decision it should have the same gravitational and inertial mass as the electron, but opposite charge, spin, etc.It was the best solution at the time, causing the least problems and solving their immediate questions. Now, with inexplicable problems arising in cosmology over unexpected entities like dark matter and dark energy, scientists are revisiting that original decision, and now we may be able to do the experiments. In Dirac's time they could not even see the anti-particles, much less measure the tiny gravitational force between an electron and a positron. If there is a repulsion between particles and antiparticles, (and experiment, not theory, must discover this) the fundamentals of gravitational theory (ie: General Relativity) will have to be tweaked. It appears this may cause the appearance of more force in galaxies than is at present expected without the presence of "dark matter", and it also appears the galaxies will be accelerating away from each other in a manner at present explained (rather desperately) by the invention of "dark energy". Of course the idea of anti-matter having negative gravitational mass (but still having positive inertial mass) may be disproved by experiment. But note: it cannot be disproved by theory. Not in physics, anyway.

Dark energy was not concocted to explain the expansion of the universe, but only it's accelerated expansion rate. We did not need any special explanation for why the universe is expanding. Anti matter particles with anti gravity would not be able to come together to form anything relevant. They would repel each other, and the fact that antimatter does not last long in our universe anyway due to it's annihilation makes it an unreliable entity to be used to explain much anyway. Anti gravity is not proven nor needed to explain anything, but if it ever could be proven it would raise far more questions than it would answer. We'll see.

I don't talk about "anti-gravity" or other science fiction jargon, but billions of antineutrinos are passing through us each microsecond as we speak, and only a handful are annihilated over measurable times. I f these have mass, which appears increasingly likely, and if they have negative gravitational mass, they will affect the gravitational force around our star, where they are made, and all the antineutrinos created by our galaxy of 3 00 000 000 stars will affect the dynamics of the galaxy. And rather than speculate on dark stuff of one sort or another we can look at this question in laboratories on Earth and in space. The ideas may be proved wrong; they are still good physics ideas. The physicists who are checking them deserve as much respect as those who merely explain things in terms of stuff we cannot see. The observations that lead people to speculate in terms of dark energy are real enough. They are the current problems that make physics interesting. But the theories  of dark matter, etc. are just theories. They should be treated with healthy skepticism and questioned to their (somewhat frail) limits. Physics is an experimental science, not a belief system. "Dark energy was.. concocted..." I prefer experiments to concoctions, however clever the concoction or famous the concoctor.  

Check out the LATEST Dark Energy Theory on the Thread below, which explains what it is, and where it comes from, with utmost clarity. It also explains the Pioneer Anomaly, and even has an experiment already designed ready to be build (once funding and an organisation takes it on) to support its claims, and that Dark Energy actually is real and exists.

http://cs.astronomy.com/asycs/forums/t/40219.aspx

stonewallnz : I would think science could determine the gravitational influence on the positron by simply observing the correction factor ( while completing the large number of revolutions) necessary in the Fermi lab, as I recall while working in a cal lab back in the 60's we corrected the scopes downward deflection (due to gravity) of the electron beam while the deflection plates were all set to zero volts differential potential, we also turn the scope upside down to equate this drop to the accelerating potential.

 If this is not enough I can also use a thought experiment equating the energy transfer by the positron for a solution.

However you are correct about the solution to Mr. Dirac's equation the result was in positive and negative "energy". The only answer I can offer is the total rest mass is dependent on charge, for with out charge the positron and electron would not exist, so the photon's relativistic mass is converted into 2 opposite charges of potential energy with rest mass representative of its energy, that between the two can readily be converted into relativistic mass ( the gamma photon) representative of it's energy.

You are right this could be a detail needing explanation. It could be involved with virtual particles that pop in and out through out the universe, or it could be the math used to equate momentum to energy.

I noticed I had a lot of extra notes in this part of my old text book about this equation. I only slightly remember taking a close look at this problem back then.

 Thank you for bringing it up.