Finding Dark Matter in the Dark
Dark matter is the mysterious material that holds the Universe together, yet no one has seen it; or heard, smelled, tasted or touched it either.
But that may soon change, and a laboratory 1000 metres below the ground in the Stawell gold mine halfway between Melbourne and Adelaide could be the epicentre of this discovery.
Physicists have had a good run recently at detecting the seemingly undetectable. First there was the Higg’s Boson, confirmed by experiments at the Large Hadron Collider in 2012, nearly 50 years after it existence was first proposed. Then in 2015 the LIGO detectors found gravitational waves, a century after Einstein predicted them. Both discoveries were rewarded with Nobel Prizes.
If all goes to plan, in the next few years dark matter will move from the realm of the hypothetical to the observable, opening a new era in experimental physics, and a major step towards a fundamental theory of nature.
Professor Elisabetta Barberio is leading the Australian effort to detect dark matter, as the Director of the Centre for Dark Matter Particle Physics. The University of Melbourne physicist says Australia is uniquely positioned to confirm the existence of dark matter.
How do we know what we are looking for?
It started with some simple calculations based on Newton’s Law of Gravity.
“If I look at the solar system, there’s the sun and all the planets, and if I know the velocity of a planet and its distance from the sun, I can calculate the mass of the sun,” says Professor Barberio.
“We can do the same with our galaxy. We can take the motion of a star, and, knowing the distance of the star from the centre of the galaxy, we can calculate how much material there is in the galaxy.
“When we do this calculation, the amount of material that we see and the amount of material that should be there by our calculations don’t match. Our calculations say that there is much more material in the galaxy than what we can see. And this is dark matter.”
Physicists think dark matter is made up from an as-yet-unknown fundamental particle that has no electric charge, doesn’t produce light, and doesn’t interact very much with anything. But they also think that there will be the occasional interaction that we could perhaps detect, given the right equipment and the right location.
“We know that there is a lot of dark matter in the galaxy – between 70 and 80 percent of the material in the galaxy is dark matter,” says Professor Barberio, “and so every second our bodies are traversed by billions of these dark matter particles that don’t do anything to us. We are transparent to these particles.”
The problem is that other things also interact with the atomic nuclei; notably cosmic rays and radioactivity.
“The probability that dark matter interacts with my nucleus is one event per 10 kg of material per day,” says Professor Barberio. “The probability that radioactivity or cosmic rays interact with my nucleus is 10 billion times per 10 kg of material per day.”
In other words, 1 in every 10 billion of these interactions is dark matter, making it impossible to distinguish any signal from the noise.
Going underground
To improve those odds we need to reduce the number of other interactions occurring. The first step is to head underground – way underground. Cosmic rays are absorbed by rock so if you go deep enough you can reduce these to almost zero.
“By going underground we’ve already eliminated a few billion interactions,” says Professor Barberio.”And then we also need to eliminate all the residual radioactivity in the material we build our detector from, because even if we take a banana into our lab, it will have so much radioactivity that there will be a few counts, a few interactions, per day, with my nuclei, and it will shade dark matter.”
“We choose the right material, or build a material with very low radioactivity, and then we construct our detector underground and we start waiting, and count how many times there is this interaction.”
Several underground dark matter detectors exist, and one even claims to see dark matter. The Gran Sasso Laboratory, built inside a mountain in Italy, tracks what they say is the annual modulation of dark matter arriving on Earth.
As the Earth goes around the sun, its velocity with respect to the centre of the galaxy changes. In June the Earth is travelling around the galaxy at about 260 km per second, whereas in December it is more like 200 km per second. Therefore we would expect the Earth to be hit by more dark matter in June than in December. And this is what the Gran Sasso team observes in their data.
“If you are on a bicycle and you go faster or slower you have more or less wind,” says Professor Barberio.
“However, we think that very, very rarely, a dark matter particle interacts with the nucleus of an atom in a material that we can see – what we call normal matter.”
Australia’s dark matter detector
Seasonal changes, from summer to winter, could also lead to a cycle in the rate of interactions on the dark matter detectors. And this is where Australia comes in.
To remove this potential error, we need to repeat the experiments in the Southern Hemisphere, where the seasons are flipped. If we see a seasonal pattern, with a peak in summer and a minimum in winter, then the data from Italy needs to be rethought. If we see the same annual pattern, however, with a peak in June and a minimum in December, this could be the evidence that finally confirms the existence of dark matter.
The Stawell gold mine in western Victoria is one of the few places in Australia that can house a dark matter detector.
“You need to find a very deep mine or a very high mountain,” says Professor Barberio.
“We don’t have very high mountains so we needed to find a mine. There are very few mines in Australia that have the necessary depth and the necessary access. Thankfully, we have great support from the mine owners and the local Stawell community for our laboratory.”
Professor Barberio’s team hopes to have the Stawell Underground Physics Laboratory will be up and running this year. This will be the first dark matter detector in the southern hemisphere, and, when combined with data from other detectors around the world, could finally confirm the existence of dark matter.
Read more at phys.org
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Joseph Olson
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Dark energy and dark matter are only required for false expanding big bang hypothesis.
“Mysterious Dr X says, Universe is not Expanding” > CanadaFreePress
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Charles Higley
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The astronomers screwed up royally when they jumped to the Big Band Theory and never properly disposed for the Steady State Universe. Occam’s Razor has never been properly applied. Cobbling up Dark Matter, Dark Force, and Dark Energy to band-aid the Big Bang and opening the stupidity that there might be a multiverse of universes or some such idiocy is much more complex than simply recognizing the dominance to EM forces in the known universe.
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Robert Beatty
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“How do we know what we are looking for?
It started with some simple calculations based on Newton’s Law of Gravity”
This assumes G is constant.
IMO G can only be accepted as a constant – within the limits of measured accuracy – at our Solar system. It seems to me that we are located at a low point in our gravitational sphere, as reported https://principia-scientific.com/new-paper-our-redshift-environment/
It all gets back to how sure can we be that G is constant throughout the universe?
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Herb Rose
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If you believe in something you will find it whether it exists or not. This experiment seems like hybrid of the Michelson-Morley experiment and the search for the neutrino. I am sure they will find their imaginary “dark Mater” or if not they an use the negative results to prove its existence just as they use the negative results of the Michelson-Morley experiment to prove the constant speed of light. I have proof that Einstein was wrong. He said a single experiment would prove him wrong but nothing can prove him wrong bad results only result in the creation of more undetectable imaginary subatomic particles to make him right.
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Robert Beatty
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Now, now, Herb. Don’t go throwing the baby out with the bath water. It is worth remembering the rule of unintended consequences. It is interesting to note the comment “The Gran Sasso Laboratory, built inside a mountain in Italy, tracks what they say is the annual modulation of dark matter arriving on Earth.”
If this annual modulation can be confirmed it should lead to the conclusion that G is a vector quantity and which direction it is coming from.
That would be a significant finding.
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Herb Rose
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Hi Robert,
We have a fundamental disagreement on gravity. You believe that gravity is a product of mass while I believe it is a function of energy. To me the data determining the mass of the sun, M(s).=V(p)^2 x d(p) gives the energy of the sun. The mass only comes from G which Newton created to provide a source for his force. (Question: How did they determine the mass of Venus, Mercury, and the moon before they were able launch satellites to orbit them?) If gravity is a result of energy there is no need to create potential energy, dark matter, dark energy, and you can explain binary asteroids. It is good to keep the debate going and eventually we both will be shown to be wrong.
The problem I have with these types of experiments is that when searching for something you must eliminate all other possible explanations while never being able to know them all. In the experiment to discover the neutrino where the neutrinos collided with nucleus of chlorine atoms, how did they eliminate the probability that there were radioactive impurities in the materials used or introduced by the people conducting the experiment? The results of the experiment were to fine considering the size of the experiment.
Have a good day,
Herb
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Robert Beatty
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Hi Herb, you state “We have a fundamental disagreement on gravity. You believe that gravity is a product of mass while I believe it is a function of energy.”
The GRAVIMASS report (http://www.bosmin.com/PSL/GRAVIMASS.pdf) on page 11 highlights the difference between fixed and elastic links concluding that the nature of gravity is elastic and can transmit energy to objects operating within its gravitational field. This is a function of energy not mass.
There is nothing wrong with Newton introducing a constant to make field measurements fit with calculated measurements. I surmise the constant ‘fit’ only applies to our Solar system. Do you have a view on this?
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Herb Rose
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Hi again Robert,
I don’t believe that G even works in our solar system and the calculated masses derived for the different planets are wrong.
If you look at the binary asteroids there is no way the masses of these asteroids could produce enough force to cause one to orbit another. When the Japanese sent a probe to explore an asteroid that discovered it was strewn with boulders. At the rotation rate of the asteroid the velocity of the boulders exceeded the escape velocity of the force of gravity holding them on the asteroid.
The Earth’s atmosphere is held to the Earth by the force of gravity and its magnetic field protects the atmosphere from being swept away by the solar winds. Venus is exposed to stronger solar winds, has no magnetic field and yet, with less mass, holds an atmosphere that is about 100 times that of the Earth’s.
I cannot see how Mars, with no water, can be less dense than the Earth and believe the early failed attempts to soft land probes on Mars was a result of a bad estimate of its mass and force of gravity.
I think the plumes resulting from the fragments of the comet striking Jupiter were characteristic of them hitting a solid object not plunging into a gas giant and the calculated massif Jupiter is way off.
As more exploration of the solar system is done we will learn more and find the answer. We did discover that the moon is not made of green cheese.
Have a good day,
Herb
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Robert Beatty
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Thanks Herb, I will give your comment more thought.
Robert Beatty
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Herb Rose. Responding to your five points:
1. “I don’t believe that G even works in our solar system and the calculated masses derived for the different planets are wrong.”
You would need to provide some cals to substantiate this statement.
Taking this thought further afield, suns rapidly orbiting points in space (black holes) appears to be responding to much higher forces of gravity – hence my view that gravity varies throughout the universe and this can be expressed mathematically by altering the value for G.
2. Binary asteroids and triples are a challenging mathematical calculation described in the abstract to (PDF) Orbit Determination of Binary Asteroids – ResearchGatehttps://www.researchgate.net › publication
“In addition to the detection of an asteroid moon or a binary asteroid, the knowledge of the satellite’s true orbit is of high importance to derive fundamental physical parameters of the binary system such as its mass and to shed light on its possible formation history and dynamical evolution (prograde/retrograde orbit, large/small eccentricity or inclination, etc.). A new methodology for preliminary orbit determination of binary asteroids – and visual binaries in general – is proposed. It is based on Thiele-Innes method combined with a ’trial and error’ Monte-Carlo technique.”
3. “When the Japanese sent a probe to explore an asteroid that discovered it was strewn with boulders. At the rotation rate of the asteroid the velocity of the boulders exceeded the escape velocity of the force of gravity holding them on the asteroid.”
Why stop at the boulders? If it was spinning that fast the whole dust cloud would be gone. Seems the boulders’ centripetal force is not enough to reach escape velocity.
4. Your concerns about Earth and Venus atmospheres (and Mars) is another great conundrum. My view is that it is due to the planets’ respective sizes and development histories. Details at PSL
I understand some of the problem landing on Mars was due to a mix up between imperial and metric distances. It would be great if we could settle on one universal system of units.
5. Your doubts about the depth of the Jupiter cloud bank seem to be well founded:
Jupiter Ref https://www.news.com.au/technology/science/space/inside-jupiters-storms-australian-study-reveals-whats-going-on-beneath-the-clouds/news-story/65553a547ce94d1a59eae128086d11b4
Thanks to Juno, we now know these enormous funnels of wind extend some 3000km deep. And that’s not as far as expected. “Scientists have long debated how deep the jet streams reach beneath the surfaces of Jupiter and other gas giants, and why they do not appear in the sun’s interior,” Dr Constantinou says.
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jerry krause
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Hi Bob,
#5. I have often read that the ‘gas’ planets have surfaces. I have my idea what and where this surface is. But I would like you to explain for me and any readers who may ask: How can a gas planet have a surface? And, what is the matter beneath this surface, which I assume to be at some definite distance from its center. And I cannot remember there being a cloud bank. So what is the composition of the cloud?
I could research this on my own but it so much easier to ask some one who probably knows the accepted answers to these questions.
Have a good day, Jerry
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Ken Hughes
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Newton is only applicable WITHIN a particular frame of reference. General Relativity states this to be the case. We have rushed to an assumption that DM is the cause of deviations from Newtonian velocities over the galactic radius. We should also be considering if the frames of reference of our observations are significantly different. Since a frame of reference is defined by its time rate, then we should be looking at how the changing time rates with increasing radius, might affect our observations of he speeds of stars throughout the galaxy. If this were indeed the reason for the deviations from Newton, then Newton is still correct, General Relativity is still correct, there is no magical Dark Matter, and the only change in our understanding would be that the mass of the central black hole is far greater than currently calculated using Newton, but ignoring the time rate changes over the diameter of the galaxy.
The neglect of this idea is, frankly, unscientific.
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Robert Beatty
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Hi Ken, I agree with these sentiments, particularly “Newton is only applicable WITHIN a particular frame of reference.” I would refer to a particular frame of reference as a Gravisphere.
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Robert Beatty
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Maybe Herb Rose and Steve Crothers should unite to write a new version of Principia Mathematica?
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Herb Rose
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Hi Robert,
I tried to read Newton’s Principia and didn’t get far. I understand no-one attended his lectures because they were incomprehensible.
I have a problem with an object traveling in a right line unless a force acts upon it. Since nothing in the universe, including light, travels in a right line how do you know if a line is right? My premise for gravity is better. An object will maintain its energy unless energy is added to it or given off by it.
Have a good day,
Herb.
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Herb Rose
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Hi Ken and Robert,
All objects other than pure matter are composed of energy and matter. Matter gives an object substance while energy gives it structure. Objects will have a matter field (electric which repels) and an energy field which attracts. A hydrogen atom is a neutron with energy. Energy fields combine with other objects to form larger objects with then have their own energy and matter fields.The correct reference perspective for any object is the center of the organizing energy field to which it belongs. Satellites orbiting the Earth have a speed and location referenced to the Earth’s energy field. The moon has its own energy field and its own center point of reference. The energy fields of the Earth and moon combine to form a larger unit which is part of the sun’s system and is referenced to the center of the sun’s energy field. The moon has no speed or position relative to the sun because that is not the organizing energy field controlling it. The sun and objects orbiting it are a unit that combines with the energy of other solar systems to form the galaxy with its own central reference point. I call this the theory of units where objects equalize with the energy of other units to form larger units.
Have a good day,
Herb
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Steve Crothers
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General Relativity is not correct. (1) It violates the usual conservation of energy and momentum for a closed system; (2) It has not been able to model more than one mass; (3) there are forces in General Relativity but gravity is not one of them because it is ‘spacetime curvature’; (4) it cannot localise its ‘gravitational energy’; (5) ‘spacetime’ does not exist; (6) gravity manifests in experiments as a force between at least two masses, as codified in Newton’s theory.
Crothers, S.J., LIGO — Its Claims for Black Holes and Gravitational Waves | EU2017, https://www.youtube.com/watch?v=ev10ywLFq6E&t=496s
Crothers, S.J., Black Hole Escape Velocity, Sky Scholar, 2018,
Crothers, S.J., Does spacetime exist? Sky Scholar, 2018,
Crothers, S.J., Black Hole Geometry Analyzed, Sky Scholar, 2018,
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Skeptic
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Dark matter is complete nonsense. If cosmologists would start accounting for electromagnetism throughout the universe they would find that’s what drives everything from solar to galactic formation. Not one claim about dark matter has been confirmed through either observation or through experimentation. Dark matter advocates are just like the climate alarmists and eventually both will be throughly discredited.
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