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martedì 6 dicembre 2016

The Fifth Force

"If confirmed by further experiments, this discovery of a 
possible fifth force would completely change our 
understanding of the universe," says UCI professor of 
physics & astronomy Jonathan Feng, including what 
holds together galaxies such as this spiral one, called 
NGC 6814

Recent findings indicate that the possible discovery of a previously unknown subatomic particle may be evidence of a fifth fundamental force of nature.
The paper is published in the journal Physical Review Letters by theoretical physicists at the University of California, Irvine.
If true, it’s revolutionary,” said Jonathan Feng, professor of physics & astronomy.
For decades, we’ve known of four fundamental forces: gravitation, electromagnetism, and the strong and weak nuclear forces.”
“If confirmed by further experiments, this discovery of a possible fifth force would completely change our understanding of the universe, with consequences for the unification of forces and dark matter.”
The UCI researchers came upon a mid-2015 study by experimental nuclear physicists at the Hungarian Academy of Sciences who were searching for “dark photons,” particles that would signify unseen dark matter, which physicists say makes up about 85 percent of the universe’s mass.
The Hungarians’ work uncovered a radioactive decay anomaly that points to the existence of a light particle just 30 times heavier than an electron.
“The experimentalists weren’t able to claim that it was a new force,” Feng said. “They simply saw an excess of events that indicated a new particle, but it was not clear to them whether it was a matter particle or a force-carrying particle.”
The UCI group studied the Hungarian researchers’ data as well as all other previous experiments in this area and showed that the evidence strongly disfavors both matter particles and dark photons.
They proposed a new theory, however, that synthesizes all existing data and determined that the discovery could indicate a fifth fundamental force.
The UCI work demonstrates that instead of being a dark photon, the particle may be a “protophobic X boson.”
While the normal electric force acts on electrons and protons, this newfound boson interacts only with electrons and neutrons – and at an extremely limited range.
Analysis co-author Timothy Tait, professor of physics & astronomy, said, “There’s no other boson that we’ve observed that has this same characteristic. Sometimes we also just call it the ‘X boson,’ where ‘X’ means unknown.”
Feng noted that further experiments are crucial.
“The particle is not very heavy, and laboratories have had the energies required to make it since the ’50s and ’60s,” he said.
“But the reason it’s been hard to find is that its interactions are very feeble. That said, because the new particle is so light, there are many experimental groups working in small labs around the world that can follow up the initial claims, now that they know where to look.”

Citation: Feng JL, et al. (2016). Protophobic Fifth-Force Interpretation of the Observed Anomaly in [Math Processing Error] Nuclear Transitions. Physical Review Letters, 117: 071803.

Scientists confirm possible discovery of fifth force of nature December 5, 2016

Einstein’s General Relativity provides an elegant description of how space, time and matter affect one another. It makes precise predictions of gravitational effects, which have been verified by many measurements.

But if we use the theory to try to understand the motion of galaxies, we get the wrong answer, unless we invent a new form of so-called ‘dark’ matter. This is not a small correction – there needs to be much more of the Dark Matter than normal matter, and what is more, it doesn’t seem to be made up of quarks and electrons like all other matter. In fact it doesn’t seem to be made up of any of the particles in the Standard Model of particle physics. 

Furthermore, the universe is expanding at an increasing rate, rather than – as you might expect if it started of with a big bang and then gravity takes over – slowing down. This effect we ascribe to something we call ‘Dark Energy’. Dark Energy can be accommodated within General Relativity, but only by adding an absurdly precise ‘cosmological constant’, which looks very weird, or “unnatural” as a theoretical physicist would put it.

It gets worse. Dark Energy is a sort of ‘energy in empty space’, and particle physics also predicts this kind of energy, due to quantum fluctuations of the Standard Model – including and especially the Higgs boson. But these fluctuations would naively lead to so much Dark Energy that atoms themselves (never mind theoretical physicists) would never form in the first place.

That’s wrong, obviously.

And then there’s the nagging, possibly connected, fact that we don’t have a way of making General Relativity and quantum theory work together at very high energies.

Since gravity is a common thread here, all of these problems might seem to imply that General Relativity needs to be modified in some way. That’s a thought that has occurred to many physicists. However, General Relativity is so subtle, and so, well, General, that replacing it, or even successfully tweaking it, is a very hard thing to do.

Still, physicists are persistent, and there are new ideas coming forward all the time. One possible tweak is to postulate a new particle which carries a ‘fifth force’ (the other four forces being electromagnetism, the weak and strong interactions, and gravity).

To explain Dark Energy, this force has to affect all matter – as gravity itself does – and operate over large distances. Such forces have been looked for already, and if they affect the motion of the planets in the solar system, for example, they have to be enormously more feeble than gravity, otherwise we would have seen them already. But if they are enormously more feeble than the gravity between stars and galaxies, they won’t make any difference to the Dark Energy or Dark Matter problems, so that’s a waste of time.

One way potential way around this conundrum is a process called ‘screening’, in which the strength of a force depends upon the environment it is in. A recent paper from a group at the University of Nottingham describes a model in which the force is screened by matter itself. 
In dense regions of the universe (like the Earth, for instance) the force is hidden, while in empty space, the force can operate. In the case of the Dark Energy problem, which is what the theory was aiming for, this can provide exactly what the data need. The force can make the universe accelerate at large distances, while having no measurable effect on the orbit of the planets. As a bonus, this new force can also have a significant impact on the way galaxies rotate, which might at least partially solve the dark matter issue as well.
To a physicist, the way this new force works is reminiscent of the way the theory of Brout, Englert and Higgs gives mass to fundamental particles. It involves a scalar boson – a particle like the Higgs boson, which has no spin – and it involves the idea of symmetry breaking¹. But I am aware that using the Higgs as an analogy to explain something to a general audience is not a winning strategy, so here’s a better attempt, I hope. 
  • Speculative ideas are one thing we expect from theorists. Another thing we expect is testable predictions, and this model seems to be testable in an excitingly wide range of experiments. Upcoming observatories, such as the European Space Agency EUCLID mission and the Dark Energy Spectroscopic Instrument, will characterise gravity and dark energy on astrophysical scales. Precise atomic physics experiments could measure the effect of the fifth force on atoms, and most interestingly to me personally (since I work on it), this is the first plausible theory I have come across in which the Large Hadron Collider can contribute to the understanding Dark Energy.
Jon Butterworth’s book Smashing Physics is available as “Most Wanted Particle in Canada & the US.

How to hide a 'fifth force' – and how to find one Jon Butterworth 4 December 2016 

Dark Energy Spectroscopic Instrument enters construction phase 27 October 2016

Radiative Screening of Fifth Forces Clare Burrage, Edmund J. Copeland, Peter Millington 20 Apr 2016

Credit: Pieter van Dokkum, Roberto Abraham, Gemini Observatory/AURA

Evidence for dark matter was first spotted in the 1930s, but it wasn't until the 1980s that astronomers started really searching for it. And they're still searching today.
The particles are believed to make up a large percentage of the Universe's mass but have remained 'invisible.' Instead, astronomers have been studying the force they have on other parts of the Universe that we can see, to try to learn more about them.
Now, physicists have used elaborate computer calculations to come up with at least an outline of the particles of this unknown form of matter.
"Dark matter is an invisible form of matter which until now has only revealed itself through its gravitational effects. What it consists of remains a complete mystery," explained co-author Dr Andreas Ringwald from Deutches Elektronen-Synchotron (Desy).
The adjective 'dark' does not simply mean it doesn't emit visible light. "It does not appear to give off any other wavelengths either - its interaction with photons must be very weak indeed," Ringwald explained.

What is clear, however, is that these particles must lie beyond the Standard Model of particle physics, and while that model is extremely successful, it currently only describes the conventional 15 percent of all matter in the cosmos.
Direct searches for heavy dark-matter particles using large detectors in underground labs and the indirect search for them using large particle accelerators are still ongoing, but have not turned up any dark matter particles so far. However, extremely light particles, dubbed axions, may be easier to spot, and it could even be possible to detect direct evidence of them.
To carry out the computer calculations, Ringwald – along with Professor Zoltán Fodor from the University of Wuppertal, Eötvös University in Budapest and Forschungszentrum Jülich – extended the Standard Model of particle physics which helped them to predict the mass of these axions. They used Jülich's supercomputer JUQUEEN.
The results show that if axions do make up the bulk of dark matter, they should have a mass of 50 to 1500 micro-electronvolts, making them be up to ten billion times lighter than electrons.
This would mean every cubic centimetre of the Universe should contain, on average, ten million such ultra-lightweight particles. Dark matter is not spread out evenly in the Universe, however, but forms clumps and branches of a weblike network. Because of this, our local region of the Milky Way should contain about one trillion axions per cubic centimetre.
These calculations will now provide physicists with a concrete range in which their search for axions is likely to be most promising.
"The results we are presenting will probably lead to a race to discover these particles," said Fodor. Their discovery would not only solve the problem of dark matter in the Universe, but at the same time answer the question why the strong interaction is so surprisingly symmetrical.
The scientists expect it will be possible within the next few years to either confirm or rule out the existence of axions experimentally.
The research is published in the journal Nature.
The Institute for Nuclear Research of the Hungarian Academy of Sciences in Debrecen, the Lendület Lattice Gauge Theory Research Group at the Eötvös University, the University of Zaragoza in Spain, and the Max Planck Institute for Physics in Munich were also involved in the research.

Dark matter now has a 'face' and it could help us finally find the elusive particles VICTORIA WOOLLASTON 4 November 2016 

Extreme: con un touch screen si può distruggere una galassia 31 AGOSTO 2016

Despite huge advances in scientists’ understanding of the Universe in recent decades, where the Cosmos came from remains a mystery.
Equally mysterious to experts are black holes – but now some experts are starting to consider whether the two are connected in some way.
At the beginning of time, 13.8 billion years ago, there was a dense and super-hot energetic point where the laws of physics did not apply – what is known as a singularity.
The only other thing in the Universe where a singularity occurs and the laws of physics are thrown out of the window is at the event horizon of a black hole, which is unexplainable by current scientific methods.
What is fascinating about black holes is that the event horizon is two-dimensional in our three-dimensional universe.
This means that there is something that we are unable to perceive and the theory, which was first suggested in 2014 and is now under serious scrutinisation, claims that our Universe is the result of a singularity of a huge black hole.
In simpler terms, there is a possibility that our three-dimensional Universe is surrounding the event horizon of a four-dimensional Universe.
A 2014 study from the Perimeter Institute and University of Waterloo stated: "In this scenario, our Universe burst into being when a star in a four-dimensional universe collapsed into a black hole.”
Re-visiting the theory recently, Ethan Siegel, a professor of physics and astronomy at Lewis & Clark College in Portland, explained how a black hole could have formed in another universe which led matter to “fall” into our Universe.
Dr Siegel wrote for Forbes: "As the black hole first formed, from a star’s core imploding and collapsing, the event horizon first came to be, then rapidly expanded and continued to grow in area as more and more matter continued to fall in.
“If you were to put a coordinate grid down on this two-dimensional wrapping, you would find that it originated where the gridlines were very close together, then expanded rapidly as the black hole formed, and then expanded more and more slowly as matter fell in at a much lower rate. 
“This matches, at least conceptually, what we observe for the expansion rate of our three-dimensional Universe."

Our Universe was born from black hole in 4D Universe, astonishing theory suggests SEAN MARTIN Oct 29, 2016

In a newly published paper, Stephen Hawking, the eminent physicist has theorised that black holes, which scientists still know little about, could be a portal to another universe.
It had been thought that black holes have such a strong gravitational pull that even light cannot escape from them and that they are all consuming of everything within their reach.
However, the 74-year old has now said that they might not be as dangerous as previously thought and may just be a door to another universe.
Writing in a paper, alongside Andrew Strominger from Harvard and Malcolm Perry from Cambridge University, Hawking addressed the belief that black holes have “no hair”.
The study, Physical Review Letters, said that anything that went into a black hole was lost forever.
However, the basic laws of the universe state that anything that has ever been in the universe is preserved via its “information”.
This led to a paradox as it was assumed that anything that fell into a black hole was gone.
But since last year, Hawking has been stating that all is not lost inside a black hole.
He said last year: “Black holes are not the eternal prisons they were once thought.
“If you feel you are trapped in a black hole, don’t give up. There is a way out.
“The existence of alternative histories with black holes suggests this might be possible.
“The hole would need to be large and if it was rotating it might have a passage to another universe. But you couldn’t come back to our universe.”
His latest paper states that black holes do indeed have “hair” which either stores the information on the boundary or the event horizon.
This would mean, according to the paper, that if you were looking at a black hole in the right way – in the distant future for example – you would be able to see the hairs of a black hole which store the information.

Stephen Hawking: Black holes are a PORTAL to another universe SEAN MARTIN Jun 8, 2016

Evidence of Stephen Hawking's famous prediction about black holes was just observed for the first time Ali Sundermier Aug. 15, 2016 

An X-Ray Surprise! When Black Holes Stop Eating, Galaxies Fade Away DEC 5, 2016 

Black hole paints stunning picture as it shapes distant galaxy Eric Mack December 2, 2016 

The so-called ‘Many Interacting Worlds Theory’ argues that multiple universes coexist in the same space and time as our own. Scientists believe that these even interact on a quantum level.  

The idea of Parallel universe has captured the imagination of many experts around the globe. The idea of a parallel universe has given birth to numerous movies and even TV series. However, there could be more about the Parallel universe than just science fiction.
According to Howard Wiseman of Griffith University in Australia and his team, a new groundbreaking theory indicates that multiple universes coexist in the same space and time as our own. Interestingly, scientists believe that these even interact on a quantum level. The study was published in the journal Physical Review X.
The paper basically introduces ‘Many Interacting Worlds’ theory as an alternative to the more famous ‘Many Worlds’ theory that was proposed in the 1950s.
The ‘Many Worlds’ theory speculated that after an event occurs, several universes arises offering all possible outcomes for given event.
These universes are believed to exist parallel to ours in a separate space, and at the same time, never interacting. This, however, is wrong according to the ‘Many interacting Worlds’ theory, as the name clearly indicates.
The Many interacting Worlds theory suggests that all of the multiple worlds overall and occupy the same space and time at once, just like a quantum state.
All possibilities are therefore realized – in some universes the dinosaur-killing asteroid missed Earth. In others, Australia was colonized by the Portuguese,” Wiseman said in a press release. “But critics question the reality of these other universes, since they do not influence our universe at all. On this score, our “Many Interacting Worlds” approach is completely different, as its name implies.”
The theory presupposes that there could be worlds in the parallel universe that are nearly identical. Others are entirely different, and the so-called ‘Butterfly effect’ is responsible for different outcomes. Furthermore, each universe is considered a reality.
The similarities that may exist between worlds interact through quantum forces which on the other hand influence the outcome of a world by making them somewhat dissimilar.
Interestingly, Wiseman argues that while the theory states that different worlds interact with one another on a quantum level and not larger scale, the new theory DOES NOT make it impossible.
The response within the scientific community is mixed. There are those who argue that the theory is a huge waste of time as Luboš Motl, while others believe it offers a peculiar and interesting explanation to everything around us.
“The beauty of our approach is that if there is just one world our theory reduces to Newtonian mechanics, while if there is a gigantic number of worlds it reproduces quantum mechanics. In between it predicts something new that is neither Newton’s theory nor quantum theory,” Wiseman continued. “We also believe that, in providing a new mental picture of quantum effects, it will be useful in planning experiments to test and exploit quantum phenomena.”

Scientists Confirm Parallel Universes Exist 30 Nov 2016 

Many-Interacting Worlds Theory May Prove that Parallel Universes Are Real and Interacting! Rhenn Anthony Taguiam Nov 29, 2016

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