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58514.  Thu Mar 09, 2006 3:27 pm Reply with quote

So, here's a novel way to explain away Black Holes, Dark Matter and Dark Energy - using (yes, you guessed it) Quantum Mechanics!

"That was when we had our epiphany," Chapline says. He and Laughlin realised that if a quantum critical phase transition happened on the surface of a star, it would slow down time and the surface would behave just like a black hole's event horizon. Quantum mechanics would not be violated because in this scenario time would never freeze entirely. "We start with effects actually seen in the lab, which I think gives it more credibility than black holes," says Chapline.

Sure enough, in place of black holes their analysis predicts a phase transition that creates a thin quantum critical shell. The size of this shell is determined by the star's mass and, crucially, does not contain a space-time singularity. Instead, the shell contains a vacuum, just like the energy-containing vacuum of free space. As the star's mass collapses through the shell, it is converted to energy that contributes to the energy of the vacuum.

The team's calculations show that the vacuum energy inside the shell has a powerful anti-gravity effect, just like the dark energy that appears to be causing the expansion of the universe to accelerate. Chapline has dubbed the objects produced this way "dark energy stars".

So, that's that sorted then. For a while.

58569.  Fri Mar 10, 2006 4:43 am Reply with quote

Having read the whole article it is a very intriguing idea that they have had. The only information I felt was ommitted is why they believe that "Quantum Critical Phase Transition" can occur on the surface of a star. I'm assuming that this explanation was too complicated to place in the article because I would expect this question to have been explored in some detail.

The one good thing is that their predictions are easily testable, at least using technology that should be available in the next decade.

58599.  Fri Mar 10, 2006 6:24 am Reply with quote

And I like the fact that it might also explain (some of the) gamma ray bursters that we've seen in the last few decades, as they go super-critical. They're the 'right' wavelength too...

It's always a pleasure to see (if this is really what's going on) a number of seemingly separate phenomena and theories all ending up being different views of the same thing. I actually find myself 'hoping' it'll work out.

58606.  Fri Mar 10, 2006 6:38 am Reply with quote

The only trouble is that this theory still does not disprove the theory of blackholes.

58659.  Fri Mar 10, 2006 8:14 am Reply with quote

You can't disprove the theory of black holes. You can only abandon it in favour of another theory that explains the mathematics and observations more simply (and raises fewer 'problems'). Until recently there's not really been another serious contending theory.

58799.  Fri Mar 10, 2006 2:15 pm Reply with quote

I thought black holes had been almost-directly observed? In twin star systems when one goes black and sucks the material out of the other? Or have I just been sucked into a "belief" and mistakenly took artists impressions for actual observations?

58800.  Fri Mar 10, 2006 2:18 pm Reply with quote

It is not possible to see black holes, due to the fact that it is impossible for light to escape from them. It may be possible to infer their existence from effects mentioned above. I expect this qualifies as 'almost directly observed'.

58808.  Fri Mar 10, 2006 2:45 pm Reply with quote

The "discs of matter being sucked onto a tiny dense star that give out beams of x-rays" that we observe were/are thought to be black holes, but anything sufficiently gravitationally 'hungry' would do - doesn't have to be a complete breakdown of the fab of the STC.

Gravitational lensing definitely occurs - this is very observable, but again, anything very, very dense that we can't see would also fit the bill.

60837.  Sun Mar 19, 2006 12:53 pm Reply with quote

On the subject of gravity, there is a QI article in this week's NS on the search for gravitons. Quantum theory suggests that all forces are transmitted by a particle (photons = electromagnetic force, W and Z bosons = weak force, and gluons = strong force). Gravitons are the theoretical particle believed to transmit gravity, however, the fact that gravity is an incredibly weak force means that a graviton virtually never interacts with atoms. Thus detecting them is very difficult:

When a photon of light with enough energy strikes an atom of certain materials it kicks out an electron, generating a small electric current that signals the arrival of the photon: this is the normal photoelectric effect. There should, in theory, also be a "gravitoelectric effect", although no one has ever seen it: a graviton with enough energy to kick out an electron ought to produce an electric current that would reveal its presence.

But there is still a snag. Compared with the electromagnetic force, gravity is extremely feeble. To get an idea of just how feeble, consider a fridge magnet. Despite the whole of the Earth pulling on the magnet, its magnetic field holds it firmly to the fridge's steel body. The gravitational force between a proton and an electron in a hydrogen atom is about 10[to the power of]40 times weaker than the electromagnetic force between them. This weakness reflects the extreme rarity with which gravitons interact with particles of matter.

If anyone knows the ins and outs of how to detect weakly interacting particles it is those physicists who study neutrinos. Neutrinos interact with matter solely through the weak nuclear force. Although about 100 billion neutrinos from the sun are passing through every square centimetre of your skin every second, not one of them is likely to be stopped by the atoms in your body. To maximise their chances of bagging one of these elusive particles, neutrino hunters build huge detectors containing a large amount of matter. Even though a neutrino is extremely unlikely to be stopped by a single particle, it has a reasonable chance of being stopped by one of the trillions upon trillions of particles that make up the detector. "This would also be the strategy for detecting a graviton," Rothman says.

The biggest neutrino detector, now being built at the South Pole, will use a cubic kilometre of Antarctic ice to search for neutrinos. "The graviton, however, is 10[to the power of]21 times less likely to interact with matter than even a neutrino," Rothman says. "Because of its phenomenally weak interaction with matter, we're talking about a detector that utterly dwarfs a neutrino detector."

He's talking about something very large indeed. In fact, according to Rothman and Boughn's calculations it would have to be the biggest detector conceivable, something similar in mass to Jupiter. "Much bigger and the detector would shrink under its own gravity and become a brown dwarf," says Rothman. Drifting through interplanetary space, the detector's vast surface would be a web of glistening electronics. Building such a behemoth is clearly way beyond anything conceivable today.

But let's suppose it will one day be possible to build one. Would such a detector be capable of bagging a graviton? Rothman and Boughn calculate that during the lifetime of the universe, a detector placed as far from the sun as Earth is now would detect about 1000 gravitons. Placing the detector the same distance from a super-dense white dwarf or neutron star would collect up to a billion gravitons. That's one every decade or so.

Even supposing that the detector works perfectly, and each graviton hit produces an electrical pulse, the problems go on. Millions of other particles would rain down on such a vast detector every second, and many of them would produce the same electrical signals as gravitons. The most troublesome particles are expected to be neutrinos, but the good news is that although they rarely interact with matter they are positively sociable compared with gravitons and so, in principle, could be shielded. Yet there is a problem: that you would need an impossible amount of shielding material. "Neutrinos can penetrate light years of lead," says Rothman. "That much shielding would collapse into a black hole."

And there is another possible pitfall. It took physicists more than 10 years to accept that the photoelectric effect proved the existence of photons, as Einstein had postulated in 1905. The clinching evidence came in 1916 when Robert Millikan of the California Institute of Technology in Pasadena plotted the number of electrons detected against the frequency of the light he used. "In other words, we might have to detect large numbers of gravitons in order to persuade physicists of their existence," says Rothman. Given the monumental practical difficulties, it comes as no surprise to learn that Rothman and Boughn see no realistic chance of ever detecting a graviton. "I'd bet my house that nobody in this universe will ever detect one," says Rothman.

A QI subject for the G series don't you think (although I'm sure gravity will be making an appearence)

60840.  Sun Mar 19, 2006 12:59 pm Reply with quote

.. but in a non-serious form, we hope.

60844.  Sun Mar 19, 2006 1:04 pm Reply with quote

Well if the researchers can get their hands on a mini-black hole, they shall each deserve many nobel prizes

124563.  Thu Dec 07, 2006 4:43 am Reply with quote

Here's some interesting news just in:

After decades of intensive effort by both experimental and theoretical physicists worldwide, a tiny particle with no charge, a very low mass and a lifetime much shorter than a nanosecond, dubbed the "axion," has now been detected by the University at Buffalo physicist who first suggested its existence in a little-read paper as early as 1974.

Because it's so freaking hard to detect - being chargeless - it might explain where a lot of the universe's projected mass has been hiding...

124648.  Thu Dec 07, 2006 10:09 am Reply with quote

If they only "live" for less than a nanosecond, where do they come from and where do they go?

The Luggage
124654.  Thu Dec 07, 2006 10:24 am Reply with quote

I refer everyone to the Upcoming opening of the Large Hadron Collider due in 2007.

The Large Hadron Collider is currently being installed in a 27-kilometer ring buried deep below the countryside on the outskirts of Geneva, Switzerland. When its operation begins in 2007, the LHC will be the world’s most powerful particle accelerator. High-energy protons in two counter-rotating beams will be smashed together in a search for signatures of supersymmetry, dark matter and the origins of mass.

The beams are made up of bunches containing billions of protons. Traveling at a whisker below the speed of light they will be injected, accelerated, and kept circulating for hours, guided by thousands of powerful superconducting magnets.

For most of the ring, the beams travel in two separate vacuum pipes, but at four points they collide in the hearts of the main experiments, known by their acronyms: ALICE, ATLAS, CMS, and LHCb. The experiments’ detectors will watch carefully as the energy of colliding protons transforms fleetingly into a plethora of exotic particles.

The detectors could see up to 600 million collision events per second, with the experiments scouring the data for signs of extremely rare events such as the creation of the much-sought Higgs boson.
Mike Lamont, CERN

And the experments :

124833.  Thu Dec 07, 2006 5:51 pm Reply with quote

If they only "live" for less than a nanosecond, where do they come from and where do they go?

They 'condense' out of pure energy, hang around for a bit, then disappear back into it. There are quite a few particles that do that, the cheeky buggers.


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