Archive for the ‘Sparks 'n' thunderbolts’ Category

The LHC’s dodgy dossier?

Monday, March 2nd, 2009

lhc-higgs

There’s no reason to worry about the Large Hadron Collider that is due to to be switched on later this year for the second time. The chances of it creating a planet-swallowing black hole are tiny. Hardly worth mentioning really.

But last month, Roberto Casadio at the Universita di Bologna in Italy and a few pals told us that the LHC could make black holes that will hang around for minutes rather than microseconds. And they were rather less certain about the possibility they the  black holes could grow to catastrophic size. Far from being utterly impossible, they said merely that this outcome didn’t “seem” possible.

This blog complained that that was hardly the categorical assurance we’d come to expect from the particle physics community. The post generated many comments, my favourite being that we shouldn’t worry because of the Many Worlds Interpretation of quantum mechanics. If the LHC does create Earth-destroying black holes, we could only survive in a universe in which the accelerator broke down.

Thanks to Slashdot, the story got a good airing with more than few people pointing out that we need better assurances than this.

Now we can rest easy. Casadio and co have changed their minds. In a second version of the paper, they’ve removed all mention of the black hole lifetime being many minutes (”>> 1sec” in mathematical terms) and they’ve changed their conclusion too. It now reads: “the growth of black holes to catastrophic size is not possible.”

What to make of this? On the one hand, these papers are preprints. They’re early drafts submitted for peer review so that small problems and errors can be ironed out before publication. We should expect changes as papers are updated.

On the other, we depend on the conclusions of scientific papers for properly argued assurances that the LHC is safe. If those conclusions can be rewritten for public relations reasons rather than scientific merit, what value should we place on them?

Either way, we now know that a few minutes work on a wordprocessor makes the LHC entirely safe.

Ref: arxiv.org/abs/0901.2948: On the Possibility of Catastrophic Black Hole Growth in the Warped Brane-World Scenario at the LHC version 2

Thanks to Cap’n Rusty for pointing out the new version

The forecast for hydrogen peroxide snow on Mars

Tuesday, January 27th, 2009

martian-windblown-sand

On Earth, wind blown dust storms generate powerful electric fields of up to 200 kV/m, with the ground becoming positively charged and the dust particles negatively charged.

The mechanism behind this is poorly understood but various scientists have assumed that a similar process takes place on Mars and that it leads to bizarre phenomenon.

One idea is that the excess electrons in dust break down methane in the atmosphere. Methane is a potential biological  marker so estimating how much is produced is important.
The significance of this is that any methane we see in the martian atmosphere today must have survived both this and the ravages of sunlight.

Another idea is that the excess electrons catalyse the production of hydrogen peroxide in the atmosphere which then falls as a unique and rather nasty form of Martian snow.

But both these ideas are probably wrong, say Jasper Kok and Nilton Reno at the University of Michigan today. They’ve put together the most advanced model to date of how windblown dust on Mars becomes electrified and worked out how it affects the atmospheric chemistry.

“We find that the production of hydrogen peroxide and the dissociation of methane by electric fields are much less significant than previously thought,” they say.

Another thing that electrification leads to is lightning and there has been  precious little evidence of that on Mars, which perhaps backs this team’s claims.

So it looks as if electric fields play a much smaller role in the  Martian atmosphere than they do on Earth

Shame really, hydrogen peroxide snow sounds cool.

Ref: arxiv.org/abs/0901.3672: The Electrification of Wind-Blown Sand on Mars and its Implications for Atmospheric Chemistry

Black holes from the LHC could survive for minutes

Friday, January 23rd, 2009

lhc-black-holes

There is absolutely, positively, definitely no chance of the LHC destroying the planet when it eventually switches on some time later this year.  Right?

Err, yep. And yet a few niggling doubts are persuading some scientists to run through their figures again. And the new calculations are throwing up some surprises.

One potential method of destruction is that the LHC will create tiny black holes that could swallow everything in their path including the planet. In 2002, Roberto Casadio at the Universita di Bologna in Italy and a few pals reassured the world that this was not possible because the black holes would decay before they got the chance to do any damage.

Now they’re not so sure.  The question is not simply how quickly a mini-black hole decays but whether this decay always outpaces any growth.

Casadio have reworked the figures and now say that:  ” the growth of black holes to catastrophic size does not seem possible.”

Does not seem possible? That’s not the unequivocal reassurance that particle physicists have been giving us up till now.

What’s more, the new calculations throw up a tricky new prediction. In the past, it had always been assumed that black holes would decay in the blink of an eye.

Not any more. Casadio and co say:  “the expected decay times are much longer (and possibly ≫ 1 sec) than is typically predicted by other models”

Whoa, let’s have that again: these mini black holes will be hanging around for seconds, possibly minutes?

That doesn’t sound good. Anybody at CERN care to clarify?

Ref: arxiv.org/abs/0901.2948: On the Possibility of Catastrophic Black Hole Growth in the Warped Brane-World Scenario at the LHC

Harvesting energy from the airwaves

Monday, January 12th, 2009

nanohelices

Antennae are the most fundamental energy harvesting devices that we know, says Sung Nae Cho at the Samsung Advanced Institute of Technology in south Korea. So why aren’t they more widely used?

Turns out that helical antennae are already used to harvest energy and most of us probably own one already in the form of a transformers. These contain a helical winding that rectifies  AC into DC.

Cho points out that it has recently become possible to build nanohelices and that these might also be used for rectification. He’s designed a device that rectifies, not current, but electromagnetic waves. It consists of a nanohelix layer, a diode  layer and a capacitor layer, all the components of a standard rectifying circuit.

The nanohelix layer consists of an array of  100 million “pixels” which each contain a single nanohelix. That makes the array no bigger than the imaging chips in digital cameras . Cho calculates that if only 10 per cent of the nanohelices harvest energy from ambient electromagnetic waves to the tune of 130 nA, then the device would produce 1.3A.

If he’s right, that’s a handy amount by any standards. Anybody volunteer to prove him right.

Ref: arxiv.org/abs/0901.0769: Energy Harvesting by Utilization of Nanohelices

The day the solar wind disappeared

Tuesday, July 29th, 2008

coronal-hole.jpg

It happened on 11 May 1999…nobody knows  why and the event was not related to well known drivers of solar weather such as coronal mass ejections or large flares.

According to Durgess Tripathi at the University of Cambridge, UK, and pals, the cause seems to be linked to the appearance a few days earlier of a coronal hole, where the Sun’s corona appeared darker than usual. Exactly how this could have reduced the solar wind to nothing isn’t yet known.

Ref: http://arxiv.org/abs/0807.2697: The Solar Wind Disappearance Event of 11 May 1999: Source Region Evolution

Why small black holes cannot grow

Monday, July 28th, 2008

Quantum mechanics places a fundamental limit on the minimum quanta of energy that can be associated with a bit of energy.  It’s about 10^-50 Joules, which ain’t much.

That has important implications for black holes, says Scott Funkhouser, a physicist at The Citadel, the military college of South Carolina, in Charleston. As black holes accretes mass, its total energy increases but the energy per bit decreases,  he says.

And this decrease must always be greater than the minimum quanta of energy allowed by quantum mechanics. That only happens when black holes are bigger than 10^11 kg, which is only about a thousandth of the mass of Halley’s Comet.

That’s small on astrophysical  terms. But it should also come as a relief to anybody worried about the possibility of the production of tiny black hole at particles accelerators such as the LHC. According to Funkhouser, these black holes must be safe because they cannot grow.

Phew!

Ref: arxiv.org/abs/0807.1938: The Minimum Mass of a Black Hole that is Capable of Accretion in a Universe with a Cosmological Constant

Why black holes could be antimatter factories

Tuesday, June 24th, 2008

Black hole

Here’s an interesting chain of thought…

Imagine a black hole sucking in protons and electrons. With their higher mass,  protons are likely to be preferentially sucked, giving the black hole a positive charge. (That’s not so unusual in space: a similar mechanism can give planets a charge because electrons escape their gravity more easily.)

But black holes also create such strong electrostatic fields at the horizon that positrons and electrons simply appear out of the vacuum.

In those circumstances, it’ll look as if the protons being sucked into the black hole are being converted into positrons.

So these kinds of black holes will look and behave like antimatter factories, say Cosimo Bambi from Wayne State University in Detroit and pals.

How might we we spot these exotic objects? Bambi and friends say a sure signature would be an excess of positrons in cosmic rays  with an energy between 1 and 100 MeV coming from a black hole.

Anybody seen any of these?

Ref: arxiv.org/abs/0806.3440: Black Holes as Antimatter Factories

How to bury an ion (and find it again later)

Tuesday, June 17th, 2008

Buried ions

The future of computing depends on our ability to bury single ions within the crystal structure of silicon and diamond in a way that allows us to find them again, quickly and repeatably.

The burying part of all this isn’t difficult: simply aim a beam of ions at a substrate and you can be pretty sure one or two of them will end up buried inside the crystal structure. The trick is to know where they’re buried so you can find them again later.

That’s a trick that Thomas Schenkel and pals at the Lawrence Berkeley National Laboratory overlooking San Francisco, seem to have perfected for the first time. Their technique is to fire the ion beam through a hole in the tip of a scanning force microscope. The hole defines the position of the burial while the scanning force microscope can easily find the location again later.

Schenkel has used the technique to bury nitrogen atoms in diamond and antimony in silicon, which is impressive. (The team even says it has discovered that antimony doesn’t migrate when the substrate is later heated, which is an important result in itself. Ions that move after you bury them are difficult to find later!)

But the bigger picture is that ion burial is one of the enabling technologies that will make quantum computing possible. So it’s just possible that Schenkel and co have created the first facility in which quantum computers will be forged.

Ref: arxiv.org/abs/0806.2167: Single-atom Doping for Quantum Device Development in Diamond and Silicon

Why ET will phone using neutrinos not photons

Tuesday, May 20th, 2008

Neutrino communication

The search for extraterrestrial intelligence assumes that ET will be communicating using photons. But despite decades of listening out, we’ve heard nothing.

But today, John Learned from the University of Hawaii and pals say forget photons. We should be looking for evidence of ET using neutrinos.

The reason is that any civilisation advanced enough to colonise the galaxy would need a reliable way to communicate over intragalactic distances and photons simply don’t pass muster. There is a huge amount of noise in the electromagnetic spectrum, photons are easily scattered and would almost certainly be absorbed if they had to travel from one side of the galaxy to the other.

By contrast, the neutrino spectrum is relatively noise free and neutrinos intereact so weakly with matter that a signal could travel unhindered from one side of the galaxy to the other.

They propose testing the idea by generating a neutrino signal using a particle acclerator to genreate Z nought particles which decay into neutrinos of a relatively easily detectable energy. They would encode information in the time structure of the beam, like Morse code.

What’s more, Learned and co say that the kind of neutrino signals that ET might be expected to beam should be detectable by the generation of neutrino detectors now under construction.

Ref: arxiv.org/abs/0805.2429: Galactic Neutrino Communication

How orbiting electrons can lengthen nuclear half-life

Friday, May 16th, 2008

Fission

Nuclear fission is the process in which a nucleus decays into two fragments. For large nucleii, this process is a complicated one in which the nucleus undergoes several stages of deformation before tearing itself apart.

In recent years, physicists have predicted that fission ought to be affected by the presence of electrons in orbit about the nucleus. That’s because any change in the shape of the nucleus naturally affects the electrons which tend to absorb energy making fission less likely. And the more electrons there are, the more energy they absorb. But the effect has never been observed because ordinary, naturally ocurring elements simply don’t have enough electrons to make this effect significant.

Today, Vlad Dzuba and Vic Flambuam at the University of New South Wales in Australia have calculated the strength of this effect for superheavy elements which would have more electrons. They say that although the effect is tiny for naturally ocurring nuclei with fewer than 100 or so protons, it would be hugely significant for these larger nuclei. In fact, they calculate that an atom with 160 protons would have double the expected half life because of this effect.

That could have significant implications for how much of this stuff we’re likely to find because elements that decay quickly tend to be rarer) . Last week, arxivblog reported on the potential discovery of element 122 (with 122 protons). Perhaps the groups looking for superheavies should be setting their sights much, much higher.

Ref: arxiv.org/abs/0805.1961: The Effect of Atomic Electrons on Nuclear Fission