Archive for the ‘Seein’ the light’ Category

Questioning the Big Bang

Friday, March 28th, 2008


The Big Bang dominates current thinking in cosmology. But the experimental evidence that backs it up is surprisingly thin. In fact there are only two pieces of evidence: the galactic redshift and the cosmic background radiation.

The Big Bang explains these observations but only by introducing problems of their own. So are there any alternative hypotheses that do a better job? Robert Soberman and Maurice Dubin have developed an idea that they say better explains the observations. They also make some testable predictions which should be able to tell which theory is right.

The main problem with the Big Bang theory is that the cosmic background radiation does not have the characteristics you’d expect to see from a Big Bang-type event. For a start, the radiation curve has the distinct whiff of a black body about it, something that can only be produced by ordinary matter radiating at a specific temperature (according to quantum mechanics, anyway). Most theorist do not imagine the Big Bang like this.  Next, the cosmic background seems to cover the sky smoothly in all directions, unlike the matter we see which is clumped into galaxies. Even the microvariations discovered by satellites such as COBE and WMAP bear no relation to the distribution of visible matter.

So what is Soberman and Dubin’s alternative? They hypothesize that interstellar space is filled with tiny clumps of hydrogen and helium atoms called cosmoids (short for cosmic meteroids). The pair have calculated that cosmoids ought to radiate at 2.735K which is exactly the temperature of the cosmic microwave background and this explains the blackbody curve (they say these cosmoids could be easily created and tested in the lab). This  radiation need only be produced by a locally smooth distribution of cosmoids for it to look the same in all directions to us.

The cosmoid idea also explains the galactic redshift. Soberman and Dubin say that cosmoids absorbing and re-emitting light from distant galaxies should redshift the light albeit in a way that is subtely different from a doppler redshift generated by an expanding universe. That subtle difference shuld be relatively easy to spot with a few observations, they say.

The pair add that evidence that cosmoids exist has already been found by experiments onboard the Pioneer and Helios spacecraft.

Oh, and as a by product, the cosmoids make up the missing mass that astronomers call dark matter.

A cracking idea! I’m looking forward to seeing how the cosmologists dismantle it.

Ref: arxiv.org/abs/0803.3604: Was There A Big Bang?

New type of pulsating star discovered

Wednesday, March 19th, 2008

Pulsating dwarf

New types of stars aren’t found very often but last year, Patrick Dufour and pals discovered several white dwarfs with carbon atmospheres. Before then white dwarfs were thought to come in two flavours: with atmopsheres dominated by either hydrogen or helium. Astronomers suddenly had a new toy to play with.

Dufour found nine examples of his carbon dwarfs in the data regurgitated by the Sloan Digital Sky Survey and more are likely to be found as the skies continue to be searched.

So what are white dwarfs with carbon atmospheres like? Dufour and some theorists have been working out the details and today publish their results. Carbon dwarfs should be great throbbing balls of fire. Yep, pulsating stars.

They’ve had a bit of luck here. Turns out that Gilles Fontaine at the University of Montreal produced a theoretical study of carbon-based white dwarfs for his phd thesis 35 years ago, long before they were even discovered.

A quick look through his notes has revealed that these stars should pulsate as carbon is cycled through the atmosphere by convection (although the exact details depend on the amount of carbon in the stellar atmosphere).

Now the hunt is on to find more of these rare white dwars and to measure the amount of light they produce. “We are eagerly awaiting the results,” say Fontaine and Dufour.

Ref: arxiv.org/abs/0803.2255: Might Carbon-Atmosphere White Dwarfs Harbour a New Type of Pulsating Star?

UPDATE

Having eagerly waited all of one day, Dufour and a few buddies have announced the discovery of a pulsating carbon-rich white dwarf.

Congratualtions to them but there is a potential fly in the ointment: what looks like a pulsating dwarf could actually be a binary system of two white dwarfs. Dufour is unfazed. He points out that the characteristics of the system are unique so either way, they’ve found a new class of something or other.

He finishes with this: “We will continue the search for other objects of this exciting and enigmatic class.”

The world expects!

Ref: arxiv.org/abs/0803.2646: SDSS J142625.71+575218.3, a Prototype for a New Class of Variable White Dwarf

Future brightens for quantum imaging

Tuesday, March 18th, 2008

Quantum illumination

This is the idea behind quantum imaging: create an entangled pair of photons and send one towards the object you want to image and hang on to the other.

But then what? For some time, physcists have been whisperin’ about the extraordinary potential of this technique. Some imagine that it might be possible to create images of objects that cannot otherwise be seen, objects inside black boxes, for example, or black holes.

The thinking is that the photon you hold in your hand can somehow tell you something about the object it’s entangled cousin has hit. So you can create an image of an object without ever seeing its reflection.

But pin physicists down about what they mean and they start a-mumblin’ and a-dribblin’ incoherently. Despite rumours from places like Boston University where various bods are testing the idea in the bowels of the physics department, nobody has ever provided experimental evidence that quantum illumination is anything but a hatful of hot air.

So if ever a field needed an injection of common sense, this is it. Step forward quantum theorist and all round bright spark Seth Lloyd from MIT. He’s taken the thinkin’ and given it a thorough shakin’ by the scruff of its neck.

Lloyd doesn’t give any credence to the ideas of reflection-free imaging but he’s found something almost as good. Lloyd has calculated that illuminating an object with entangled photons can reduce increase the signal to noise ratio of the reflected signal by a factor of 2^e, where e is the number of bits of entanglement. That’s an exponential improvement.

What’s more, the improvement occurs even if the entanglement is completely destroyed during the process of reflection. So quantum illumination could help image anything that is currently hard to distinguish because of noise.

That’s impressive but Lloyd’s ideas raise quite a few questions, such as how to perform the required entanglement measurement on the returning photon. That’s for the experimentalists to sort out although there’s no easy and obvious answer.

So although a clever piece of work, it could be a while before we’re posing for quantum snapshots from Kodak.

Ref: arxiv.org/abs/0803.2022: Quantum Illumination

Dark matter: we’ve been staring at it all along

Friday, February 29th, 2008

Dark nuggets

Astrobods have been searching for dark matter for a decade or so now. And despite it filling the known Universe, there’s been no sign of the stuff .

But could it be that we’ve been staring at it all along without knowing what we’ve been looking at?

That’s the claim of a couple of theorists in North America. They say that dark matter is in the form of large nuggets of dense quark matter or quark anti-matter and that this could explain a number of mysterious observations that astronomers have been making in recent years.

Michael Forbes of University of Washington, in Seattle and Ariel Zhitnitsky from the University of British Columbia in Vancouver say these nuggets float around in the form of tiny 10 ton lumps and would emit thermal radiation that should be straightforward to measure.

And sure enough, astronomers have been puzzling over a number of unexplained bands of radiation coming from the center of our galaxy that have been picked up by orbiting telescopes in recent years. The gamma ray observatory Integral has spotted a mysterious 511 KeV glow, the Compton gamma ray observatory has found an unexplained signal between 1- 20 MeV, the Chandra x-ray telescope sees a diffuse keV x-ray emission all over the place and WMAP has detected an excess of GHz microwave radiation from the inner core of the galaxy called the WMAP haze.

All this can be explained by quark nuggets, say the pair of astronomers. Interestingly, they also make a number of predictions about the nature and distrbution of the radiation emitted by nuggets that should be straightforward to test. So unlike most dark matter theories, this one will stand or fall relatively quickly.

The theory also explains why none of the detectors on Earth have spotted these nuggets–the nuggets are distributed too sparsely to have been seen yet.

But when one of these ten ton beauties does come floating by, we’re not likely to miss its impact.

Ref: arxiv.org/abs/0802.3830: WMAP Haze: Directly Observing Dark Matter?

First 3D image of a streamer

Thursday, February 28th, 2008

3d-streamer



Streamers are the whispy electronic filaments that feel their way towards the ground in the fraction of a second before a lightning strike. They differ from the main strike in that they do not significantly increase the gas temperature.

They are also seen in nature as sprites, giant electronic discharges that sit 100 kilometres or so above active thunderstorms.

A number of groups have captured ordinary 2D images of streamers, which have a complex, fragmented shape. But nobody has determined their 3D structure.

Now Sanders Nijdam and pals at Eindhoven University of Technology in the Netherlands have captured the first 3D image of a streamer.

Their set up is pretty straigthforward. A stereo camera photographing a discharge in air. They then digitised the images to create a model of the streamer.

That’s handy because streamers may be useful in various applications such as ozone generation, bio fuel processing and plasma assisted combustion, say the group.

Cool huh?

Ref: arxiv.org/abs/0802.3639: Stereo-photography of Point-Plane Streamers in Air

Saving Earth from the Sun’s expansion

Monday, February 18th, 2008

Sun’s expansion

About 7 billion years from now the Sun will have swelled into a red giant with a radius larger than Earth’s orbit. We’re doomed. Or so we thought.

A ray of hope has been thrown our way by astronomers who say that as the Sun expands it will lose a significant portion of its mass (perhaps almost a third) in the form of a solar wind that is blown away. And as the mass drops, the radius of Earth’s orbit should increase.

That complicates things so Robert Connon Smith from the University of Sussex and a pal took on the task of determining whether this new thinking means Earth will survive or not.

And the answer is…cue drum roll.. that the planet will still be engulfed.

But they offer another ray of hope. Earth’s angular momentum around the smaller Sun need only be increased by 8 per cent to avoid engulfment and that, says Smith, could be achieved by engineering a series of asteroid swingbys that gradually lift us into a wider orbit.

If we start planning now, there’s hope for Mother Earth yet.

Ref: arxiv.org/abs/0801.4031: Distant Future of the Sun and Earth Revisited

How to spot a wormhole

Monday, January 7th, 2008

Wormhole

I know ya’ll heard of wormholes, tunnels in the fabric of the cosmos that connect one region of the universe to another. These ain’t just the fanciful dreams of impressionable young astrobods: wormholes represent real solutions of Einstein’s equation of general relativity. If general relativity is correct, wormholes ought to be out there somewhere.

But how to spot ’em? It’s easy to imagine that a wormhole, being a kinda hole in spacetime, would be indistinguishable from a black hole. Turns out that ain’t the case. Alexander Shatskiy, an astrothinker from the Lebedev Physical Institute in Moscow, says wormholes are fundamentally different from black holes because they have no event horizon. He’s even worked out what a wormhole should look like.

The key difference is that light entering one end of a wormhole comes out at the other but in a highly characteristic way. The angular intensity distribution of this light has a minimum at the center, regardless of wavelength. This allows background stars to shine through giving the wormhole the appearance of a semi-transparent hollow sphere (see image above).

Where to look? Shatskiy suggests that the next generation of supersensitive radio telelscope interferometers should have the resolution capable of distinguishing black holes from wormholes in active galactic nuclei.

So the message to all you radio astronomers out there is: keep ’em peeled.

Ref: arxiv.org/abs/0712.2572: Passage of Photons Through Wormholes and the Influence of Rotation on the Amount of Phantom Matter around Them

Black holes may convert dark matter into cosmic rays

Friday, December 21st, 2007

M87 Active Galactic Nucleus

Active galactic nuclei are the brightest objects in the universe and among the most puzzlin’. Astrobods think they are supermassive black holes that spew out huge amounts light over some or all of the electromagnetic spectrum.

Now a coupla Ruskies are saying that active galactic nuclei are capable of converting dark matter into high energy protons. Here’s how. Yurii Pavlov at The Herzen University in St Petersburg and his tovarich Grib, hypothesise that dark matter particles are big critturs, about 15 times heavier than protons, and that they can decay into pairs of other particles.

Near an active galactic nucleus, one of these particles can get sucked into the black hole, and accelerated to huge energies in the process, while the other escapes. But some of those that escape will collide with incoming particles creating collisisons of mind boggling energy.

It is in these collisions, says Pavlov, that ordinary visible protons can form, accept they’d have huge energies beyond anything that can be created on Earth.

Interesting idea but ah know what you’re thinkin’: this is all too neat ‘n’ theoretical. What ya need is good hard evidence, right?

Pavlov says he’s got it in the form of ultra high-energy cosmic rays, particles such as protons that smash into the Earth having been accelerated to such extreme energies that astrobods have yet to figure out how it’s done.

Now get this: data from the Auger telescope and other places have recently determined that ultra high-energy cosmic rays come from active galactic nuclei.

Could active galactic nuclei be converting dark matter into ultra high-energy cosmic rays?

I know ya’ll will want a lil bit more evidence than this. Fair enough but a lotta crazier ideas have gained a popular followin’ on less.

Ref: arxiv.org/abs/0712.2667: Do Active Galactic Nuclei Convert Dark Matter into Visible Particles?

The puzzling presence of DIBs

Tuesday, December 18th, 2007

Diffuse interstellar bands

For more than 80 years, astrobods have a-pondered and a-peered at strange sets of dark bands that appear in the spectra of distant stars. These bands are entirely different from the absorption sepctra of specific ions, atoms and molecules which absorb light at specific, sharp frequencies. Instead these bands are broad and diffuse. And there are hundreds of ’em.

Ain’t nobody got any idea what generates these so-called diffuse insterstellar bands. Astrobods assume that something in interstellar space is absorbing the light in these bands, perhaps dust, perhaps ice or perhaps complex oranic molecules such as polyaromatic hydrocarbons. A number of groups have tried to reproduce the absorption spectra in labs in Earth but all have failed miserably. So the origin of DIBs remains a mystery.

It seems clear, however, that a number of different things must be behind DIBs cos if one species of interstellar stuff were responsible it would have to be fiendishly complex.

So alotta interesting questions remain unanswered. Why are DIBs diffuse and not sharp like other absorption spectra? Why so many? And (obviously) what’s causing them?

All this talk of DIBs is brought on by a light and rather bland review of the topic by Bogdan “Dobs” Wszolek at the Institute of Physics in Poland. If you want a quick intro (it’s just three pages), give it a scan.

Ref: arxiv.org/abs/0712.1553: Puzzling Phenomenon of Diffuse Interstellar Bands

Near-to-far field image magnification

Monday, November 12th, 2007

Near field lens

There was a time when magnifying glasses were good for nothing but fryin’ ants and helping the over-60s with newsprint. Now everyone’s a-peekin’ and a-peerin’ at things that are even smaller than the wavelength of visible light.

The conventional thinkin is that you can’t see nothing smaller than about a quarter of the wavelength of light; light’s just gonna go round anything as small as that, right?

Not quite. Turns out that in the region within a wavelength of a light emitter, the so-called near field, light interacts with things in all kindsa interesting ways. And if ya could only see the near field, you might get a handle on what’s going on.

There are various attempts to do this, such as near-field microscopy, which all involve circumventing the near field in some way such as sticking a probe into this forbidden region.

Now Vlad Shalaev at Purdue University in Indiana has designed the gadget we’ve all been a-waitin’ and a-hopin’ for: a lens that can magnify a near-field image into a far field one. Shalaev’s lens is made outta metamaterial that channels electric and magnetic fields away from a point source and redistributes them over a broader area, in other words it magnifies them.

There’s no hope for them ants now.

Ref: arxiv.org/abs/0711.0183: Engineering Space for Light via Transformation Optics