RelativeCosmos.com – Astrophysics, Astronomy & Cosmology

By Estelle Asmodelle

SKA Image courtesy: Paul Bourke and Jonathan Knispel and supported by WASP (UWA), iVEC, ICRAR, and CSIRO

Recent reports on the selection of the site for the Square Kilometre Array (SKA) have suggested that South Africa offers the best site and a panel of advisors recommended the SA site over Australia. The argument was put that the SA site was cheaper for construction, yet Australia had lower insurance fees, and primarily that the SA site was at a higher altitude.

The issue of altitude is really irrelevant here for at higher frequencies water vapour, or Scintillation (the distortion of waves moving through varying densities) can become a problem, but not so much for long radio waves, the bigger problem there is  radio frequency interference. Australia would be the best place for SKA, especially in WA which is ‘radio quite,’ not so in South Africa. Most long wave radio dishes are low lying. Altitude is more important for millimetre or sub-millimetre arrays.

I think this is really a political issue, South Africa really needs help financially and the SKA would boost their economy. I just hope that Australia is chosen, for South Africa’s site is not as remote and within 10 years, of completion, the site could suffer considerable radio interference problems, which would seriously degrade its operational status.

And also South Africa has many other issues, such as social unrest which could affect the operation of the telescope, or the employees. The argument that SA would be best as they have already started building the array, but it’s also true of Australia, who under the project name ASKAP, or the Australian Square Kilometre Array Pathfinder have already deployed some of the planned 36 dishes which will be complete in 2013, and can be integrated into the SKA if Australia is chosen, some dishes have already seen first light. See the site:

ASKAP, or the Australian Square Kilometre Array Pathfinder

http://www.atnf.csiro.au/projects/askap/index.html

See the status of the ASKAP site here in real time – updated often:

http://www.atnf.csiro.au/projects/askap/askap-live/

Don’t take my word for it – see Brian Boyle’s burb on the advantages Australia offers for the SKA:

http://www.ska.gov.au/Pages/BrianBoyle’s2012SKAUpdate.aspx

Some say that people who are astronomers, or students like me who will be looking for placement soon, are just feathering their nest – not true, for most of the people who will work on these sites will be from all over the world, the very cream of the crop, and probably not be Australian to a large extent.

So in fact we are further along than SA. So why the support for SA – word is, as I’ve eluded too, it’s really about politics not science – see this article:

http://www.gizmodo.com.au/2012/02/ska-bid-should-come-down-to-science-not-politics/

The last thing to bear in mind – Australia will soon have the NBN rolled out all over the country – this will assist the data handling to a very large extent – certainly by the time the SKA is complete we will have one of the best broadband networks in the world!

Interestingly the last big astronomy project SA was involved in had endless imaging problems (Although an optical site), and still does to an extent, and even more recently, poor broadband and operating problems:

http://www.salt.ac.za/

And read more here:

http://www.southafrica.info/about/science/salt-telescope.htm

All in all the remote WA site is best suited for such an astronomical site for several reasons but most importantly the size of our site  - see the map for details:

Potential SKA array station placement in Australia and New Zealand overlaid on a population density map. Major broadband network links (existing and planned) are also shown. Credit: CSIRO

By Estelle Asmodelle

The transit of Venus is happening 5th-6th June 2012.

There are plenty of Astronomical Societies who are holding ‘transit parties,’ including two that I do presentations to: The first one, here is a page from the Newcastle Astronomical Society with their ‘transit party’ and they had ABC radio there as well:

http://www.nas.org.au/HTML%20Pages/venus_transit_event_2004.htm

I understand they will be doing the same thing this year… and I will be going as well.

The second is the Sutherland Astronomical Society (largest such group in Sydney) – they have their own observatory, and it’s a good one too. They too are going to have a ‘transit party’

http://www.sasi.net.au/index.php

Incidentally, I am giving  a presentation to this group (in response to an invite from them after reading some of my articles in Cosmos) entitled: “Cosmology and the role of the General Theory of Relativity.” Which will be 2 nights after the transit – this will be the first time that I’ve given a presentation to this group, and I feel a bit intimidated by it as it’s a 90 minute presentation and they usually get university lecturers to do such presentations – fingers crossed that I have my ducks all in a row…

I didn’t see the 2004 transit as I was overseas at the time but I won’t miss this one! Here is an Australian site dedicated to the transit that you may find interesting as well:

http://www.transitofvenus.com.au/HOME.html

Incidentally, Jeremiah Horrocks was the first person to successfully predict and observe the transit of Venus in 1639.

But the BIG news is really the total solar eclipse in Cairns, which is at the top of Queensland, that is the big news. Cairns is 3 hour flight and 2 hour drive from my home but we have our flight booked and our hotel booked ready – I am taking my two nephews as well, one is at Uni and the other is very interested in astronomy as well. Here in Australia its big news for many people and most of Cairns is booked out – I will taking my telescope and HD video camera, together with a suitable filter, to film the event – so it’s really exciting – it’s my first total eclipse. I have seen a couple of partials but never a total! Here is an Australian website with some more details:

http://www.eclipsecairns.com/

By November it should be dry, also Cairns gets tropical rain and as the eclipse is just after sunrise it will 95% be dry, I just hope it’s clear skies!

By Estelle Asmodelle

Last December I joined the Newcastle Astronomical Society [NAS: http://www.nas.org.au/ ], that’s in Newcastle here in NSW, Australia – not the UK. When they had learned that I write the Space | Astronomy | Cosmology news for Cosmo magazine (sometimes) they invited me to give a series of talks – which I was surprised about as they usually have academics delivering such presentations, but agreed nervously. Still nervous about it :-)

Anyway, then came the problem about what to talk about – as there is so much but being an Astronomical society they aren’t interested in mathematical or highly technical presentations, and so I borrowed some work from this course for the 1st presentation:

I wrote my Essay about Moon discoveries, the title being: “Moon Discoveries & The Presence of Water” It’s a very interesting subject, and there has been many more tests and detections of water, in some form, on the Moon than most realise – so I decided to turn this essay, into a 1 hour presentation, it had to be expanded somewhat, with more photos etc., but it should go well.

The title of the talk is “Water on the Moon,” and is to at University of Newcastle, 3rd February – would invite any who are interested but it’s a bit far to travel – check out the link:

http://www.nas.org.au/HTML%20Pages/NAS%20Meetings.htm

GOSFORD: New insight into how waves spread in different kinds of artificial materials could shed light on how disorder affects quantum materials such as superconductors.

Since waves are used in all kinds of applications, from medical imaging to electronics, the physics behind disorder is fundamental to the understanding of how imperfections in the materials that compose these technologies affect wave behaviour.

“While disorder and imperfections are impossible to avoid in materials, there is much we do not understand about how disorder affects their properties,” said co-author Brian DeMarco from the University of Illinois in the U.S., of the paper published in Science today.

Read full news item here.

Sep 13, 2011

Could the Sun test alternative theories of gravity?

Alternatives to Einstein’s general theory of relativity can be investigated by studying the Sun. That is the claim of a group of physicists in Portugal who have found that a variation of a theory put forward nearly a century ago by Arthur Eddington is constrained but not ruled out by observations of solar neutrinos and solar acoustic waves.

General relativity, which describes gravity as the curvature of space–time by massive objects, has so far passed every experimental and observational test dreamed up by physicists. But the theory does present a number of problems. In addition to the difficulty of unifying it with quantum mechanics and the challenge to explain the nature of dark matter and dark energy, there remains the conceptual problem of singularities, where the laws of physics break down.

Since Einstein introduced general relativity in 1916, many alternatives have been proposed. Last year Máximo Bañados of the Pontifical Catholic University in Chile and Pedro Ferreira of Oxford University reported a variant of a theory originally put forward by the British astrophysicist Arthur Eddington that adds a repulsive gravitational term to general relativity. This has the virtue of not requiring singularities, and as a result does not predict that the universe originated from a Big Bang, nor does it imply the formation of black holes.

Looking inside a star

When considering a gravitational field within a vacuum, this Eddington-inspired theory is equivalent to general relativity but predicts different effects for gravity acting within matter. The ideal place to look for such differences would be inside neutron stars – but the interiors of neutron stars are not understood sufficiently to compare the theories.

The answer, say Jordi Casanellas and colleagues at the Technical University of Lisbon, is to use the Sun. While a much less extreme source of gravity than a neutron star, the inner workings of the Sun are described accurately by solar models. Casanellas’s group has calculated that even in its non-relativistic Newtonian form, the Eddington-inspired theory should predict measurable differences in solar output compared with standard gravitational theory.

The Lisbon researchers have shown that the presence of the repulsive gravity term in the theory of Bañados and Ferreira is similar to setting a different value for the gravitational constant inside matter. And with the strength of gravity higher or lower than it would otherwise be inside the Sun, the inner solar temperature is also modified because the Sun is assumed to be in hydrostatic equilibrium. This means that the inward pressure of its mass is balanced by the outward thermal pressure generated by the fusion reactions within it. A higher temperature implies a greater rate of fusion burning, which in turn implies higher emission rates of solar neutrinos.

Altering acoustic waves

Similarly, a different strength of gravity inside the Sun implies a variation in its density distribution, which should modify the propagation of acoustic waves measured using the techniques of helioseismology.

Casanellas and co-workers have shown that observations made by neutrino telescopes of the solar neutrino flux coming from the proton–proton chain reaction that produces boron-8 significantly constrain the correction to general relativity, calculating an upper limit to the effective gravitational constant. Combined with a lower limit obtained from helioseismic data, the researchers are able to put a significant constraint on the Eddington-inspired theory. However, they point out that their calculations do not rule out such a theory.

The researchers say that improving on these upper and lower limits will be difficult because of uncertainties in a few of the parameters within solar models, such as the abundance of helium on the solar surface. As such, more sensitive measurements of neutrino fluxes are unlikely to have much of an impact. But they believe their approach could be used to constrain other alternative theories of gravity.

Further testing on Earth

Ultimately, adds team member Paolo Pani, such theories could be tested experimentally by measuring, for example, the gravitational attraction between a metal ball inserted into a hole in the ground and the mass of the Earth surrounding it. The idea would be to make the hole just big enough for the ball to fit and no more, so that what is measured is the strength of gravity through matter and not the surrounding void (in this case air). However, Pani points out that doing so would be a considerable experimental challenge.

Clifford Will of Washington University in St Louis, US, described the latest work as a “nice example of using the Sun as a laboratory for probing fundamental physics” but added that “it’s not yet clear whether the bounds proposed by this paper present serious threats to alternative gravity theories”.

The research is reported at arXiv:1109.0249.

Aug 23, 2011

Who discovered that E = mc²? It’s not as easy a question as you might think. Scientists ranging from James Clerk Maxwell and Max von Laue to a string of now-obscure early 20th-century physicists have been proposed as the true discovers of the mass–energy equivalence now popularly credited to Einstein’s theory of special relativity. These claims have spawned headlines accusing Einstein of plagiarism, but many are spurious or barely supported. Yet two physicists have now shown that Einstein’s famous formula does have a complicated and somewhat ambiguous genesis – which has little to do with relativity.

One of the more plausible precursors to E = mc² is attributed to Fritz Hasenöhrl, a physics professor at the University of Vienna. In a 1904 paper Hasenöhrl clearly wrote down the equation E = 3/8mc². Where did he get it from, and why is the constant of proportionality wrong? Stephen Boughn of Haverford College in Pennsylvania and Tony Rothman of Princeton University examine this question in a paper submitted to the arXiv preprint server.

Hasenöhrl’s name has a certain notoriety now, as he is commonly invoked by anti-Einstein cranks. His reputation as the man who really discovered E = mc² owes much to the efforts of the antisemitic and pro-Nazi physics Nobel laureate Philipp Lenard, who sought to separate Einstein’s name from the theory of relativity so that it was not seen as a product of “Jewish science”.

‘Leading Austrian physicist of his day’

Yet all this does Hasenöhrl a disservice. He was Ludwig Boltzmann’s student and successor at Vienna, and was lauded by Erwin Schrödinger among others. “Hasenöhrl was probably the leading Austrian physicist of his day”, Rothman told physicsworld.com. He might have achieved much more if he had not been killed in the First World War.

The relationship of energy and mass was already being widely discussed by the time Hasenöhrl considered the matter. Henri Poincaré had stated that electromagnetic radiation had a momentum and thus effectively a mass, according to E = mc². German physicist Max Abraham argued that a moving electron interacts with its own field, E₀, to acquire an apparent mass given by E₀ = 3/4 mc². All this was based on classical electrodynamics, assuming an ether theory. “Hasenöhrl, Poincaré, Abraham and others suggested that there must be an inertial mass associated with electromagnetic energy, even though they may have disagreed on the constant of proportionality”, says Boughn.

Photo of Fritz Hasenöhrl published in 1933. (Courtesy: AIP Emilio Segrè Visual Archives, Brittle Books Collection, Physics Today Collection)Photo of Fritz Hasenöhrl published in 1933. (Courtesy: AIP Emilio Segrè Visual Archives, Brittle Books Collection, Physics Today Collection) Fritz Hasenöhrl

Robert Crease, a philosopher and historian of science at Stony Brook University in New York, agrees. “Historians often say that, had there been no Einstein, the community would have converged on special relativity shortly”, he says. “Events were pushing them kicking and screaming in that direction.” Boughn and Rothman’s work, he says, shows that Hasenöhrl was among those headed this way.

Hasenöhrl approached the problem by asking whether a black body emitting radiation changes in mass when it is moving relative to the observer. He calculated that the motion adds a mass of 3/8c² times the radiant energy. The following year he corrected this to 3/4c².

A different style of scientific paper

However, no-one has properly studied Hasenöhrl’s derivation to understand his reasoning or why the prefactor is wrong, claim Bough and Rothman. That’s not easy, they admit. “The papers are by today’s standards presented in a cumbersome manner and are not free of error. The greatest hindrance is that they are written from an obsolete world view, which can only confuse the reader steeped in relativistic physics.” Even Enrico Fermi apparently did not bother to read Hasenöhrl’s papers properly before concluding wrongly that the discrepant 3/4 prefactor was due to the electron self-energy identified by Abraham.

“What Hasenöhrl really missed in his calculation was the idea that if the radiators in his cavity are emitting radiation, they must be losing mass, so his calculation wasn’t consistent”, says Rothman. “Nevertheless, he got half of it right. If he had merely said that E is proportional to m, history would probably have been kinder to him.”

But if that’s the case, where does relativity come into it? Actually, perhaps it doesn’t. While Einstein’s celebrated 1905 paper, “On the electrodynamics of moving bodies”, clearly laid down the foundations of relativity by abandoning the ether and making the speed of light invariant, his derivation of E = mc² did not depend on those assumptions. You can get the right answer with classical physics, says Rothman, all in an ether theory without c being either constant or the limiting speed. “Although Einstein begins relativistically, he approximates away all the relativistic bits, and you are left with what is basically a classical calculation.”

A controversial issue

Physicist Clifford Will of Washington University in St Louis, a specialist on relativity, considers the preprint “very interesting”. Boughn and Rothman “are well-regarded physicists”, he says, and as a result he “tend[s] to trust their analysis”. However, the controversies that have been previously aroused over the issue of priority perhaps account for some of the reluctance of historians of physics to comment when contacted by physicsworld.com.

Did Einstein know of Hasenöhrl’s work? “I can’t prove it, but I am reasonably certain that Einstein must have done, and just decided to do it better”, says Rothman. But failure to cite it was not inconsistent with the conventions of the time. In any event, Einstein asserted his priority for the mass–energy relationship when this was challenged by Johannes Stark (who credited it in 1907 to Max Planck). Both Hasenöhrl and Einstein were at the famous first Solvay conference in 1911, along with most of the other illustrious physicists of the time. “One can only imagine the conversations”, say Boughn and Rothman.

Rothman told physicsworld.com that he had run across Hasenöhrl’s name a number of times but with no real explanation as to what he did. “One of my old professors, E C G Sudarshan, once remarked that he gave Hasenöhrl credit for mass–energy equivalence. So around Christmas-time last year, I said to Steve, ‘why don’t we spend a couple hours after lunch one day looking at Hasenöhrl’s papers and see what he did wrong?’ Well, two hours turned into eight months, because the problem ended up being extremely difficult.”

About the author

Philip Ball is a science writer based in the UK

http://physicsworld.com/cws/article/news/46941

Viewing image 1 of 2

In the diagram a light trajectory is shown. The light ray enters the device, completes a loop, bounces off the mirror twice and leaves the cloak with its original direction restored (A).

Credit: Perczel et al & New J. Phys.

Panel (B) gives a closer view of the vicinity of the inner branch of the cloak. Objects placed within the white region are invisible.

Credit: Perczel et al & New J. Phys.

PERTH: One of the roadblocks in the development of invisibility cloaking has been cleared by an unlikely new inventor – an undergraduate student from the UK.

By introducing a unique optical device into a cloaking system, Janos Perczel from the University of St Andrews in Scotland has discovered that invisibility cloaking can still operate at speeds below the normal speed of light, known as subluminal light speeds.

See full article here