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Einstein and your Gas Bill

Posted in History, Television, The Universe and Stuff with tags , , , , , on October 11, 2011 by telescoper

Taking refuge in my office this lunchtime for a sandwich and a cup of coffee I turned to the latest edition of Physics World and came across an funny little story about a physicist (who is completely new to me) with the splendid name of Fritz Hasenöhrl.

The news story relates to a paper on the arXiv, part of the abstract of which I’ve copied below:

In 1904 Austrian physicist Fritz Hasenohrl (1874-1915) examined blackbody radiation in a reflecting cavity. By calculating the work necessary to keep the cavity moving at a constant velocity against the radiation pressure he concluded that to a moving observer the energy of the radiation would appear to increase by an amount E=(3/8)mc^2, which in early 1905 he corrected to E=(3/4)mc^2…

Since I’ve been doing a bit of dimensional analysis with first-year students, I’m a bit surprised that the authors of this paper read so much into the fact that Hasenöhrl’s formula bears a superficial resemblance to Einstein’s most famous formula E=mc^2, probably the best known and at the same time worst understood equation in physics. In fact any physicist worth his or her salt no matter how incorrect their reasoning would have to get something like E =\alpha mc^2, with \alpha some dimensionless number, simply because the answer has to have the correct dimensions to be an energy.

Expressing energy in terms of the basic dimensions mass M, length L and time T is probability easiest to do when you think of mechanical work (force×distance). Since Newton’s laws give a force equal to mass×acceleration, a force has dimensions MLT^{-2}, so work (a form of energy) has dimensions ML^{2}T^{-2}. Now try to make this out of a combination of a mass (M) and a velocity (LT^{-1}) and you’ll find that it has to be mass×velocity2. You can’t get the dimensionless constant this way, but the combination of m and c must be the way it is in Einstein’s formula.

Anyway, all this suddenly reminded me of a day long ago when I appeared on peak-time television in the consumer affairs programme Watchdog, explaining – or, rather, attempting to explain – the physics behind the way gas bills are calculated. Apparently someone had written in to the programme asking why it was that they weren’t just being charged for the volume of gas that had flowed through their meter, but that the cost involved a complicated calculation involving something called the calorific value of the gas.

The answer is fairly obvious, actually. The idea is that to make competition fairer between different forms of energy (particularly gas and electricity) the bills should be for the amount of energy you have used rather than the amount of gas. Since the source of fuel varies from day to day so does its chemical composition and hence the amount of energy that can be extracted from it when it is burned. Gas companies therefore monitor the calorific value, using it to convert the amount of gas you have used into an amount of energy.

On the programme I was confronted by the curmudgeonly Edward Enfield (father of comedian Harry Enfield) who took the line that it was all unnecessarily complicated and that the bill should just be for the amount of gas used, rather in the same way that petrol is sold. When I tried to explain that the way it was done was really fairer, because  it was really the energy that mattered, it quickly became obvious that he didn’t really understand what energy was or how it was defined.  He didn’t even get the difference between energy and power. I suspect that goes for many members of the general public.

It was all a bit tongue-in-cheek, but I enjoyed the sparring. Eventually he came out with a question about why energy was given by E=mc^2 rather than mc^3 or something else. So I launched into an explanation of dimensional analysis and why mc^3 couldn’t be an energy because it has the wrong dimensions. His eyes glazed over. The shoot ended. My splendidly erudite and logically rigorous exposition of dimensional analysis never made it into the broadcast programme.

My brief career on BBC1 was over.

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Have you been Drexlered?

Posted in The Universe and Stuff with tags , , , , on October 10, 2011 by telescoper

Every time something interesting is announced in astrophysics or cosmology – which is quite often, these days – I get an email from a chap called Jerome Drexler. Last week’s announcement of the 2011 Nobel Prize for Physics  proved to be no exception and this morning I got yet another message.

It’s interesting that Drexler always writes about himself in the third person, e.g.

Beginning in 2002, Bell Labs-educated (under a three year
fellowship) applied physicist Jerome Drexler utilized this same astronomical set of non-homogeneous-expansion-rate data in conjunction with his dark matter cosmology to find a compatible explanation for the accelerating expansion of our universe. The compatible explanation he discovered did not use either Friedmann’s solutions or the General Theory of Relativity, which rely entirely on gravitational forces. The successful results from his endeavor are reported in Chapter 21 of Drexler’s March 2008 paperback book entitled “Discovering Postmodern Cosmology” and in Chapter F of his October 2009 paperback book “Our Universe via Drexler Dark Matter.”

Indeed, having read a few of Drexler’s publications – none of which has actually appeared in an authentic scientific journal – it seems that his output will be of much greater interest to psychologists than physicists. Drexler, you see, insists that the dark matter, whose presence astronomers have inferred from the dynamics of self-gravitating systems, exists in the form of highly relativistic protons.

There are many problems with this suggestion, most of which will be obvious to anyone with first-year undergraduate knowledge of physics. Most important of all is the fact that protons are charged and therefore accelerate in the presence of a magnetic field. Protons accelerating in the Milky Way’s magnetic field would produce copious electromagnetic radiation and would not therefore be at all dark! Still, we don’t want a little bit of basic physics get in the way of a mania for self-promotion.

Incidentally, it’s not a crazy idea that dark matter could be charged but, if it is, it must consist of particles with mass many thousands of times greater than that of a proton. That way their inertia will keep their acceleration low and restrict the radiation they produce.

I’ve often thought that it might be an interestingly novel way of teaching physics to get students to unpick contributions like this. I’ve got a filing cabinet full of similar “alternative” theories of the Universe and from time to time give one to a student to find fault with. Usually it doesn’t take long. Sometimes they’re wrong, sometimes they’re not even that. I’ll therefore leave it to my highly educated and knowledgeable readership to suggest other failings of the Drexler Universe.

I don’t know what I did to deserve the honour of being placed on Drexler’s mailing list and in any case suspect that I’m just one among many recipients of his missives. I’m sure others have tried to convince him that his model doesn’t make any sense from the point of view of physics, but I’m sure that their attempts have fallen on stony ground. It’s another aspect of the psychology of such individuals that it is inconceivable to them (a) that they could be wrong about anything and (b) that anyone else might know more than they do. Real scientists have quite the opposite attitude.

Here’s how Jerome Drexler describes himself on his email:

Jerome Drexler is a former member of the technical staff and group supervisor at Bell Labs, former research professor in physics at New Jersey Institute of Technology (NJIT), founder and former Chairman and chief scientist of LaserCard Corp. (Nasdaq: LCRD). He has been awarded 76 U.S. patents (see Google Scholar), honorary Doctor of Science degrees from NJIT and Upsala College, a degree of Honorary Fellow of Israel’s Technion, an Alfred P. Sloan Fellowship at Stanford University, a three-year Bell Labs graduate study fellowship in applied physics, the 1990 “Inventor of the Year Award” for Silicon Valley and recognition as the original inventor in 1978 of the now widely-used digital optical disk “Laser Optical Storage System” and the LaserCard(R) nanotech data memory used in six countries. He is a member of the Board of Overseers of New Jersey Institute of Technology and an Honorary Life Member of the Technion-Israel Institute of Technology Board of Governors.

Anyone know any more about Professor Doctor Mr Drexler? If so, the comments box awaits your contribution…

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Dark Energy’s Day

Posted in The Universe and Stuff with tags , , , on October 4, 2011 by telescoper

Following hard on the heels of the announcement of a Nobel Prize for cosmology earlier this morning, the European Space Agency has this afternoon officially announced the two candidates which have been chosen for its next M-class missions from a shortlist of three.

One of the successful candidates, EUCLID, is directly relevant to the topic covered by the Nobel Prize announced this morning. “Euclid will address key questions relevant to fundamental physics and cosmology, namely the nature of the mysterious dark energy and dark matter. Astronomers are now convinced that these substances dominate ordinary matter. Euclid would map the distribution of galaxies to reveal the underlying ‘dark’ architecture of the Universe.”

Now that it’s definitely been selected, I hope to devote time in due course for a longer post about EUCLID’s capabilities and intentions, but in the meantime I’ll just say that it’s been a very good day for Dark Energy.

P.S. The other successful candidate is called Solar Orbiter. Commiserations to advocates of the third mission on the shortlist of three, PLATO. Close, but no cigar…

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Another Nobel Prize for Cosmology!

Posted in The Universe and Stuff with tags , , , , , , , on October 4, 2011 by telescoper

Just time in between teaching and meetings for a quick post on today’s announcement that the 2011 Nobel Prize for Physics has gone to Saul Perlmutter, Brian P. Schmidt and Adam G. Riess “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae.”

I’ve taken the liberty of copying the following text from the press release on the Nobel Foundation website

In 1998, cosmology was shaken at its foundations as two research teams presented their findings. Headed by Saul Perlmutter, one of the teams had set to work in 1988. Brian Schmidt headed another team, launched at the end of 1994, where Adam Riess was to play a crucial role.

The research teams raced to map the Universe by locating the most distant supernovae. More sophisticated telescopes on the ground and in space, as well as more powerful computers and new digital imaging sensors (CCD, Nobel Prize in Physics in 2009), opened the possibility in the 1990s to add more pieces to the cosmological puzzle.

The teams used a particular kind of supernova, called type Ia supernova. It is an explosion of an old compact star that is as heavy as the Sun but as small as the Earth. A single such supernova can emit as much light as a whole galaxy. All in all, the two research teams found over 50 distant supernovae whose light was weaker than expected – this was a sign that the expansion of the Universe was accelerating. The potential pitfalls had been numerous, and the scientists found reassurance in the fact that both groups had reached the same astonishing conclusion.

For almost a century, the Universe has been known to be expanding as a consequence of the Big Bang about 14 billion years ago. However, the discovery that this expansion is accelerating is astounding. If the expansion will continue to speed up the Universe will end in ice.

The acceleration is thought to be driven by dark energy, but what that dark energy is remains an enigma – perhaps the greatest in physics today. What is known is that dark energy constitutes about three quarters of the Universe. Therefore the findings of the 2011 Nobel Laureates in Physics have helped to unveil a Universe that to a large extent is unknown to science. And everything is possible again.

I’m definitely among the skeptics when it comes to the standard interpretation of the supernova measurements, and more recent complementary data, in terms of dark energy. However this doesn’t diminish in any way my delight that these three scientists have been rewarded for their sterling observational efforts. The two groups involved in the Supernova Cosmology Project on the one hand, and the High Z Supernova Search, on the other, are both supreme examples of excellence in observational astronomy, taking on and overcoming what were previously thought to be insurmountable observational challenges. This award has been in the air for a few years now, and I’m delighted for all three scientists that their time has come at last. To my mind their discovery is all the more exciting because nobody really knows precisely what it is that they have discovered!

I know that Brian Schmidt is an occasional reader and commenter on this blog. I suspect he might be a little busy right now with the rest of the world’s media right to read this, let alone comment on here, but that won’t stop me congratulating him and the other winners on their achievement. I’m sure they’ll enjoy their visit to Stockholm!

Meanwhile the rest of us can bask in their reflected glory. There’s also been a huge amount of press interest in this announcement which has kept my phone ringing this morning. It’s only been five years since a Nobel Prize in physics went to cosmology, which says something for how exciting a field this is to work in!

UPDATE: There’s an interesting collection of quotes and reactions on the Guardian website, updated live.

UPDATE on the UPDATE: Yours truly gets a quote on the Nature News article about this!

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Galaxies con Alma

Posted in The Universe and Stuff with tags , , , , on October 3, 2011 by telescoper

It’s back to School with a vengeance today, so not much time for the blog. However, I couldn’t resist mentioning the fact that the European Southern Observatory’s Atacama Large Millimetre Array, known to its friends as ALMA, has at last opened its eyes. Or at least some of them. ALMA in fact is an interferometer which eventually will comprise 66 dishes,   working together to with baselines as long 16km to synthesize a single huge aperture. The preliminary results that have just been released were obtained using just 16 dishes so they only offer a taste of what the full ALMA will do when it’s completed in 2013.

ALMA works in the millimetre wave region of the spectrum, operating at wavelengths between 0.3 and 9.6 mm. The overlap with the  wavelength range probed by the Herschel Space Observatory together with its much higher resolution than Herschel, which is a single telescope of only 3.5m diameter, makes the two very complementary: Herschel is good for surveying large parts of the sky, because it has a large field of view, whereas ALMA can do high-resolution follow-up of selected regions.

Anyway, here is ALMA’s view of the Antennae Galaxies (left) shown next to an optical image taken with the Very Large Telescope (VLT).

The system consists of two galaxies so close together that they interact strongly with each other via enormous tidal forces, hence the disturbed structure. The coloured regions in the ALMA image show radiation emanating from carbon monoxide present in huge clouds both in and between the galaxies. Altogether these clouds contain several billion solar masses worth of gas which has never been viewed before.

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Telescoping

Posted in The Universe and Stuff with tags , , , , , on October 2, 2011 by telescoper

I stumbled upon the following cartoon on Youtube and, since it’s about a mad astronomer, I thought I’d post it here.

It strikes me how  comic depictions of astronomical observatories, such as the example on the left,  always seem to show the telescope pointing out of the dome like the barrel of a gun poking out of a turret, which they never do. I venture to suggest that a great many members of the general public think that’s how they work also. I wonder why?

Perhaps it’s connected with the origins of the verb form of telescope which the OED gives as

a. trans. To force or drive one into another (or into something else) after the manner of the sliding tubes of a hand-telescope: usually said in reference to railway carriages in a collision. Also fig. to combine, compress, or condense (a number of things) into a more compact or concise form; to combine or conflate (several things, or one thing with another); to shorten by compression.

b. intr. To slide, run, or be driven one into another (or into something else); to have its parts made to slide in this manner (see quot. 1882 for telescoping n. and adj. at Derivatives, s.v. telescoping below); to collapse so that its parts fall into one another (quot. 1905).

The inference being that large astronomical telescopes must extend in the same way as the much smaller hand-held variety. Anyway, this idea is taken to a ludicrious extreme in the cartoon, with hilarious consequences…

 

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Euclid Alone Has looked On Beauty Bare

Posted in Euclid, Poetry, The Universe and Stuff with tags , , on September 25, 2011 by telescoper

Euclid alone has looked on Beauty bare.
Let all who prate of Beauty hold their peace,
And lay them prone upon the earth and cease
To ponder on themselves, the while they stare
At nothing, intricately drawn nowhere
In shapes of shifting lineage; let geese
Gabble and hiss, but heroes seek release
From dusty bondage into luminous air.
O blinding hour, O holy, terrible day,
When first the shaft into his vision shone
Of light anatomized! Euclid alone
Has looked on Beauty bare. Fortunate they
Who, though once only and then but far away,
Have heard her massive sandal set on stone.

by Edna St Vincent Millay (1892-1950)

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Neutrinos on Speed

Posted in The Universe and Stuff with tags , , , on September 23, 2011 by telescoper

The internet, twitterdom, blogosphere, and even the mainstream media are all alive today with wild speculations about a curious claim that neutrinos might travel faster than light.

If you’re interested in finding the source of this story, look at the arXiv paper here. I haven’t got time to go through the paper in detail, but I think it must be an instrumental artefact or some other sort of systematic error.

One major reason for doubting the veracity of the claim that neutrinos travel faster than light is provided by astronomical observations. Neutrinos produced by the explosion of Supernova SN1987a were detected when it went boom in 1987, approximately three hours before the visible light from SN 1987A reached the Earth.

The few hours delay between neutrinos and photons is explained by the fact that neutrino emission occurs when the core of the progenitor star collapses, whereas visible light is released only when a shock wave reaches the surface of the imploding object. Three different experiments detected (anti)neutrinos: Kamiokande II found 11 , IMB 8 and Baksan 5, in a burst lasting less than 13 seconds.

If the time delay reported by the OPERA detector over the distance between CERN and Gran Sasso were extrapolated to the distance between Earth and SN1987a then the neutrinos should have arrived not a few hours early, but a few years, and there would not have been coincident arrivals at the different detectors on Earth.

Do neutrinos go faster than light?
Some physicists think that they might.
In the cold light of day,
I am sorry to say,
The story is probably shite

UPDATE: Now that I’ve read the paper let me point out that the OPERA result is essentially

δv/c = (2.48 ± 0.28(stat) ± 0.30(syst)) × 10-5,

whereas the constraints from Supernova 1987a work out to be   δv/c < 2 × 10-9 for  neutrino energies of 10 MeV. See the comments below for discussion.

I’ll also mention at this point that the analysis done in the paper is entirely based on frequentist statistics. Somebody needs to do it properly.

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What’s the Matter?

Posted in The Universe and Stuff with tags , , , , , on September 19, 2011 by telescoper

I couldn’t resist a quick comment today on a news article to which my attention was drawn at the weekend. The piece concerns the nature of the dark matter that is thought to pervade the Universe. Most cosmologists believe that this is cold, which means that it is made of slow-moving particles (the temperature of  a gas being related to the speed of its constituent particles).  They also believe that it is not the sort of stuff that atoms are made of, i.e. protons, neutrons and electrons. In particular, it isn’t charged and therefore can’t interact with electromagnetic radiation, thus it is not only dark in the sense that it doesn’t shine but also transparent.

Cold Dark Matter (CDM) particles could be very massive, which would make them much more sluggish than lighter ones such as neutrinos (which would be hot dark matter), but there are other, more complicated, ways in which some exotic particles can end up in a slow-motion state without being massive.

So why do so many of us think the dark matter is cold? The answer to that is threefold. First, this is by far the simplest hypothesis to work on. In other words, good old Occam’s Razor. It’s simple because if the dark matter is cold there is no relevant physical scale associated with the speed of the particles. Everything is just dominated by the gravity, which means there are fewer equations to solve. Not that it’s exactly easy even in this case: huge supercomputers are needed to crunch the numbers.

The second reason is that particle physics has suggested a number of plausible candidates for non-baryonic candidates which could be cold dark matter particles. A favourite theoretical idea is supersymmetry, which predicts that standard model particles have counterparts that could be interesting from a cosmological point of view, such as the fermionic counterparts of standard model bosons. Some of these candidates could even be produced experimentally by the Large Hadron Collider.

The final reason is that CDM seems to work, at least on large scales. The pattern of galaxy clustering on large scales as measured by galaxy redshift surveys seems to fit very well with predictions of the theory, as do the observed properties of the cosmic microwave background.

However, one place where CDM is known to have a problem is on small scales. By small of course I mean in cosmological terms; we’re still talking about many thousands of light-years! There’s been a niggling worry for some time that the internal structure of galaxies, especially in their central regions,  isn’t quite what we expect on the basis of the CDM theory. Neither do the properties of the small satellite galaxies (“dwarfs”) seen orbiting the Milky Way seem to match what what we’d expect theoretically.

The above picture is taken from the BBC website. I’ve included it partly for a bit of decoration, but also to point out that the pictures are both computer simulations, not actual astronomical observations.

Anyway, the mismatch between the properties of dwarf galaxies and the predictions of CDM theory, while not being exactly new, is certainly a potential Achilles’ Heel for the otherwise successful model. Calculating the matter distribution on small scales however is a fearsome computational challenge requiring enormously high resolution. The disagreement may therefore be simply because the simulations are not good enough; “sub-grid” physics may be confusing us.

On the other hand, one should certainly not dismiss the possibility that CDM might actually be wrong. If the dark matter were not cold, but warm (or perhaps merely tepid), then it would produce less small-scale structure whilst not messing up the good fit to large-scale structure that we get with CDM.

So is the Dark Matter Cold or Warm or something else altogether? The correct answer is that we don’t know for sure, and as a matter of fact I think CDM is still favourite. But if the LHC rules out supersymmetric CDM candidates and the astronomical measurements continue to defy the theoretical predictions then the case for cold dark matter would be very much weakened. That might annoy some of its advocates in the cosmological community, such as Carlos Frenk (who is extensively quoted in the article), but it would at least mean that the hunt for the true nature of dark matter would be getting warmer.

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“Cosmic Anomalies” Talk, Copenhagen, August 2011

Posted in Art, Books, Talks and Reviews, Cosmic Anomalies, The Universe and Stuff with tags , , on August 31, 2011 by telescoper

I think I’m getting the hang of this slideshare malarky so I thought I’d try it out by posting the slides I used for my (short) talk at the workshop in Copenhagen I told you about two or three weeks ago. I’m not sure how useful they will be to anyone, as I suppose it will be quite hard to reconstruct the talk using only the small amount of information I bother to put on the slides..

If you’re wondering about the presence of various apparently random works of art then what can I say? I like paintings!

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