Archive for Cosmology

A Dark Energy Mission

Posted in The Universe and Stuff with tags , , on November 16, 2013 by telescoper

Here’s a challenge for cosmologists and aspiring science communicators out there. Most of you will know the standard cosmological model involves a thing, called Dark Energy, whose existence is inferred from observations that suggest that the expansion of the Universe appears to be accelerating.

That these observations require something a bit weird can be quickly seen by looking at the equation that governs the dynamics of the cosmic scale factor R for a simple model involving matter in the form of a perfect fluid:

\ddot{R}=-\frac{4\pi G}{3} \left( \rho + \frac{3p}{c^2}\right) R

The terms in brackets relate to the density and pressure of the fluid, respectively. If the pressure is negligible (as is the case for “dust”), then the expansion is always decelerating because the density of matter is always positive quantity; we don’t know of anything that has a negative mass.

The only way to make the expansion of such a universe actually accelerate is to fill it with some sort of stuff that has

\left( \rho + \frac{3p}{c^2} \right) < 0.

In the lingo this means that the strong energy condition must be violated; this is what the hypothetical dark energy component is introduced to do. Note that this requires the dark energy to exert negative pressure, ie it has to be, in some sense, in tension.

However, there’s something about this that seems very paradoxical. Pressure generates a force that pushes, tension corresponds to a force that pulls. In the cosmological setting, though, increasing positive pressure causes a greater deceleration while to make the universe accelerate requires tension. Why should a bigger pushing force cause the universe to slow down, while a pull causes it to speed up?

The lazy answer is to point at the equation and say “that’s what the mathematics says”, but that’s no use at all when you want to explain this to Joe Public.

Your mission, should you choose to accept it, is to explain in language appropriate to a non-expert, why a pull seems to cause a push…

Your attempts through the comments box please!

Tension in Cosmology?

Posted in Astrohype, Bad Statistics, The Universe and Stuff with tags , , , on October 24, 2013 by telescoper

I noticed this abstract (of a paper by Rest et al.) on the arXiv the other day:

We present griz light curves of 146 spectroscopically confirmed Type Ia Supernovae (0.03<z<0.65) discovered during the first 1.5 years of the Pan-STARRS1 Medium Deep Survey. The Pan-STARRS1 natural photometric system is determined by a combination of on-site measurements of the instrument response function and observations of spectrophotometric standard stars. We have investigated spatial and time variations in the photometry, and we find that the systematic uncertainties in the photometric system are currently 1.2% without accounting for the uncertainty in the HST Calspec definition of the AB system. We discuss our efforts to minimize the systematic uncertainties in the photometry. A Hubble diagram is constructed with a subset of 112 SNe Ia (out of the 146) that pass our light curve quality cuts. The cosmological fit to 313 SNe Ia (112 PS1 SNe Ia + 201 low-z SNe Ia), using only SNe and assuming a constant dark energy equation of state and flatness, yields w = -1.015^{+0.319}_{-0.201}(Stat)+{0.164}_{-0.122}(Sys). When combined with BAO+CMB(Planck)+H0, the analysis yields \Omega_M = 0.277^{+0.010}_{-0.012} and w = -1.186^{+0.076}_{-0.065} including all identified systematics, as spelled out in the companion paper by Scolnic et al. (2013a). The value of w is inconsistent with the cosmological constant value of -1 at the 2.4 sigma level. This tension has been seen in other high-z SN surveys and endures after removing either the BAO or the H0 constraint. If we include WMAP9 CMB constraints instead of those from Planck, we find w = -1.142^{+0.076}_{-0.087}, which diminishes the discord to <2 sigma. We cannot conclude whether the tension with flat CDM is a feature of dark energy, new physics, or a combination of chance and systematic errors. The full Pan-STARRS1 supernova sample will be 3 times as large as this initial sample, which should provide more conclusive results.

The mysterious Pan-STARRS stands for the Panoramic Survey Telescope and Rapid Response System, a set of telescopes cameras and related computing hardware that monitors the sky from its base in Hawaii. One of the many things this system can do is detect and measure distant supernovae, hence the particular application to cosmology described in the paper. The abstract mentions a preliminary measurement of the parameter w, which for those of you who are not experts in cosmology is usually called the “equation of state” parameter for the dark energy component involved in the standard model. What it describes is the relationship between the pressure P and the energy density ρc2 of this mysterious stuff, via the relation P=wρc2. The particularly interesting case is w=-1 which corresponds to a cosmological constant term; see here for a technical discussion. However, we don’t know how to explain this dark energy from first principles so really w is a parameter that describes our ignorance of what is actually going on. In other words, the cosmological constant provides the simplest model of dark energy but even in that case we don’t know where it comes from so it might well be something different; estimating w from surveys can therefore tell us whether we’re on the right track or not.

The abstract explains that, within the errors, the Pan-STARRS data on their own are consistent with w=-1. More interestingly, though, combining the supernovae observations with others, the best-fit value of w shifts towards a value a bit less than -1 (although still with quite a large uncertainty). Incidentally  value of w less than -1 is generally described as a “phantom” dark energy component. I’ve never really understood why…

So far estimates of cosmological parameters from different data sets have broadly agreed with each other, hence the application of the word “concordance” to the standard cosmological model.  However, it does seem to be the case that supernova measurements do generally seem to push cosmological parameter estimates away from the comfort zone established by other types of observation. Could this apparent discordance be signalling that our ideas are wrong?

That’s the line pursued by a Scientific American article on this paper entitled “Leading Dark Energy Theory Incompatible with New Measurement”. This could be true, but I think it’s a bit early to be taking this line when there are still questions to be answered about the photometric accuracy of the Pan-Starrs survey. The headline I would have picked would be more like “New Measurement (Possibly) Incompatible With Other Measurements of Dark Energy”.

But that would have been boring…

Planck and Being Human

Posted in The Universe and Stuff with tags , , , on October 23, 2013 by telescoper

On Saturday 19th October the instruments and cooling systems on the European Space Agency’s Planck spacecraft were switched off, marking the end of the scientific part of the Planck mission, after about four years of mapping the cosmic microwave background.  Later, a piece of software was uploaded that would prevent  the spacecraft systems being  accidentally switched on again after being switched off and the transmitter from causing interference with any future probes.  Planck is already “parked” indefinitely in a what is called a “disposal” orbit, far from the Earth-Moon system, having been nudged off its perch at the 2nd Lagrangian Point (L2) in August by a complicated series of manoeuvres. On October 21st the spacecraft’s thrusters were fired to burn up the last of its fuel, an important aspect of rendering the spacecraft inert, as required by ESA’s space debris mitigation guidelines.

Planck

These preliminaries having been completed, today, at 12.00 GMT,  a final instruction will be transmitted to the spacecraft  to close it down permanently; thereafter Planck will circle the Sun as a silent memorial to the stunning success it achieved when active. I’m sure all those who worked on the Planck mission will pause as the final shutdown command is given and ponder the lonely future  of the spacecraft that had supplied so much interesting data.

But although this will be the end of the Planck mission, it is by no means the end of the Planck Era. Vast amounts of data still need to be fully analysed and key science results are still in the pipeline,  relating in particular to the polarization of the microwave background radiation. Moreover, the numerous maps, catalogues and other data products will be a priceless legacy to this generation, and no doubt many future generations, of scientists.

The fate of Planck illustrates two contrasting aspects of the human experience. On the one hand, there’s the fragility of our existence in a cosmos too vast for us to comprehend. Like the defunct spacecraft, our Earth too circles this little Sun of ours in a precarious orbit while the rest of the Universe – with its countless billion upon billion of other suns – carries on, oblivious to our very existence. Planck makes us painfully aware of our own insignificance.

But on the other hand there’s the sense of fulfillment, and even of joy, at finding things out. We may have puny monkey brains and many things are likely to remain forever beyond our mental grasp, but trying to figure things out is one of the things that defines us as human.  Experiments like Planck (and, for that matter, the Large Hadron Collider) are not the wasteful extravagance some people claim them to be. We need them not just for the sake of science, but to remind us of our common humanity.

UPDATE: And now, from ESA, confirmation that Planck has received its last command. Goodbye, and enjoy your retirement!

Updates for Cosmology: A Very Short Introduction?

Posted in Books, Talks and Reviews, The Universe and Stuff with tags , , , , , on October 21, 2013 by telescoper

Yet another very busy day, travelling in the morning and then in meetings all afternoon, so just time for another brief post. I thought I’d take the opportunity to do a little bit of crowdsourcing…

A few days ago I was contacted by Oxford University Press who are apparently considering the possibility of a second edition of my little book Cosmology: A Very Short Introduction, which is part of an extensive series of intensive books on all kinds of subjects.

I really enjoyed writing this book, despite the tough challenge of trying to cover the whole of cosmology in less than 35,000 words and was very pleased with the way it turned out. It has sold over 25000 copies in English and has been published in several other languages.

It is meant to be accessible to the interested layperson but the constraints imposed by the format mean it goes fairly quickly through some quite difficult concepts. Judging by the reviews, though, most people seem to think it gives a useful introduction to the subject, although you can’t please all of the people all of the time!

However, the book was published way back in 2001 and, well, one or two things have happened in the field of cosmology since then.  I have in fact had a number of emails from people asking whether there was going to be a new edition to include the latest developments, but the book is part of a very large series and it was basically up to the publisher to decide whether it wanted to update some, all or none of the series.

Now it seems the powers that be at OUP have decided to explore the possibility further and have asked me to make a pitch for a new edition.  I have some ideas of things that would have to be revised – the section on Dark Energy definitely needs to be updated, and of course first WMAP and then Planck have refined our view of the cosmic microwave background pretty comprehensively?

Anyway, I thought it would be fun to ask people out there who have read it, or even those who haven’t, what they feel I should change for a new edition if there is to be one. That might include new topics or revisions of things that could be improved. Your comments are therefore invited via the famous Comments Box. Please bear in mind that any new edition will be also constrained to be no more than 35,000 words.

Oh, and if you haven’t seen the First Edition at all, why not rush out and buy a copy before it’s too late? I understand you can snap up a copy for just £3 while stocks last. I can assure you all the royalties will go to an excellent cause. Me.

Yesterday in Parliament

Posted in Science Politics, The Universe and Stuff with tags , , , , , on October 9, 2013 by telescoper

Yesterday afternoon I arrived in a rather muggy Westminster to attend a reception at the Houses of Parliament associated with an exhibition called Unveiling the Universe in all its Light which is currently set up inside the Palace of Westminster but will later go on tour around the UK.

Parliament

It took me a while to find the way in. I lived in London for the best part of 9 years but never bothered to visit the Houses of Parliament (at least not the interior), so I was quite excited as, clutching my invitation in a rather sweaty hand, I eventually joined the queue to go through the security checks. That didn’t take very long, so despite getting lost in the corridors of power en route – it’s a bit of a maze inside – I had plenty of time to see the exhibition before joining the assembled throng in the Strangers’ Dining Room. There, surrounded by walls covered in expensive but tasteless flock wallpaper, I had a couple of couples of glasses of wine and ate some posh sandwiches while chatting to various astronomers, particle physicists and others, including a contingent of familiar faces from the Science and Technology Facilities Council.

It was a coincidence, of course, that this event took place on the day that the Nobel Prize for Physics was announced; it was impressive that posters were already there celebrating the award to Peter Higgs. General opinion was delight that Higgs had won a share of the prize, but sadness that Tom Kibble had been left out.

There were upbeat speeches by Minister for Universities and Science David Willetts (who isn’t as tall as he looks on telly), Andrew Miller (Chair of the Parliamentary Select Committee on Science and Technology), John Womersley (Chief Executive of STFC) and Lord Rees (Astronomer Royal). I think everyone present came away with a strong sense that astronomy and particle physics had strong political backing. Martin Rees in particular said that he thought we were living in a “golden age” for fundamental science, involving an exciting interplay between the inner space of subatomic particles and the outer space of cosmology. I couldn’t agree more.

Science, Religion and Henry Gee

Posted in Bad Statistics, Books, Talks and Reviews, Science Politics, The Universe and Stuff with tags , , , , , , , , , on September 23, 2013 by telescoper

Last week a piece appeared on the Grauniad website by Henry Gee who is a Senior Editor at the magazine Nature.  I was prepared to get a bit snarky about the article when I saw the title, as it reminded me of an old  rant about science being just a kind of religion by Simon Jenkins that got me quite annoyed a few years ago. Henry Gee’s article, however, is actually rather more coherent than that and  not really deserving of some of the invective being flung at it.

For example, here’s an excerpt that I almost agree with:

One thing that never gets emphasised enough in science, or in schools, or anywhere else, is that no matter how fancy-schmancy your statistical technique, the output is always a probability level (a P-value), the “significance” of which is left for you to judge – based on nothing more concrete or substantive than a feeling, based on the imponderables of personal or shared experience. Statistics, and therefore science, can only advise on probability – they cannot determine The Truth. And Truth, with a capital T, is forever just beyond one’s grasp.

I’ve made the point on this blog many times that, although statistical reasoning lies at the heart of the scientific method, we don’t do anywhere near enough  to teach students how to use probability properly; nor do scientists do enough to explain the uncertainties in their results to decision makers and the general public.  I also agree with the concluding thought, that science isn’t about absolute truths. Unfortunately, Gee undermines his credibility by equating statistical reasoning with p-values which, in my opinion, are a frequentist aberration that contributes greatly to the public misunderstanding of science. Worse, he even gets the wrong statistics wrong…

But the main thing that bothers me about Gee’s article is that he blames scientists for promulgating the myth of “science-as-religion”. I don’t think that’s fair at all. Most scientists I know are perfectly well aware of the limitations of what they do. It’s really the media that want to portray everything in simple black and white terms. Some scientists play along, of course, as I comment upon below, but most of us are not priests but pragmatatists.

Anyway, this episode gives me the excuse to point out  that I ended a book I wrote in 1998 with a discussion of the image of science as a kind of priesthood which it seems apt to repeat here. The book was about the famous eclipse expedition of 1919 that provided some degree of experimental confirmation of Einstein’s general theory of relativity and which I blogged about at some length last year, on its 90th anniversary.

I decided to post the last few paragraphs here to show that I do think there is a valuable point to be made out of the scientist-as-priest idea. It’s to do with the responsibility scientists have to be honest about the limitations of their research and the uncertainties that surround any new discovery. Science has done great things for humanity, but it is fallible. Too many scientists are too certain about things that are far from proven. This can be damaging to science itself, as well as to the public perception of it. Bandwagons proliferate, stifling original ideas and leading to the construction of self-serving cartels. This is a fertile environment for conspiracy theories to flourish.

To my mind the thing  that really separates science from religion is that science is an investigative process, not a collection of truths. Each answer simply opens up more questions.  The public tends to see science as a collection of “facts” rather than a process of investigation. The scientific method has taught us a great deal about the way our Universe works, not through the exercise of blind faith but through the painstaking interplay of theory, experiment and observation.

This is what I wrote in 1998:

Science does not deal with ‘rights’ and ‘wrongs’. It deals instead with descriptions of reality that are either ‘useful’ or ‘not useful’. Newton’s theory of gravity was not shown to be ‘wrong’ by the eclipse expedition. It was merely shown that there were some phenomena it could not describe, and for which a more sophisticated theory was required. But Newton’s theory still yields perfectly reliable predictions in many situations, including, for example, the timing of total solar eclipses. When a theory is shown to be useful in a wide range of situations, it becomes part of our standard model of the world. But this doesn’t make it true, because we will never know whether future experiments may supersede it. It may well be the case that physical situations will be found where general relativity is supplanted by another theory of gravity. Indeed, physicists already know that Einstein’s theory breaks down when matter is so dense that quantum effects become important. Einstein himself realised that this would probably happen to his theory.

Putting together the material for this book, I was struck by the many parallels between the events of 1919 and coverage of similar topics in the newspapers of 1999. One of the hot topics for the media in January 1999, for example, has been the discovery by an international team of astronomers that distant exploding stars called supernovae are much fainter than had been predicted. To cut a long story short, this means that these objects are thought to be much further away than expected. The inference then is that not only is the Universe expanding, but it is doing so at a faster and faster rate as time passes. In other words, the Universe is accelerating. The only way that modern theories can account for this acceleration is to suggest that there is an additional source of energy pervading the very vacuum of space. These observations therefore hold profound implications for fundamental physics.

As always seems to be the case, the press present these observations as bald facts. As an astrophysicist, I know very well that they are far from unchallenged by the astronomical community. Lively debates about these results occur regularly at scientific meetings, and their status is far from established. In fact, only a year or two ago, precisely the same team was arguing for exactly the opposite conclusion based on their earlier data. But the media don’t seem to like representing science the way it actually is, as an arena in which ideas are vigorously debated and each result is presented with caveats and careful analysis of possible error. They prefer instead to portray scientists as priests, laying down the law without equivocation. The more esoteric the theory, the further it is beyond the grasp of the non-specialist, the more exalted is the priest. It is not that the public want to know – they want not to know but to believe.

Things seem to have been the same in 1919. Although the results from Sobral and Principe had then not received independent confirmation from other experiments, just as the new supernova experiments have not, they were still presented to the public at large as being definitive proof of something very profound. That the eclipse measurements later received confirmation is not the point. This kind of reporting can elevate scientists, at least temporarily, to the priesthood, but does nothing to bridge the ever-widening gap between what scientists do and what the public think they do.

As we enter a new Millennium, science continues to expand into areas still further beyond the comprehension of the general public. Particle physicists want to understand the structure of matter on tinier and tinier scales of length and time. Astronomers want to know how stars, galaxies  and life itself came into being. But not only is the theoretical ambition of science getting bigger. Experimental tests of modern particle theories require methods capable of probing objects a tiny fraction of the size of the nucleus of an atom. With devices such as the Hubble Space Telescope, astronomers can gather light that comes from sources so distant that it has taken most of the age of the Universe to reach us from them. But extending these experimental methods still further will require yet more money to be spent. At the same time that science reaches further and further beyond the general public, the more it relies on their taxes.

Many modern scientists themselves play a dangerous game with the truth, pushing their results one-sidedly into the media as part of the cut-throat battle for a share of scarce research funding. There may be short-term rewards, in grants and TV appearances, but in the long run the impact on the relationship between science and society can only be bad. The public responded to Einstein with unqualified admiration, but Big Science later gave the world nuclear weapons. The distorted image of scientist-as-priest is likely to lead only to alienation and further loss of public respect. Science is not a religion, and should not pretend to be one.

PS. You will note that I was voicing doubts about the interpretation of the early results from supernovae  in 1998 that suggested the universe might be accelerating and that dark energy might be the reason for its behaviour. Although more evidence supporting this interpretation has since emerged from WMAP and other sources, I remain sceptical that we cosmologists are on the right track about this. Don’t get me wrong – I think the standard cosmological model is the best working hypothesis we have _ I just think we’re probably missing some important pieces of the puzzle. I don’t apologise for that. I think sceptical is what a scientist should be.

The Open Journal for Astrophysics – Update and Request

Posted in Open Access, The Universe and Stuff with tags , , , , , on August 22, 2013 by telescoper

I’ve been getting quite a few questions about my modest proposal The Open Journal for Astrophysics. I don’t want to give too much away before the site is revealed, but I can say that after a very positive meeting in London last week the project is right on track and will go live pretty soon for beta testing. We have an Editorial Board (names to be revealed in due course), a very nice website, a web team, and an excellent interface for editors and reviewers which, in my opinion, is far better than any offered by a “professional” journal. When the site does go live I’ll explain in more detail how it works and introduce all the people whose contributions enabled this project to get off the ground.

We are going to test everything extensively before the OJFA goes public, however, so please be patient. We will be testing the site initially using papers in a relatively restricted area of astrophysics (largely extragalactic astrophysics and cosmology), but hope to expand by the addition of other members to the Editorial Board. In anticipation of this future expansion, volunteers in areas of astrophysics outside this specialism are welcome!

That’s the update. Now time for the request. Although not essential for the initial testing phase of the project, we do think that it would benefit from a distinctive layout for the papers, which would be easily achieved by having our own Latex style. This came up in discussion some time ago when I first floated the idea of this project and somebody emailed me offering to design an appropriate Latex package. Unfortunately, however, in transit from Cardiff to here I appear to have lost the email and can’t remember who sent it. I’m therefore going to enlist the help of the blogosphere to remedy this act of incompetence. Is there anybody out there among the interwebs who is sufficiently keen and has the necessary expertise to construct a latex style for our new journal? If so please contact me, either through the comments or via email. I can’t do it myself because I have never had any sense of style…

Please pass this on via Twitter, etc.

A Three-dimensional Map of the Early Universe

Posted in The Universe and Stuff with tags , , , , on August 14, 2013 by telescoper

I found this video via a web page describing the FastSound project, which is surveying galaxies in the Universe which are at such a huge distance that we are seeing them as they were over nine billion years ago. Using the Subaru Telescope‘s impressive new Fiber Multi-Object Spectrograph (FMOS). This project is “work in progress”. The survey so far contains only 1,100 galaxies, but while that is small by the standards of a modern redshift survey, and will in fact still only comprise about 5000 galaxies when complete, what is amazing about it is that the galaxies are at such enormous distances. Even using a telescope with an 8.2 metre primary mirror, this survey will take another year or so to be completed.

A survey of a representative region of the Universe at such high redshift allows astrophysicists to test theories of the growth of the large-scale structure of the Universe. In the standard cosmology, these form by a process of gravitational instability: small irregularities in the distribution of matter get amplified by the action of gravity to become large structures such as galaxies and galaxy clusters. Comparing the level of clustering at early times with that observed around us today allows us to check whether this growth matches theoretical predictions. There should be much less clumpiness earlier on if the theoretical picture is right.

I began my PhD DPhil at the University of Sussex in 1985, working on the large-scale structure of the Universe. Coincidentally, the largest redshift survey available at that time, the CfA1 Survey, also contained 1,100 galaxies – as displayed in the famous “stick man map”:

cfa2.n30

The galaxies mapped out in that survey, however, are all (relatively speaking) in our back yard: none is further than a few hundred million light years away…

An Integral Appendix

Posted in Biographical, Cute Problems, The Universe and Stuff with tags , , , , , , on August 7, 2013 by telescoper

After the conference dinner at the Ripples in the Cosmos meeting in Durham I attended recently, a group of us adjourned to the Castle bar for a drink or several. I ended up chatting to one of the locals, Richard Bower, mainly on the subject of beards. I suppose you could call it a chinwag. Only later on did  we get onto the subject of a paper we had both worked on a while ago. It was with some alarm that I later realized that the paper concerned was actually published twenty years ago. Sigh. Where did all that time go?

Anyway, Richard and I both remembered having a great time working on that paper which turned out to be a nice one, although it didn’t exactly set the world on fire in terms of citations. This paper was written before the standard “concordance” (LCDM) cosmology was firmly established and theorists were groping around for ways of reconciling observations of the CMB from the COBE satellite with large-scale structure in the galaxy distribution as well as the properties of individual galaxies. The (then) standard model (CDM with no Lambda) struggled to satisfy the observational constraints, so in typical theorists fashion we tried to think of a way to rescue it. The idea we came up with was “cooperative galaxy formation”, as explained in the abstract:

We consider a model in which galaxy formation occurs at high peaks of the mass density field, as in the standard picture for biased galaxy formation, but is further enhanced by the presence of nearby galaxies. This modification is accomplished by assuming the threshold for galaxy formation to be modulated by large-scale density fluctuations rather than to be spatially invariant. We show that even a weak modulation can produce significant large-scale clustering. In a universe dominated by cold dark matter, a 2 percent – 3 percent modulation on a scale exceeding 10/h Mpc produces enough additional clustering to fit the angular correlation function of the APM galaxy survey. We discuss several astrophysical mechanisms for which there are observational indications that cooperative effects could occur on the scale required.

I have to say that Richard did most of the actual work on this paper, though all four authors did spend a lot of time discussing whether the idea was viable in principle and, if so, how we should implement it mathematically. In the end, my contribution was pretty much limited to the Appendix, which you can click to make it larger if you’re interested.

t2png

As is often the case in work of this kind, everything boiled down to evaluating numerically a rather nasty integral. Coincidentally, I’d come across a similar problem in a totally different context a few years previously when I was working on my thesis and therefore just happened to know the neat trick described in the paper.

Two things struck me looking back on this after being reminded of it over that beer. One is that a typical modern laptop is powerful enough to evaluate the original integral without undue difficulty, so if this paper had been written nowadays we wouldn’t have bothered trying anything clever; my Appendix would probably not have been written. The other thing is that I sometimes hear colleagues bemoaning physics students’ lack of mathematical “problem-solving” ability, claiming that if students haven’t seen the problem before they don’t know what to do. The problem with that complaint is that it ignores the fact that many problems are the same as things you’ve solved before, if only you look at them in the right way. Problem solving is never going to be entirely about “pattern-matching” – some imagination and/or initiative is going to required sometimes- but you’d be surprised how many apparently intractable problems can be teased into a form to which standard methods can be applied. Don’t take this advice too far, though. There’s an old saying that goes “To a man who’s only got a hammer, everything looks like a nail”. But the first rule for solving “unseen” problems has to be to check whether you might in fact already have seen them…

Just a minute! Is space really expanding?

Posted in Astrohype, The Universe and Stuff with tags , , , on August 2, 2013 by telescoper

Now then. I’m sure this little video will get a few cosmologists’ hackles rising:

The video was produced by minutephysics, so presumably the expansion of time accounts for the fact that lasts more than two minutes. More importantly, though, is the content. Here’s an old  discussion of mine on this question. Let me know what you think via the comments box!