Archive for the The Universe and Stuff Category

Fun with Vortex Rings

Posted in Education, The Universe and Stuff with tags , , on November 5, 2012 by telescoper

I decided to squeeze in a little bit about vortex rings into this morning’s lecture, partly because they illustrate the connections between fluid vorticity and magnetism, and partly because they’re fun…

Here’s an animation of a vortex ring showing how the fluid elements move around it (you might need to click on it to make it animate):

It’s quite easy to generate vortex rings in everyday situations, the simplest way being when a mass of fluid is impulsively pushed from an enclosed space through a narrow opening. In this case the poloidal flow is set in motion, at least in part, by interaction between the outer parts of the fluid mass and the edges of the opening. This results in fluid elements travelling in little circles, like those above, around a “core”; the direction of the vorticity is at right angles to these circles, i.e. in the toroidal direction. A vortex line can be formed from by joining together the vorticity vectors from each little circle to form a circle defining the core of the vortex ring. The behaviour of vortex lines in flows like this is entirely analogous to that of magnetic field lines. In this case, the vortex line follows the motion of the fluid, which is at right angles to it, so it propagates more-or-less without disruption. This is how most vortex ring toys work, such as shown in the two examples here; the second is far more dramatic!

The last video features some naturally-occurring vortex rings (as well as some  distinctly man-made examples). What I didn’t realise until I found this video last night is that whales and dolphins know how to make vortex rings too, only underwater. Why do they do this? Is there an evolutionary explanation? I doubt it! I think they’re just having fun.

At the Mountains of Madness

Posted in Literature, The Universe and Stuff with tags , , , , on November 1, 2012 by telescoper

Well, I don’t know whether it is some sort of Hallowe’en skit or what, but the estimable arXiv has certainly served up something unusual today, in the form of a paper by one Benjamin K. Tippett with the intriguing title Possible Bubbles of Spacetime Curvature in the South Pacific. Here is the abstract:

In 1928, the late Francis Wayland Thurston published a scandalous manuscript in purport of warning the world of a global conspiracy of occultists. Among the documents he gathered to support his thesis was the personal account of a sailor by the name of Gustaf Johansen, describing an encounter with an extraordinary island. Johansen`s descriptions of his adventures upon the island are fantastic, and are often considered the most enigmatic (and therefore the highlight) of Thurston`s collection of documents.

We contend that all of the credible phenomena which Johansen described may be explained as being the observable consequences of a localized bubble of spacetime curvature. Many of his most incomprehensible statements (involving the geometry of the architecture, and variability of the location of the horizon) can therefore be said to have a unified underlying cause.

We propose a simplified example of such a geometry, and show using numerical computation that Johansen`s descriptions were, for the most part, not simply the ravings of a lunatic. Rather, they are the nontechnical observations of an intelligent man who did not understand how to describe what he was seeing. Conversely, it seems to us improbable that Johansen should have unwittingly given such a precise description of the consequences of spacetime curvature, if the details of this story were merely the dregs of some half remembered fever dream.

We calculate the type of matter which would be required to generate such exotic spacetime curvature. Unfortunately, we determine that the required matter is quite unphysical, and possess a nature which is entirely alien to all of the experiences of human science. Indeed, any civilization with mastery over such matter would be able to construct warp drives, cloaking devices, and other exotic geometries required to conveniently travel through the cosmos.

Despite the unusual subject matter, it certainly doesn’t read like a skit, which means that if that’s what it is then it’s a very good one. Alternatively, it could just be that Dr Tippett might be taking it all a bit too literally. However, the paper is full of names that will ring a bell to anyone familiar with the works of H.P. Lovecraft, especially those relating to Cthulhu. Anyway, sounds like an ideal topic for further investigation. Time to put my grant-writing hat on!

P.S. The title of this post is taken from ref. [2] in the aforementioned arXiv paper.

A Sense of Proportion – Postscript

Posted in The Universe and Stuff with tags , , on October 30, 2012 by telescoper

It took all day to do so, evidently because I’m old and slow, but this morning’s post eventually got round to reminding me of this cartoon, the context of which is described here. Was that really in 1992? That was twenty years ago!

The Total Perspective Vortex

Posted in The Universe and Stuff with tags , , on October 30, 2012 by telescoper

Vortices are swirling around in my mind these days. Not only because of Hurricane Sandy, but also because I’ve got to prepare a couple of lectures about vorticity in fluid mechanics to give next week. Anyway, all that reminded me of this classic sequence from the original radio series The Hitchhiker’s Guide to the Galaxy, by the late great Douglas Adams. I particularly agree with the conclusion “that if life is going to exist in a Universe of this size, then the one thing it cannot afford to have is a sense of proportion”.

Gravity Waves Detected!

Posted in The Universe and Stuff with tags , , on October 29, 2012 by telescoper

At last, for all you sceptics out there, Hurricane Sandy has finally provided definitive proof of the existence of gravity waves, clearly visible to the South West of the storm…

Apologies if you thought I meant gravitational waves. The confusion was entirely intentional.

Philosophy of Science Poll

Posted in The Universe and Stuff with tags , , on October 20, 2012 by telescoper

I’m told the following quotation from esteemed theoretical physicist Stephen Hawking is very profound:

Because there is a law such as gravity, the universe can and will create itself from nothing.

Huh? I can’t make sense of it at all. Is it just me that finds it entirely devoid of either logic or  meaning?

Please tell Mr Polldaddy what you think….

You might even try to explain it to me via the comments box, but be patient because I’m thick.

A Particle Physics Job at Sussex

Posted in The Universe and Stuff with tags , on October 19, 2012 by telescoper

Following hard on the heels of Tuesday’s news, and the subsequent advert for astronomy jobshere is an announcement of a permanent job in theoretical particle physics at the University of Sussex. I quote from the advertisement:

Candidates are expected to hold a doctorate in theoretical physics and have a strong track record of internationally recognised research in the areas of collider phenomenology, physics beyond the Standard Model, flavour physics, and/or precision tests. The successful applicant will be expected to teach at both the undergraduate and postgraduate level.

Sussex has in recent years invested in SM and BSM phenomenology through faculty appointments both in theoretical and experimental physics. We seek an individual suited and committed to further strengthening and developing this effort.

The group’s wider research interests include model-building, quantum field theory, quantum gravity, and early universe cosmology. It benefits from a close relationship with the Sussex Experimental Particle Physics group, currently expanding its ATLAS effort, an STFC-funded research consortium with Royal Holloway, University of London, and membership of the NExT Institute. The University of Sussex is part of the South East Physics Network (SEPnet).

I’ll be interested to see how many people apply as a result of seeing this here announcement, so if you do fill in an application form  be sure to answer the question “Where did you see this post advertised” with “In the Dark”!

Three Astronomy Jobs at Sussex

Posted in The Universe and Stuff with tags , , , on October 18, 2012 by telescoper

Following hard on the heels of Tuesday’s news, here is an announcement of three (new, permanent) jobs in Astronomy at the University of Sussex. Full details are in the above link, but the gist is that applications are invited for 3 permanent, full-time faculty positions within the Astronomy Centre.

The 8 existing faculty have research interests that span the observation, modelling/simulation and theory of extragalactic astronomy and cosmology.  We are seeking talented and ambitious colleagues whose research interests complement and extend our current activity.

This advertisement will in due course appear elsewhere, e.g. in the November AAS Jobs Register.

I’ll be interested to see how many people apply as a result of seeing this here announcement, so if you do fill in an application form  be sure to answer the question “Where did you see this post advertised” with “In the Dark”!

This Week’s Bridge Problem, No. 236

Posted in The Universe and Stuff with tags , , on October 15, 2012 by telescoper

Rolling Boulders…

Posted in Bad Statistics, The Universe and Stuff with tags , , , , , , , , on October 13, 2012 by telescoper

I’m a bit slow to get started this morning, since I didn’t get home until the wee small hours after a trip to the Royal Astronomical Society yesterday, followed by a pleasantly tipsy dinner at the Athenaeum with the RAS Club. Anyhow, one of the highlights of the meeting was a presentation by Prof. Gerald Roberts from Birkbeck on Marsquakes: evidence from rolled boulder populations, Cerberus Fossae, Mars.  The talk was based on a recent paper of his (unfortunately behind a paywall), which is about trying to reconstruct the origin and behaviour of “Marsquakes” using evidence from the trails made by rolling boulders, dislodged by seismic activity or vulcanism.  Here is a sample picture showing the kind of trails he’s using – the resolution is such that one pixel is only 20cm!

There are enough trails to allow a statistical analysis of their distribution in space and in terms of size (which can be inferred from the width of the trail). I had some questions about the analysis, but I haven’t been able to read the paper in detail yet so I won’t comment on that until I’ve done so, but the thing I remember most from the talk were these remarkable pictures of what a rolling boulder can do on Earth. They were taken after the earthquake in Christchurch, New Zealand, in 2011.

A large boulder was dislodged from the top of the hill behind the house in the second picture. It didn’t just roll, but bounced down the slope (see the large furrow in the first picture; similar bouncing trajectories can be seen in the picture from Mars), smashed straight through the house, exited the other side and came to rest on a road. Yikes.