Archive for May, 2017

Summertime – Albert Ayler

Posted in Jazz with tags , , on May 26, 2017 by telescoper

George Gershwin’s beautiful song Summertime has been recorded countless times in countless ways by countless artists, but if you’re expecting it to be performed as a restful lullaby, as it is normally played, you’ll probably be shocked. This version is a heartbreaking expression of pain and anguish performed by the great Albert Ayler, and it was recorded in Copenhagen in 1963.

P.S. The painting shown in the video is by Matisse….

The Sundial of Trevithick 

Posted in The Universe and Stuff with tags , , on May 26, 2017 by telescoper

Since it’s a lovely sunny day in Cardiff – and already very warm – I thought I’d step outside the office of the Cardiff University Data Innovation Research Institute which is situated in the Trevithick Building and take a picture of our new sundial:

This flat sundial was installed by a company called Border Sundials and is designed very carefully to be as accurate as possible for the particular wall on which it is place. It’s also corrected for longitude.

However, I took the photograph at about 10.30am, and you’ll notice that it’s showing about 9.30. That’s because it hasn’t been corrected for British Summer Time so it’s offset by an hour. Moreover, a sundial always shows the local solar time rather than mean time which is shown on clocks. These differ because of (a) the inclination of the Earth’s orbit around the Sun relative to the equator and (b) the eccentricity of the Earth’s orbit around the Sun, which means that it does not move at a constant speed. The difference between mean time and solar time can be reconciled using the equation of time. The maximum correction is about 15 minutes, which is large enough to be seen on a sundial of this type. Often a graph of the equation of time is placed next to a sundial so one can do the correct oneself, but for some reason there isn’t one here.

The sundial adds quite a lot of interest to what otherwise is a featureless brick wall and we often notice people looking at it outside our office.

The Art of Jupiter

Posted in Art, The Universe and Stuff with tags , on May 25, 2017 by telescoper

This amazing closeup image is of the North polar region of Jupiter. It was taken by NASA’s Juno spacecraft. Here’s a wider view:


I think it will take scientists quite some time to figure out what is going on in all those complex vortex structures!

In the meantime, though, I think these picture and the others that have been released can be enjoyed as a work of art! As a matter of fact reminds me of van Gogh’s Starry Night...

Yellow Stars, Red Stars and Bayesian Inference

Posted in Bad Statistics, The Universe and Stuff with tags , , , , , , on May 25, 2017 by telescoper

I came across a paper on the arXiv yesterday with the title `Why do we find ourselves around a yellow star instead of a red star?’.  Here’s the abstract:

M-dwarf stars are more abundant than G-dwarf stars, so our position as observers on a planet orbiting a G-dwarf raises questions about the suitability of other stellar types for supporting life. If we consider ourselves as typical, in the anthropic sense that our environment is probably a typical one for conscious observers, then we are led to the conclusion that planets orbiting in the habitable zone of G-dwarf stars should be the best place for conscious life to develop. But such a conclusion neglects the possibility that K-dwarfs or M-dwarfs could provide more numerous sites for life to develop, both now and in the future. In this paper we analyze this problem through Bayesian inference to demonstrate that our occurrence around a G-dwarf might be a slight statistical anomaly, but only the sort of chance event that we expect to occur regularly. Even if M-dwarfs provide more numerous habitable planets today and in the future, we still expect mid G- to early K-dwarfs stars to be the most likely place for observers like ourselves. This suggests that observers with similar cognitive capabilities as us are most likely to be found at the present time and place, rather than in the future or around much smaller stars.

Athough astrobiology is not really my province,  I was intrigued enough to read on, until I came to the following paragraph in which the authors attempt to explain how Bayesian Inference works:

We approach this problem through the framework of Bayesian inference. As an example, consider a fair coin that is tossed three times in a row. Suppose that all three tosses turn up Heads. Can we conclude from this experiment that the coin must be weighted? In fact, we can still maintain our hypothesis that the coin is fair because the chances of getting three Heads in a row is 1/8. Many events with a probability of 1/8 occur every day, and so we should not be concerned about an event like this indicating that our initial assumptions are flawed. However, if we were to flip the same coin 70 times in a row with all 70 turning up Heads, we would readily conclude that the experiment is fixed. This is because the probability of flipping 70 Heads in a row is about 10-22, which is an exceedingly unlikely event that has probably never happened in the history of the universe. This
informal description of Bayesian inference provides a way to assess the probability of a hypothesis in light of new evidence.

Obviously I agree with the statement right at the end that `Bayesian inference provides a way to assess the probability of a hypothesis in light of new evidence’. That’s certainly what Bayesian inference does, but this `informal description’ is really a frequentist rather than a Bayesian argument, in that it only mentions the probability of given outcomes not the probability of different hypotheses…

Anyway, I was so unconvinced by this description’ that I stopped reading at that point and went and did something else. Since I didn’t finish the paper I won’t comment on the conclusions, although I am more than usually sceptical. You might disagree of course, so read the paper yourself and form your own opinion! For me, it goes in the file marked Bad Statistics!

The Beautiful Sun, by William McGonagall

Posted in Poetry with tags , , , on May 24, 2017 by telescoper

Beautiful Sun! with thy golden rays,
To God, the wise Creator, be all praise;
For thou nourisheth all the creation,
Wherever there is found to be animation.

Without thy heat we could not live,
Then praise to God we ought to give;
For thou makest the fruits and provisions to grow,
To nourish all creatures on earth below.

Thou makest the hearts of the old feel glad,
Likewise the young child and the lad,
And the face of Nature to look green and gay,
And the little children to sport and play.

Thou also givest light unto the Moon,
Which certainly is a very great boon
To all God’s creatures here below,
Throughout the world where’er they go.

How beautiful thou look’st on a summer morn,
When thou sheddest thy effulgence among the yellow corn,
Also upon lake, and river, and the mountain tops,
Whilst thou leavest behind the most lovely dewdrops!

How beautiful thou seem’st in the firmament above,
As I gaze upon thee, my heart fills with love
To God, the great Creator, Who has placed thee there,
Who watches all His creatures with an eye of care!

Thou makest the birds to sing on the tree,
Also by meadow, mountain, and lea;
And the lark high poised up in air,
Carolling its little song with its heart free from care.

Thou makest the heart of the shepherd feel gay
As he watches the little lambkins at their innocent play;
While he tends them on the hillside all day,
Taking care that none of them shall go astray.

Thou cheerest the weary traveller while on his way
During the livelong summer day,
As he admires the beautiful scenery while passing along,
And singing to himself a stave of a song.

Thou cheerest the tourist while amongst the Highland hills,
As he views their beautiful sparkling rills
Glittering like diamonds by the golden rays,
While the hills seem to offer up to God their praise.

While the bee from flower to flower does roam
To gather honey, and carry it home;
While it hums its little song in the beautiful sunshine,
And seemingly to thank the Creator divine —

For the honey it hath gathered during the day,
In the merry month of May,
When the flowers are in full bloom,
Also the sweet honeysuckle and the broom.

How beautiful thy appearance while setting in the west,
Whilst encircled with red and azure, ’tis then thou look’st best!
Then let us all thank God for thy golden light
In our prayers every morning and night!

by Wiliam Topaz McGonagall (1825-1902)

 

Wave Mechanics and Large-scale Structure

Posted in Books, Talks and Reviews, The Universe and Stuff with tags , , , on May 24, 2017 by telescoper

I thought I’d share the slides I used for the short talk I gave last Thursday at the Osservatorio Astronomico di Bologna, on the topic of Wave Mechanics and Large-scale Structure. I’ve posted about the general idea underpinning this workhere, and here are some links to references with more details of the cosmological setting, including a couple of papers by myself and Chris Short on some of whose old slides I based the talk.

http://adsabs.harvard.edu/abs/1993ApJ…416L..71W
http://adsabs.harvard.edu/abs/1997PhRvD..55.5997W
http://adsabs.harvard.edu/abs/2002MNRAS.330..421C
http://adsabs.harvard.edu/abs/2003MNRAS.342..176C
http://adsabs.harvard.edu/abs/2006JCAP…12..012S
http://adsabs.harvard.edu/abs/2006JCAP…12..016S
http://adsabs.harvard.edu/abs/2010MNRAS.402.2491J

I had a few problems with the movies during the actual talk, and they probably don’t work in this embedded version. There are a few formatting errors in the slideshare version too, but hopefully you can figure out what’s going on!

The Shaw Prize goes to Simon White

Posted in The Universe and Stuff with tags , , , on May 23, 2017 by telescoper

MPI Astro Physik – Prof .Simon White

To happier things. I was delighted to see just now that Simon White (above) has won this year’s Shaw Prize for Astronomy. The prize was awarded..

for his contributions to understanding structure formation in the Universe. With powerful numerical simulations he has shown how small density fluctuations in the early Universe develop into galaxies and other nonlinear structures, strongly supporting a cosmology with a flat geometry, and dominated by dark matter and a cosmological constant.

The citation seems a bit strange to me because Simon’s contributions to astronomy and cosmology are many and varied, but it’s in any case an extremely well-justified award. In a field filled with very many very clever people, Simon is definitely one of the cleverest!

The announcement of this awarded reminded me that I was one of the co-authors of a paper with Simon White, but looking it up I realized that was way back in 1993! Where does the time go?

Anyway, hearty congratulations to Simon! I think it’s his round…