Happy Birthday, Harry Nyquist!

Posted in History, The Universe and Stuff with tags , on February 7, 2014 by telescoper

Harry_NyquistThis morning I learned via Twitter that today is the 125th anniversary of the birth of Harry Nyquist, a physicist and electrical engineer, who was a prolific inventor who made fundamental theoretical and practical contributions to the field of telecommunications. He also gave his name to the Nyquist frequency and the Nyquist sampling theorem, now usually known as the Nyquist-Shannon sampling theorem.

Harry Nyquist (left) was born on February  7, 1889, in Nilsby, Sweden but moved to the United States in 1907. In 1917, after earning a Ph.D. in physics from Yale University, he joined the American Telephone and Telegraph Company (AT&T). There he remained until his retirement in 1954, working in the research department and then (from 1934) at Bell Laboratories.  Apparently he didn’t have a beard, but he seems to have overcome this obstacle and had an illustrious career in research.

In my opinion, Harry Nyquist’s achievements are not sufficiently appreciated either by physicists or by the wider world, so here’s a quick summary of some of his greatest hits:

Some of Nyquist’s best-known work was done in the 1920s and was inspired by telegraph communication problems of the time. Because of the elegance and generality of his writings, much of it continues to be cited and used. For example, his 1928 paper Certain Topics in Telegraph Transmission Theory refined his earlier results and established the principles of sampling continuous signals to convert them to digital signals. The Nyquist sampling theorem showed that the sampling rate must be at least twice the highest frequency present in the sample in order to reconstruct the original signal. These two papers by Nyquist, along with one by R.V.L. Hartley, are cited in the first paragraph of Claude Shannon’s classic essay The Mathematical Theory of Communication (1948), where their seminal role in the development of information theory is acknowledged.

In 1927 Nyquist provided a mathematical explanation of the unexpectedly strong thermal noise studied by J.B. Johnson. The understanding of noise is of critical importance for communications systems. Thermal noise is sometimes called Johnson noise or Nyquist noise because of their pioneering work in this field.

In 1932 Nyquist discovered how to determine when negative feedback amplifiers are stable. His criterion, generally called the Nyquist stability theorem, is of great practical importance. During World War II it helped control artillery employing electromechanical feedback systems.

I think that demonstrates the tremendous debt the modern world of telecommunications owes to Harry Nyquist, and why we should remember him on his 125th birthday..

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Mad about the Boy

Posted in LGBTQ+, Music with tags , , on February 6, 2014 by telescoper

I came across this a while ago and thought I’d save it for a rainy day. Today is very rainy indeed so here it is. Mad about the Boy was written by Noel Coward and published in 1932. It’s a song about an infatuation with a movie star  and has generally been performed by female singers, although it was apparently inspired by Coward’s own crush on Douglas Fairbanks Jnr (which wasn’t reciprocated). The song became popular again in 1992 when a version recorded by Dinah Washington was used in a famous Levi commercial, but I love this wonderfully world-weary performance by Greta Keller.

 

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Was it right to drop Pietersen?

Posted in Cricket with tags , , on February 5, 2014 by telescoper

Big sporting news this morning was the decision by a panel representing the  England and Wales Cricket Board to part company with Kevin Pietersen.   In his Test career Pietersen has scored 8,181 runs at an average of 47 in 104 Tests, which is pretty outstanding – certainly compared with other current England batsmen. And at 33 he’s probably still got a few years of international cricket in him. Can England really afford to cast him aside just because some of his team-mates find him a bit difficult?

I’m perfectly well aware that Pietersen is not the kind of player who always puts the team first, and being such a maverick he must be a very frustrating player to captain, but he is clearly also a prodigiously talented batsmen. It’s true that he didn’t play well in Australia, but then who did (other than Ben Stokes)? In fact Pietersen averaged better with the bat than his Captain, so you could argue that it’s Alastair Cook who should be dropped if the problem is between the two of them (as some have suggested).

And then there’s the fact that – love them or hate them – it’s players like KP who are the crowd-pullers. It’s never just been about the ability to play the game. People like to see larger-than-life characters in sport.

Anyway, I know that opinions differ  on this issue so I thought I’d try a quite poll:

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Did Hawking Say “There Are No Black Holes”?

Posted in Astrohype, The Universe and Stuff with tags , , , on February 5, 2014 by telescoper

Last week there was a rather tedious flurry of media activity about Stephen Hawking’s alleged claim that there are no black holes after all. Here’s a nice blog post explaining what Hawking actually said. Also, check out the link at the start of this article to a very nice layperson’s guide to the Black Hole Information Paradox.

Matt Strassler's avatarOf Particular Significance

Media absurdity has reached new levels of darkness with the announcement that Stephen Hawking has a new theory in which black holes do not exist after all.

No, he doesn’t.

[Note added: click here for my new introduction to the black hole information paradox.]

First, Hawking does not have a new theory… at least not one he’s presented. You can look at his paper here — two pages (pdf), a short commentary that he gave to experts in August 2013 and wrote up as a little document — and you can see it has no equations at all. That means it doesn’t qualify as a theory. “Theory”, in physics, means: a set of equations that can be used to make predictions for physical processes in a real or imaginary world. When we talk about Einstein’s theory of relativity, we’re talking about equations. Compare just the look and…

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A Matter of Life and Death

Posted in Film, Poetry with tags , , , , on February 4, 2014 by telescoper

One for the file marked “they don’t make films like this any more”. Here is a clip from very near the beginning of the extraordinarily imaginative romantic fantasy A Matter of Life and Death. It’s not quite the opening sequence as titled, though: there’s an astronomically themed preamble before the sequence shown in the clip.

Directed by Michael Powell and Emeric Pressberger and released in 1946, A Matter of Life and Death has remained in most film critics’ lists of top British movies for almost seventy years. If you really want to know why then you’ll have to watch the whole film, but this is a memorable opening to a film if ever there was one.

Incidentally, the splendid poem by Sir Walter Raleigh from which Peter Carter character (played by David Niven) quotes is called The Passionate Man’s Pilgrimage. Here it is in full:


GIVE me my scallop-shell of quiet,
My staff of faith to walk upon,
My scrip of joy, immortal diet,
My bottle of salvation,
My gown of glory, hope’s true gage;
And thus I’ll take my pilgrimage.

Blood must be my body’s balmer,
No other balm will there be given;
Whilst my soul, like a quiet palmer,
Travelleth towards the land of heaven;
Over the silver mountains,
Where spring the nectar fountains:
There will I kiss
The bowl of bliss;
And drink mine everlasting fill
Upon every milken hill:
My soul will be a-dry before;
But after, it will thirst no more.
Then by that happy blestful day,
More peaceful pilgrims I shall see,
That have cast off their rags of clay,
And walk apparelled fresh like me.
I’ll take them first
To quench their thirst,
And taste of nectar suckets,
At those clear wells
Where sweetness dwells
Drawn up by saints in crystal buckets.

And when our bottles and all we
Are filled with immortality,
Then the blessed paths we’ll travel,
Strowed with rubies thick as gravel;
Ceilings of diamonds, sapphire floors,
High walls of coral, and pearly bowers.
From thence to heavens’s bribeless hall,
Where no corrupted voices brawl;
No conscience molten into gold,
No forged accuser bought or sold,
No cause deferred, nor vain-spent journey ;
For there Christ is the King’s Attorney,
Who pleads for all without degrees,
And he hath angels, but no fees.
And when the grand twelve-million jury
Of our sins, with direful fury,
‘Gainst our souls black verdicts give,
Christ pleads his death, and then we live.

Be thou my speaker, taintless pleader,
Unblotted lawyer, true proceeder!
Thou giv’st salvation even for alms ;
Not with a bribèd lawyer’s palms.
And this is my eternal plea
To him that made heaven, earth, and sea,
That, since my flesh must die so soon,
And want a head to dine next noon,
Just at the stroke, when my veins start and spread,
Set on my soul an everlasting head.
Then am I ready, like a palmer fit;
To tread those blest paths which before I writ.

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Big Trouble with Big G

Posted in The Universe and Stuff with tags , , on February 4, 2014 by telescoper

An Antonymous email correspondent this morning drew my attention to an interesting article in the latest Physics World about the trials and tribulations of groups of physicists trying to measure Newton’s Gravitational Constant,  G. This is probably the first physical constant that most of us encounter when we’re learning the subject so it might seem strange that it’s the one which is known to the lowest accuracy. That’s not for want of trying to make the measurements more precise, just that gravity is such a very weak force that it’s very difficult to eliminate systematic effects down to the necessary level.

Just how difficult it is to measure Big G is demonstrated by the following graphic which shows the latest measurements:

Big_G

Here’s the caption, so you can identify the various groups responsible for the various measurements:

Disagreeing over “big G” This chart shows wildly differing values of the gravitational constant, G, as measured by various high-profile research groups (blue). The values do not agree even within their error bars. Also shown are two values of G adopted by the Committee on Data for Science and Technology (CODATA) as international standards (red). The groups are based at the National Institute of Standards and Technology (NIST), the University of Washington (UWASH), the International Bureau of Weights and Measures (BIPM), the Measurement Standards Laboratory of New Zealand (MSL), the University of Zurich (UZURICH), the Huazhong University of Science and Technology (HUST) and the Joint Institute for Astrophysics (JILA).

Clearly there’s quite a lot of disagreement between recent results, with some a long way outside each other’s error bars. They can’t all be right, but who’s most likely to be wrong? Answers on a postcard.

I’m by no means an expert on experimental gravity so I won’t attempt to suggest who is right and who is wrong. What I will say is that although this kind of research is clearly extremely important it is clearly also fiendishly difficult. I’m not really surprised that the pieces of the puzzle haven’t fallen into place yet. The dedicated teams who have been tackling this problem for many decades deserve the deep admiration as well as the continued support of the physics community. Theoretical physics is generally perceived to be more glamorous and exciting than its experimental counterpart, but the subject as a whole is nothing without its empirical foundations. That said, I’m glad it’s not my job to measure Big G. I have neither the practical skill nor the patience to cope with so many frustrations!

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The super-compressible Cosmic Microwave Background

Posted in The Universe and Stuff with tags , , on February 3, 2014 by telescoper

I just came across this blog post, one of a series on cosmology from the African Institute for Mathematical Sciences, which is in Muizenberg near Cape Town, South Africa. I thought I’d reblog it, partly because it’s on a topic I often discuss in talks and partly because I wanted to draw your attention the site and the other interesting posts on it.

In this article Bruce Bassett explains just how much of the information we get from measurements of the Cosmic Microwave Background can be squeezed into precise estimates of just a few parameters. The only point I would add is that this does assume at the outset that all relevant information is contained within the angular power spectrum; that’s not necessarily the case, but we don’t have any compelling evidence that it’s a wrong assumption for the CMB; see here for a previous discussion of this.

Bruce Bassett's avatarCosmology at AIMS

One of the most striking features about the Cosmic Microwave Background (CMB) is that it is incredibly compressible from an information content point of view. The Planck satellite produced maps with of order a billion pixels whose information could be compressed almost perfectly into a power spectrum of order one thousand real numbers.

This already is a massive compression. But in addition, most of this information can be compressed further into just six of the parameters of the standard model, yielding a total compression of about one billion to one. This is both remarkable and annoying because we want to be surprised and find things that we can’t explain. And if there are things we can’t explain we want to have clear signals data about them, not just vague hints of their existence.

Anyway, to illustrate just how efficient the compression is, I took the binned WMAP 9 TT power spectrum…

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Irony 101

Posted in Uncategorized with tags , on February 3, 2014 by telescoper

birmingham_image

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Scott Tremaine on “Astrohype”

Posted in Astrohype, The Universe and Stuff with tags on February 2, 2014 by telescoper

I recently came across a post by distinguished astrophysicist Scott Tremaine who works at the Institute for Advanced Study in Princeton. The piece is entitled “Overblown Statements in Press Releases Undermine Science”, something that exercised me so much that I invented the category Astrohype so I could post particularly egregious examples on this blog.

Soctt Tremaine’s piece is on the American Astronomical Society website, but I’m reposting the text here to give it wider circulation as I think it makes some very important points that we’d all do well to heed. And of course in the interest of full disclosure I should point out that I am a theoretical astrophysicist myself, so may be a bit biased…

–o–

In a recent column, AAS President David Helfand argued correctly that negative public messages about subfields within our own discipline, or even about other disciplines — “shooting inward at each other” — damage all of us.

Consider, then, the following public messages:

  • from a major research university, a press release titled “Astronomers Discover Planet that Shouldn’t Be There,”
  • from the European Southern Observatory, a press release titled “Turning Planetary Theory Upside Down,”
  • from the National Radio Astronomy Observatory, a press release containing the quote, “Much of what we thought we understood about the physics of pulsars and neutron stars may be wrong,”
  • from the Space Telescope Science Institute, a press release stating, “New observations from NASA’s Hubble Space Telescope challenge 30 years of scientific theory about quasars,” and
  • from a respected news organization, an interview with a prominent exoplanet researcher containing the quote, “Theory has struck out.”

The point is not whether these messages provide accurate characterizations of the state of theoretical understanding in their respective subject areas (though in most cases they do not). The point is that by belittling and trivializing the efforts of theoretical astrophysicists — who try to understand extremely complex processes in exotic environments, with limited clues from observations — they damage the public perception of the entire astronomy community. As just one example, statements from press releases such as those above are often repeated on creationist websites, where they carry extra weight because they have the imprimatur of NASA or a major observatory or university.

Advances in observational astronomy are spectacular enough to appeal to the public on their own merits, without “shooting inward” at efforts to understand these observations. Astronomers and press officers can provide a more realistic picture of the synergy between observation and theory, and in so doing would improve the public perception of astronomy research in particular and of the scientific enterprise more generally.

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Mirror in February

Posted in Poetry with tags , , , on February 2, 2014 by telescoper

The day dawns with scent of must and rain,
Of opened soil, dark trees, dry bedroom air.
Under the fading lamp, half dressed – my brain
Idling on some compulsive fantasy-
I towel my shaven jaw and stop, and stare,
Riveted by a dark exhausted eye,
A dry downturning mouth.

It seems again that it is time to learn,
In this untiring, crumbling place of growth
To which, for the time being, I return.
Now plainly in the mirror of my soul
I read that I have looked my last on youth
And little more; for they are not made whole
That reach the age of Christ.

Below my window the awakening trees,
Hacked clean for better bearing, stand defaced
Suffering their brute necessities,
And how should the flesh not quail that span for span
Is mutilated more? In slow distaste
I fold my towel with what grace I can,
Not young and not renewable, but man.

by Thomas Kinsella (b. 1928)

 

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