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## The BICEP2 Dust-Up Continues

More on the controversy over the BICEP2 results which claimed back in March to have discovered the B-mode polarisation due to gravitational waves in the very very early Universe. It seems others claim that BICEP2 did not correctly subtract the polarisation signal from dust in our own Milky Way.

The controversy continues to develop over the interpretation of the results from BICEP2, the experiment that detected “B-mode” polarization in the sky, and was hailed as potential evidence of gravitational waves from the early universe, presumably generated during cosmic inflation. [Here’s some background info about the measurement].

Two papers this week (here and here) gave more detailed voice to the opinion that the BICEP2 team may have systematically underestimated the possible impact of polarized dust on their measurement.  These papers raise (but cannot settle) the question as to whether the B-mode polarization seen by BICEP2 might be entirely due to this dust — dust which is found throughout our galaxy, but is rather tenuous in the direction of the sky in which BICEP2 was looking.

I’m not going to drag my readers into the mud of the current discussion, both because it’s very technical and because it’s rather…

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## Update on the GRB in M31

Well, it would seem it was all a false alarm. For one of the best and most detailed explanations of why the false detection happened, check out this link.

So, no spectacular supernova in Messier 31 yet. But we can live in hope.

## Everybody Hurts – R.E.M. (song)

Today I thought I would share this beautiful song by R.E.M. “Everybody Hurts” was released as a single in 1993 and is from their 1992 album “Automatic For the People”. It reached number 7 in the Disunited Kingdom singles charts, and got to number 29 in the US.

The song was composed by all four of the band’s members, although the drummer Bill Berry wrote most of it. Here are the lyrics.

And the night, the night is yours alone
When you’re sure you’ve had enough
Of this life, well hang on

Don’t let yourself go
‘Cause everybody cries
And everybody hurts sometimes

Sometimes everything is wrong
Now it’s time to sing along
When your day is night alone (Hold on, hold on)
If you feel like letting go (Hold on)
If you think you’ve had too much
Of this life, well hang on

Everybody hurts
Everybody hurts
Don’t throw your hand, oh no

If you feel like you’re alone
No, no, no, you are not alone

If you’re on your own in this life
The days and nights are long
When you think you’ve had too much of this life to hang on

Well, everybody hurts sometimes
Everybody cries
Everybody hurts sometimes
And everybody hurts sometimes

So hold on, hold on
Hold on, hold on, hold on, hold on, hold on, hold on
Everybody hurts

Enjoy!

## A gamma ray burst in the Andromeda galaxy?

A few days ago news broke that NASA’s gamma ray satellite called Swift had detected what was possibly a burst of powerful gamma rays coming from the Andromeda galaxy (Messier 31), the closest large galaxy to our Milky Way galaxy.

This is how NBC were covering the story as of Wednesday (28/05/2014)

This story still seems to be in the early stages, so I have not been able to find too much information as of yet, except that it has happened. Further analysis should show whether it was really a gamma ray burst, or a high energy x-ray event. Also, within the next few days, we should be able to detect an optical counterpart to this event, which will enable us to not only determine its precise location but also determine the nature of the object which has caused the burst.

The story as it appears on the Universe Today website

If it is a gamma ray burst then this is tremendously exciting. There has not been a gamma ray burst anywhere like as close to us anytime in the 50-odd years that we’ve had the ability to detect them. Gamma ray bursts are amongst the most energetic phenomena in the Universe, and are thought to be associated with such cataclysmic events such as the explosion of a star (a supernova), the formation of a black hole or the merging of e.g. two neutron stars. I am crossing my fingers that this event is related to a supernova, because if it is it should be close enough to see very easily with the naked eye. However, although I haven’t looked into this, it would seem to me that a supernova would also have led to a huge flux of neutrinos, and to my knowledge no such neutrino flux has been detected, so maybe it isn’t a supernova. We shall have to wait and see.

## The 10 best Bob Dylan songs – no. 9 – “Visions of Johanna” (song)

At number 9 in Rolling Stone Magazine’s 10 best Bob Dylan songs is “Visions of Johanna” from his seminal 1966 album Blonde on Blonde. I blogged about this album and this song here, so I won’t add much here except to re-post the lyrics to this incredible song. You can find the link to this song on Bob Dylan’s official website here, which not only includes the lyrics but also various audio clips including the original studio version and a couple of live versions.

At number 9 in Rolling Stone Magazine’s 10 greatest Bob Dylan songs is “Visions of Johanna”

Ain’t it just like the night to play tricks when you’re tryin’ to be so quiet?
We sit here stranded, though we’re all doin’ our best to deny it
And Louise holds a handful of rain, temptin’ you to defy it
Lights flicker from the opposite loft
In this room the heat pipes just cough
The country music station plays soft
But there’s nothing, really nothing to turn off
Just Louise and her lover so entwined
And these visions of Johanna that conquer my mind

In the empty lot where the ladies play blindman’s bluff with the key chain
And the all-night girls they whisper of escapades out on the “D” train
We can hear the night watchman click his flashlight
Ask himself if it’s him or them that’s really insane
Louise, she’s all right, she’s just near
She’s delicate and seems like the mirror
But she just makes it all too concise and too clear
That Johanna’s not here
The ghost of ’lectricity howls in the bones of her face
Where these visions of Johanna have now taken my place

Now, little boy lost, he takes himself so seriously
He brags of his misery, he likes to live dangerously
And when bringing her name up
He speaks of a farewell kiss to me
He’s sure got a lotta gall to be so useless and all
Muttering small talk at the wall while I’m in the hall
How can I explain?
Oh, it’s so hard to get on
And these visions of Johanna, they kept me up past the dawn

Inside the museums, Infinity goes up on trial
Voices echo this is what salvation must be like after a while
But Mona Lisa musta had the highway blues
You can tell by the way she smiles
See the primitive wallflower freeze
When the jelly-faced women all sneeze
Hear the one with the mustache say, “Jeeze
I can’t find my knees”
Oh, jewels and binoculars hang from the head of the mule
But these visions of Johanna, they make it all seem so cruel

The peddler now speaks to the countess who’s pretending to care for him
Sayin’, “Name me someone that’s not a parasite and I’ll go out and say a prayer for him”
But like Louise always says
“Ya can’t look at much, can ya man?”
As she, herself, prepares for him
And Madonna, she still has not showed
We see this empty cage now corrode
Where her cape of the stage once had flowed
The fiddler, he now steps to the road
He writes ev’rything’s been returned which was owed
On the back of the fish truck that loads
While my conscience explodes
The harmonicas play the skeleton keys and the rain
And these visions of Johanna are now all that remain

I have hunted down this live version of Visions which is from one of Dylan’s concerts in 1966, the tour where he was roundly booed during each performance when he played the second half of his act as an “electric” set, with a backing band, instead of his acoustic folk style that many of his fans had come to hear.

Enjoy!

## Dark Matter Debates

A very interesting summary of a recent conference on our current understanding of dark matter…….

Last week I attended the Eighth Harvard-Smithsonian Conference on Theoretical Astrophysics, entitled “Debates on the Nature of Dark Matter”, which brought together leading figures in astronomy, astrophysics, cosmology and particle physics. Although there wasn’t much that was particularly new, it was a very useful conference for taking stock of where we are. I thought I’d bring you a few selected highlights that particularly caught my eye.

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## National Geographic “Traveler” contest

Last week I stumbled across this wonderful link on the National Geographic website, a travel photography competition. There are dozens and dozens of wonderful photographs here, and I highly recommend following the link and spending a few tens of minutes taking a good browse, but here are (only) some of my favourites.

A mother’s smile, Namibia

Enjoy!

## Divergence of a vector field

Quite a while ago I posted a blog about the statue in Edinburgh to the Scottish mathematical physicist James Clerk Maxwell. On this statue are his famous equations, Maxwell’s equations, which describe electromagnetism. I also mentioned these equations in my blog about James Clerk Maxwell in my list of the “ten best physicists” (here and here).

Let me remind you of the four equations we now know as Maxwell’s equations. They succinctly describe electromagnetism, and are the equivalent in electromagnetic theory to Newton’s laws of motion and his three equations of motion in classical mechanics.

$\boxed{ \begin{array}{lcll} \nabla \cdot \vec{D} & = & \rho & (1) \\ & & & \\ \nabla \cdot \vec{B} & = & 0 & (2) \\ & & & \\ \nabla \times \vec{E} & = & - \frac{\partial \vec{B}}{\partial t} & (3) \\ & & & \\ \nabla \times \vec{H} & = & - \frac{\partial \vec{D}}{\partial t} + \vec{J} & (4) \end{array} }$

Here I have written equation (1), also known as Gauss’s equation, in terms of the electric displacement field $\vec{D}$. This is related to the electric field $\vec{E}$ in a vacuum via its definition, $\vec{D} = \epsilon_{0} \vec{E}$, where $\epsilon_{0}$ is the permittivity of free space [in the case of the displacement field when it is not in a vacuum, the equation becomes $\vec{D} = \epsilon_{0} \vec{E} + \vec{P}$ where $\vec{P}$ is the density of the induced and permanent electric dipole moment, also known as the polarisation density]. So we can also write Maxwell’s first equation as

$\nabla \cdot \vec{E} = \frac{ \rho }{ \epsilon{0} }$

In this previous blog I discussed the vector differential operator, often known as “del” and given the symbol $\nabla$ in mathematics. Today I thought I would discuss a key concepts in vector field theory, namely the “divergence” of a vector field. This crops up a lot in physics and engineering, and going back to Maxwell’s equations, the first two are the divergence of the electric and magnetic fields $\vec{E} \text{ and } \vec{B}$ respectively.

## The divergence $\nabla \cdot$

The vector operator, $\nabla \cdot \vec{F}$ is also known as the divergence (or div) of the vector field. Mathematically, it is

$\nabla \cdot \vec{F} = \frac{\partial F_{x}}{\partial x} + \frac{\partial F_{y}}{\partial y} + \frac{\partial F_{z}}{\partial z}$

The resulting quantity is a scalar, as the so called dot product produces a scalar (see my blog on the scalar product of two vectors here).

What the divergence of a vector field is actually measuring is how much of the vector field flows outwards from a given point. This is best illustrated by a few diagrams. First I will show a uniform vector field, then secondly a vector field with no divergence, even though it is not a uniform vector field.

A uniform vector field, each vector has the same direction and size.

A vector field with no divergence. This could be, for example, a vector field representing the flow of cars either side of a central reservation (middle row), with the length of the vectors showing the cars are going faster further from the central line.

In these last two diagrams I show two examples of vector fields with divergence. The first shows positive divergence (a source), the second shows negative divergence (a sink).

A vector field with divergence. This example shows positive divergence, or a “source” of flux.

This shows negative divergence, or a “sink” of flux.

In a future blog I will explain how the divergence of an electric field is related to the charges enclosed within a surface surrounding the charges (Gauss’s law or the first of Maxwell’s equations).

## “Oliver’s Army” – Elvis Costello and the Attractions (song)

Today I thought I’d share this great song “Oliver’s Army” by Elvis Costello and the Attractions. It was released in February 1979 and got to number 2 in the Disunited Kingdom singles charts.

It has been suggested that the title refers to Oliver Cromwell, whose “new model army” wreaked terror on much of the British Isles, in particular Ireland.

Don’t start me talking
I could talk all night
My mind goes sleepwalking
While I’m putting the world to right
Called careers information
Have you got yourself an occupation?

[Chorus:]
Oliver’s army is here to stay
Oliver’s army are on their way
And I would rather be anywhere else
But here today

There was a checkpoint Charlie
He didn’t crack a smile
But it’s no laughing party
When you’ve been on the murder mile

Only takes one itchy trigger
One more widow, one less white nigger

[Chorus]

Hong Kong is up for grabs
London is full of Arabs
We could be in Palestine
Overrun by a Chinese line
With the boys from the Mersey and the Thames and the Tyne

But there’s no danger
It’s a professional career
Though it could be arranged
With just a word in Mr. Churchill’s ear

If you’re out of luck or out of work
We could send you to Johannesburg

[Chorus]

There’s recently been a bit of controversy over the use of the “n-word” in this song, with the BBC censoring it. But, if you read the words carefully you will realise that this is an anti-war and <anti-colonialism song, so others argue that the use of the “n-word” is justified in this context, which is that it is apparently a pejorative term that the British army used for the Irish in Northern Ireland.

Which is your favourite Elvis Costello song?

## Will BICEP2 Lose Some of Its Muscle?

Another excellent discussion of the skepticism over the BICEP2 results. As Matt correctly states in the penultimate paragraph, what we are seeing here is the scientific process in action. A discovery is always treated with a certain amount of disbelief by the scientific community, and the more spectacular the discovery the more this is the case. BICEP2’s result is now being analysed, scrutinised and picked apart by cosmologists around the World, and it will not be treated as correct until other experiments confirm the result, and if they don’t or if a flaw is found in the BICEP2’s analysis, then the result will be treated as a false detection.

A scientific controversy has been brewing concerning the results of BICEP2, the experiment that measured polarized microwaves coming from a patch of the sky, and whose measurement has been widely interpreted as a discovery of gravitational waves, probably from cosmic inflation. (Here’s my post about the discovery, here’s some background so you can understand it more easily. Here are some of my articles about the early universe.)  On the day of the announcement, some elements of the media hailed it as a great discovery without reminding readers of something very important: it’s provisional!

From the very beginning of the BICEP2 story, I’ve been reminding you (here and here) that it is very common for claims of great scientific discoveries to disappear after further scrutiny, and that a declaration of victory by the scientific community comes much more slowly and deliberately than it often does…

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