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## A new window on the Universe

Last Thursday (11 February 2016) the very exciting news broke that scientists had directly detected gravitational waves for the very first time. I briefly blogged about it here, but now that I am back from giving talks in South America I have a little more time (and a much better internet connection) to write a more complete blogpost about it.

This direct detection, hopefully the first of many, was made by two international teams (including colleagues of mine at Cardiff University) using the Laser Interferometer Gravitational-Wave Observatory (LIGO), which is in the United States. The link to the actual paper, which appears in Physical Review Letters, is here. As you can see from the abstract of the paper (see below), the signal was detected by both LIGO detectors simultaneously, which is a very important point as it strongly suggests that the detection is real.

The abstract of the paper by Abbott et al. announcing the first ever detection of gravitational waves (from Physical Review Letters)

If you read the last sentence of the abstract, you will notice that it states that not only is this the first ever direct detection of gravitational waves, but is also the first ever observation of two black holes merging. This illustrates nicely that being able to detect gravitational waves opens up a whole new way of learning about the Universe; so this detection marks a significant step forward in our capabilities to “observe” our Universe. In my mind, it is as significant as William Herschel’s accidental discovery of infrared light in 1800, which was the first ever detection of radiation outside of the visible part of the spectrum.

## What are gravitational waves?

Gravitational waves were predicted by Albert Einstein in 1916, as a natural consequence of his new theory of gravity – general relativity. Unlike Newton’s theory of gravity, which argued that gravity acts instantaneously, Einstein’s general theory of relativity predicts that gravity is due to a bending of spacetime. The bending (warping) is produced by masses (e.g. the Sun, black holes, galaxies, clusters of galaxies); and changes in any gravitational field travel through space at the speed of light from the place of change as ripples , distorting spacetime as they spread outwards.

Although predicted one hundred years ago by Einstein’s theory, up until now there has only been indirect evidence for gravitational waves. The best example of indirect evidence is from observations of pulsars, spinning neutron stars. Back in 1974 it was noticed by Russell Hulse and Joseph Taylor that the period of a particular pulsar, PSR B1913+16 (which happens to be one of a pair of orbiting neutron stars) was slowing down. It was argued that this was due to the neutron stars spiralling towards each other and losing energy, with this energy being taken away in the form of gravitational waves. The calculations matched, the loss of energy being measured agreed with the predicted energy which should be carried away as gravitational waves. Hulse and Taylor received the 1993 Nobel Prize in Physics for this work.

Since then, there have been other similar observations, all agreeing with the predictions of general relativity; but until now there had been no direct observations of the elusive gravitational waves.

## ‘Seeing’ back to the beginning of time

The cosmic microwave background, the subject of my recent book, comes about from when the Universe became transparent.

My book “The Cosmic Microwave Background – how it changed our understanding of the Universe” is published by Springer and can be found by following this link.

But, when I say ‘transparent’, I mean transparent to electromagnetic (EM) radiation. Gravitational waves are not EM radiation, so the opacity of the Universe before about 400,000 years into its existence does not apply to gravitational waves. These should be detectable back to the very tiniest fraction of the first second, a time when gravity and the other three forces separated. The ‘surface of last scattering’ (from where the CMB comes), effectively acts as a wall to EM radiation,  but it is transparent to gravitational waves.

We have a very long way to go before we are able to detect gravitational waves directly from anything but nearby objects. But, the potential is there at some point in the future to be able to use gravitational waves to probe back to the beginning of time. That is a truly exciting possibility!

## Jupiter at opposition

A few days ago I was contacted by the Western Mail to give some information about the upcoming opposition of Jupiter, which will happen on March 8. The article to which I contributed can be found here, but I thought I would add some more detail here in my blog to the few brief sentences I was asked to contribute to the Western Mail article.

When we say that a planet is at opposition, what we mean is that it is in the opposite direction in the sky to where the Sun is, as shown in the figure below. In fact, the Sun-Earth-planet make a straight line when a planet is at opposition, with the Earth being the middle object in the straight line. The other straight line configuration formed by the Sun-Earth-planet is when the planet lies beyond the Sun with the Sun in the middle. We call this configuration conjunction.

Only planets further from the Sun can be at opposition; Mercury and Venus can only ever be at conjunction, either on our side of the Sun (inferior conjunction) or on the other side (superior conjunction).

Only planets outside of the Earth’s orbit (superior planets) can be at opposition, and this is usually the best time to see them

The average distance from the Earth to the Sun, just a little under 150 million kilometres, is called the Astronomical Unit (AU). It is a convenient unit to use when discussing the Solar System. On this scale Jupiter, which is roughly five times further away from the Sun that the Earth, is 5 AUs.

It takes Jupiter roughly 12 years to orbit the Sun. This means that it appears to move through one zodiacal constellation each year, as there are 12 zodiacal constellations.  This year it is in Leo, last year (2015) it was in Cancer, and next year (2017) it will be in Virgo. This also means that, whilst it is currently visible in our winter and spring skies, in 6 years’ time it will become more of a summer object and disappear from our winter skies.

Although Leo is a fairly easy to find constellation (much easier than Cancer), Jupiter outshines all the stars in Leo. In fact, even when at its furthest from Earth, Jupiter outshines all of the stars in the sky, even Sirius. The only point-like object in the sky which can appear brighter than Jupiter is Venus, which is currently in the evening sky towards the west and setting within a few hours of sunset. You will never seen Venus in the middle of the night, whereas Jupiter is currently visible nearly all night.

How Jupiter should appear through a small telescope. The Galilean moons (Io, Europa, Ganymede and Callisto) should be clearly visible, and if you are lucky you may also see the bands and the great red spot

## The varying brightness of Jupiter

Because oppositions happen when Earth is passing Jupiter, and in a year Jupiter has moved about one twelfth of its path around the Sun, each opposition of Jupiter is spaced by about 13 months. The opposition in 2015 was on February 6 and in 2017 it will be on April 7. When Jupiter is at opposition, it is about 4 AUs from Earth, whereas when it is at conjunction it is about 6 AUs from Earth.

Although this is 50% further away, it means that Jupiter’s brightness in the sky does not vary as much as Mars, which varies a huge amount between when it is at opposition and when it is near conjunction (I say ‘near’ as you cannot see a planet when it is at conjunction). When at opposition, Jupiter has a magnitude of about -2.5 (it doesn’t vary much as both Earth and Jupiter have quite circular orbits); when it is near conjunction its magnitude is about -1.7. This is a luminosity difference of $10^{0.4(2.5-1.7)} = 10^{0.32} = 2.1$, so just over twice as bright when at opposition compared to when it is near conjunction.

Compare this to Mars, which brightens considerably when at opposition. This is because Mars is much closer to Earth, with an orbit which is roughly 1.5 AUs. If it were a circular orbit (which it is not, Mars has a more elliptical orbit than either the Earth or Jupiter), this would mean that at opposition it would be about 0.5 AUs from Earth, but when near conjunction it is about 2.5 AUs, so about 5 times further away! If you move something 5 times further away its brightness goes down by a factor of $5^{2}=25$! This is why the brightness of Mars varies so much in different parts of its orbit.

## When can I see Jupiter in March?

When a planet is at opposition not only is it at its brightest, but it is also in the night-time sky essentially all night. It transits the local meridian around midnight, and when an object transits the meridian it is at its highest point in the sky. But, even a month or two before opposition or a month or two after opposition, Jupiter is in the sky for most of the night. It is easy to see in the late evening sky at the moment, and as we move past March and into April it will rise earlier and earlier and so be easily visible soon after sunset. In May it will already be up quite high by the time the Sun sets.

Jupiter is well worth seeing, even without a telescope or binoculars. Remember, if you are not sure whether you are looking at Jupiter just ask yourself is it the brightest point-like object in the sky. If it is, and it is not over towards the west just after sunset, then you are almost certainly looking at Jupiter. Compare its light to the stars near it; you will notice that Jupiter’s light is steady whereas the stars near it usually twinkle. Stars twinkle, planets don’t.

If you have access to either a small telescope or binoculars you should be able to see the Galilean moons. These were first seen by Galileo in January 1610, and provided the first piece of evidence that not everything orbited the Earth. Io, the closest of the four to Jupiter, takes less than two days to orbit its parent planet, and so even in a few hours you can see a shift in its position. This never ceases to amaze and excite me, even though I have seen it dozens of times. If you are really lucky, you may make out the bands of Jupiter and even its great red spot. I have seen the great red spot a few times. It is a truly memorable sight to see it with your own eyes rather than a photograph in a book or on the web.

## The 100 best Beatles songs – number 28 – ‘Here Comes the Sun’

At number 28 in Rolling Stone Magazine’s list of the 100 greatest Beatles songs is George Harrison’s 1969 masterpiece “Here Comes the Sun”, one of my favourite Beatles songs. This song was composed by Harrison during a difficult time when the Beatles were frequently bickering. One day, Harrison decided to play truant from a planned business meeting at the band’s Apple Corps organisation. Instead, he went to see his friend Eric Clapton; the song was composed in Clapton’s garden. According to Clapton, it was April 1969.

“Here Comes the Sun” was recorded over the summer of 1969, and appears as the first track on the second side of their 1969 album Abbey Road, which was released in September 1969. The song was never released as a single, although it has gone on to be one of Harrison’s best known compositions.

At number 28 in Rolling Stone Magazine’s list of the 100 greatest Beatles songs is “Here Comes the Sun”.

Here comes the sun, here comes the sun
And I say it’s all right

Little darling, it’s been a long cold lonely winter
Little darling, it feels like years since it’s been here

Here comes the sun, here comes the sun
And I say it’s all right

Little darling, the smiles returning to the faces
Little darling, it seems like years since it’s been here

Here comes the sun, here comes the sun
And I say it’s all right

Sun, sun, sun, here it comes
Sun, sun, sun, here it comes
Sun, sun, sun, here it comes
Sun, sun, sun, here it comes
Sun, sun, sun, here it comes

Little darling, I feel that ice is slowly melting
Little darling, it seems like years since it’s been clear

Here comes the sun, here comes the sun
And I say it’s all right
Here comes the sun, here comes the sun
It’s all right, it’s all right

I cannot find a video of the Beatles’ version of Here Comes the Sun on YouTube, but I have found this version of George Harrison performing it live in concert. Enjoy!

## 2016 6 Nations – 2nd weekend review

The second weekend of the 2016 6 Nations is over and two countries remain undefeated. France have two wins from two, Wales have one win and one draw from two, and England have also won two from two. Saturday saw France take on Ireland at home, followed by Wales play Scotland at home. Sunday’s match was Italy against England.

France scraped a win against Ireland, winning what sounds like a very dour game by 10 points to 9. There was only one try, and although I have not seen the match the little I have read about it suggests that it is not a match worth trying to see on catch-up TV. After being absolutely hammered by New Zealand in the World Cup in November, France have started the 2016 6 Nations well under their new coach.

Wales beat Scotland in Cardiff by 27 points to 23 in what sounds like a much more entertaining match, with 5 tries being scored (Wales scoring three and Scotland scoring two). Scotland, in fact, went into half-time 13-10 ahead, but in the second half Wales exerted their dominance and scored two tries to go 27-16 ahead. A last minute consolation try by Scotland made the match appear closer than it apparently was; and this result leaves Scotland still searching for their first win over Wales since 2007. They have not won in Cardiff since 2002.

Wales beat Scotland 27-23 at home in the second weekend of the 2016 6 Nations

Sunday’s match in Rome between Italy and England saw England win convincingly 40-9. The exciting outside centre Jeffries scored a hat rick and England look to have found a new lease of life under Eddie Jones, their first ever foreign coach.

Ireland, who were chasing three 6 Nations titles in a row, now look to have no chance of defending their title with only a draw from two matches. It would seem their heavy defeat by Argentina in the quarter finals of the World cup has dented their self-confidence just as much as I thought it might.

The 6 Nations now takes a fortnight’s break before the third round of matches. The first match of the third round is on the evening of Friday the 26th of February, when Wales take on undefeated France in Cardiff. England will take on Ireland at Twickenham and Scotland will take on Italy. If Wales can defeat France (and obviously I hope that we can), it will set things up nicely for our match against England in Twickenham on March 12. The wiley Warren Gatland is already suggesting that the England v Wales match could be the title decider, and if Wales beat France and England beat Ireland in the third round of matches he could well be right.

## The first ever detection of gravitational waves

A major science story broke on Thursday (11th of February 2016) – the first ever detection of gravitational waves. I am currently in South America giving astronomy talks on a cruise, and therefore my internet access is very slow and very very expensive.

So, I will do a more detailed blogpost about this later next week, hopefully by Tuesday (17th). In the meantime, you can find out more about this very exciting announcement and what it means for astronomy by going to your favourite news website. From the little that I have been able to see, the coverage and explanations on the BBC’s science pages is hard to beat.

More next week!!

## The 100 greatest songwriters – number 14 – Bruce Springsteen

At number 14 in Rolling Stone Magazine’s list of the 100 greatest songwriters is Bruce Springsteen. Springsteen is one of my favourite songwriters, I would rank him in my personal top 10. I first came across Springsteen in the late 1970s, when I became aware of his 1975 song “Born to Run”, and bought the album Born to Run on the strength of liking this song.

Springsteen was born in 1949 and grew up in a working class home in New Jersey. His father was mainly unemployed, and this poor upbringing coloured much of his music throughout his career; many of his songs deal with despair and desperation. Springsteen’s first album was the 1973 Greetings From Asbury Park N.J. (Asbury Park is a city in New Jersey and located on the Jersey shore. It is part of the New York City metropolitan area).

The first track on this debut album, “Blinded by the Light”, was released as a single, but failed to make any impact on the charts. It was later covered by Manfred Mann’s Earth Band, who had a number 1 hit with  it in 1977. I remember this song in 1977, but at the time I had no idea that it was written by Bruce Springsteen; I had no idea who Springsteen was until about 1979.

At number 14 in Rolling Stone Magazine’s list of the 100 greatest songwriters of all time is Bruce Springsteen.

Springsteen’s breakthrough album was his third, Born to Run, which was released in 1975. This album opens with the incredibly energetic song “Born to Run”, one of the great rock anthems of all-time. This song was released as a single in August 1975 and was Springsteen’s first single to be released worldwide. Its chart success was modest, but it has since gone on to be considered one of the greatest songs of all time, Rolling Stone Magazine ranked it at 21 in their list of the 500 greatest songs of all time, I blogged about it here.

After Born to Run, Springsteen went on to have a string of hit albums and singles, including “Hungry Heart”, “The River” (which I blogged about here), “Dancing in the Dark” (one of his biggest hits), “Born in the U.S.A” (one of his best known songs) and “Streets of Philadelphia”.

The song which I have decided to share today is his 1994 hit “Streets of Philadelphia”. This poignant song was written for the movie Philadelphia, a movie starring Tom Hanks, who won an Oscar for his performance of a lawyer who contracts HIV and is fired from his job. It illustrates beautifully Springsteen’s songwriting skills, both with its wonderful lyrics but also its haunting melody.

I was bruised and battered, I couldn’t tell what I felt.
I was unrecognizable to myself.
Saw my reflection in a window and didn’t know my own face.
Oh brother are you gonna leave me wastin’ away

I walked the avenue, ’til my legs felt like stone,
I heard the voices of friends, vanished and gone,
At night I could hear the blood in my veins,
It was just as black and whispering as the rain,

Ain’t no angel gonna greet me.
It’s just you and I my friend.
And my clothes don’t fit me no more,
I walked a thousand miles
Just to slip this skin.

Night has fallen, I’m lyin’ awake,
I can feel myself fading away,
Or will we leave each other alone like this

Here is the official vide of this wonderful song. Enjoy!

As I mentioned in this blog here, a few months ago I contributed some articles to a book called 30-Second Einstein, which will be published by Ivy Press in the not too distant future. One of the articles I wrote for the book was on Indian mathematical physicist Satyendra Bose. It is after Bose that ‘bosons’ are named (as in ‘the Higgs boson’), and also terms like ‘Bose-Einstein statistics’ and ‘Bose-Einstein condensate’. So, who was Satyendra Bose, and why is his name attached to these things?

Satyendra Bose was an Indian mathematical physicist after whom the ‘boson’ and Bose-Einstein statistics are named

Satyendra Bose was born in Calcutta, India, in 1894. He studied applied mathematics at Presidency College, Calcutta, obtaining a BSc in 1913 and an MSc in 1915. On both occasions, he graduated top of his class. In 1919, he made the first English translation of Einstein’s general theory of relativity, and by 1921 he had moved to Dhaka (in present-day Bangladesh) to become Reader (one step below full professor) in in the department of Physics.

It was whilst in Dhaka, in 1924, that he came up with the theory of how to count indistinguishable particles, such as photons (light particles). He showed that such particles follow statistics which are different from particles which can be distinguished. All his attempts to get his paper published failed, so in an act of some desperation he sent it to Einstein. The great man recognised the importance of Bose’s work immediately, translated it into German and got it published in Zeitschrift für Physik, one of the premier  physics journals of the day.

Because of Einstein’s part in getting the theory published, we now know of this way of counting indistinguishable particles as Bose-Einstein statistics. We also name particles which obey this kind of statistics bosons; examples are the photon, the W and Z-particles (which mediate the weak nuclear force), and the most famous boson, the Higgs boson (responsible for mediating the property of mass via the Higgs field).

With the imminent partition of India when it was gaining independence from Britain, Bose returned to his native Calcutta where he spent the rest of his career. He died in 1974 at the age of 80.

You can read more about Satyendra Bose, Bose-Einstein statistics and Bose-Einstein condensates in 30-second Einstein, out soon from Ivy Press.