Physics Nobel Prize 2017

Last month  the Nobel Prize for Physics has been awarded to three American physicists for their ” decisive contributions to the LIGO detector and the observation of gravitational waves”

Here they are, from left to right Rainer Weiss (85), Barry Barish (81), Kip Thorne (77) .

All are retired professors and quite old, not unusual for Nobel Prize winners…:-; More unusual is that this Nobel Prize has been awarded for the observation of gravitational waves in September 2015, only two years ago! The time between a discovery and the Nobel Prize is often 10-20 years and tends to increase

In this case the physics community was pretty sure that the Nobel Prize would go to  LIGO, the Laser Interferometer Gravitational-Wave Observatory, where the gravitational waves were observed. Problem is that a Nobel Prize (with the exception of the Peace Prize) can not be awarded to an organisation but only to a maximum of three individuals (and never posthumously). And the article in Physical Review Letters, where the discovery was published in February 2016, has more than 1000(!) authors. Here is the beginning of the author list

In this blog I will explain why these three people were selected. But first I must tell a bit more about gravitational waves, and why physicists are so excited that they have been observed.

In 1687 Newton publishes his  masterwork “Principia” in which he presents the three laws of motion  and the universal law of gravitation.

Motion takes place in 3-dimensional space as a function of time. Both space and time are absolute concepts, independent of each other.

Newtonian mechanics works extremely well, but there is one disturbing fact, the speed of light c in vacuum turns out to be always the same, no matter how fast the light source is moving itself. Einstein  “solved” the problem in 1905 by accepting the constancy of c as a fact, which resulted in  his Theory of Special Relativity (TSR)

But it came at a price! Space and time are no longer absolute and independent in this theory, together the three dimensions of space and the single dimension of time form a 4-dimensional continuum, called spacetime .

Gravitation doesn’t play a role in the TSR, but in 1916  Einstein publishes his Theory of General  Relativity (TGR). In this theory gravitation is described as a curvature of  spacetime. A massive object like the Sun curves the spacetime in its surroundings and a planet like Earth just “follows” this curvature.

A consequence of this theory is that even light would follow this curved spacetime and will be deflected when it passes close to the Sun. This prediction was successfully confirmed only a few years later. During a solar eclipse the stars near the Sun became visible and their position was shifted in complete agreement with the TGR. It was front page news and made Einstein world famous.

 

Another prediction of the TGR was that (accelerated) motion of massive objects could produce waves and ripples in this fabric of spacetime. Mind you, in spacetime itself ! However, these waves and ripples were estimated to be very small, maybe only measurable if  those objects were extremely massive.

For example, two black holes or neutron stars, orbiting each other.

Here is an artist impression of the gravitational waves caused by two orbiting black holes. I have hesitated to include this image, because I find it very confusing, suggesting that the cells of the spacetime fabric are moving up and down, whereas the cells themselves are changing shape, stretching and contracting. But the image comes from LIGO, so who am I…:-)?

After this long(?) introduction it is time to go back to LIGO and the three Nobel Prize winners.

LIGO has a long and complicated history, starting in the 1960!  Here are some important dates. The names of the three Nobel Prize winners in blue.
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In 1968, almost 50 (!) years ago, Kip Thorne (Caltech) did calculations about the gravitational waves of black holes. Which, by the way, had not yet been discovered at that time, but their existence followed from the TGR! He came to the conclusion that detection should be possible. Also in the 1960s, Rainer Weis (MIT) proposed to use interferometry to detect the incredibly small variations in the fabric of spacetime. See below for more about interferometry.

In 1980, under pressure of the American National Science Foundation (NSF) , MIT and Caltech joined forces in the LIGO project. But progress was slow and funding not easy.

In 1994Barry Barish (Caltech) was appointed director of the project. He was a good organiser, proposed to build the LIGO detector in two phases. This proposal was approved by NSF and got a budget of  USD 395 million,  the largest project in NSF history!

In 2002, the first phase of LIGO became operational, but no gravitational waves were detected.

In 2004, funding and groundwork started for the second phase, “Enhanced LIGO”, four times more sensitive than the first phase.

In September 2015, after a 5 year overhaul of USD 200 million was completed, Enhanced Ligo started operating.

Within days, on 14 September at 9:50:45 UTC,  Enhanced LIGO detected gravitational waves for the first time in history.
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So, what is an interferometer? Here is a sketch of the LIGO interferometer

And who could better explain how it works than Rainer Weis himself?

What may not be fully clear from the video is the huge scale of this LIGO project.

Two “identical” interferometers have been built in the US, about 3000 km apart

Here is an aerial view of  the Hanford interferometer, each of the arms is 4 km long!

Both interferometers can be seen easily on Google Earth. Left Hanford, right Livingston.

As Weis explained, gravitational waves cause small differences in the length of the arms. Very, very small. In the order of  10-19 m, that is about 1/10.000 part of the size of a proton. Read that again and again, I still find it difficult to believe..:-)

The sensitivity must be about 1/10.000 part of the size of a proton.

New technology had to be developed to reach this sensitivity. Ultra-high vacuum, very precise mirrors, extremely stable lasers. Noise reduction (thru seismic vibrations, a passing truck, etc) is the main problem. That is also the main reason that two interferometers were built. Accidental noise should be different in both detectors, but a gravitational wave should reach both (with a slight time difference, because of the distance between the two detectors).

Critical is the suspension of the mirrors. They must be absolutely stable. Here two images of the damping and suspension systems. Click here for details

What kind of signal do we actually expect? Let’s concentrate on orbiting back holes (it is called a binary), like Thorne did. As shown in the earlier image, they produce gravitational waves, but those are way too small to be detected. However, the binary will loose energy sending out these waves, as a result over time the two black holes will get closer and closer. Until they come so close that they will merge into one larger black hole, a cataclysmic process that may take less than a second! It is during this phase that the gravitational waves are much stronger and might be detectable.

Here is a computer simulation of the merger of two black holes. The simualtion has been SLOWED down about 100 times, in reality the merger occurs in a split second. The “moving” background stars are a result of the extreme distortion of spacetime.

Click here to see the gravitational waves, sent out during the merger.

You will notice that before merging the two black holes spin faster and faster, distorting the fabric of spacetime more and more. It is a bit similar to a bird chirp: increasing frequency and loudness.  After they merge into one, no more gravitational waves.

So, what happened on 14 September 2015? The two interferometers were to start the first research run on 18 September and were already in fully operational “engineering mode”, when at 9:50:45 UTC both detected  the typical “chirp” signal.  For testing purposes sometimes “fake” signals were injected, to test the alertness of the system and the scientists. It took a few hours before it became clear that this was a real signal and not a test!

Here is the “Nobel Prize winning” signal. The red graph is from Hanford, the blue one from Livingston (the Hanford signal is also shown, inverted and shifted in time)  Notice the time scale, the whole merger takes place in a few tenths of a second!

The lower two graphs show a fit to the data, using Numerical Relativity. It is surprising how much information can be extracted from these two graphs. Here is a (partial) result

Two black holes, with a mass of 35 and 30 M☉. (solar mass) , at a distance of about 1.4 billion lightyear away from Earth, merged into a single black hole of 62 M☉. .

The mass difference of 3 M , was radiated during the merger as gravitational waves. That is an awful lot of energy!  The estimated peak emission rate was greater than the  combined power of  all light radiated by all the stars in the observable universe! If you don’t believe me, click here.

This first event has been named GW150914. GW stands for Gravitational Wave and is followed by the detection date 14-9-2015. In the past two years more gravitational waves have been detected, here is a list

If you look at the location, you see that in the first five events the location of the binary is not well-defined. The reason is that you need more detectors to determine the location accurately, two is not enough.

The sixth event, GW170814 was not only detected by LIGO, but also by Virgo , the European counterpart of LIGO. This interferometer is located near Pisa in Italy. Same setup as LIGO, slightly smaller arms (3 km)

Virgo was also designed in two phases. The first phase did not detect gravitational waves. In 2106 Advanced Virgo became operational and is now cooperating with LIGO.  Another interferometer will be built in India: INDIGO .

The last event, detected until now, GW170817 (about three months ago), is an interesting one, because it is not a merger of black holes! For the first time a merger of two orbiting neutron stars has been observed. The masses of the two stars are comparable with the Sun and the binary is closer to Earth, although still a respectable 130 million lightyear!  It is not sure if the merger resulted in a neutron star or a black hole. But anyway, a merger of neutron stars should result in visible light coming from the debris after the merger.

Because of the detection with three interferometers, it was possible to narrow the region of space where the gravitational waves came from.  The location predicted by LIGO/Virgo was still large, about 150 times the area of a full moon. Within hours after detection, alerts were sent to astronomers all over the world and a massive search started.

A few hours later the Swope telescope in Chili reported they had found  the source in galaxy NGC 4993  , 140 million lightyear away. This was soon confirmed by other observatories.

Here is an image of this elliptical galaxy. The inset shows the light coming from the merger, getting weaker and weaker, as expected.

More interesting discoveries can be expected in the future, this is just the beginning.

When you want to learn more about this fascinating new field of astronomy, you should read the book Ripples in Spacetime, written by Govert Schilling

 

More museums in Den Haag

In my last blog post I visited the MORE museum in Gorssel , where MORE stands for MOdern REalism. In this post I visit more museums in Den Haag, where more stands for two…:-). I went there with my soulmate Inez, who suggested to visit the Gemeentemuseum and the Mauritshuis

The Gemeentemuseum is a masterpiece of the Dutch architect  Berlage. Built in Art-Deco style, 1931-1935. It is a spectacular building, both from the outside and the inside

We visited the exhibition Tumult in the City, one day before it closed!

In the 1880’s a group of young artists  no longer painted the countryside, like the Hague School, but became interested in city life. George Hendrik Breitner, Isaac Israels, Willem Witsen and others explored the city, especially Amsterdam, so they are sometimes called the Amsterdam impressionists

Here are a few examples of their style. They painted the everyday life of the city, street action, fashion ladies, entertainment, labourers, construction sites.

And more paintings

We had our lunch in the museum restaurant

There is a lot more to see in the Gemeentemuseum, for example the world-famous collection of Mondriaan paintings, but we left that for another visit and went to the Mauritshuis. This magnificent building was built as a home between 1636 and 1641 by Jacobus van Campen (his masterpiece was the Townhall of Amsterdam)

It now houses the Royal Cabinet of Paintings which consists of 841 objects, mostly Dutch Golden Age paintings

A visit to this museum is really a joy of recognition. Rembrandt, Vermeer, Avercamp, the famous bull of Paulus Potter…:-)

Here are more paintings

In 2007 the museum announced that it needed to expand. The architect Hans van Heeswijk designed the expansion, the project started in 2010 and the museum was reopened in 2014. This is the same architect who designed the MORE museum in Gorssel!

Here a few pictures of the expansion. Nice combination of new and old

It was an interesting museum excursion

MORE Museum in Gorssel

Five years ago, in 2012, business tycoon and art collector Hans Melchers bought more than 1200  artworks from the bankrupt DSB bank. He owned already a large number of paintings by Carel Willink and wanted to create a museum for his collection. He found a suitable location in Gorssel, a village south of Deventer in the province of Gelderland. The MORE museum was opened in 2015 and is now the largest museum  for Dutch Modern Realism.

When I am back in the Netherlands, I always try to meet Nellie, my friend of more than 55 (!) years. We both like art and this time we decided to visit this new museum. She traveled from Friesland where she is living, I took the train from Amsterdam, we met in Deventer, took the bus to Gorssel, and started with coffee in a nice cafe opposite the museum

The museum is housed in the former town hall of Gorssel and a new extension. A very successful combination of old and new.

A few months ago Melchers opened a second museum in nearby Ruurlo, specially dedicated to Carel Willink, the most famous Dutch “magic realist” painter. We decided to keep this museum for a next visit, fortunately quite a few of Willink’s masterpieces were still on view in this museum.

Carel Willink (1900-1983)

Zeppelin (1933)

Terrace with Pergola (1951)

City Square (1958)

Towards the Future (1965) and Landing on Mars (1969)

Willink’s Imaginary Realism is easily recognisable, it was a surprise for me to see that he has been experimenting with other styles when he was young. This is also Willink, when he was 24 year old!

The Silver Wedding (1924)

The ground floor of the museum houses (part of)  the  permanent collection. Well-designed exhibition halls

Here are  a few examples of Dutch “modern realist” artists. Still-lifes are a popular genre. Click on the links for Wikipedia info.

Raoul Hynckes (1893-1973)

Jan van Tongeren (1897-1991)

Wim Schuhmacher (1894-1986)

Portraits are also common

Philip Akkerman (1957- )   He painted thousands of self-portraits!

Charley Toorop  (1891-1955) Easily recognisable style…:-)

Pyke Koch  (1901-1991) Another favourite of mine..:-)

Resting Somnambulist (1930)

The Signal  (1975)


Herman Gordijn (1932 – 2017)

And of course various other subjects

Co Westerik (1924 -)

Jan Mankes  (1889-1920)

One hall is dedicated to photography. Not my main interest

But I am a fan of Erwin Olaf…:-)

Erwin Olaf (1959 – )

We had lunch in the museum cafe and continued with the first floor of the museum.

 

The first floor is for temporary exhibitions. We were lucky, a retrospective of the versatile artist Herman Berserik had just opened.

Herman Berserik (1921 – 2002)

When we left, the weather had become clouded, I could not really take pictures from the outside. I have to come back, it is really a very interesting museum, worth a second visit.