Registration to the Gravity! on-line course opens again

The registrations to the course Gravity!  have just reopened on the Futurelearn platform . The first session of this course had attracted 70 000 registered learners last Fall. This new session follows the same programme: it revisits the emergence of the main concepts from Galileo to Newton and Einstein before discussing some of the main aspects of gravity in the Universe -Big Bang, expansion and cosmic inflation, cosmic microwave background, dark matter and dark energy, black holes. And no doubt that gravitational waves will be centre stage on this course!

Classes start on Monday 9 May for six weeks.  You may register here on  the FutureLearn platform. The course is free and registration is open to everyone.

Gravity! is for all those of you curious about the mysteries of the Universe and invites you to understand, without any prerequisite in physics, the foundations of Einstein’s theory that makes gravity “the engine of the Universe”.


LISAPathfinder arrives at its destination

After a six-week journey, LISA Pathfinder arrived today at its destination, the Lagrange point L1, a point on the virtual line joining the Earth to the Sun, some 1.5 million km from Earth, where the gravitational effects are balanced by the centrifugal force.

LISA Pathfinder’s arrival came after a final thruster burn using the spacecraft’s propulsion module on 20 January. The small, 64-second firing was designed to slightly change its speed and just barely tip the craft onto its new orbit about L1. “We had planned two burns to get us into final orbit at L1, but only one was needed,” says Ian Harrison, Spacecraft Operations Manager at ESA’s ESOC operation centre in Darmstadt, Germany, where the mission control and science teams are located.

LISAPathfinder journey from the Earth to L1

LISAPathfinder journey from the Earth to L1

Since launch, the propulsion module raised the orbit around Earth six times, the last of which kicked it towards L1.


The propulsion module separated from the science section at 11:30 GMT (12:30 CET) after the combination was set spinning for stability.

“Heat and vibration from the regular, hot thrusters on the propulsion module would cause too much disturbance during the spacecraft’s delicate technology demonstration mission,” notes Ian. “Primary propulsion during the rest of the mission will be provided by microthrusters to keep us at L1.”

These small thrusters were used in the hours after separation to kill the spin and stabilise the spacecraft.

Next week, LISA Pathfinder’s trajectory will be fine-tuned with a series of three micro-thruster bursts, taking it onto its final orbit, a 500 000 km × 800 000 km orbit around L1.

The next delicate step will be the final release of the test masses on 15 and 16 of February.


Pierre Binétruy and the Gravity! team meet you in the Paris Science Museum

Pierre Binétruy and members of the Gravity! team are in residence at the Palais de la Découverte, the Paris science museum located in the Grand Palais at the bottom of the Champs-Elysées.

This is part of the celebration of the 100th anniversary of General Relativity.

Meet us in person on some of the afternoons of January till March 2016, and perform with us some simple experiments revealing the true nature of gravity. We are located in the entrance rotunda: un chercheur, une manip (“one researcher, one experiment”).



Time 2.30pm-5pm on the following dates:


Wed 6         Antoine Petiteau

Sun 10        Pierre Binétruy

Wed 13       Antoine Petiteau

Sun 17        Pierre Binétruy

Sat 23         Hubert Halloin

Sun 24        Henri Inchauspe

Wed 27        Philippe Bacon

Sat 30         Philippe Bacon


Wed 3          Hubert Halloin

Sat 6           Pierre Binétruy

Sun 7          Pierre Binétruy

Sat 13         Pierre Binétruy

Sun 14        Henri Inchauspe

Wed 17        Pierre Binétruy

Tue 23         Hubert Halloin

Fri 26           Hubert Halloin

Sat 27          Pierre Binétruy

Sun 28         Pierre Binétruy


Sat 5             Henri Inchauspe

Sun 6             Hubert Halloin




Brzmienia/Sonoridades: Gorka Alda celebrates Chillida in Wroclaw

The composer of the music and sounds of Gravity!, Gorka Alda, has conceived two sound installations for the exhibition “Brzmienia/Sonoridades” (Sonorities) dedicated to the sculptures of Eduardo Chillida in Wroclaw, European Capital of Culture 2016.



Gravitación, Eduardo Chillida

The theme of gravitation is recurrent in the work of Eduardo Chillida (1924-2002). Surprisingly, he is using paper for the sculptures on this theme, and the vacuum between the different paper sheets plays a significant role as well.

The exhibition opens this Friday 15  at Awangarda Gallery, in Wroclaw, and continues until March 13 (curators: Inés R. Artola and Ignacio Chillida).

A new particle hint at CERN? Could it tell us something about gravity?

Last December 15, the two experiments which have discovered the Higgs particle at CERN, ATLAS and CMS, have presented the first results of the LHC collider at the highest 13 TeV collision energy and they both announced an excess of 2-photon events at 750 GeV.


This might be the sign of the existence of a new particle with a mass energy of 750 GeV, decaying into two photons like the Higgs. But the evidence is still very preliminary: one only sees small bumps when one plots the number of events versus the energy.


In technical terms, one talks of standard deviations: ATLAS has seen a 3.6 standard deviation, and CMS a 2.6 standard deviation, when the scientific community agrees to talk of a discovery only for standard deviations larger than 5. The excitement comes from the fact that both experiments see an excess at the same mass. But one will probably have to wait another year to accumulate more data and see whether the excess builds up… or disappears if it was just an unhappy coincidence.


But theoretical papers have rushed to provide interpretations of these events. Nature has recently counted almost one hundred papers appearing on the web arXive where the scientific community uploads their papers (108 to this date, see here). Why such an interest? And has it anything to do with gravity?


Well, the Higgs particle discovered in 2012 was the last building block of the Standard Model, which realizes the unification between the electromagnetic and the weak nuclear force. A new particle of mass energy 750 GeV (decaying into two photons) is not accommodated by the Standard Model; it would be a clear sign that this Standard Model has to be revised, or rather enlarged: one would have to go beyond the Standard Model, as we physicists say.


For many of us in the scientific community, this is expected because the Standard Model answers very fundamental questions but leaves many other open. For example, it does not provide a candidate for a dark matter particle. Could the new hypothetical particle be this dark matter particle? Most probably not, but many theoretical papers stress that this first signal of new physics would lead to the discovery of further particles. There is the hope to discover among them this dark matter particle, and thus to solve a puzzle which has been with us since the 1930s (remember that the only signs of dark matter have been so far gravitational, which led some to propose modifications of general relativity to account for the observations).


Another motivation is of a more theoretical nature. The Standard Model only realizes the unification of two fundamental forces (electromagnetic and weak nuclear forces). What about the two others (strong nuclear force and gravitation)? Well, a larger unification requires new dynamics and thus new particles. But the Higgs particle, which provides the masses of all other particles, is very special: its own mass is destabilized by the quantum fluctuations associated with the new particles. In other words, if there is indeed a new particle of mass energy 750 GeV, this would tend to increase the Higgs mass to the same value. But the Higgs mass is measured to be 125 GeV, that is six times smaller. It will then be fascinating to see what protects the Higgs mass from such fluctuations. A new symmetry, for example? In any case, this will give first hand information on the dynamics that may eventually lead to a unification of the microscopic forces with gravity, at a much higher energy. The long sought marriage of quantum physics with general relativity.


2016 thus appears full of promises of major discoveries in fundamental physics. Will it fulfil its promises?


Best wishes to all for this new and exciting year.


Pierre Binétruy

After one week orbiting Earth, heading to L1


Since LISAPathfinder launch, on Thursday December 3rd 2015, teams from the European Space Observations Centre (ESOC) in Darmstadt are working day and night to ensure the orbital operating steps. As illustrated in the figure, these maneuvers consist in correcting the path and increasing by successive pushes the  altitude of the apogee, that is to say, the point on the orbit which is farthest from the Earth . Each time the engine of the propulsion module is activated for several tens of minutes.

Just after the launch the apogee was at an altitude of 1,540km. The first push took place Saturday 07/12/2015 at 5:02 with an increase in speed of 393 m/s which rose the apogee at 3,392km. Then the same day another push at 17:20 rose the apogee at 7.105 km (+ 552 m/s). Then, Tuesday 08/12/2015, two new pushes allowed to reach orbits with apogees at 14,488 km (+ 603 m/s) and then 44,526 km (+ 807 m/s). And the fifth push was operated on 10/12/2015 at 0:34 with an increase in speed of 398 m/s which rose the apogee to 129,122 km.

Finally after running tests on its performance, the engine was activated  on Saturday 12 at 5:18 during 6 minutes to make the final push (+ 234 m/s). This allowed to eject LISAPathfinder outside the Earth’s orbit and to put the satellite on its trajectory towards the Lagrangian point L1. We will have now nearly fifty days to cover the 1.5 million kilometers from the Earth to L1.

Have a good journey LISAPathfinder, arrival late January 2016!

Antoine Petiteau


“Гравитация!” на русском

Gravity! in Russian

Thanks to the dedication and hard work of Mikhail Stolpovskiy, a version of the Gravity! course dubbed in Russian is now available.

Благодаря стараниям Михаила Столповского стал доступен курс “Гравитация!”, продублированный на русском языке.

This will allow all Russian-speaking enthusiasts to get a first contact with the gravitational Universe, and maybe to join later the full course when it is repeated on Futurelearn.

Это позволит русскоязычным слушателям узнать о гравитирующей Вселенной и, возможно, присоединиться позже к полному курсу на платформе Futurelearn.

See below the videos of the first week, where you will follow Galilei, Newton and Einstein to focus on the main concepts of gravity.

Смотрите видео первой недели, где вы проследуете за Галилеем, Ньютоном и Эйнштейном и изучите основные концепции гравитации.

Soon, other videos on PCCPTv on Youtube.

Следите за новыми видео на PCCPTv и Youtube.

Добро пожаловать/Welcome


Галилей и падающие объекты/Galilei and the falling bodies



Первая встреча с относительностью/First encounter with relativity



Ньютон и падающая Луна/Newton and the Moon falling



Эйнштейн в пространстве-времени/Einstein and the space-time



Эйнштейн в падающем лифте/Einstein and the fall of the lift



 Focus: Эксперимент с гравитацией/Experimenting with gravity


Watch with us the launch of LISAPathfinder: launch rescheduled Dec. 3 at 4:04 GMT

After a great hangout with the LISApathfinder technical team, join us here on Gravity! to watch live the images of the launch of the mission from Kourou.

The launch is rescheduled on December 3 at 4:04 GMT (5:04 am Paris time, 1:04 am Kourou time). 

We will start broadcasting at 3.45 GMT (4.45 Paris time). You may watch the event on Arianespace TV:

Good morning. Follow the event here and comment below.

Lift off.

First stage is now separated.

Altitude 97 km

Fairing separated. One can see the satellite now!

Altitude 300 km from Earth

Altitude 370 km, 4400 km from Earth: everything nominal

Altitude 400 km, first ballistic phase

Next important phase at 5:45 GMT! TV comments restart on at 5.42 GMT.

Separation performed.

First signal from LISAPathfinder satellite separated.

Separation confirmed! Everybody applauds and congratulates in Kourou. Launch is a success. LISAPathfinder is on its way to Lagrange point L1.

See the video of the launch (final countdown at minute 13:00: you may recognize Jon Harr who participated to the hangout on Monday; the video is also commented by Paul McNamara, LISAPathfinder project scientist, who was our host in Kourou for the hangout; and you will recognize also Cesar Garcia, project manager, very busy at this time, e.g. at minute 22:20):



Visit of the facilities of the Space Centre


Ariane 5 launch pad

This morning we toured for 3 hours the facilities of the Space Centre. We started with a viewpoint on the Vega and the Ariane 5 launch pads. The Vega rocket is still in its building : it will only leave it 2h 40 minutes before the launch. It is rather moving to think that the LISAPathfinder is in front of us, waiting to be sent into space.




We then visited the bunker which hosts the control rooms of Ariane 5 and Vega. They are truly the flight decks of launchers. On the way, we could get a glimpse of the countdown (1h27m48s) and a direct view on the rocket.


Next Ariane 5

We went on to the assembly hall of Ariane 5. The Ariane 5 was majestically standing on its control table.

Ariane 5 launch pad

Ariane 5 construction ramp

Next to the launcher was the ramp, the umbilical cord which feeds the rocket with fuel until 5 seconds before launch. Finally, we went to the Soyuz launch pad with an impressive view on the pit which allows the evacuation of the blaze at launch.


Soyuz launch pad with the evacuation pit

December 1, 15:30 GMT

Antoine Petiteau
Text: Antoine


Joseph Martino

Photos: Joseph

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