In Warsaw at GR20

The library with Maxwell's equations

This post is obviously overdue since GR20 was a conference that happened last summer. But I thought it better to write about it now than never. The GR meetings are the biggest conferences in the field of gravitation. They are attended by many scientists from all over the world who give many oral and poster presentations. So, I  will not aim to describe everything that happened since that's impossible. I will just write about what I remember.

Mihai next to our apartment

I gave a talk on the atomic clock work and we also had two posters. One on cosmology and another on Chameleon models and STE-QUEST written by Andreas, my first student. STE-QUEST is a medium size mission candidate to be launched by ESA in 2022+. This mission would investigate the behavior of time and matter near Earth by using an atom interferometer and atomic clocks.

me on the day of my talk

In terms of setting, Warsaw is beautiful in July. We rented an apartment in a building with high ceilings that felt very much like being home. We each had our own room, and it was cheaper and better than a hotel. The "us in front road construction" pictures were taken for Edward and David who are still fascinated by bulldozers, and because Mihai and I like construction sites, too. We saw the benches that each played different pieces Chopin's music and the public library, which had art made from equations and a beautiful rooftop garden. The streets were full of people dressed in their national costume, who were performing in various ways. They were all surprisingly good looking (nothing like the beggars from other major cities). The restaurants were good, and served special dishes like wild boar soup.

While there was no scientific discovery that dominated the conference, there were a number of interesting talks. eLISA has just been selected by ESA to fly as one of the next large missions, and the development for LISA Pathfinder is almost done! The Pathfinder will be launched in July 2015 to test LISA technology. There is a proposal to extend the trajectory of LISA Pathfinder so that it can test alternative theories to dark matter (MOND & TeVes). These theories rely on the potential existence of some minimal acceleration that could explain the flatness of the rotation curves in galaxies without invoking a dark matter halo made from unknown particles.  The LISA Pathfinder will fly through the Sun-Earth Lagrangian L1 point to constrain these theories. At the Lagrange points the gravitational forces balance allowing the satellite to be stationary relative to the Sun and the Earth. The Pathfinder will be placed in a Lissajous orbit around L1, which is about 200 000 km from Earth and pass within 10 km or so of L1 at a speed of about 1 km/second.

There were some interesting presentations on atomic clock technology. While atomic clocks can be used to test gravity in various settings, they are very much a different field. However, I do believe they are important enough for every scientist to want to know more about them. The major breakthrough in clocks came a few years ago when they switched from the microwave band (10¹⁰ Hz)  to the optical band (10¹⁵ Hz). Some of the the best clocks now measure the frequency to 1 part in 10¹⁷ in about 30 minutes, which is pretty amazing. This means that they can measure the difference in tick rate between two clocks positioned 10 cm one above the other. The clock at the bottom will tick slightly slower than the one at the top. As part of the QUEST project there are developing a portable clock that is moved between PTB and Paris. They plan to measure the difference in the solid Earth tide via clocks. Tides shift the clock frequencies at the 10^-17 level. The GPS clocks are all in the microwave band. They reach an accuracy of 10^-15 after one day of integration, while an optical clock reaches an accuracy of 10^-18 in 7 hours, which is about 3 orders of magnitude better. It's important to  propose ideas of using this clock technology on Earth and in space.

What will the future bring? I cannot predict the future (obviously), but it's always tantalizing to think about the next major jump! Clocks: Will they be able to switch from the optical band to the X-ray band? use transitions of the nucleus? charged ions? Or since there is no floor yet reached by current clocks through integrating longer, improving the technology may be sufficient for many years to come. An obvious desire is to see these amazing optical clocks made reliable, and portable enough to be used on a large scale (ideally without compromising their accuracy too much). The hope is to be able to use these clocks for practical purposes of interest not just to science, but to industry.

I attended some of the presentations on neutron star physics.  It was suggested that superfluidity could provide a natural cut-off for the r-mode amplitude at the order of 10^-6, which would still cause significant heating of the star, or the movement flux tubes could in some way prevent such modes from growing. Their viscosity may also be increase by coupling to modes in the crust. It also appears that an active R-mode instability would heat isolated radio pulsars to higher than estimated temperatures. This is not a problem in accreeting systems since they are expected to be heated up by the accretion process anyway. This is a problem that is perhaps worth investigating.

The public lecture was on quantum gravity, where we learned that space is granular and that time does not exist (at Planck scale). The Big Bang could be a Big Bounce where after shrinking the universe will expand again. And, of course, infinities are not physical, the only thing that appears infinite to these really bright people is ignorance.

Mihai and I also spent some time talking to a Romanian colleague who was educated in the best Russian University from Siberia. It was very interesting. We got a glimpse of what deportation and relocation means - it's hard to think of losing everything in a few hours (or days) - including lives of (mostly children & elderly, but not only) people who could not survive the cold, property, money, friends. He had fought in the war in Transnistria from 1990s and has son who was attended Harvard. Deportation and relocation in places like Transnistria (a tiny country at the border between Moldova and Russia) can still happen for being on the wrong side of politics. The conditions are not quite as harsh as before and so (un)intentional loss of life happens less, but they lose everything else. I suppose that I should not be surprised, but I was because I forgot that such unfairness still exits so close to home. I don't even want to think about the many refugees from Syria or about the closing of the borders of Ukraine to perhaps thwart their many attempts to move towards the EU. On the bright side, this amazing gentleman we talked to is alive and now worries about mathematical formulas instead of guns.

The conference ended with a bus tour of Warsaw.  We saw flowers and people still praying for 96 members of the parliament of Poland who died in the plane crash in Russia in 2010 - although the bus did not stop there. Our guide talked about the aftermath of the second world war, which flattened most of Warsaw, and the afferent deportations/murders, and, of course, about some of their monuments and parks.   Most concentration camps (including the most notorious ones) were on polish territory. This is now a touristic attraction - although, nothing is left from them since they were all bombed in the end.