It is widely accepted that the Moon was created by a collision of a Mars size object with the Earth a few billion (thousands of years) years ago. One open question about it was on the tilt of the Moon's orbits. This week's Nature issue might give an answer to it and seems to be related with gold fever.

When the solar system was being formed, the Earth was just a very hot ball, and many bodies were flying through the solar system, one big object collided with the forming Earth and the debris of that collision ended orbiting the Earth at about just 20,000 miles from it. Gravitational pull of the Sun, the Moon-Earth system and other objects made both objects draw away slowly to its current 200,000 miles (and still drawing away). The gravitational dance of the Earth and the Moon should have made the Moon to move in the same plane as the Earth is doing. But it happens that the orbit of the Moon is tilted about 5 degrees from the orbit of the Earth. This has been an open question until Kaleh Pahlevan and Alessandro Morbidelli from CNRS, Nice, France, published this week on Nature their research (Collissionless encounters and the origin of the lunar inclination).

The solar system is not empty at all. There are lots of small objects moving through it, some of which impact into planets or satellites (Schoemaker-Levy), some of them are ejected from the solar system due to gravitational effects, some of them are swallowed by the Sun or might fall into a periodic stable orbit (Halley). The letter just published claims that collisionless impacts have been affecting Moons orbit to be those 5 degrees apart from Earth's orbit. Their simulations point in this direction and seem to be robust enough to a wide range of parameters.

But the research also points to the fact that most of the impacts of objects have been on Earth and not on the Moon. The fact that the Moon is filled out of craters and not the Earth is due to the fact Earth has atmosphere, life on its surface and tectonics dynamics, which clear off any footprint of an impact, while the Moon hasn't. Between 9% and 25% of the objects that impact on the Earth-Moon system will do it on the Moon, while the rest on the Earth. This higher number of impacts could be the reason that the Earth has heavy metals on its surface, while the Moon hasn't. When the Earth was being formed, heavy, more dense metals should have gone deeper into the interior of the planet. Metals such as gold or platinum should not be found on its crust. The ones we find could provide from these impacts.

Maybe yes, the gold fever was a lunatics matter.

Congratulations!

​100 years ago today, on Thursday, November 25th, 1915, Albert Einstein presented his General Theory of Relativity. After having been working on it for eight years he finished one of the most beautiful and robust scientific theories.

In these 100 years, the theory has passed from not being accepted at first, to not having found any deviation from the observations and experimental tests.

In 1905 Einstein presented his special theory of relativity, that unified space and time, matter and energy. This first theory showed us how these values depended on the observer and changed our view of space and time as non being rigid, but deformable. At that time, many scientists were about to find it: Poincare, Lorentz, Fitzerald. Indeed, these scientists had already found the equations that Einstein presented in his theory. But they didn't understand their meaning. They though those mathematical expressions weren't but artifacts to get to the right numbers to agree with experiments. They believed they didn't have any physical significance, though. Einstein, in a very elegant manner, presented those same equations from simple principles and gave them physical meaning. Conceptually, he had to work on the theory for ten years to understand it, and only three weeks to develop the mathematics to describe the phenomena.

The General Theory of Relativity went the other way round. He visualized the physical theory with one thought experiment, but he needed eight years to develop the mathematical description. The Special theory was on the air in science at the time Einstein came through it. If it hadn't been him, another would have presented and understood it in a few years. The General theory was much more complex to envision, and Einstein had the great vision of a bright mind that could have taken decades to others at that time.

It was not a straightforward work, Einstein went back and forth and had to learn mathematical concepts he didn't know. Due to the geometric aspect of the theory, it soon attracted the attention of many mathematicians.

The first test to the new theory was the total eclipse of the Sun in 1919 (Einstein had preciously calculated the orbit of Mercury, where Newton's theory had a little discrepancy, Einstein's theory hadn't). At that time, the equipment was not very precise and the pictures taken by Eddington in that eclipse wouldn't have been published today [1]. But he was right. Since then, the theory of relativity has been tested in many different ways, showing always to be a correct theory [2, 3, 4, 5, 6,  7, 8, 9, 10].

But we have not yet managed to reconcile General Relativity with Quantum Mechanics. The fact that the first rules physics when huge masses are in play, and the latter rules physics of elementary particles makes it difficult to observe or design experiments where both aspects are into play. Masses of elementary particles don't have enough mass to create a detectable gravitational field. There are many theories that try to unify both of them.  The most relevant are string theory and quantum loop gravity. Both approaches introduce new perspectives to our view of the universe and matter, but their predictions are far from being tested, which makes it almost impossible to verify whether one of them is correct. Physics final goal is to describe Nature and we need to test theories. If one theory doesn't describe Nature, it doesn't matter how beautiful it is, we can not consider it as a real physical theory.

Also, the dark matter and dark energy conundrums we are dealing with in the latest years, have pushed some physicists to think that, maybe, General Relativity has to be reconsidered and it needs some modifications to account for the Universe as a whole. In any case, up to date, none of this alternative gravity theories has better success than relativity to describe the universe with or without the dark sector.

But, besides the unification with quantum mechanics, and the understanding of dark matter and dark energy, the last 100 years have given us great success of General Relativity. We understand much better the universe, stars, galaxy formation that we did one century ago. And we also have General Relativity in our pockets.  Due to the difference in speed and in gravitational field between us and the GPS satellites, our clocks don't run at the same pace as those in the satellites. There is a difference of 43 nanoseconds in one whole day. This difference is predicted by relativity and it might seem small, but if we don't consider it in the GPS protocol, our devices would be wring by 11 kilometers after 24 hours, making this positioning system useless.

So, we should be very happy and thankful to Einstein and his General Relativity for letting us understand better our Universe, and for helping us drive our way to where we are going to have our turkey this Thanksgiving Day.

Read here the post at the Duke Research Blog by Anika Ayyar talking about my class of Science and Fiction at OLLI (Osher Lifelong Learning Institute at Duke).

NASA has just confirmed that there were lakes of salty liquid water on Mars billions of years ago, but magnetic activity from the sun affected Mars such that it began to loose its atmosphere. That is a great peace of a new from the scientific perspective but, does that affect our daily lives? Yes, for sure!

Human beings are a particular species on Earth. Since the dawns of time, humankind has being making questions on her place in the universe. Science has been working to answer those questions in the last few centuries, generating many new more questions for each answered one. Maybe that is the main reason why we scientists do research. But our experience has shown us that lots of technological advances for our society come out thanks to basic science. As Richard Feynman said once “Science is like sex, it may give some practical results, but that’s is not why we do it".

Last week, in the Physics Research Seminar course that I coordinate at Duke University, Dr. Sara Haravifard came to talk about her research in the field of the magnetic properties of crystals at very low temperatures and very high pressures. She creates specific types of crystals, to which she then applies those extreme conditions to understand how they behave, and how their structure is affected when different phases emerge, such as superconductivity.

Superconductivity is the lack of resistance to an electrical current that some materials have at very low temperature (lower than -100C approx., but some at lower than -200C). Although there are a couple of models that describe this phenomenon for some of the superconducting materials, it is not well understood how or why some others are superconductors. Understanding it, could help researchers to design superconductors at room temperature, for our use, giving our society a great tool for telecommunications, transport industry, and energy.

To investigate their properties, Dr. Haravifard needs to submit her samples to many different measurement, as X-rays or neutron scattering. Those measurements imply complex and big instruments, most of them huge facilities such as synchrotron accelerator or Spallation Neutron and Pressure Diffractometer (SNAP). These big facilities are huge instruments that most research centers or universities can not acquire or maintain. That is why there are just a few in the U.S. and in other countries around the world. The budgets to build and maintain them are big, although smaller than yearly budget of most soccer teams in Europe.

Sometimes it is difficult for newspapers to explain why we need a new synchrotron, for example, but without it we might not have that useful medicine you need, or that synthetic molecule to reduce cars pollution, or that light and resistant material that can be used in some prothesis.

It is good to have in mind that, when you use your laptop, or send a text massage to your loving ones, or watch the Super Bowl on cable TV, or have a medical diagnosis, you are having it due to people like Dr. Haravifard, doing basic research to understand Nature. Discoveries such as that of water on Mars, which a priori could seem not directly related to you, are present in your daily life.