CSIRO's Compact Array in Australia under the night lights of the Milky Way Alex Cherney

A 50-year-old puzzle about the movement of our Solar System, and maybe the origin of life, may have been solved thanks to data collected in the 1920s.

Cosmic Background Radiation is the imprint of leftover heat and radiation from the Big Bang, and can be seen universally in the sky, in all directions. To an outside observer -- if such a thing were possible -- this radiation would have almost the exact same temperature.


The problem is that the Earth is known to move through the CBR, as shown in 1977 by Smoot, Gorenstein and Muller, and as such it had been expected that very small but clear variations in the temperature should be observable. This is because the Earth, and the entire Solar System, is not static but moving at 370 km/s towards a specific point in the sky.

As a result there should be a type of Doppler effect visible in the CBR, with different temperatures in different directions, that would provide a frame of reference in the sky. This so-called "temperature gradient" has never been observed in a laboratory.

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But new research has shown that data from as far back as the 1920s, collected for very different experiments, might be enough to show the effect is real. The paper, published by Maurizio Consoli and Alessandro Pluchino from the Istituto Nazionale di Fisica Nucleare (INFN) and Andrea Rapisarda from the University of Catania in Italy, was highlighted by Phys.org and published in the journal Europhysics Letters.

The relatively ancient data was collected for a very different reason; in fact, it was first gathered as part of a long series of experiments to try to explain why light was able to travel in the apparent vacuum of space. In the 19th century it was assumed that light needed to pass through a medium, even in space. We now know different, thanks in part to Einstein, but in the meantime scientists searched for that medium wherever they could. Their solution, in theory, was the existence of 'ether', a strange substance that would allow for the travel of light. Many scientists were unconvinced, rightly, however, that such a thing existed and carried out experiments to show that light travelled at the same speed in perpendicular arms of an interferometer instead of -- as would be expected -- slower in one direction.


Our result could also be relevant for those research areas which look for the origin of complexity in nature. Maurizio Consoli

Further experiments on this theme have followed, up to the present day (and to ludicrous levels of exactitude) partly due to its continuing relevance in examining the mechanics of special relativity. Einstein's theory necessitated that light move at the same speed in all directions, regardless of your movement through space -- there is no 'outside reference' grid for space, only movement relative to different observers.

All these experiments have been consistent with first disproving the existence of ether, and later the correctness of Einstein. But where this becomes relevant to the CMB -- and Consoli et al. -- is when the experiments appeared to go wrong. In particular, an experiment by Dayton Miller in 1933 showed 'fringe shifts' in measurements of energy that, at the time, were thought to be down to problems in methodology.

Not so, according to Consoli.

As he and others have argued in earlier papers, these 'residual' effects have been seen in many different ether-drift experiments, and were not due to specific problems with any one experiment. In fact, it appears they correspond nicely to the temperature gradient you might expect to see in the CMB if the Solar System is powering towards one point at roughly 370km/s.


The new paper argues that a similar effect would be seen in other gaseous systems too -- the data from the 1920s and 30s studies all stems from experiments that relied on air or helium to test the effect -- but would vary based on the speed and direction of travel. "This motion is called 'peculiar' because it is characteristic of our local position in the universe," Pluchino told Phys.org. "In fact, it is obtained by combining the motion of our galaxy, and of the local group of galaxies, with a velocity of about 600 km/sec toward what is called the Great Attractor (a large concentration of matter situated at about 100 Mpc from us), along with the motion of the solar system within our galaxy. Therefore, an observer placed at the opposite site of our galaxy will also see a dipole anisotropy but, for him, the kinematical parameters will be different."

The implications are significant, and the team hopes for further tests with precise laser systems. Better tests could even have relevance for the origins of life. "This flow is now very weak but, in the past, was substantially stronger when the CBR temperature was higher. Therefore, it has represented (and still represents) a sort of background noise which is independent of any localised source," said Consoli. "It is known that such non-equilibrium condition can induce (or it could have induced) forms of self-organisation in matter. Therefore, our result could also be relevant for those research areas which look for the origin of complexity in nature."

That much is currently speculation -- the idea that a 'signal' in the CBR could create all life as we know it is intriguing, or at the very least poetic. Either way, finding new insight in the work of scientific forebears has a poetry of its own -- even if it turns out to be even more complex than they, or we, could imagine.