Dark matter findings are something and nothing


Scientists trying to unlock the mysteries of antimatter say they’ve spotted extremely preliminary signs that one theory about the make up of space may be correct.

The findings come in an article in Physical Review Letters and detail the first results from the Alpha Magnetic Spectrometer (AMS), a device housed on the International Space Station.

The project is based around the idea of dark matter, which is something scientists have deduced to exist but can’t see because it doesn’t appear to emit or absorb light. Its existence would explain why the way in which bodies orbit in various star systems doesn’t match up to the gravity effects you would expect based on the known mass of various physical objects such as stars and planets.

The AMS is based around the idea of the universe being split into matter amd antimatter. In the same way that matter is made up of particles including the electron (which carries an electrical charge), antimatter is made up of antiparticles. These include the positron, which is the electron’s counterpart and is almost identical but has an opposite charge.

One of the biggest stumbling blocks for most attempts to explain how the universe works is that the expectation is that there should have been an equal number of electrons and positrons produced by the Big Bang. However, attempts to measure them suggest there are far more electrons. Possible explanations include the idea that actually it would have been easier for electrons to have been produced; that we’re only sampling part of the universe and there are unexplored areas where positrons are more common; and that we’ve got the whole thing wrong.

The AMS detects and counts electrons and positrons in the cosmic rays that fall upon it. The first published results show that there’s a higher proportion of positrons that expected: around 1 for every 100 electrons, rather than every 10,000. (This has been reported with the phrase “an excess of positrons”, but that shouldn’t be misinterpreted as meaning more positrons than electrons.)

This is a consistent pattern that doesn’t seem to be affected the direction from which the electrons and positrons arrive. That in turn makes it less likely the results have been distorted by a specific “local” event such as a pulsar, a neutron star that is rotating.

However, what the scientists really want to see is how the positron:electron ratio changes over time. They believe that if they can spot a trend of the positron level rising and then suddenly falling, it will back their theory that the extra positrons are the result of dark matter colliding with itself rather than coming from a pulsar.

In an appropriately “reverse” logical sequence, showing that dark matter has collided with itself would act as evidence that the dark matter exists in the first place.

The results also show the positron:electron ratio can vary across space, giving more weight to the explanation that though there are an equal number of the two, they aren’t evenly divided.

(Computer-generated image courtesy of NASA.)

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