Physics

Does antimatter fall upwards? New CERN gravity experiments aim to get to the bottom of the matter

Does antimatter fall upwards? ...
The ALPHA-g experiment being set up at CERN, which will drop antimatter to see how gravity affects it
The ALPHA-g experiment being set up at CERN, which will drop antimatter to see how gravity affects it
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The ALPHA-g experiment being set up at CERN, which will drop antimatter to see how gravity affects it
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The ALPHA-g experiment being set up at CERN, which will drop antimatter to see how gravity affects it

Physics tells us that a hammer and a feather, dropped in a vacuum, will fall at the same rate – as famously demonstrated by an Apollo 15 astronaut on the Moon. Now, CERN scientists are preparing to put a spooky new spin on that experiment, by dropping antimatter in a vacuum chamber to see if gravity affects it the same way it does matter – or if antimatter falls upwards instead.

For every particle of matter there's a corresponding antimatter particle, which is identical in every way except that it has the opposite charge. That means that if matter and antimatter touch, they annihilate each other in a flash of energy – which understandably makes it tricky to study. Scientists at CERN first managed to trap and study the stuff back in 2010, albeit only for a fraction of a second. The following year that time was increased to a more useful 16 minutes.

Predictions say that antimatter particles should mostly follow the same rules as their normal counterparts, but it's worth double-checking to be sure – after all, any other differences could bring into question the entire Standard Model of particle physics. A few years ago, the CERN team trapped and studied the optical spectrum of antihydrogen for the first time and, breathing a big sigh of relief, found that it was identical to that of hydrogen.

Another fundamental question is whether antimatter reacts to gravity the same way. Again, predictions say it should fall like regular matter, but there's about a one-in-a-million chance that it actually falls up instead. So far, antimatter has only been studied while suspended in an electromagnetic trap, since letting it fall to the bottom (or top?) of any normal container will destroy it.

Two new experiments at CERN are ready to test out the problem. In both cases, after the antimatter is created, the scientists will switch off the electromagnetic traps holding it, then examine where in the tube the annihilations occur. That will allow them to measure the effects of gravity on antiatoms, and see if there are any discrepancies.

The main difference between the two experiments is how they go about creating the stuff, and getting it ready for the drop. The first, known as ALPHA-g, is based on the existing ALPHA equipment that allows scientists to create and trap antimatter, but turns it vertically. Antiprotons are collected from the Antiproton Decelerator (AD) and bound to positrons (or anti-electrons) to create neutral anithydrogen atoms. That neutrality is important, since carrying a charge could have an effect on the results and obscure the influence of gravity.

The second experiment, known as GBAR, gets its antiprotons from the ELENA deceleration ring, and combines them with positrons from a small linear accelerator. Together, that makes antihydrogen ions, which are then ultracooled to 10 microkelvin and made neutral by stripping them of a positron by hitting them with a laser. The resulting neutral antihydrogen is then subjected to the drop test.

Unfortunately, both experiments are racing the clock. In a few weeks' time, CERN's accelerators are due to be shut down for two years as the facility undergoes an intensive upgrade known as the High-Luminosity Large Hadron Collider (HL-LHC). Ideally, one or both will be able to be conducted before that happens.

The team describes the ALPHA-g experiment in the video below.

Source: CERN

Introducing ALPHA-g, a new experiment to measure the effect of gravity on antimatter

8 comments
piperTom
Physicists expect -- make that WANT -- the gravitational charge of antimatter to be positive, so they don't have to rework their theories. But finding gravitational repulsion between the two helps solve the biggest mystery in cosmology: Why do we see no sign of antimatter in the observable universe? It's because we live in one of the many clumps of matter. There are also big clumps of antimatter. In the early universe, a slight concentration of matter would pull on its like and repeal the other.
guzmanchinky
This kind of science makes my brain hurt. But like a hot pepper, I love it.
Malatrope
If antimatter repels itself, how could there exist large clumps of it? It should spread evenly out into low-density gas.
ChgoSTrider
Sounds like they have FINALLY found the long lost mine that contains the rare mineral Upsadayseum. Rocky and Bullwinkle were right!!!
a.l.
It should make no difference as to the charge or spin of the particles in antimatter — mass is mass, and according to Einstein it’s what distorts space to produce gravity. CERN was conceived and constructed largely to isolate and prove the existence of the Higgs Boson, the fundamental particle that, according to the theory CERN proved, gives all matter mass. Unless there’s such a thing as an anti-Higgs, and nothing I’ve read indicates that there is any theoretical basis for such a possibility, or a possibility that any fundamental particles, such as as quarks, muons, tachyons, etc. even have anti-particle counterparts, then there is no way that anti-matter interacts with gravity an differently than normal matter. As a postscriptum, one can only hope that there is such a thing as an anti-Higgs, as it would make genuine, practical antigravity a theoretical possibility but, as I stated above, nothing in current thinking or observation even suggests that H.G. Wells’s magical gravity-blocking Cavorite will ever be in the labs or on the drawing boards. More’s the pity.
anthony88
If it's anti-matter, does that mean it doesn't matter?
vanisleman
Anti Matter has Anti-Gravity properties (imo) at the big bang most matter and anti matter self destructed. However as anti-matter has anti-gravity it repulsed both matter and other anti-matter. The end result was that the matter left over ended up forming galaxies, and the anti-matter in the form of anti-hydrogen fills the space between galaxies. Anti-matter can not naturally form a atom larger than anti-hydrogen due to its repulsion. This explains why the universe is still expanding and galaxies accelerating away from each other ... the mass of anti-gravity that exists between galaxies is pushing them further apart contrantly. Scientific proof -- none , hopefully these boys validate my theory... Where did my theory come from --- common sense and logic :-) Regards .... VanIsleMan ....
azor_romao
If matter and antimatter repel, there may be whole superclusters of antimatter. They would be equally distributed throughout the universe in the same way as normal matter, so there would be symmetry between the amount of matter and antimatter.