- 4238 - ANTIMATTER - responds to gravity? Theory has it that the universe expanding out of nothing? There equal amounts of matter and antimatter that add up to zero. There were equal charges of electrons and protons that add up to zero..... etc. What about gravity and antigravity?
--------------------- 4238 - ANTIMATTER - responds to gravity?
- Theory has it that
the universe expanding out of nothing?
There equal amounts of matter and antimatter that add up to zero. There were equal charges of electrons and
protons that add up to zero.....
etc.
-
- Antimatter should
fall up not up not down. CERN
experiment confirms theory that it falls down just like matter does. Observing this simple phenomenon had eluded
physicists for decades.
-
- Inside the ALPHA
experiment facility at CERN, where physicists can make antihydrogen. They have shown that, like everything else
experiencing gravity, antimatter falls downwards when dropped.
-
- This outcome is not
surprising. A difference in the
gravitational behavior of matter and antimatter would have huge implications
for physics. But, observing it directly
had been a dream for decades.
-
- Because gravity is
much weaker than other ubiquitous forces such as electrostatic attraction or
magnetism, separating it from other effects in the laboratory is a delicate
trick. Gravity is just so weak by
comparison to all other forces.
-
- Similar experiments
will aim to test whether gravity acts with the same strength on antimatter as
it does on matter. Any tiny discrepancies could help to solve one of the
biggest problems in physics. How the
Universe came to be made almost exclusively of matter, even though equal
amounts of matter and antimatter should have arisen from the Big Bang.
-
- In the world of
antimatter, atomic nuclei are made of negatively charged antiprotons, orbited
by positively charged antielectrons, or positrons. According to the standard
model of particle physics, however, the opposite charges should be pretty much
the only difference: particles and antiparticles should have nearly all the
same properties.
-
- In particular,
experiments have confirmed that positrons and antiprotons have the same masses
as their matter counterparts, within the limits of experimental errors. According to Einstein’s general theory of
relativity, all objects of the same mass should weigh the same. They should experience exactly the same
gravitational acceleration.
-
- To put this
principle to the test scientists wanted to design an experiment that would show
what happened when the neutral atom antihydrogen was dropped. It’s almost impossible to do this experiment
with a charged particle, so antihydrogen is the perfect candidate.
-
- Antimatter
particles are routinely created in laboratories. Most particles produced by high-energy
particle collisions are made in pairs.
One particle of matter and its antiparticle. But it is hard to get
antiparticles to combine into antiatoms because antimatter particles are
typically very short-lived.
-
- When an
antiparticle meets a particle, they both cease to exist and turn back into
energy, in a process called annihilation. In a world made primarily of matter,
this makes it hard for antimatter particles to find each other.
-
- CERN is currently
the only place in the world where antihydrogen can be made. It has an
accelerator that makes antiprotons from high-speed proton collisions, and a
‘decelerator’ called ELENA that slows them down enough to be held for further
manipulation. Several different experiments feed off ELENA in CERN’s antimatter
research hall. ALPHA-g is one of them, and it combines antiprotons with
positrons it collects from a radioactive source.
-
- After making a
thin gas of thousands of antihydrogen atoms, researchers pushed it up a
3-meter-tall vertical shaft surrounded by superconducting electromagnetic
coils. These can create a kind of magnetic ‘tin can’ to keep the antimatter
from coming into contact with matter and annihilating.
-
- Next, the
researchers let some of the hotter antiatoms escape, so that the gas in the can
got colder, down to just 0.5 °C above absolute zero and the remaining antiatoms
were moving slowly.
-
- The researchers
then gradually weakened the magnetic fields at the top and bottom of their
trap, akin to removing the lid and base of the can, and detected the antiatoms
using two sensors as they escaped and annihilated.
-
- When opening any
gas container, the contents tend to expand in all directions, but in this case
the antiatoms’ low velocities meant that gravity had an observable effect. Most
of them came out of the bottom opening, and only one-quarter out of the top.
-
- To make sure that
this asymmetry was due to gravity, the researchers had to control the strength
of the magnetic fields to a precision of at least one part in 10,000. This was
perhaps their most remarkable feat.
-
- The results were
consistent with the antiatoms experiencing the same force of gravity as
hydrogen atoms would. The error margins are still rather large, but the
experiment can at least conclusively rule out the possibility that antihydrogen
falls upwards.
-
- In 2010 they
succeeded in trapping antihydrogen for an extended time, and starting in 2016
they were able to measure how the antiatoms absorb light. But the gravity
experiment required a new level of sophistication.
-
- No one would have
expected antimatter to fall up, if nothing else, because antiprotons are made
of antiquarks, but these only constitute less than 1% of an antiproton’s mass:
the rest is the energy that keeps them together. Insiders have long expected that any
violation, if it exists, cannot be over 1%. Going beyond that would subvert not
only the theory of gravitation, but also the standard model of particle
physics.
-
- A third CERN
experiment, called AEgIS, will attempt to measure the gravitational force on a
beam of antihydrogen atoms in the absence of any magnetic fields. They will aim to reach 1% precision by first
making positive antihydrogen ions (antihydrogen with an extra positron), which
will help to cool the gas down to a fraction of a degree above absolute zero.
-
- Other efforts aim
to measure gravity acting on positronium, a short-lived particle made of one
electron and one positron orbiting each other. ALPHA-g itself plans to aim for
1% precision by letting antihydrogen atoms bump up and down and form a quantum
superposition with themselves.
-
- These are out of
this world experiments!
-
-
-November 24, 2023
ANTIMATTER - responds to gravity? 4238
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