Matter and missing matter
The 94% of the mass of the visible Universe is made up of neutrons, protons and electrons. Nearly ALL science deals with this atomic matter. Exotic hadrons and mesons are all very unstable with half-lives generlly between 10 –10 and 10 –24 seconds. Protons have a half-life greater than the age of the Universe ... free neutrons have a half-life of about 10 minutes, but, within the haven of the atomic nucleus, they are effectively stable.
It turns out that normal matter is made up of a dazzling array of subatomic particles ... and then there’s antimatter. But how do we explain the fact that most of the matter and energy in the Universe is invisible and, as yet, undetectable? Well, we can’t. Yet.
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Baryons (3 quarks) Exotic 38 observed 36 predicted
Neutrons
Protons
H
Electrons
Muon
atte mal m r – 4.9% Nor
Neutrinos
s–
6%
s–1
0.2 %
The Universe ... as we know it ..
What form does normal matter take?
– 81.6%
3
ino
.6 %
m eliu dh an
Leptons
em
–0
Free h ydr og en
Atomic matter
What is normal matter made of?
r el
s en t
S t ar
Mesons (2 quarks)
27 observed 5 predicted
ie eav
tr Neu
Dar km at t
Hadrons (made of quarks)
% 8 . 6 2 –
Tau
Electrons (along with neutrons and protons) are the other main ingredient of normal matter. They are stable and have a mass more than 1,800 times smaller than that of a proton. There are three flavours of neutrino (they can change in mid-flight) and they have a mass more than 500,000 times smaller than that of an electron. Muons and tau particles are massive and very short-lived.
Antihadrons (made of antiquarks) Antibaryons Exotic 38 observed 36 predicted
Antineutrons
Antiprotons
Antimatter Antimesons
27 observed 5 predicted
Atomic antimatter
Antileptons 3
Antineutrinos
Antimuon
Positrons
Antitau
All subatomic particles have twin anti-particles. Antimatter and matter annihilate completely on contact, releasing hugely energetic photons.
Dark energy is actually not energy. It is tension – a combination of pressure and energy density – but like energy, dark energy isn’t an object or set of objects, but a property that fields, or combinations of fields, or spacetime itself seem to have. We don’t yet know what is responsible for the dark energy whose presence we infer from the accelerating Universe. In another sense it is just a constant to balance out the results of our equations. And it may be quite a while before we do know!
Dark energy – 68.3%