We live in both spatial dimensions (three of them!) as well as a time dimension, which seems to always tick forwards. We don’t know why we never see it tick backwards, all physics we know of work the same way when time is reversed aside from weird weak force shenanigans. This is called time reversal symmetry, and is part of the larger CPT symmetry, which is a topic I have researched before!
C stands for charge conjugation, while P stands for parity. C symmetry is to do with the reversal of the charges of all particles in a system, while P is, in a nutshell, the same process but in a “mirror world”, so a particle with clockwise spin becomes anticlockwise, your left hand becomes your right. Originally, it was thought that C symmetry always holds in the universe, but this was proven to be incorrect due to weak force shenanigans. The same was true with CP invariance, the combination of C and P symmetries thought to always hold, more weak force weirdness led to the breaking of that. This finally led to the theory of CPT invariance, which added time reversal symmetry. This means CP violating processes must also break time reversal symmetry!
C and CP violation is super important for the study of the baryon asymmetry, which, in a nutshell, is the question of why there is more matter (mostly made up of baryons) than antimatter. Our current physics doesn’t have a good explanation for this, since most processes produce and destroy the two equally. C and CP violation would mean antimatter (which has opposite charge to their matter counterparts) can act differently to normal matter, giving rise to an asymmetry between the two. Investigations towards new extended models of physics usually include additional CP violation (in the form of new processes, particles, etc.) for this reason.
Baryons are subatomic particles composed of three quarks. You might have heard of the proton and neutron, which have uud and udd quark configurations respectively, where u is the symbol for the up quark and d is the down quark. Most matter is made up of these baryons.
Electrons are not made of quarks, they are fundamental particles (not made of smaller bits) categorised as leptons. Another lepton you might have heard of is the neutrino, which you might have heard of as the “ghost particles” since they are nearly massless and rarely interact with anything. Because of their ghostlike nature, it is difficult to measure them, which is why focus is directed towards baryon asymmetry over lepton asymmetry.
If there was an equal number of matter and antimatter particles, everything would annihilate and you would be left with only photons. Stars, planets, etc. were all able to form, meaning there must have been some process that created a matter-antimatter asymmetry. And of course, we are made of matter, our existence tells us that some amount of matter must have survived annihilation.
Our measurements of the CMB as well as the abundances of light elements show us that, during the early universe, there was one additional baryon for every million anti-baryons. Without these literal one-in-a-million baryons, no matter would have been left in the universe.
CPT invariance and CP violation is a really interesting topic with very deep implications for how our universe formed. If you are in any way interested in physics or astronomy, I would really recommend reading into it!
We live in both spatial dimensions (three of them!) as well as a time dimension, which seems to always tick forwards. We don’t know why we never see it tick backwards, all physics we know of work the same way when time is reversed aside from weird weak force shenanigans. This is called time reversal symmetry, and is part of the larger CPT symmetry, which is a topic I have researched before!
C stands for charge conjugation, while P stands for parity. C symmetry is to do with the reversal of the charges of all particles in a system, while P is, in a nutshell, the same process but in a “mirror world”, so a particle with clockwise spin becomes anticlockwise, your left hand becomes your right. Originally, it was thought that C symmetry always holds in the universe, but this was proven to be incorrect due to weak force shenanigans. The same was true with CP invariance, the combination of C and P symmetries thought to always hold, more weak force weirdness led to the breaking of that. This finally led to the theory of CPT invariance, which added time reversal symmetry. This means CP violating processes must also break time reversal symmetry!
C and CP violation is super important for the study of the baryon asymmetry, which, in a nutshell, is the question of why there is more matter (mostly made up of baryons) than antimatter. Our current physics doesn’t have a good explanation for this, since most processes produce and destroy the two equally. C and CP violation would mean antimatter (which has opposite charge to their matter counterparts) can act differently to normal matter, giving rise to an asymmetry between the two. Investigations towards new extended models of physics usually include additional CP violation (in the form of new processes, particles, etc.) for this reason.
Baryons are subatomic particles composed of three quarks. You might have heard of the proton and neutron, which have uud and udd quark configurations respectively, where u is the symbol for the up quark and d is the down quark. Most matter is made up of these baryons.
Electrons are not made of quarks, they are fundamental particles (not made of smaller bits) categorised as leptons. Another lepton you might have heard of is the neutrino, which you might have heard of as the “ghost particles” since they are nearly massless and rarely interact with anything. Because of their ghostlike nature, it is difficult to measure them, which is why focus is directed towards baryon asymmetry over lepton asymmetry.
If there was an equal number of matter and antimatter particles, everything would annihilate and you would be left with only photons. Stars, planets, etc. were all able to form, meaning there must have been some process that created a matter-antimatter asymmetry. And of course, we are made of matter, our existence tells us that some amount of matter must have survived annihilation.
Our measurements of the CMB as well as the abundances of light elements show us that, during the early universe, there was one additional baryon for every million anti-baryons. Without these literal one-in-a-million baryons, no matter would have been left in the universe.
CPT invariance and CP violation is a really interesting topic with very deep implications for how our universe formed. If you are in any way interested in physics or astronomy, I would really recommend reading into it!
Went on a little bit of an off-topic tangent there, but I hope you learned something neat!