A setup of the system used by the BaBar collaboration to probe time-reversal symmetry violation directly. The ϒ(4s) particle was created, it decays into two mesons (which can be a B/anti-B combination), and then both of those B and anti-B mesons will decay. If the laws of physics are not time-reversal invariant, the different decays in a specific order will exhibit different properties. This was confirmed in 2012 for the first time: the first direct violation of T-symmetry. (APS / ALAN STONEBREAKER)

This Is The One Symmetry That The Universe Must Never Violate

The combination of charge conjugation, parity, and time-reversal symmetry is known as CPT. And it must never be broken. Ever.

The ultimate goal of physics is to accurately describe, as precisely as possible, exactly how every physical system that can exist in our Universe will behave. The laws of physics need to apply universally: the same rules must work for all particles and fields in all locations at all times. They must be good enough so that, no matter what conditions exist or what experiments we perform, our theoretical predictions match the measured outcomes.

The most successful physical theories of all are the quantum field theories that describe each of the fundamental interactions that occur between particles, along with General Relativity, which describes spacetime and gravitation. And yet, there’s one fundamental symmetry that applies to not just all of these physical laws, but for all physical phenomena: CPT symmetry. And for nearly 70 years, we’ve known of the theorem that forbids us from violating it.

There are many letters of the alphabet that exhibit particular symmetries. Note that the capital letters shown here have one and only one line of symmetry; letters like “I” or “O” have more than one. This ‘mirror’ symmetry, known as Parity (or P-symmetry), has been verified to hold for all strong, electromagnetic, and gravitational interactions wherever tested. However, the weak interactions offered a possibility of Parity violation. The discovery and confirmation of this was worth the 1957 Nobel Prize in Physics. (MATH-ONLY-MATH.COM)