 For most of us, symmetry is straightforward. A shape is symmetrical if it remains the same after reflection or rotation. For particle physicists, however, a key question is whether all physical laws exhibit a specific type of symmetry called CPT symmetry. Just like a shape that remains the same after you rotate, reflect, and then translate it, a physical law with CPT symmetry remains the same if the particles in an interaction governed by that law undergo three specific transformations, namely, the particles reverse charge, the particles are replaced with their mirror images, and time is run backwards. In a new study from the Alice experiment at CERN's Large Hadron Collider, researchers measured the difference in the mass to charge ratio of a nucleus and its corresponding antinucleus to an unprecedented precision and found evidence suggesting that this fundamental symmetry holds for the force-binding protons and neutrons into nuclei. Since becoming operational in 2009, the Large Hadron Collider has made headlines as the world's largest and most powerful particle accelerator. The project, known as Alice, or a Large Ion Collider experiment, studies the collisions of lead nuclei at very high energies. These collisions create a variety of particles and their corresponding antiparticles, including heavy hydrogen and light helium nuclei and antinuclei. By measuring the energies of these nuclei and antinuclei and the time they take to travel from the point of collision to the detector, the authors were able to determine the mass to charge ratio difference between each nucleus and its corresponding antinucleus. If CPT symmetry is upheld, the mass to charge ratio of each nucleus should be the same as that of its antinucleus. The authors also inferred the differences in the energy required to keep the components of each hydrogen or helium nucleus bound together, called the binding energy, with respect to their antimatter counterparts. Within the measurement errors, the hydrogen nuclei and antinuclei had the same mass to charge ratio, as did the helium nuclei and antinuclei. This result provides further evidence that the forces binding nuclei together do indeed obey CPT symmetry, as any asymmetry would have created a difference in the matter and antimatter mass values. The values for these ratios are between 10 and 100 times more precise than those obtained from previous direct mass measurements in the same systems. Combined with the findings of other studies, these results will help physicists determine which of the many theories about the fundamental laws of our universe are most likely to be true. Because these laws describe the nature of all interactions between matter, insights in this field shed light on many topics within fields ranging from quantum mechanics to cosmology.