Recent advances in experimental physics have allowed very large molecules to exist in two places at once.
While physicists have been able to do this for quite some time with smaller particles, this is the farthest we've successfully achieved in replicating this effect on a larger scale.
Let's backtrack a bit to where it all started.
For a long time, scientists, all the way from Democritus to Descartes, to Newton, have been debating whether light acted as a particle or as a wave. However, an experiment done by Thomas Young in 1801 called the "double-slit experiment" was able to prove that light acted as both a particle and a wave, called particle–wave duality.
The experiment shone light through two slits onto a screen behind. If particle acted solely as a particle, the light would have concentrated in the shape of the slit, which didn't happen. Instead, a pattern of bright and dark spots appeared on the screen due to the light from both slits interfering with each other, called matter–wave interference. When they added up, they became brighter on the screen, but if they cancelled out, they appeared dark on the screen. This created an alternating pattern of bright and dark areas called an interference pattern.
Because of the double-slit experiment, we now know that matter behaves as both a particle and a wave. What's interesting is that when matter acts as a wave, it can occupy two places at once. This phenomenon is called quantum superposition.
While it's much easier to do this experiment with smaller particles like light, it's more difficult to replicate it for larger molecules. Since it's harder to observe the wave-like behavior of larger chunks of matter, their interference patterns are harder to measure as well. In addition, since you're dealing with a matter that's much larger than a single photon of light, several factors need to be accounted for in experimentation, such as the Earth's rotation and gravity.
Published in the September 2019 issue of Nature Physics, the researchers were able to report interference with a type of molecule called functionalized oligoporphyrins. These molecules, up to 2000 atoms in size and with masses over 25,000 times larger than hydrogen atoms, are the heaviest molecules to date which show matter–wave interference and quantum superposition. The experiment was even able to reach 90% of the expected visibility in the interference fringes.
What's also interesting about the study is that the results show excellent agreement with quantum theory while they cannot be explained by classical mechanics.
With the scalability of this experiment and forthcoming advances in experimental physics technologies, future experimentation can likely push the boundaries further for testing matter–wave interference and quantum superposition in even larger molecules.
And while it's a long time until we can test this experiment out on any famous physicists' feline friends, the data gathered from the experiment give us greater insight into the world of quantum theory and the progress we've made in the world of physics.
