Credit: Faculty of Physics, University of Warsaw

Per the big bang theory (the most widely accepted theory that details the origin of the universe), the whole of the cosmos- with its three dimensions of space and one dimension of time - was created in mere nanoseconds almost 14 billion years ago. Notably, the big bang theory does not simply offer an explanation for the origin of the matter that now permeates spacetime, it offers an explanation for creation of spacetime itself. Many believe that the big bang theory is problematic for precisely this reason i.e., it is problematic because it seems to assert that something came from nothing. However, there is an idea that could make sense of this little conundrum, and it is getting a strong foothold among many in the scientific community. This idea proposes something quite interesting - that spacetime may NOT be the same for all elementary particles.


Say what?


For quite a number of years now, physicists have been attempting to reconcile classical quantum mechanics with general relativity in a way that would hopefully allow us to determine the laws of quantum gravity. One such model is called loop quantum gravity (or LQG), which we have discussed before. This model postulates that spacetime itself is likely similar in structure to fabric (like a tapestry), comprised of a series of minutely small fibers that are twisted and curved to form loops. Under this scenario, the tapestry would contain some million trillion trillion trillion trillion trillion (10^66) fibers (per square centimeter!)


The model is accompanied by two separate, but corresponding fields: a gravitational field and a scalar field. The former is needed to input the influence of gravity in spacetime (this is important because as far as we know, mass warps the very fabric of spacetime, which in turn, is responsible for the effects of gravity). While the latter (the scalar field) would be used to basically map out and assign numbers to the numerous "points" of space (with each point representing matter). Obviously, the movement of atoms on a microscale is very much outside of the realm of the things we generally see (and experience) here on Earth. So actually verifying the existence of the fibers that make up LQG - with the two corresponding fields - has been difficult, up until this point.


Source: Wikicomons

Recently though, a team of physicists (who hail from the Warsaw University), have been hard at work developing a model that accurately depicts the interactions between quantum gravity for zero rest mass particles and non-zero rest mass ones (said interactions are charted in the standard model of particle physics). Some particles are known to have zero rest masses. Non-zero rest mass particles- such as the proton, neutron and the Higgs Boson, the particle that plays a crucial role in imparting mass on certain particles (along with its corresponding field, the Higgs field), make ideal case studies because they tend to be simplistic mathematically.


The team, using the appropriate equations that represent the suggested behavior of certain particles under the loop quantum gravity idea, compared the aforementioned mathematical models to several different ones, which could differ based on the symmetry of spacetime. Particularly, they used the preferred model, which says spacetime is isotropic - or generally the same when viewed  in all different directions. It's expected that regardless of the mass, momentum or energy level of photons, this should remain constant. What they found though is unexpected -- this is true for massless particles, but not for the particles with tangible mass. This leads them to postulate that the particles that fall under the latter category may very well experience a slightly different spacetime than the others. Furthermore, the type of spacetime can vary depending on the direction in which a particle in motion is traveling in.


In this image, the "preferred" direction is on the left, in contrast to the opposite hemisphere (right) (Credit: Cai, et al)

If correct, the implications would literally be astounding. Such a finding *COULD* possibly mean that there is a universal disconnect between what the massless particles would experience in space, and particles there have mass. Even more so astounding would be the fact that the findings could mean there is a preferential direction in space (and no, I am not speaking of the great attractor, but something else entirely) for particles that are in motion. However, this is of very little important to us in a physical sense, as we exist outside of a quantum system. Our observations of photons - regardless of their direction of travel - will always show that the particles generally posses the same characteristics. Still. This is a giant leap in helping us understand quantum systems (and by proxy, the universe as a whole).

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