For decades there has been a unanimous agreement in the scientific community regarding the size of the proton (Lambert, 2013). Through various experiments, the size of the proton has been proven to be 0.8768 femtometers in radius. This value was widely accepted and considered to be as absolute as the speed of light in a vacuum (Pappas, 2013). Shockingly, recent studies and experiments argue that the radius is actually 4% less than scientists believed it to be (Grossman, 2013). From a particle physics perspective, this small difference is a big deal!
The “old” method of finding the proton’s size utilizes the theory of quantum electrodynamics. This process involves analyzing the wave function and energy of photons emitted by an excited hydrogen atom. In doing so, scientists can determine how far the positively charged proton must extend (Grossman, 2013). This method, other experiments and theoretical calculations confirm a radius of 0.8768 femtometers.
The new technique of measuring proton size involves using muonic hydrogen, a variety of hydrogen in which the orbiting electron is replaced with a heavier particle called the muon (Lancaster, 2011)(Figure 1). Used in conjunction with quantum electrodynamics, physcists attempted to add a few more decimals to the proton’s radius. Instead, the results gave rise to a completely new proton radius of 0.841 femtometres (Lambert, 2013). Both the old and new methods are completely valid in determining the size of the proton. Therefore, the size of the proton seems to fluctuate (Grossman, 2013).
So, what exactly do these different values mean? One idea simply suggests that there might be experimental errors with the “muonic method”. However, this experiment has been repeated countless times. Another theory says that the apparent size of the proton is dependent on the particles in which the proton interacts with (Grossman, 2013). This seems absurd to many scientists, as they believed the size of the proton was fixed.
Physicists Itay Yavin and Maxim Pospelov, from the Perimeter Institute of Physics, proposed that this change is the result of a new fundamental force. They theorize that this proves the existence of a new force-carrying particle. In other words, the proton’s size can vary because of this force. Amazingly, the existence of this new force would clear up discrepancies in the standard model and would explain the measurement of the muon’s gyromagnetic ratio (Lambert, 2013). These unknown new force-carrying particles could also be a candidate for dark matter (Grossman, 2013)!
The rise of quantum mechanics and modern physics has led to many remarkable, innovative and unsettling discoveries in the scientific world. As we venture deeper into the quantum realm we realize that there are fewer knowns than unknowns in our understanding of the universe.
Works Cited
Gualtieri, Dev. Fat Protons. 12 July 2010. Web: http://tikalon.com/blog/blog.php?article=fat_protons [Accessed: 19 Sept. 2013]
Grossman, Lisa. Shrinking Proton Puzzle Persists In New Measurment. 24 Jan. 2013. Web: http://www.newscientist.com/article/dn23105-shrinking-proton-puzzle-persists-in-new-measurement.html#.UjuZVha5z-Y [Accessed: 16 Sept. 2013]
Lambert, Lisa. Case of the Shrinking Proton.23 Aug. 2013. Web: http://perimeterinstitute.ca/node/92070 [ Accessed: 17 Sept. 2013]
Lancaster, Mark. My Favourite Particle: The Muon. 14 May 2011. Web: http://www.theguardian.com/science/life-and-physics/2011/may/14/1 [15 Sept. 2013]
Pappas, Stephanie. Proton size smaller than physicists thought, puzzling new measurements suggest. 13 Apr. 2013. Web: http://www.huffingtonpost.com/2013/04/14/proton-size-smaller-physicists-new-measurements_n_3080196.html [Accessed: 16 Sept. 2013]