But could there be a fifth force still waiting to be discovered?
Nature News reports that a team of physicists led by Attila Krasznahorkay of the Hungarian Academy of Sciences published a rather provocative paper late last year in Physical Review Letters pre-print version available here claiming that a strange radioactive decay anomaly is indicative of an unknown fundamental force.
Speculation about this elusive fifth force has existed for years, partly driven by the inability of the standard model of particle physics to explain dark matter — a hypothetical form of matter that comprises a huge portion of the mass and energy in the observable universe.
When the protons smashed against the lithium at the precise angle of 140 degrees, more electrons and positrons poured out than expected.
As the Nature News article points out, there s a decent mix of scepticism and excitement about the experimental results.
Researchers at the Thomas Jefferson National Accelerator Facility and other groups in the United States and Europe are now working on the problem, and expect to confirm or invalidate the Hungarian experimental results in about a year.