Fifth force
A hypothetical force beyond the four known fundamental interactions.
In physics, a fifth force is a hypothetical fundamental interaction beyond the four known forces: gravitational, electromagnetic, strong nuclear, and weak nuclear. Proposed to explain anomalous observations not fitting existing theories, no evidence supporting these models has been found.
- type
- Hypothetical fundamental interaction
- based_on
- Reanalysis of Eötvös experiment
- key_parameter_strength
- α (around 1% of gravity)
- key_parameter_range
- λ (a few hundred meters)
- status
- No compelling evidence found
Lore & Background
Theoretical proposals for a fifth force are driven by inconsistencies between general relativity and quantum field theory, as well as the hierarchy problem and cosmological constant problem. Some physicists speculate that a form of dark energy called quintessence could be a fifth force. Other theories assume spin-dependent exotic interactions, where the force depends on particle spin orientation. Experimental searches include tests of the equivalence principle, extra dimensions, and cepheid variable stars, but no variation from Einstein's theory has been found.
Reader's Guide
The fifth force remains a speculative concept in physics, proposed to address anomalies not explained by the four known forces. Its significance lies in its potential to bridge gaps between general relativity and quantum mechanics, and to explain phenomena like dark energy. Despite numerous experimental searches—including tests of the equivalence principle, measurements in mines and boreholes, and studies of cepheid variables—no compelling evidence has been found. The search continues, but the fifth force remains unconfirmed.
Did You Know?
- Fischbach's model proposed a Yukawa-like term with strength α around 1% of gravity and range λ of a few hundred meters.
- Australian researchers measuring gravity in a mine shaft found a discrepancy that could be explained by a repulsive fifth force with a range from centimetres to a kilometre.
More in Relativity And Gravitation 1-20
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