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New Method of Searching for Fifth Force

A UCLA-led team has discovered a new way of probing the hypothetical fifth force of nature using two decades of observations at W. M. Keck Observatory, the worlds most scientifically productive ground-based telescope.
There are four known forces in the universe: electromagnetic force, strong nuclear force, weak nuclear force, and gravitational force. Physicists know how to make the first three work together, but gravity is the odd one out. For decades, there have been theories that a fifth force ties gravity to the others, but no one has been able to prove it thus far.

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Title: No fifth force in a scale invariant universe
Author: Pedro G. Ferreira, Christopher T. Hill, Graham G. Ross

We revisit the possibility that the Planck mass is spontaneously generated in scale invariant scalar-tensor theories of gravity, typically leading to a "dilaton." The fifth force, arising from the dilaton, is severely constrained by astrophysical measurements. We explore the possibility that nature is fundamentally Weyl-scale invariant and argue that, as a consequence, the fifth force effects are dramatically suppressed and such models are viable. We discuss possible obstructions to maintaining scale invariance and how these might be resolved.

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LHC scientists to search for 'fifth force of Nature'

The next couple of years will be make or break for the next big theory in physics called supersymmetry - SUSY for short. It might make way for a rival idea which predicts the existence of a 'fifth force' of nature.
Next Spring, when the Large Hadron Collider (LHC) resumes its experiments, scientists will be looking for evidence of SUSY.

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Researchers Propose New Way to Probe Earth's Deep Interior

Researchers from Amherst College and The University of Texas at Austin have described a new technique that might one day reveal in higher detail than ever before the composition and characteristics of the deep Earth.
There's just one catch: The technique relies on a fifth force of nature (in addition to gravity, the weak and strong nuclear forces and electromagnetism) that has not yet been detected, but which some particle physicists think might exist. Physicists call this type of force a long-range spin-spin interaction. If it does exist, this exotic new force would connect matter at Earth's surface with matter hundreds or even thousands of kilometres below, deep in Earth's mantle. In other words, the building blocks of atoms - electrons, protons, and neutrons - separated over vast distances would "feel" each other's presence. The way these particles interact could provide new information about the composition and characteristics of the mantle, which is poorly understood because of its inaccessibility.
 
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Is a cosmic chameleon driving galaxies apart?

A shape-shifting fifth fundamental force could neatly explain the mystery of dark energy - and some other puzzling astronomical observations

The basic idea for this fifth force was hatched in 2004 by Justin Khoury  and Amanda Weltman, then members of a team led by well-known string theorist Brian Greene at Columbia University in New York City. String theory is the favoured route to unifying gravity, the odd one out among the four forces, with the other three under the umbrella of quantum mechanics. It is a great playground for devising new fields and forces. The theory is formulated in 11 dimensions, seven of which are assumed to be curled up so small that we cannot see them. Disturbances in those curled-up dimensions might make themselves felt as "extra" forces in the four dimensions of space and time we do see.
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Occasionally, physicists have postulated the existence of a fifth force in addition to the four known fundamental forces. The force is generally believed to have roughly the strength of gravity (i.e. it is much weaker than electromagnetism or the nuclear forces) and to have a range of anywhere from less than a millimetre to cosmological scales.
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