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From my basic understanding of popular-level physics articles and books and such, the 4 forces (Electromagnetism, Gravity, Strong and Weak Force) used to be 1 force in the early universe, then split off into the 4 forces as the universe expanded and cooled down.

I'm wondering, if the universe is continuously expanding and cooling down, could the 4 forces split off or "decay" again in the far future? Has anyone theorized about this at all? Billions of trillions of years in the future, might magnets cease to induce electrical currents, or could electrical activity cease to carry a magnetic component, or could the Weak Force break up into its individual components?

Steven Bensics
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    Related: Vacuum decay – Alfred Centauri May 02 '15 at 00:55
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    That all forces can be unified is a hope and a program. It is by no means certain that gravity is even a "force" in the same sense as the electroweak and the color force are. Searches for a fifth, sixth etc. force are constantly under way. One can probably make a scale argument that there should be a cascade of new effects/forces at very low energies, but that is not a question that can, at this time, be answered experimentally. – CuriousOne May 02 '15 at 00:59
  • Do you have a source for there being one force that "split" into others? – Christopher King May 02 '15 at 01:59
  • @PyRulez: It sounds like the OP has heard that e.g. the electroweak force, at low energy, expresses itself as electromagnetism for one and the weak force, for another, and that, at sufficiently high temperature, the two can be thought of as a single unified force. One can argue about how useful that image is. – CuriousOne May 02 '15 at 02:31

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There are a number of issues with this question - it rests on false assumptions. The short answer is: No, we do not expect more forces to appear in any way.

Yet, to say "the four forces used to be one force in the early universe" is overstating the knowledge we have. It is the basic idea of Grand Unified Theories to merge the three forces excluding gravity into a single force, and beyond that, we need a new kind of theory altogether, because gravity does not fit into the framework of quantum field theory that the grand unification is supposed to happen in.

All that we know so far is that the weak and the electromagnetic force unify into the electroweak force above the electroweak scale, or rather, especially after the discovery of the Higgs, we are reasonably certain that electroweak theory is correct. There is no universally accepted candidate theory for unifying the strong force with the electroweak force.

Nevertheless, we might say quite easily that we do not expect further splitting up of the forces: Whether the forces are unified or not does not depend on time in any way (which you seem to imply when speaking of "the early universe"), it simply depends on which energy scale we are at - how "hot" is the system we are looking at. If the energy scale of the system drops below the unification scale, then it will behave as if the forces have been split up. Our present universe is very cool compared to the early universe, and it would be highly surprising if there is further symmetry breaking lurking below our current scale - especially because we ought to have seen the particle/field that might acquire a vacuum expectation value already.

ACuriousMind
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