B Understanding the GUT Scale: Merging Fundamental Forces at High Energies

[nolxiii]

So I've heard it talked about how how at high energies all the strength of all fundamental forces are expected to merge together to single force, but don't quite get how you get from "all the forces have the same strength at high energies" to "all the forces are really the same force."

Couldn't they have the same strength but still act differently? And if they acted the same at high energies wouldn't their behavior at low energies still differentiate them into separate phenomenon?

 

[nikkkom]

So I've heard it talked about how how at high energies all the strength of all fundamental forces are expected to merge together to single force, but don't quite get how you get from "all the forces have the same strength at high energies" to "all the forces are really the same force."

You are right, it does not follow. It's just a "maybe", a hint from the data that maybe it's one force.

And if they acted the same at high energies wouldn't their behavior at low energies still differentiate them into separate phenomenon?

We have an example. Electroweak SU(2) force is one force, but at low energies it "breaks" into two seemingly completely different things: W+- bosons are quite different from that part of SU(2) which is part of photons.

 

[nolxiii]

Right on. Still struggling somewhat to build a mental model of how the electroweak symmetry breaking works, the link below I think helped a bit though. Am I understanding this right that if the symmetry just happened to break in such a way that W bosons were (nearly?) massless that the weak and electromagnetic forces would still behave more or less identically?

http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/unify.html

 

[nikkkom]

An unbroken SU(2) force would not be identical to electromagnetism.
An unbroken U(1) force is identical to electromagnetism.

 

[Blue Scallop]

An unbroken SU(2) force would not be identical to electromagnetism.
An unbroken U(1) force is identical to electromagnetism.

what would this unbroken SU(2) force look like?

 

[nikkkom]

It would be a long-range force, IIRC attractive for any SU(2) charges (unlike electricity, where like charges repel).