# Could there be some process or event that would make the universe to be Lorentz non-invariant?

As far as we know the universe is invariant under the Lorentz symmetry and does have many other fundamental symmetries from which we derive the fundamental laws of physics.

But could there be any process or event that would violate all these symmetries making the universe non-invariant to Lorentz symmetry and all the other symmetries that exist?

It depends on what you mean by "could".

"Could there be any process or event that would violate all these symmetries, based on what we know today?" NO, otherwise we wouldn't derive the fundamental laws of physics from these symmetries.

"Could there be any process or event that would violate all these symmetries, considering processes that we've never seen yet?" YES, and that would mean that our "fundamental laws of physics" derived by these symmetries aren't that fundamental after all.

To be clear: there have been many symmetries that, in the past, were believed to be fundamental (parity symmetry, for a start). We then performed some more precise experiments, and we found out that the so-thought symmetries were violated. We can still assume they're conserved (if we're concerned with low-precision experiments) but we know they aren't. Lorentz symmetry still hasn't made this jump, and we don't know if it ever will.

[...] if we found that the Standard Model was complete (or that at least it was in a true vacuum state), would these vacuum phase transitions (from the true vacuum into a false one and then decaying) change the particle physics we know [...]?
And if that would be possible, then, since physics could change depending on the energy and the characteristics of the vacuum, could one of these vacuum phase transitions result in a specific configuration of particles, forces, fields, symmetries and groups that would be compatible with a vacuum from a Lorentz-symmetry violating theory [...]?

A "theory" is what you can make from some degrees of freedom (fields) and some symmetries. Please take a look at this (very simplistic) pictorial diagram: The red ball is the state (our universe) while the green profile is the theory (the Standard Model in the upper left). The symmetries of the theory are represented by the shape of the profile, while the symmetries of the state are represented by the position of the ball with respect to the axis of symmetry of the profile. In the upper left, for example, the theory has a left-right symmetry, and the state has the same symmetry (because it sits at the center).
Now, you say that there is an "injection" of energy: you're right, this is theoretically possible. After this injection, the state sits in a new, higher, metastable vacuum (lower left in the image).
Now one of three things can happen (called $$a$$, $$b$$, and $$c$$ in the image):

• $$a$$ - the state goes back to the same position as it was before. The SM is restored (it still has a left-right symmetry) and maybe even enhanced with more symmetries. The state isn't fully symmetric anymore (because it doesn't sit at the center) but it still has the same symmetries it had before (it just doesn't have the possible new symmetries).
• $$b$$ - the state goes to another, similar, vacuum. The SM is restored (it still has a left-right symmetry) and maybe even enhanced with more symmetries. The state is a different one, there might be different particles laying around, but it didn't lose any symmetry!
• $$c$$ - the state goes to another, different, vacuum. The SM is destroyed (it doesn't have a left-right symmetry). The state is a different one, there might be different particles laying around, and probably with different symmetries. This is what I mean by "not mainstream".
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– rob
May 31, 2022 at 12:12