# B "The search for Relativity Violations"

1. May 8, 2017

### oquen

I'm reading the 100 years anniversary edition of Sci-am and there is an article called "The Search for Relativity Violations". Some passages perplexed me:

"In the case of relativity violations,
the equations describing the stick and
the applied force are replaced by the
equations of the ultimate theory. In
place of the stick are the quantum fields
of matter and forces. The natural background
strength of such fields is usually
zero. In certain situations, however,
the background fields acquire a nonzero
strength. Imagine that this happened
for the electric field. Because the electric
field has a direction (technically, it is a
vector), every location in space will
have a special direction singled out by
the direction of the electric field. A
charged particle will accelerate in that
direction. Rotational symmetry is broken
(and so is boost symmetry). The
same reasoning applies for any nonzero
“tensor” field; a vector is a special case
of a tensor.

Such spontaneous nonzero tensor
fields do not arise in the Standard Model,
but some fundamental theories, including
string theory, contain features
that are favorable for spontaneous
Lorentz breaking."

It mentioned electric field breaks Lorentz symmetry yet it added the standard model doesn't break Lorentz symmetry.. isn't electric field part of the standard model?

When you add magnetic field to electric field to become electromagnetic field.. does it break Lorentz symmetry (so called rotational symmetry and boost symmetry)

And what does it mean the fundamental theory may break Lorentz symmetry. Is the consequence for example the strings may all be non-locally connected throughout the universe but at large scale, relativity is a low energy limit. But if the strings can communicate.. won't this cause backward in time causality problem in the low energy limit? How do you make it compatible the low energy obey relativity while at high energy it doesn't?

2. May 8, 2017

### Staff: Mentor

It said a "background" electric field--i.e., one that is present even though everything is in a vacuum state. In other words, it's describing a hypothetical model in which the vacuum is no longer Lorentz invariant.

Yes, but in the Standard Model the vacuum is Lorentz invariant--there is no "background" electric field that is present if everything is in a vacuum state.

It can mean one of two things: that the vacuum is not Lorentz invariant (as described above), or that the underlying Lagrangian itself is not Lorentz invariant (which is a stronger breaking of Lorentz symmetry).

3. May 8, 2017

### oquen

If at lower energy (large scale) the vacuum is Lorentz invariant.. and at high energy (small scale) the vacuum is not Lorentz invariant.. what will prevail? And does it mean if you use high energy, you can find a preferred frame and relativity not valid?

4. May 8, 2017

### Staff: Mentor

What do you mean by "prevail"? In such a hypothetical model, if you do a low energy, larger scale experiment, you will see Lorentz invariance; if you do a high enough energy (small enough scale) experiment, you will see violations of Lorentz invariance.

In such a hypothetical model, yes.

5. May 8, 2017

### oquen

The consequence if such hypothetical model was true is that at large scale you can't send signal faster than light.. but at small enough scale (high enough energy) you can send signal faster than light because relativity was overridden? but how does it make sense? Because if your do the small enough scale experiment and the signal was instantaneously received a light year away, there would be some inertial frame where it could go backward in time.. or does it mean the large scale won't be able to see the small scale instantaneous signal.. hypothetically??

6. May 8, 2017

### Staff: Mentor

Lorentz invariance violation doesn't necessarily mean you can send signals faster than light; you would have to have a specific model to see if it allowed that. But if the model did allow it, yes, it would be on a small scale only.

Then it isn't a small scale experiment.

7. May 8, 2017

### oquen

You mean the faster than light only occurs in the small scale or say within dozens times the planck length only and won't even reach outside the laboratory and if it hits Neptune instantaneously, then since it's no longer small scale and big scale obeys relativity.. then it won't happen at all? No exceptions? Is there no current model or physicists that described such?

8. May 8, 2017

### Staff: Mentor

That's the kind of hypothetical model that the SciAm article appears to be describing. But it's just a hypothetical model; AFAIK nobody has actually constructed one and tried to make definite predictions from it. It's just speculation.

Not that I'm aware of.