I Lorentz Invariance?

[Purge]

[Mentor Note: Two thread starts merged into one]

So what I've been thinking about is how Lorentz Invariance was never proven, it was only assumed to be true. And when I think about the Universe, nothing is actually truly in an inertial reference frame. Everything is accelerating at relativistic speeds, including Earth. Doesn't that mean that no matter how many observations we make, we will always be blind to Lorentz violations that only happen at low speeds?

And if Lorentz Invariance doesn't hold, then one of the three assumptions that CPT symmetry relies on is broken and CPT violation is possible.

 

[Orodruin]

First of all, physics doesn’t prove things. It is an empirical science where you can test the predictions of a theory within the measurement errors of your experiment.

Second, (local) Lorentz invariance has been tested to high precision.

Third, at low speeds you just recover Newtonian classical mechanics. It is unclear why you think this has not been tested.

 

[Purge]

First of all, physics doesn’t prove things. It is an empirical science where you can test the predictions of a theory within the measurement errors of your experiment.

Second, (local) Lorentz invariance has been tested to high precision.

Third, at low speeds you just recover Newtonian classical mechanics. It is unclear why you think this has not been tested.

Lorentz Invariance has never truly been tested from a "zero-velocity" reference frame, so we may be moving through a preferred Higgs- or gravity-defined vacuum without knowing it. Like I already said, everything, including Earth, is accelerating at relativistic speeds.

Also, we can't test for Lorentz symmetry at the Planck scale, which means that it's possible that Lorentz symmetry becomes approximate or emergent.

Edit: To your third point, what I'm trying to say is that you cannot make that claim. NOTHING has ever been tested at low speeds. Ever. The Earth orbits the Sun, the Sun orbits a supermassive black hole, and the Milky Way galaxy as a whole is accelerating away from other galaxies toward the Great Attractor.

 

[renormalize]

Lorentz Invariance has never truly been tested from a "zero-velocity" reference frame.

Suppose you were given a capable spaceship in which to fly that contains whatever test equipment you desire. How would you maneuver that vehicle to achieve "zero velocity"? What measurements would you make to verify that you really were in that exact reference frame?

Like I already said, everything, including Earth, is accelerating at relativistic speeds.

Speed and acceleration are not the same. Please use accurate terminology.

NOTHING has ever been tested at low speeds. Ever.

Can you quantify "low speed"? The Milky Way is moving toward the Great Attractor at less than 0.2% of light speed. How low do you have to go to be satisfied?

 

[Purge]

Suppose you were given a capable spaceship in which to fly that contains whatever test equipment you desire. How would you maneuver that vehicle to achieve "zero velocity"? What measurements would you make to verify that you really were in that exact reference frame?

Speed and acceleration are not the same. Please use accurate terminology.

Can you quantify "low speed"? The Milky Way is moving toward the Great Attractor at less than 0.2% of light speed. How low do you have to go to be satisfied?

That's why I put "zero velocity" in quotes. It is difficult to define what "zero velocity" truly is, so physicist typically use the rest frame of the CMB.

As for speed, it doesn't necessarily have to be low to test for Lorentz Invariance. The key is that the test be conducted from a true inertial reference frame. I was simply pointing out that tests conducted so far are all at relativistic speeds (significant relativistic corrections).

 

[renormalize]

The key is that the test be conducted from a true inertial reference frame. I was simply pointing out that tests conducted so far are all at relativistic speeds (significant relativistic corrections).

An inertial frame is not defined in terms of speed, it is characterized as having zero acceleration. And that's true in both Newtonian and relativistic physics; i.e., any frame moving at any uniform velocity is inertial. So I think you argue from a misconception.

 

[PeterDonis]

Lorentz Invariance has never truly been tested from a "zero-velocity" reference frame

That's because there is no such thing.

we may be moving through a preferred Higgs- or gravity-defined vacuum without knowing it.

If it's vacuum, it doesn't have a preferred frame. That's part of the definition of "vacuum"--that it has no preferred state of motion.

everything, including Earth, is accelerating at relativistic speeds.

Relative to what?

we can't test for Lorentz symmetry at the Planck scale, which means that it's possible that Lorentz symmetry becomes approximate or emergent.

There are plenty of papers in the literature about hypothetical models along these lines. If you want to discuss one, please start a new thread and give the paper you want to discuss as a reference.

NOTHING has ever been tested at low speeds. Ever.

Nonsense. Practically everything on Earth itself is moving at "low speeds" relative to other things on Earth. We all effectively run thousands of tests of the validity of the low speed approximation of our best current physical theories every day as we go about our daily business. And of course physicists have done many such tests to much higher precision.

 

[Orodruin]

Lorentz Invariance has never truly been tested from a "zero-velocity" reference frame, so we may be moving through a preferred Higgs- or gravity-defined vacuum without knowing it. Like I already said, everything, including Earth, is accelerating at relativistic speeds.

This demonstrates a fundamental misunderstanding of relativity - even Galilean relativity. There is no such thing as an absolute zero velocity. In fact, if there were then that in itself would imply Lorentz violation.

 

[Dale]

Lorentz Invariance has never truly been tested from a "zero-velocity" reference frame,

That doesn't make a lot of sense. Lorentz invariance doesn't need to be tested from a "zero-velocity" frame. What specific experiment do you think depends on being tested from a “zero-velocity” frame?

When SR is tested we use a test theory. The test theories don’t require that the frame of the test be a “zero velocity” frame, but they are able to distinguish whether such a frame exists or not through their parameters.

If such a frame existed then we could measure that it exists and how fast we are moving with respect to it, based on the parameters of the test theory that we measure.

The key is that the test be conducted from a true inertial reference frame.

It is not necessary to test in a true inertial frame either. Most valid tests of relativity are insensitive to the acceleration. Those that are sensitive to it simply measure it and account for it.

You are putting in meaningless restrictions. There no test theories or alternate theories that require such tests.

As an exercise, pick an experiment and pick a test theory. Determine the relevant parameter for the test theory and calculate its value under the assumption that the apparatus is moving at velocity $v$. Find the value of the parameter that corresponds to special relativity, and see if it depends on $v$.

 

[Demystifier]

nothing is actually truly in an inertial reference frame. Everything is accelerating at relativistic speeds, including Earth.

In addition to what others already told you, it seems that you don't even understand the difference between acceleration and velocity.