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In Newtonian mechanics and relativity, inertia is typically considered an intrinsic property of mass. However, if an object’s inertia were observed to increase under certain conditions, could this be interpreted as evidence of absolute motion?

Specifically:

Would such an effect be consistent with known physics, or would it contradict relativity?

Are there any theoretical models or experimental setups that explore a possible link between inertia and absolute motion?

I’d appreciate any insights from classical mechanics, relativity, or alternative physics frameworks.

Assad Hamad
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3 Answers3

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However, if an object’s inertia were observed to increase under certain conditions, could this be interpreted as evidence of absolute motion?

Kind of. When we write our physical laws, we typically do so in the form of a Lagrangian. For electromagnetism, for example, we would write $$\mathcal{L}=-\frac{1}{4\mu_0} F^{\alpha\beta}F_{\alpha\beta}-A_{\alpha} J_{free}^{\alpha} + \frac{1}{2} F_{\alpha\beta} M^{\alpha \beta}$$

It can be shown that this Lagrangian leads to an action which is symmetric under time translations, spatial translations, spatial rotations, and boosts. Per Noether's theorem, this leads to conservation of energy, conservation of momentum, conservation of angular momentum, and conservation of the velocity of the center of mass-energy respectively.

So, if we were to find an experiment in which momentum is fundamentally not conserved, then that would indicate that the laws of physics do not have spatial translation invariance. If we were to find an experiment in which the velocity of the center of mass-energy is not conserved, then that would indicate that the laws of physics do not have invariance under boosts. I would consider either of those results to be evidence of absolute motion.

Any experiment that checks for the conservation of momentum or the conservation of the velocity of the center of mass-energy would qualify as an experiment that tests for this. Thus far, all such experiments have been consistent with the principle of relativity.

Are there any theoretical models or experimental setups that explore a possible link between inertia and absolute motion?

Yes, there are many.

There is the parameterized post Newtonian formalism for gravity, the standard model extension (SME) for particle physics, and the Robertson Mansouri Sexl framework for special relativity.

In particular, the SME is especially useful because it captures all possible Lorentz violations to the entire standard model. There is a rich and evolving literature using the SME to test for ever more subtle Lorentz violations.

It is precisely because we have such theories that we can experimentally test the idea that there is no absolute motion. It is because we have such theories that we can analyze and design experiments searching for Lorentz violations.

Dale
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Are there any theoretical models or experimental setups that explore a possible link between inertia and absolute motion?

No. There is no current theory that incorporates "absolute motion." Absolute motion is an idea that physicists discarded more than one hundred years ago.

You appear to be seeking help to design an experiment that will prove our current understanding of nature to be wrong. You won't get much help from people who believe that it's correct. You can try random experiments until, completely by accident, you observe some new phenomenon that nobody ever has observed before; but good luck with that! It might take a while.

A better strategy would be to base your experiments on a deep understanding of the thing that you are trying to disprove. Study all that is known about mechanics, study the theory and all of the experiments that support the theory. Then, look for the flaw. Look for some detail that somebody missed, and use that information to guide your experimentation.

Solomon Slow
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If an object’s inertia were observed to increase under certain conditions, could this be interpreted as evidence of absolute motion ?

It depends what you mean by "under certain conditions". As pointed out in other answers, if an object's invariant mass changes then we expect its inertia to change too. As it stands, this question is too vague to answer.

Would such an effect be consistent with known physics, or would it contradict relativity ?

One of the axioms of relativity is the equivalence principle which postulates the equivalence of inertial and gravitational mass. If we found experimental evidence that the equivalence principle did not apply in some circumstances then, yes, this would contradict relativity as we understand it.

Are there any theoretical models or experimental setups that explore a possible link between inertia and absolute motion ?

Almost certainly there are - although I doubt whether any professional physicist would commit time and money to such research. It is not hard to dream up novel and complex experiments which, if they produced certain results, would change our understanding of the laws of physics. The hard part is carrying out those experiments and getting the required results.

gandalf61
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