B Detecting Gravitational Waves: Earth-Like Planet Possibility

[PeterDonis]

Is the equivalence principle defined in such a way that it is experimentally non-falsifiable?

No. @Ibix described how it could be falsified.

Is it falsifiable without invoking physics-defying materials?

This is the wrong way to look at it. Falsifying the EP would mean falsifying our current theories of physics, so of course if our current theories of physics are correct the EP will not be falsified. But that doesn't mean the EP is not falsifiable. It is perfectly possible to test whether the EP is true. It just so happens that in our universe it passes the test.

 

[DaveC426913]

Is the equivalence principle defined in such a way that it is experimentally non-falsifiable?

For example: the region is defined to always be smaller than the area that any future equipment will be able to measure?

Have a look at an analogous principle:

"A sphere has every point on its surface equidistant from its center." (that is, in fact, the definition of a sphere)

What you are asking is: "If I look at the sphere with a powerful enough microscope, can I invalidate that principle?"

You have a real-world sphere that is not perfect, and a powerful microscope would indeed detect irregularities in a sphere made of atoms.

Does that invalidate the principle above? No.

 

[PeterDonis]

Have a look at an analogous principle I just made up.

It's not analogous. Your "principle" is a tautology, since part of the definition of a sphere is that it has the same radius at every point on it.

The EP is not a tautology; it is not a logically necessary proposition.

 

[DaveC426913]

It's not analogous. Your "principle" is a tautology, since part of the definition of a sphere is that it has the same radius at every point on it.

The EP is not a tautology; it is not a logically necessary proposition.

It's not the best analogy, granted. The point is that the Equivalence principle doesn't have a minimum resolution, below which it's not valid. That seems to be what the OP thinks.

 

[PeterDonis]

the Equivalence principle doesn't have a minimum resolution, below which it's not valid

Yes, agreed. It is a local proposition; the best way to formulate it is actually in terms of properties of worldlines and tetrads carried by observers on those worldlines, not properties of regions of spacetime.

 

[Ibix]

Is it falsifiable without invoking physics-defying materials?

I don't think it's all that outrageously physics-defying. In Newtonian physics, all we need to do is say that $F=kGMm/r^2$, where $k=1$ for normal matter and $k=2$ for this hypothetical matter. That $k$ is always 1 is merely something we happen to have observed - there's no other reason for it.

Relativity insists that there is a reason, that matter follows geodesics. This means that the coordinate acceleration of a free-falling body cannot depend on its mass, only on its position - i.e. the equivalence principle. So observing masses accelerating at different rates would falsify the equivalence principle.

 

[Dale]

Not sure this helps the OP.

Is it falsifiable without invoking physics-defying materials?

@Ibix is correct. Since our universe follows the equivalence principle of course a violation will be “physics defying”. But the point is that you can take any pair of materials and perform the experiment. If you ever find one that behaves as @Ibix described then the principle is falsified. Until we did similar experiments it was not a forgone conclusion.

 

[berkeman]

Thread closed temporarily for Moderation...

 

[Dale]

Since the OP is on vacation, this thread will remain closed. In short, gravitational waves are a prediction of GR so obviously they do not falsify GR nor any of the basic GR principles.