What if Einstein equivalence principle is proven wrong one day?

[only1god]

What would be the consequences of such thing? How it will affect physics theories and the world?

 

[Dale]

The equivalence principle has been tested to very high precision. So a future experiment that showed it to be wrong would be a very small effect. So the impact on physics theories would be to place limits on the domain of validity of general relativity that are currently not known.

Within the currently tested domain, GR would continue to be as valid as it ever was. Just as the development of GR did not mean that Newtonian gravity was wrong in the domain where it had been experimentally confirmed.

However, that discovery would definitely be informative in developing the next theory of gravity.

 

[only1god]

So a future experiment that showed it to be wrong would be a very small effect.

Why and How?

 

[Dale]

Why and How?

Current limits are $10^{-15}$. See https://en.m.wikipedia.org/wiki/MICROSCOPE

 

[only1god]

Current limits are $10^{-15}$. See https://en.m.wikipedia.org/wiki/MICROSCOPE

What did you meant by very small effect? effect in what

 

[Dale]

What did you meant by very small effect? effect in what

The experiment measured the acceleration of different objects in free fall. As predicted by the equivalence principle, those accelerations were equal to each other to within 0.0000000000001 %. That is a small effect.

 

[only1god]

The experiment measured the acceleration of different objects in free fall. As predicted by the equivalence principle, those accelerations were equal to each other to within 0.0000000000001 %. That is a small effect.

That's the weak equivalence principle which is true and we can experiment it ourselves. I'm talking about Einstein's equivalence principle which says you cannot distinguish an accelerated rocket going at 1G for example from the Earth gravitational field. My question was about what if some experiment prove that what Einstein said was wrong, and how will that affect modern physics.

 

[BWV]

The experiment measured the acceleration of different objects in free fall. As predicted by the equivalence principle, those accelerations were equal to each other to within 0.0000000000001 %. That is a small effect.

 

[Dale]

I'm talking about Einstein's equivalence principle which says you cannot distinguish an accelerated rocket going at 1G for example from the Earth gravitational field.

Well, you say you are talking about the Einstein equivalence principle, but what you actually describe here is the weak equivalence principle.

However, if you are interested in the Einstein equivalence principle, it has been tested down to $10^{-7}$. Not as small as the weak equivalence principle, but still pretty small. Any future experiment that showed a violation in the Einstein equivalence principle would have to fit within that small limit.

 

[only1god]

Well, you say you are talking about the Einstein equivalence principle, but what you actually describe here is the weak equivalence principle.

However, if you are interested in the Einstein equivalence principle, it has been tested down to $10^{-7}$. Not as small as the weak equivalence principle, but still pretty small. Any future experiment that showed a violation in the Einstein equivalence principle would have to fit within that small limit.

No, it's not. Weak equivalence principle is about objects with different mass falling at the same time but it don't have the "challenge" that Einstein put.
About that limit, What limit you are talking about? or What that limit means?

 

[only1god]

Well, you say you are talking about the Einstein equivalence principle, but what you actually describe here is the weak equivalence principle.

However, if you are interested in the Einstein equivalence principle, it has been tested down to $10^{-7}$. Not as small as the weak equivalence principle, but still pretty small. Any future experiment that showed a violation in the Einstein equivalence principle would have to fit within that small limit.

Do you mean the distance or size with that limit?

 

[Dale]

No, it's not. Weak equivalence principle is about objects with different mass falling at the same time but it don't have the "challenge" that Einstein put.

You probably should read the Wikipedia entry for the equivalence principle. You have a misunderstanding about the different equivalence principles.

https://en.m.wikipedia.org/wiki/Equivalence_principle

One specific statement of the weak equivalence principle is “The local effects of motion in a curved spacetime (gravitation) are indistinguishable from those of an accelerated observer in flat spacetime”. This is what you mistakenly described as the Einstein equivalence principle in post 7.

Do you mean the distance or size with that limit?

No, it is an accuracy limit. The predictions of the Einstein equivalence principle have been verified accurate to within 0.00001 %. That is the standard way to report such things, as a fractional error. So a limit of $10^{-7}$ means that if the Equivalence principle predicted some value is $1$ then it was actually measured to be $1\pm 0.0000001$

 

[only1god]

One specific statement of the weak equivalence principle is “The local effects of motion in a curved spacetime (gravitation) are indistinguishable from those of an accelerated observer in flat spacetime”. This is what you mistakenly described as the Einstein equivalence principle in post 7.

But isn't the weak equivalence firstly supposed to be quote by galileo?

 

[only1god]

I still don't understand the limit because, if Einsten EP is proven to be wrong, What that limit has to do with it?

 

[Dale]

I still don't understand the limit because, if Einsten EP is proven to be wrong, What that limit has to do with it?

It means that any violation of the EP must be very small (or we would have already seen it). If we find such a small violation then that establishes a “domain of applicability” for general relativity. We can still use GR within that domain, including all of the experimental domains tested to date.

Something similar happened to Newtonian gravity when experiments confirmed GR. We could still use Newtonian gravity to launch rockets into orbit and every other scenario that Newtonian gravity had already been experimentally confirmed. It was still a valid theory and was still taught in school. But once GR was confirmed there were situations where we knew we could not use Newtonian gravity

 

[only1god]

But what small means? and What for example a big violation would be? and What are the consequences of a big violation?

 

[Dale]

But what small means?

There is no hard cut off, but I consider $10^{-7}$ and $10^{-15}$ to be small.

What are the consequences of a big violation?

It doesn’t matter since the violations cannot be big. They must be less than $10^{-7}$ which is already small. So any violations must be smaller than small.

 

[DaveC426913]

But what small means? and What for example a big violation would be? and What are the consequences of a big violation?

I think the trouble you are experiencing is that we already know it is correct, down to a small fraction of measurement.

It makes no sense for you to speculate that observations and measurements we have already confirmed are now, suddenly and inexplicably wrong.

 

[only1god]

For example, if an observer inside the box find a way to distinguish, Would that mean small or big violation of the EP?

 

[DaveC426913]

For example, if an observer inside the box find a way to distinguish, Would that mean small or big violation of the EP?

The mostly likely thing that would mean is that they misunderstand the EP.

 

[only1god]

I think the trouble you are experiencing is that we already know it is correct, down to a small fraction of measurement.

It makes no sense for you to speculate that observations and measurements we have already confirmed are now, suddenly and inexplicably wrong.

Maybe some experiment or idea are still without being tested?

 

[DaveC426913]

Maybe some experiment or idea are still without being tested?

Sure. But that experiment will not show an error greater than those already cited in this thread. i.e. best it can do is show an error of, say, one part in ten million.

And that does not constitute "wrong"; it simply constitutes further refinement in the figure - which happens all the time in science.

 

[only1god]

The mostly likely thing that would mean is that they misunderstand the EP.

Why it's impossible? I don't think all ideas or experiments were tested...

 

[DaveC426913]

Why it's impossible? I don't think all ideas or experiments were tested...

You are having trouble understanding what work has gone before.

We already know the EP holds down to one part in millions.

 

[only1god]

You are having trouble understanding what work has gone before.

We already know the EP holds down to one part in millions.

One thing will make me understand if you respond it as clear as it possible. Imagine some idea that prove us indeed we can distinguish between an accelerated frame and a gravitational field, some idea that was not discovered nor tested before. The question here is, leaving apart that limit, Will that mean if the idea is true that Einstein's EP is wrong?

 

[DaveC426913]

Will that mean if the idea is true that Einstein's EP is wrong?

I'm sorry to say that what it will surely mean is that the idea has not taken into consideration the conditions of principle of equivalence.

For example, when I was young, I too thought I had figured out how to tell the difference between gravity and acceleration in a closed room. Obviously, gravity has tides, whereas acceleration does not!

Except the EP is specifically limited to local conditions. Local, in this case, means I can't check the force at the two ends of my room. Which means I cannot measure differences within the room; I can only take my measurements at a single point. And that leaves me with no way to test for tides.

See?

It doesn't mean your idea is wrong; it simply means - sorry if this seems glib, but - if you want to try thinking outside the box, you first need to spend enough time studying so you learn where the box is.

 

[PAllen]

One thing will make me understand if you respond it as clear as it possible. Imagine some idea that prove us indeed we can distinguish between an accelerated frame and a gravitational field, some idea that was not discovered nor tested before. The question here is, leaving apart that limit, Will that mean if the idea is true that Einstein's EP is wrong?

It would mean that general relativity fails in some case, and that, as a result, there would be no known theory of gravity consistent with experiment. Some unknown theory would be needed that duplicates all the great many validated predictions of general relativity, while also explaining this anomalous experiment.

 

[only1god]

I'm sorry to say that what it will mean is that the idea has not taken into consideration the conditions of principle of equivalence.

For example, when I was young, I too thought I had figured out how to tell the difference between gravity and acceleration in a closed room. Obviously, gravity has tides, whereas acceleration does not!

Except the EP is specifically limited to local conditions. Local, in this case, means I can't check the force at the two ends of my room. Which means I cannot measure differences within the room; I can only take my measurements at a single point. And that leaves me with no way to test for tides.

See?

It doesn't mean your idea is wrong; it simply means - sorry if this seems glib, but - if you want to try thinking outside the box, you first need to spend enough time studying so you learn where the box is.

Local means i cannot go out of the box?

 

[DaveC426913]

Local means i cannot go out of the box?

Correct.
More than that, you can't even take measurements at different places inside the box.

(To clarify: It's not that you can't take measurements at different places; it's that the EP is not meant to apply in that condition.)

 

[PAllen]

Local means i cannot go out of the box?

Local means limited in spatial extent such that tidal gravity is undetectable, and also limited in duration, because you can trade duration for size. That is, pick an arbitrarily small box, if you make some observations over a long enough time, they can detect tidal gravity. Omitting this fact is the error in a whole series of false claims by Ohannian about the equivalence principle. And, of course you cannot go or look outside the box.

 

[DaveC426913]

Local means limited in spatial extent such that tidal gravity is undetectable...

Yah. This.

 

[only1god]

Correct.
More than that, you can't even take measurements at different places inside the box.

Thanks, now i understand. Einstein put a lot of limits lol.
What if someone indeed find an idea that is local, and that idea turns out to be right? What would be the impacts?

 

[DaveC426913]

What if someone indeed find an idea that is local, and that idea turns out to be right? What would be the impacts?

A lot of scientists would show up at your door.
Some with notepads.
Many with pitchforks.

 

[PAllen]

Correct.
More than that, you can't even take measurements at different places inside the box.

(To clarify: It's not that you can't take measurements at different places; it's that the EP is not meant to apply in that condition.)

I don’t think this is required, as long as the measurements are close in both location and time

 

[PAllen]

Thanks, now i understand. Einstein put a lot of limits lol.
What if someone indeed find an idea that is local, and that idea turns out to be right? What would be the impacts?

See post #27