I don't understand the Michelson–Morley experiment

[PeterDonis]

Why you think that circulation theory not get correct lift values?

Correct circulation theory does give correct lift values. But correct circulation theory does not claim that air goes around the wing in a circle. It only says that the circulation of the actual airflow is nonzero and contributes to the lift the wing provides, as I said in post #23.

The "theory" that "air goes around the wing in a circle" does not make correct predictions. But we only know that because we can observe the actual airflow and see that it isn't a circle.

 

[PeterDonis]

There are theories that get same results as GR but use different concepts, teleparallel Gravity (TEGR), Symmetric Teleparallel Gravity (STEGR).

How do you know those "different concepts" are wrong?

Note that (at least AFAIK) teleparallel gravity theories are mathematically equivalent to GR, which is why they all make the same predictions.

 

[Herman Trivilino]

If car travel 100km/h and you trow a ball forward at 10km/h inside the car cabine, ball will always have 10km/h if we measure from car, but we need to measure from outside of car ("rest frame") to ball have 110km/h.

Yes, but suppose you throw the ball at 110 km/h from OUTSIDE the car. That is, relative to the road the car has a speed of 100 km/h and the ball 110 km/h.

What is the speed of the ball relative to the car?

That is the scenario analogous to MM.

Wouldn't you expect it to be 10 km/h?

 

[Dale]

For me space is nothing

There is 1 astronomical unit of space between the sun and the earth.

You can use the word “nothing” to refer to space if you like. That is a reasonable choice. But having made that choice you imply that “nothing” has amounts which can be measured.

You can choose your words, but the facts remain: space can be measured.

so nothing cant be curved

Why not? Space can be measured, so if space is “nothing” then “nothing” can be measured. And since that is the case, why can’t the measurements indicate that it is curved?

I think we still don't know how gravity really works, because we have problems in micro world and large scales.

This is reasonable. Either our knowledge of gravity or our knowledge of matter must be incomplete. Or both, of course.

 

[Nugatory]

For me space is nothing,

Then what does a ruler measure?

 

[A.T.]

I don't understand why people in Michelson-Morley experiment expect that light speed in direction in Earth motion would be light speed + earth speed, if they measure speed from earth frame?

Since light shows some wave-like properties, and for other types of waves their propagation depends on the motion of some medium, they wanted to check if the motion of the Earth relative to such a medium can be detected.

If car travel 100km/h and you trow a ball forward at 10km/h inside the car cabine, ball will always have 10km/h if we measure from car, but we need to measure from outside of car ("rest frame") to ball have 110km/h

That's not how light behaves either, as other observations have shown.
https://en.wikipedia.org/wiki/Emission_theory_(relativity)

 

[A.T.]

For me space is nothing, so nothing cant be curved,

Not being curved but flat is also a geometrical property. Why is it OK to assume that 'nothing' is specifically flat.

 

[Sagittarius A-Star]

For me space is nothing, so nothing cant be curved

Can it be explained without spacetime curvature, that the magnitude of light deflection near the Sun (1.75 arcseconds, as measured 1919 by Eddington) is twice the value, which is predicted by Newton's law of gravity?

 

[Herman Trivilino]

For me space is nothing, so nothing cant be curved, twisted etc etc, so I look this theory as physically incorrect,

In your mind you are debating yourself, which is good. It's a sign of higher order thinking.

But you are creating your own personal straw man argument. You begin with the premise that space is nothing, then go on to draw some false conclusions from that premise.

Your conclusions are wrong because your premise is wrong.

When you have an idea about Nature's behavior that contradicts her actual behavior, then your idea is incorrect.

It has taken our civilization centuries to learn this lesson. Our very lives have been enhanced by the many inventions that have resulted.

 

[gen x]

Then what does a ruler measure?

Ruler show the shortest distance between two object is straight line, and if you are on sphere, drill a tunnel.

Not being curved but flat is also a geometrical property. Why is it OK to assume that 'nothing' is specifically flat.

In your mind you are debating yourself, which is good. It's a sign of higher order thinking.

But you are creating your own personal straw man argument. You begin with the premise that space is nothing, then go on to draw some false conclusions from that premise.

Your conclusions are wrong because your premise is wrong.

When you have an idea about Nature's behavior that contradicts her actual behavior, then your idea is incorrect.

It has taken our civilization centuries to learn this lesson. Our very lives have been enhanced by the many inventions that have resulted.

I just said space is nothing, but if we talk about space as mathematical object then it can be any shape you want in this theory, flat, curved, twisted etc

Einstein quote: "Space and time or spacetime are not conditions of existence but models of thinking"

 

[Ibix]

Ruler show the shortest distance between two object is straight line

So you are assuming your "nothing" obeys Euclidean geometry. Why?

 

[Sagittarius A-Star]

Einstein quote: "Space and time or spacetime are not conditions of existence but models of thinking"

Are you sure the quoted text is from Einstein?
In which paper did Einstein write this?

 

[Nugatory]

Ruler show the shortest distance between two object is straight line, and if you are on sphere, drill a tunnel.

I'm not asking what it shows, I am asking what the thing it measures is. I am trying to get you to reconcile your statement that "space is nothing" when something is being measured by a ruler.

 

[Dale]

I just said space is nothing,

Space can be measured. So if space is “nothing” then “nothing” can be measured. And if “nothing” can be measured then why couldn’t those measurements indicate curvature.

 

[Herman Trivilino]

I just said space is nothing, but if we talk about space as mathematical object [...]

If you "talk about" it as an object, mathematical or otherwise, then you contradict yourself when say it's nothing.

 

[A.T.]

Ruler show the shortest distance between two object is straight line

Grids of rulers can also measure intrinsic curvature, not just distances. If 'nothing' can have measurable distances, then 'nothing' can also have measurable intrinsic curvature.

 

[gen x]

@Dale
@A.T.

Why I can't set my abstract mathematical absolute ref. frame with x,y,z axis and from here observe universe?

Ref. frames are math constructs not real thing like apple, so why I cant set it like this?

 

[Ibix]

Why I can't set my abstract mathematical absolute ref. frame with x,y,z axis and from here observe universe?

You need a time value as well, even if you don't call it a coordinate.

Ref. frames are math constructs not real thing like apple, so why I cant set it like this?

You can. Of course you can pick any frame to call the "absolute" one, and other people are free to pick a different one and there's no physics reason to prefer one over another, so calling it an absolute frame would be misleading, but you can do it.

 

[gen x]

You need a time value as well, even if you don't call it a coordinate.

You can. Of course you can pick any frame to call the "absolute" one, and other people are free to pick a different one and there's no physics reason to prefer one over another, so calling it an absolute frame would be misleading, but you can do it.

Isn't that how Newton set his absolute frame?

 

[Ibix]

Isn't that how Newton set his absolute frame?

Newton assumed that there was an undetectable inertial frame. I'm not aware of him specifying which one it was. In any case it doesn't affect anything and you're free to label any frame (or, more usually, none) as the absolute one.

The equivalent formulation of SR is Lorentz Ether Theory, which is just SR with a free choice of one frame that's somehow more real than any other. Again, it affects nothing and you're free to choose any or none.

In both cases, since there is no experimental evidence of a preferred frame Occam's razor prefers "none". That's why you only find this stuff in the context of the history of science.

 

[gen x]

Newton assumed that there was an undetectable inertial frame

Yes he imagine this frame in his brain, just like I did. So why he was wrong?

 

[Ibix]

Yes he imagine this frame in his brain, just like I did. So why he was wrong?

Because the laws he (and later Einstein) deduced were identical whatever frame they chose to label as the absolute one. So including it in the final theory is an unjustified and unjustifiable assumption. You can still include it if you want - it just doesn't add anything except one more thing to keep track of.

Consider a counterfactual case where $F=m(1+|v/c|)a$ and $v$ is measured with respect to some particular frame. You'd be able to identify the state of motion where the resistance to acceleration was minimal - then you'd have a reason to track that state of motion because you'd need it to do calculations. We just appear not to live in such a universe.

 

[Dale]

@Dale
@A.T.

Why I can't set my abstract mathematical absolute ref. frame with x,y,z axis and from here observe universe?

Ref. frames are math constructs not real thing like apple, so why I cant set it like this?

I am not sure what exactly you are asking. Can you clarify? Are you just asking if I can label some arbitrary coordinate system as “absolute”?

 

[gen x]

I am not sure what exactly you are asking. Can you clarify? Are you just asking if I can label some arbitrary coordinate system as “absolute”?

In short, I just ask what is wrong with Newton absolute frame. I dont understand why his choice/assumption is wrong.

 

[Ibix]

In short, I just ask what is wrong with Newton absolute frame. I dont understand why his choice/assumption is wrong.

Short version of what I wrote above:

A theory with a detectable absolute frame is inconsistent with experiment, so would be inaccurate. A theory with an undetectable absolute frame is indistinguishable from the identical theory with no absolute frame, and the latter is preferred under Occam's razor.

You would not be wrong to add an undetectable absolute frame to our current theories. But you will never need to use it, so it's an unnecessary and arbitrary feature.

 

[Dale]

In short, I just ask what is wrong with Newton absolute frame. I dont understand why his choice/assumption is wrong.

One thing that is wrong with Newton is that the transformation between different inertial frames does not have the form that he thought it did. He thought the transformation between different inertial frames was the Galilean transform, and that is excluded by experiments.

In the Mansouri Sexl test theory the parameter for absolute time is $\alpha$ which has been measured to be $0.5$ to eight digits. The Galilean absolute time of $\alpha=0$ is well excluded.

 

[Ibix]

A theory with a detectable absolute frame is inconsistent with experiment, so would be inaccurate.

And, just to add, serious scientists do search for violations of Lorentz covariance (a detectable absolute frame would be one such violation). Nothing has been found.

 

[gen x]

Where Newton write that we have detectable absolute frame?
You cant detect something that dont exist, frame/ space dont exist, nothing by definition do not exist.

 

[Ibix]

Where Newton write that we have detectable absolute frame?

I don't think he did.

 

[gen x]

One thing that is wrong with Newton is that the transformation between different inertial frames does not have the form that he thought it did. He thought the transformation between different inertial frames was the Galilean transform, and that is excluded by experiments.

Can you explain this?

Did Newton knew that in non inertial frame we must introduce pseudo forces?