"Stick and Rudder Moments" - redux

MAKG1 said:
Yes, it needs correction. The microwave background is not an object, and you can measure velocity and acceleration relative to it. Space itself determines inertia, even if it has nothing in it. You can still determine if you are accelerating even in an empty universe and even if you can't look outside. That's Einsteins elevator thought experiment.
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You keep responding before I'm done editing.:) Can there be acceleration in an empty universe?

MAKG1 said:
Space itself determines inertia
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Can you reconcile that with the classical definition of inertia? I don't see it.
 
Cooter143 said:
You keep responding before I'm done editing.:) Can there be acceleration in an empty universe?


Can you reconcile that with the classical definition of inertia? I don't see it.
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That IS the classical definition of inertia.

Yes, there can be acceleration in an (otherwise) empty universe. No gravity, but acceleration due to other forces you generate.
 
MAKG1 said:
You can still determine if you are accelerating even in an empty universe and even if you can't look outside. That's Einsteins elevator thought experiment.
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I love that thought experiment. It was that, inside that windowless elevator, it would be theoretically impossible to determine if 1G (let's say) was due to the gravity of another body or from acceleration. The genius was the leap to say that gravity and acceleration are essentially the same thing.

I think.
 
MAKG1 said:
Yes, there can be acceleration in an (otherwise) empty universe. No gravity, but acceleration due to other forces you generate.
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You're losing me here, what generates the force?

Dan Thomas said:
it's relative to space that inertia is effective
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This is the post that I responded to. Please explain how inertia is effective against space? I am more than happy to be corrected and learn something new.
 
MAKG1 said:
That IS the classical definition of inertia.

Yes, there can be acceleration in an (otherwise) empty universe. No gravity, but acceleration due to other forces you generate.
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Hmm. Interesting thought: I suppose you can define acceleration relative to previous motion (i.e. object is moving faster/slower at delta T than T), but how does one define motion in an empty universe? Doesn't motion imply relative to some frame of reference? (I'm thinking out loud so to speak here). With an empty universe there is no frame of reference.

John
 
FastEddieB said:
I love that thought experiment. It was that, inside that windowless elevator, it would be theoretically impossible to determine if 1G (let's say) was due to the gravity of another body or from acceleration. The genius was the leap to say that gravity and acceleration are essentially the same thing.

I think.
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Yes, but it assumes an elevator which is comprised of matter and your feet which is another object comprised of matter. Someone help me out here, I don't see how that applies to MAKG1 claim that emptiness exerts force.
 
jsstevens said:
Hmm. Interesting thought: I suppose you can define acceleration relative to previous motion (i.e. object is moving faster/slower at delta T than T), but how does one define motion in an empty universe? Doesn't motion imply relative to some frame of reference? (I'm thinking outlier so to speak here). With an empty universe there is no frame of reference.

John
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That is my point.
 
Cooter143 said:
You're losing me here, what generates the force?



This is the post that I responded to. Please explain how inertia is effective against space? I am more than happy to be corrected and learn something new.
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Inertia doesn't operate on space. It operates on you. You tend to keep moving in a straight line (or at least as straight as possible) at constant velocity. And you can detect deviations from that purely internally, without any reference to anything outside.

Anything you might bring along can generate the force. You can throw something, for instance, and you'll impart the same force to yourself as you do to the projectile. And it doesn't matter what else is in the universe.
 
Cooter143 said:
Yes, but it assumes an elevator which is comprised of matter and your feet which is another object comprised of matter. Someone help me out here, I don't see how that applies to MAKG1 claim that emptiness exerts force.
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OK, there's your misconception. Inertia IS NOT a force. It merely means you move in a straight line at constant velocity unless there is some external force.

I think you need to spend more than a couple of minutes thinking about the Einstein elevator. There need be no matter involved. The "elevator" is there only to keep you from looking outside. There are some nice articles on the web about this, though most of them go on rather quickly to the equivalence between gravity and acceleration.
 
MAKG1 said:
Inertia doesn't operate on space. It operates on you. You tend to keep moving in a straight line (or at least as straight as possible) at constant velocity. And you can detect deviations from that purely internally, without any reference to anything outside.

Anything you might bring along can generate the force. You can throw something, for instance, and you'll impart the same force to yourself as you do to the projectile. And it doesn't matter what else is in the universe.
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Ah. I see. You can measure acceleration by forces exerted on you. (Like in the elevator example posted after my previous post.) But this is even more strange because you can measure acceleration but still have no motion, since you have no frame of reference. Hmmm. Acceleration without motion.

John
 
This is getting off track.
MAKG1 said:
Inertia IS NOT a force
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I never said it was. It is the resistance to force. Force cannot be exerted by nothingness i.e. space.
What I'm saying is pretty simple. Inertia is meaningless unless two "somethings" exist.

Read my signature line!
 
jsstevens said:
Ah. I see. You can measure acceleration by forces exerted on you. (Like in the elevator example posted after my previous post.) But this is even more strange because you can measure acceleration but still have no motion, since you have no frame of reference. Hmmm. Acceleration without motion.

John
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You have a frame of reference. Just not relative to outside matter. It doesn't have to be like pilotage. You can define reference frames without other matter. It's now conventional to do so, as we have good measurements of the microwave background temperature. There is one frame where it is at rest. And it's all made of photons, so no matter is involved.
 
Cooter143 said:
This is getting off track.

I never said it was. It is the resistance to force. Force cannot be exerted by nothingness i.e. space.
What I'm saying is pretty simple. Inertia is meaningless unless two "somethings" exist.
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No, it isn't. If you fart, you'll get some thrust and see some motion. And it's all self contained. You could even fart photons

Rockets do work in vacuum. They don't need to "push" against anything. And your butt will feel the acceleration even without looking outside.
 
MAKG1 said:
You have a frame of reference. Just not relative to outside matter. It doesn't have to be like pilotage. You can define reference frames without other matter. It's now conventional to do so, as we have good measurements of the microwave background temperature. There is one frame where it is at rest. And it's all made of photons, so no matter is involved.
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I was taking "empty" to mean without anything. Not just without matter. No microwave background, no photons, nothing except the body being accelerated. You can impose a mathematical frame of reference, but still have nothing by which to measure it. So you have acceleration (based on force measurements on the body in question), but no motion. Intriguing little conundrum.

John
 
MAKG1 said:
They don't need to "push" against anything.
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You're wrong about that. Do they need fuel? What causes the acceleration of a rocket in space? It is the mass of the expanding rocket fuel against the rocket itself.
 
MAKG1 said:
No, it isn't. If you fart, you'll get some thrust and see some motion. And it's all self contained. You could even fart photons

Rockets do work in vacuum. They don't need to "push" against anything. And your butt will feel the acceleration even without looking outside.
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The fart isn't empty space, the amount of thrust generated will be determined by the mass of the air expelled. Same for rockets as mentioned above.
 
jsstevens said:
I was taking "empty" to mean without anything. Not just without matter. No microwave background, no photons, nothing except the body being accelerated. You can impose a mathematical frame of reference, but still have nothing by which to measure it. So you have acceleration (based on force measurements on the body in question), but no motion. Intriguing little conundrum.

John
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Acceleration is impossible without some other force. SOMETHING is required to generate that force, keeping it in the realm of classical physics.
 
Cooter143 said:
The fart isn't empty space, the amount of thrust generated will be determined by the mass of the air expelled. Same for rockets as mentioned above.
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OK, so fart photons. No mass. But you'll still move (they do have energy and momentum).

You're confusing yourself with extraneous details. You don't need outside references to determine acceleration. And acceleration can exist due to forms of energy other than matter. Magnetic fields are a classic example. And no, you don't necessarily need something to generate the field; there is a primordial magnetic field.
 
Cooter143 said:
Acceleration is impossible without some other force. SOMETHING is required to generate that force, keeping it in the realm of classical physics.
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Not really.

The universe's expansion is accelerating. The reason appears to be a background energy field (called "dark energy" for the moment, though it's indistinguishable from the cosmological constant). This means everything in the universe is accelerating away from everything else, with no force to do it.
 
Cooter143 said:
Acceleration is impossible without some other force. SOMETHING is required to generate that force, keeping it in the realm of classical physics.
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Correct. In fact, if the entire universe were empty save for one small test object, that hypothetical object could never experience acceleration. There would also not be any centrifugal/petal force when it rotates around itself, since there would be no external frame of reference (with mass/energy) for that rotation. I believe that's discussed in Einstein's General Relativity paper.
 
MAKG1 said:
OK, so fart photons. No mass. But you'll still move (they do have energy and momentum).

You're confusing yourself with extraneous details. You don't need outside references to determine acceleration. And acceleration can exist due to forms of energy other than matter. Magnetic fields are a classic example. And no, you don't necessarily need something to generate the field; there is a primordial magnetic field.
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I think that you are the one confused, it's not photons coming out of your arse. If it is I'd like to see it. There is a difference between space and air. Air has mass, space doesn't.
 
Cooter143 said:
I think that you are the one confused, it's not photons coming out of your arse. If it is I'd like to see it.
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Not like its impossible.

Unicorns mastered it a long time ago.

giphy.gif
 
MAKG1 said:
Not really.

The universe's expansion is accelerating. The reason appears to be a background energy field (called "dark energy" for the moment, though it's indistinguishable from the cosmological constant). This means everything in the universe is accelerating away from everything else, with no force to do it.
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FastEddieB said:
Not like its impossible.

Unicorns mastered it a long time ago.

giphy.gif
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MAKG1, is that what you meant? If so, I stand corrected. And, I'd still like to see it.
 
MAKG1 said:
Not really.
The universe's expansion is accelerating. The reason appears to be a background energy field (called "dark energy" for the moment, though it's indistinguishable from the cosmological constant). This means everything in the universe is accelerating away from everything else, with no force to do it.
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Not being able to define the force doesn't mean it doesn't exist. I get the idea you're just being contentious. I'm all for edifying discussion, but it seems you have no real grounds for disagreeing with my first post. You've essentially denied classical physics the best I can tell. Again, I'm always happy to learn something new if I'm off base.
 
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RotorDude said:
Correct. In fact, if the entire universe were empty save for one small test object, that hypothetical object could never experience acceleration. There would also not be any centrifugal/petal force when it rotates around itself, since there would be no external frame of reference (with mass/energy) for that rotation. I believe that's discussed in Einstein's General Relativity paper.
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In fact, that's exactly the opposite of what Einstein says. And it's well before GR. That's Equivalence.
 
Cooter143 said:
Not being able to define the force doesn't mean it doesn't exist. I get the idea you're just being contentious. I'm all for edifying discussion, but it seems you have no real grounds for disagreeing with my first post. You've essentially denied classical physics the best I can tell. Again, I'm always happy to learn something new if I'm off base.
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No, you're insisting that there is no such thing as a reference frame without matter, and that acceleration is not possible in an empty universe. That is not true. I gave some modern physics examples that might actually be true. But if you really want classical, you'll have to deal with unfamiliar and undeveloped terminology, but it's in the Principia. You won't get any more "classical" than that.

I won't write a textbook on it; several good ones already exist. One example is Taylor & Wheeler's "Spacetime Physics" (New York: Freeman, 1963). There are many others, including one pop physics primer by Einstein himself, if you can find it.
 
MAKG1 said:
No, you're insisting that there is no such thing as a reference frame without matter, and that acceleration is not possible in an empty universe. That is not true. I gave some modern physics examples that might actually be true. But if you really want classical, you'll have to deal with unfamiliar and undeveloped terminology, but it's in the Principia. You won't get any more "classical" than that.

I won't write a textbook on it; several good ones already exist. One example is Taylor & Wheeler's "Spacetime Physics" (New York: Freeman, 1963). There are many others, including one pop physics primer by Einstein himself, if you can find it.
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You brought in frame of reference and I mostly see that as a distraction. My post basically said mass against space is not inertial force. It requires SOMETHING else to act as a force against it. This isnt even a physics discussion, go read the definition of inertia. I'm just stating the definition. Take up your beef with Newton if you don't like it. In your efforts to disagree with me, you are denying the very definition. While you're at it, go investigate the difference in space and air. Several of your posts display confusion about the fact that matter is not defined by what we can see. If you want to press your point I will point out several places that you're wrong that you haven't responded to. I'm not physicist or anything even close but I can follow an argument and you haven't refuted my first post.
 
jsstevens said:
Hmm. Interesting thought: I suppose you can define acceleration relative to previous motion (i.e. object is moving faster/slower at delta T than T), but how does one define motion in an empty universe? Doesn't motion imply relative to some frame of reference? (I'm thinking out loud so to speak here). With an empty universe there is no frame of reference.
John
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Or for that matter, how would you define time in an empty universe?
 
Cooter143 said:
You brought in frame of reference and I mostly see that as a distraction. My post basically said mass against space is not inertial force. It requires SOMETHING else to act as a force against it. This isnt even a physics discussion, go read the definition of inertia. I'm just stating the definition. Take up your beef with Newton if you don't like it. In your efforts to disagree with me, you are denying the very definition. While you're at it, go investigate the difference in space and air. Several of your posts display confusion about the fact that matter is not defined by what we can see. If you want to press your point I will point out several places that you're wrong that you haven't responded to. I'm not physicist or anything even close but I can follow an argument and you haven't refuted my first post.
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OK, I'll go turn in my cosmology dissertation just 'cause SGOTI can't understand what he reads.

That's right, you're not a physicist. You're misquoting Newton, very badly. You can either believe me when I tell you that mass has NOTHING to do with an inertial reference frame, or you can go read the Principia yourself (or one of the thousands of books based upon it) and perhaps understand it, without attacking me if you don't.

I don't deny THE definition. I deny YOUR definition, because it is wrong.

No, I'm not going to write a textbook, and I'm not going to try to teach you physics because you think you already know it. First question, what does "mass against space" even mean? What does "inertial force" mean? All forces are noninertial by their nature.

The point I keep coming back to is that you can define and measure (non)inertial motion without any reference to anything external whatsoever. Either you can believe that or you can write a paper on why Newton (and Galileo and Einstein) was wrong. Inertial motion is not defined in terms of other matter. Period.

Trust me, I understand the difference between space and air. I don't know where that even came from. I'm not sure you understand the difference between matter and energy, and that's why you don't understand that your "first post" was refuted within a few minutes. Matter is defined as having fixed mass. If it doesn't have mass, it isn't matter. So, looking at microwaves immediately refutes your "first post."
 
I'll interact with some of what you said when I get a few more minutes, but if you have a doctorate in Cosmology how could you possible make the statement you did about rockets? Or farts? Physicist don't always make good philosophers, I'll go back and re-read and see if I got hung up on a distraction but some of what you said appeared to be utter non-sense.

I will break down a few of the statements and want to see your response. I am happy to be schooled on the Physics of it, but you'll have to follow the regular rules of logic to convince me.
 
MAKG1 said:
In fact, that's exactly the opposite of what Einstein says. And it's well before GR. That's Equivalence.
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Leaving Einstein aside for the moment, would the hypothetical rotating small object experience centrifugal force if the universe were otherwise devoid of matter/energy?
 
I've now posted a new thread in Hangar Talk so as not to interrupt the regular programming here. I will gladly continue the conversation there, until the name calling and vitriolic ridicule commence, then I'll gracefully bow out. BTW, the first resume has already hit the table so it may not last long.:)
 
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RotorDude said:
Leaving Einstein aside for the moment, would the hypothetical rotating small object experience centrifugal force if the universe were otherwise devoid of matter/energy?
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A very good question.

And the answer is, yes. A rotating object would try to fly apart even if there were nothing else in the universe.

I'll suggest moving over to Cooter143's thread after this. It's a good idea to separate it from stick and rudder moments.
 
FastEddieB said:
In that case, would not the hypothetical rotating small object be the universe?
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That's exactly right. Which would mean the primary frame of reference in that universe would be the object's, which would not be rotating relative to itself.
 
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