Clarification on Gravity

Quote from: sokarul on September 19, 2008, 09:20:48 AM

Free-fall FOR are accelerating and are still inertial.

Which is why they are only accelerating if you look at them in a non-inertial coordinate system. But then, any object can be said to be accelerating if one creates a non-inertial coordinate system around it. The only absolute measure of acceleration is whether one is following the shortest possible path through spacetime, more commonly referred to as a geodesic. If one is doing so, then one is not accelerating; otherwise, one is accelerating because something is causing one to deviate from that natural path.

Please look up free-fall again. 

Quote from: sokarul on September 19, 2008, 09:48:37 AM

Please look up free-fall again. 

I know what free-fall is. It does not make sense, in a model where spacetime is curved and simultaneity is relative, to speak of acceleration in absolute terms, except in terms of inertial and non-inertial frames of reference.

Free-fall is inertial and accelerating.  If you have a problem with this talk to Einstein. 

It does not make sense, in a model where spacetime is curved and simultaneity is relative, to speak of acceleration in absolute terms, except in terms of inertial and non-inertial frames of reference.

Quote from: sokarul on September 19, 2008, 09:53:04 AM

Free-fall is inertial and accelerating.  If you have a problem with this talk to Einstein. 

Accelerating relative to what? Again:

Another inertial FOR with constant velocity.

Quote from: sokarul on September 19, 2008, 10:00:04 AM

Another inertial FOR with constant velocity.

Of course. But that inertial frame of reference itself is accelerating relative to the object in question, and so cannot be used as an absolute reference point.

Then why do you use it as one? 

Actually, I just thought of something. To prevent the sure to come noob rant on physics revisionism, please note that this view of gravity is undisputed and held by RE'ees and FE'ers alike, as this is relativity.

General Relativity does not exclude gravity as a force to my knowledge.

Quote from: sokarul on September 19, 2008, 01:34:35 PM

Then why do you use it as one? 

At this point it may be beneficial to imagine that A and B begin in a distant orbit around the black hole, before a small impulse is applied to A who is then allowed to free-fall towards the event horizon, otherwise Osama's wording of the initial conditions can introduce confusion...

Quote from: Osama  bin Laden on September 19, 2008, 10:01:35 AM

Quote from: sokarul on September 19, 2008, 10:00:04 AM

Another inertial FOR with constant velocity.

Of course. But that inertial frame of reference itself is accelerating relative to the object in question, and so cannot be used as an absolute reference point.

Then why do you use it as one? 

I sometimes think sokarul and cbarnett97 are the same person.  Neither will admit their failings, no matter how many people point them out.

gravitation=acceleration

I still want to know how he plans to use Atomic Clocks to prove the surface of the earth isn't accelerating.

I'm still waiting for an answer. You said an accelerating FOR cannot be used, yet you use one to make the claim the claim the earth's surface is accelerating.

Quote from: sokarul on September 22, 2008, 09:46:47 AM

I'm still waiting for an answer. You said an accelerating FOR cannot be used, yet you use one to make the claim the claim the earth's surface is accelerating.

Back, are you? My, those were a peaceful two days.

Anyway, I didn't.

Not talking about the current topic but acceleration in general, atomic clocks are used to show time dilation.  Did you look up the twin paradox and the answer? 

You most certainly did. 
You took the FOR of freefall and then claimed the earth was accelerating up, even though a freefall FOR is clearly accelerating. 

Quote from: sokarul on September 22, 2008, 09:52:04 AM

You most certainly did. 
You took the FOR of freefall and then claimed the earth was accelerating up, even though a freefall FOR is clearly accelerating. 

A freefalling frame of reference is only accelerating relative to non-inertial and other inertial frames of reference. No frame of reference can be said to be the absolute measure of zero acceleration. Therefore, the only way in which it makes sense to speak of acceleration in absolute terms is whether or not the observer is inertial. If they are not, they are accelerating.

An object can be both inertial and accelerating.

Quote from: sokarul on September 22, 2008, 10:00:32 AM

An object can be both inertial and accelerating.

Yay, something to post in the Top Ten Lists thread!

Sok's fail just never stops entertaining me.

I suggest you research the Equivalence Principle before you make yourself look like an idiot. 

Apparently Sokarul is the only member on FES who understands the Equivalence Principle.

Everything in relativity is exactly that - relative. Any problem has to be laid out in the format of observer and object under consideration.  If the observer is free-falling, he is justifiably 'at rest' in a relativistic sense, since the only thing all observers can agree on is "Does anyone have their jetpack switched on right now?".  It doesn't matter if that 'jetpack' is just that, or whether it's contact acceleration from the ground, or an asteroid hitting you in the face.  Let's assume the Earth is made of glass and cannot be seen by eye - someone standing on the ground is accelerating upwards, as seen by someone free-falling above them.

Likewise, to the person on the ground the free-faller appears to be accelerating downwards towards them - the difference is that when the two look at their accelerometers the free-faller reads zero, and the guy on the ground measures an upwards acceleration of g. Consequently we can conclude that, in any meaningful definition of acceleration, the person on the ground is accelerating, whereas the person free-falling towards the ground is not.

Everything in relativity is exactly that - relative. Any problem has to be laid out in the format of observer and object under consideration.  If the observer is free-falling, he is justifiably 'at rest' in a relativistic sense, since the only thing all observers can agree on is "Does anyone have their jetpack switched on right now?".  It doesn't matter if that 'jetpack' is just that, or whether it's contact acceleration from the ground, or an asteroid hitting you in the face.  Let's assume the Earth is made of glass and cannot be seen by eye - someone standing on the ground is accelerating upwards, as seen by someone free-falling above them.

Likewise, to the person on the ground the free-faller appears to be accelerating downwards towards them - the difference is that when the two look at their accelerometers the free-faller reads zero, and the guy on the ground measures an upwards acceleration of g. Consequently we can conclude that, in any meaningful definition of acceleration, the person on the ground is accelerating, whereas the person free-falling towards the ground is not.

Quote from: Matrix on September 22, 2008, 10:10:37 AM

Everything in relativity is exactly that - relative. Any problem has to be laid out in the format of observer and object under consideration.  If the observer is free-falling, he is justifiably 'at rest' in a relativistic sense, since the only thing all observers can agree on is "Does anyone have their jetpack switched on right now?".  It doesn't matter if that 'jetpack' is just that, or whether it's contact acceleration from the ground, or an asteroid hitting you in the face.  Let's assume the Earth is made of glass and cannot be seen by eye - someone standing on the ground is accelerating upwards, as seen by someone free-falling above them.

Likewise, to the person on the ground the free-faller appears to be accelerating downwards towards them - the difference is that when the two look at their accelerometers the free-faller reads zero, and the guy on the ground measures an upwards acceleration of g. Consequently we can conclude that, in any meaningful definition of acceleration, the person on the ground is accelerating, whereas the person free-falling towards the ground is not.

I think if he hasn't got it by now, any further attempts to convince him will constitute a waste of keystrokes.

Equivalence principle

A person in a free-falling elevator experiences weightlessness during their fall, and objects either float alongside them or drift at constant speed. Since everything in the elevator is falling together, no gravitational effect can be observed. In this way, the experiences of an observer in free fall are indistinguishable from those of an observer in deep space, far from any sufficent source of gravity. Such observers are the privileged ("inertial") observers Einstein described in his theory of special relativity: observers for whom light travels along straight lines at constant speed.[2]

Einstein hypothesized that the similar experiences of weightless observers and inertial observers in special relativity represented a fundamental property of gravity, and he made this the cornerstone of his theory of general relativity, formalized in his equivalence principle. Roughly speaking, the principle states that a person in a free-falling elevator cannot tell that they are in free fall. Every experiment in such a free-falling environment has the same results as it would for an observer at rest or moving uniformly in deep space, far from all sources of gravity.

They would each see the other as accelerating.  But the free-faller is the one who is really accelerating based on a coordinate system.  That is why freefallers at both poles of the earth will hit the ground.