Clarification on Gravity

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sokarul

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Re: Clarification on Gravity
« Reply #600 on: September 17, 2008, 08:29:11 AM »
And the ground feels like it's being pushed down by the person. 

Or, equivalently, that it is being pushed upwards into the person.
 
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The normal force is present because of contact.  Look up normal force and see how it arises.  As for the accelerometer gravitation accelerates objects without a force.

...

I know, I just thought we were having a state the obvious contest. 
We have no disagreement on the origin of the normal force, or on the nature of gravitation from what I can see here. I believe the issue was over whether the ground accelerating upwards is equivalent to gravitation, which it is.  As I have mentioned before, though, don't take my word for it:
Here  is where you are wrong.  I am not arguing the EP.  I am arguing the net acceleration of someone standing on the ground is zero.  They are claiming it is not zero and in the upwards direction.  I already know about GR and SR.  YOU DO NOT NEED TO LECTURE ME ON IT. 

Please research before you post again. 
Find me a quote in GR where it says we are not undergoing a constant upward physical acceleration. I doubt you can.
Acceleration due to gravitation is towards the mass, not away. 

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I rest my case.

Umm, ok
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Jack

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Re: Clarification on Gravity
« Reply #601 on: September 17, 2008, 08:33:10 AM »
Acceleration due to gravitation is towards the mass, not away. 
So you can't? I thought so.

Umm, ok
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sokarul

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Re: Clarification on Gravity
« Reply #602 on: September 17, 2008, 08:42:27 AM »
Moving clocks tick slower.

They do, but they don't appear to move slower.

http://www.astrophysicsspectator.com/topics/generalrelativity/BlackHoleEventHorizon.html

I don't need education on what goes on around a black hole, thanks. You said it yourself; the observer that experiences time dilation is the observer that experiences acceleration.
Yes, because it is. 
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What would happen if, at t=0, observer A just outside the event horizon of a black hole switches on his jet pack to hover where he is, while observer B allows herself to enter freefall along a path that will take her right alongside observer A, and just as she reaches him, he switches off his jetpack so that they are both inertial? Whose worldline will have been dilated when the two are in the same frame of reference, and therefore who has undergone acceleration?
Well it should be observer B still.  Although since observer A is in a non-inertial FOR its kinda of tricky.  The time dilation formula only uses velocity thought. 

What I was getting at is the twin paradox.  The solution answers who is time dilated by who has accelerated.
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The surface accelerates up in both FET and RET.

Why would the surface of the earth be accelerating upwards?  That would cause the earth to expand in all directions.   
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Parsifal

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Re: Clarification on Gravity
« Reply #603 on: September 17, 2008, 08:47:53 AM »
Well it should be observer B still.  Although since observer A is in a non-inertial FOR its kinda of tricky.  The time dilation formula only uses velocity thought. 

What I was getting at is the twin paradox.  The solution answers who is time dilated by who has accelerated.

Okay, so let t=0 where observers A and B are both in the same place away from the black hole, and then observer A freefall inwards until he is right beside the event horizon while observer B watches from afar. From there, things proceed as previously described. Whose worldline has been most dilated when they are reconciled?

Why would the surface of the earth be accelerating upwards?  That would cause the earth to expand in all directions.   

Unless there were something else trying to make it collapse inwards, like gravitation.
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Dr Matrix

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Re: Clarification on Gravity
« Reply #604 on: September 17, 2008, 08:52:52 AM »
Here  is where you are wrong.  I am not arguing the EP.  I am arguing the net acceleration of someone standing on the ground is zero.  They are claiming it is not zero and in the upwards direction.  I already know about GR and SR.  YOU DO NOT NEED TO LECTURE ME ON IT. 

Without meaning to sound childish, you had just told me that we were having a 'state the obvious contest'. While I should have remained mature and ignored that comment, I had to just wade on in and patronise you. Tell you what, I'll just man-up and apologise for it.

I will summarise my position:
- person on the ground feels a non-zero force upwards (accelerometer says so)
- person on the ground is not going anywhere (zero net co-ordinate acceleration)
- person on the ground can equally conclude that either they are in a gravitational field with the centre of mass beneath them, or that they are being accelerated upwards by the ground (there is nothing they can do to tell the two possibilities apart, a la EP)

That's all I'm asserting here... do you disagree with any of that?
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sokarul

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Re: Clarification on Gravity
« Reply #605 on: September 17, 2008, 08:57:21 AM »
Here  is where you are wrong.  I am not arguing the EP.  I am arguing the net acceleration of someone standing on the ground is zero.  They are claiming it is not zero and in the upwards direction.  I already know about GR and SR.  YOU DO NOT NEED TO LECTURE ME ON IT. 

Without meaning to sound childish, you had just told me that we were having a 'state the obvious contest'. While I should have remained mature and ignored that comment, I had to just wade on in and patronise you. Tell you what, I'll just man-up and apologise for it.

I will summarise my position:
- person on the ground feels a non-zero force upwards (accelerometer says so)
- person on the ground is not going anywhere (zero net co-ordinate acceleration)
- person on the ground can equally conclude that either they are in a gravitational field with the centre of mass beneath them, or that they are being accelerated upwards by the ground (there is nothing they can do to tell the two possibilities apart, a la EP)

That's all I'm asserting here... do you disagree with any of that?


I do not.  They however do.  This is the current argument. 

They are claiming:
- person on the ground feels a force upwards (normal force)
- person on the ground is accelerating upwards due to normal force
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sokarul

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Re: Clarification on Gravity
« Reply #606 on: September 17, 2008, 09:00:01 AM »
Well it should be observer B still.  Although since observer A is in a non-inertial FOR its kinda of tricky.  The time dilation formula only uses velocity thought. 

What I was getting at is the twin paradox.  The solution answers who is time dilated by who has accelerated.

Okay, so let t=0 where observers A and B are both in the same place away from the black hole, and then observer A freefall inwards until he is right beside the event horizon while observer B watches from afar. From there, things proceed as previously described. Whose worldline has been most dilated when they are reconciled?
Observer A. 

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Unless there were something else trying to make it collapse inwards, like gravitation.
So the net acceleration is?  Also, it appears I should of asked you where the normal force comes from, so where does it come from? 
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Parsifal

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Re: Clarification on Gravity
« Reply #607 on: September 17, 2008, 09:04:24 AM »
Okay, so let t=0 where observers A and B are both in the same place away from the black hole, and then observer A freefall inwards until he is right beside the event horizon while observer B watches from afar. From there, things proceed as previously described. Whose worldline has been most dilated when they are reconciled?
Observer A.

How, in your model, has observer A accelerated more than observer B?

So the net acceleration is?

Up.

Also, it appears I should of asked you where the normal force comes from, so where does it come from?

Electrostatic repulsion.
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sokarul

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Re: Clarification on Gravity
« Reply #608 on: September 17, 2008, 10:01:30 AM »
Okay, so let t=0 where observers A and B are both in the same place away from the black hole, and then observer A freefall inwards until he is right beside the event horizon while observer B watches from afar. From there, things proceed as previously described. Whose worldline has been most dilated when they are reconciled?
Observer A.

How, in your model, has observer A accelerated more than observer B?
My model? 
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Up.
Then there would be motion.  Where is the motion?
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Electrostatic repulsion.
And that is present because?
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Parsifal

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Re: Clarification on Gravity
« Reply #609 on: September 17, 2008, 08:16:16 PM »
How, in your model, has observer A accelerated more than observer B?
My model?

The one where you are claiming that we do not accelerate up.

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Up.
Then there would be motion.  Where is the motion?

Assume an inertial frame of reference by jumping off a tall building. Now tell me the surface of the Earth isn't moving when it reaches you.

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Electrostatic repulsion.
And that is present because?

Negative charges repel other negative charges.
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sokarul

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Re: Clarification on Gravity
« Reply #610 on: September 17, 2008, 09:16:34 PM »


The one where you are claiming that we do not accelerate up.

Because observer A is in free-fall.
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Assume an inertial frame of reference by jumping off a tall building. Now tell me the surface of the Earth isn't moving when it reaches you.
The earth's surface isn't accelerating.  Atomic clocks will prove this. 
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Negative charges repel other negative charges.

And the negative charges are together why? 
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Re: Clarification on Gravity
« Reply #611 on: September 17, 2008, 09:40:28 PM »
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Assume an inertial frame of reference by jumping off a tall building. Now tell me the surface of the Earth isn't moving when it reaches you.
The earth's surface isn't accelerating.  Atomic clocks will prove this. 
Sorry to jump in here, but how exactly?
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Roundy the Truthinessist

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Re: Clarification on Gravity
« Reply #612 on: September 17, 2008, 09:44:34 PM »
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Assume an inertial frame of reference by jumping off a tall building. Now tell me the surface of the Earth isn't moving when it reaches you.
The earth's surface isn't accelerating.  Atomic clocks will prove this. 
Sorry to jump in here, but how exactly?

It's this funny thing REers like to throw around.  Apparently, they have these atomic clocks that keep perfect time, and something about them running at different times far above the surface of the earth, which somehow proves that the earth is round.  idk, I'm sure someone else could explain it better than me.
Where did you educate the biology, in toulet?

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Parsifal

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Re: Clarification on Gravity
« Reply #613 on: September 18, 2008, 12:07:12 AM »
Because observer A is in free-fall.

Not for the entire duration of the experiment. I suggest you go back and read my posts more carefully.

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Assume an inertial frame of reference by jumping off a tall building. Now tell me the surface of the Earth isn't moving when it reaches you.
The earth's surface isn't accelerating.  Atomic clocks will prove this.

No, they will prove that it is, if an experiment is conducted properly.

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Negative charges repel other negative charges.

And the negative charges are together why? 

Gravitation.
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Dr Matrix

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Re: Clarification on Gravity
« Reply #614 on: September 18, 2008, 01:43:43 AM »
Any observer who has an atomic clock sitting on their lap will see it tick at the same rate (locally) since locally space has to be flat (Minkowski metric). Unless you are near a black hole or have invented a new atomic clock that is better than the best frequency standards available today, you can take 'local' to mean human-scale. Atomic clocks will show (compared to a distant observer) that someone standing on the ground is in a non-inertial frame, which could equally be interpreted as being caused through gravitation or acceleration.  Atomic clocks (or, in fact, any other local experiment) are therefore not valid for distinguishing gravitation from acceleration.

It is reasonable to talk about a person on the ground being accelerated upwards, since that is the action that is required to deviate from your geodesic in such a way that you see zero co-ordinate velocity.
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Re: Clarification on Gravity
« Reply #615 on: September 18, 2008, 03:39:06 AM »
Atomic clocks (or, in fact, any other local experiment) are therefore not valid for distinguishing gravitation from acceleration.
See you're spoiling my fun there. I am dying to know how he thought they could be used to prove it.
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Dr Matrix

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Re: Clarification on Gravity
« Reply #616 on: September 18, 2008, 04:10:31 AM »
See you're spoiling my fun there. I am dying to know how he thought they could be used to prove it.

You never know, he may yet prove me wrong... let's wait and see! ;)
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All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.

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sokarul

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Re: Clarification on Gravity
« Reply #617 on: September 18, 2008, 09:41:22 AM »
Because observer A is in free-fall.

Not for the entire duration of the experiment. I suggest you go back and read my posts more carefully.
Observer A free falls to the back hole and then leaves it to meet up with observer B.  Saying it like that, observer A then has to accelerate away from the black hole. 


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No, they will prove that it is, if an experiment is conducted properly.
I agree to that. 

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Gravitation.
Well you are getting there. 

See you're spoiling my fun there. I am dying to know how he thought they could be used to prove it.
I know exactly why I said it.  You on the other hand, had no idea why. 
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Parsifal

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Re: Clarification on Gravity
« Reply #618 on: September 18, 2008, 09:46:01 AM »
Because observer A is in free-fall.

Not for the entire duration of the experiment. I suggest you go back and read my posts more carefully.
Observer A free falls to the back hole and then leaves it to meet up with observer B.  Saying it like that, observer A then has to accelerate away from the black hole. 

No, Observer A freefalls to the black hole and stays where he is relative to the event horizon. Observer B then begins freefalling to the event horizon where Observer A is.

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No, they will prove that it is, if an experiment is conducted properly.
I agree to that. 

But that contradicts what you just said. :-\

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Gravitation.
Well you are getting there.

Oh, I'm there. You still have a way to go, it seems.
I'm going to side with the white supremacists.

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sokarul

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Re: Clarification on Gravity
« Reply #619 on: September 18, 2008, 09:53:46 AM »


No, Observer A freefalls to the black hole and stays where he is relative to the event horizon. Observer B then begins freefalling to the event horizon where Observer A is.
That's not what you said. 

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But that contradicts what you just said. :-\
No contradiction at all. 

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Oh, I'm there. You still have a way to go, it seems.
Did you look up normal force yet? 
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Parsifal

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Re: Clarification on Gravity
« Reply #620 on: September 18, 2008, 09:57:06 AM »
That's not what you said.

You not being able to read doesn't change what I said.

No contradiction at all.

Really?

The earth's surface isn't accelerating.  Atomic clocks will prove this.
No, they will prove that it is, if an experiment is conducted properly.

Did you look up normal force yet? 

I know what a normal force is.
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sokarul

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Re: Clarification on Gravity
« Reply #621 on: September 18, 2008, 10:34:59 AM »
That's not what you said.

You not being able to read doesn't change what I said.
Show it.

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Really?
Yeah

The earth's surface isn't accelerating.  Atomic clocks will prove this.
No, they will prove that it is, if an experiment is conducted properly.

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I know what a normal force is.
I don't think you do. 
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Parsifal

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Re: Clarification on Gravity
« Reply #622 on: September 18, 2008, 03:14:35 PM »
That's not what you said.

You not being able to read doesn't change what I said.
Show it.

What would happen if, at t=0, observer A just outside the event horizon of a black hole switches on his jet pack to hover where he is, while observer B allows herself to enter freefall along a path that will take her right alongside observer A, and just as she reaches him, he switches off his jetpack so that they are both inertial? Whose worldline will have been dilated when the two are in the same frame of reference, and therefore who has undergone acceleration?

I later expanded on this so that they start in the same frame of reference, too.
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sokarul

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Re: Clarification on Gravity
« Reply #623 on: September 18, 2008, 04:04:48 PM »
That's not what you said.

You not being able to read doesn't change what I said.
Show it.

What would happen if, at t=0, observer A just outside the event horizon of a black hole switches on his jet pack to hover where he is, while observer B allows herself to enter freefall along a path that will take her right alongside observer A, and just as she reaches him, he switches off his jetpack so that they are both inertial? Whose worldline will have been dilated when the two are in the same frame of reference, and therefore who has undergone acceleration?

I later expanded on this so that they start in the same frame of reference, too.
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Okay, so let t=0 where observers A and B are both in the same place away from the black hole, and then observer A freefall inwards until he is right beside the event horizon while observer B watches from afar. From there, things proceed as previously described. Whose worldline has been most dilated when they are reconciled?

So previously described means what?  That doesn't match the previous post.   
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Parsifal

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Re: Clarification on Gravity
« Reply #624 on: September 18, 2008, 04:08:35 PM »
So previously described means what?  That doesn't match the previous post.   

The situation at the end of that post is identical to that at the beginning of the previous one. If you can't see that, there really isn't any point debating with you.
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sokarul

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Re: Clarification on Gravity
« Reply #625 on: September 18, 2008, 04:10:52 PM »
So previously described means what?  That doesn't match the previous post.   

The situation at the end of that post is identical to that at the beginning of the previous one. If you can't see that, there really isn't any point debating with you.
So the observers are right next to each other yet observer B's path will "take her right alongside observer A, and just as she reaches him, he switches off his jetpack so that they are both inertia?".
I don't think you thought your cunning plan all the way through. 
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Parsifal

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Re: Clarification on Gravity
« Reply #626 on: September 18, 2008, 04:16:02 PM »
So the observers are right next to each other yet observer B's path will "take her right alongside observer A, and just as she reaches him, he switches off his jetpack so that they are both inertia?".
I don't think you thought your cunning plan all the way through. 

I don't think you read my second post all the way through.
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sokarul

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Re: Clarification on Gravity
« Reply #627 on: September 18, 2008, 04:17:45 PM »
I asked for you to show it once.  I know you can't, that's why you haven't yet. 
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Parsifal

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Re: Clarification on Gravity
« Reply #628 on: September 18, 2008, 04:19:10 PM »
Here it is again, with the relevant part increased in size so that you don't skip over it this time:

Okay, so let t=0 where observers A and B are both in the same place away from the black hole, and then observer A freefall inwards until he is right beside the event horizon while observer B watches from afar. From there, things proceed as previously described. Whose worldline has been most dilated when they are reconciled?
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sokarul

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Re: Clarification on Gravity
« Reply #629 on: September 18, 2008, 04:24:19 PM »
Here it is again, with the relevant part increased in size so that you don't skip over it this time:

Okay, so let t=0 where observers A and B are both in the same place away from the black hole, and then observer A freefall inwards until he is right beside the event horizon while observer B watches from afar. From there, things proceed as previously described. Whose worldline has been most dilated when they are reconciled?

Which is completely different than the original post. UNDERSTAND?  Also different than your post
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No, Observer A freefalls to the black hole and stays where he is relative to the event horizon. Observer B then begins freefalling to the event horizon where Observer A is.
Unless "watches from afar" means to leave and going join the other observer. 

So back to my answer. 
OBSERVER A IS DILATED MORE. 
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