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Author Topic: Is this a new paradox of energy?  (Read 27313 times)

Offline Geezer

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Is this a new paradox of energy?
« Reply #50 on: 01/03/2011 21:34:02 »
I think you missed my last post.

It depends on the perspective of the observer. Just because the observer cannot detect the presence of gravity, that does not mean it does not exist.

As an alternative, in my suggested experiment, you could also try chanting, "I cannot detect you gravity, therefore you do not exist."
 

Offline Geezer

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« Reply #51 on: 01/03/2011 22:18:40 »

And any uniform motion, including the one seen as a gravitational acceleration when standing on Earth is defined by no 'gravity' perceptible inside a 'black box'.


That's my whole point. If the system boundaries are confined within the black box, the Earth, and the rest of the Universe do not exist! (It's impossible to prove they do.)

If you are going to involve the Earth, the "black box" better include the Earth too, otherwise you are simply moving the goal posts around.
 

Offline yor_on

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Is this a new paradox of energy?
« Reply #52 on: 01/03/2011 22:20:17 »
Did you read the pdf?

Try it.
 

Offline Geezer

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« Reply #53 on: 01/03/2011 22:38:29 »
Did you read the pdf?


No. If you try to blow me off with PDFs, I'll have to assume you don't understand your model well enough to explain it in your own words.

How about you try to explain my objection to your black box argument instead? It's not a very complicated argument, is it?


 

Offline yor_on

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Is this a new paradox of energy?
« Reply #54 on: 01/03/2011 22:50:45 »
I just meant that it is a very nice explanation of those 'straight lines'. It also gives an excellent example of how A. an apple thrown up, falling down is described, as well as B. the difference in Newtons theory compared to Einsteins holding a apple over the ground. It's the best one I've seen actually. But you don't need to read it if you don't want too.

As for you arguing that in a black box nothing can be 'real'?
Take it up with Einstein :)
==

And Newton too btw:)

Both used them, in Einsteins world the assumption is that all laws of physics existing, also will exist in a 'black box scenario/laboratory'. And if they are equivalent, as in a constant uniform acceleration, with for example 'gravity'. Then it is 'gravity'. And if you can't differ your speed from the inside, uniformly moving, then all uniform motion is the same, however you then want to define that, as being at rest or not. But that's where the idea of inertial frames come from as I understands it. That you can't differ a uniform motion from being at rest. There are a lot of other assumptions you can draw from those concepts too, But you have to accept them first. And doing so will clash with the world of Newton, although both are very good at describing the world we live in.
« Last Edit: 01/03/2011 23:15:03 by yor_on »
 

Offline Geezer

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« Reply #55 on: 01/03/2011 23:08:08 »
Everything is real in a black box. That is the only possible reality within its confines. However, you cannot simply superimpose that reality on to a different black box, because that black box has a different reality.

I am confident that Einstein would agree that if we want to talk in terms of black boxes we have to define their boundaries carefully. I suspect he would take a very dim view if we continually moved the boundaries around.
 

Offline yor_on

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Is this a new paradox of energy?
« Reply #56 on: 01/03/2011 23:15:30 »
Geezer.

I'll let it rest now.
==

One thing though "However, you cannot simply superimpose that reality on to a different black box, because that black box has a different reality." In a way it's the opposite actually. If you can create a 'black box scenario' in where you find an exact equivalence to what you observe otherwise then the chances are pretty good that they are the same. That's why all black boxes uniformly moving are seen as the same, no matter their speed relative each other. and that's why a constant acceleration at one G is equivalent to Earths gravity (or any gravitational field of one G). It's a minimalistic approach to 'reality' you might say.

But if you meant "superimpose that (uniformly moving) reality on to a different (accelerating) black box, because that black box has a different reality." then I agree, and that's also what black boxes test, if they are the same or not (the physical laws).
« Last Edit: 01/03/2011 23:29:59 by yor_on »
 

Offline Geezer

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« Reply #57 on: 01/03/2011 23:18:37 »
Too late! I was just about to post this.

The flaw in the argument about the "black box" elevator is that it is decribed as an elevator. From the perspective of the occupants, if it really is a "black box" they cannot "know" it is an elevator. All they know is that it's a black box.

Other observers might know it is an elevator, but only because they have a different frame of reference, so they define the system differently.
« Last Edit: 01/03/2011 23:21:03 by Geezer »
 

Offline yor_on

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« Reply #58 on: 01/03/2011 23:26:33 »
Hmm, read my post before, and you'll see how I see it :)
Seems we wrote 'past each other' there.

But try the pdf. It's really good.
 

Offline JP

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« Reply #59 on: 01/03/2011 23:28:34 »
???

Sorry to butt in, but I'm trying to figure out where this gravity discussion ties in to the original question.  Is it that general relativity says one thing about energy being put into a system that's raised under gravity, while Newtonian gravity says another?
 

Offline yor_on

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Is this a new paradox of energy?
« Reply #60 on: 01/03/2011 23:31:05 »
Ahh, yes, I'm sort of confused too. But hey, no news there :)
And the discussion is lively.. :)
 

Offline Geezer

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« Reply #61 on: 01/03/2011 23:32:41 »
No - (at least I don't think so.)

It's simply that Yoron refuses to bow to my obviously superior intellect.
 

Offline yor_on

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« Reply #62 on: 01/03/2011 23:39:03 »
We have saying in Sweden, loosely interpreted it states that 'opinions reminds of an a*s, there will aways be found a split somewhere." ah, that was very loosely interpreted.

=
I need to work on that one some more, don't I?
(As the boy said to the girl)

Da*n,
Can't seem to stop this. Maybe we should put a X-rating on this topic?
« Last Edit: 01/03/2011 23:42:34 by yor_on »
 

Offline Geezer

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« Reply #63 on: 01/03/2011 23:44:51 »
Aw come on!

Have you never heard of proof by loud assertion???

......

It's interesting to note that JP has relocated to Switzerland.
« Last Edit: 01/03/2011 23:50:17 by Geezer »
 

Offline yor_on

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« Reply #64 on: 01/03/2011 23:49:33 »
Yeah, well.. Ahh, yes. :)

...

Tricky tricky ::))
« Last Edit: 01/03/2011 23:57:48 by yor_on »
 

Offline Geezer

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« Reply #65 on: 02/03/2011 00:21:04 »

I'm trying to figure out where this gravity discussion ties in to the original question.


Seems fairly clear to me JP. Which part of

"On lifting a system from the floor to a height..."

did you not understand?
 

Offline yor_on

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« Reply #66 on: 02/03/2011 00:30:47 »
"Is it that general relativity says one thing about energy being put into a system that's raised under gravity, while Newtonian gravity says another."

I think that is perfectly clear too?

What JP meant was that when we lift a system on the floor the gravity naturally need to be adjusted to whom it is. And as it states, it's either Newton nor Einstein?

But he seems to forget to adjust for the apple?
==

Maybe you didn't read the pdf JP?
There you can find everything about it.

It's important in all systems under, as well as over, gravity.
Ultimately it's EMR that needs to be considered of course.

Apples or no apples.


« Last Edit: 02/03/2011 00:42:45 by yor_on »
 

Offline JP

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« Reply #67 on: 02/03/2011 01:09:30 »
Maybe you didn't read the pdf JP?
There you can find everything about it.

It's 94 pages!  :o

I'm curious, but (no offense) I don't think I'll find the time to read all that!
 

Offline JP

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« Reply #68 on: 02/03/2011 01:36:20 »
I know I'm going to get PBLA'ed for this, but aren't you just arguing over which of two models is right, even though they happen to agree?  Newtonian gravity deals with forces and potentials, while general relativity deals with topology and geodesics.  They both agree very well for something being lifted off the earth, though, since gravity is relatively weak and slowly varying.  In that case, it's a bit silly to use general relativity, since the equations are a nightmare to solve.

Thermodynamics generally relies on energy and work, so I'm pretty sure you couldn't easily use general relativity to describe what happens to a thermodynamic system as you lift it.  I guess you could work out the coordinate transformations and particle geodesics needed for that case in general relativity and apply those to the equations of thermodynamics, but... isn't that a bit overkill?  Plus, it should still agree with the Newtonian result here on earth.
 

Offline Geezer

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« Reply #69 on: 02/03/2011 02:46:08 »
I know I'm going to get PBLA'ed for this, but aren't ....

Actually, I'm not using a Newtonian model  ;D

Geodesics are all about the interaction between space-time and matter. But whatever model we choose to use, the laws of thermodynamics (until they are repealed) will still govern the energy transactions.
 

Offline Geezer

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« Reply #70 on: 02/03/2011 06:56:06 »
"However, you cannot simply superimpose that reality on to a different black box, because that black box has a different reality." In a way it's the opposite actually. If you can create a 'black box scenario' in where you find an exact equivalence to what you observe otherwise then the chances are pretty good that they are the same. That's why all black boxes uniformly moving are seen as the same, no matter their speed relative each other. and that's why a constant acceleration at one G is equivalent to Earths gravity (or any gravitational field of one G). It's a minimalistic approach to 'reality' you might say.

But if you meant "superimpose that (uniformly moving) reality on to a different (accelerating) black box, because that black box has a different reality." then I agree, and that's also what black boxes test, if they are the same or not (the physical laws).

Let's try a practical experiment.

You are in a black box. Within the black box, you are completely weightless. Because you are in a black box, you cannot have any knowledge of your position relative to anyting else (otherwise, it would not be a black box).

I am in a different black box. My black box happens to include your black box, as well as the Earth. I can see that your black box is accelerating towards the Earth at 9,81 m/s/s.

You cannot know that your black box is accelerating towards the Earth at 9,81 m/s/s. Does that mean it will not collide with the Earth?

Seems like a fairly straightforward question to me. I hope it does not require a 92 page answer.
 

Offline yor_on

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« Reply #71 on: 02/03/2011 09:54:23 »
:)

Of course I will collide with Earth, if you say so :)
How can I avoid it?

But the proper way as they say on the British telly is to use 'black boxes'  to test how physics work, or not work. To do that you make some assumptions, one is that any law in physics will, if found being the exact same in your 'black box' as well as outside it, have an connection. For example the idea of gravity being equivalent to a constant acceleration. If that would have been wrong then the equivalence would not be there. It's not Russian boxes in boxes in .. It's just a minimalistic way to test the laws of physics.
==

Geezer, if we had a real acceleration, energy expended, so to speak I think you might be right in the energy changing in the books 'SpaceTime distortion'. It's just that we don't have a acceleration in this case. You might argue that any motion increase the energy in the geometric properties of space-time but to me it's a question about what is measurable. What you can measure is the distortion, but if that is 'energy'? Maybe, but if so it's not anything 'tapped' by the object moving uniformly. In a acceleration there will be a difference though.

'Energy' is a very slippery subject that we seem to use to connect 'events' with each other. I prefer to look at it as something causing something to 'jiggle', adding to a mass, and if it does not do so then it's not what I call 'energy'. That 'SpaceTime' distorts both in a uniform motion and a acceleration seems to me to be a proof for it not being any 'energy' at all, in fact. There is nothing measurable 'jiggling' anywhere there. The distortion is something connected to SpaceTime itself, brought about by motion. But if we like to use 'energy', and also believe in the conservation of 'energy', and think that a Lorentz contraction is real, then we 'concentrate' the universes 'energy' locally by any 'motion', uniform or not as the universe contracts locally. And if you like turn the complementary 'slowing/time dilation' into a proof for SpaceTime needing to 'concentrate' its 'energy' relative the moving frame.

But I don't like it. All motion, except uniform motion, expend some 'energy', and that fuel transforming into energy gets used up too, some of it as 'radiation', which in its turn gets used up in other interactions, leaving? 'Used Energy?' or 'work done' if you like. :) that nobody ever have touched or seen, more than as a mental crutch, a concept. At the same time as all 'uniform motions', no matter what 'speeds' you assign to them, are the same in that none of them is distinguishable from each other, inside that black box, and also in that none of them expend any 'energy', ever.

I'm not happy over that use of 'energy'. But yeah, if I stop looking at 'energy' as something measurable as 'jiggling'? Maybe you can define it your way. But the book will still not have any more 'energy' :) But to me such a definition of energy seem to set a uniform motion equivalent to a acceleration? And that one clash with my ideas rather strongly. Then 'energy' seems to become a description of geometries, not anything specifically connected to the difference between 'work' and 'work done'.
« Last Edit: 02/03/2011 14:56:40 by yor_on »
 

Offline JP

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« Reply #72 on: 02/03/2011 15:35:34 »
I know I'm going to get PBLA'ed for this, but aren't ....

Actually, I'm not using a Newtonian model  ;D

Geodesics are all about the interaction between space-time and matter. But whatever model we choose to use, the laws of thermodynamics (until they are repealed) will still govern the energy transactions.

I know we've been through this in another thread in great detail, but gravitational energy in general relativity doesn't always satisfy energy conservation.  You can't always define a general work-energy theorem.  There are special cases where you can, such as over tiny patches of space-time, where things are close to flat, or when you move far away from gravitating objects where things are also flat.

The actual problem, as I remember, is that conservation of gravitational energy gives you an equation that needs only hold for one observer.  Another observer might look in and see it violated.  This would be a problem for thermodynamics, since some observers would see the second law broken if you chose to write it in terms of energy.

The thing is that if you go back to derive the laws of thermodynamics, they start off as much simpler equations involving the motions of various particles.  Energy arrives because energy can describe the motions of particles and from that you can build the second law of thermodynamics in terms of energy.  In general relativity, the motions of the particles are described by geometry, and so you'd arrive at a second law of thermodynamics governed by geometry if you worked it up from first principles.  It should then hold for all observer in GR, and in the Newtonian limit, it should agree with the energy formulation.

Of course, my disclaimer here is that I'm not a GR expert, so I don't really know how badly conservation of energy breaks down in GR and in what cases it does so, but I'm pretty sure that when it does, you can't formulate the second law in terms of energy transactions and expect it to be general-relativistically sound.
 

Offline yor_on

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« Reply #73 on: 02/03/2011 16:20:28 »
Thanks for that one JP.

Nice to see that I don't have to start thinking of 'energies' from a solely geometric perspective. Not that I would. It would make all understanding I have of that concept wrong, and if it is something I cherish it has to be my presumptions :) So easy to get, almost impossible to lose ::))

Whatever I mean by that?
==

I will need to think about it of course. Still, 'energy' as a concept is alway connected to interactions, either happening or at least having the 'potential of them happening'. So in that motto you can use it for describing the effects of relativistic motion too. Myself I prefer to use it in it's measurable form (interactions), as it simplifies a lot that otherwise would get me confused.

And if you look at radiation interacting with your eye then that 'energy' surely 'transform', but its final stage can't be 'energy'. The only definition I have for that is 'work done' which I see as a thermodynamic concept. And as such actually better than the idea of 'energy' that I find so hard to define.

In thermodynamics doing work is often seen as heat, like a gas driving a piston in your cars engine. There it is the heat that does work on your engine, not the 'energy'.


"The First Law of Thermodynamics is the law of Conservation of Energy. It states that energy cannot be created or destroyed. Instead it is converted from one form to another, such as from mechanical work to heat, from heat to light, from chemical to heat or such."

Now, this is all good and fine, but what happened with that photon hitting your eye? Isn't heat, all said and done, just something 'jiggling'? I think it is, and it has three ways to make stuff do so. Convection (warmer areas of a liquid or gas rises to cooler areas mixing in the process), Conduction (two object at different temperatures in contact with each other equalizing their temperature) and Radiation (a method of heat transfer that does not rely upon any contact between the heat source and the heated object.)

But when the 'jiggling' stops then? Well, that's what I call 'work done', and where that 'stuff' went that made it 'jiggle'? Dissipating into the universe if we want the conservation laws to hold, but as what? Not 'heat' as that makes stuff 'jiggle'? Not 'energy' as that also causes a 'jiggling'? And this 'jiggling' had stopped.

But, it's definitely 'work done' in its most simple meaning.
« Last Edit: 02/03/2011 18:03:19 by yor_on »
 

Offline Geezer

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« Reply #74 on: 02/03/2011 19:19:54 »

but what happened with that photon hitting your eye? Isn't heat, all said


Wouldn't some of the energy also be converted int chemical energy? Ultimately, I would think all the energy in the photon will be conserved, even if it only goes to increase the entropy in the Universe.
 

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