Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Anukshan Ghosh on 19/02/2011 03:42:19

Title: Is this a new paradox of energy?
Post by: Anukshan Ghosh on 19/02/2011 03:42:19: On lifting a system from the floor to a height does the energy I expended get added to the system's internal energy? Cause change in Internal Energy in a isothermal process is given by nCv(T2-T1),which predicts ΔU to be zero.
Title: Is this a new paradox of energy?
Post by: CPT ArkAngel on 19/02/2011 09:15:27: where do you see a paradox? More explanations, please... It seems to be a simple problem.
Title: Is this a new paradox of energy?
Post by: yor_on on 19/02/2011 15:40:58: No, they are two different processes. You may lift a book from the floor to the table, while you're acting on the book you loose some 'energy' but the book gain no energy from you. The only thing changing for the book is the position it have relative gravity, that is, you just moved it a little further away from 'gravity's center'. That means that its 'potential energy' might be seen to grown a little versus Earths center although if measured you will find no extra 'energy' expressed as mass in that book. At the same time as you lifted that book and put it on the table you also, if you like, decreased its 'potential energy' relative the moon if doing so at night, daytime you might assume that you increased its 'potential energy' relative the moon as the moon then could be in a opposite position relative the direction you moved that book.

If you on the other hand define gravity as a 'force', you actually decreased that 'force' by removing the book from the Earths floor, relative Earth/book at the same time as you, if at night, increased the moons 'force/gravity' acting on that book. And that's why I find myself mixing those two at times. It's hard not looking at gravity as a 'force' as that is exactly as we experience it normally, it acting on us. but it's no 'force' in a normal manner, it's more like a invincible dynamic topology.
==

It's slightly confusing as I ignore Earth when discussing the moon/book. But it is true in that you can define any two objects as a system if you like, depending on what you try to define. I had to look at this twice to get it right :) Also it is a question about how to define the possible interaction from that 'potential energy' to me. If I move something away from gravity we can assume that it, if following the geodesics moving into that 'gravity well' its 'interaction' will become stronger the further it have to travel, hitting the ground. But when we have several gravity wells acting in different directions on that book it becomes more confusing to me. And that's why I ignore Earth for this moon/book. A cheap escape I know :)

==

The only way I know to increase the 'energy' aka mass of that book is if you 'compress' it and then somehow make it stay in a compressed state. The rest is variables of 'potential energy' relative what you define as your system, be it Earth/book or Moon/book, well, as I see it.
==

It naturally depends on how you define your system but even if defining it as a system including you, the book and the gravity wells acting on you you will find that the book do not gain any measurable energy, only a potential and that 'energy' not relative you, only relative gravity.
Title: Is this a new paradox of energy?
Post by: Anukshan Ghosh on 20/02/2011 03:01:58: To summarize it, you say not a measurable potential energy gain in the system.
Thank you
Title: Is this a new paradox of energy?
Post by: Anukshan Ghosh on 24/02/2011 06:42:03: I got my answer and everything else is crap actually what happens is that a systems internal energy is defined from a frame of reference in which the center of mass is at rest and hence adding potential energy to the system does not add to its internal energy. A steady state is established in terms of internal energy for these works performed.
Title: Is this a new paradox of energy?
Post by: Geezer on 24/02/2011 08:14:05: Actually, if the book is part of the system which has the internal energy, because you did work to move the book, you did change the internal energy of the system. If you didn't, you'd have violated the first law of thermodynamics.
Title: Is this a new paradox of energy?
Post by: yor_on on 24/02/2011 10:17:37: No Geezer, you're not transferring any energy to the book, and I think that was what this question was about? 'Potential energy' is a conceptual framework describing possible interactions under the influence of the arrow of time. Not 'now' but 'when/if' the book falls down. you can move the moon if you like, without adding any energy to it by moving it, same as you move a starship by 'expending' energy. The star-ships 'invariant mass' will not increase as far as I know, the possible exception to it being its Lorentz contraction that just might add a invariant mass.

We had this discussion before methinks :) (http://www.thenakedscientists.com/forum/index.php?topic=33720)
Title: Is this a new paradox of energy?
Post by: Geezer on 24/02/2011 19:02:26: Yoron,

It's a thermodynamic question, and internal energy is a thermodynamic concept. Whenever work is done on a "system", it alters the internal energy of the system.

Check out

Daemons - Systems at http://www.thermofluids.net/
Title: Is this a new paradox of energy?
Post by: yor_on on 25/02/2011 11:39:56: Nice site Geezer, and I agree on that looked at as a system the 'internal energy' have changed for it. But a system is very much a conceptual exercise wherein you are free to define it like you need, for the validation of your experiment, within limits of course but..

The 'internal energy' you refer too I see a as a common description for all relations involved between, and in, the objects you defined as belonging to that same 'system'. And you need only to change what objects you refer to to get a new and different 'system'. As I see it not unlike the idea of 'potential energy'. But even so, that book has no extra energy collected in it by you lifting it up on a table. The potential energy that it refer too is not measurable as any new mass, its atoms are not jiggling faster. In fact, nothing have changed for the book itself. The only thing changing is the relation it will have relative gravity. And that's the plain truth, nothing more :) But the 'systems' possible energy have changed, if we remember that it's the 'possible' energy we're talking about, that is the 'potential energy'.

Gravity is no force, to me it's more of a 'topology'. What you could assume, possibly, is that when getting compressed, like moved close to the event horizon, or past, it should express itself as more mass. At least it seems reasonable to assume that, also there is the question about what a Lorentz contraction does to a piece of lasting matter. Those two are really interesting :)
Title: Is this a new paradox of energy?
Post by: Geezer on 25/02/2011 19:23:28: Quote from: yor_on on 25/02/2011 11:39:56
Nice site Geezer, and I agree on that looked at as a system the 'internal energy' have changed for it. But a system is very much a conceptual exercise wherein you are free to define it like you need, for the validation of your experiment, within limits of course but..

The 'internal energy' you refer too I see a as a common description for all relations involved between, and in, the objects you defined as belonging to that same 'system'. And you need only to change what objects you refer to to get a new and different 'system'. As I see it not unlike the idea of 'potential energy'. But even so, that book has no extra energy collected in it by you lifting it up on a table. The potential energy that it refer too is not measurable as any new mass, its atoms are not jiggling faster. In fact, nothing have changed for the book itself. The only thing changing is the relation it will have relative gravity. And that's the plain truth, nothing more :) But the 'systems' possible energy have changed, if we remember that it's the 'possible' energy we're talking about, that is the 'potential energy'.

Gravity is no force, to me it's more of a 'topology'. What you could assume, possibly, is that when getting compressed, like moved close to the event horizon, or past, it should express itself as more mass. At least it seems reasonable to assume that, also there is the question about what a Lorentz contraction does to a piece of lasting matter. Those two are really interesting :)

Yes, but I think you'll find that if the book was part of a system, and the work done to raise it came from outside the system, the internal energy of the system increased. If you can explain how it's possible to elevate the book without doing work, I might start to believe you. [:D]
Title: Is this a new paradox of energy?
Post by: yor_on on 25/02/2011 20:01:05: I'm just saying that there is no 'energy' transfered to the book Geezer? Where the 'energy' used by lifting the book went? Where does any 'work done' go? We have this formulation of 'work' transforming into 'work done', and what differs between them is 'energy expended', but exactly where it goes in any system? It depends on what you define as it I guess, in a rocket you might say that it transformed into its 'speed' and 'heat/radiation'. In the case of a human chemical processes should be the most important I guess?

As for the 'energy' increasing?
Not sure I follow you there?

The only thing changing is work being done on the book? Maybe you're thinking of the books 'potential energy' relative gravity?
==

Let's make it simple.
I say there is no energy transfered to the book?
That was the original question as I understood it.

Are you saying that there is an added energy in the book?
Prove it.
==

Maybe you're thinking of a enclosed system? Like a container in where you pour something hot, increasing the systems energy, the pouring taking place from outside the defined system? Then I would agree. If we define it as lifting something really heavy inside a closed container then the systems 'energy' will transform, but not increase. If we define it as a open system, no physical enclosure, but still including someone lifting a book against gravity, then I expect the system to lose its 'energy expended', in form of heat and other chemical processes, diminishing the systems 'energy'. If we define the system as only the book versus gravity and let the lifter be outside our 'system' then work is being done on the book and its 'potential energy' relative gravity is increased but its own internal measurable mass/energy will not increase as far as I know? To actually increase the 'energy' for the system? If I compressed it I would expect the books internal energy to increase, no gravity needed other than the books own invariant mass/energy increasing, produced by a compression, just like making a black hole.
Title: Is this a new paradox of energy?
Post by: Geezer on 25/02/2011 20:28:05: Hey! They're not my rules. I'm only applying the laws of thermodynamics [:D]

"The internal energy of a system can be changed by heating the system or by doing work on it;[1] the first law of thermodynamics states that the increase in internal energy is equal to the total heat added and work done."

From http://en.wikipedia.org/wiki/Internal_energy
Title: Is this a new paradox of energy?
Post by: yor_on on 25/02/2011 20:44:51: Well, we define 'potential energy' too Geezer. We have a lot of laws describing transformations, but as for how they are measurable? A compression should be measurable.
==

"In thermodynamics, the internal energy is the total energy contained by a thermodynamic system. It is the energy necessary to create the system, but excludes the energy to displace the system's surroundings, any energy associated with a move as a whole, or due to external force fields."
Title: Is this a new paradox of energy?
Post by: Geezer on 25/02/2011 20:49:31: Quote from: yor_on on 25/02/2011 20:44:51
Well, we define 'potential energy' too Geezer. We have a lot of laws describing transformations, but as for how they are measurable? A compression should be measurable.

Not quite sure I understand your point there Yoron, but I do know that work and heat are fairly easy to quantify.
Title: Is this a new paradox of energy?
Post by: yor_on on 25/02/2011 20:55:22: What is your point Geezer?
Title: Is this a new paradox of energy?
Post by: Geezer on 25/02/2011 21:01:58: Oh, I'm only saying it's not hard to quantify the amount of work or heat added to a system (in thermodynamics).

I didn't understand what you meant by "A compression should be measureable."
Title: Is this a new paradox of energy?
Post by: yor_on on 25/02/2011 21:06:38: Conservation of energy. (http://en.wikipedia.org/wiki/Energy#Conservation_of_energy)

"The first law of thermodynamics simply asserts that energy is conserved,[17] and that heat is included as a form of energy transfer. A commonly used corollary of the first law is that for a "system" subject only to pressure forces and heat transfer (e.g., a cylinder-full of gas), the differential change in energy of the system (with a gain in energy signified by a positive quantity) is given as the following equation:

***

where the first term on the right is the heat transfer into the system, defined in terms of temperature T and entropy S (in which entropy increases and the change dS is positive when the system is heated), and the last term on the right hand side is identified as "work" done on the system, where pressure is P and volume V (the negative sign results since compression of the system requires work to be done on it and so the volume change, dV, is negative when work is done on the system). Although this equation is the standard textbook example of energy conservation in classical thermodynamics, it is highly specific, ignoring all chemical, electric, nuclear, and gravitational forces, effects such as advection of any form of energy other than heat, and because it contains a term that depends on temperature. The most general statement of the first law (i.e., conservation of energy) is valid even in situations in which temperature is undefinable.

Energy is sometimes expressed as the following equation:

***

which is unsatisfactory[11] because there cannot exist any thermodynamic state functions W or Q that are meaningful on the right hand side of this equation, except perhaps in trivial cases.
==

What I meant was that if you compress a spring, and leave it compressed, that should be measurable as an added 'invariant' mass. But if we're discussing heat, fluids and gases it's different than with our 'lifting a book'.
Title: Is this a new paradox of energy?
Post by: Geezer on 25/02/2011 21:38:54: All good stuff, but I'm not sure how to apply it in this particular case.

Try this:

We define a system consisting of the Moon, a table and a book only.

Initially, the book is sitting on the surface of the Moon. A big hand comes down from above and moves the book onto the table.

We then might try to answer questions like:
Was work done on the book?
Was work done on the system?
Did the internal energy of the system change?
Is it even possible to answer these questions by applying Thermodynamics? (I have a suspicion the answer may be no.)
Title: Is this a new paradox of energy?
Post by: yor_on on 25/02/2011 22:03:55: :)

Sh*

I really liked that big hand, reminded me of MP:n. Sorry, I was away for a while, helped me mum. The first law is about conservation of energy as I think of it. You're probably all too right in it being tricky defining where the 'energy' went though :) heat? This one might help us, ah, maybe?

"The total energy of the universe does not change. This does not mean that the form of the energy cannot change. Indeed, chemical energies of a molecule can be converted to thermal, electrical or mechanical energies.

The internal energy of a system can change only by work or heat exchanges. From this the change in the free energy of a system can be shown by the following equation:

ΔE = q – w

When q is negative heat has flowed from the system and when q is positive heat has been absorbed by the system. Conversely when w is negative work has been done on the system by the surrounding and when positive, work has been done by the system on the surroundings.

In a reaction carried out at constant volume no work will be done on or by the system, only heat will be transferred from the system to the surroundings. The end result is that:

ΔE = q

When the same reaction is performed at constant pressure the reaction vessel will do work on the surroundings. In this case:

ΔE = q – w

where

w = PΔV

When the initial and final temperatures are essentially equal (e.g. in the case of biological systems):

ΔV = Δn[RT/P]

therefore,

w = ΔnRT

By rearrangement of the above equations one can calculate the amount of heat released under constant pressure:

q = ΔE + w = ΔE + PΔV = ΔE + ΔnRT

In this last equation, Δn is the change in moles of gas per mole of substance oxidized (or reacted), R is the gas constant and T is absolute temperature. "

From there it gets constantly more scientific :) (http://themedicalbiochemistrypage.org/thermodynamics.html#standard)
==

And as that hand is involved we probably need to look at 'Standard State Conditions in Biological Reactions'. It's easier to call it an 'Act Of God' and leave it be I think :)
Title: Is this a new paradox of energy?
Post by: Geezer on 25/02/2011 22:36:26: Here's another one:

A system consists of a mechanical clock that is powered by a spring.

A big hand comes down from the sky and winds up the spring.

Was work done on the system? (Yes, I think.)
Did the internal energy of the system change? (Yes, I think.)
Is this really any different from the book and moon model? (No, I think.)
Title: Is this a new paradox of energy?
Post by: yor_on on 25/02/2011 22:48:35: I would put this way. The hand expended energy drawing up the spring, the spring is now in a more or less compressed state, containing a very slight added invariant mass that it will expend, finally in form of mechanically induced 'heat' also driving levers, cogs etc in the process, moving the hands of the clock.

Was work done by the hand. Yep.
Did (some/most of) that work get stored as 'energy' by that spring. Yep
Did that spring finally lose that 'energy' to the rest of the machinery. Yep.
Did that machinery gain any energy? (final state) Nope.

Did the clock as a system gain energy? Yep, momentarily it did.

Your hand, did that expend energy? As long as it's mortal it did :)
Did the book gain any energy by being lifted. Nope
Where did the energy expended go then? I would say it got 'lost' into the universe as 'heat/radiation' ultimately that is. But if we really want to pinpoint where the he* it went we should ask Bored Chemist :)

I'm pretty sure he's having a good time reading us :)
Title: Is this a new paradox of energy?
Post by: Geezer on 25/02/2011 23:18:20: Quote from: yor_on on 25/02/2011 22:48:35

Did that machinery gain any energy? (final state) Nope.

Ah! But it did.

Imagine the system (the clock) is in a perfectly insulated box and we can read the temperature of the air in the box. After the spring has wound down again, the temperature of the system will have increased.

The reason for this is that all the mechanical energy that was in the spring is eventually converted into heat in overcoming friction in the mechanism. If you keep repeating the wind/unwind cycle the temperature will continue to increase with each cycle.

Now let's try it with a weight powered grandfather clock in a perfectly insulated box. We'll get a similar result. (We should really include the Earth in the insulated box to get the most accurate measurement, but that could be a bit tricky.)
Title: Is this a new paradox of energy?
Post by: yor_on on 25/02/2011 23:36:54: Yes, I agree, in a enclosed system you will find the temperature go up as the energy gets expended transforming into radiation. If you define the universe as 'closed' you might want to define the same happening there. So loosely we can say that the hands 'energy' got transfered to the universe in form of heat, and assume that some of it momentarily was existing in form of 'energy' in the book too. But that kind of 'energy' is not there any longer time, and, as the universe is infinite, and conservation of energy assume that there always is a equilibrium?

You might want to argue that there should be a temperature difference to the universe after the hand expended its energy but even if so I don't expect it to be measurable and as the universe finally is expected to end in a Heat Death. (http://en.wikipedia.org/wiki/Heat_death_of_the_universe) in where nothing 'jiggle' anymore I would expect any heat/radiation coming from the hand lifting to dissipate very quickly. My view :)
Title: Is this a new paradox of energy?
Post by: Geezer on 26/02/2011 00:04:37: Quote from: yor_on on 25/02/2011 23:36:54
If you define the universe as 'closed' you might want to define the same happening there.

I don't think that works. If the hand that wound up the spring is part of the system, it cannot alter the internal energy of the system. The internal energy of a system only increases if external work or energy is added to or removed from it. That's why the big hand has to mysteriously appear from nowhere.

The book situation is no different. You can lift the book against the force of gravity, or, if you prefer, you are doing work to distort space-time. Either way it's not so different from winding a spring or lifting the weight on a grandfather clock. If you allow the book to fall, all the work that went into changing the position of the book will be dissipated as friction (heat).
Title: Is this a new paradox of energy?
Post by: yor_on on 26/02/2011 07:42:47: Well, I expect it to be different though :) To disprove it you have to show there is a measurable energy collected into that book, after lifting it. It's a interesting thought in that it also should mean that gravity was a 'force', and that we then could expect it to do different work on us throughout the universe. If that was so you might also assume that it could lose 'energy' itself, but as far as I know it doesn't? You have another 'force' reminding of gravity though, permanent magnetism doesn't lose 'energy' either as I understands it, levitating something. At least not by applying the magnetic 'force'.
Title: Is this a new paradox of energy?
Post by: Geezer on 26/02/2011 08:00:54: It won't be different. All the kinetic energy of the book will be converted into thermal energy.

If you define the system so that it really captures all of the thermal energy while the book fell, it will precisely equal the energy spent in elevating the book.

If it does not, you'll have to rewrite the laws of energy conservation.
Title: Is this a new paradox of energy?
Post by: yor_on on 26/02/2011 09:23:57: You're right there :) I assume that you mean a 'closed system' for that though. We can define all interactions as expending some energy, that then, no matter how small, will add, or rather transform, some energy in the 'system' and actually the whole SpaceTime you're in. Do you agree?

I don't know if you're right in that, although it's also about how we should see this 'energy expended' in a interaction. To my eyes 'energy' is just a description of something 'not there' but needed to explain why a transformation can express itself as a 'force' doing work. Looked at that way, assuming that we have a conservation of 'energy', whatever that is thought to be, (would have been better to call it 'conservation of transformation' heh, Alchemy here we come :) You still have to define how this 'energy' find its new state as work done in the final stage. 'Energy' is not measurable, radiation is but the radiation clings out in interacting releasing its work into work done. It would be very nice to find some way to measure 'energy' on its own, not only the interactions transforming 'work' into 'work done'.

But I still withhold that you will find no new 'energy/mass' added to that book :). That's also why we need 'potential energy'.
Title: Is this a new paradox of energy?
Post by: yor_on on 26/02/2011 09:30:49: It's like most subjects in physics, looked at from basic we will find that they build on axioms and 'statistics/probability' or 'experience' if you like. That's what we used when we invented 'potential energy', and that's what we used when we invented 'energy'.
==

That is why I speak of compressing a spring as the only way I know of actually proving that something have happened 'energy wise' or as I see it 'mass wise'. Assuming that this have been tested that is :) But I do believe this to be correct, and that's also why I wonder about a Lorentz contraction.
==

Another question is where 'work done' goes ultimately, and if it lose something in the transformation? We say it change but never disappear, still, what did it 'lose' in its transformation? If the ultimate state is radiation? Won't that interact too? And when it interact, doesn't it annihilate?

You might ask yourself what you think to exist when the radiation too have interacted? 'Energy'? Or should I call it 'Work done'? What the he* is it? Not measurable, not defined, existing as a very useful concept, but nothing more as I know.
Title: Is this a new paradox of energy?
Post by: Geezer on 27/02/2011 06:54:14: Quote from: yor_on on 26/02/2011 09:23:57

You're right there :) I assume that you mean a 'closed system' for that though.

In thermodynamics you have to define a boundary for the system. It does not have to be closed necessarily. For example, the mass within the system could be changing. However, you do need to be able to quantify what is changing in the system.

In the book case (not the bookcase [;D]) there is no reason for the mass within the system to change, so it could be completely closed.

"Internal energy" and "system" are just simplifying constructs that allow us to model what we are interested by eliminating a lot of stuff that is not relevant to the problem we are trying to solve.

Potential energy produced by elevating the book is just the same as winding up the spring in a clock. The only difference is that the energy happens to be a distortion of space-time rather than distortion of the atomic lattice in a piece of spring steel.
Title: Is this a new paradox of energy?
Post by: McQueen on 27/02/2011 09:12:35: If you hold the book at arms length, even if you feel you are doing work and there is a perceptible strain on your arms, you are not doing any work because the book remains stationary. If you pick up the book and move it somewhere else you have done work because you have moved it over a distance.
Title: Is this a new paradox of energy?
Post by: yor_on on 27/02/2011 12:51:50: Yep, displacement theory :)
And in neither case the book will weight more, that is have an added 'energy'.

If we want to discus 'energy' and 'gravity' as 'forces' then we should start to look at virtual particles and why we expect them to be more the nearer we get to an EV (Event horizon).

I'll suggest this phenomena will be a direct result of 'space' getting 'folded' the closer you get. Not a result of 'gravity's magnitude' as some magnetic force increasing.

As for thermodynamics relative any other system. They are the same, you always need to define boundaries. Not doing so makes it impossible to 'count' on whatever you are trying to define. Don't mistake this for not being allowed to set a 'boundary' as being open though, you can do so as I did when I stated that the radiation/energy disappear into the Universe. That we found conservation laws makes perfect sense, Without them this universe would be unstable and prone to disappearing, us included.

Those laws I expect to be a 'emergence' too.
Title: Is this a new paradox of energy?
Post by: Geezer on 27/02/2011 22:18:03: Quote from: yor_on on 27/02/2011 12:51:50

And in neither case the book will weight more, that is have an added 'energy'.

It's not the book that has added energy. It's the system that that has added energy, and the book is only one part of that system. When you let the book fall, the Earth is accelerating towards the book while the book is accelerating towards the Earth.
Title: Is this a new paradox of energy?
Post by: yor_on on 28/02/2011 00:12:04: "Potential energy produced by elevating the book is just the same as winding up the spring in a clock. The only difference is that the energy happens to be a distortion of space-time rather than distortion of the atomic lattice in a piece of spring steel."

Nope :)
Title: Is this a new paradox of energy?
Post by: yor_on on 28/02/2011 00:18:10: "It's not the book that has added energy. It's the system that that has added energy, and the book is only one part of that system. When you let the book fall, the Earth is accelerating towards the book while the book is accelerating towards the Earth."

Can you tell me what you mean by the system having an 'added energy'?

There is a equilibrium existing, that's what the conservation laws are about. The thing happening in all interactions as I see it are 'transformations', all of them ending with some or all of the 'energy' getting transformed into our idea of 'work done' meaning that we won't be able to use it any more.

So, while we can speak of a object getting an added energy, SpaceTime as a whole always should be in a equilibrium. I'm not sure what your 'system' is here? The only way you can transfer new energy into SpaceTime is by divine intervention :) Well, that and entanglements/tunneling and possibly, virtual pair production involving a EV (Event horizon).
Title: Is this a new paradox of energy?
Post by: Geezer on 28/02/2011 01:10:56: Quote from: yor_on on 28/02/2011 00:18:10

Can you tell me what you mean by the system having an 'added energy'?

Sure can.

In the case of the clock, the "big hand" appeared and added energy to the system, which, in this case happens to be within the boundaries of the clock.

In the case of the book, the "big hand" appeared and added energy to the system, which, in this case happens to be within the boundaries of the book and the gravitational system that exists between the book and the Moon, Earth, or whatever.

The only difference is that in one case the energy is stored in the distortion of a piece of steel while in the other case the energy is stored in the distortion of space-time.
Title: Is this a new paradox of energy?
Post by: yor_on on 28/02/2011 01:40:33: Seems we have a difference of opinion here Geezer. A 'potential energy' is a definition that change with how you define that system, you can have as many 'potential energy's' you like, simultaneously, just by defining the book relative Earth, or the moon, or a passing meteor, or anything differing, from whatever frame you look at.

As for the 'big hand' :) Okay, i kind'a like that one. But when it comes to comparing doing mechanical work on a spring, winding it up and storing the energy, that also will express itself as a added 'invariant mass' if measured with lifting a book? Nope. It's not the same.

In the case of that same book there is no extra energy stored in any 'distortion'. Whatever distortion that book will create by its invariant mass and possible uniform motion will be the same, the only thing differing being what position it has relative the gravitation at large represented of those objects you define as your system. Although in a real experiment you will find that whatever gravity you measure, in any point of SpaceTime, will be the sum of all gravity existing as gravity has no limits, as shown by inertia.

You might assume though that the closer you are to a gravity well, the more 'deformed' will you be as observed from a far observer, but in that case the distortion will diminish for that same observer as the book is moved from the gravity well.
Title: Is this a new paradox of energy?
Post by: Geezer on 28/02/2011 03:10:34: Quote from: yor_on on 28/02/2011 01:40:33
As for the 'big hand' :) Okay, i kind'a like that one. But when it comes to comparing doing mechanical work on a spring, winding it up and storing the energy, that also will express itself as a added 'invariant mass' if measured with lifting a book? Nope. It's not the same.

Sure is.

If gravitational force is the result of a distortion of space-time, the work that was done in raising the book simply increased that distortion. If space-time is distorted by the position of matter, it acts like a sort of spring because it always tries to return to the least distorted state.

I think you may be neglecting the fact that the book also creates a gravitational well. When the force that is keeping the Earth's gravitational well separate from the book's gravitational well is removed, space-time reverts to its most relaxed state by joining the two wells together.

Of course, the analogy with the spring probably breaks down when you compare the measurable forces compared with distance. It's also interesting to note that the concept of a "gravitational well" employs an assumption that things will fall into a well, so we are using the assumption that gravity causes things to "fall" to prove that there is no such thing as gravity. Hmmmm???

I have only three things to say.
Well, well, well.
Title: Is this a new paradox of energy?
Post by: yor_on on 28/02/2011 08:34:45: "If space-time is distorted by the position of matter, it acts like a sort of spring because it always tries to return to the least distorted state." That's a really nice idea Geezer, you might assume that if 'gravity' was like our 'virtual particles'. An expression of something we can't really touch, even though we find it coupled to mass, and then imagine a totally empty SpaceTime, without matter. If so, how would gravity express itself, as a 'plane'? And would space then .?

As for the rest, I think we both will exhaust ourselves defending our viewpoints :) the thing I saw questioned was if the book got some added energy/mass by being lifted. I say no, and I think we both agree on that? When it comes to how the energy used by the hand should be defined I say it gets lost into 'space', whereas you think of it as adding to a distortion of sort, if I got it right?

Now, we are of different views there, and, until someone can point us to that definite experiment proving one or another, and I don't mean Monte Python :) we will differ on that.
Title: Is this a new paradox of energy?
Post by: Geezer on 28/02/2011 21:35:33: Well, I would like to disagree with you, but as I'm not sure how you explain what causes the book to fall, it's kind of difficult to disagree. Maybe you could try to explain what happens in your model?
Title: Is this a new paradox of energy?
Post by: yor_on on 01/03/2011 16:08:29: You mean if the book falls of the table? Ignoring the hand then? It will follow a geodesic until it meet a obstacle, like the ground. Are you moving the discussion from if the book had a energy or not, to what happens when/if it falls?

Are you saying gravity is a force containing a energy Geezer?
Title: Is this a new paradox of energy?
Post by: Geezer on 01/03/2011 18:15:06: Quote from: yor_on on 01/03/2011 16:08:29
Are you saying gravity is a force containing a energy Geezer?

No. I'm saying the system which, in this case, consists of the book, the Earth and space-time, causes the book to fall. We can obtain work from that system, so, if you like, there is energy stored in it, but it's not stored in any particular element of the system. It's an interaction between matter and spacetime.

It's the same as the rubber sheet model that demonstrates how the distortion of space-time produces the gravitational effect that keeps bodies in orbits. It also demonstrates how bodies are apparently attracted towards each other.

When you say "follows a geodesic", I'm not sure what that means.
Title: Is this a new paradox of energy?
Post by: yor_on on 01/03/2011 18:40:46: As I see it.

It will follow a geodesic in what you refer to as falling. If standing on Earth we would define it as accelerating too. Though if we were gnomes living inside the book we would not find any gravitation acting upon us, making it inseparable from any other uniform motion, excepting tidal forces. The definition I have on a acceleration is that you will feel 'gravity work/act' upon you. And in the case of the book falling there is nothing acting, as told by our gnomes. It's more like it's 'out of bounds' relative the gravity well and search its equilibrium, well, sort of :)

==

If you define uniform motion as being 'at rest' as there is no way to define any 'speed', you can also say that it already are in a equilibrium, and finally will find that equilibrium disturbed by Earths surface acting upon it, as long as it rests there, squashed or not :)
Title: Is this a new paradox of energy?
Post by: Geezer on 01/03/2011 19:26:29: I think I'll stick with the rubber sheet [;D] Gnomes are not to be trusted.
Title: Is this a new paradox of energy?
Post by: yor_on on 01/03/2011 19:40:16: Think of SpaceTime like a topology. If we could color it you would find all those bends twists and curves. The roller coaster tracks to a planet is really 'deep' so the book has only one way to go, its speed 'accelerating' as seen from Earth is no acceleration at all, it's a free fall all the way to the surface. Any acceleration has to act on the object accelerating, creating the equivalent to a 'gravitational force', a weight if you like. Without it, no acceleration exist. Try this one, chapter two and forward. (http://www.relativitet.se/Webtheses/tes.pdf). It seems nice.
Title: Is this a new paradox of energy?
Post by: yor_on on 01/03/2011 19:57:23: The funniest thing with this 'topology' we have, is that all of it are representing 'straight lines', although through 'SpaceTime'. So if we could roll it out on a flat surface? Which we can't really, it would tear up, we would see how it looks in 'reality' :) Although I can't imagine exactly how it would look then, I'm mighty sure that it would look pretty weird. And even though the book to us Earthlings is 'accelerating' it does not expend any energy, neither does it gain any. The thing changing is only its position inside space and time, in the 'topology' as I call it :)

What one can do, and as I think you do too(?) is to define different 'gravitational potentials' to different positions in a 'system', and then state that relative this position the books 'potential energy' relative Earth will be ??, assuming that it would 'fall' from there. It's one way to think of it.
==

In fact, it's close to how I wonder about matter too, if you just let matter be 'spread out' on that flat plane. I've been thinking of it for some time now :) If that isn't how it really is, 'virtuality' included. Think of the explanation to how the Casimir force is thought to 'work' relative its wavelengths. What such an explanation starts with is assuming that those wavelengths matters, and 'classically' they don't, exist I mean. So, what are they? And how can they be excluded from the plate and sphere proving it. Doesn't all matter include 'virtual particles'? It's sort of weird, but interesting.
Title: Is this a new paradox of energy?
Post by: Geezer on 01/03/2011 20:52:21: Quote from: yor_on on 01/03/2011 18:40:46

Though if we were gnomes living inside the book we would not find any gravitation acting upon us, making it inseparable from any other uniform motion,

Only because you are defining a system that does not include the Earth and space-time. If you define the system to include the Earth, the gnomes, and space-time, which you must if you recognize that the gnomes and Earth get closer together, you will discover that they really are accelerating towards Earth and the Earth is accelerating towards them.

It's like a game of football. If you keep moving the goal posts around, you can always win. It you don't define the boundaries of your system, you can talk yourself in to believing almost anything.
Title: Is this a new paradox of energy?
Post by: yor_on on 01/03/2011 20:58:13: Geezer, that won't work. Either you have a acceleration in that book, then you also have a 'weight' acting on our gnomes. Or you don't have a acceleration at all. Using that definition you also can define 'inertia' as an acceleration, as that is exactly what it is. And the direction of that 'acceleration' have no importance at all. What is important is that either you expend some energy, or something else expend it, acting on you forcing you to break your uniform motion.
Title: Is this a new paradox of energy?
Post by: Geezer on 01/03/2011 21:12:36: The gnomes are no different from trainee astronauts experiencing "weightlessness" in the Vomit Comet. If the system is confined to the aircraft, they are weightless. If the system includes the Earth, they are accelerating towards it, just as they would if they were not contained within the aircraft.

It's all about boundaries and frames of reference. You can say the gnomes are not accelerating as long as you keep the Earth out of it. But you cannot use an argument that ignores the Earth to prove that they are not accelerating towards the Earth.
Title: Is this a new paradox of energy?
Post by: Geezer on 01/03/2011 21:28:15: Try this.

Step out of an aeroplane at 20,000 feet. Close your eyes. Keep repeating "Yippee! I am weightless! I can fly anywhere I want to!"

As long as you don't open your eyes, you'll be OK.
Title: Is this a new paradox of energy?
Post by: yor_on on 01/03/2011 21:28:55: Remember how you could define two uniformly moving object, moving relative each other, as any of them using the total 'motion' with the other becoming a 'inertial frame' without motion. This is the same but instead of motion we're discussing gravity. 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'. If you can't define the 'gravity' in there it do not exist for you. It is a function of space, matter and time, the 'topology'.
==

To see SpaceTime you will have to accept that both statements above actually is true. If you don't you will have to use Newtons definitions. They work perfectly on Earth, but becomes slightly 'out of sync' with the universe at large
Title: Is this a new paradox of energy?
Post by: Geezer 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."
Title: Is this a new paradox of energy?
Post by: Geezer on 01/03/2011 22:18:40: Quote from: yor_on on 01/03/2011 21:28:55

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.
Title: Is this a new paradox of energy?
Post by: yor_on on 01/03/2011 22:20:17: Did you read the pdf?

Try it.
Title: Is this a new paradox of energy?
Post by: Geezer on 01/03/2011 22:38:29: Quote from: yor_on on 01/03/2011 22:20:17
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?
Title: Is this a new paradox of energy?
Post by: yor_on 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.
Title: Is this a new paradox of energy?
Post by: Geezer 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.
Title: Is this a new paradox of energy?
Post by: yor_on 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).
Title: Is this a new paradox of energy?
Post by: Geezer 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.
Title: Is this a new paradox of energy?
Post by: yor_on 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.
Title: Is this a new paradox of energy?
Post by: JP 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?
Title: Is this a new paradox of energy?
Post by: yor_on 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.. :)
Title: Is this a new paradox of energy?
Post by: Geezer 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.
Title: Is this a new paradox of energy?
Post by: yor_on 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?
Title: Is this a new paradox of energy?
Post by: Geezer 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.
Title: Is this a new paradox of energy?
Post by: yor_on on 01/03/2011 23:49:33: Yeah, well.. Ahh, yes. :)

...

Tricky tricky ::))
Title: Is this a new paradox of energy?
Post by: Geezer on 02/03/2011 00:21:04: Quote from: JP on 01/03/2011 23:28:34

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?
Title: Is this a new paradox of energy?
Post by: yor_on 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.
Title: Is this a new paradox of energy?
Post by: JP on 02/03/2011 01:09:30: Quote from: yor_on on 02/03/2011 00:30:47
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!
Title: Is this a new paradox of energy?
Post by: JP 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.
Title: Is this a new paradox of energy?
Post by: Geezer on 02/03/2011 02:46:08: Quote from: JP on 02/03/2011 01:36:20
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.
Title: Is this a new paradox of energy?
Post by: Geezer on 02/03/2011 06:56:06: Quote from: yor_on on 01/03/2011 23:15:30
"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.
Title: Is this a new paradox of energy?
Post by: yor_on 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'.
Title: Is this a new paradox of energy?
Post by: JP on 02/03/2011 15:35:34: Quote from: Geezer on 02/03/2011 02:46:08
Quote from: JP on 02/03/2011 01:36:20
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.
Title: Is this a new paradox of energy?
Post by: yor_on 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'.

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fhyperphysics.phy-astr.gsu.edu%2Fhbase%2Fthermo%2Fimgheat%2Ffirlaw2.gif&hash=8f227a4c51cb174935231f5905137adf)

"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.
Title: Is this a new paradox of energy?
Post by: Geezer on 02/03/2011 19:19:54: Quote from: yor_on on 02/03/2011 16:20:28

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.
Title: Is this a new paradox of energy?
Post by: JP on 02/03/2011 20:13:49: Quote from: yor_on on 02/03/2011 16:20:28
But, it's definitely 'work done' in its most simple meaning.

Except that in general relativity, two observers don't necessarily agree on gravitational work and gravitational energy conservation, so there is no general work-energy theorem. Energy conservation doesn't necessarily hold in general relativity if you try to account for gravitational energy. That's why it's so confusing to try to get the GR picture to agree with conservation of gravitational energy--it doesn't in all cases.
Title: Is this a new paradox of energy?
Post by: Jolly- Joliver on 02/03/2011 20:24:31: Quote from: Anukshan Ghosh on 24/02/2011 06:42:03
I got my answer and everything else is crap actually what happens is that a systems internal energy is defined from a frame of reference in which the center of mass is at rest and hence adding potential energy to the system does not add to its internal energy. A steady state is established in terms of internal energy for these works performed.

Doesn't it depend on the material? Our bodies produce heat, as form of energy, if the materail has the ability to store that heat then surely there would be an energy increase and so a weight change in the material while that heat was present. As a simple point.
Title: Is this a new paradox of energy?
Post by: Geezer on 02/03/2011 21:23:36: Quote from: JP on 02/03/2011 20:13:49
Quote from: yor_on on 02/03/2011 16:20:28
But, it's definitely 'work done' in its most simple meaning.

Except that in general relativity, two observers don't necessarily agree on gravitational work and gravitational energy conservation, so there is no general work-energy theorem. Energy conservation doesn't necessarily hold in general relativity if you try to account for gravitational energy. That's why it's so confusing to try to get the GR picture to agree with conservation of gravitational energy--it doesn't in all cases.

JP - Is that because the observers will disagree about distance, force, distance and force, or something else?
Title: Is this a new paradox of energy?
Post by: yor_on on 02/03/2011 21:45:18: "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."

One of the truly strange things that Geezer :) I don't know, but I sure would like too. And yeah, a body produces heat, and heat is a form of 'energy' that should be expressed as mass, but here we were talking about if a book would gain energy by getting moved in a gravity well. I think we was at some point at least? :)

And yes, I agree on that JP. There is very little resembling 'energy' in gravity although there will be more or less 'energy' freed in a interaction depending on the books position in the gravity well.

So, if the energy released can't be situated in the book and neither, as I see it, in the uniform motion as that 'gravitational acceleration' becomes to me, where do I find the reason for it? In the relation between its original position relative its interaction?

But I can't speak of any 'work' being done by gravity, and there is no measurable 'energy build up' introduced by that uniform motion either, even though it do accelerates relative the Earth. In fact, all real acceleration presumes a energy loss, doesn't it? One way or another someone has to expend energy to get a object accelerating.

What is 'speed', and what is 'energy'?
It would be easy if we could ignore the Lorentz contraction, then we could say that there is a 'objective' way to define the relation, but with the contraction nothing becomes clear as we now have two points of view, and both valid, the far observer being 'still', and the gnomes in the book. And in a uniform motion there is no 'energy', and in a acceleration you expend energy to accelerate.

I'm sure we will solve this :)
==

As soon as I write Lorentz contraction it is as well to assume that I include the time dilation, because i do. I do do :) It's just that I find the Lorentz contraction the one most weird, for the moment :)

==

Could I assume a slower 'energy burn' with a time dilation? Assume that normal earth time/speed is one meter per second. If I now go ten meters in five seconds, being the moving twin, could the earthly observer equate that 'time dilation' he find me to have done later (coming back), with a slower 'metabolism/ energy consumption?' How would that fit with him having watched me move in his telescope the whole time? There he saw me move ten meters in ten seconds, did he not? From the moving twins position it becomes simpler in that the distance actually have 'halved' so that he find himself moving at normal 'speed' but only needing to do half the distance from what he expected from the starmaps on Earth. He would agree to needing 'half the energy' I think, but our earth friend with the telescope I doubt to agree, even though finding his twin being 'time dilated' at his return.
Title: Is this a new paradox of energy?
Post by: JP on 02/03/2011 22:24:08: Quote from: Geezer on 02/03/2011 21:23:36
Quote from: JP on 02/03/2011 20:13:49
Quote from: yor_on on 02/03/2011 16:20:28
But, it's definitely 'work done' in its most simple meaning.

Except that in general relativity, two observers don't necessarily agree on gravitational work and gravitational energy conservation, so there is no general work-energy theorem. Energy conservation doesn't necessarily hold in general relativity if you try to account for gravitational energy. That's why it's so confusing to try to get the GR picture to agree with conservation of gravitational energy--it doesn't in all cases.

JP - Is that because the observers will disagree about distance, force, distance and force, or something else?

It's something about gravitational energy itself. If you add up all other forms of energy, they satisfy a conservation law in any reference frame in GR. If you try to do the same for gravitational energy, it doesn't. I understand the math pretty well, so I'm confident in this. What I don't have is a physical intuition for it.

Certainly other forms of energy are distributions living over a region of curved space-time. The laws of GR are set up so that equations relying on these functions remain the same as you change reference frames within that geometry. The difference is that gravitational energy somehow "is" the geometry, rather than being a distribution on top of it. That makes it special, and makes formulating conservation of energy over regions of curved space-time difficult.

By the way, I believe the problem only occurs when you want to look at regions of space-time living within a larger, curved region. If you look at the entire system of gravitating objects all within a volume such that the "curviness" is minimal by the edges of the volume, then you can define an energy of the entire box. But when you peek in and ask about the energy of a tiny piece of space-time within that box, you run into trouble.

Edit: here's a link on the subject (not quite 90 pages). It explains it in words, but I still think it's lacking physical intuition.
http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Relativity/GR/energy_gr.html
Title: Is this a new paradox of energy?
Post by: yor_on on 02/03/2011 22:34:53: Gravitational energy is weird. It's the stress-energy tensor and what more JP?
The way Space shapes to motion?

That's included in a way in the tensor, isn't it? Its when you put a whole SpaceTime together it becomes more than weird. Because treating each description/frame by it self you have a skewed SpaceTime although possible to connect to your own frame by untwisting it, but when all descriptions come together SpaceTime becomes a contradiction in terms. There is no simple way to describe the 'wholeness' of it that we see looking out. As long as you assume it to be geometric twistings you can calm yourself, but then you also will need to assume that a time dilation and Lorentz contraction is a illusion. As I understands it?

But I still think I find GR treatment of 'energy' making more sense than the idea of an unmeasurable 'energy' hiding in the book, created in its motion relative that gravity well. And if it now isn't definable other than as a expression of its curvature, then that still gives a consequent measurement. I like that. Because then we do change the 'energy' by moving that book relative the gravity well. But we don't change any objects 'energy' per se, we change the relation they have in SpaceTimes 'stress-energy tensor 'field'/potential gravity' instead. And by doing so they get a new 'energy definition' which in fact will reflect relative all other objects you compare their 'potential energy' too.

It's like the universe/space was a dynamically changing tension, and when you move matter inside in it, that tension will adapt to your motion, giving each object moved a new definition, what we call energy. But the energy, even though unique to what we moved don't rest inside the object but as a property of that position relative the object, if that now makes sense :)
==

If I look at 'energy' that way it becomes easy to see why a uniform motion, although not expending any energy by itself, still will have an added 'energy' relative its position in this tension. And looking at it that way transforms space from being a nothing to a something even classically. Space is a 'tension' but not as something resisting. What we see as its 'tension' is to space being at 'rest' creating no resistance relative anything we can measure. And its 'energy' is a intrinsic property relative the dynamics influencing that specific position we look at. Then comes the question if we can say that the 'tension' will be the same for two different observers? And there I don't think so, because that tension is very much a relation to who observes, but if the observers can agree on a time and position translating each other frames they should find it to be the same, I think ::))

Maybe?

Da*n, this one was tricky, but very nice..
Title: Is this a new paradox of energy?
Post by: Geezer on 03/03/2011 01:09:17: Quote from: yor_on on 02/03/2011 21:45:18

But I can't speak of any 'work' being done by gravity,

Yoron, I don't think you could be saying that gravity "cannot do work" are you? There are lots of examples of work being done that seem to depend on gravity. Hydroelectric generation might be a reasonable example. [:D]
Title: Is this a new paradox of energy?
Post by: Geezer on 03/03/2011 01:12:40: Thanks JP. Looks fairly couterintuitive as you say, but then, so does most of GR!
Title: Is this a new paradox of energy?
Post by: yor_on on 03/03/2011 12:24:46: Nooo :)

It does no work.. I'm sure about that. To me it's like Earth, you can as easily say that the hill are doing work upon your body as you climb it. And in a way it does, it's like all definitions we use. They become ambiguous and that's why you see mathematician's barricaded behind equations, ready to defend them down to their smallest dissolution. Don't you ever tease a physicist or mathematician Geezer, fearsome in deed, defenders of truth. Ahh, might have gone a little overboard here? Maybe??
==

But the idea of 'energy' is a weird one, just like transformations. It suits me admirably to find 'energy' removed from 'reality' into the fabric of SpaceTime. That's where I think it belong, it's such a weird concept. But if you let it be a property instead of a 'substance' then it's acceptable as description between 'work' and 'work done'. And as always it's nothing 'set', just a description of something constantly changing, depending on relations. We live in a relational universe, from how we define a speed to energy. What I've been wondering about is why matter exist? It has to be a function of 'time' and ?

But definitely what we call time. That's so simple to see if we are correct in our ideas of virtual particles able to become real. That has to be a function of time. But then again, if 'time' is part of the fabric it seems very difficult to lift time out from it, they all fuse into one SpaceTime, don't they? But we can lift out is its arrow, and that one we seem to be able to influence by gravitation and 'speed'. The funny thing about that 'arrow' that it seems to belong only to you, and you, and you. It's easy to see why we 'invented' thermodynamics as those concepts never looks away from the processes taking place locally, as I understands it? It's a way of defining the 'arrow' as decay.
Title: Is this a new paradox of energy?
Post by: Geezer on 03/03/2011 18:33:37: Quote from: yor_on on 03/03/2011 12:24:46
Nooo :)

It does no work.. I'm sure about that.

So, if no work is done, how do you explain what's producing the electricity? Or is the electric power generated completely imaginary? Or, is it instance of perpetual motion?

Give me something to work with here.
Title: Is this a new paradox of energy?
Post by: yor_on on 03/03/2011 20:41:25: It's ambiguous I agree. If you look at it as something wanting to go in one direction then all matter, and light, will do so relative gravity. And it produces a lot of things, like electricity, as it do so. But gravity is no 'force' acting on those. Gravity is more of a 'topology' that 'stuff' follows. What it really is, and why it can do those things I don't know.

Imagine a universe without matter in where you assume that gravity still 'exist'. Myself I think of it as a 'plane' then, and that this plane should be smooth, having no granularity to it. Like a invisible sphere maybe made of those planes but still without any differentiating signs in any direction. It's not 'energy' but if you introduce stuff like matter and light I expect us to get energy from the interactions created. You could also consider such a universe as a 'point' only, getting 'stretched' into 'dimensions' as we introduce matter and light. This is my way of looking at it only, and I think I'm free to do so as long as we can't say what gravity is.

If gravity is like that then it is at rest, not a force. And what introduce the topology is the rest of what makes our universe. That this also deform gravity into a topology is no problem to me, as you could imagine that 'pure gravity' as a singularity, which then makes all motion into something searching to be at rest relative what gravitational potential they meet. And the unlimited possibly 'original' type of gravity should then be the singularities we think us have, Black Holes. That also transform everything we call 'speed' into something just searching a equilibrium, unless we accelerate it, expending 'energy'.

How's that?
==

If you look at gravity this way it should exist at a QM level too as that is quanta, not smooth, and if you ask yourself how virtual particles can become real for us then the logical conclusion seems to be that they already was 'real', although not accessible for us, and that as a function of SpaceTime, expressed through 'times arrow'. That we can't define limits to virtual particles is no stranger than imagining a 'limitless' gravity. If I take one single particle and place it in my 'original gravity sphere' I expect gravity to equal out, no tidal forces introduced, and to the particle become as 'not existing'. Gravity seems coupled to light and mass, and to the 'energy' we define from their interactions.
Title: Is this a new paradox of energy?
Post by: Geezer on 03/03/2011 21:19:21: Yes, but how can a generator produce electricty without work being done on it? Something has to be doing the work.
Title: Is this a new paradox of energy?
Post by: JP on 03/03/2011 22:06:07: Maybe this could be cleared up if you defined work? I think I see at least part of the confusion, which is that work classically is defined as force applied over distance. Due to the way that forces are related to energy, this is equivalent to energy transferred into a system.

In general relativity, you give up the concept of a gravitational force, but you can still transfer gravitational energy into a system. Since you literally cannot define force times distance within the theory, does this mean that gravitational work doesn't exist in the model? I don't know, but certainly Geezer's example does show that there must be some quantity that accounts for energy transfer into a system due to gravity.
Title: Is this a new paradox of energy?
Post by: Geezer on 03/03/2011 22:35:51: You can take the term "work" out of it if you like. It's just a form of energy, and that energy has to be coming from somewhere, although it might be very difficult to exclude the term "work" entirely, because even if gravity is not doing work on the turbine, the turbine has to be doing work on the generator, and, at that point, it clearly is a torque (force) times distance.

So, I'll still be able to prove that gravity did work, or at least produced equivalent work.
Title: Is this a new paradox of energy?
Post by: JP on 03/03/2011 22:45:19: Quote from: Geezer on 03/03/2011 22:35:51
So, I'll still be able to prove that gravity did work, or at least produced equivalent work.

I definitely agree with the second part!
Title: Is this a new paradox of energy?
Post by: yor_on on 03/03/2011 23:05:29: Depends on what I should define 'energy' as doesn't it? If I do it by saying what it's not? Then 'energy' isn't 'measurable' in itself. There is no such thing as 'pure energy'. Either you define it as something that you know 'exist' in a future interaction as well as existing in any interaction you observe, or as I like to do, as only existing as a concept. We have a lot of concepts that we can't measure, thoughts being a perfect example. We can observe the brains electrochemical activities but you can't weight a thought, you don't even know how it comes to be or how it 'look'. Still, nobody here is going to argue that thoughts doesn't exist I presume :) And so I have to assume that 'energy' exist too.

The difference between work and 'work done' is 'energy expended' as i see it. If I thought of the universe as one kg of 'ka' this 'ka' transforms constantly, and what it ultimately expend is 'work done'. Energy should belong to 'work' in all transformations, but what 'work done' is I don't know? You might want to call it 'energy expended' instead? But as we expect the conservation laws to be valid, that too should stay inside our universe, in some form.

Space is empty classically, that's what planets and suns move through, meeting no 'resistance' from space itself, if they did the universe should be constantly retarding. I don't need to define what 'work' is really, we all agree on it being transformations, don't we?

The really weird thing is that we have a universe in where it exist, and also that we can't see where 'work done' goes. It would be simpler to assume that you can't have it. That all universes only consist of one substance that just 'is'. If it was heat our universe might be assumed to heat up, but heat is also radiation. I've never seen any proofs for the universe getting warmer, or producing more radiation?

What we are trying to do is to find some few components that will build us a universe working as ours, but if the Big Bang is correct it's rather weird to assume that it spewed out ah, let's say 44 elements :) seems more probable that it just was one, why not SpaceTime itself? And so I'm perfectly comfortable with thinking of 'energy' as something expressed as/in SpaceTimes curvature, as that 'curvature' is 'everywhere'.
Title: Is this a new paradox of energy?
Post by: Geezer on 03/03/2011 23:11:54: Yes, but where does the generator get its energy from?
Title: Is this a new paradox of energy?
Post by: yor_on on 03/03/2011 23:30:15: Geezer, that question is impossible to answer. Do you believe in the conservation laws? That nothing ever is 'lost'? Can you tell me where that energy goes then? Can you measure 'work done'. What you measure is differences giving that difference a name and counting on it. How many 'Giga tons' 'work done' has the universe produced until now for example? It should, if you believe in that all transformations come to a state from where only 'work done' is possible. Or else you know a substance unknown to me that represent just that?

Where does anything get 'energy' from Geezer? Perhaps you can tell me where I can measure pure energy? How about the 'energy' thought to exist in SpaceTime?
Title: Is this a new paradox of energy?
Post by: yor_on on 03/03/2011 23:48:27: It has to do with 'time' I think? As all transformations macroscopically uses our arrow to express itself. If I was to assume that a Feynman diagram actually described a reality in where 'times arrow' could go two ways simultaneously then QM:s arrow becomes very weird. If so it doesn't just go forward or backward but actually has the ability to do both, simultaneously. So the way we have a arrow is a must for the causality chains we see.
==

And if you to that add Feynman's idea of 'many paths' with probability deciding which path that will be chosen you will find all paths taken from a QM perspective, the arrow being no hindrance to choosing which one that should 'exist' for us. In fact you might imagine all paths being taken for real, then unraveling themselves, leaving only one existing, creating a 'clock tick' in our macroscopic 'reality'.
Title: Is this a new paradox of energy?
Post by: Geezer on 04/03/2011 00:16:28: "Geezer, that question is impossible to answer."

Ah! So it's the trolls at work again [;D]

"Do you believe in the conservation laws? That nothing ever is 'lost'?"

Yes.

"Can you tell me where that energy goes then?"

It all ends up as heat in the Universe.

"Can you measure 'work done'."

Yes. It's just a form of energy.

"What you measure is differences giving that difference a name and counting on it. How many 'Giga tons' 'work done' has the universe produced until now for example?"

I don't know, but I'm only interested in the generator at the moment.

"It should, if you believe in that all transformations come to a state from where only 'work done' is possible. Or else you know a substance unknown to me that represent just that?"

It's just a way of expressing energy.

"Where does anything get 'energy' from Geezer?"

Lot's of places. It can get it from position, change of position, chemical reaction, etc.

"Perhaps you can tell me where I can measure pure energy?"

The energy stored in a rotating flywheel would be a pretty good example. A photon with a particular wavelength might be another.

"How about the 'energy' thought to exist in SpaceTime?"

Well, we could measure it by elevating a certain mass, then see how much work it could do, which would be equivalent to the energy it had gained by a change in position.
Title: Is this a new paradox of energy?
Post by: yor_on on 04/03/2011 00:50:30: Okay, you say it ends up as heat. If so you won't be able to prove it other than as interactions with invariant mass, as space don't 'interact' with radiation, it's a interesting thought. And 'work done' is also 'energy'?

Okay.

And no, I withhold that there is no extra energy in that book :)
As for how a water driven turbine gets its electricity :)

You don't measure the 'energy' itself but the strength of the photons interaction. 'energy' transform and ultimately disappear in interactions, just as that 'photon' you measured did. And that's what I'm trying to point out too. And your flywheel may have a certain momentum/energy but you cant lift that energy out from the interaction to measure by itself, as I know?

Depending on how you look at it you can say that 'energy' exist as a property of SpaceTime, but that doesn't say that it is gravity. All energy 'measured', as you look at it, will need to interact to be measured. Not measuring a interaction but just counting on the possibility becomes 'potential energy'. If you measured that book it will have the same invariant mass no matter where you put it.
Title: Is this a new paradox of energy?
Post by: Geezer on 04/03/2011 01:20:17: OK - try this experiment.

We make a small model of the water reservoir and turbine which we test. Not surprisingly, it produces electrical energy which we can use to produce, for example, photons.

We transport this model far into outer space and park it there. Not surprisingly, it produces no electrical energy at all.

The only thing that changed was the model's proximity to other massive objects. It seems reasonable to conclude that the energy produced is something to do with proximity to mass.

BTW, I didn't mention "work", "force", or even "gravity".
Title: Is this a new paradox of energy?
Post by: yor_on on 04/03/2011 01:44:13: Maybe we are talking past each other?
Here are some of my definitions.

'Energy' is a description of a relation relative a interaction.

'Potential energy' is a description of what a 'potential/possible interaction' might bring.

'Relative mass' and its 'energy' is a description of invariant mass relative motion, that is motion as defined relative a 'inertial frame' as our Earth. I guess you could define it relative other objects too, like accelerating frames, but then it would lose all meaning.

Invariant mass is a definition of a invariant quality belonging to matter, invariant in all frames, and motions.

When something moves faster we find that its inertia grows, that is, it gets more 'unwilling' to budge from its direction of motion. We also find it to have more 'energy' when interacting, as colliding. You may want to look at that as an effect of the object only but, as I see it, it is a combined effect of the objects invariant mass and relative motion in space and time (and inertia is one of the things that, to me, seem to point to that SpaceTime have its own way of defining 'absolute' motion?). When Einstein referred to mass I understand that as 'invariant mass'

"Energy may be stored in systems without being present as matter, or as kinetic or electromagnetic energy. Stored energy is created whenever a particle has been moved through a field it interacts with (requiring a force to do so), but the energy to accomplish this is stored as a new position of the particles in the field-- a configuration that must be "held" or fixed by a different type of force (otherwise, the new configuration would resolve itself by the field pushing or pulling the particle back toward its previous position).

This type of energy "stored" by force-fields and particles that have been forced into a new physical configuration in the field by doing work on them by another system, is referred to as potential energy.

A simple example of potential energy is the work needed to lift an object in a gravity field, up to a support. Each of the basic forces of nature is associated with a different type of potential energy, and all types of potential energy (like all other types of energy) appears as system mass, whenever present. For example, a compressed spring will be slightly more massive than before it was compressed. Likewise, whenever energy is transferred between systems by any mechanism, an associated mass is transferred with it."

So yes, a compressed spring has more measurable energy, the book on the other hand won't. As I see it :)
==

Actually the wiki is wrong there as I see it. The compressed spring will have a greater 'invariant mass' and so 'energy' in its rest frame, as well as all other frames, whilst the other examples discuss 'relative mass/momentum and 'potential energy' (invariant mass+motion).
==

Saying that gravity 'does work' on Earth but not in Space is true but, as I see it again, that is a relative effect of matters equilibrium, where it can be 'at rest', as I call it, relative that gravitational potential. If you could 'hang' that model above a black hole in space I would expect the water to start running :) as it then would find a gravitational potential giving it a direction. I'm not saying that I know what 'gravity' is, neither do I know what 'energy' is. I'm more or less using what I think me know it not to be to define it I'm afraid. Your definitions makes sense too Geezer, it's just that looking at it my way won't really destroy any of your calculations, but helps me see what Einstein thought.
==

If you were the only thing existing in a universe, and you affected a course change/acceleration, would inertia exist? If it does it's definitely a support for my weird idea of gravity, as any reaction to a course change/acceleration should be the result of a 'interaction' with something, or a relation if you like.

I mean, why would there be a 'inertial reaction' otherwise?
Against what, SpaceTime itself? Then inertia and gravity should be two different things, right?
Title: Is this a new paradox of energy?
Post by: Geezer on 05/03/2011 23:40:03: That's all very well Yoron, but how do you explain what is doing the work on the generator?

The input to the generator is driven by the water turbine. We know work is being done on the generator, otherwise it would not produce useful electricity, so we are forced to conclude that the work is coming from the water turbine.

Now, from the little I know about water turbines, the reason they function is because of the kinetic energy of the water impinging on their blades. So, if gravity was not responsible for creating that kinetic energy and therefore doing the work, what was?
Title: Is this a new paradox of energy?
Post by: yor_on on 06/03/2011 04:19:36: "how do you explain what is doing the work on the generator"

The water :)

It has to do with matter (water) free falling in a geodesic, following the gravitational potential. And as it get obstructed by the impellers, interacting with them, delivering the 'kinetic energy'. Gravity is no force in itself, but matters interactions under its influence is.

Or you go for Newtons concept.
Your choice, I'll stay with my geodesics.
Title: Is this a new paradox of energy?
Post by: yor_on on 06/03/2011 04:32:03: "Gravity cannot be shielded in any way. Intervening objects, whatever their make-up, have no effect whatsoever on the attraction between two separated objects. This means that no antigravity chamber can be built in the laboratory. Neither does gravity depend on the chemical composition of objects, but only on their mass, which we perceive as weight (the force of gravity on something is its weight — the greater the mass, the greater the force or weight.) Blocks composed of glass, lead, ice or even styrofoam, if they all have equal mass, will experience (and exert) identical gravitational forces. These are experimental findings, with no underlying theoretical explanation." Eötvös experiment. (http://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment)

Gravity permeates SpaceTime, as I see it even when undetectable. That quantum field theories want to find a 'particle' has very much to do with the idea of 'discrete quanta' defining SpaceTime in QM.
==

This one is Interesting too. (http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Relativity/GR/grav_speed.html)
==

As we might have had a inflationary period, and if gravitation 'propagates' at 'c' you might wonder if there then could be 'areas' without gravity. No, there can't be, not if gravity is one of the properties (yeah, I know, but it's better than calling it a 'force':) defining SpaceTime. But if gravity would be just a property of mass and 'space' be something uncoupled to gravity you might assume that such areas could exist. And as Space is thought to be isotropic you could then find those areas 'symmetrically' placed out everywhere. Which makes no sense to me :) But.. To do so you would have to assume that space was a entity of its own, only coupled, if that, to time. But not really, as a inflationary period seems to exclude time, well, as long as we're not ready to assume that 'everything' was Lorentz contracted at that point? But if it was so we have a very weird idea as a infinite, more or less, Lorentz contraction implies no 'distance' at all for the inflation, and opens for the question for whom it would have become a 'distance'?

But it's interesting :)
Title: Is this a new paradox of energy?
Post by: Geezer on 06/03/2011 19:10:52: Quote from: yor_on on 06/03/2011 04:19:36
"how do you explain what is doing the work on the generator"

The water :)

It has to do with matter (water) free falling in a geodesic, following the gravitational potential. And as it get obstructed by the impellers, interacting with them, delivering the 'kinetic energy'. Gravity is no force in itself, but matters interactions under its influence is.

Or you go for Newtons concept.
Your choice, I'll stay with my geodesics.

Ah, right. So is it true to say that matter interacting with other matter at a distance does the work then? (Avoiding the use of Newtonian terms)

(I bet you can see where this is going [;D])
Title: Is this a new paradox of energy?
Post by: syhprum on 06/03/2011 20:13:46: Although on a practical level it is quite true to say that no shielding against gravity is possible if in fact it is mediated by Gravitons and they have non zero mass some shielding must be possible.
It is has not been proven that the mass of the graviton is less than 10-23 eV something like 23 orders or less than that of the Neutrino against which some shielding is possible but only by vast amounts of very dense materiel.
Title: Is this a new paradox of energy?
Post by: yor_on on 06/03/2011 23:04:55: Yes, Gravitons are one of the pillars of string theory too it seems. We will have to wait and see what LHC can 'dig up' :)

"matter interacting with other matter... At a distance?" :)
Explain thyself Sire :)
Title: Is this a new paradox of energy?
Post by: Geezer on 07/03/2011 00:33:13: Quote from: yor_on on 06/03/2011 23:04:55
"matter interacting with other matter... At a distance?" :)
Explain thyself Sire :)

Isn't that what produces the analgesic of which ye speak, that causes the Moon to remain in the general vicinity of Earth?
Title: Is this a new paradox of energy?
Post by: yor_on on 07/03/2011 11:31:52: So we are looking at it through the eyes of dentistry now, are we?
'analgesic' indeed Sire :)
Title: Is this a new paradox of energy?
Post by: Geezer on 07/03/2011 19:14:50: Quote from: yor_on on 07/03/2011 11:31:52
So we are looking at it through the eyes of dentistry now, are we?
'analgesic' indeed Sire :)

No. Only if we consider it to be geodontic.
Title: Is this a new paradox of energy?
Post by: yor_on on 07/03/2011 21:52:55: Geochelones and geoducks, in the end it's all a matter of geodesics. No matter where you are :)
Title: Is this a new paradox of energy?
Post by: JP on 08/03/2011 02:07:10: Is Geozer being curmudgeonly again?
Title: Is this a new paradox of energy?
Post by: yor_on on 08/03/2011 02:16:59: Nah, under his hardened crust resides a sunny personality.
Geophysically speaking :)

"salt of the earth' as we say, orbitaling.