how should i time my eggs

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Offline fontwell

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« Reply #50 on: 17/03/2010 23:25:57 »
 


Having hunted around it seems to be accepted that mass bends space-time, and bends in space-time cause gravity e.g. see http://en.wikipedia.org/wiki/Gravity#General_relativity [nofollow]  -> "the effects of gravitation are ascribed to spacetime curvature"... "Einstein proposed that spacetime is curved by matter." By 'matter' he implies mass.

I have only found a few places where they explicitly say the gradient (derivative) of space-time is gravity but it always seems to be understood this way.

Famous quote: ‘Matter tells space how to curve. Space tells matter how to move.’
Translation: Mass bends space-time. Bent space-time causes gravity.

I feel pretty confident to say:

Mass curves space-time, the gradient of the space-time curve is gravity. Time dilation is a function of the space-time curve's magnitude, not its gradient.

To be honest, I haven't ever come across any discussions on GR where anyone thought other than this, its just mainstream GR isn't it?


« Last Edit: 18/03/2010 13:44:19 by fontwell »

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Offline yor_on

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« Reply #51 on: 18/03/2010 00:54:17 »
No worrys :) it's just that I haven't thought of it that way before, I have always seen those geodesics as the true 'straight paths' sort of. To me mass and space are very much the same thing, I haven't really thought to separate them. Like we say that a black hole (Schwarzwild solution) opens to infinite (?) distances inside the EV according to some thoughts, and even more so for a spinning one. To me it seems that they go together (Space and mass), so when you used the sheet analogy this way it made me curious. I can see the idea, but then my thought visually became how to set this flat sheet 'pulled together' and wonder how mass could be represented from such a view. That is if we assume that a free fall is equivalent to another free fall, no matter internal time rates differing, and that both represent the same 'flat sheet' ?
==

Or is there some way of describing that 'weightlessness' without using the idea of a free fall? Uniform motion for example, when the motion is zero relative something else, like we have in those innards of our earth, we can still say that A even if at rest with B still have a uniform motion when compared to C, right? So that thingie in the middle do have an uniform motion, even if not relative Earth? So in one way you might say that it share a free fall with our Earth, but as it also is 'weight less' relative Earth its equivalence seems to have more to do with 'space' than with our Earth?
« Last Edit: 18/03/2010 01:04:18 by yor_on »
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Offline JP

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« Reply #52 on: 18/03/2010 01:12:55 »
Doesn't time dilation/length contraction have to do with how you measure space-time distances, which is in turn defined by the metric tensor?  http://mathworld.wolfram.com/MetricTensor.html  The metric tensor appears to measure curvature, which involves derivatives, rather than magnitudes.

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Offline JP

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« Reply #53 on: 18/03/2010 02:27:23 »
By the way, I think there is an error in my previous reasoning about drilling into the earth, as the Schwarzschild solution assumes that you're solving the equations in a vacuum (where the stress-energy tensor is zero).  Inside the earth, this wouldn't be the case.  I don't know what the proper form of the solution would be or if it's solvable without numerical simulations.

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Offline yor_on

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« Reply #54 on: 18/03/2010 04:04:06 »
I saw an explanation on it somewhere where every 'bit' of matter was treated as having, that is if I remember right now, an equal effect on every other bit? I think it was a Newtonian concept though? But it came to the conclusion that in the middle they would 'negate' the 'attraction', or as we say the 'bending of space'? Hyperphysics takes this approach when digging a hole to the problem.

Another question relating to that middle of out Earth? If I assume that it is equivalent to a free fall, can there be a pressure acting at that point? There can, right? As it is a part at rest in a bigger system Earth / 'It' :) Analogous to your black box can be inside a bigger pressurized black box..

As for the metric tensor JP? Want to explain how you think for us more , ah, solid ones there? No, not 'thick headed' solid I said. By 'curvature involves derivatives' you would then mean that? It measures difference instead of magnitude for those points in space? Or am I getting it all wrong? That's a subtle one JP :)
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Offline JP

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« Reply #55 on: 18/03/2010 05:12:31 »
I saw an explanation on it somewhere where every 'bit' of matter was treated as having, that is if I remember right now, an equal effect on every other bit? I think it was a Newtonian concept though? But it came to the conclusion that in the middle they would 'negate' the 'attraction', or as we say the 'bending of space'? Hyperphysics takes this approach when digging a hole to the problem.

That works in Newtonian gravity.  That's what I tried to apply to GR.  I have a feeling you can't simply apply those ideas to GR, though.

Quote
As for the metric tensor JP? Want to explain how you think for us more , ah, solid ones there? No, not 'thick headed' solid I said. By 'curvature involves derivatives' you would then mean that? It measures difference instead of magnitude for those points in space? Or am I getting it all wrong? That's a subtle one JP :)
A metric tensor is a mathematical object that tells you about the curvature of a "surface" (or in mathematics what is called a manifold) at a point in space.  You use it to define lengths on that manifold. 

In general relativity, you have to measure  "lengths" in space-time, and they are called intervals, since they involve events separated in time and in space.  The metric tensor tells you how to define intervals locally (the definition depends on your reference frame).  Since you're measuring intervals in space and time, it therefore tells you how the definitions of length and of time differ.  The definition of the metric tensor involves derivatives, and derivatives tell you about slopes instead of magnitude.  It seems to me that because the metric tensor involves derivatives, it's probably based on how space-time curves rather than on the magnitude of the space-time curve.  By the way, there's a number called curvature that you can calculate from the metric, which isn't what we're talking about here.

In addition to the link I posted above, there's this description: http://en.wikipedia.org/wiki/Metric_tensor_%28general_relativity%29#Local_coordinates_and_matrix_representations

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Offline fontwell

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« Reply #56 on: 18/03/2010 08:58:26 »
If it helps, try to imagine that instead of being solid, the earth was made out a big sphere of liquid (which is probably true near the centre anyway. If you were at the centre you would be crushed by the pressure of all the mass but still feel no gravity.

Although this is a dubious way to think about the situation here it does indicate how mass can have an effect that is not detectable by measuring local gravity.

The idea of every piece of matter affecting every other piece by a gravitational pull is a Newtonian way to sum the net effects of masses. This kind of calculation results in a Newtonian explanation for zero gravity at the centre of a mass. But in GR gravity is caused by the bending of space-time and the bending of space-time is caused by mass. So in GR we do not ask how every piece of matter affects each other, we ask how do all the pieces curve space-time. Gravity is then derived from the curvature of space-time.

Really, this whole thing comes down to this; Is time dilation caused by mass, which bends space-time, thus making the centre of mass the most dilated place? Or is it caused by gravity, which is caused by the curve of space-time?

Well, the GR view of gravity is that it is only an effect of curved space-time. The GR view is that mass curves space-time. And the equations for time dilation refer to the centre of mass. The clock at the earth's centre is slowed by the combined pressure of all that mass around it. It does not care that it is in an inertial frame with zero gravity.

Also, distant orbiting satellites have faster clocks compared nearer to orbiting satellites, due to being further from the mass of the earth. But they also experience themselves as being in an inertial frame with zero gravity.
« Last Edit: 18/03/2010 18:17:25 by fontwell »

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Offline JP

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« Reply #57 on: 18/03/2010 11:34:51 »
If it helps, try to imagine that instead of being solid, the earth was made out a big sphere of liquid (which is probably true near the centre anyway. If you were at the centre you would be crushed by the pressure of all the mass but still feel no gravity.

Yes, and I think that what you're saying here agrees with the reason my earlier reasoning was wrong.  The extra forces you're describing are likely components of the stress-energy tensor which we can't ignore within the earth.  Therefore you can't just extrapolate from the solution outside the earth to get the solution within the earth--the form of the equations changes.

I also think I see how the timer within the earth should measure time differently than the timer in deep space.  Even if things "curve" the same way at the center of the earth (since you're experiencing no net gravity), the entire space is squashed down.  Think of a piece of graph paper in deep space.  As you move down towards the center of the earth, it distorts because of the curvature and gets squashed, so it's no longer flat and the lines aren't parallel to each other.  At the center of the earth, it's flat again and all the lines are parallel but it's been squashed to a smaller size.  You can kind of see that if you look at the left-hand figure you show here: http://www.thenakedscientists.com/forum/index.php?topic=29156.msg304011#msg304011 .

I have to think a bit more to get it to make sense with the (little) mathematics of GR that I know, but it seems right...

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Offline fontwell

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« Reply #58 on: 18/03/2010 13:43:20 »
Quote
Even if things "curve" the same way at the center of the earth (since you're experiencing no net gravity), the entire space is squashed down.  Think of a piece of graph paper in deep space.  As you move down towards the center of the earth, it distorts because of the curvature and gets squashed, so it's no longer flat and the lines aren't parallel to each other.  At the center of the earth, it's flat again and all the lines are parallel but it's been squashed to a smaller size

Yes!
« Last Edit: 18/03/2010 13:45:30 by fontwell »

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Offline yor_on

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« Reply #59 on: 18/03/2010 13:57:47 »
Yes, that's what I'm wondering too. Pressure and Gravity. You will have a pressure at the middle, that much seems clear but you can't equal that to a 'gravity', can you? Thanks for the explanations btw :) they're helpful. So one could say that in a mathematical sense the steeper the slope the slower the clock? And as all sides are extremely steep at a VMO f.ex you will have a very slow time where those slopes come together, no matter if they plan out there. Like some sort of 'gravitational vectors' pointing towards that 'flat point' in the middle of our VMO?

Hah I refuse to accept that, I just have to find some paper and a pencil, just wait and see:)

Nah, I'm sort of joking. But yes I can see how that view comes naturally from treating it as slopes with vectors pointing to the middle, that is if I got it correct ::)) But I still would like to see an experiment proving the concept?
==

Ah, in the Jules Vernian sense I mean, measuring time differences. And then we have two different types of 'weightlessness' if this is correct, don't we? Or maybe not? You could compare it to an uniform acceleration giving you a constant gravity?? Nah, that's not being weightless, weightless is a 'free fall' as I understands it? In what way does that 'weightlessness' in the middle have anything to do with a free fall if so??  Awh..
« Last Edit: 18/03/2010 14:08:23 by yor_on »
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Offline fontwell

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« Reply #60 on: 18/03/2010 15:32:38 »
Quote
Yes, that's what I'm wondering too. Pressure and Gravity. You will have a pressure at the middle, that much seems clear but you can't equal that to a 'gravity', can you?

Correct, you can't. But it makes the point that an effect due to mass (pressure) can occur in a region where there is no gravity. Indicating that time dilation due to mass can occur in a place with no gravity.

Quote
So one could say that in a mathematical sense the steeper the slope the slower the clock?


No. Not if you mean the slope of curved space-time. You could say the steeper the slope the stronger the attraction of masses - which we observe as gravity. Gravity would be the steepness, time dilation would be the amount of stretch.

Quote
Ah, in the Jules Vernian sense I mean, measuring time differences. And then we have two different types of 'weightlessness' if this is correct, don't we? Or maybe not? You could compare it to an uniform acceleration giving you a constant gravity?? Nah, that's not being weightless, weightless is a 'free fall' as I understands it? In what way does that 'weightlessness' in the middle have anything to do with a free fall if so??  Awh..

Exactly!

As I understand it 'weightlessness' is 'weightlessness' but also 'mass' is 'mass' :)

By which I mean, free fall and being weightless in the centre of a large mass are the same in that an observer in either condition can't do a local experiment which would give different results (to him).

However, the presence of mass is a real thing which makes the two situations unequal. They will both agree on who has the faster clock - the one furthest from the mass. This is unlike inertial frames in SR where both parties observe the other to have a slow clock. Mass allows the situation to be absolutely unbalanced.

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Offline yor_on

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« Reply #61 on: 18/03/2010 15:52:16 »
So in what way would I be able to differ the weightlessness inside my black box at the middle of our earth, against being in a free fall? You could argue that pressure will do it, but you can set up a equal situation in a free fall I think, creating that pressure, can't you?

Either it will differ or?
Consider the definition of gravity as being equal to a uniform accelerating?
This one is still strange to me, even though your point of view makes eminent sense Mr fontwell :)

And the idea of equivalence doesn't build on looking at a situation with 'the eye of a God' as I understands it? It builds on the opposite, being in a black box unable to define anything except from your own frame?
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Offline fontwell

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« Reply #62 on: 18/03/2010 17:26:47 »
So in what way would I be able to differ the weightlessness inside my black box at the middle of our earth, against being in a free fall? You could argue that pressure will do it, but you can set up a equal situation in a free fall I think, creating that pressure, can't you?

Either it will differ or?
Consider the definition of gravity as being equal to a uniform accelerating?
This one is still strange to me, even though your point of view makes eminent sense Mr fontwell :)

And the idea of equivalence doesn't build on looking at a situation with 'the eye of a God' as I understands it? It builds on the opposite, being in a black box unable to define anything except from your own frame?

I agree, to my understanding, inside a block box there is no difference between the two situations, that is why relativity is still 'relativity'.

The difference is that near a mass everyone agrees clocks run slower than further away. But this does not create a privileged position, just different positions. The clock near the mass still measures local seconds but he measures clocks further away as running as too fast. Who is correct? There is no correct.

It is like we look at the clock on a GPS satellite and correct it to our local time. But the Sun affects us both, so the Sun thinks we are both too fast. But the centre of the Galaxy thinks the Sun is too fast. Even our observable universe is perhaps too fast for someone else!

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Offline yor_on

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« Reply #63 on: 18/03/2010 18:55:04 »
Yep :)
You're all to fast for me.

*Oh no, Those men in their white coats again, where do they grow them?*
Ah, gotta run now Mr Fontwell :)
==

I'll be back ::))

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Offline gem

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« Reply #64 on: 18/03/2010 21:20:10 »
Hi all
       gosh you have all been busy, font well certainly has helped clarify space time theory a little clearer for me as to how it can come to the same conclusions for different reasons. such a lot to take in i have read through every ones posts but will have to read through some more to make sure i have understood it all properly,

At the moment my grasp on it is 'newton' mass causes gravitational attraction force and when within a sphere of mass the attraction vectors cancell each other giving a resulting zero force on a body within.

Einstein separates gravity from the mass, gravity does not attract and the reason mass acceleration diminishes as you get nearer the center is because the curve of space becomes less

one question that comes to mind straight away though is about this statement that G R postulates


The difference is that near a mass everyone agrees clocks run slower than further away. But this does not create a privileged position, just different positions. The clock near the mass still measures local seconds but he measures clocks further away as running as too fast. Who is correct? There is no correct.

It is like we look at the clock on a GPS satellite and correct it to our local time. But the Sun affects us both, so the Sun thinks we are both too fast. But the centre of the Galaxy thinks the Sun is too fast. Even our observable universe is perhaps too fast for someone else!

Does this mean there is not a universe standard law of conservation of energy [work heat equivilance] ?

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Offline fontwell

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« Reply #65 on: 19/03/2010 00:41:03 »
I'm glad you are finding this helpful :)

Quote
Does this mean there is not a universe standard law of conservation of energy [work heat equivilance] ?

I'm pretty certain that conservation of energy is one of the few laws that always works. I'm not really very clear about energy in SR or GR but isn't it the case that everything works due to differences in potential energy (what ever that is!). So if it turns out that we are  all affected (more or less) the same by a huge but distant mass it doesn't affect the local differences in potential.

This is actually our experience anyway - when we raise 1kg by 1m it takes 1Joule. We do not notice that this raising took place in the context of the Sun's gravity, that just adds an equal potential energy to both positions.

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Offline JP

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« Reply #66 on: 19/03/2010 02:27:56 »
We've had a few discussions about conservation of energy in GR lately.  (There isn't a problem with conservation of energy in SR as far as I know.)  Basically, GR has issues defining an energy, since when you include gravitational energy, the quantity that acts like a conserved energy doesn't transform appropriately when you change reference frames.   

The two links I include below were useful in trying to understand this:
http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Relativity/GR/energy_gr.html
http://www.physics.ucla.edu/~cwp/articles/noether.asg/noether.html

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Offline gem

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« Reply #67 on: 19/03/2010 20:17:47 »
Just to say something on the issue of the zero gravity at the earth's centre versus 1G at the surface. I think the bending of space-time and slowing of clocks is due to mass, not gravity. Gravity is an effect of curved space-time. The centre of the earth is at the bottom of a local curve and so there is no gravity there. However, the actual curve is at its lowest point so the time is most slowed down. I think.

OK another question,
 how is time slowest at the center ?
 
Because as i understand it Einstein used inverse square law and the earths radius, and one times one equals one.  So it would seem to be the same as at earths surface, or am i missing something ? [i must be otherwise there would be no more down once your on earths surface]

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Offline geo driver

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« Reply #68 on: 19/03/2010 20:34:03 »
3 minites
board of ignorance

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Offline gem

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« Reply #69 on: 21/03/2010 23:26:20 »




Well, the GR view of gravity is that it is only an effect of curved space-time. The GR view is that mass curves space-time. And the equations for time dilation refer to the centre of mass. The clock at the earth's centre is slowed by the combined pressure of all that mass around it.

 

I will say again in case the relevance of my previous question was not understood if the equations for time dilation were referring to the centre how is it possible that the time dilation is any different one radius away?, the values should be the same according to the radius squared part of the equation.

Meaning no curvature from the centre to the surface.
[Newton addressed this issue did Einstein]

 Also i don't see how mass applies pressure other than as a consequence of gravity

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Offline JP

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« Reply #70 on: 22/03/2010 01:21:11 »
I will say again in case the relevance of my previous question was not understood if the equations for time dilation were referring to the centre how is it possible that the time dilation is any different one radius away?, the values should be the same according to the radius squared part of the equation.
Time dilation occurs wherever gravity curves space-time so that one point in space experiences a different rate of time than another.  Since gravity starts curving space-time well outside of the earth and continues all the way down to the center, you would expect time dilation to occur between any two all radial points you chose.  Only if you chose two points the same radial distance from the earth's center would you get the same rate of time.  (And all this assumes the earth is a perfect sphere--in reality it would be slightly different.)

Quote
Also i don't see how mass applies pressure other than as a consequence of gravity
There's a term in the equations of general relativity called the stress-energy tensor.  This is the term that tells space-time how to bend.  Mass contributes to this term.

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Offline fontwell

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« Reply #71 on: 22/03/2010 09:17:28 »

OK another question,
 how is time slowest at the center ?
 
Because as i understand it Einstein used inverse square law and the earths radius, and one times one equals one.  So it would seem to be the same as at earths surface, or am i missing something ? [i must be otherwise there would be no more down once your on earths surface]

I'm not quite sure what you are asking. Inside the earth, distances from the mass of the earth are less than one earth radius. So time runs slower. There are some pictures near the top of the page in one of my earlier  posts indicating the way that space-time is warped by mass. The warping isn't the same at the surface and the centre.

Also i don't see how mass applies pressure other than as a consequence of gravity

Of course. I may have confused the issue here by using an analogy comparing regular pressure of a liquid with the bending of space-time due to mass.

In a normal Newtonian way of thinking the pressure at the centre of the earth is huge. But there is zero local gravity (if you dropped a stone while at the centre it would not accelerate away from you). The only point of this is to show that just because a location has no gravity itself, it is not free from the surrounding effects of gravity and mass, even in Newton's world. So, just because there is zero gravity it doesn't mean we can say it is the same as a point at infinite distance, either for Newton or Einstein.

In GR thinking, mass bends space-time in an analogous way to the pressure inside a Newtonian Earth. But the GR curving isn't caused by being squashed under a mass by gravity. Space-time bending is caused purely by the presence of mass. A 'way you could think' about this is as a 'pressure' to due to mass - like in the pictures above. This is a mental model of 'pressure' due to mass, and this pressure slowing down time. But it isn't an actual pressure in the everyday meaning. The 'GR pressure' which bends space-time is highest at the centre of the Earth because in this location the effect of all the mass of the Earth is at is maximum (the sum of the 1/r^2 equations over all the mass), not anything to do with gravity.


Time dilation occurs wherever gravity curves space-time so that one point in space experiences a different rate of time than another...

Please! I thought we had agreed that mass curves space-time! Gravity doesn't do anything to space-time, it is a consequence of how curved it is.
« Last Edit: 22/03/2010 12:21:15 by fontwell »

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Offline JP

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« Reply #72 on: 22/03/2010 09:59:42 »
Please! I thought we had agreed that mass curves space-time! Gravity doesn't do anything to space-time, it is a consequence of how curved it is.

True.  Poor choice of words on my part in trying to simplify things. To be more precise, the stress-energy tensor (which includes mass) is the source of the curvature and the curvature is a mathematical description of gravity.

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Offline gem

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« Reply #73 on: 22/03/2010 21:15:21 »
Right i have got the concept of mass pressure in the way it applies in general relativity, and it answers my question as to how it is postulated that time runs slowest at the centre.

So the difficulty is how to get nature to ask a question of both theory's that will separate out which one is closest to what is observed,

And because both theory's include the same dynamics happening, albeit for different reasons it would seem at first glance to be insurmountable.

However i can think of one which could isolate there differences

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Offline yor_on

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« Reply #74 on: 22/03/2010 21:43:37 »
Yep I can follow that thinking, gravity would then be the consequence of SpaceTimes geodesics (dips, bends and heights) called forward by the stress-energy tensor that is the direct result (expression) of mass acting on space.

The problem here being that both the geodesics and the stress energy tensor are mathematical descriptions versus gravity that really is what we feel :) I mean, we don't say, "Hey Alex, watch out for that stress energy tensor man, you're gonna fall !!" Do we, huh? ... "Why thanks Charles, that geodesic really took me by surprise."

:)

But it do make sense, all the way down to how to accept the idea that a free fall in the middle won't be equal to a free fall outside, time dilation wise that is. But then again, if they're not then it seems to me that the same should hold for free falling frames outside too. And if that would be right then different velocity in free fall (uniform moving) will be able to create different time dilations relative a common originator (like starting two rockets from Earth)?

Awh..

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« Last Edit: 22/03/2010 21:58:08 by yor_on »
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Offline Geezer

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« Reply #75 on: 23/03/2010 05:36:39 »
Anyway, I suspect Geo Driver is quite correct. If you want a three minute egg, time it for three minutes. (I'm assuming we are conducting the experiment at something close to one atmosphere and boiling the egg in water rather than molten iron.)

The timing device and the egg will both experience three minutes in, well, three minutes, or did we conclude the answer would be different?
There ain'ta no sanity clause, and there ain'ta no centrifugal force ćther.

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Offline fontwell

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« Reply #76 on: 23/03/2010 09:08:41 »
yor_on, you seem to have it in your grasp. The trouble is that some examples you use jump between GR and SR. A free falling body (or orbiting) compared to the Earth's surface (or centre) has time dilation due to the relative velocities (ignores mass). This is an SR effect. There is also another effect due to being near mass, this is a GR effect.

@Geezer, yes three minutes is three minutes but don't use an hour-glass style egg timer :)
« Last Edit: 23/03/2010 09:43:49 by fontwell »

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« Reply #77 on: 23/03/2010 18:43:36 »
@Geezer, yes three minutes is three minutes but don't use an hour-glass style egg timer :)

Ah yes! I suppose any device that relied on gravity (pendulums etc) would be suspect  [;D]
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« Reply #78 on: 23/03/2010 21:12:33 »

@Geezer, yes three minutes is three minutes but don't use an hour-glass style egg timer :)
Not if it contravenes the laws of conservation of energy it isn't. below is an extract from a link J P provided in regards to wether G R voilated energy conservation ...........

An infinitesimal piece of spacetime "looks flat", while the effects of curvature become evident in a finite piece.  (The same holds for curved surfaces in space, of course).  GR relates curvature to gravity.  Now, even in newtonian physics, you must include gravitational potential energy to get energy conservation.  And GR introduces the new phenomenon of gravitational waves; perhaps these carry energy as well?  Perhaps we need to include gravitational energy in some fashion, to arrive at a law of energy conservation for finite pieces of spacetime?.........

Looks to me like there turning gravity back in to a force field.

Anyone else come up with a way to test wether gravity is an attractive force or a bending of time ??


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« Reply #79 on: 23/03/2010 21:49:12 »
We think we have indirect evidence of gravitational waves acting as a energy Gem.

"The smoking gun is a system of orbiting neutron stars with the catchy name PSR1913+16. Einstein's theory predicts that gravitational waves carry away energy. For a system of orbiting stars, such a decrease in total energy leads to an ever faster and closer orbit. Over decades, radio astronomers have monitored the time that it takes the stars of PSR1913+16 to complete each successive orbit, and lo and behold: this orbital period decreases over time exactly as predicted by general relativity. This is strong evidence that the speed-up is indeed due to the radiation of gravitational waves, and the reason Russell Hulse and Joseph Taylor were awarded the Nobel prize for physics for the year 1993." Gravitational waves.

But, what exactly is this 'energy' we're speaking of, is it the same type we find in our combustible engine? and furthermore, if there exist this kind of phenomena, why couldn't we speak about gravity as a 'force'?
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« Reply #80 on: 23/03/2010 21:51:08 »

@Geezer, yes three minutes is three minutes but don't use an hour-glass style egg timer :)
Not if it contravenes the laws of conservation of energy it isn't. below is an extract from a link J P provided in regards to wether G R voilated energy conservation ...........

An infinitesimal piece of spacetime "looks flat", while the effects of curvature become evident in a finite piece.  (The same holds for curved surfaces in space, of course).  GR relates curvature to gravity.  Now, even in newtonian physics, you must include gravitational potential energy to get energy conservation.  And GR introduces the new phenomenon of gravitational waves; perhaps these carry energy as well?  Perhaps we need to include gravitational energy in some fashion, to arrive at a law of energy conservation for finite pieces of spacetime?.........

Looks to me like there turning gravity back in to a force field.

Anyone else come up with a way to test wether gravity is an attractive force or a bending of time ??



Well, I'm not sure what it has to do with energy conservation, but I'm pretty sure if it was not three minutes, some other significant law would be violated. I'm not sure what the law is called (or if it even exists!) but, according to my understanding, it is impossible to detect any "variation" in time within a local space. In other words, if your egg required more or less than three minutes of boiling to "behave" like an egg that had been boiled for three minutes, you would have created a means of detecting a "variation" in time without reference to some other time frame.

I'm sure JP will straighten me out if this is not right.
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« Reply #81 on: 23/03/2010 22:11:14 »
We think we have indirect evidence of gravitational waves acting as a energy Gem.

"The smoking gun is a system of orbiting neutron stars with the catchy name PSR1913+16. Einstein's theory predicts that gravitational waves carry away energy. For a system of orbiting stars, such a decrease in total energy leads to an ever faster and closer orbit. Over decades, radio astronomers have monitored the time that it takes the stars of PSR1913+16 to complete each successive orbit, and lo and behold: this orbital period decreases over time exactly as predicted by general relativity. This is strong evidence that the speed-up is indeed due to the radiation of gravitational waves, and the reason Russell Hulse and Joseph Taylor were awarded the Nobel prize for physics for the year 1993." Gravitational waves.


That's interesting. We know that the Earth manages to transfer energy to the Moon, but I don't think there is any need to invoke gravitational waves to explain the phenomenon.
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« Reply #82 on: 24/03/2010 10:38:40 »
Why is energy conservation suddenly coming up and what does it have to do with time dilation?  All you really need to know is what Geezer was saying--that if you put your timer and egg next to each other, then they should both agree on what three minutes is.

The gravitational wave stuff is nice, but it has to do with gravitational energy being carried far away from a gravitational system, doesn't it?  Orbits might decay faster than normal as a result of this, but what does it have to do with timing an egg?

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« Reply #83 on: 24/03/2010 19:19:24 »
Why is energy conservation suddenly coming up and what does it have to do with time dilation?  All you really need to know is what Geezer was saying--that if you put your timer and egg next to each other, then they should both agree on what three minutes is.

The reason i brought energy conservation up was that to time and cook the egg you need a set amount of energy in a set amount of time

 And a joule is a unit of energy in the International System of Units,  It measures heat, electricity and mechanical work.

The joule is a derived unit equivalent to a newton-meter, or a kilogram-meter squared per second per second.

A joule is also:

A unit of electrical energy equal to the work done when a current of one ampere is passed through a resistance of one ohm for a period of time of one second.

A unit of energy equal to the work done when a force of one newton* acts through a distance of one meter.

In the meter-kilogram-second (MKS) system, a newton is the unit of force required to accelerate a mass of one kilogram one meter per second per second,

So you will notice time is a factor in the measurement of the work heat equivalence and as we have already noted earlier in this post at the center where in GR time is slower will the energy interactions there not disagree with the International System of Units as regards the laws thermodynamics.

similar to the fact that a particle at the centre of the earth would seem to travel faster than one at the surface according to G R, so distance travelled would disagree with the International System of Units.



But, what exactly is this 'energy' we're speaking of, is it the same type we find in our combustible engine? and furthermore, if there exist this kind of phenomena, why couldn't we speak about gravity as a 'force'?

Energy is Energy it just takes different forms and yes even in GR they must be trying to detect a variation in gravity as some kind of force or maybe they will detect a variation in the gravitational force.

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« Reply #84 on: 24/03/2010 20:23:24 »
Could you minimize that post a little and make it clearer to me Gem. I sort of lose myself reading it? Are you saying that the units we use are wrong? I'm not sure I'm following you rightly here?

Thinking of the conservation of energy. It just states that we always will have an equivalence in our universe. It may change form when using it, like gasoline comes out as water, heat and CO2 etc, as it also goes up as 'energy' driving the pistons in our engine. but it doesn't come from nothing as far as we know, and it won't disappear into a nothingness. The gasoline just becomes unusable for 'new work', as its usable energy gets transformed into such things as water, CO2 and heat. And the idea is similar to thermodynamics idea of work and 'work done' describing 'usable energy' transforming to 'unusable' energy.

And looking at it that way the only thing requested of this egg in any frame of reference is that the 'work' will be equivalent to the same amount of 'work done', unusable to us after its transformation(s) for it to hold true. So it doesn't really have to do with time dilation or mass. It's a principle of equivalence to me, describing how we think our universe 'works' :)

Like we also speaks of our universe to be a 'closed one' instead of 'open ended'. and that statement have nothing to do with its 'inflation' or 'expansion' but is a statement saying the same as above, that we don't lose any energy, it only transforms, like being in a bubble of a sorts where the 'walls' won't allow any penetration of new 'energy'. At least that's my understanding? That's also why Hawking radiation is so interesting, as we on one side calls Black Holes enigmas and 'singularities' meaning that we can't look past the Event horizons of them, and that they are 'closed' to our universe, but on the other hand according to some theories, still would have some sort of 'information exchange' due to that radiation with our universe.

But I'm not really sure if that was what you were thinking of here Gem?
« Last Edit: 24/03/2010 20:37:37 by yor_on »
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« Reply #85 on: 24/03/2010 21:39:44 »
So you will notice time is a factor in the measurement of the work heat equivalence and as we have already noted earlier in this post at the center where in GR time is slower will the energy interactions there not disagree with the International System of Units as regards the laws thermodynamics.

I think Gem is concerned that time dilation will affect the quantity of energy required to boil the egg.

Well, no. I don't believe it has any effect on the energy required. Everything at the center of the Earth runs a bit faster (or is it slower - I can never remember) than it does at the surface. By "everything" I really mean everything. All atomic activity, every chemical process, human thought, human metobilism, all physical motion etc. etc. is governed by the local time.

If it actually did require a different amount of energy, you would have invented a mechanism to detect time dilation locally, and that is a big no no. (Sorry for the less than scientific phrase.)

If you use an atomic clock to time your egg for three minutes, the atomic clock measures local time, so it will "tick" exactly the same number of times in three minutes, regardless of its location.

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« Reply #86 on: 24/03/2010 22:00:44 »
You know Geezer, I think you're right. That thoughts too are regulated by time I mean. They seem so unrelated to what we deem as being materially 'there', as if they wasn't connected to anything materialistic, but they are.

That was a nice one.

Now, how about 'photons' ::))
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« Reply #87 on: 24/03/2010 23:51:36 »
You know Geezer, I think you're right. That thoughts too are regulated by time I mean. They seem so unrelated to what we deem as being materially 'there', as if they wasn't connected to anything materialistic, but they are.


Well, I think thinking(!!) is mainly a chemical processes, so it would have to be governed by local time. I can't see why anything would be exempt - even photons. That's not to say the speed of light is any different. Light still travels the same distance in unit time. It would kind of have to, wouldn't you think?

(I'm not sure that the photon bit is necessarily correct. It sounds logical, but photons have a nasty habit of defying my logic. Let's see if JP thinks this is legit.)
« Last Edit: 25/03/2010 05:20:52 by Geezer »
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« Reply #88 on: 25/03/2010 11:57:10 »
The general rule of thumb is that locally, space-time is flat, so you only need to use special relativity, not GR.  In that case, everything should be governed by special relativity instead of general relativity and as long as things are moving fairly slow, everything is governed by the same "local clock" where the only time dilation you need to consider is from special relativity (i.e. if something is moving fast).  Light you're watching move about should seem to do so at the speed of light no matter what with the appropriate doppler shift if you're moving with respect to the source. 

Was that a long answer to a short question or what?  :)

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« Reply #89 on: 25/03/2010 18:28:52 »
Quite nice JP, and by flat you're using the idea that it is so vast (the universe I mean) that to us locally all 'curves' will be a straight line? Like we thought the Earth was too, some time ago (last year in my case::))
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« Reply #90 on: 25/03/2010 22:11:45 »
The general rule of thumb is that locally, space-time is flat, so you only need to use special relativity, not GR. 
I thought fontwell posted diagrams that showed that space time curves between the surface of a planet and the centre in G R.? And this from a link Jp provided seems to contradict.

An infinitesimal piece of spacetime "looks flat", while the effects of curvature become evident in a finite piece.  (The same holds for curved surfaces in space, of course).  GR relates curvature to gravity.  Now, even in newtonian physics, you must include gravitational potential energy to get energy conservation. 
 

And also if space time is flat locally there would be no gravity according to fontwell that is what happens only at the centre.


If you use an atomic clock to time your egg for three minutes, the atomic clock measures local time, so it will "tick" exactly the same number of times in three minutes, regardless of its location.

when the clock at the centre has ticked the same amount of times as the one at the surface it will have travelled further in its orbit around the sun.

And as mass according to G R is the cause of gravity where will the mass at the centre be bending space time compared to mass at the surface,If what you say below is correct.

By "everything" I really mean everything. All atomic activity, every chemical process, human thought, human metabolism, all physical motion etc. etc. is governed by the local time.


Please explain how ALL PHYSICAL MOTION IS GOVERNED BY LOCAL TIME because according to the atomic clocks the mass at the centre is traveling faster.

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« Reply #91 on: 26/03/2010 00:37:26 »
And also if space time is flat locally there would be no gravity according to fontwell that is what happens only at the centre.

Not at all.  Think about how the earth's surface looks pretty flat to you, even though the earth is (roughly) a huge sphere.  Gravity and curvature come in when you look at how you travel from one tiny locally flat patch to another.

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« Reply #92 on: 26/03/2010 00:47:02 »
Please explain how ALL PHYSICAL MOTION IS GOVERNED BY LOCAL TIME because according to the atomic clocks the mass at the centre is traveling faster.

Local time is time measured locally.  The local time at the center faster than the local time at the surface.  What's meant by that quote is that how something moves is related to the time that thing experiences, i.e. it's own local time.  So if you put the timer and egg next to each other at the center of the earth, they would pretty much agree on what a second was.  They wouldn't agree with someone on the surface or in deep space, however.  The more curved space-time is the closer your timer and egg would have to be in order to "see" the same local time. 

To really experience the exact same time, they'd have to be at the same point, but since the earth isn't a powerful source of gravity, being next to each other is "good enough."  (Actually for egg timing, the time dilation of the earth isn't even important since microseconds don't matter).

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« Reply #93 on: 26/03/2010 02:12:38 »
By "everything" I really mean everything. All atomic activity, every chemical process, human thought, human metabolism, all physical motion etc. etc. is governed by the local time.


Please explain how ALL PHYSICAL MOTION IS GOVERNED BY LOCAL TIME because according to the atomic clocks the mass at the centre is traveling faster.

It's not really correct to say it's travelling faster. Locally, it's travelling at the same speed. Speed is distance in time. Everything is governed by local time, so locally speed would be the same at the two locations.

If you had some amazing device that allowed you to observe the two egg timers simultaneously, if both started simultaneously, you would be able to observe that the one at the center of the earth would finish before the one at the surface.

However, locally, both eggs would cook for three minutes because three minutes of local time had elapsed. If you could see two objects moving at 10 mph at the two locations, you would observe that one was moving faster than the other from your perspective, but from the perspective of local observers, they would both be moving at 10 mph.

Don't worry. It only took me about twenty years to get my head around this strange situation. [:D]
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« Reply #94 on: 26/03/2010 18:29:18 »

If you had some amazing device that allowed you to observe the two egg timers simultaneously, if both started simultaneously, you would be able to observe that the one at the center of the earth would finish before the one at the surface.
After
  (Actually for egg timing, the time dilation of the earth isn't even important since microseconds don't matter).
No but for the integrity of the theory micro seconds do matter


Local time is time measured locally.  The local time at the center faster than the local time at the surface. 
Slower.

It's not really correct to say it's travelling faster. Locally, it's travelling at the same speed. Speed is distance in time. Everything is governed by local time, so locally speed would be the same at the two locations.

If you had some amazing device that allowed you to observe the two egg timers simultaneously, if both started simultaneously, you would be able to observe that the one at the center of the earth would finish before the one at the surface.


Can you not see the contradiction in those two statements.

For the clock to seem to be traveling faster it has to be running slow to allow it to travel further.

But the point of the contradiction is lets pretend earth is a vessel traveling through space at speed and on this vessel there are two atomic clocks running at different rates so giving a different velocity for the said vessel. 

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« Reply #95 on: 26/03/2010 20:07:34 »
Nope. I don't see a contradition and I don't think I can add any more to my explanation.
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« Reply #96 on: 27/03/2010 08:02:57 »

Local time is time measured locally.  The local time at the center faster than the local time at the surface. 
Slower.

Touche.  It still doesn't change the rest of the explanation, though.

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« Reply #97 on: 27/03/2010 19:27:18 »
It's 'frames of reference' we're speaking of here right?

1. Your own 'frame' will always show you the same time, as measured by your wristwatch against your heartbeats, in any 'frame' you exist in.

2. To show a really large 'time dilation' you will have to do a 'twin experiment' more or less, but that it exist is already proved, by muons and GPS amongst others.

3. Without that 'twin experiment' whatever you will observe outside your 'frame of reference' will give you an answer time-wise, as related to you both, but without you being to measure any difference relative time-dilation (naively seen without foreknowledge.)

And 3. is the really remarkable thing to me, making us able to see the universe as a 'whole experience' no matter that according to the 'twin experiment' one of the returning twins won't have aged (accelerating one).

What one might say? Is that we have no way to 'slow down' the universe as a whole. It have it's own 'arrow of time' it seems(?) Ticking at a even pace. What we can do is to 'slow ourselves down' against the universe, and so, relative our place of origin, measure a time dilation.

But I can't see how we ever would be able to 'slow it down'?
That means you aging faster than the universe as a 'whole'.

That is, if you accept my definition of the universe as a 'whole experience' aging of course. Otherwise you might say that there are things/objects aging 'faster' than you. But if it is that way then the experience of being able to observe a 'whole universe' have to be explained from something else it seems to me?

Can you see what I think here? That what we call 'times arrow' then is a very localized phenomena and that our 'universal arrow of time' then becomes even more remarkable, as will all causality-chains observed, following our 'entropy'.
« Last Edit: 27/03/2010 19:29:24 by yor_on »
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« Reply #98 on: 27/03/2010 23:08:16 »
welcome back yor on, i thought the white coats had finally caught up with you.


That is, if you accept my definition of the universe as a 'whole experience' aging of course. Otherwise you might say that there are things/objects aging 'faster' than you. But if it is that way then the experience of being able to observe a 'whole universe' have to be explained from something else it seems to me?

Can you see what I think here? That what we call 'times arrow' then is a very localized phenomena and that our 'universal arrow of time' then becomes even more remarkable, as will all causality-chains observed, following our 'entropy'.

And this from the man that helped bring Einsteins theory's to prominence in the scientific community

http://en.wikipedia.org/wiki/Arrow_of_time [nofollow]
Eddington then gives three points to note about this arrow:

1  It is vividly recognized by consciousness.
 
2   It is equally insisted on by our reasoning faculty, which tells us that a     reversal of the arrow would render the external world nonsensical.
 
3  It makes no appearance in physical science except in the study of organization of a number of individuals.

Here, according to Eddington, the arrow indicates the direction of progressive increase of the random element. Following a lengthy argument into the nature of thermodynamics, Eddington concludes that in so far as physics is concerned time's arrow is a property of entropy alone.
 

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« Reply #99 on: 28/03/2010 04:30:16 »
Not bad Gem, there is another guy that recently described gravity as a product of entropy too, if I remember right. Entropy is a very strange idea as it, as a product, don't have to be equal over the whole area it acts on, that is to my understanding. You can have limited areas with a decreased entropy, yet still with the overall effect being an increased entropy. If I lifted that up to the concept of times arrow, it then seems to state that if entropy and times arrow is the same, we c/should have areas where time 'ticked backwards'?
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