Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: williampcochran on 05/01/2011 18:07:53
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ψ
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My first inclination would have been to answer simply no but then I read this and now have my doubts.
http://metaresearch.org/cosmology/speed_of_gravity.asp
PS I now see the significance of the Little Greek squiggle (sigma ?)
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The graviton, the mediator of the gravitational wave travels always at lightspeed. I have some math written down in some old jotters some where which I will seek out if I can :)
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Right ok. The deAlembertian, a four dimensional wave equation will be represented as ▼. Not usual notation but box notation cannot be used here.
▼hμν=0
This is the same as saying
∂μ∂μhμν=0
This means it will follow the speed of light since ▼∂t2 - c2∂2x.
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Here is a rebuttal to Van Flandern's beautiful arguments. Aberration and the Speed of Gravity (http://xxx.lanl.gov/pdf/gr-qc/9909087v2)
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I'll look thanks. But if someone says its faster than light, there is no proof. If they say its slower, it would be a short range distance which does not work either.
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My first inclination would have been to answer simply no but then I read this and now have my doubts.
http://metaresearch.org/cosmology/speed_of_gravity.asp
Interesting article, I think it needs more study, along with some of the referenced articles:
http://xxx.lanl.gov/abs/gr-qc/9706082 (see full text PDF&PS Links)
http://metaresearch.org/cosmology/gravity/possiblenewpropertiesofgravity.asp (another good summary article).
Light may be limited in speed by the particle nature of the photon which has the effect of a positive mass.
Gravity doesn't seem to have a corresponding particle (graviton), and thus wouldn't be limited by the same mass effect.
As far as gravity though, there seems to be two issues.
Static Field as in the planet orbiting around a central body which seems to be the easiest to measure with respect to the direction of the gravitational pull of the central body, however, it may only be measuring the interaction of bodies in a pre-existing field which may not adequately measure the speed of gravity (except with respect to the movement of our sun, which should then cause a measurable effect depending on the orbital position of the earth with respect to the center of the Milky Way and the direction of the sun's orbit if there was a delay).
Dynamic Field, as in two bodies progressing along a parallel path (or synchronously orbiting a third body as in the spiral arm model of many galaxies). For the two parallel bodies, if there was a time delay with the gravity, then the gravity vector of the "partner" object would actually be behind each of the bodies, and there would be a significant gravitational drag component exerted on both bodies.
It would be hard to tease out this gravitational drag component if it existed, but it would be predicted to be greater on two parallel bodies (or 2 bodies such as planets passing each other in an orbit) than would be exhibited by a body traveling alone in its orbit.
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I've been thinking a lot about gravity recently funnily enough, about how to approach a unified theory. Apparently according to a few sources the problem with doing this lyes in gravity being a gauge theory and how mass does not couple to the gravitational field. I think this can be approached by having a coupling term Ψ*ΦGMμΨ where it plays an alternative mass term in replacement of the Higgs field. In other words, the gravitational field provides a moving mass in a field with mass instead of a superfluous Higgs field.
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Maybe you could see 'space' as an imprint of gravitation. That meaning that 'space's' topology 'remember' at the speed of light. Then you have a topology communicating itself at the speed of light at the same time that it will keep whatever topology it express until a new such communication comes.
So does that mean that there have to be 'something' communicating it?
We would like to think so :) as we work with particles and 'forces' but, maybe not?
If Lorentz contraction is 'real' as in 'really, you know, like real' :) then that same space can 'shrink, contract and decease' from the 'reality' we know normally, turning itself into some weird point possibly.
What do that do to our topology?
And why would the guys & gals in that spaceship be wrong saying that it have?
You would be dead I better remind you, so their answer would in fact be the final one :)
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Ah this answer was to ye all.
Okay:)
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And what would that 'alternative mass term in replacement of the Higgs field' do?
Are you thinking of it as a relation only QC, needing no 'virtual' existence?
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Like waves on top of an ocean?
And those possibly 'waves' being 'everywhere' in that ocean?
But you still need a reason to why, don't you?
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Well, I think that some kind of interaction between a particle which has an internal energy reduced to some kind of condensed existence as an inertial mass is a particle by definition a particle which internally interacts with a field. The spark inside a particle therefore when in contact with a local graviational potential field around it ΦG creates some kind of inertial matter.
Ok, enough of my words, i'll get banned this way! lol
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Okay, a particle that communicates through 'fields' with itself. that makes a sort of sense, I've though about it similarly, especially when considering those examples and experiments where the electron seems to be superpositioned, in two places simultaneously.
Why not:)
like it all being 'densities' but in the form of fields.
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That is, if we give those 'fields' a topology resembling what I gave space. But then the question becomes, why do they stay the same? What are the constants defining their existence if it is so?
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Well, a particle under electromagnetism can interact with its field, so I don't see why we give such a superior credence with gravitons.
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Yeah, I'm not particularly enthralled by gravitons myself :)
The Higgs field seems more 'understandable' to me. But they both involves some Sort of particles, don't they?
Let me ask you all a question. I have two exactly identical springs, one that I compress and leave compressed, the other I don't do a thing to. I now take my perfectly sensitive atomic scale and weight them.
Will they weight the same?
And if you say no.
What have changed?
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And do you expect time to rectify it, if you said yes (to no) that is :)
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To see it we first need to consider if something have 'changed' here.
Well the spring that's compressed isn't 'normal' any more, and that's because I compressed it.
And when I did, I expended 'energy', right?
So where did that 'energy' go?
Yep, straight into that spring. And the springs new energy have an equivalence to mass according to Einstein. So according to him this spring will weight more than when it was 'normal' and untouched.
But won't that 'energy' cling off as the spring cools? Nope, it's not kinetic energy only, it's 'energy' as I understands it. That as I would expect 'kinetic energy' to dissipate with time, but as long as we keep this spring compressed it will weight more.
All as I understands it?
Weird? Yeah..
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So how about heat, will that add a weight too?
As long as it's hot, yep.
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Anyone remember Einsteins cosmological constant?
That's how he defined it. If energy could make something weight more, then there had to be a effect that contradicted it. He came to it when noticing that the galaxies was expanding instead of coming together, he needed to find a reason why the invariant mass (gravity) didn't bring it all into one big clump. And if we instead of energy call it pressure then normal gravity is a positive 'pressure' whilst a repulsive gravity is a negative 'pressure'.
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So, the cosmological constant exerted a negative pressure according to him. But why the he* would that make the galaxies expand? Shouldn't a negative pressure just 'close up' under the positive pressure surrounding it?
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Interesting question - I wonder what the experimentalist have to say about it???
"Standard experimental techniques exist to determine the propagation speed of forces. When we apply these techniques to gravity, they all yield propagation speeds too great to measure, substantially faster than lightspeed. This is because gravity, in contrast to light, has no detectable aberration or propagation delay for its action, even for cases (such as binary pulsars) where sources of gravity accelerate significantly during the light time from source to target." (Tom Van Flandern)
Conclusion: The Speed of Gravity is > 20,000,000,000 times the speed of light (c)
But can it be infinite? (ie instananeous?)
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Don't expect me to be able to explain this one, but according to Einstein the negative pressure in fact 'pushes' on 'space'. Graham gave me this explanation when discussing dark energy and I compared it to the concept of invisible boxes.
"There are two aspects to the properties of matter that contribute to the gravitational attraction; one is mass density and the other is "pressure". This results from Stress-Energy tensor component in Einstein's Field Equations. The concept, in this case, is that dark energy has a negative pressure so that as the universe expands the pressure gets greater (making it expand more)."
What you're saying here, if I get you right, is that you can imagine space as something in where we have a lot of invisible boxes containing a negative pressure, restricting and constraining those boxes in a inverse direction, and as space around them grows bigger due to the 'expansion' the inverse pressure automatically become larger? The problem here is that you will need a 'box' it seems to me, to explain how this can happen?
"Yor-on, I think you have it right. The negative pressure concept means that as the universe's volume (V) increases, the vacuum energy increases (dW = -PdV) because P is itself negative. So the vacuum energy density stays the same. However the Pressure term in Einstein's field equations will dominate, and being a negative term, results in a net increasing gravitational repulsion.
However, I don't think this explains anything but rather just says what the equations reveal. I can't think of any analogy with everyday familiar behaviour that can help. I have tried to find a clear explanation on the web but have failed to do so."
So the reasoning we have when it comes to dark energy seems directly traceable to Einsteins Cosmological constant.
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And reading I realize why it would expand more between galaxies than inside. It's not true that we don't expand inside the galaxies. We do expand inside them too. But the more Space we have the more 'pressure'. So the intergalactic wastes, as Buck Roger would have expressed it, will have a greater pressure than space inside the galaxies. And also, if there is no measurable expansion inside a galaxy it might be that the 'positive' pressure of gravitation is able to take out the 'negative pressure' repulsing 'space'
I don't think he made a 'blunder'.
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But it sure gives me a headache :)
We now have negative and positive pressure classically, as well as a positive and negative 'energy' non-classically, aka the Casimir effect (QM)
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Interesting question - I wonder what the experimentalist have to say about it???
"Standard experimental techniques exist to determine the propagation speed of forces. When we apply these techniques to gravity, they all yield propagation speeds too great to measure, substantially faster than lightspeed. This is because gravity, in contrast to light, has no detectable aberration or propagation delay for its action, even for cases (such as binary pulsars) where sources of gravity accelerate significantly during the light time from source to target." (Tom Van Flandern)
Conclusion: The Speed of Gravity is > 20,000,000,000 times the speed of light (c)
But can it be infinite? (ie instananeous?)
Probably tunnels to reduce such an inconceivable idea in relativity.
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Anyway, yoron, to reduce the probability I will end up banned for posting rogue theories - I am now terminating this lol :)
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It's cool, post it in new theories if you like. Then we can be at like wolfs :)
Not really, but it would be interesting to see how you think :)
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Oh I don't know... I could end up regretting it :)
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It depends, to me it doesn't matter if your idea is perfect or not. It seems that we learn anyway :) And its the learning that's the ultimate kick for me :)
It's not the richest dying wins, it's the most knowledgeable :)
Maybe you're thinking of publishing it though.
Then it's another matter.
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And QC, why I asked about the springs :)
Because you were thinking of a 'relational influences' instead of 'particles'
If we look at the compressed spring, how the he* does it keeps weighting more the whole time?
How could something I didn't 'send' get stored as mass?
What I sent was what I think of as 'kinetic energy' like kicking a ball.
That energy dissipates, doesn't it?
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Interesting question - I wonder what the experimentalist have to say about it???
"Standard experimental techniques exist to determine the propagation speed of forces. When we apply these techniques to gravity, they all yield propagation speeds too great to measure, substantially faster than lightspeed. This is because gravity, in contrast to light, has no detectable aberration or propagation delay for its action, even for cases (such as binary pulsars) where sources of gravity accelerate significantly during the light time from source to target." (Tom Van Flandern)
Conclusion: The Speed of Gravity is > 20,000,000,000 times the speed of light (c)
But can it be infinite? (ie instananeous?)
Probably tunnels to reduce such an inconceivable idea in relativity.
Meaning?
Experimental evidence shows that the propagation of gravity is at least 20,000,000,000 times the speed of light (Tom Van Fandern)
The question is can this value be infinite?
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It's cool, post it in new theories if you like. Then we can be at like wolfs :)
Not really, but it would be interesting to see how you think :)
This forum forbids speculation.
Only broing conservative scientific dogma is to be propagated in here.
Humour is banned
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Humour is tolerated here, subjecting idea's to the wrong subforum however, is not.
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I also found Van Flandern interesting Foolosophy. but I found this pdf later, that I linked to above, and reading it I think he might be wrong. But I know what you mean, and yes, in some aspects I too see gravity as instantaneous. Inertia will be happening as fast here as in deep space not caring about where you are. And that's also why I think of it as a 'topology' that is circumstanced by lights speed in a vacuum. The weird thing is how this topology is able to 'remember' itself.
That one is instantaneous if so, and no, people smile when we joke :)
You've made me smile at least :)
We're not that serious. If we was I would be banned here.
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Inertia= the reaction you feel to a change in direction or acceleration.
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Humour is tolerated here, subjecting idea's to the wrong subforum however, is not.
And what is the punishment for this ULTIMATE moral crime?
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I also found Van Flandern interesting Foolosophy. but I found this pdf later, that I linked to above, and reading it I think he might be wrong. But I know what you mean, and yes, in some aspects I too see gravity as instantaneous. Inertia will be happening as fast here as in deep space not caring about where you are. And that's also why I think of it as a 'topology' that is circumstanced by lights speed in a vacuum. The weird thing is how this topology is able to 'remember' itself.
That one is instantaneous if so, and no, people smile when we joke :)
You've made me smile at least :)
It does look as though the Newtonian assumption of gravity acting instantaneously over any distance may indeed be the case.
I tend to think that the reason for this is that space is not perfectly FLAT everywhere in the universe. That is, even if there was only one speck of dust in existence in the entire universe, the distortion in the space-time continuum that it will create will head off to infinity. Even in this extreme case space will have some value of curvature at any distance away from this speck of dust - the delusional axioms of mathematics DEMAND this to be so.
The issue then becomes one of semantical mathematical lunacy
this is right up my alley
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Humour is tolerated here, subjecting idea's to the wrong subforum however, is not.
And what is the punishment for this ULTIMATE moral crime?
That is not within my purview.
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Humour is tolerated here, subjecting idea's to the wrong subforum however, is not.
And what is the punishment for this ULTIMATE moral crime?
That is not within my purview.
...then are you able to direct me towards a Forum master or Tyrannical Thought lord so that I can obtain the details concerning this torturous punishment that is dished out for THE ULTIMATE MORAL CRIME?
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The mods, would be a thoughtful place to start.
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"I tend to think that the reason for this is that space is not perfectly FLAT everywhere in the universe. That is, even if there was only one speck of dust in existence in the entire universe, the distortion in the space-time continuum that it will create will head off to infinity. Even in this extreme case space will have some value of curvature at any distance away from this speck of dust "
Okay, I follow your idea abut how even a speck of dust will distort SpaceTime. I would expect that to be true too, to some infinitesimal degree. But from there to saying that it is the reason? For gravity being instantaneous? Do you mean that all objects of invariant mass carry its own 'distortions' with them and that inertia would act in those?
Or how do you see it, as if gravity would be a constant field created by invariant mass maybe, a spiders web? That's one analogy I like to use :)
There have been observations describing gravitational waves propagating when observing binary stars if I remember right so I think Einsteins idea of it taking 'time' to build is correct. the thing left is to explain why it creates a net, instantly reacting to inertia. That's what the Higg's particle (God particle:) try to do, but I I'm not sure if there is needed to be any particles?
And you seem to share that idea, even though I'm not sure how you see it?
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I begin to believe in instantaneous gravity, there are two other phenomena that are similar entanglement of particles and the reaction to rotation as postulated by Mach.
I cannot recall the source of the quote but I have heard that you have to believe in three impossible things before breakfast (was it Dodgson ?)
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"I tend to think that the reason for this is that space is not perfectly FLAT everywhere in the universe. That is, even if there was only one speck of dust in existence in the entire universe, the distortion in the space-time continuum that it will create will head off to infinity. Even in this extreme case space will have some value of curvature at any distance away from this speck of dust "
Okay, I follow your idea abut how even a speck of dust will distort SpaceTime. I would expect that to be true too, to some infinitesimal degree. But from there to saying that it is the reason? For gravity being instantaneous? Do you mean that all objects of invariant mass carry its own 'distortions' with them and that inertia would act in those?
Or how do you see it, as if gravity would be a constant field created by invariant mass maybe, a spiders web? That's one analogy I like to use :)
There have been observations describing gravitational waves propagating when observing binary stars if I remember right so I think Einsteins idea of it taking 'time' to build is correct. the thing left is to explain why it creates a net, instantly reacting to inertia. That's what the Higg's particle (God particle:) try to do, but I I'm not sure if there is needed to be any particles?
And you seem to share that idea, even though I'm not sure how you see it?
I will elaborate further on the points I made in early September 2012
This gives you plenty of time to show how some Mathematical assumptions are referred to as axioms - the elite immutable constructs that may well trun out to be mere illusions
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Pardon me. I must have stepped into the wrong room. I didn't realize this was the carping and moaning thread.
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"As viewed from the Earth’s frame, light from the Sun has aberration. Light requires about 8.3 minutes to arrive from the Sun, during which time the Sun seems to move through an angle of 20 arc seconds. The arriving sunlight shows us where the Sun was 8.3 minutes ago. The true, instantaneous position of the Sun is about 20 arc seconds east of its visible position, and we will see the Sun in its true present position about 8.3 minutes into the future."
Surely this is evidence for gravity travelling faster than light only if gravity is regarded as a force, which GR says it is not. If gravity is a distortion of spacetime, then the distortion which holds the Earth in orbit around the sun is already in place, and has been since the sun formed. Any change, e.g. if the sun suddenly vanished, would, presumably, take 8.3 mins to reach Earth, but there is no comparison between light which is constantly travelling, and gravity which, according to GR, remains "in place".
OK, that's a non-scientist's interpretation, and could well be wrong, but it seem to me to make sense. [:P]
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If gravitational propagation were instantaneous, then it would allow you to send FTL signals by moving a large mass back and forth and measuring the change in apparent gravitational strength from some distant sensor...
Doesn't make sense to say it's instantaneous.
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If gravity is a distortion of spacetime, then the distortion which holds the Earth in orbit around the sun is already in place, and has been since the sun formed.
Yes,
I think I mentioned that too.
However, my question was that while you have a stable earth-sun frame of reference. The sun is actually orbiting around the Milky Way (which is also moving through space).
However, should one expect this "speed" to be slightly variable.
So, on the forward side of the movement, the speed of gravity would be measurably slower than the trailing side of the sun's orbit?
If the speed of gravity was equal to the speed of light, perhaps the difference could be measured.
If the speed was 1010c, then it may not be significant.
I suppose I still have troubles imagining if this really would be measuring the speed of propagation of gravity, or perhaps something else like bow shock.
A gravitational drag on 2 parallel bodies (or two next to each other in an orbit) seems like a better way to calculate the speed of gravity as mentioned above with the diagram.
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If the force of gravity propagates faster than light how could we explain General Relativity that says that acceleration and gravity act the same way??? The maximum of the speed of light is the limiting factor of speed and acceleration which creates Relativity...
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Pardon me. I must have stepped into the wrong room. I didn't realize this was the carping and moaning thread.
No sensual moments in here - you must be mistaken
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You misunderstand. I said carping.
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If gravitational propagation were instantaneous, then it would allow you to send FTL signals by moving a large mass back and forth and measuring the change in apparent gravitational strength from some distant sensor...
Doesn't make sense to say it's instantaneous.
.....and yet instantaneous action at a distance (entanglement) is an intergral part of Quantum Phsyics. The EPR paradox was propoased by EInstein, Podolski and Rosen decades ago in order to challenge the entanglement principle and yet it still failed to expose it as false.
The experiments of Faldern show that the speed at which gravity propagates is AT LEAST 20,000,000,000 times greater than the speed of light. This experimental conculsion does not however dismiss the possibility of gravity propagating at an infinite speed - ie instantaneously
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You misunderstand. I said carping.
You misunderstand - I was referring to the moaning
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I think the argument boils down as to which is right, Einstein with his rubber sheets or QED with its Gravitons.
The idea of instant communication as put foward by Supercryptid via gravity waves would certainly work but the problem would be generating sufficient power to get a decent S/N ratio at the receiver
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I think the argument boils down as to which is right, Einstein with his rubber sheets or QED with its Gravitons.
The idea of instant communication as put foward by Supercryptid via gravity waves would certainly work but the problem would be generating sufficient power to get a decent S/N ratio at the receiver
The so called argument that you describe between the Qauntum world and the large scale world and gravity hasnt been resolved yet.
The Theory of Everything as its called is supposed to merge the large scale with the micro world (ie gravity with Quantum mechanics)
So its not really a choice between QED and General Relativity.
Its likely that both will be superceded with a theory that can tackle the whole scale spectrum.
At the moment String Theory is main candidate but as ST stands at the moment it is really just a mathematical philosophy (there is not single scrap of experimental eveidence to support ST sadly - so its in the RELIGION basket still - a lot of faith needed)
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the speed of light is only constant in a vacuum. even gravity affects the relative "speed" of light. as photons cannot achieve escape velocity in deep gravitational wells. gravitons on the other hand are not in any way hindered.
if photons can be captured and gravitons cannot, can we assume that gravity can and does travel faster than light?
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if photons can be captured and gravitons cannot, can we assume that gravity can and does travel faster than light?
Have I got this right: the graviton is a hypothetical particle, which might mediate the force of gravity, which is not really a force?
This force, that is not a force, might propagate at the speed of light, or 20,000,000,000 times faster, or perhaps instantaneously.
Then again, as CliffordK mentioned, it could be just a distortion of spacetime.
Surely it couldn't be that Mark McCutcheon is right and gravity is just an illusion brought about by the fact that everything in the Universe is expanding!
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Surely it couldn't be that Mark McCutcheon is right and gravity is just an illusion brought about by the fact that everything in the Universe is expanding!
He isn't.
And stop calling me Shirley!
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if photons can be captured and gravitons cannot, can we assume that gravity can and does travel faster than light?
Have I got this right: the graviton is a hypothetical particle, which might mediate the force of gravity, which is not really a force?
This force, that is not a force, might propagate at the speed of light, or 20,000,000,000 times faster, or perhaps instantaneously.
Then again, as CliffordK mentioned, it could be just a distortion of spacetime.
Surely it couldn't be that Mark McCutcheon is right and gravity is just an illusion brought about by the fact that everything in the Universe is expanding!
The gravitational attraction would be a hypothetical particle which mediates gravity and travels at lightspeed. As I stated The deAlembertian, a four dimensional wave equation will be represented as ▼. Not usual notation but box notation cannot be used here.
▼hμν=0
This is the same as saying
∂μ∂μhμν=0
This means it will follow the speed of light since ▼∂t2 - c2∂2x.
Saying the particle might be a distortion is an oxymoron by the way. By definition, particles are fluctuations in spacetime which are completely analogous to saying particles are distortions of spacetime itself.
But Mark is not right, and gravity is no illusion. It's a real force, more correctly said a psuedoforce, and may very well not require a graviton.
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It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy. Perhaps the idea that it is a pseudoforce might be a way round at least some of this. I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true." would this be your definition?
When is a force not a force? [;D]
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It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy. Perhaps the idea that it is a pseudoforce might be a way round at least some of this. I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true." would this be your definition?
When is a force not a force? [;D]
I have a similar difficulty, but I think it goes something like this:
The Earth seeems to be orbiting the Sun, but it isn't. It's really following a straight path through spacetime, so no force is required.
It strikes me that it's a bit "iffy" to talk about spacetime being curved (the old rubber sheet model), because if it is curved, that means there is a force being exerted on the Earth to keep it on its "tracks", so to speak, in which case the "non-force" argument sort of falls apart.
I'm confident that cleared things up a lot.
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It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy. Perhaps the idea that it is a pseudoforce might be a way round at least some of this. I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true." would this be your definition?
When is a force not a force? [;D]
Electricity is not a force either - and Magnetism
They are phenomena that can induce forces or effects upon other bodies
Gravity in the Relativity sense, is simply a distortion of space (time) by matter.
Its this curvature of space that can induce a force upon a body.
Semantics I suppose
Magnetism, Magnetic fields, Magnetic FORCE
Gravity, Gravitational fields, Gravitational FORCE
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Electricity is not a force either - and Magnetism
They are phenomena that can induce forces or effects upon other bodies
Foolosophy,
Pardon me, but you appear to be waffling. Whoever said that electricity and magnetism are forces?
Not only that, but if the curvature of spacetime exerts a force, then gravity exerts a real force. If gravity does not exert any real force on a body, then spacetime cannot be curved. And, if it is not curved, we better come up with a better explanation for how gravity actually works.
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Electricity is not a force either - and Magnetism
They are phenomena that can induce forces or effects upon other bodies
Foolosophy,
Pardon me, but you appear to be waffling. Whoever said that electricity and magnetism are forces?
Not only that, but if the curvature of spacetime exerts a force, then gravity exerts a real force. If gravity does not exert any real force on a body, then spacetime cannot be curved. And, if it is not curved, we better come up with a better explanation for how gravity actually works.
I certainly didnt say that - just highlighting the semantics involved in becoming confused as to whether gravity is a force.
Gravity is an end product of the curvature of space-time (on current theory)
The gravitational force experienced by a body is a direct result of there being a gravitational potential or field acting upon it.
Its all about terminology and semantics.
Magnetism is not a force, but a magnetic potential or field exerts a magnetic force (on a point charge for example).
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It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy. Perhaps the idea that it is a pseudoforce might be a way round at least some of this. I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true." would this be your definition?
When is a force not a force? [;D]
There are perhaps, many types of forces, so when stating ''when is a force not a force'' maybe an erreneous statement. More like ''when is a particular force not another force''.
For instance, do you accept the Coriolis effect is a force by definition? If so - the gravitational mechanism for it is identical to gravitation in the laws of motion we would find in GR. Both are by definition, psuedoforces.
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It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy. Perhaps the idea that it is a pseudoforce might be a way round at least some of this. I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true." would this be your definition?
When is a force not a force? [;D]
There are perhaps, many types of forces, so when stating ''when is a force not a force'' maybe an erreneous statement. More like ''when is a particular force not another force''.
For instance, do you accept the Coriolis effect is a force by definition? If so - the gravitational mechanism for it is identical to gravitation in the laws of motion we would find in GR. Both are by definition, psuedoforces.
....and so according to that rationale, the reaction to gravity is also fake?
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It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy. Perhaps the idea that it is a pseudoforce might be a way round at least some of this. I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true." would this be your definition?
When is a force not a force? [;D]
There are perhaps, many types of forces, so when stating ''when is a force not a force'' maybe an erreneous statement. More like ''when is a particular force not another force''.
For instance, do you accept the Coriolis effect is a force by definition? If so - the gravitational mechanism for it is identical to gravitation in the laws of motion we would find in GR. Both are by definition, psuedoforces.
....and so according to that rationale, the reaction to gravity is also fake?
It's not exactly fake, because psuedoforces have real effects in the world. They are real, just by standard definition a different type of force, or if you like, a different way to view a force.
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Electricity is not a force either - and Magnetism
They are phenomena that can induce forces or effects upon other bodies
Foolosophy,
Pardon me, but you appear to be waffling. Whoever said that electricity and magnetism are forces?
Not only that, but if the curvature of spacetime exerts a force, then gravity exerts a real force. If gravity does not exert any real force on a body, then spacetime cannot be curved. And, if it is not curved, we better come up with a better explanation for how gravity actually works.
Well here's part of the problem. I assume we all agree on what classical forces are. In Newtonian mechanics (and including E&M), fundamental forces are actions-at-a-distance which cause acceleration according to F=ma. If you replace Newtonian mechanics with another model, you give up this idea of forces.
With general relativity, you basically keep the idea of the electromagnetic force being action at a distance, but replace the idea of gravity as a similar action with gravity as a change in geometry of space-time. Acceleration due to gravity is then modeled as motion along geodesics (the equivalent of straight lines). Would you still call that a force since it's modeled differently from electromagnetic force?
If you go to QM, then forces are described differently again--as exchanges of particles. But now you have a description of three fundamental forces in terms of particles, while gravity is still modeled in terms of geometry. Is it still a force if it's described completely differently from other forces?
I think it just boils down to semantics, since we know perfectly well how the model of gravity differs from the other forces in GR. If you call gravity a force, you're kind of lumping it together with the other forces, when it causes motion through completely a different model. If you don't call it a force, then you're left with the oddity that in the Newtonian description, it is a force, and causes motion just like any other force--so why is it unique?
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....String Theorists also define and describe "forces" in a different way
So the truth is where exactly?
It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.
I think I will reserve my judgement until a deterministic theory surfaces that can describe the atomic and sub-atomic world. (most likey NOT in my lifetime)
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It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.
Why not?
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It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.
Why not?
,,,the fundamentals of QED are based upon the admission of "error" - that's why ridiculous counter intuitive conclusions are spawned. (the fact that QED has great predictive accuracy and is a useful mathematical tool is not relevant)
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It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.
Why not?
,,,the fundamentals of QED are based upon the admission of "error" - that's why ridiculous counter intuitive conclusions are spawned. (the fact that QED has great predictive accuracy and is a useful mathematical tool is not relevant)
How is it founded upon the admission of "errors"? Can you give specific examples? (I'm not saying you're wrong here--there are reasons not to think that QED is the full story, but these claims seem a bit strong from what I know of it.)
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It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.
Why not?
,,,the fundamentals of QED are based upon the admission of "error" - that's why ridiculous counter intuitive conclusions are spawned. (the fact that QED has great predictive accuracy and is a useful mathematical tool is not relevant)
How is it founded upon the admission of "errors"? Can you give specific examples? (I'm not saying you're wrong here--there are reasons not to think that QED is the full story, but these claims seem a bit strong from what I know of it.)
Stochastic methods are based on the quantification of errors
Thats what the statistical nature of QED is founded upon
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It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.
Why not?
,,,the fundamentals of QED are based upon the admission of "error" - that's why ridiculous counter intuitive conclusions are spawned. (the fact that QED has great predictive accuracy and is a useful mathematical tool is not relevant)
How is it founded upon the admission of "errors"? Can you give specific examples? (I'm not saying you're wrong here--there are reasons not to think that QED is the full story, but these claims seem a bit strong from what I know of it.)
Stochastic methods are based on the quantification of errors
Thats what the statistical nature of QED is founded upon
Ah. That's the problem. It isn't based on quantifying errors. It's built on probability from the ground up, not on quantifying errors.
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It isn't based on quantifying errors. It's built on probability from the ground up, not on quantifying errors.
If it was based on errors, I'm sure I could make a fortune in Vegas (until they realized I'd cracked the system of course.)
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We seem to have wandered some way from the OP, so let's not spoil the fun by getting back on track. [;)]
One (almost on track) question that comes to mind is: if gravity is a distortion of spacetime, is energy expended in maintaining that distortion?
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We seem to have wandered some way from the OP, so let's not spoil the fun by getting back on track. [;)]
One (almost on track) question that comes to mind is: if gravity is a distortion of spacetime, is energy expended in maintaining that distortion?
If I understand your question, I do not believe energy or matter is physically expanded, only the space between particles expand.
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Oh dear... i read expended as ''expanded''.
Forgive me, I don't have my glasses with me.
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If I understand your question, I do not believe energy or matter is physically expanded, only the space between particles expand.
I believe Bill really did mean expended - as in "used up".
I would not think so Bill. If it was, where would the energy be coming from, and would it not tend to run out from time to time, in which case things might tend to "fly off the handle" and zoom off into outer space. I think we've got enough problems without having to worry about that scenario as well.
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Yeah, I said in the post afterwards I seem to have made a critical reading error :)
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My view is that forces is perfectly applicable. It's what we see after all, although when trying to define what's behind our perception of forces, then we may need to find new descriptions. We use what we find useful, don't we:) Like horsepower, not joule. so I agree with you all :) Heh ::))
When you discuss stochastic methods Foolosophy, can you give an example of how you think there? what I find questionable is not that some things are found to be undefinable, I expect much of what we find in QM to create a new way of seeing, and with it new ways to look at 'indeterminacy'. Although if it was the way we use 'renormalization' I see what you mean.
We use them where wee need a 'cut off' to make that equation give us a definite answer, don't we? So in that motto it's not the perfect tool, but it works, and it's also open for redefinition if we find better 'limits' as I see it.
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I would not think so Bill. If it was, where would the energy be coming from, and would it not tend to run out from time to time,
What you, and numerous P S authors, seem to be saying is:
1. The presence of mass (ignore energy for the moment) causes a distortion of spacetime over an unbounded distance.
2. If the mass were suddenly removed, spacetime would revert to its undistorted state.
3. Causing and maintaining this distortion, in spite of spacetime's natural tendency to resist it, requires no energy.
If the Universe is not the ultimate "free meal", could this be?
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Pretty much. Of course, a lot of energy had to go into the orbiting systems in the first place, so it's not as if there really is a free lunch. All gravity (or distorted spacetime etc etc) does is provides a force, or a pseudo force or some other name of your own choosing, that captures the kinetic energy of the orbiting system so that it operates like an exceedingly large flywheel.
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3. Causing and maintaining this distortion, in spite of spacetime's natural tendency to resist it, requires no energy.
This is where the rubber sheet analogy breaks down. A rubber sheet is naturally flat because there is a resistive force keeping it that way. To bend it, you need to provide a force to overcome this. Just putting something on the sheet isn't enough--you have to push it into the sheet with force to get the sheet to bend.
Space-time and gravity isn't like this. Just having mass there is enough to bend space-time. There is no additional force required to create or maintain the bending. To use a mechanical engineering term, things are in static equilibrium, so no additional energy is required to keep them this way.
Causing the distortion in the first place would require energy, but this is accounted for by mass-energy equivalence. The mass has energy associated with it, and it is this energy that accounts for creating the curvature in the first place.
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It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.
Why not?
,,,the fundamentals of QED are based upon the admission of "error" - that's why ridiculous counter intuitive conclusions are spawned. (the fact that QED has great predictive accuracy and is a useful mathematical tool is not relevant)
How is it founded upon the admission of "errors"? Can you give specific examples? (I'm not saying you're wrong here--there are reasons not to think that QED is the full story, but these claims seem a bit strong from what I know of it.)
Stochastic methods are based on the quantification of errors
Thats what the statistical nature of QED is founded upon
Ah. That's the problem. It isn't based on quantifying errors. It's built on probability from the ground up, not on quantifying errors.
QED is not a deterministic theory that is based on first principles
Quantum behaviour that is explained using probability is a temporary approach that offers non-sensical irrational approximations and estimates of what is really going on in the atomic and sub-atomic worlds
Although QED generates accurate predictions, its conclusions are insane and should not be taken literally.
QED is on its last legs. It will be superceded in the next 2 or 3 centuries by a deterministic theory that can be validated using first principles and basic logic and rationale
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Maybe you are right in a way Foolosophy. I read somewhere that the Eskimos had 2-300 word describing snow. that's what I expect to happen in QM too. We will find new descriptions that suddenly will make a new sense to us. But I expect us to need to modify what we call a 'linear' behavior to fit this new paradigm.
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Still, I don't see the beef you have with it. Do you accept Heisenberg uncertainty principle? Why? If you want to find a deterministic logic built on Newtonian principles you will have to refute it. Starting to think of it I'm sure I can find a lot examples like that. Indeterminacy as we see it Foolosophy is only as we see it. That's what the Feigenbaum constant tells me.
(Sorry, used the wrong name. Slept overlong, again, corrected now though:)
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2. If the mass were suddenly removed, spacetime would revert to its undistorted state.
Not sure this is a valid statement at all Bill. Even a gedanken needs to follow some rules - masses do not suddenly disappear. If one postulates a complete transfer to energy, then this energy will cause exactly the same distortion in spacetime as its corresponding mass did (although some it will then radiate away). With the conservation of energy there is just no way you can correctly ask/answer that question. If you change the rules to ask the question then you cannot use the rules to answer it.
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If the mass were suddenly removed, spacetime would revert to its undistorted state.
I read in a P S book (don't remember which one)an account of what the Earth would experience if the sun suddenly vanished. The author was not suggesting that this was a physical possibility, it was more in the nature of a thought experiment (OK,gedanken, if you will). My intention was simply to impute an elasticity to spacetime, not to suggest magical effects.
This is where the rubber sheet analogy breaks down. A rubber sheet is naturally flat because there is a resistive force keeping it that way. To bend it, you need to provide a force to overcome this.
I was trying to avoid the rubber sheet, but since you mention it, I agree that "To bend it, you need to provide a force". If I sit on a trampoline I cause an indentation, the "force" causing and maintaining this is gravity, but gravity is not a force and expends no energy. (?)
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“There is no additional force required to create or maintain the bending”……… “Causing the distortion in the first place would require energy”.
Is it me, or is there a contradiction here? [???]
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“There is no additional force required to create or maintain the bending”……… “Causing the distortion in the first place would require energy”.
Is it me, or is there a contradiction here? [???]
I don't see a contrdiction. For example, it required energy to put the Moon in orbit around the Earth (possibly as the result of a collision with another large object) but once the Moon began to orbit the Earth, regardless of the model you choose, no additional energy or force is required.
The graviational effect is similar to a piece of string that connects the two objects.
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Let's focus in a little.
"no additional force required to create...the bending"
"Causing the distortion in the first place would require energy"
Still no contradiction? It's late at night, I might not be thinking straight. [:P]
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My point was this:
You need to put a mass there to create the bending initially. E=mc2, so that matter is energy. Therefore you need energy to create the bending. But that mass is all the energy you need (if we assume you somehow created the mass from energy at that point, so you didn't need to push it there).
Once the mass is there no further energy needs to be put in and the bending will stay forever.