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Also is EP a Lorentz symmetry or Poincare symmetry or what symmetry does EP fall under and why is that?

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Also is EP a Lorentz symmetry or Poincare symmetry or what symmetry does EP fall under and why is that?

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In the

Something like the equivalence principle emerged in the late 16th and early 17th centuries, when

The equivalence principle was properly introduced by Albert Einstein in 1907, when he observed that the acceleration of bodies towards the center of the Earth at a rate of 1

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So Phinds. The consequence of it is the iron and cotton falling at same time. If this is not exactly called EP. Then what term do you use to describe it?

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Simon Bridge

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The Einstein equivalence principle is how come you feel heavier when riding an accelerating lift upwards... just as if you were under higher gravity.

The equal independence of gravity on the mass of an object was famously verified experimentally by Galileo.

Galileo made his own equipment and so should you - it's not expensive or difficult.

So make a hollow ball that you can put weights in and time how long it take to fall with different weights... or look up how Galileo did it.

The short answer to your question is that there is no commercially available test rig for what you are asking because the equipment is universally available and cheap.

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An easier test would be to construct two pendulums (i.e., tie two things to pieces of string). Make the string lengths equal but let the weights at the bottom have different masses, or the same mass but different materials, or whatever. Time the period of each pendulum, or let them swing next to each other so you can visually compare their periods. If inertial mass is exactly proportional to gravitational mass, both pendulums should have the same period of oscillation.

Probably you want both weights to be relatively heavy to minimize the effects of air resistance and the weight of the string.

Newton wrote about performing such an experiment: http://www.mathpages.com/home/kmath582/kmath582.htm

Probably you want both weights to be relatively heavy to minimize the effects of air resistance and the weight of the string.

Newton wrote about performing such an experiment: http://www.mathpages.com/home/kmath582/kmath582.htm

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Simon Bridge

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To do this properly, you need Borda and Cassini's experiment... much more complicated than just dropping stuff or running weights down ramps.

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My impressions of the connection between the test and EP came from the so called Eotvos experiment in such (wiki):

The Einstein equivalence principle is how come you feel heavier when riding an accelerating lift upwards... just as if you were under higher gravity.

The equal independence of gravity on the mass of an object was famously verified experimentally by Galileo.

Galileo made his own equipment and so should you - it's not expensive or difficult.

So make a hollow ball that you can put weights in and time how long it take to fall with different weights... or look up how Galileo did it.

The short answer to your question is that there is no commercially available test rig for what you are asking because the equipment is universally available and cheap.

"The

But Simon. If the Equivalence Principle didn't occur in nature. The iron and cotton won't fall at same time, would it? so they are kinda related...

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Simon Bridge

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The words "the equivalence principle" has a special meaning in physics - it refers (usually) to the principle in general relativity where gravitation is equivalent to an accelerating reference frame. It is not usually understood to mean the equivalence between inertial and gravitational mass. Sometimes you do find lectures etc talking about the equivalence of inertial and gravitational mass as the *weak* equivalence principle. Notice that the passage you quoted is careful to distinguish them?

It is easy to see how someone could get confused.

That passage also points out that the modern understanding of gravitational effects, like how come gravitational and inertial mass are the same, is now understood in terms of the equivalence principle. It does not say that these experiments demonstrate the*Einstein* equivalence principle - which is what you [seemed to be saying] you wanted the apparatus to do.

(Note: the Eotvos experiment does not demonstrate that different masses fall in the same time.)

Of course the fall-time and the Einstein equivalence principle are*related* ... they are both about gravity.

But demonstrating the first does not demonstrate the second. Otherwise GR would have been invented much earlier.

I believe your question has been answered.

You can purchase commercial Borda Pendulum apparatus if you are keen - or construct two of them cheaply.

You can reproduce the Galileo experiments (ramps and balls, not leaning towers) cheaply.

The usual high-school demo is just to drop stuff off high places and time the fall.

There are other cheaper experiments you can do.

It is easy to see how someone could get confused.

That passage also points out that the modern understanding of gravitational effects, like how come gravitational and inertial mass are the same, is now understood in terms of the equivalence principle. It does not say that these experiments demonstrate the

(Note: the Eotvos experiment does not demonstrate that different masses fall in the same time.)

Of course the fall-time and the Einstein equivalence principle are

But demonstrating the first does not demonstrate the second. Otherwise GR would have been invented much earlier.

I believe your question has been answered.

You can purchase commercial Borda Pendulum apparatus if you are keen - or construct two of them cheaply.

You can reproduce the Galileo experiments (ramps and balls, not leaning towers) cheaply.

The usual high-school demo is just to drop stuff off high places and time the fall.

There are other cheaper experiments you can do.

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NASA sent a "test kit" to the Moon and verified that objects of very different masses (a feather and a hammer) fall at the same rate there; you can watch the video here:Would there be a commercially available test kit

http://science.nasa.gov/science-news/science-at-nasa/2007/18may_equivalenceprinciple/

Note that NASA attributes this to the "equivalence principle", illustrating (as has already been remarked on in this thread) that that term has several different possible meanings. Whether you call it that or not, though, this NASA experiment tests what you said you wanted to test in the OP.

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Simon Bridge

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MIT has a setup too:

http://video.mit.edu/watch/feather-and-coin-in-a-vacuum-6407/

... again, all the apparatus is commercially available but I don't think they are sold as kits - but by the look of the one in the vid, maybe.

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Good point. :DAlthough the NASA test kit (hammer and feather) are commercially available (purchase separately), the lab-space may be difficult to access without some more substantial financial outlay.

Cool, I hadn't realized they had this.MIT has a setup too

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Simon Bridge

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Thanks. I learnt the distinction between the weak EP and the Einstein EP.. but there is a third one called the Strong EP.. Wiki defined or differentiates them as:The words "the equivalence principle" has a special meaning in physics - it refers (usually) to the principle in general relativity where gravitation is equivalent to an accelerating reference frame. It is not usually understood to mean the equivalence between inertial and gravitational mass. Sometimes you do find lectures etc talking about the equivalence of inertial and gravitational mass as theweakequivalence principle. Notice that the passage you quoted is careful to distinguish them?

It is easy to see how someone could get confused.

That passage also points out that the modern understanding of gravitational effects, like how come gravitational and inertial mass are the same, is now understood in terms of the equivalence principle. It does not say that these experiments demonstrate theEinsteinequivalence principle - which is what you [seemed to be saying] you wanted the apparatus to do.

(Note: the Eotvos experiment does not demonstrate that different masses fall in the same time.)

Of course the fall-time and the Einstein equivalence principle arerelated... they are both about gravity.

But demonstrating the first does not demonstrate the second. Otherwise GR would have been invented much earlier.

I believe your question has been answered.

You can purchase commercial Borda Pendulum apparatus if you are keen - or construct two of them cheaply.

You can reproduce the Galileo experiments (ramps and balls, not leaning towers) cheaply.

The usual high-school demo is just to drop stuff off high places and time the fall.

There are other cheaper experiments you can do.

Einstein EP

The outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity of the laboratory and its location in spacetime.

Strong EP

The difference between the above is the word "non-gravitational" in the former and "gravitational or not" in the latter meaning the latter is valid to all wheras the former is only valid to non-gravitational.

What does it really mean?

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Vanadium 50

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Universality of free fall.The same time-to-fall for iron or cotton, afaik, has no formal name - it just is itself.

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Simon Bridge

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Wikipedia is not a recommended source.

You've probably seen the discussion:

http://en.wikipedia.org/wiki/Equivalence_principle

- notice there is a "cleanup needed" notice on this article. The "weak" section, in particular, seems to mix up bits of each of the other sections.

I think the wikipedia article is trying to distinguish the case where gravity is treated an extra force (so it needs a special rule to cope) vs being an effect of geometry (which dosn't) but it is difficult to be sure. Look elsewhere for clarification.

Also have a look at:

http://www.mathpages.com/home/kmath629/kmath629.htm

... takes a historical perspective, points out that the definitions change with time and context. It's more consistent than Wikipedia.

Cultural history perspective, closer examination:

http://einstein.stanford.edu/STEP/information/data/gravityhist2.html

An example of an introductory lesson on the same:

https://briankoberlein.com/2013/09/07/equivalent-principles/

TLDR: http://www.reference.com/browse/equivalence+principle [Broken]

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/grel.html

@Vanadium50: thanks, I just found that out in the histories above.

That's the neat thing about answering these sorts of questions...

You've probably seen the discussion:

http://en.wikipedia.org/wiki/Equivalence_principle

- notice there is a "cleanup needed" notice on this article. The "weak" section, in particular, seems to mix up bits of each of the other sections.

I think the wikipedia article is trying to distinguish the case where gravity is treated an extra force (so it needs a special rule to cope) vs being an effect of geometry (which dosn't) but it is difficult to be sure. Look elsewhere for clarification.

Also have a look at:

http://www.mathpages.com/home/kmath629/kmath629.htm

... takes a historical perspective, points out that the definitions change with time and context. It's more consistent than Wikipedia.

Cultural history perspective, closer examination:

http://einstein.stanford.edu/STEP/information/data/gravityhist2.html

An example of an introductory lesson on the same:

https://briankoberlein.com/2013/09/07/equivalent-principles/

TLDR: http://www.reference.com/browse/equivalence+principle [Broken]

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/grel.html

@Vanadium50: thanks, I just found that out in the histories above.

That's the neat thing about answering these sorts of questions...

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Thanks for the references above. They have alternatives ideas of gravitons instead of geometry as cause of gravity. But the iron ball should have more gravitons interchange with earth versus the cotton and yet they are attracted to earth the same degree. Why do they fall together at same time in the theory of the gravitons? Do you know what are these people reasonings?Wikipedia is not a recommended source.

You've probably seen the discussion:

http://en.wikipedia.org/wiki/Equivalence_principle

- notice there is a "cleanup needed" notice on this article. The "weak" section, in particular, seems to mix up bits of each of the other sections.

I think the wikipedia article is trying to distinguish the case where gravity is treated an extra force (so it needs a special rule to cope) vs being an effect of geometry (which dosn't) but it is difficult to be sure. Look elsewhere for clarification.

Also have a look at:

http://www.mathpages.com/home/kmath629/kmath629.htm

... takes a historical perspective, points out that the definitions change with time and context. It's more consistent than Wikipedia.

Cultural history perspective, closer examination:

http://einstein.stanford.edu/STEP/information/data/gravityhist2.html

An example of an introductory lesson on the same:

https://briankoberlein.com/2013/09/07/equivalent-principles/

TLDR: http://www.reference.com/browse/equivalence+principle [Broken]

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/grel.html

@Vanadium50: thanks, I just found that out in the histories above.

That's the neat thing about answering these sorts of questions...

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Vanadium 50

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B. This "graviton theory" of yours is not the graviton theory of everybody else. I don't know where you got these ideas, but they are totally wrong.

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I wrote this thread because I'm interested in violations of Lorentz invariance CPT, EP and there are many tests that search for them. I originally

B. This "graviton theory" of yours is not the graviton theory of everybody else. I don't know where you got these ideas, but they are totally wrong.

saw this:

http://www.physics.indiana.edu/~kostelec/faq.html

I thought Equivalence Principle violation is part of Lorentz violations. What kind of spacetime symmetry does EP fall under.. is it Lorentz symmetry? Whatever. I read Lorentz violation is related to search for gravitons. And Im trying to understand how it is related to gravitons. If we have gravitons.. does it mean the geometry is not needed anymore? and gravitons artificaly created the geometry in the computations? In wiki:

"In physics, the

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A.T.

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And in an accelerating reference frame, all free falling object experience the same coordinate acceleration, which is exactly what the drop experiment demonstrates.The words "the equivalence principle" has a special meaning in physics - it refers (usually) to the principle in general relativity where gravitation is equivalent to an accelerating reference frame.

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Vanadium 50

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I know that. What I don't know is where you got your statements in #16 from.In physics, thegravitonis a hypotheticalelementary particlethat mediates the force ofgravitationin the framework ofquantum field theory.

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An airplane and cotton falls at same rate to earth. If gravity is caused by attraction between particles.. there are more particles in the airplane than the cotton so the airplane should attract the earth more. I guess this attraction is not what graviton is. I'm reading all archives now about gravitons in this forum. It seems some theorize them as just quanta of the gravitational waves. Meaning without gravitational wave, there are no gravitons. Since the airplane falling to earth doesn't produce gravitatational waves, there is no graviton exchange between the earth and the airplane.I know that. What I don't know is where you got your statements in #16 from.

Whatever, since gravity is not a force, why call it a fundamental force... we should have 3 fundamental forces only..

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Yes, I would definitely suggest that you continue your reading. These things will be cleared up better that way than by some brief comments on an internet forum.An airplane and cotton falls at same rate to earth. If gravity is caused by attraction between particles.. there are more particles in the airplane than the cotton so the airplane should attract the earth more. I guess this attraction is not what graviton is. I'm reading all archives now about gravitons in this forum. It seems some theorize them as just quanta of the gravitational waves. Meaning without gravitational wave, there are no gravitons. Since the airplane falling to earth doesn't produce gravitatational waves, there is no graviton exchange between the earth and the airplane.

Whatever, since gravity is not a force, why call it a fundamental force... we should have 3 fundamental forces only..

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Ok. Going back to the Equivalence Principle.. so the airplane and cotton falling at same rate in vacuum is called the Weak Equivalance Principle (so calling it an EP is not far off at all). But then it is not so strange at all. Larger object has more inertia, larger object has greater amount of quantum fields.. so there should naturally be more resistance in the vacuum producing inertia.. this means the airplane and cotton could fall at same rate due to the cotton having much lighter inertia. Don't you think so?Yes, I would definitely suggest that you continue your reading. These things will be cleared up better that way than by some brief comments on an internet forum.

Anyway. If we need to be forced to think Gravity is geometry and the airplane and cotton fall at same rate because they are in geodesic path in curved spacetime.. in other words, time is why the airplane falls down.. but in the Wheeler-Dewitt Equation, time is zero. So how could the geodesic thing occur when time is zero?

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It does; the force between the airplane and the Earth is larger than the force between the cotton and the Earth. But there are also more particles in the airplane, so it has more inertia and therefore accelerates less in response to a given force. The two effects exactly cancel out; that's what experiments like the Eotvos experiment are verifying. When people talk about inertial mass being equal to gravitational mass, that's what they're talking about.If gravity is caused by attraction between particles.. there are more particles in the airplane than the cotton so the airplane should attract the earth more.

The graviton is the (hypothesized) particle associated with the quantum aspects of gravity. But gravity is so weak as an interaction that we have no prospect of measuring quantum aspects of it any time soon.I guess this attraction is not what graviton is.

That's one aspect of them, yes; gravitational waves are fluctuations in spacetime curvature, and the quantum aspects of those fluctuations are one kind of graviton. But not the only kind; see below.It seems some theorize them as just quanta of the gravitational waves.

This is not correct. The interaction between the Earth and the airplane involves virtual gravitons, just as any quantum interaction that appears as a static force involves virtual particles. (At least, that's what the best model we have of gravitons as the quantum aspect of gravity predicts. As I said above, we aren't going to be able to experimentally test any of this any time soon.)Since the airplane falling to earth doesn't produce gravitatational waves, there is no graviton exchange between the earth and the airplane.

From a quantum field theory point of view, gravity is an interaction like the others. (Note that I used the word "interaction", not "force"; it's a better word because it's more general. Not all aspects of the fundamental interactions appear as what we usually think of as a "force".)since gravity is not a force, why call it a fundamental force... we should have 3 fundamental forces only..

Oh, definitely. See above. This is not a new idea. (Except for the part about "greater amount of quantum fields", which I don't understand.)Larger object has more inertia, larger object has greater amount of quantum fields.. so there should naturally be more resistance in the vacuum producing inertia.. this means the airplane and cotton could fall at same rate due to the cotton having much lighter inertia. Don't you think so?

This is not inconsistent with viewing gravity as an interaction. It's just a different model. Both models are applicable within their domains of validity. From a quantum field theory point of view, the reason gravity can be viewed at the classical level as geometry is that the quantum interaction mediated by the graviton has certain properties (in particular, it couples to all mass-energy and has spin 2).If we need to be forced to think Gravity is geometry and the airplane and cotton fall at same rate because they are in geodesic path in curved spacetime..

I don't see how you get this from what you said in your previous sentence.in other words, time is why the airplane falls down

I think you are misunderstanding the Wheeler-DeWitt equation. I also think you need to get a better grounding in the basics before you tackle something as advanced as the Wheeler-DeWitt equation.in the Wheeler-Dewitt Equation, time is zero

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Hi, I've been reading the archives here on all gravitons entry for long time and there are many interesting ones. But there is one where I don't know the meaning of the acronym. It's in the thread "Why are we looking for graviton particles". What does "d.o.f" mean? depth of field? tom.stoer wrote:It does; the force between the airplane and the Earth is larger than the force between the cotton and the Earth. But there are also more particles in the airplane, so it has more inertia and therefore accelerates less in response to a given force. The two effects exactly cancel out; that's what experiments like the Eotvos experiment are verifying. When people talk about inertial mass being equal to gravitational mass, that's what they're talking about.

The graviton is the (hypothesized) particle associated with the quantum aspects of gravity. But gravity is so weak as an interaction that we have no prospect of measuring quantum aspects of it any time soon.

That's one aspect of them, yes; gravitational waves are fluctuations in spacetime curvature, and the quantum aspects of those fluctuations are one kind of graviton. But not the only kind; see below.

This is not correct. The interaction between the Earth and the airplane involves virtual gravitons, just as any quantum interaction that appears as a static force involves virtual particles. (At least, that's what the best model we have of gravitons as the quantum aspect of gravity predicts. As I said above, we aren't going to be able to experimentally test any of this any time soon.)

From a quantum field theory point of view, gravity is an interaction like the others. (Note that I used the word "interaction", not "force"; it's a better word because it's more general. Not all aspects of the fundamental interactions appear as what we usually think of as a "force".)

Oh, definitely. See above. This is not a new idea. (Except for the part about "greater amount of quantum fields", which I don't understand.)

This is not inconsistent with viewing gravity as an interaction. It's just a different model. Both models are applicable within their domains of validity. From a quantum field theory point of view, the reason gravity can be viewed at the classical level as geometry is that the quantum interaction mediated by the graviton has certain properties (in particular, it couples to all mass-energy and has spin 2).

I don't see how you get this from what you said in your previous sentence.

I think you are misunderstanding the Wheeler-DeWitt equation. I also think you need to get a better grounding in the basics before you tackle something as advanced as the Wheeler-DeWitt equation.

"The reason why gravitons may be a useful concept is rather simple: in the weak gravity regime with gravitational waves propagating on a background metric the theory looks similar to a field theory which would result in a quantum theory of a spin-2 particle.

However the are mathematical reasons why this picture does not apply in general: the graviton as fundamental d.o.f. derived for the weak gravity regime fails to provide a consistent quantization of gravity in the non-perturbative regime where quantum effects will become relevant. Therefore all theories of quantum gravity are based on diffent quantization schemes (e.g. LQG) where gravitons are no longer fundamental d.o.f. but derived concepts applicable in a certain approximation, or they are based on a different classical setup (supergravity, strings) where there is hope that the above mentioned difficulties do not apply and where gravitons could play a fundamental role (in string theory the graviton is just one special oscillation of the string)

But in practice the regimes where quantum gravity becomes important are not accessable experimentally! All current searches for gravitational waves are entirely classical and do not deal with gravitons."

Peterdonis. So gravity as purely geometry may just be a temporary thought to make. It's like Newtonian physics as effective field theory. In Newtonian, their spacetime is a stage where things move with respect to it and diffeomorphism invariance doesn't exist. Likewise gravity as purely geometry only and nothing more is also an effective field theory or temporary. And we must not think it is the final thing. It's like we shouldn't treat women as simply geometry (because of their curves), the stone age men may think such but we have complex biology now. I concluded this after reading the following gem by jtbell in the thread (do you also think geometry is just temporary)?

"Theories of quantum gravity (which include gravitons) assume that the "warping" will turn out

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