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Gravity - Acceleration Equivalence





Dennise
A. Einstein was a principle figure in the gravity - acceleration equivalence principle which was more or less proven during a solar eclipse. This is part of Einstein's general theory of relativity.

Does anyone know any experiment or theory that has determined gravity and acceleration are NOT equivalent?
Bikerman
Try:

F. J. M. Farley, J. Bailey, R. C. A. Brown, M. Giesch, H. J¨ostlein, S. van der Meer, E. Picasso and M. Tannenbaum, Nuovo Cimento 45, 281-286 (1966), "The anomolous magnetic moment of the negative muon"

Bailey, J., Borer, K., Combley, F., Drumm, H., Eck, C., Farley, F.J.M., Field, J.H., Flegel, W., Hattersley, P.M., Krienen, F., Lange, F., Lebée, G., McMillan, E., Petrucci, G., Picasso, E., Rúnolfsson, O., von Rüden, W., Williams, R.W., and Wojcicki, S., “Final report on the CERN muon storage ring including the anomalous magnetic moment and the electric dipole moment of the muon, and a direct test of relativistic time dilation”, Nucl. Phys. B, 150, 1-75, (1979).

Carey, R.M. et al., “New Measurement of the Anomalous Magnetic Moment of the Positive Muon”, Phys. Rev. Lett., 82, 1632-1635, (1999).
Dennise
Well with just two college physics courses in the 60s (I loved 'em both), papers Bikerman's suggested are a couple orders of magnitude over my head.

What seems to come out of those papers - and others - is the EP (Equivalence Principle) as written by Einstein may not apply in the quantum world or in tiny non warped space-time regions ... if I understand correctly.

Also, some feel doing macro experiments that take different interpretations of Einstein's words (e.g. lateral acceleration) clam to disprove his EP. But on the other hand, many sophisticated experiments done by physicists claim to support EP.

So, I guess the verdict depends on what papers one reads, who you talk to and whether one thinks about EP in the macro world or the quantum world.

Anyone else?
badai
didn't gravity is the cause and acceleration is the effect?
LxGoodies
Dennise wrote:
A. Einstein was a principle figure in the gravity - acceleration equivalence principle which was more or less proven during a solar eclipse. This is part of Einstein's general theory of relativity.

Does anyone know any experiment or theory that has determined gravity and acceleration are NOT equivalent?


Einstein had no idea of practical space travel. He assumed that the observer sits still and does nothing. In that case acceleration and (equivalent) gravity feel the same. Einstein even postulated that there exists no experiment that can show wether you are in a gravitation field or experiencing accelleration in a non-gravity environment (eg space)

I found a very funny experiment that can distinguish though,

ubavontuba on another forum wrote:

Here goes:

To accomplish my feat, I need some very specialized equipment.

I need a snifter of brandy (make it full to the brim) and myself.

Let's proceed:

Step 1. Drink half the brandy. "Ah... good stuff."

Step 2. Place brandy snifter on the floor, but to the side a bit.

Step 3. Begin leaping laterally (from side to side) in the room.

Step 4. Observe the brandy.

If the brandy sloshes, I am in a relatively low mass room and therefore must be accelerating, or at least be separated from the Earth (suspended). If sloshes, go to the next step. If not, then you are in a fixed room on a heavy mass. You are feeling gravity (end of experiment).

Step 5. Start leaping from side to side. Build up as much pendulum acceleration as you can (swing the room like a child on a swing). Stop. Does the room continue swaying normally? Then you are hanging over a heavy mass and are experiencing gravity. If it stops rather suddenly, or it has an unusual and increasing resonance, then you are accelerating (Oh no! It's gone out of control!). In the latter case, disaster is soon to follow.

You can qualify things by adding shock absorbers and whatnot to a suspended room or make the accelerating room's ship unusually massive, but this just defeats the spirit of the experiment and makes it so in that particular room it is hard to distinguish between gravity and acceleration. This wouldn't be applicable to a supposedly universal principal.


http://www.physicsforums.com/showthread.php?t=108809

.. of course, this may not be a sound way to prove Einstein wrong (6 pages of discussion follow Razz ) but it comes close ..

Lx
kelseymh
Dennise wrote:
A. Einstein was a principle figure in the gravity - acceleration equivalence principle which was more or less proven during a solar eclipse. This is part of Einstein's general theory of relativity.

Does anyone know any experiment or theory that has determined gravity and acceleration are NOT equivalent?


Gravity and uniform, linear acceleration are only equivalent in what is called a local rest frame, that is, a region which is "small" compared to the gravitational field you're dealing with. I put "small" in quotes because this is a qualitative statement, not quantitative: with sufficiently precise measurements, you can distnguish gravity from uniform acceleration over quite small distances.

The simplest way to distinguish them is to observe that all of the sources of gravity we deal with are effectively point sources, meaning that we observe gravity as a radial force which decreases with distance from the source. Uniform acceleration, by definition, doesn't depend on the observer's position in space.

So there are two ways, on the surface of the Earth, to tell that you aren't really inside a magic elevator Smile First, measure the acceleration due to gravity where you are now, then go up to the top of a tall building and do it again. If you're using a high-precision method, you'll see that the acceleration is lower at the top of the building (because you're farther from the center of the Earth). Second, hang two pendulums in such a way that you can observe them both at the same time. With sufficiently good measurements, you'll see that the strings aren't actually parallel, but converge ever so slightly downward, because the bobs are both being pulled along radii toward the center of the Earth.

None of that invalidates the equivalence principle. The latter is a mathematical statement about measurements made locally, which technically means at a single point. The principle has a multitude of consequences for observations throughout physics, many of which have been tested quite thoroughly so far.
Dennise
Quote:
None of that invalidates the equivalence principle. The latter is a mathematical statement about measurements made locally, which technically means at a single point. The principle has a multitude of consequences for observations throughout physics, many of which have been tested quite thoroughly so far.


So are you saying the Equivalence Principle does hold true for measurements made at a single point?
_AVG_
badai wrote:
didn't gravity is the cause and acceleration is the effect?


This holds in Newtonian mechanics when gravity is concerned a conservative force. In General Relativity however, mass and energy affect the curvature of spacetime so that remaining fixed in the presence of gravity and accelerating in free space seem equivalent to a local observer. The "lift" thought experiment is famous here. A ray of light appears bent for a lift accelerating through free space and for a lift stationary in a gravitational field.
kelseymh
Dennise wrote:
Quote:
None of that invalidates the equivalence principle. The latter is a mathematical statement about measurements made locally, which technically means at a single point. The principle has a multitude of consequences for observations throughout physics, many of which have been tested quite thoroughly so far.


So are you saying the Equivalence Principle does hold true for measurements made at a single point?


Yes. That's what "local" really boils down to in the statement of the principle. Of course, now it's up to you to figure out how to do it Smile
kelseymh
badai wrote:
didn't gravity is the cause and acceleration is the effect?


You're misunderstanding the equiavlence principle (or have never heard of it?).

Consider the following thought experiment (imaginary situation). You are in a small room (say, about the size of a closet) with no windows or openings, and with whatever measuring instruments you like. If you hold something in your hand, or hang it from a spring, you feel in pressing down. If you let go, it falls to the floor. If you shine a light beam across the room, you notice (with precise measurements) that the spot on the far wall is a little bit lower than it "should be".

What could be causing these effects? Remember, you have no way of looking "outside the room", so all you can do is hypothesize. Here are two possibilities:

1) The box you're in is an elevator, floating out in space. It is being pulled by a cable faster and faster, that is, with a constant acceleration. Naturally, if you let go of something under those conditions, it will "fall" to the back end (floor) of the box as the box accelerates forward ("upward") to meet it.

2) The box you're in a resting on the surface of a planet. Gravity from the planet, as usual, pulls everything downward to the floor.

What Einstein's equivalence principle says is that, provided the box is small enough, you cannot make measurements to distinguish (1) and (2). Being at rest in a gravitational field is locally equivalent to being in a uniformly accelerating reference frame.

As I noted in my long reply to Dennise, "small enough" depends on how precise your measuring instruments are. On Earth, you can compare the top vs. bottom of a skyscraper and discover that the accelerations in those places are different (hence, you're in a spatially varying gravitational field, not a uniformly accelerating box).
Dennise
Quote:
As I noted in my long reply to Dennise, "small enough" depends on how precise your measuring instruments are. On Earth, you can compare the top vs. bottom of a skyscraper and discover that the accelerations in those places are different (hence, you're in a spatially varying gravitational field, not a uniformly accelerating box).


I like that explanation best. Alternately, in the converging pendulum 'strings' experiment, the pendulums would have to be arbitrarily separated by a large horizontal distance to measure the string convergence consistent with the accuracy of the measuring equipment, right?

Interesting that the skyscraper experiment requires a large vertical separation, while the pendulum experiment needs a large horizontal separation. Is that just a cool coincidence?
kelseymh
Dennise wrote:
Quote:
As I noted in my long reply to Dennise, "small enough" depends on how precise your measuring instruments are. On Earth, you can compare the top vs. bottom of a skyscraper and discover that the accelerations in those places are different (hence, you're in a spatially varying gravitational field, not a uniformly accelerating box).


I like that explanation best. Alternately, in the converging pendulum 'strings' experiment, the pendulums would have to be arbitrarily separated by a large horizontal distance to measure the string convergence consistent with the accuracy of the measuring equipment, right?


Not arbitrarily large, just large enough that you can use your fancy surveying transit to see that the two strings are not parallel to one another.

Of course, in this experiment there's the added complication that the two masses would attract each other gravitationally, which would also lead to the strings being non-parallel! And the masses will be attracted in some other direction by nearby mass concentrations (building walls, mountains, whatever).

Actually doing the precision measurement involves some pretty careful calculations of all those different effects, in order to tease out the radial-gravity effect you're interested in.

Quote:
Interesting that the skyscraper experiment requires a large vertical separation,


It doesn't necessarily. I just gave that as an example you could readily understand. The most precise experiment of this kind actually involves measuring gravitational time-dilation as a function of altitude. A paper published last year reported a 10^-15 effect (perfectly consistent with general relativity) over a vertical difference of just 33 cm (about one foot)!

Quote:
while the pendulum experiment needs a large horizontal separation. Is that just a cool coincidence?


I don't think it's a coincidence, but rather a simple reflection of the precision of your apparatus. If you have relatively crude measurements, then you need a long baseline in order to observe a violation of the equivalence principle.
droshal
Matter and energy within a given point of space induce a warping of space through quantum-mechanical interactions, which in turn causes that region of space to accelerate. The acceleration of space itself is what produces the force of gravity, as space itself is what is moving massive objects towards each other as opposed to massive objects passively following the curvature of warped space-time as proposed by Albert Einstein. Particles of matter gain mass through their quantum-mechanical interactions with the Higgs field. By interacting with the Higgs field particles of matter slow down and dissipate their energies. The energy released through this interaction does not go to waste, but instead contributes to the acceleration or warping of the surrounding space. This is why more massive objects cause surrounding space to accelerate with greater magnitude and therefore generate more intense gravitational effects. Space is therefore a dynamical structure that plays a very active role in the emergence of gravity at the quantum level. Dark matter and dark energy warp or accelerate space in a different way from regular matter and energy. On the largest scales, the universe is expanding because space itself is accelerating (repulsive force due to dark matter and dark energy) and carrying everything in it with it. On the scale of stars, planets, and galaxies (regular matter) space is being told to accelerate in a different direction (attraction), and that is gravity. It seems that anti-gravity is predominating the universe as there is a lot more dark matter/energy than regular matter/energy. Space can therefore behave differently depending on what kind of matter and energy is in it.
kelseymh
droshal wrote:
Matter and energy within a given point of space induce a warping of space


Yup. So far so good...

Quote:
through quantum-mechanical interactions,


Nope! General relativity is a purely classical theory. Only the ill-informed resort to "quantum-mechanical" to explain things they don't understand.

Quote:
which in turn causes that region of space to accelerate.


Nope! Curved spacetime causes a test particle in that region to accelerate. The spacetime itself does not "accelerate;" indeed, such a statement is meaningless word salad.

Quote:
The acceleration of space itself is what produces the force of gravity,


Nope. The "force of gravity" is the gradient of the curvature induced by mass-energy density, as described by general relativity.

Quote:
as space itself is what is moving massive objects towards each other as opposed to massive objects passively following the curvature of warped space-time as proposed by Albert Einstein.


Ah! You're making up your own theory (okay, word salad) because you either don't like, or just don't understand, general relativity. Remaining nonsense left unquoted. Curious readers can go back to the original post.
Bikerman
I'm grateful to kelseymh for pointing out the nonsense above. He was far more gentle than I would have been - for which droshal will, no doubt, be grateful.
On the general point - please don't post personal crank 'theory' in the science forums because:
a) If it isn't peer-reviewed science then it cannot be presented here as such
b) There are enough scientifically literate (and, indeed, expert) readers to point out the idiocy of such dribblings.
kelseymh
Bikerman wrote:
I'm grateful to kelseymh for pointing out the nonsense above. He was far more gentle than I would have been - for which droshal will, no doubt, be grateful.
On the general point - please don't post personal crank 'theory' in the science forums because:
a) If it isn't peer-reviewed science then it cannot be presented here as such
b) There are enough scientifically literate (and, indeed, expert) readers to point out the idiocy of such dribblings.


By the way, "Droshal" posted the identical wall of world-salad text in Ethan Siegel's "Starts with a Bang" astrophysics blog (http://scienceblogs.com/startswithabang/) on the same day.
Bikerman
[MOD]
Ahh...thanks for that - appropriate action taken.
[/MOD]
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