Does the existance of relativity prove that gravity's wrong?

jefswat

I know I was just poking fun. Your concern is a good one. As someone else said, solving a problem just raises 2 more "whys"

D H

Both of these statements are in a sense wrong. Newton's equations are not so much wrong as they are inaccurate. They do an amazingly accurate job of predicting the orbits of the planets, even Mercury's orbit, over centuries. General relativity is a pretty small effect, even on Mercury. General relativity results in a small precession of Mercury's perihelion angle: 43 seconds of arc per century, or 3 million years per 360 degrees. The time scale on which general relativistic effects become apparent (unless you are looking for meter-level accuracy) is much, much greater than that for all but Mercury.

That 3 million years is about the same as the solar system's Lyapunov time. Beyond this time scale any predictions are pretty much garbage, even those with a full relativistic model.

Bob S

I think that general relativity proved that gravity is correct. Consider a Mossbauer effect experiment, with a Mossbauer source on top of a 100 foot tall tower, and the Mossbauer detector at the base of the tower (and vice versa). Experiments show that the photons gain energy (just like Newton's apple) while falling from the tower, so either the source or the detector has to be moved vertically to compensate for the energy gained by the photons. Harvard did this experiment using the Fe^57 source mounted on a loudspeaker coil.

Fredrik

A classical theory proved a phenomenon in the real world to be "correct", and the way to see that is to consider a quantum physics experiment?

The experiment you describe is interesting, and I appreciate that you posted it. I just couldn't let that first sentence slide

DaleSpam

In GR the source of gravity is not mass; it is the stress-energy tensor. The stress-energy tensor includes energy, momentum, pressure, and stress, all of which together "generate" gravity.

Bob S

In accelerators like the Fermilab Tevatron, where protons and antiprotons are accelerated to energies equal to 1000 rest masses, the Newtonian mechanics formula F = ma is still correct. Each revolution, RF cavities (where the electric fields provide the force) add a few thousand electron volts to the total proton energy, and the total energy keeps increasing. When particle velocities approach the speed of light and a no longer increases, the relativistic mass m (NOT the rest mass) increases instead. This is also true for the particle momentum p = mv, which approaches mc. It is also true for antimatter like antiprotons.

D H

You don't need to go so far as invoking general relativity to debunk nonsense such as this:
All it takes is observing that planets have moons, and that moons can have satellites of their own (e.g., the satellites we have on occasion put in orbit around our Moon). Think about it.

Coulomb's law and Newton's law of gravity are superficially similar in that both are inverse square laws. That the two laws have a difference in sign (like charges repel but masses attract), that mass has magnitude only but charge has sign and magnitude, and a largish conglomeration of mass is close to electrically neutral makes gravitation and electrostatics considerably different.


As noted by many, general relativity did not so much disprove Newtonian gravity so much as disprove that Newton's law of gravitation is universal. Newtonian gravity still has its place. There is no reason to use general relativity to model the motion of a satellite in low Earth orbit. Uncertainties in atmospheric drag, Earth's non-spherical nature, solid body tides, and even ocean tides vastly overwhelm the tiny error induced by ignoring general relativity.

Strictly speaking, all scientific theories are incorrect. We just don't know yet where some of them (e.g., general relativity) are "wrong". Looking for absolute correctness in a scientific theory is asking too much of science.

Al68

That's because they both assume Euclidean geometry. The inverse square law is a feature of Euclidean geometry. Is the radiation level from a radioactive source one and the same force as gravity, since they both follow the inverse square law? How about the noise level from a siren? How about the intensity of light from a lamp? Same thing as gravity because it follows the inverse square law?

DaleSpam

Thanks for being careful to emphasize that you were specifically talking about "relativistic mass", that avoids all sorts of confusion. The more common approach in modern physics is to say F = dp/dt and to say that p is a non-linear function of velocity which increases without bound as v approaches c and to use only the rest mass, but of course your approach works too.

Vanadium 50

Like Naty1 said, your original question was reasonable. Your post #7 is simplistic and silly. Your post #15 is completely contrary to the facts.

Gnosis

Your supposition that “electromagnetism” is the force responsible for pulling the book to the floor as “each and every atom is acted on by the electromagnetic field of the Earth” is fundamentally flawed and is easily dispelled. Here’s why…

The planet Mars has no global magnetic field (magnetosphere) and at best, it only has very isolated magnetic fields at various locations around the planet attributed to local iron concentrations. Even so, Mars manages to muster roughly 1/3 as much gravitational attraction as the Earth’s rate gravitational attraction regardless of an object’s orientation around its surface. How, in the complete absence of a global magnetic field, do objects free-fall to the Mars surface at the same rate regardless of their location?

The answer is evident. Objects are attracted per the gravitational field of Mars, which is essentially uniform in all directions per the planet’s center of mass. Objects cannot be attracted to the planet’s surface via electromagnetism because Mars is lacking of a magnetosphere. This is essentially true of Venus as well. The Pioneer Venus Orbiter (1979~1981) measured the intrinsic magnetic field of Venus to be just 10^-5 that of Earth, comparatively, no magnetosphere to speak of. How then, does Venus produce the rate of attraction that it does in the absence of any significant magnetic field? Again, the means of attraction is by gravitational fields, not electromagnetism.

You must remember to look at the entire picture when attempting to derive theories and they must in essence hold true when applied to all models. Gravity is present on all heavenly bodies to lesser and greater extents, but it is also clear that not all of these heavenly bodies possess a significant magnetosphere that could proportionately explain the heavenly body’s observed rate of gravitational attraction.

Associated Links…

NASA reference to Mars lack of global magnetic field…

http://mgs-mager.gsfc.nasa.gov/

Additional NASA on Mars…

http://science.nasa.gov/headlines/y2001/ast31jan_1.htm

Mars…

http://www-ssc.igpp.ucla.edu/personn...pers/mars_mag/

Venus…

http://www-ssc.igpp.ucla.edu/personn...ers/venus_mag/

alxm

It just so happens Newton's gravity works as a pretty good approximation, quite beyond the accuracy of the data Newton had at hand.

Magellan's expedition circumnavigated the globe first and Aristotle never ever said the world was flat. Nor was it ever a common belief in the western world.

Newton also believed "That which causes fermentation" was a fundamental force of nature.
We're perfectly capable of thinking outside his 'box'. Tell me, why do you keep measuring your height in inches or centimeters when you know for a fact it's not an exact number of them?

jefswat

I wasn't going to say anything else but I like that

I don't remember gravity making electrons or protons fly off into space either(As if there aren't enough nails in the coffin)

Al68

Aha! And my Physics prof thought I was crazy for stating my height in plank lengths!

cragar

whos to say that gravity is a pull and not a push.

russ_watters

It's not a push.

cragar

why is it not a push . i thought gr describes it as following the curves in space.