Relativity Question *waves at TheEngineer*

Is Gravity A Fictitious Force?
     There is one situation in which we see accelerations which are the same, and presume that the forces causing those accelerations are real -- namely, when we see objects falling toward the Earth, under the influence of gravity. No matter what the objects are made of, or how big or small they are, all objects fall under the influence of gravity with exactly the same acceleration, the acceleration of gravity. Solids, liquids, gases, green cheese, moonbeams, fairy dust and horsefeathers would all fall the same under the influence of gravity, as would sand grains, pebbles, boulders, mountains, moons and planets. Because of this we write the Force Law in a special way for the force of gravity, replacing the force F with the object's weight W, and the acceleration a with the acceleration of gravity, g, thusly
W = m g

     The fact that gravity, like fictitious forces, involves a constant acceleration, makes us wonder whether gravity could be a fictitious force. It's hard to imagine that anything so pervasive and seemingly real could be "fictitious", but the forces experienced by the person in the accelerated car feel real, and are presumably fictitious. Is there some way that we could create the phenomenon of gravity, without the force?
     There is indeed such a way. Suppose that you were in a rocket ship, headed upwards at the acceleration of gravity, so that anything not attached to the ship seems to "fall" with a mirror image of that upward acceleration. Then every such object would fall toward the back of the ship, at the acceleration of gravity, and trying to stop such a fall would require a force, in the direction of the acceleration, proportional to the object's mass, which would be equal to, and appear to be, its real weight.
     Of course, we can't explain gravity in that way, as that would require every part of the Earth to be accelerating upward and outward, which would make the Earth bigger and bigger, which is not observed. So the simplest explanation is to assume that, peculiar though it may be, gravity -- although a perfectly real force -- acts as though it is a fictitious force. No other real force is known to act in this way, but perhaps gravity is "special", and it is merely a coincidence that it looks like a fictitious force.
     The strange and in some ways disturbing answer to this supposition is that the phenomenon of gravity (the fact that things fall, and have weight) is real, but the force of gravity, as described by Newton, is not a real force, but a fictitious force. According to Einstein's General Theory of Relativity, gravity is a curvature of space-time such that in the future, things are closer together than they are now, even if they are moving in straight, parallel lines, with no force between them. For in curved space-time, there is no such thing as a straight line, but instead, only curved lines, called geodesics, which are the straightest possible paths in curved space-time, but are always and inexorably curved. (for now, see the chapter on black holes and general relativity in the text for a more detailed discussion) And since curved paths, in our experience, require some centripetal force to create them, the motion of things along geodesics seems to require some force to explain the acceleration observed, as a result of that curvature.
     So we see things falling, with an acceleration which we call the acceleration of gravity, and thinking that we live in a straight-line, uniformly moving or stationary inertial reference frame, we attribute that acceleration to a force, the force of gravity. Whereas in reality, objects falling toward the Earth are moving along geodesic paths, with no acceleration, and according to a modified version of the Law of Inertia (objects which are at rest tend to remain at rest, and objects which are moving tend to move along geodesic paths with uniform motion, unless some force acts on them), have no force acting on them. They fall simply because the curved space-time near the Earth makes it natural for them to be closer to us in the future, than they are now.
     But if no force is required to make them fall, why do they seem to have weight, when we hold them? In Newton's physics, the weight we perceive is a direct measure of the force of gravity acting on them. How can they have weight, if there is no force acting on them?
     The answer is, that if we are holding them, there is a force acting on them, namely the upward force we are exerting, which keeps them from doing what they are supposed to do, namely fall. And of course that upward force on the object we're holding creates a reaction force, which is downward and equal to the upward force we are exerting, and that is what we are observing, when we observe that something has weight. In fact, even when we perceive our own weight, that is what we are observing. Whatever is keeping us from falling is pushing us upward, with a force equal to our "weight", and what we think is our weight, pushing downward, is just a reaction to that upward push. If there weren't anything pushing us upward -- if, for example, we were to jump off the top of the D building -- we would feel no upward force, and would therefore feel "weightless". We would presume that we weren't really weightless, because the ground is rapidly rising to meet us, but that isn't because we have weight, but because it is natural, in the absence of a force preventing it, for us to fall toward the Earth, along a space-time geodesic. (splat conveying the distinct notion that there's some force around here, somewhere, Einstein's Theory or not)

I'll post again:

"It occurred to Einstein – thinking first of all in visual terms, as was usual for him – that if a man were falling from the roof of his house and tried to let anything drop, it would only move alongside him, thus indicating the equivalence of acceleration and gravity. In Einstein's words, "the acceleration of free fall with respect to the material is therefore a mighty argument that the postulate of relativity is to be extended to coordinate systems that move nonuniformly relative to one another . . . .""
- http://www.aip.org/history/einstein/essay-einsteins-third-paradise.htm

"Einstein said that gravity is a function of mass alright but not as a force exerted by the mass! To the scientists of his day these words amounted to scientific heresy. If gravity is not a force, they asked, then what is it? Einstein's answer is no less than life changing! Gravity, he said, is the result of the mass of an object bending space! Bending Space! Can you imagine? I cannot!

What Einstein was saying is that objects do not fall because of an attractive force reaching out of an object and pulling it to itself, as Newton said."

"Einstein revolutionized modern science by putting forward the theory that gravity is not a force like other forces, but is a result of the fact that space-time is not flat."

"About 50 years ago, Albert Einstein gave us a revolutionary explanation for the gravity we are familiar with. Einstein said gravity is not a force of attraction, as Isaac Newton described it, but rather, comes from the warping of space-time itself."

"This special theory of relativity , was inconsistent with the Newtonian theory of gravity , which said that objects attracted each other with a force that depended on the distance between them.

In 1915 Einstein made the revolutionary suggestion that gravity is not a force like other forces"

I'll post again:

Quote from: Gulliver on July 18, 2007, 01:21:47 PM

I'll post again:

Hey!  That's the same thing TomB does when he has lost. 

What challenges is he avoiding?

Quote from: CommonCents on July 18, 2007, 01:37:02 PM

What challenges is he avoiding?

My money says Gulliver is currently arguing for whatever he started arguing against. Any takers? I'll give you great odds.

Quote from: narcberry on July 18, 2007, 01:42:03 PM

Quote from: CommonCents on July 18, 2007, 01:37:02 PM

What challenges is he avoiding?

My money says Gulliver is currently arguing for whatever he started arguing against. Any takers? I'll give you great odds.

I'm in for $1,000,000.00 US.

Quote from: Gulliver on July 18, 2007, 01:45:42 PM

Quote from: narcberry on July 18, 2007, 01:42:03 PM

Quote from: CommonCents on July 18, 2007, 01:37:02 PM

What challenges is he avoiding?

My money says Gulliver is currently arguing for whatever he started arguing against. Any takers? I'll give you great odds.

I'm in for $1,000,000.00 US.

(you need the cash to start with G...)

What challenges is he avoiding?

...
Oh and speaking of evading... Where's the FoR and explanation of how gravity as a force isn't need in the two-person on opposite sides of the Earth that we need to get into Wikipedia? Where's that quote from Einstein that "gravity as a force does not exist"? Where's that proof that nature is an observer? Where's that reference after 1998 that Nature does not send information FTL? That's four open issues that you've been evading for almost a whole day.

The first one has been answered.  Consult the other thread where THE SAME EXACT THING is being debated.

Quote from: CommonCents on July 18, 2007, 01:53:19 PM

The first one has been answered.  Consult the other thread where THE SAME EXACT THING is being debated.

You asked for a list. I provided it. I also disagree that the first one has been answered.

Quote from: Gulliver on July 18, 2007, 02:12:31 PM

Quote from: CommonCents on July 18, 2007, 01:53:19 PM

The first one has been answered.  Consult the other thread where THE SAME EXACT THING is being debated.

You asked for a list. I provided it. I also disagree that the first one has been answered.

Just because you disagree doesn't mean it was avoided.  My point about staying in the other thread is to keep the arguments in one place.

Well, it's official. Gulliver sux.

His own source proves him wrong, so it must be that the article, in its entirety no less, is now out of context.   But prior to this realization, the article was just fine, in its entirety, no less.

Quote

Oh, and please ratchet up the quality of your references. Wikipedia just pales so much against APL, don't you think?

No.

The Earth's shape is very close to an oblate spheroid—a rounded shape with a bulge around the equator—although the precise shape (the geoid) varies from this by up to 100 metres (327 ft).[18]

I think just quoting wikipedia just shows that you lack a solid understanding of the subject, if you had a good working knowledge of the subject then it see,s that you should be able to properly explain it yourself, I think the only links should be to where actual studies have been done so we can read them ourselves.

and yet when someone defends a statement that they have made that person should be able to explain the stance that they took in thier own words, not just quote what somone else said because it sounds smart.

I think just quoting wikipedia just shows that you lack a solid understanding of the subject, if you had a good working knowledge of the subject then it see,s that you should be able to properly explain it yourself, I think the only links should be to where actual studies have been done so we can read them ourselves.

I think just quoting wikipedia just shows that you lack a solid understanding of the subject, if you had a good working knowledge of the subject then it see,s that you should be able to properly explain it yourself, I think the only links should be to where actual studies have been done so we can read them ourselves.

<snip>
Explaining something yourself allows people to question your words. Using sources allows for points to be better made, and understood.

Just because Wikipedia happens to allow revision doesn't make it any less credible, nor does it mean you don't understand what you're reading.

Wikipedia also makes it easier to get a concise summary. Googling something incredibly specific for use as a source would be time-consuming and there'd be no guarantee you'd find anything.

Perhaps. I must admit, however, that explaining something in your own words does demonstrate a better understanding of the subject. Here’s what pisses me off Divito, I have read this entire thread as well as others in this forum with similar topics and am now not sure who believes what!?

TheEngineer is clearly an intelligent, educated individual that invokes very interesting, spirited discussions, many of which I’ve learned from. However, he seems to exist on this forum merely to antagonize Gulliver (TomG?). And Gulliver seems to be some kind of strange conduit to Wikipedia!?

The rest of the cast on this forum merely exists to fill in the gaps between their (TE and TG’s) posts. At first I was intrigued, now I’m simply bored with the whole damn thing… 

Quote from: TheEngineer on July 19, 2007, 03:31:34 PM

His own source proves him wrong, so it must be that the article, in its entirety no less, is now out of context.   But prior to this realization, the article was just fine, in its entirety, no less.

Still waiting on that quote from Einstein that "gravity as a force does not exist". Still waiting on your proof that Nature is an observer. Still waiting on any proof that the 1998 AIP web page is wrong about Nature sending info FTL. I will consider your geodesics explanation, but still haven't seen any evidence that Einstein thought we should stop treating gravity as a force in all cases.