The "Intelligent Falling" Theory

[Erik Mesoy]

You must be kidding?

Yes, I was kidding. I was hoping it would have been clear from my earlier post that I was parodying the normal creationist approach: Ignore specific posts, make a general statement with "proofs" as to why the "theory" doesn't work, then claim that an intelligent force must be responsible. Imply that it's God.

---

Alternative response: Ha! You gravitationists can't answer the question, you're dodging!

 

[frob2900]

Yes, I was kidding. I was hoping it would have been clear from my earlier post that I was parodying the normal creationist approach: Ignore specific posts, make a general statement with "proofs" as to why the "theory" doesn't work, then claim that an intelligent force must be responsible. Imply that it's God.

Ok, yeah, I actually guessed that, but I thought I'd take the opportunity to point out that general relativity isn't a paradox-frought as people often believe

 

[Gladi]

But if gravity moves faster than light, we can use it to transmit information by putting up a gravity detector and moving some heavy lead balls around. Which would lead to sending information back in time, which doesn't work either, because of paradice. (Plural of paradox. )

Bright day
Ah, my biggest problem with high school physics, we are just told that because light has a top speed, time has one too and we are never told what are the teachers smoking...

 

[Mise]

Not only are they contradicting one another, but both positions are wrong.

If gravity moves slower than instantaneous, we get "couple" effects where things go out of orbit. But we're still in orbit.

But if gravity moves faster than light, we can use it to transmit information by putting up a gravity detector and moving some heavy lead balls around. Which would lead to sending information back in time, which doesn't work either, because of paradice. (Plural of paradox. )

I'm thoroughly confused, because both of these make perfect sense.

Going back to what brennan said about two magnets:

Yes, but the field from the first magnet would still be there. So you would see 'instantaneous' action at the electromagnet (which is sitting in an EM field when it is switched on) and delayed action at the magnet (which has to wait for the change in EM field caused by activation of the electromagnet to reach it).

How does that square up with Newton's 3rd law? Does it hold in GR? Is it supposed to...?

If the magnet (M1) is moving, and the electromagnet (M2) is stationary, such that, if M2 was switched on at the right time, and if gravity acted instantaneously, M1 would orbit M2 in a circular orbit, what would happen if gravity acted at the speed of light?

 

[frob2900]

I'm thoroughly confused, because both of these make perfect sense.

Going back to what brennan said about two magnets:

How does that square up with Newton's 3rd law? Does it hold in GR? Is it supposed to...?

If the magnet (M1) is moving, and the electromagnet (M2) is stationary, such that, if M2 was switched on at the right time, and if gravity acted instantaneously, M1 would orbit M2 in a circular orbit, what would happen if gravity acted at the speed of light?

I wouldn't worry about it too much. You can give yourself migraines already without introducing gravity when you study causality w.r.t. electromagnetic fields. Try reading up on Cherenkov radiation and advanced/******** potentials.. (Jacksons "Classical Electrodynamics" is a good book on such things)

Remember to have a fair supply of caffeine and ibuprofen

 

[El_Machinae]

If angels cause falling, then they also cause the thermodynamic 'falling' responsible for life existing.

 

[Masquerouge]

@Masquerouge:
You were probably taught that gravity is instant because you studied gravity in a Newtonian physics course. Then when you took a special relativity/electromagnetism course they told you that the speed of light is the fastest speed possible.

Many teachers are like that. They can compartmentalize the universe into small courses in which it works completely different from every other course

Nah, both were part of my senior year physics class in high school.

I freely admit I'm thoroughly confused now. I didn't understand a single thing about why space curvature allows gravity to be instant but not faster than the speed of light :

Or that gravity is a durable distortion in space-time. Why does the Earth act as though the sun is where the sun is? because the geometry of space around the sun is constantly distorted by a gravitational field. If I moved a magnet to a point within the magnetic field of another magnet do I have to wait for an LS delay before a force is felt? No; the field (and its associated electroweak interaction particles) is already there.

What? I think I dimly understand it. But what if the Sun were suddenly removed?

 

[frob2900]

Nah, both were part of my senior year physics class in high school.

I freely admit I'm thoroughly confused now. I didn't understand a single thing about why space curvature allows gravity to be instant but not faster than the speed of light :

Who said its instant? It cant travel faster than light.

What? I think I dimly understand it. But what if the Sun were suddenly removed?

Any information that the sun has been moved cannot reach earth faster than the speed of light.

 

[brennan]

Going back to what brennan said about two magnets:

How does that square up with Newton's 3rd law? Does it hold in GR? Is it supposed to...?

Remember that you have to throw a load of charges down a wire to activate the electromagnet. If you analyse the situation fully the 3rd would hold.

Edit: pardon me, I forgot: energy in the EM fields themselves count towards the third, you have to take that into account to.

 

[brennan]

What? I think I dimly understand it. But what if the Sun were suddenly removed?

Space would snap 'flat' - to refer to the rubber sheet analogy - within a sphere that would expand at the speed of light (so the Earth would cease moving in its orbit in a little over 8 minutes and fly off through the galaxy).

The change in gravitational field would be one helluva gravitational wave. It would take a seriously exotic event for that to happen though.

 

[LordRahl]

You can actually have things traveling at faster than light speeds, as long as no information can be carried by them.

 

[frob2900]

You can actually have things traveling at faster than light speeds, as long as no information can be carried by them.

Do you have examples?

 

[Erik Mesoy]

Do you have examples?

I have some. Shadows or lights. Point a laser pen at one side of the Moon, flick your wrist, red dot travels to other side of Moon at FTL speeds. (Spread of light notwithstanding, also assuming that you flick your wrist fast enough.)

 

[LordRahl]

Do you have examples?

Look up "group velocity" on wiki.

 

[frob2900]

Look up "group velocity" on wiki.

I thought you'd say that. That's just quantum mechanical wavepacket hocus-pocus. That isn't a "thing" that's travelling faster than light, in the objective sense of the word "thing".

I have some. Shadows or lights. Point a laser pen at one side of the Moon, flick your wrist, red dot travels to other side of Moon at FTL speeds. (Spread of light notwithstanding, also assuming that you flick your wrist fast enough.)

The only "things" in that example are photons, and I can most empathically assure you that not a single photon has travelled faster than light in the whole setup.

 

[LordRahl]

hat isn't a "thing" that's travelling faster than light, in the objective sense of the word "thing".

The same can be said about light now, can't it?

 

[frob2900]

The same can be said about light now, can't it?

No. Light is photons, i.e. energy packets. Those are most certainly "things" since they can push other things (i.e. transfer momentum to them when they collide with them)

 

[Erik Mesoy]

The only "things" in that example are photons, and I can most empathically assure you that not a single photon has travelled faster than light in the whole setup.

The red dot, as watched by an observer observing the moon, ignorant of the pen, is moving faster than light, is what I meant.

Expand the principle to being in a shell ~>1 light seconds wide, being in the center, and playing with a laser pen. Imagine something on the inside of the shell trying to run after the red dot. It'll get away from them.

No information, though.

 

[brennan]

If the observer took a really close look, he'd find that he was just seeing a succession of different red dots and not the same one at all.

 

[mdwh]

See http://en.wikipedia.org/wiki/Speed_of_gravity for some info, and details of experiments supporting a speed equal to the speed of light.

(Edit: That guy's also been caught editing original research into the Wikipedia article!)

Actually it doesn't suggest gravity is instantaneous, it suggest that gravity propagates 200 Million times faster than the speed of light.

But it also uses as an argument that a finite speed would lead to unstable orbits!

Anyhow, isn't the solar system unstable anyway? Unstable doesn't mean the planets will all fly off randomly, it just means there isn't a stable solution, and the changes happens over long periods of time.