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View Full Version : Gravity; a space warper or a force? Or another duality?

sirius0
2007-Feb-25, 01:20 PM
There seems to be two effedcts of gravity. One warps space the other is to attract locally. I mean I can understand an orbiting body to be rolling around in a space warp around the primary mass but it also seems easy to understand this in term of gravity exerting a force.

Nevertheless I have trouble reconciling my cup of coffee fallling of the table with the idea of space warping due to gravity. Can a falling coffee cup be explained in terms of warped space due to gravity or is this an instance of true force?

Can gravitational lensing be explained in terms of gravity exerting a force on light???

speedfreek
2007-Feb-25, 04:37 PM
But are those two things separate effects, or just different descriptions of the same thing?

If mass warps space, causing smaller objects to fall towards larger ones (meteorites curving towards the Earth due to it's gravitational pull or the warping of the space around it) then wouldnt the same apply at the scale of your coffee cup, knocked sideways into freefall and then falling in an (almost) straight line to the ground due to the large warping of space at the bottom of the gravitational well (relative between the Earth and the coffee cup)?

publius
2007-Feb-25, 05:14 PM
Sirius,

This is why it's important to realize the gravity warps space-*time*, not just space (as some local observer would define it). The reason the cup falls off the table is actually due to the time part of the curvature more than the anything else.

The "reason" for that is "distance" in the time dimension is ct. Since the speed of light is so great, a small interval of time is a large "distance", and the slightest curvature there makes a big difference over what we perceive as a small interval of time.

That is really a matter of perception. Saying the speed of light is fast is another way of saying our minds are slow. :) If our time scale were nanoseconds, that is our consicious minds operated as fast as microprocessor, you wouldn't think your coffee cup falling off the table was all that fast. It would just seem to float, and you'd have to wait "ages" to notice it accelerated.

The earth's gravity field here is in GR terms pitifully weak. There is the slighest spatial curvature, deviation from Euclidean geometry but it is very small. Gravity Probe B, besides looking for frame dragging, is also looking for another type of precession, "geodetic precession", which is an effect of that spatial curvature. It's very small, but if observered, that's more confirmation that GR is correct.

-Richard

sirius0
2007-Feb-25, 11:12 PM
Thank you this has given me the enlightenment I required!

About where I am at with metrics.
Chris

sirius0
2007-Feb-26, 12:08 AM
Richard,
Are you saying that a falling object is inheriting some of the velocity that we hurtle through time at (c)? You posted else where that an object on the other side of an event horizon (black hole) has swapped one of it's spatial dimensions with the time like one from our perspective. I am wondering if this is what is happening with a falling object but in a proportional sense for gravity as weak as the earth?

publius
2007-Feb-26, 12:41 AM
Sirius,

That is indeed one way to look at it. We all move along our world lines at 'c'. The "direction" of our world line at any spot is the "direction of time". To us, doing our thing, we don't notice anything different. Our local clock runs as normal, and we think everyone else is doing something weird.

So, with that in mind, here's a little picture of a stationary Schwarzschild observer watching something radially fall:

Because of the curvature, that free-falling test particle's clock slows down. So that means we think its "rest energy", mc^2 locally to us is less as it moves. The total energy is conserved, and so the difference in that energy goes to *what we perceive* as kinetic energy, motion through space.

So we can say, that *relative to us*, some of that free-faller's motion through time is being converted to motion through space. Now, what happens when that free faller hits the ground. The kinetic energy gets dispersed, and the free faller is sitting there with a slow clock and lower energy than he had we he started.

Suppose he wants to get back up to us. The 'mgh' work done to lift him back up, is simply supplying that energy back to "speed up his motion through time" back to where it started. In this view "rest energy" is the kinetic energy of motion through time. :)

This is a picture, a perspective on what's going on, mind you, not "absolute truth". It's a very cool picture, and certainly "explains alot", but keep in mind it is just a way to picture things.

Note this is a totally different picture than the traditional Newtonian potential energy view. The work done to lift something goes directly to "speeding up the clock" of the mass being lifted. There is no energy associated with the "gravitational field" at all. And that is pretty much the GR view. However, that is not really so simple when time-varying metrics are afoot, such as with gravitational radiation. Defining an energy there is a most vexing problem, and not so well-defined. But suffice it to say that gravitational radiation does indeed "act like" it carries both energy and momentum away from some system, and can even "deposit it" to some other system.

But that is well beyond me, and that's about all I know about it.

-Richard

Peter Wilson
2007-Feb-26, 08:12 PM
Can gravitational lensing be explained in terms of gravity exerting a force on light???
Gravity produces acceleration, not force.

This is obtusely acknowledge by the mainstream, refering to gravitational acceleration as "curvature of space," but in the simplest terms, gravity should be thought of as acceleration, not force. Acceleration is easy to picture; I think everyone understands what acceleration is.

But curvature of space? What does that mean? Who knows? It is a term tossed about, without anyone really being able to picture what it means. Keep it simple: gravity accelerates. And yes, gravitational lensing can be explained in terms of gravity accelerating light.

sirius0
2007-Feb-26, 08:39 PM
Are the other fields different? Magenetic electrostatic etc.
Do they curve space-time in their own way?

publius
2007-Feb-26, 10:17 PM
Are the other fields different? Magenetic electrostatic etc.
Do they curve space-time in their own way?

Apparently not. Now, the *energy* of EM fields is a source of gravity, so EM fields do cause gravitational effects, but that's the same as other mass-energy. See the "exact solutions" thread for some interesting stuff about this.

But, is there a "geometric interpretation" of EM, and other fields? Again, apparently not. That's what Einstein was trying to do at the last, unify gravity and EM into one thing. It didn't work out.

This attempt is sometimes called Einstein Unified Field Theory (UFT) and you can find some stuff about it here and there if you look hard enough. He was going well beyond 4D space-time with more dimensions, and well beyond Riemannian geometry to try to pull this off. This geometry was to Riemann as Riemann is to Euclid.

But it didn't work out. Interestingly there are conspiracy theories that Einstein did pull it off, but what he found was so powerful that the US government covered it up, and kept it for themselves to make secret weapons, not to mention "antigravity" spacecraft, warp drive, etc, etc. :lol:

There was another guy, Gabriel Kron, an electrical engineer, who got some coupling of EM and gravity beyond the EFE in his head. I notice in your profile you're an electrician -- well, I'm something of a shade-tree electrician myself, power mostly, not electronics, and power systems are something some say I'm obsessed with. Well, my interests wax and wane. Anyway, this Kron business caught my eye one time.

Anyway, this Kron business caught my eye. Kron was a brilliant guy and came up with a *tensor* description of synchronous machines (for lurkers, these are basically the big generators that make the grid go, although they motor just easily as generate). While it was mathematically elegant, it was just too much candy for a nickel -- too complex compared to normal methods. Sort of like using the full GR picture to try to explain to a child why the cup falls of the table.

Anyway, Kron got it his head that his tensor model produced gravitational effects, and further claimed that "hunting" and other little hiccups of synchronous machine behavior (just basically considered random little mechanical glitches from a host of little perturbations) were actually due to those gravitational effects. He claimed he could predict hunting behavior because of that. What became of that, I don't know; whether he could accurately predict the hunting and other little hiccups, I don't know.

And finally, google on "Heim Theory" -- Heim has 8 or 10 dimensions, and claims a strong coupling between EM and gravity as well. IIRC, he's got the EM potential being a full 4-tensor, with lots more terms that are coupled to gravity, too. :)

Consider this "fringe". Everybody has his wild side, and this stuff is mine, actually. I don't put more than one grain of salt into any of it, but I sure do like to read about it.

My fantasy is finding a strong EM-gravity coupling and making some device that, well, "warps space-time strongly" at will via EM means. Turn on the "gravitic drive", float up off the earth at reasonable pace, then get up there and turn on your warp drive............. :lol:

-Richard

sirius0
2007-Feb-26, 10:38 PM
Oooohh yeah luv it!
And I will look up this Kron chap.
Hunting & Gravity fascinating.
I am right there with those fantasies too.

On another level I suppose youve heard of dodgy people using syncronous motors to spin there Kwhr meters backwards? An extrerme of powerfactor correction!

publius
2007-Feb-26, 11:22 PM
Oooohh yeah luv it!
And I will look up this Kron chap.
Hunting & Gravity fascinating.
I am right there with those fantasies too.

On another level I suppose youve heard of dodgy people using syncronous motors to spin there Kwhr meters backwards? An extrerme of powerfactor correction!
Sirius,

This may well get off topic here, and we might ought to open up another thread somewhere else about. Let's see you're in Australia right? You're 50Hz, too, like most of Europe? I don't know how your typical meters down there work. Another question about your local distribution while I'm thinking about it, too:

I heard that in Australia (and I might be getting this confused) you guys you use sort "low voltage" bus distribution system, rather than one transformer per service that we mostly use here (with minor variations). That is, take a rought suburban block. You've got your HV distribution, then you run LV buses under that that cover a section, with multiple transformers feeding that bus, and just tap off of it for each service. There are advantages and disadvantages to that. Is this true?

And about the kH-hr meters. Again, I don't know how your meters work. Here, many utilities are converting to electronic metering, which has lots of cool features, but how reliable it will be in the long run, I don't know. Our old mechanical meters, for single phase 120/240V three-wire service, have always been true real power meters. Reactive power doesn't affect them at all, at least within their intended range.

There have been a few devices sold by dubious individuals that purport to "fool" 'em by drawing heavy reactive current, usually capacitive, but they don't work. :) Now, some of the "twin stator" meters for 3-wire 3-phase services (deltas) did have a problem if the power factor went negative (capactive, rather than inductive, which was rate) past a certain range. This was entirely a "calibration defect", that I forget the details of. IIRC, a power factor of less than 30% on the capacitive side would throw 'em off and they would read low.

{ETA: DOH! Bab, bad AC power terminology: The reactive power goes negative is what I meant. Power factor itself remains positive, as defined. Phase angle goes leading, rather than lagging. Sorry about that}

As near as I can tell, this is where the idea that a heavy capacitive load would slow a meter came from. But it only applied to twin-stator meters of a certain design and manufacture, not single phase meters.

Now, there is a way to slow down a mechanical meter for real, which I won't mention. It's not dangerous, but it takes a pretty big magnetic field......and it will not work at all with the electronic meters.

-Richard

publius
2007-Feb-27, 12:16 AM
Another EM having strong gravitational effects thing was this character Art Bell had on several years ago, back in the good ol' days when he had Hoagland or Ed Dames on every week spinning some tall tales. Of course, of all of them, this lunatic named Mel, of "Mel's Hole" fame was probably the best tall tale I've ever heard.

Anyway, Art had this character on a few times who claimed he had a lab in Long Island, and that he had discovered a way, via EM means, to control the clock rate in a small region of space at will.

He would not give any details, saying it was proprietary, other than it involved large static E and B fields, modulated with RF and microwave frequencies riding on top of a certain pattern, followed by the kicker of using high powered lasers concentrated in the field region. He claimed that by doing that he could control the clock rate inside a small region at will, speeding up or slowing it down by 3 - 5 times. He said he tested clocks of all types, mechanical and electronic, and they all agreed, and even tested seed germination rates -- said he could speed that up or slow it down in exact agreement with his clocks. And he said he stumbled on this from playing around with "GR equations".

Art had him on a few times, then he stopped answering the phone according to Art. And that went right along with Art's conspiracy mindset -- "They" got to him because "They" didn't want that knowledge out. :lol:

Again, not more than one grain of salt for that, you do something like that and can reproduce your results, you publish the heck out of it, not go on Art Bell.

But that kind of stuff does indeed fascinate me.

-Richard

sirius0
2007-Feb-27, 02:49 AM
I once exposed a watch to a strong alternating magnetic field and it only tells the right time twice a day!

I will give a serious answer to our distribution scheme (electric power) soon.

As you suggest in another thread probably the of topic forum.
Regards Chris

Kaptain K
2007-Feb-27, 06:01 AM
The scary thing is that Art Bell is positively skeptical compared to George "professional believer" Noory!

publius
2007-Feb-27, 06:31 AM
Sirius,

Upon re-reading your previous post, I saw you said "spin the meter backwards", not slow it down or otherwise render it inaccurate.

Yep, you can generate with a synchronous motor hooked up to a prime mover, and if you can supply your own load, you can feed back power to the local system. A good meter, which mechanical meters are, will faithfully see current "bucking" voltage according to its directional sense, and run backwards.

That is not stealing power at all, merely supplying power back. Someone who does that isn't getting anything for free, he's supplying ever bit of energy back to the power company that he is cancelling out on his meter. :) And his own prime mover, unless he's getting a deal on his fuel, is costing him more per kW-hr than the grid, anyway, (and less efficiently no matter what the cost -- he's burning more fuel that the power company per kW-hr).

So one is not gaining anything with that at all, loosing most probably, but even then, the power company does not want people willy nilly hooking generation to their system for a variety of reasons. There are idiots who feed back dead power lines during power outages with generators. That's a safety issue for lineman.

That is one way to make lineman very angry. Now, being able to feed back the HV lines like that depends on it being open, and not faulted out and certainly no other loads on it. No little generator is going to be able to supply a local neighborhood on one leg of the distribution system. :) It's just isolated cases.

Several linemen I know have told me amusing stories about how they discovered some idiot backfeeding, and how they "blew his generator up". Just grounding out the HV line will trip him out, but the best way to do it, if you're repairing lines and have a live feed is to connect him up, unsynchronized right to the grid. :) In one case, they specifically waited until they had a live feed available just so they could do that.

For any lurkers not familiar with this stuff, this can be compared to a freight train hitting a lawn mower. That train just knocks that lawn mower flying and doesn't feel a thing.

-Richard

publius
2007-Feb-27, 06:48 AM
The scary thing is that Art Bell is positively skeptical compared to George "professional believer" Noory!

Amen. One thing about George that I can't abide is he entertains these 911 conspiracy kooks and similiar "New World Order" crap. I enjoy Hoagie, Ed Dames, good ghost stories, etc, but that stuff I will not tolerate. Click goes the radio when that stuff comes on. Art has made it pretty clear he has no truck for it either, from what I've heard.

-Richard

DyerWolf
2007-Feb-27, 02:33 PM
There are idiots who feed back dead power lines during power outages with generators. That's a safety issue for lineman.

That is one way to make lineman very angry.

This is also one way to make Plaintiff's lawyers happy and widow(er)s of the lineman's NOK.

Sounds like some linemen found a way to "repay" the offense, but not a technique I'd recommend either...

sirius0
2007-Feb-27, 09:14 PM
This is also one way to make Plaintiff's lawyers happy and widow(er)s of the lineman's NOK.

Sounds like some linemen found a way to "repay" the offense, but not a technique I'd recommend either...

In Australia lines workers do use shorting links. This would not serve dimwits that back feed generators to the grid I am sure.
Or are you talking about briging the HV to the LV like an auto transformer? Very nasty!

sirius0
2007-Feb-27, 09:55 PM

publius
2007-Feb-27, 10:18 PM
In Australia lines workers do use shorting links. This would not serve dimwits that back feed generators to the grid I am sure.
Or are you talking about briging the HV to the LV like an auto transformer? Very nasty!

They just call those grounding jumpers here mostly. Experience and safety have resulted in some pretty stringent safety protocols. When you're working 7200V (or higher) to ground hot, it ain't exactly caution to the wind time -- there are old electricians and bold electricians, but no old, bold ones. And grounding any phase, no matter if it's obviously dead, is one of them. And that comes from accidents where miscommunication caused someone upstream to mistakenly energize a line someone downstream was working on and that kind of stuff.

Failure to follow those rules is usually a firing offense. And any accident, making some fireworks, requires filling out a detailed "splash report" (why "splash", well, molten metal splashes pretty good. :) ). Failure to file a splash report is a firing offense right then and there, from what they tell me.

What I'm talking about with the generators is throwing it on, in parallel with the main grid supply unsynchronized. The effect is much worse than a regular short. To parallel two generators, they have to be in phase at the moment you throw the switch. Worst case is when they are 180 degrees out of phase, at which time the effect is 2x voltage being shorted out.

You've probably seen reference to various synchronizing schemes using light bulbs. One techique is just put the light bulbs between the two generators are synchronize "on dark". The other is to cross wire the bulbs so you synchronize "on bright", throwing the switch when the light bulbs are at their brightest. However, modern electronic controls can do it far it better than manual techniques.

Two synchronous generators running in parallel is very interesting and complex system. Lots of interesting stuff there. Without rambling on about, when you throw a generator in parallel with a much larger supply system ("inertia" one can call it) out of sync, the rotor gets quite a mechanical jerk. Now, that's the real power part, when mechanical work goes one way of the other. Add the complex reactive "dance" that can occur with machines in parallel depending on the excitation (rotor field), and you've got yourself quite a complex little math problem to puzzle over.

Depending on things, that can be one *heck* of a mechanical jerk before any local breakers have time to act -- "throw it through the roof".

-Richard

sirius0
2007-Feb-27, 10:39 PM
Yes publius I have done this sort of sync personally fortunately I have never done it wrong!

Another effect is circuit breaker selectivity. The sorts of currents occuring (as well as effectively higher frequencies in the breakers detection coil giving a false sense of a higher current) can get out of the local breakers TEM curve. This can cause a much larger breaker upstream to trip first; causing a blackout!