61–70 of 139 posts
I always wondered about this. If changes in gravity propagated faster than light, could you build a transmitter by modulating a gravity field by colliding matter with anti-matter?
If you're thinking that the matter and antimatter have gravity and that gravity disappears when they annihilate because their mass is gone, that's not the case. All energy and momentum produces gravity, not just mass.
So I think this article says: - the earth revolves around where the sun is almost precisely and rules out: - the earth revolves around where the sun was ~8 minutes ago (where 8 minutes is about the travel time at c). Can anyone confirm?
Here's another way to understand it. The difficultly: Despite the propagation delay, gravity always points to where the object should be, instead of where it was when the gravity was "emitted". The explanation: Just like the object itself is moving, the gravitational field (or electric/magnetic field) is ALSO moving! It moves at exactly the same speed, and in the same direction as the object which created it. It's "d…
Now, here's the thing that confuses me. Say some advanced civilization can move around some large mass - an asteroid, a planet, a black hole, whatever, we'll just call it "the big mass". They can, at will, fly it back and forth between two distinct positions we'll call 0 and 1. And let's say some distance away - a light-year, say - they have an facility where they can measure with excruciating precision the force of…
This is not to say that the object will actually end up there. If the velocity changes, the gravitational field changes direction according to the new velocity. The change propagates at the speed of light.
People may be interested in experiments to detect these waves. From the Wikipedia page on LIGO: "LIGO, which stands for the Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational waves. [...] At the cost of $365 million (in 2002 USD), it is the largest and most ambitious project ever funded by the NSF. Observations at LIGO began in 2002 and end…
I was fascinated with LIGO when I learned about it. It seems the best plans for such devices exist in the planned space-bound installations, such as LISA ( http://lisa.nasa.gov/ )
In general, in fact, space interferometers have been held up and moved to ground-based systems. (See also SIM and TPF.)
Earlier quoted context omitted.
Now, here's the thing that confuses me. Say some advanced civilization can move around some large mass - an asteroid, a planet, a black hole, whatever, we'll just call it "the big mass". They can, at will, fly it back and forth between two distinct positions we'll call 0 and 1. And let's say some distance away - a light-year, say - they have an facility where they can measure with excruciating precision the force of…
It takes a while for the test mass to notice that the big mass moved. So the test mass is pulled in a direction where the big mass no longer is, but rather where it was.
"Indeed, the vector (2.5) does not point toward the “instantaneous” position of the source, but only toward its position extrapolated from this retarded data" (which is pretty much the same location)
That's mind bending, never thought of gravity that way (being a force like EM, and subject to a propagation speed). In my mind, gravity was just some sort of "vacuum" the mass leaves as it moves, and other bodies get "pulled in" because that's the space where the "energy" (mass) levels are smaller, and the system tends to a stable state. But not something like a wave that propagates, just a side effect of the global…
Actually, the "gravity" that propagates at the speed of light isn't really a "force"; it's more like changes in a force. A completely static gravity field doesn't have to "propagate" at all, because it never changes; but it can still produce a "force" (i.e., it can still cause objects to freely fall towards the source).
Here's another way to understand it. The difficultly: Despite the propagation delay, gravity always points to where the object should be, instead of where it was when the gravity was "emitted". The explanation: Just like the object itself is moving, the gravitational field (or electric/magnetic field) is ALSO moving! It moves at exactly the same speed, and in the same direction as the object which created it. It's "d…
Now, here's the thing that confuses me. Say some advanced civilization can move around some large mass - an asteroid, a planet, a black hole, whatever, we'll just call it "the big mass". They can, at will, fly it back and forth between two distinct positions we'll call 0 and 1. And let's say some distance away - a light-year, say - they have an facility where they can measure with excruciating precision the force of…
Earlier quoted context omitted.
The linked article directly disagrees with this post (except the last paragraph, which itself disagrees with the rest of the post), however: > The fact that gravitational damping is measured at all is a strong indication that the propagation speed of gravity is not infinite. If the calculational framework of general relativity is accepted, the damping can be used to calculate the speed, and the actual measurement con…
That... doesn't contradict anything.
That's not true. Our ability to measure the "speed of gravity" gives us measurements that say "the speed of light":
> the actual measurement confirms that the speed of gravity is equal to the speed of light to within 1%.
I eliminated the cruft so it was more obvious. RobotRollCall's information is older than the linked article (that's from 1998).
Here's another way to understand it. The difficultly: Despite the propagation delay, gravity always points to where the object should be, instead of where it was when the gravity was "emitted". The explanation: Just like the object itself is moving, the gravitational field (or electric/magnetic field) is ALSO moving! It moves at exactly the same speed, and in the same direction as the object which created it. It's "d…
Now, here's the thing that confuses me. Say some advanced civilization can move around some large mass - an asteroid, a planet, a black hole, whatever, we'll just call it "the big mass". They can, at will, fly it back and forth between two distinct positions we'll call 0 and 1. And let's say some distance away - a light-year, say - they have an facility where they can measure with excruciating precision the force of…
No, the remote facility won't notice the thing moved until the gravity wave hits and that only moves at the speed of light. If it's a light year away, it'll take a year before the remote facility notices the shift.
This is the winning comment from the reddit discussion from /u/RobotRollCall * This is a far more interesting question than it might seem at first glance, and it deserves some attention because it tells us something fundamental and wonderful and just bloody awesome about the universe. But I don't know how to tell the story succinctly. So I'm going to do that thing I do. I am very, very sorry. Please feel free to move…
The concept people might think you walk off a cliff and suddenly you're waiting for gravity from the ground to come up is bizarre.
No one thinks that. Most people would think the gravity is the same as when you were one foot the other way on dirt.
There's no instantaneous since nothing has changed (Except a bit of dirt below you is missing)
It's seems more like a bad attempt to sound cute talking about cartoons.