xxxxx - 28-11-2006 at 07:06
i was wondering if it might be possible to cancellate gravity waves in the same manner that sound waves are cancellated. of course, since gravity
waves cannot yet be detected directly, it may be some time before they can be successfully propagated.
12AX7 - 28-11-2006 at 10:54
Sure, just oscillate a huge mass opposite the incoming waves. Power usage (think linear actuators as used acoustically, but driving a mass instead)
will be "astronomical", of course.
Tim
Mr. Wizard - 28-11-2006 at 11:50
Sound waves are not 'cancelled', except when they are converted to some other form of energy. I'm guessing you are refering to the 'sound cancelling'
earphones that send an out of phase complimentary sound wave into your ear to enhance listening in a noisy environment. Sending a wave that matches
the incoming wave will seem to make the noise disappear at one spot, your eardrum, but doesn't actually cancel the sound.
Imagine a bird on a long suspended rope. A person at one end shakes the rope, sending a complex wave down the rope toward the bird. A person at the
other end of the rope who is a little nearer to the bird quickly decides the opposite wave pulse and sends it down the rope to arrive at the bird at
the same time, negating the motion of the rope at that one point. The actual amount of energy in the system is actually greater, but the bird doesn't
notice the rope moving.
The whole story vastly oversimplifies the process, but it was fun.
As to gravitation waves, you would have to find a way to generate them in the correct phase. This will be difficult because they theoretically travel
at the speed of light, and you wouldn't have time to generate the oppropriate phase negating pulse, as you could do with a much slower sound wave. I
won't say it isn't possible because I didn't think they could counteract the spreading effects of a laser beam through air either, and they found a
way to do just that with the phase conjugate laser. Scientific American, Dec. 1985
froot - 29-11-2006 at 01:55
How did people arrive at the conclusion that gravitational force is propogated in 'waves' as such? Surely it requires energy to generate waves in a
medium and considering all bodies of matter have their own gravity which is dependant on their mass, these bodies can't for eternity be consuming
energy to maintain their gravity. A similar concept to magnetism as I see it with regards to energy and field effects on other bodies, but non-polar.
12AX7 - 29-11-2006 at 07:35
Fast rotating pulsars have been shown to lose parts per billion in frequency over some period of time (years/decades?), in close proportion to the
theorized power loss due to gravity wave emission.
Gravity is a field much as electromagnetism is a field; it just happens to be >2000 times faster (effectively instantaneous).
Now what's really interesting that I was wondering, could it be possible to make mechanical oscillators massive enough and lossless enough that
gravity waves of a very specific (i.e. resonant) frequency could be transmitted and recieved? Indeed, a phased array could be built according to
electromagnetic design (accounting for the propagation speed difference) and perhaps frequency modulated (by a small amount, in order that power
consumption isn't entirely astronomical). An atomic clock would set the precise transmission and reception frequency, so as to require only small
adjustments (microhertz or nanohertz, say), saving on power.
Truely something Tesla would be proud of (in terms of resonant gain), but I don't think something with a Q > 10^6, say, can actually be made (at
that rate, even if eddy currents are somehow cut out altogether, you have subtle things like the Casmir effect and dispersion forces cutting into your
action!). I have no idea what kind of transmission gravity waves are capable of, but I'm willing to bet it's a lot like a Tesla coil: small antennas
at low frequency radiate very little with respect to loss, regardless of magnetic or electric field strength, whereas large antennas (on par with the
wavelength--but what IS the wavelength if propagation is instantaneous?!) deliver most of their power to the medium. If power loss can be cut, a
smaller antenna (perhaps a few million tonnes?) can be oscillated precisely (a tight frequency control allows the weak signal to be distinguised among
background noise) and still recieved clearly. A phased array can direct the radiated power into a tight beam, allowing greater gain at both ends.
Tim
[Edited on 11-29-2006 by 12AX7]
unionised - 29-11-2006 at 11:26
"Gravity is a field much as electromagnetism is a field; it just happens to be >2000 times faster (effectively instantaneous)."
Does that mean it can send data faster than light?
"Truely something Tesla would be proud of (in terms of resonant gain), but I don't think something with a Q > 10^6, say, can actually be made"
The crystal in my watch is probably close to that and here
http://www.fsm.physics.uwa.edu.au/clock.html
they do about 4 orders of magnitude better.
The problem with gravity waves is that they are roughly 1E34 times weaker than electromagnetism. If we are lucky we might, with current technology,
spot a nearby supernova's gravity waves.
Baphomet - 29-11-2006 at 20:57
Gravity is only considered as a 'wave' for the purposes of simplifying thought experiments. Theoretical particles called 'gravitons' are sent between
each atom in the universe at ridiculous speed to transmit gravity information.
If you look into higher dimensions 5, 6, ... up to string dimensions then gravity might appear to take the appearance of a wave, but then your gravity
machine would need to inhabit one of those higher dimensions to manipulate the waveform directly.
Can't be done