mugaliens
2008-Aug-15, 10:53 AM
Time and again I observe others using the term "gravity wave" and "radiation" as if a mass actually radiates something, and that something has, as do all waves, both positive and negative peaks, the difference of which is referred to as "amplitude."
Yet no masses in existence actually pulsate and thereby radiate positive and negative "gravity waves."
The closest we get to that is a binary star system with rapidly orbiting partners, whose gravitational tug varies with a maximum fluctuation occurring in the plane of rotation. Even here, the variance between max and min is but a tiny fraction of a percent difference from the mean gravitational attraction.
This is analogous to the faintest of whispers, which produce an exceedingly slight variance around the mean atmospheric pressure of 14.7 psi. In that sense, the variances in gravitational attraction could be considered to be "waves."
However, the mean orbital period for binaries is approximately 100 years. Since the gravitational peaks occur when the angular distance between the binaries is at a minimum, which happens twice per orbit, the wavelength of these waves would be approximately 50 light-years long.
That's one big (long) wave - but very, very tiny with respect to amplitude. It's comparable to the tiniest of ripples on the surface of a pond spread out over the length of the pacific ocean (with a corresponding reduction in amplitude, required to keep the wave's energy constant).
If a mass were to pass near the solar system, we'd experience an increase in gravitational attraction, in the direction where we perceive the object to be by it's light, as gravity and light both propogate at c. However, unlike water, sound and light waves, the gravity "wave" would merely be an increase and a decrease. Stated in terms of systems, it is "over-damped." That is, there's only a rise and a reduct from the ambient gravitational field due to it's passing.
There's never any fluctuation below ambient, no "negative phase" to the cycle.
Thus, it really doesn't behave like a wave at all.
And what about supernovas, where a bunch of mass is converted to EM waves, the conversion of which is said to produce gravity waves.
But does it? The mass is gone, but mass/energy is neither created nor destroyed - only it's form has changed. Is there really a change in the gravitational tug? What if a 0.5 solar mass of matter and a 0.5 solar mass of antimatter came together, resulting in a total conversion of the mass to energy?
Immediately prior to their mutual annihilation, they'd exert a gravitational attraction of 1 solar mass. Immediately afterwards, the centroid of the rapidly expanding ball of EM energy still exerts a gravitational attraction equal to that of 1 solar mass.
(please correct me if I'm wrong, here, and let me know why, with online references, if possible)
Since gravity from any source only changes when the measurement is taken from inside the spheroid of the mass/energy, such as a scale lowered into the crust a mile below sea level, provided we're outside that spheroid, regardless of how fast it's expanding, there would be no change in gravitational attraction.
However, since by the time the light of a supernova has reached us, the leading edge o that expanding spheroid has passed us, and the more time that passes, the greater the amount of energy from that supernova has passed.
From what I understand, however, a distant supernova's energy takes from days to weeks to build to max intensity before beginning to subside. Thus, the 1/2 wavelength from nominal to peak would be between a few light-days and several light-weeks in length.
Even if it's just an hour, for a particularly close and intense supernova, that's still a wavelength of 1,079,252,848 km (1 Billion km), which is a wavelength nearly twice the orbital radius of Saturn.
Will some please explain to me how we're supposed to detect these gravity "waves" with Earth-bound detectors when their wavelength is 2 Billion km or more?
Yet no masses in existence actually pulsate and thereby radiate positive and negative "gravity waves."
The closest we get to that is a binary star system with rapidly orbiting partners, whose gravitational tug varies with a maximum fluctuation occurring in the plane of rotation. Even here, the variance between max and min is but a tiny fraction of a percent difference from the mean gravitational attraction.
This is analogous to the faintest of whispers, which produce an exceedingly slight variance around the mean atmospheric pressure of 14.7 psi. In that sense, the variances in gravitational attraction could be considered to be "waves."
However, the mean orbital period for binaries is approximately 100 years. Since the gravitational peaks occur when the angular distance between the binaries is at a minimum, which happens twice per orbit, the wavelength of these waves would be approximately 50 light-years long.
That's one big (long) wave - but very, very tiny with respect to amplitude. It's comparable to the tiniest of ripples on the surface of a pond spread out over the length of the pacific ocean (with a corresponding reduction in amplitude, required to keep the wave's energy constant).
If a mass were to pass near the solar system, we'd experience an increase in gravitational attraction, in the direction where we perceive the object to be by it's light, as gravity and light both propogate at c. However, unlike water, sound and light waves, the gravity "wave" would merely be an increase and a decrease. Stated in terms of systems, it is "over-damped." That is, there's only a rise and a reduct from the ambient gravitational field due to it's passing.
There's never any fluctuation below ambient, no "negative phase" to the cycle.
Thus, it really doesn't behave like a wave at all.
And what about supernovas, where a bunch of mass is converted to EM waves, the conversion of which is said to produce gravity waves.
But does it? The mass is gone, but mass/energy is neither created nor destroyed - only it's form has changed. Is there really a change in the gravitational tug? What if a 0.5 solar mass of matter and a 0.5 solar mass of antimatter came together, resulting in a total conversion of the mass to energy?
Immediately prior to their mutual annihilation, they'd exert a gravitational attraction of 1 solar mass. Immediately afterwards, the centroid of the rapidly expanding ball of EM energy still exerts a gravitational attraction equal to that of 1 solar mass.
(please correct me if I'm wrong, here, and let me know why, with online references, if possible)
Since gravity from any source only changes when the measurement is taken from inside the spheroid of the mass/energy, such as a scale lowered into the crust a mile below sea level, provided we're outside that spheroid, regardless of how fast it's expanding, there would be no change in gravitational attraction.
However, since by the time the light of a supernova has reached us, the leading edge o that expanding spheroid has passed us, and the more time that passes, the greater the amount of energy from that supernova has passed.
From what I understand, however, a distant supernova's energy takes from days to weeks to build to max intensity before beginning to subside. Thus, the 1/2 wavelength from nominal to peak would be between a few light-days and several light-weeks in length.
Even if it's just an hour, for a particularly close and intense supernova, that's still a wavelength of 1,079,252,848 km (1 Billion km), which is a wavelength nearly twice the orbital radius of Saturn.
Will some please explain to me how we're supposed to detect these gravity "waves" with Earth-bound detectors when their wavelength is 2 Billion km or more?