Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Bogie_smiles on 02/09/2017 17:20:23
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This link, http://hyperphysics.phy-astr.gsu.edu/hbase/grav.html#grav (http://hyperphysics.phy-astr.gsu.edu/hbase/grav.html#grav), says, in regard to gravity, that “From Einstein's treatment in general relativity, gravity is associated with a curvature of space-time and changes in mass configuration can produce gravitational waves.”
According to LIGO discoveries, in-swirling black holes have been shown to produce detectible gravitational waves, and the measurements confirm that gravity travels at the speed of light, so Einstein was right. What conditions qualify as a change in mass configuration, and does an apple falling from a tree produce gravitational waves of some undetectable magnitude?
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What conditions qualify as a change in mass configuration in GR?
Accelerating an electric charge radiates electromagnetic waves.
Similarly, accelerating a mass radiates gravitational waves.
So the Earth circling the Sun radiates gravitational waves - about 200 Watts, as I recall.
An apple dropping to the Earth would also radiate gravitational waves - but an incredibly tiny amount.
Two merging black holes of about 30 solar masses each can radiate about a solar mass of energy as gravitational waves, in about 40 milliseconds.
LIGO discoveries... confirm that gravity travels at the speed of light
It's probably a bit early to make this statement.
Today, with just 2 gravitational wave detectors, the best you could say is that the measurements are consistent with gravitational waves traveling at the speed of light. It is theoretically possible (but unlikely) that the 3 gravitational wave events detected so far could also be consistent with gravitational waves traveling at 1/10 of the speed of light.
The problem at the moment is that with 2 detectors, you can't pinpoint where in the sky the event occurred, so you can't tell if the wave traveled between the detectors at the speed of light. However, 2 more gravitational wave detectors are planned to come online in the next couple of years. With a single event detected at 3 or more sites, you can confirm the speed of the waves travelling between the detectors, which will narrow down the speed to within 10% of the speed of light.
Even more importantly, with 3 detectors, you can localize where in the sky the event occurred. If you can identify the event in an optical telescope or radio telescope, you can confirm that the electromagnetic and gravitational waves arrived at the same time - to better than 1 part in 1010.
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Thank you. Wow, now that is first class radiation.
http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/gravwav.html#c1
I do like the word infinitesimal when it comes to the gravitational waves of apples and anything we might encounter around us.
As for the speed of light and gravity being the same; agreed, I am being premature to bank on it. No need to jump the gun, when it looks like the plans for LIGO will give us a more rigorous approximation in a not to distant future.
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Another fine example of a change in mass configuration:
https://www.thenakedscientists.com/forum/gallery/43933_28_09_17_2_30_12.jpeg
(https://www.thenakedscientists.com/forum/gallery/43933_28_09_17_2_30_12.jpeg)
https://twitter.com/i/moments/913119721716879360
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What conditions qualify as a change in mass configuration,
A change in the stress-energy-momentum tensor constitutes such a change.
.. and does an apple falling from a tree produce gravitational waves of some undetectable magnitude?
Yup.
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Welcome back, Pete!
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.. and does an apple falling from a tree produce gravitational waves of some undetectable magnitude?
Yup.
Is it true then that space is filled with undetectable gravitational waves?
Edit: 10/8/2017
Would I be right to say then, space is filled with as yet undetectable gravitational waves?