Does anyone here actually know how LIGO experiments work? I have some questions.
There are two detectors separated by over 2000 miles which means that two detectors can detect where the wave is coming from based on the delay.
What I don't understand is how the heck does this difference in time translate into pinpointing where the wave came from. How do they correlate wave to actual black holes? Wouldn't you need at least 3 detectors to do that?
Also, how do they know the masses of two black holes that are colliding? I'd understand if they were able to predict the mass of the final hole but they're actually able to tell what the individual masses are.
>Wouldn't you need at least 3 detectors to do that? No. If you know the signal travels at the speed of light, then a single station detecting a signal is like drawing a circle around the station. A second station draws a circle around this station. These two circles will intersect in at most two places, but one of the places will be ruled out because we'll know which detector got the signal first. Though we don't know the distance to the object which sent the signal, the relevant intersection of the circles as the radii vary will lie on a line, so we could just look in that direction.
With no further information, two detectors will not be able to determine distance, just direction.
Wyatt Kelly
in 3D, it's spheres.
the waveform also contains information (frequency, dampening, amplitude)
Zachary Moore
Sphericity is irrelevant. You only have two eyes but you can detect the direction of a spherical emission (e.g. the sun).
Levi Foster
because I can move my eyes. you're fucking retarded.
Josiah Robinson
>black holes When will this meme die? And how the hell they can observe "unobservable" object masses?
James Johnson
moving your eyes is not how they locate things, it's that they are directional
LIGO has poor directionality, but it is directional
In principle a gravitational wavefront will present to us as a plane at some angle which hits one detector then the other, and we know something of the angle of this plane due to the fact that the front travels at a fixed speed and we know the time difference between detections. If this was all we had, then there would be an entire surface cone (like an expanding ring) of potential directions. But LIGO detectors are not omnidirectional so the entire ring is not actually the potential search space.
Justin Miller
What happens if two black holes of 1 billion solar masses each merge?
Is it possible a gravitational wave could carry destructive energy?
Blake Reyes
it's a welfare programme for people who couldn't get a job in the industry
Daniel Moore
What I've been wondering is why they aren't bombarded with waves at all times. From the Earth, from the Sun, from the Moon, from Jupiter, from millions of objects. I'm supposed to believe that they just pinpointed THAT. PARTICULAR. black hole?
Samuel Phillips
Technically they probably are, but the amount of energy released from those events is so tiny that it's practically undetectable. It took two black holes colliding to release a signal strong enough for LIGO to detect- read up on LIGO's sensitivity to get an idea of how weak the signal really is.
Alexander Hall
If you draw two sphere at the centers of two LIGO detectors, won't they intersect at a circle?
So again, how do you pinpoint he origin of the wave?
John Mitchell
It's not just timing. They also have information from the phase an the amplitude of the signal.
No. LISA a proposed space based detector from the European Space Agency will detect supermassive black hole binaries and collisions (as well as other things) to constrain galaxy formation, cosmology and gravitational physics. These events are though to be quite rare however but not destructive.
The power of gravitational waves emitted by the Earth-Sun system is the same as a typical lightbulb, 10's of watts. It's tiny and it's very long wavelength. To have something detectable with LIGO it needs to be ten's to hundreds of hertz and have a huge amount of mass moving.
Dominic Sanders
They aren't unobservable then are they?
Angel Lewis
>It's not just timing. They also have information from the phase an the amplitude of the signal. I have no idea how that stuff works. What's a good book/course reference for this?
Michael Williams
>how do they know the masses of two black holes that are colliding?
The relative masses change the shape of the waveform before the collision.
Jose Brooks
>The power of gravitational waves emitted by the Earth-Sun system is the same as a typical lightbulb, 10's of watts. It's tiny and it's very long wavelength. To have something detectable with LIGO it needs to be ten's to hundreds of hertz and have a huge amount of mass moving.
Why? How does that correlate to the massive gravity of the Earth and the Sun? Those tiny waves somehow exert forces multiple orders of magnitude above their size?
Brody King
The only book I've really ever glanced at on the topic is Saulson, Fundamentals of interferometric gravitational wave detectors. I can't say I've read it, I've only really done GWs from a theoretical perspective with Schutz A First Course in General Relativity, it's a good book but not light reading.
Most of what I know is from undergrad, I went to a LIGO heavy department.
Brandon Nelson
Gravitational waves do not mediate gravity in GR. They are special solutions to GR. A massive body in uniform motion for example generates no gravitational waves. It still has a gravitational field though. No changing quadrapolar moment, no gravitational waves.
Josiah Barnes
Meant for:
Ayden Lewis
Thanks!
And do you have any idea how they derive masses of two black holes that are colliding?
Easton Gonzalez
So you're saying the waves are only generated during a CHANGE in gravity?
Juan Adams
They are invisible, not unobservable
Leo Gomez
Waves are generated when the source of gravity moves
Alexander Sanchez
Its like the doppler effect but with the strength of gravity rather than the wavelength of light
Charles Bennett
It's like classical dipole EM waves. If you have a static charge there is no emission. If you have an accelerating charge which then has a changing dipole moment you get EM waves. With gravitational radiation it's the quadrupolar moment instead.
Two bodies in circular orbits around each other emit gravitational waves, the gravity at neither is changing.
Invisible is a shitty word too. They do not directly reflect photons. For actually practical purposes, you might as well say distant planets don't either. Considering gravitational lensing, they are more "visible" than said distant planets.
And if we're talking about "well if you were hypothetically near one it would be invisible" - what about the photon sphere?