What's been going on at LIGO in the past few months?
They've detected the first gravitational wave within 12 days, so shouldn't there have been some more discoveries by now? It's an observatory, after all.
This topic blew up in February and then died immediately after although it's essentially an entirely new way to learn about our universe. Why?
Also gravitational waves general I guess, I've done some research on them in the past couple of weeks and I can answer questions
>>8073677
Do we need big observatories like LIGO to detect them? Is it possible to reduce the size of the observatories?
>>8073681
The bigger the observatory, the more sensitive it is. The amplitude of a gravitational wave essentially decides how large the proportional change in length of an object will be.
If you've got a really large observatory, then, the absolute length difference between the arms will also be really large in comparison to a small observatory. And the greater the length difference, the more the two light waves will be out of phase.
So you would really just want to go even bigger. You could probably lower the size if you increased the sensitivity through other means to make up for it, but that would require better technology (such as more powerful lasers or higher quality mirrors). Increasing the size is an easy way to improve the sensitivity.
Something else that might be interesting: The lasers don't just travel the 4 km of the arms, they actually travel around 1120 km. The beams get reflected between the arms for a while before hitting the photo detector which lets them travel an even longer distance.
isn't detecting gravitational waves as proof of Einstein affirming the consequent?
Also, how are gravitational waves observed and attributed?
>>8073694
Awesome, thanks anon.
>>8073677
>This topic blew up in February and then died immediately after although it's essentially an entirely new way to learn about our universe. Why?
Because it's popsci cancer. Sensible people realized it was a meaningless "discovery" pretty quickly.
>>8073903
>isn't detecting gravitational waves as proof of Einstein affirming the consequent?
It's not really proof, just further evidence that Einstein's theory does an excellent job at predicting reality. Einstein's equations predicted gravitational waves and LIGO actually detected them.
It's really just one puzzle piece, only yellow journalism would call it proof.
>Also, how are gravitational waves observed and attributed?
Gravitational waves are essentially changes in gravitational fields that propagate at the speed of light. This is different from Newton's view of gravity where it's this magic force that acts instantly across an infinite distance.
They are different to electromagnetic waves in the sense that they do not move through space, they are rather the change of space (more precisely: a moving ripple in space-time) itself.
Like all waves, gravitational waves also have a frequency (and thus a wave length) and an amplitude. The frequency determines at what rate space gets distorted for a particular object under the influence of a gravitational wave. The amplitude determines how strong this distortion is.
Essentially, gravitational waves bend objects as they pass through them. The area of the object remains the same, it just gets stretched or compressed. The gif demonstrates this for a plus-polarization. Gravitational waves can also be cross-polarized, in which case they stretch the object diagonally.
LIGO and other laser interferometric observatories use this effect to sense gravitational waves. When a wave passes through the observatory, one arm gets stretched (longer) while the other arm gets compressed (shorter). As a result, one beam has to travel a smaller distance than the other one. This is why lasers are used: They always travel at the speed of light, even when the space-time around them gets bent. (Pt. 1)
>>8073903
>>8073961
The observatory is set up so that the two beams are initially out of phase. When they combine at the photo detector, they interfere destructively and you see no light signal at all. When a gravitational wave passes through the observatory, the phase of the beams shifts and you do see a signal.
There are also other factors which can produce signals such as seismic events which is why the entire observatory is engineered to reduce the effect of these factors as much as possible. The mirrors are dampened and constructed with high quality to minimize atomic jiggling, the lasers are high-powered, there's a vacuum inside the arms to prevent the beams from colliding with gas molecules and so on.
>>8073951
>Because it's popsci cancer. Sensible people realized it was a meaningless "discovery" pretty quickly.
Can you elaborate? Because the way I see it, gravitational waves let us detect events happening billions of light years away. It's not a discovery, it's a new way to observe the universe. And I say this as someone who's done more than just watch a couple of Youtube videos about the topic.
>>8073677
Other researchers basically found that there was a 99% chance the results were just cause of dust, because the guys who discovered the waves were incompetent
But since they had got so much publicity this info was buried in some arxiv print
>>8073977
Since I have no way to disprove your statement, can you post proof? I don't want to say you're wrong, but I also don't want to believe you without any evidence.
>>8073977
You're confusing LIGO with the BICEP2/Keck announcement from 2 years ago. They are not related, they are completely different observations. Everyone is aware of this, it's not buried.
