I LIGO: Detecting Differences Less Than a Proton Length - How is It Possible?

AI Thread Summary
The LIGO detector achieves remarkable sensitivity by measuring relative changes in the lengths of its perpendicular arms, rather than absolute positions, which simplifies the detection of gravitational waves. It employs highly precise mirror mounts, operates in a vacuum, and uses stable lasers to minimize environmental interference. Extensive post-processing of signals helps correct for vibrations and noise, allowing it to detect changes smaller than the length of a proton. The system is designed to maintain alignment near the dark fringe of interference patterns, enhancing sensitivity to minute changes. Overall, LIGO's design and technology enable it to detect gravitational waves from cosmic events like merging neutron stars and black holes.
thegroundhog
Messages
16
Reaction score
10
TL;DR Summary
How is the LIGO detector able to be so accurate?
I read that the LIGO detector in the US was able to detect a difference of less that the length of a proton, or maybe even less than this. How is this possible? The perpendicular arms won't be the same length down to the nearest proton length. Also, at such small lengths the microclimate on each arm might be enough to shift the apparatus 1000x more than a proton length. What about minor tremors and other meteorological phenomena? I would love to know the exact detail of how it is able to be so accurate.
 
  • Like
Likes Demystifier and Dale
Physics news on Phys.org
Try this video. Veritasium answers your question with a very good explanation.

 
  • Like
Likes Demystifier and thegroundhog
Well, it took them many years to get to that level of sensitivity so it is presumably not easy...
The LIGO collaboration has published a large number of technical papers describing their setups (I have read some of them since I've used some related signal processing techniques). There are also a large number of popular articles. Have a look at the LIGO website.

Anyway, one of the key points here is they are detecting a difference between two signals/path. This is much, much easier than e.g. measuring the absolute position of two objects. That is, you don';t need to know WHERE the protons are in order to detect a relative change in position.
 
  • Like
Likes thegroundhog
Very precise mirror mounts that are extremely well isolated from their surroundings, mounted in extremely high vacuum, illuminated with extremely stable lasers, and surrounded by lots of sensors to detect uncontrolled vibration, and with extensive post processing of the signals to correct for that, is my understanding.
 
  • Like
Likes thegroundhog and Motore
LIGO and Virgo look for gravitational waves in the range of ~50-1000 Hz, optimal for merging neutron stars and stellar mass black holes. Motion that has a much lower frequency is not disturbing the measurement unless it's excessive. A multi-step pendulum suspension dampens motion in the sensitive range. They keep the interference near the dark fringe because that leads to larger relative changes in brightness from small changes in length difference. Sometimes noise is so large that they lose that alignment, during that time that individual detector cannot take data.
 
  • Informative
  • Like
Likes berkeman and Ibix
So basically, the change of interferometer arm length by a tiny fraction of laser wavelength transforms into a tiny fraction of laser light power compared to laser source power. By taking the source power big enough, even this tiny fraction of power becomes detectable.
 
Thread 'Question about pressure of a liquid'
I am looking at pressure in liquids and I am testing my idea. The vertical tube is 100m, the contraption is filled with water. The vertical tube is very thin(maybe 1mm^2 cross section). The area of the base is ~100m^2. Will he top half be launched in the air if suddenly it cracked?- assuming its light enough. I want to test my idea that if I had a thin long ruber tube that I lifted up, then the pressure at "red lines" will be high and that the $force = pressure * area$ would be massive...
I feel it should be solvable we just need to find a perfect pattern, and there will be a general pattern since the forces acting are based on a single function, so..... you can't actually say it is unsolvable right? Cause imaging 3 bodies actually existed somwhere in this universe then nature isn't gonna wait till we predict it! And yea I have checked in many places that tiny changes cause large changes so it becomes chaos........ but still I just can't accept that it is impossible to solve...
Back
Top