6 ms·

> Typical gravitational-wave events change the length of the arms by only a fraction of the width of a proton. Sensing such minute changes requires painstaking

> Typical gravitational-wave events change the length of the arms by only a fraction of the width of a proton. Sensing such minute changes requires painstaking isolation from noise coming from the environment and from the lasers themselves. i find it utterly fascinating that we're able to detect such a minuscule deviation

pfdietz 3y ago
Lasers beams are bounced back and forth many times, so the deviation builds up. The beams have to be very powerful (100s of kW) to reduce photon counting noise sufficiently.
- wwarner 3y ago
  Kip Thorne explains it pretty clearly in this 2002 lecture https://youtu.be/mGdbI24FvXQ https://youtu.be/mGdbI24FvXQ
dekhn 3y ago
interferometry is indeed amazing. When the ultra-important Michelson-Morley experiment was run some ~100 years ago, they were doing interferometry but in those days there wasn't really good vibration isolation technology. They had to float their whole experiment on a pool of mercury (!) in the sub-sub basement of an idle building, and even then, deliveries nearby (by horse) would cause problems. Nowadays, physics students do the MM experiment in a lab on a benchtop in a day.
- acqq 3y ago
  I'd like to read how these problems are solved "in a lab on a benchtop" today!
  - funac 3y ago
    you can build very good hydrostatic vibration isolators in a home machine shop nowadays; commerical optical tables are /very/ steady
    - deleted 3y ago
      [deleted]
  - dekhn 3y ago
    the original experiment is pictured here: https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_exper... what makes it possible to do in a desktop lab course combination of a large number of different innovations. The first is that we know how to make extremely stiff/rigid/strong/flat/thermally stable tables (https://www.thorlabs.com/navigation.cfm?guide_id=41 https://www.thorlabs.com/navigation.cfm?guide_id=41) which can optionally be placed on active vibration-cancelling struts (https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1095 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=10...). The second is using cage systems for mounting things with everything lined up parallel and centered (https://www.thorlabs.com/navigation.cfm?guide_id=2255 https://www.thorlabs.com/navigation.cfm?guide_id=2255). The third is precise kinematic mounts which make real-time angle tuning a lot easier/more reliable (https://www.thorlabs.com/thorproduct.cfm?partnumber=KM100#ad-image-0 https://www.thorlabs.com/thorproduct.cfm?partnumber=KM100#ad...). The fourth is now we have powerful lasers and LEDs that make generating lots of light all pointing in the right direection easier (https://www.thorlabs.com/thorproduct.cfm?partnumber=CPS532-C2 https://www.thorlabs.com/thorproduct.cfm?partnumber=CPS532-C...). The fifth is that high quality standardized optical parts (mirrors, lenses, etc) are easily available from a wide range of vendors (https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=10649 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=10...). There are a number of other innovations in material science. but I'd recommend taking a look at Thorlab's Michelson-Morley educational kit. For $3K you get basically everything you need to carry out the experiment: https://www.thorlabs.com/thorproduct.cfm?partnumber=EDU-MINT2 https://www.thorlabs.com/thorproduct.cfm?partnumber=EDU-MINT... plus a nice manual https://www.thorlabs.com/drawings/5d9e11209b7d4536-820A3379-BBFA-E254-33DC018F5C832848/EDU-MINT2-EnglishManual.pdf https://www.thorlabs.com/drawings/5d9e11209b7d4536-820A3379-... that walks you through physical setup and theory behind the experiment (which among other things helped lead to special relativity). if you want more like this, see https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=11630#ad-image-0 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=11... which is a hardware kit that accompanies an actual optical lab class. The course is online: https://www.thorlabs.com/drawings/5d9e11209b7d4536-820A3379-BBFA-E254-33DC018F5C832848/EDU-OMC1-CourseNotes.pdf https://www.thorlabs.com/drawings/5d9e11209b7d4536-820A3379-... and gives a fairly straightforward introduction to optics. With this, you can easily build a microscope from components or any number of other nifty optical systems. Non-optics people (IE, programmers, etc) with enough time and money can learn how to do real-world optical experiments in their garage (this applies to astronomy too). For example after a significant time/money investment, have started building my own microscopes which use real-time object detection to track tardigrades to do behavior analysis (lest anybody feel imposter syndrome, trust me it took a ton of time and money and even then I'm not quite at the level of a good grad student). It's not my favorite but you can also read https://www.amazon.com/Perfectionists-Precision-Engineers-Created-Modern/dp/0062652567 https://www.amazon.com/Perfectionists-Precision-Engineers-Cr... If you want to truly go down the rabbit hole, https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/Moore_Tools/Foundations_of_Mechanical_Accuracy.pdf https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/M...

pfdietz 3y ago

Lasers beams are bounced back and forth many times, so the deviation builds up. The beams have to be very powerful (100s of kW) to reduce photon counting noise sufficiently.

wwarner 3y ago
Kip Thorne explains it pretty clearly in this 2002 lecture https://youtu.be/mGdbI24FvXQ https://youtu.be/mGdbI24FvXQ

dekhn 3y ago

interferometry is indeed amazing. When the ultra-important Michelson-Morley experiment was run some ~100 years ago, they were doing interferometry but in those days there wasn't really good vibration isolation technology. They had to float their whole experiment on a pool of mercury (!) in the sub-sub basement of an idle building, and even then, deliveries nearby (by horse) would cause problems. Nowadays, physics students do the MM experiment in a lab on a benchtop in a day.

acqq 3y ago
I'd like to read how these problems are solved "in a lab on a benchtop" today!
- funac 3y ago
  you can build very good hydrostatic vibration isolators in a home machine shop nowadays; commerical optical tables are /very/ steady
  - deleted 3y ago
    [deleted]
- dekhn 3y ago
  the original experiment is pictured here: https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_exper... what makes it possible to do in a desktop lab course combination of a large number of different innovations. The first is that we know how to make extremely stiff/rigid/strong/flat/thermally stable tables (https://www.thorlabs.com/navigation.cfm?guide_id=41 https://www.thorlabs.com/navigation.cfm?guide_id=41) which can optionally be placed on active vibration-cancelling struts (https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1095 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=10...). The second is using cage systems for mounting things with everything lined up parallel and centered (https://www.thorlabs.com/navigation.cfm?guide_id=2255 https://www.thorlabs.com/navigation.cfm?guide_id=2255). The third is precise kinematic mounts which make real-time angle tuning a lot easier/more reliable (https://www.thorlabs.com/thorproduct.cfm?partnumber=KM100#ad-image-0 https://www.thorlabs.com/thorproduct.cfm?partnumber=KM100#ad...). The fourth is now we have powerful lasers and LEDs that make generating lots of light all pointing in the right direection easier (https://www.thorlabs.com/thorproduct.cfm?partnumber=CPS532-C2 https://www.thorlabs.com/thorproduct.cfm?partnumber=CPS532-C...). The fifth is that high quality standardized optical parts (mirrors, lenses, etc) are easily available from a wide range of vendors (https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=10649 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=10...). There are a number of other innovations in material science. but I'd recommend taking a look at Thorlab's Michelson-Morley educational kit. For $3K you get basically everything you need to carry out the experiment: https://www.thorlabs.com/thorproduct.cfm?partnumber=EDU-MINT2 https://www.thorlabs.com/thorproduct.cfm?partnumber=EDU-MINT... plus a nice manual https://www.thorlabs.com/drawings/5d9e11209b7d4536-820A3379-BBFA-E254-33DC018F5C832848/EDU-MINT2-EnglishManual.pdf https://www.thorlabs.com/drawings/5d9e11209b7d4536-820A3379-... that walks you through physical setup and theory behind the experiment (which among other things helped lead to special relativity). if you want more like this, see https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=11630#ad-image-0 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=11... which is a hardware kit that accompanies an actual optical lab class. The course is online: https://www.thorlabs.com/drawings/5d9e11209b7d4536-820A3379-BBFA-E254-33DC018F5C832848/EDU-OMC1-CourseNotes.pdf https://www.thorlabs.com/drawings/5d9e11209b7d4536-820A3379-... and gives a fairly straightforward introduction to optics. With this, you can easily build a microscope from components or any number of other nifty optical systems. Non-optics people (IE, programmers, etc) with enough time and money can learn how to do real-world optical experiments in their garage (this applies to astronomy too). For example after a significant time/money investment, have started building my own microscopes which use real-time object detection to track tardigrades to do behavior analysis (lest anybody feel imposter syndrome, trust me it took a ton of time and money and even then I'm not quite at the level of a good grad student). It's not my favorite but you can also read https://www.amazon.com/Perfectionists-Precision-Engineers-Created-Modern/dp/0062652567 https://www.amazon.com/Perfectionists-Precision-Engineers-Cr... If you want to truly go down the rabbit hole, https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/Moore_Tools/Foundations_of_Mechanical_Accuracy.pdf https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/M...