31 ms·

I'm curious what the amplitude of these waves are: what's the (order of magnitude) change in the distance to a 1000 light year distant pulsar, as the gravitatio

I'm curious what the amplitude of these waves are: what's the (order of magnitude) change in the distance to a 1000 light year distant pulsar, as the gravitational wave passes through? Edit: Being told by @Dr_CMingarelli on twitter that it's 10 meters pr lightyear.

lucgommans 3y ago
You mean in like meters? > Each observatory has two light storage arms that are 4 kilometers in length. [...] A passing gravitational wave will slightly stretch one arm as it shortens the other. [...] Even with such long arms, the strongest gravitational waves will only change the distance between the ends of the arms by at most roughly 10⁻¹⁸ m. With the nominal hair value being 75 µm, `apt install qalc` tells me that's > 75 µm / 10^-18 m (75 * micrometer) / ((10^-18) * meter) = 7.5E13 so a change in length 7'500'000'000'000 times smaller than the width of a hair https://en.wikipedia.org/wiki/Gravitational_wave https://en.wikipedia.org/wiki/Gravitational_wave , https://en.wikipedia.org/wiki/Hair%27s_breadth https://en.wikipedia.org/wiki/Hair%27s_breadth
- beginning_end 3y ago
  I was referring to the latest results using pulsars.
- kennywinker 3y ago
  That's for the gravitational waves we can detect from LIGO. These new ones, as I understand it, are being detected by changes in pulsar frequency over 15 years of measurements - so they have a pretty different character than the ones wikipedia's talking about... I don't know how that translates to anything that makes any sense tho
kennywinker 3y ago
Per the wikipedia article: https://en.wikipedia.org/wiki/Gravitational_wave https://en.wikipedia.org/wiki/Gravitational_wave > Gravitational waves are not easily detectable. When they reach the Earth, they have a small amplitude with strain approximately 10^−21 "strain" being the unit-less measurement they use for gravitational wave. The ones we measured just now, if I'm reading this article right (https://iopscience.iop.org/article/10.3847/2041-8213/acdac6 https://iopscience.iop.org/article/10.3847/2041-8213/acdac6), are being reported as 2.4x10^-15. I can say that's a lot larger, but I can't tell you much else about what that means.

lucgommans 3y ago

You mean in like meters? > Each observatory has two light storage arms that are 4 kilometers in length. [...] A passing gravitational wave will slightly stretch one arm as it shortens the other. [...] Even with such long arms, the strongest gravitational waves will only change the distance between the ends of the arms by at most roughly 10⁻¹⁸ m. With the nominal hair value being 75 µm, `apt install qalc` tells me that's > 75 µm / 10^-18 m (75 * micrometer) / ((10^-18) * meter) = 7.5E13 so a change in length 7'500'000'000'000 times smaller than the width of a hair https://en.wikipedia.org/wiki/Gravitational_wave https://en.wikipedia.org/wiki/Gravitational_wave , https://en.wikipedia.org/wiki/Hair%27s_breadth https://en.wikipedia.org/wiki/Hair%27s_breadth

beginning_end 3y ago
I was referring to the latest results using pulsars.
kennywinker 3y ago
That's for the gravitational waves we can detect from LIGO. These new ones, as I understand it, are being detected by changes in pulsar frequency over 15 years of measurements - so they have a pretty different character than the ones wikipedia's talking about... I don't know how that translates to anything that makes any sense tho

kennywinker 3y ago

Per the wikipedia article: https://en.wikipedia.org/wiki/Gravitational_wave https://en.wikipedia.org/wiki/Gravitational_wave > Gravitational waves are not easily detectable. When they reach the Earth, they have a small amplitude with strain approximately 10^−21 "strain" being the unit-less measurement they use for gravitational wave. The ones we measured just now, if I'm reading this article right (https://iopscience.iop.org/article/10.3847/2041-8213/acdac6 https://iopscience.iop.org/article/10.3847/2041-8213/acdac6), are being reported as 2.4x10^-15. I can say that's a lot larger, but I can't tell you much else about what that means.