LIGO gravity waves

You bet there are! Some are dangerous predators.

Jeroen Belleman

It's taming time!

Then... It's time taming time.

We need to get more done with "slow light progress", if that phase (hehehe) makes any sense to you.

A Fabry-Perot with a finesse of 200,000 (you can get those commercially these days) and a milliwatt or so of input light can see displacements like that on a tabletop.

The really impressive thing is being able to do it over kilometres.

Cheers

Phil Hobbs

The REALLY impressive thing IMHO is that Einstein nailed it yet again.

Einstein wasn't infallible, but he nailed four independent physical problems in 1905, and Max Planck was a smart enough editor to publish all four papers, without sending any of them out for review.

I found this difficult to believe but Brandon R. Brown's biography asserts it as a fact.

Going on to infer that Einstein was infallible is probably a step too far. God definitely does seem to play dice.

Hi,

The vertical drilled interferometer arm might be unfeasible for various reasons but I just put it forward as an idea, probably it is already planned many years ago I wouldn't be surprised if one is built if the technical hurdles aren't too difficult.

cheers, Jamie

Hi,

Just like any successful experiment they constructed it to be sensitive enough to detect the signal they were looking for. If they want to detect a more sensitive signal they can redesign it to be more sensitive, so saying it is right at the limit of experimental science is incorrect. For example increasing the laser power gives more amplitude output from the interferometer overlap, ie 10x laser power should be proportional to 10x signal output. Of course with more laser power, there is more mirror heating and thus noise, but there are ways to deal with that too, of course a more sensitive experiment will probably be a lot more expensive with 1000's of people working on it.

cheers, Jamie

Hi,

The only drawback for a kilometers long interferometer is they can only detect low frequency gravity waves, as if the gravity wave has a full period of oscillation within the interferometer arm (stretch/shrink) then there is no change in path length to measure. Although there might still be an AC measurement that shows the high frequency I guess.

I was thinking of a compact gravity wave detector using a bundle of small diameter fiberoptic glass fibers (apparently fibers of just a few micrometers diameter have been commercially produced).

Instead of using mirrors at the ends of the interferometer arms, the fibers would be bent 180 degrees at the end of the arm, so the laser light would travel in a single ~5um diameter fiber, and the fiber itself would go up and down the interferometer arm ~1 million times, thus making the effective path length a million times longer, ie a 1 meter interferometer would be 1000km effective length, but would still respond to high frequency gravity waves with wave period greater than 2meters or so.

The lack of end mirrors imparting thermal noise into the measurement would be gone too.

However a new issue would be the internal noise in the fiberoptic cable, I don't know for sure if this noise grows faster with cable length than the gravity wave measurement gain but I think the signal would grow faster than the noise, and the fiberoptic noise should cancel out, there might be ways to reduce the noise too, since the whole setup is only 1 meter arm length, the whole thing could be cryogenically cooled etc. It might be less prone to vibrations etc since it is all in one place.

So each arm would be a bundle of fiberoptics with 180 degree winding heads at the ends, and the whole gravity wave detector would have 3 one-meter long arms orthagonal, with two laser frequencies in each arm, and three of the Fabry-Perot interferometers you mentioned. This would give a gravity wave detector sensitive to high frequency gravity waves and also be vector sensitive and portable.

cheers, Jamie

Once you detect those gravity waves, xkcd has an application...

Cheers, James Arthur

It's amazing how many bits of information you can fit into a collapsing black hole... The channel does look a little noisy. :^)

George H.

And when not using it to search for gravity waves you can also detect elecric fileds, temperature gradients, and ordinary sound waves :)

looks like a particularly inefficient MHD based electric generator to my eyes, if it works at all.

The moral to the story is that no one escapes being spammed anywhere in the entire universe.

The problem with this idea is probably that there is a minimum noise always no matter what due to the phonon interaction in the glass fiber, which creates uncertainty and dispersion of the light frequency much greater than any length offset from typically measured gravity waves.

I'm not sure if there is any way to effectively have almost zero frequency dispersion in a long glass fiber.

If the idea could work, it possibly also should use a pulsed high power laser in order to have sufficient light intensity after the long fiber length, maybe pulses of just a single wave period of light that interferes and feeds into a PMT.

There might be some form of matter ie a Bose Einstein condensate that can propagate phonons of a limited energy without any dispersion of frequency and maybe even reflect the phonons maybe so that the length gain of multiple paths in the interferometer arms could be used.

cheers, Jamie

Hi,

So basically the interferometer laser has to be isolated from all matter, and travel in free space. It would be nice to have a way to have the light take multiple paths to shorten the interferometer arms still but maybe not possible doh! :D

cheers, Jamie

Unless a quantum glass fiber can be made with zero phonon noise, and no transmission light loss, or at least reduced phonon noise by having a high electric field imposed on the fiber to essentially make a "superconducting light fiber optic cable" or alternatively have an AC electric field imposed on the cable bundle to function as a lock in amplifier for noise reduction, then I have a new idea for detecting gravity waves, that uses off the shelf technology.

...

Gravity waves could be detected with a very thin superconducting wire, wound in the same way as the fiberoptic wire would be, with 1meter straight wiring and then 180 degree turns at each end, wound onto a cylinder with a balanced wind to cancel out any stray fields.

The superconducting wire could be 1000km long, but only over a 1meter length, so that would be a half million full winds plus the winding heads.

One benefit of using superconducting wire and electrons to detect gravity waves in comparison to light is that the electrons travel ideally with no dispersion and no losses with increasing wire length.

Once the wire itself is isolated from external electromagnetic/radiation and vibration, to detect gravity waves the coil would be energized etc.

To make a pulsed superconducting coil electron interferometer for detecting gravity waves, two of these coils could be put orthogonal.

Normal current in a coil would be replaced with spin current, so that electrons would have alternating spin as they are fed into the coils, and then the two coils "outputs" would interfere, in that the electrons may have the same or opposite spin as they come out of the orthogonal coils depending on the phase. The varying spin interference should create a measurable amplitude at the interference of the electrons.

The circuit would attempt to keep the phase lined up so that the interfering electrons have opposite spin, with super sensitive circuitry and use the measured interferometer output as an error signal to keep the phase lined up with the super sensitive circuitry. This circuit is to match the effective superconducting interferometer arm lengths.

The drawback compared to a pure optical solution is the sensitivity to electric fields, but with balanced windings and massive shielding this can be minimized, and also the signal gain from adding more windings helps.

cheers, Jamie