A Detecting Gravitational Waves: Antenna Sensitivity & Weber Bars

[marcusl]

Gravity wave antennas using cryo-cooled metal bars were operated continuously from the 70's through 90's, notably at Stanford, Louisiana and Rome. How much more sensitivity (how many orders of magnitude) was needed to detect GW's? Were their resonance frequencies likely to be excited by a black-hole merger, knowing what we now today?

 

[jedishrfu]

Here's an article on early attempts at GW detection:

https://www.aps.org/units/fhp/newsletters/spring2018/weber.cfm

and this one on Weber's bars:

https://en.wikipedia.org/wiki/Weber_bar

with $10^-16m$ spatial distortion accuracy.

whereas with LIGO its $10^-20m$ spatial distortion accuracy.

https://en.wikipedia.org/wiki/Gravitational_wave

Based on that I'd say it's unlikely that Weber had a detection.

 

[marcusl]

We know that Weber never had a detection--his bars weren't even cooled--but his efforts were followed by serious attempts with far more sensitive instruments. The Stanford and Louisiana detectors used 5 ton bars cooled to 4.2 K, for example, and later detectors at CERN and Rome/Frascati were operated below 3 mK. Sensitivities for several detectors seem to be in the 10^-20 range according to
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwjkgLqdqY7nAhWYG80KHcYmDYQQFjAAegQIAhAB&url=https%3A%2F
%2Farxiv.org%2Fpdf%2F1009.1138&usg=AOvVaw2n2nak8qAwmwJ8zFIf3sSh
if I'm reading it right.
This is what prompts my question, then: if sensitivities were in the right ballpark, were they just a little short of detecting events? Or was it the nature of a resonant-mass detector with its narrow bandwidth that was the problem? Or something else altogether?

 

[jedishrfu]

I remember at the time they didn’t know what the sensitivity needed to be so it was a shot in the dark. Also funding was a tough sell without any results. It’s much easier if you get the whiff of a signal that folks will argue about than no signal or bad results.

One article said that Weber came from an EE background into physics and wasn’t versed enough in all the things experimental physicists do to get good results.

Knowing what we know now about these GW events, I shudder to think what we would experience if Weber’s detector had detected it. Would it have been cataclysmic flash of light in the sky followed by intense weather phenomena or worse world ending?

 

[marcusl]

Thank you, but you have not addressed my questions.

 

[sysprog]

Thank you, but you have not addressed my questions.

It seems to me that he well and strongly did goodly much of what in that direction could be done.

 

[jedishrfu]

Thank you, but you have not addressed my questions.

Sadly, no. Perhaps I should never have replied. My apologies.

However, I think it was more the sensitivity as the gravitational wave frequen cover a wide range of values. With a narrow band width, it would be easy to miss an event but I still think it was the sensitivity limited.

 

[sysprog]

Sadly, no. Perhaps I should never have replied. My apologies.

However, I think it was more the sensitivity as the gravitational wave frequen cover a wide range of values. With a narrow band width, it would be easy to miss an event but I still think it was the sensitivity limited.

@jedishrfu, just a fella tryin' to have your back here, and I think that it is with good reason that I in this instance so do: in my view, yes, you did very extremely well respond.

 

[mfb]

Sensitivities for several detectors seem to be in the 10^-20 range

For continuous waves. Mergers are short events that quickly change their frequency.

Orbiting neutron stars or light black holes might be in the frequency range for many orbits but then their signal is much weaker than the signals LIGO/Virgo see, so 10^-20 won't get you anywhere.

Here is a sensitivity curve that includes AURIGA.

 

[jedishrfu]

That's a nice graph of sensitivity and kind of illustrates the reason why Weber couldn't pick up anything as his equipment was frequency limited and sensitivity limited.

 

[jedishrfu]

Often when I post, I consider the readership and even If I don't know the answer to what the OP is asking I try to provide context for other readers to get upto speed.

I would hope the OP would understand and appreciate my contribution. When they don't then I try to smooth things over with an apology.