# EM length of gravitational waves

Maybe a stupid question and maybe sensless to ask, but as I don't know, I ask anyway:
what is the length of the newly found gravitational waves in terms of traditional EM wavelengths?

Maybe a stupid question and maybe sensless to ask, but as I don't know, I ask anyway:
what is the length of the newly found gravitational waves in terms of traditional EM wavelengths?

I would think it would be the same as the frequency with which the two bodies orbited one another. I'd think that would be gigameters.

davenn
Gold Member
what is the length of the newly found gravitational waves in terms of traditional EM wavelengths?

unless they finally come together in the "unified theory" that physicists are searching for
putting gravitational waves and EM waves in the same sentence doesn't make sense

Dave

jtbell
Mentor
what is the length of the newly found gravitational waves in terms of traditional EM wavelengths?

It's a range because the signal didn't have a constant wavelength and frequency. The frequency increased with time (and the wavelength decreased) in a pattern that has been described as a "chirp."

If by "in terms of traditional EM wavelengths" you mean which electromagnetic waves have similar wavelengths, look up the wavelengths referenced above, in a diagram of the electromagnetic spectrum on Wikipedia or elsewhere. I'm on my way to dinner...

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jtbell
Mentor
From the article you cited:
If two black holes are stably orbiting each other, they produce a continuous stream of gravitational waves at twice the orbital frequency, carrying away the system's rotational energy and angular momentum. Such ripples are thought to have wavelengths that are tens of light-years and are relatively weak.
(I added the boldface.) But these are not the gravitational waves that LIGO detected.

What LIGO detected was the stronger waves radiated as the two BHs were spiraling towards each other, faster and faster (higher and higher frequency), just before they merged. I can't lay my fingers on it at the moment, but I remember reading that the detected frequency varied from maybe 30 Hz up to a few hundred Hz. Choose 100 Hz as a typical value. Using v = fλ and v = c = 300000 km/s, what do you get for λ?

fresh_42
fresh_42
Mentor
From the article you cited:

(I added the boldface.) But these are not the gravitational waves that LIGO detected.

What LIGO detected was the stronger waves radiated as the two BHs were spiraling towards each other, faster and faster (higher and higher frequency), just before they merged. I can't lay my fingers on it at the moment, but I remember reading that the detected frequency varied from maybe 30 Hz up to a few hundred Hz. Choose 100 Hz as a typical value. Using v = fλ and v = c = 300000 km/s, what do you get for λ?
Thanks for clarification.

unless they finally come together in the "unified theory" that physicists are searching for
putting gravitational waves and EM waves in the same sentence doesn't make sense

Dave

Yes, but gravity waves and EM waves are quite similar in form. They are both consequences of an attractive force in 3+1D. They both propagate at c. So the wavelengths seem like the same thing to me.