Katie Mack (@AstroKatie)
nitter.1d4.us
The news is out! The @NANOGrav pulsar timing array collaboration has detected a background of cosmic gravitational waves rippling through our Universe! Let’s talk about it!(Full press conference tomorrow, https://nanograv.org/news/2023Announcement)1/n

This is the announcement that was being hyped up in that aliens or time-travel thread a few days ago.

The announcement is that the scientists who were studying gravitational waves found gravitational waves. This was perhaps a bit overhyped.

To be fair, it's a very big experiment and it's nice that they got it all to work. They also found more gravitational waves than expected.

  • culpritus [any]
    ·
    1 year ago

    Determining the speed of gravity was also an important piece of these experiments with LIGO iirc. It seems to be the same as the speed of light, but that raises some interesting questions too.

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

      • culpritus [any]
        ·
        1 year ago

        This part stood out:

        The detection of GW170817 in 2017, the finalé of a neutron star inspiral observed through both gravitational waves and gamma rays, at a distance of 130 million light years, currently provides by far the best limit on the difference between the speed of light and that of gravity. Photons were detected 1.7 seconds after peak gravitational wave emission; assuming a delay of zero to 10 seconds, the difference between the speeds of gravitational and electromagnetic waves, vGW − vEM, is constrained to between −3×10−15 and +7×10−16 times the speed of light.

    • DefinitelyNotAPhone [he/him]
      ·
      1 year ago

      Out of curiosity, what questions are brought up by light and gravity having the same speed? I thought the general consensus was that the speed of light is just the speed of the spread of information in our laws of physics, so it would make sense that all phenomenon that don't rely on mass (which is a weird thing to say about gravity, but you know what I mean) would travel at that speed?

      • culpritus [any]
        ·
        1 year ago

        First, I'm just a sciency dork. I don't have any real expertise myself.

        There's a specific distinction between gravity waves and mass aka plain ole gravity.

        Gravity waves are supposed to be space-time distortions that propagate from what I'll call strong dynamic mass events. This distortion propagates at C, but mass information itself seems to be instantaneous as far as I know. So that's pretty interesting. If the medium of space-time has an info speed limit, then how does mass work on everything everywhere all at once? And if it does work like that, then why do these special events create these distortions. Could they provide a way to examine this assumption of instantaneous-ness? Does a distortion in space-time aka gravity wave potentially represent a violation of this instantaneous-ness?

        Examining these events via special relativity seems to work pretty well, but we still have no quantum gravity understanding. And the only things that actually travel at C (or near C) are massless particles. Entanglement is the only phenomenon that provides a form of instantaneous-ness. So it would seem mass might not be related to particle info (gravitons) because that would mean they would have to move faster than C, right? So is mass just the result of some entanglement originating from the big bang? That'd be pretty freaky.