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> The gravitational waves from the collision reverberated in LIGO the morning of Aug. 17, 2017, followed by detections of gamma-rays, X-rays, radio waves, and o
by mirimir 8y ago
> The gravitational waves from the collision reverberated in LIGO the morning of Aug. 17, 2017, followed by detections of gamma-rays, X-rays, radio waves, and optical and infrared light. If gravity were leaking into other dimensions along the way, then the signal they measured in the gravitational wave detectors would have been weaker than expected. But it wasn't.
Do they really mean to say "followed by detections"? Don't gravitational waves propagate at c? Also, I'm puzzled by "weaker than expected". One issue is calculating expected intensities for gravitational waves vs electromagnetic radiation. The other is calibration of LIGO signals. It's not obvious that resulting uncertainties are small enough for drawing reliable conclusions about gravity leakage.
- Baeocystin 8y agoYes. Even if the creation events of each part of the spectrum are at the exact same time (which is unlikely) there is going to be matter in between the event and us. That matter will slow the rate of light's propagation.
- mirimir 8y agoAh. Didn't think of that. Edit: And I didn't see Animats' comment that EM radiation was delayed ~2 seconds. But also that the speed difference was very small.
- kakarot 8y agoThis conjecture also assumes that our understanding of thermodynamics applies in any other hypothetical dimension. It's entirely possible that displacement in these dimensions corresponds to an increase in energy in the system that offsets the "lost" energy.
- kawakiole 8y agoAnything is possible, but how would you falsify that hypothesis?
- mirimir 8y agoIndeed. And that's my complaint about the report itself.
- kakarot 8y agoGood question and I don't know the answer, but this unknown still helps to define the limits of what we can definitely say is and isn't taking place. We can't say "we're definitely not experiencing displacement in X dimensions" if we don't definitively know the rules of displacement are homogeneous in every dimension. Since we don't definitively know the number of dimensions, we also can't exhaustively test these rules.
- kawakiole 8y agoWe don't ever definitely know anything. That's why science and bayesian reasoning in general is so useful to begin with ;) We can be more or less confident about how stuff works though. For instance, thermodynamics is something we are very confident of having gotten right, because there are plenty of ways to test if doesn't work, and those test fail all the time (so far, at least!). So this article basically says: would it be easier to explain what we see if there were other dimensions? and the answer is it wouldn't, because we'd have to assume that things that we are very confident about (thermodynamics) are not correct, while simultaneously not providing any way to gain confidence in this new hypothesis (that there are new dimensions with different thermodynamic laws). This might change some day: before spectrography was a thing, all the theories about star composition were non-falsiable either!!
- JeromeBonnet 8y agoMy understanding is that the detection order follows the underlying phenomena: first the neutron stars fell towards each other, producing gravitational waves, and only then did the stars collide, producing electromagnetic waves.
- candiodari 8y agoAs I understand it gravitational waves aren't slowed down by anything whereas electromagnetic waves interact with matter along the way, which takes some amount of time. There isn't much matter to interact with, but not quite zero either. Something like 1e-23 of the distance had some amount of matter in it (mostly very diffuse gas clouds, nothing more).