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I was about to reply the same based on a naive Fermi estimation argument concerning the energy density three solar masses distributed equally over a shell with

by gajomi 9y ago

I was about to reply the same based on a naive Fermi estimation argument concerning the energy density three solar masses distributed equally over a shell with thickness proportional to the effective width of the pulse. But I wonder, what would be the actually mechanism that would break up a planetary body? Would sufficiently strong grativitational waves at wavelengths smaller than the planet be able to stress/shear enough to cause a breakup? Or is there some kind of gravity/gravity interaction that would be needed?

raattgift 9y ago
It's not so much nothing, as practically nothing. The main issue is that the gravitational waves only couple with you (or rather your microscopic bits) very slightly. If you get close enough (~ 10^2-10^4 GW wavelengths depending on the system) then you have several sensory systems that in principle could -- with some awkward assumptions about signal transduction in the middle of some even more awkward changes of gauge -- produce something noticeable. The principal problem is that while a cell at one end of your body may move noticeably compared to a cell at the other end of your body from the perspective of someone watching a cell in the middle of your body, these three cells don't move around much with respect to their neighbouring cells, and the "guts" of each cell move around even less with respect to the cellular membranes. Some senses rely on groups of cells moving with respect to one another; some rely on intracellular activity alone. There is the possibility of a small slosh in your inner ears, where there are some structures that are exquisitely responsive to small strains; that might make you nauseous, or it might trigger an episode of tinnitus. It might also go unnoticed. That close to the merger you're likely to be vaporized by non-gravitational radiation, though. ( https://news.ycombinator.com/item?id=15352994 https://news.ycombinator.com/item?id=15352994 ) Finally I think intuitions break down before you get to the near field regime, and nobody can really tell you what to expect within a couple of wavelengths of the source of the gravitational radiation even some time before the merger. Certainly linearized gravity fails to produce gravitational waves thanks to an explosion of non-linearities. You can only really say that the dynamical spacetime is even more full of distortions in that regime. Unfortunately if we had a purely linear gravity in reality (i.e., if gravity wasn't itself a source of gravity), it is also the regime where one would expect several human senses would be obviously stimulated.

by gajomi 9y ago

raattgift 9y ago

It's not so much nothing, as practically nothing. The main issue is that the gravitational waves only couple with you (or rather your microscopic bits) very slightly. If you get close enough (~ 10^2-10^4 GW wavelengths depending on the system) then you have several sensory systems that in principle could -- with some awkward assumptions about signal transduction in the middle of some even more awkward changes of gauge -- produce something noticeable. The principal problem is that while a cell at one end of your body may move noticeably compared to a cell at the other end of your body from the perspective of someone watching a cell in the middle of your body, these three cells don't move around much with respect to their neighbouring cells, and the "guts" of each cell move around even less with respect to the cellular membranes. Some senses rely on groups of cells moving with respect to one another; some rely on intracellular activity alone. There is the possibility of a small slosh in your inner ears, where there are some structures that are exquisitely responsive to small strains; that might make you nauseous, or it might trigger an episode of tinnitus. It might also go unnoticed. That close to the merger you're likely to be vaporized by non-gravitational radiation, though. ( https://news.ycombinator.com/item?id=15352994 https://news.ycombinator.com/item?id=15352994 ) Finally I think intuitions break down before you get to the near field regime, and nobody can really tell you what to expect within a couple of wavelengths of the source of the gravitational radiation even some time before the merger. Certainly linearized gravity fails to produce gravitational waves thanks to an explosion of non-linearities. You can only really say that the dynamical spacetime is even more full of distortions in that regime. Unfortunately if we had a purely linear gravity in reality (i.e., if gravity wasn't itself a source of gravity), it is also the regime where one would expect several human senses would be obviously stimulated.