3 ms·
On long flights, don't we expect the light to arrive after the gravitational waves because it interacts more strongly with the particles that both sets of waves
by SomeStupidPoint 9y ago
On long flights, don't we expect the light to arrive after the gravitational waves because it interacts more strongly with the particles that both sets of waves traverse?
Both kinds of waves are slowed when passing through media, but because EM is much stronger than gravity, the effect from interstellar dust should be much stronger on EM than on gravity.
Even a 1-in-a-million slowdown of the EM versus gravity would mean that everything outside of ~100ly would arrive at least an hour later. Every intergalactic bit of light is passing through at least a few thousand lightyears of galactic dust, and potentially much more.
- stefco_ 9y agoThat is a different effect. Interstellar dust is extremely diffuse; it is just vacuum with the occasional chunk of matter absorbing some fraction of light. It can then reemit blackbody radiation, but that is different than what happens in continuous media, like glass or water. In continuous media, Maxwell's equations still describe linear wave propagation but with reduced velocity.
- tzs 9y agoWhat about pulse dispersion in the pulses from pulsars? (And even more so in fast radio bursts). Doesn't that require more than just absorption plus blackbody reemission? Not that it would make much difference. The delay due to dispersion goes down quadratically with increasing frequency. At the lowest frequency that Google tells me is used in radio astronomy, 13 MHz, the delay would be (if I've understood the dispersion equations correctly and done the math correctly) about a minute compared to visible light or gravity waves, and so not very useful. If you went down to 1 MHz, the delay would be a much more respectable 3 hours, but I'd expect that there would be way too much noise from terrestrial sources to do any useful radio astronomy anywhere down around there.
- stefco_ 9y agoYeah, but I believe that those effects are usually from near the source (which is part of why we can use details of the spectrum over time to infer source structure and composition). There might be cases I'm not aware of, though.