Could there be a substance so dense and/or at the right temperature that sound could move fast enough to apporach the speed of light? Has any Doper ever read about attempts to push the speed of sound to some max??? - Jinx
In the sense that physical disturbances propagate with high speeds (which is what sound waves are), theoretically yes. In fact, the more rigid an object is, the faster disturbances propagate (oversimplified). Coupled with the SR limit on the speed of information, this leads to limits on how rigid objects can become.
I bet sound waves could travel quite fast through neutronium, probably the densest substance known.
Good bet, snailboy. As I recall, the speed of sound in neutronium is precisely 1/3 c.
How would you calculate this?
(I presume we don’t have chunks of it hooked to sound machines.)
I think that unobtainium wins hands-down. (That’s the first time I’ve ever been able to mention it in GQ before someone else.)
Well, I would use a finite element model with masses, springs and dampers to compute the natural vibration frequencies.
Not that I could do it for neutronimum, you understand.
How dense is it and what are it’s properties?
Where did you get that? I seem to recall calculating this in freshman astro class, and IIRC the result was a function of density, i.e. function of neutron star mass. As the neutron star mass approaches the upper limit (1.4 M[sub]sun[/sub]) sound speed approaches c.
It most certainly does! And it has been thoroughly demnstrated in this capacity through rigorous tests using handwavium technology.
It’s densely packed neutrons found in neutron stars after a supernova. One spoonful of neutronium weighs about as much as a train.
I think you’re thinking of a white dwarf. Density of a neutron star is on the order of 10[sup]14[/sup] g/cm[sup]3[/sup], so a teaspoon full of it would weigh 1000 times more than the heaviest freight train in the world.
This’ll teach me to post past my bedtime. The 1/3 c figure is for a radiation-dominated gas, such as existed in the early Universe (in fact, it’s the pressure differences from these sound waves which we see in the WMAP data, and which eventually evolved into galaxies and the like). For neutronium, it does indeed depend on the mass of the star, and can get quite close to c. And despite the lack of experimental samples, radiation-dominated gasses and degenerate matter are both very simple fluids, and very simple to model, so we have a fair confidence in our theoretical descriptions of both.
Would I be correct in thinking that the densest possible matter would be neutronium in a neutron star just 1 wafer-thin-mint’s-mass (M[sub]W-TM[/sub]) less than whatever mass would be required for it to collapse into a black hople/singularity?
Denser matter has been detected between the ears of… Ooops, wrong thread.
For your reading pleasure:
Well, first of all, there may be objects called quark stars which are even denser than neutron stars, but they’re only theoretical so far, and would be very difficult to form (just a tad too much mass, and you get a black hole; a tad too little, and it’s an ordinary neutron star). And it also depends on whether you want to count a black hole as “matter”, since they can in principle be much denser. But other than that, yes, a just barely almost critical neutron star would be the densest thing we know to exist which would unambiguously qualify as matter.