# Sound From a Super Nova

Let's say there exists an alternate reality from ours that is identical in every aspect save for one. There exists a substance in space that allows for the transmission of sound. Let's call this substance aether.

Aether has sound transmission qualities identical to the atmosphere here on Earth. You can't breathe it, it acts very identically the to the vacuum of space we have in our reality except for sound transmission. As far as acoustics it would be similar to that of an open plain since there isn't really much out there to echo off of.

Super novae are (usually) very far from our planet however they are also extremely energetic. Massive amounts of energy are expelled in tremendous explosions.

My question is, at what distance would the inhabitants of alternate Earth be able to hear a super nova if the sound was transmitted through the aether and to our atmosphere? Are there any stars close enough excluding our own?

EDIT: In response to @Frostfyre's comment, the aether will be as dense as it needs to be to have identical sound transmission speed to the atmosphere of Earth.

• The nearest supernova candidate we've so far identified is IK Pegasi, at 150 lightyears away. Sound does already transmit through open space, just at incredibly slow speeds and not at a point we could hear. The question, really, is how densely are you going to pack the universe with this new substance? – Frostfyre Jul 31 '15 at 15:09
• (Tangential) Your edit opens up an interesting point: Since this substance hasn't been picked up by planets, moons, and stars, it must be impervious to gravity, yes? Does this mean we have easy access to an anti-gravity mechanism? – Frostfyre Jul 31 '15 at 15:31
• Wouldn't there be a lot of other sounds going on in this universe? Like, the supposedly sublime sounds of the heavenly spheres revolving around the sun? And the sun moving around the galaxy? And the sun itself, all that energy has to be having some effect on the aether. – DaaaahWhoosh Jul 31 '15 at 16:24
• Possibly, for the purpose of this question I'm mainly interested in super novae since they are so big. "What does the universe sound like?" seems a bit broad to day the least :-). – kylie.a Jul 31 '15 at 16:28
• This is not opinion based. The question is simply asking: If space were able to transmit sound the way Earth's atmosphere does, at what distance would we be able to hear a supernova. And second, are there stars within that range to Earth? – James Aug 11 '16 at 16:13

All right, let's take a crack at this:

First, let's define a sound as a pressure wave traveling through a transmission medium. Since our aether is functionally identical to our atmosphere for those purposes, we need to find out what the threshold for human hearing is based on sound energy density, then find out how far a supernova's blast can travel before the imparted energy reaches that level.

For the first bit, Wikipedia has a chart of various sounds and their decibel level as well as the effective pressure necessary to reach that level. Looking at the chart, the auditory threshold is given as $0\;\text{dB}$, or $2 \cdot 10^{−5}\;\text{Pa}$. That's given for a constant tone rather than a single event, though, so let's bump our limit up to leaves rustling, which is $10\;\text{dB}$, or $6.32 \cdot 10^{-5}\;\text{Pa}$.

That gives a measure of how much force that we need to hear a sound, so let's move on to the supernova. Wikipedia comes to the rescue again in this case with all sorts of figures about supernovae. Since the energy released varies by the type of star, let's look at the low end, a star that has 8-10 solar masses worth of material. The chart "energetics of supernovae" on that page lists the kinetic energy released in that type of event as 1 foe, or $10^{44}\;\text{J}$.

Now for the conversion to see how far that energy will get us. A joule can be defined as a pascal times meters cubed, or pascals in a certain volume. Shuffle that around and we get joules divided by pascals equals the volume required in meters cubed.

$\frac{10^{44}\;\text{J}}{6.32 \cdot 10^{-5}\;\text{Pa}} = 1.58 \cdot 10^{48}\;\text{m}^{3}$

That's the total volume of space where the pressure wave through the aether will be a sound akin to leaves rustling. Since a supernova is an event that emanates from a single point in space, let's assume that's a perfect sphere. The radius of a sphere is given as the cubed root of three quarters pi times the volume.

$\sqrt[3]{\frac{3 \pi}{4} \cdot 1.58 \cdot 10^{48}\;\text{m}^{3}} = 1.6 \cdot 10^{16}\;\text{m} = 1.63\;\text{ly}$

1.63 light years. Not nearly as far as it would probably need to reach to hit us, but a pretty massive distance nonetheless. I took the minimum values for the supernova, too, so if there was a bigger bang, the distance would scale up appropriately.

• Actually, this is just the kinetic energy released by the supernova. If you look at the chart I referenced, you'll see that the 'core collapse' type supernova (which is what I based my figures on) expresses in total about 100 times the energy that is released as kinetic energy, mostly as neutrino energy. – Brandon Aug 1 '15 at 5:08
• neutrinos don't interact with the human ear, however, and therefore do not produce sound. – ApproachingDarknessFish Aug 11 '16 at 16:45