# Q: If you could hear through space as though it were filled with air, what would you hear?

Physicist: You’d be able to hear the Sun, and nothing else.  Maybe at night you’d be able to hear your own thoughts.

Owing to the nature of how things like sound and light spread out, the loudness and brightness of a thing is exactly proportional to how big it appears.

The amount of light we get from the Sun is a function of its temperature (around 5,500 °C) and the angle it takes up in the sky (about half a degree across).

If you could get a small metal ball to the same temperature (assuming it wouldn’t melt, which is exactly what it would do) and moved it so that it appeared to be the same size as the Sun (0.5 degrees) then it would feel exactly as warm and bright as the Sun feels from here (on Earth).

As you move away from a source the intensity of that source drops like 1/R^2, simply because the energy gets spread out over a larger area.  And, as you move away from a source, the size that the source appears to shrink the same way.  This is a useful “math hack” to figure out how big things would need to be to look/sound the same.

Similarly, the Sun, if we could hear it, would be exactly as loud as any other large-marble-sized nuclear explosion held at arm’s length.

Quite loud.

There are some issues with the nature of sound.  Notably, if sound gets too loud it stops acting like a wave and tends to break apart.  It stops acting like sound and starts to act more like a frothy foam of shock fronts.

But as long as we’re hearing through space, we may as well ignore that problem too.

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### 9 Responses to Q: If you could hear through space as though it were filled with air, what would you hear?

1. qwert says:

The last bit is extremely interesting. Are there any examples (outside of laboratories) where sounds break into a frothy foam? I wonder what that would sound like.

2. Will says:

I imagine it would mostly sound painful.

3. The Physicist says:

@qwert
There are several (reasonable) assumptions that go into the derivation of sound from the Navier-Stokes equation. Among them are things like “pressure is a continuous function of the coordinates (changes smoothly)” and “the pressure differences are small compared to the ambient pressures”.
The first, and generally both, of these conditions are violated in high explosives, and usually (but not always) in low explosives.
It should be noted that you can definitely hear a high explosive, but the clean wave-like nature of the sound breaks down near the source. As a result the 1/R^2 intensity rule may not necessarily hold up. In general, if you can survive an explosion, you’re far enough away that the sound you hear is behaving more like a wave, and less like a diffusion of energy.

4. qwert says:

Correct me if I’m wrong. In short, the answer is “yes, but the experience would kill you.”

5. Alexander Cooke says:

Number of DB=10*(12+log(W))
It would be around 150DB. Very painful.

6. Bob says:

That’s right. It would be VERY painful. 150DB would be about as loud as a jet engine from 30 meters away. Hearing damage begins at about 120DB, and you start feeling pain at about 130DB. Seriously, a sound as loud as the Sun from 93 million miles away, or a jet engine from 30m away, would seriously damage your hearing. For more details on loudnesses of everyday things, check Wikipedia .

7. Ryan says:

Hearing damage technically begins at 100DB, 120DB is major damage. Technically, all sound(at least most sounds) do little bit of damage(emphasis on little.)

8. Robocop says:

Even though the sound would be 150dB, we could have evolved with double to triple ear lobe protection to accommodate for the sound and have had quite a different physiology. We could have looked like aliens, skin covering our ears, if there would even be a need for any ears since the deafening sound would most definitely make it impossible to communicate with spoken words. We would most likely be a visual species. I came here to find the answer though to a similar question and that is would the universe even be able to exist if it was filled with air? Would it self ignite due to incredible amount of heat and would we again be left with a vacuum or what? Would the stars eat up the air for burning? I guess after reading all these answers vacuum really is the best way to have a star close to planet. Why though is everything so perfectly made? Space seems to perfect to be true. After the initial consideration of irrationality, the deeper you look the more you see that everything in the universe has it’s purpose as far as the composition, physical laws, chemistry and even us. Someone said we’re the way for the universe to look at itself for we were made by it. However, why are we the end product? Why is everything else dead and why are there these rules, why do atoms exist or stars or black holes? Why does anything exist. When you’re a kid you believe the grownups know these things but just won’t tell you until you’re old but then you grow up and find out they don’t have a clue either it gets worrisome. The vastness of space could suppose a simulation also, however that’s a whole other story.