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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8 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.

    Also, can you please, please, PLEASE, \bigg{\textit{PLEASE}} make it possible to receive comments via email? I’d love to see your response to my question above, but I probably won’t remember to come back here to check.

  2. Will says:

    I imagine it would mostly sound painful.

  3. The Physicist The Physicist says:

    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.”

    What about adding a “subscribe” option?

  5. Pingback: TWSB: The Sound of a Solar Re (and a Do, a Mi, a Fa, a So, a La, a Ti, and More Do) « Le Seul Mot Juste

  6. Alexander Cooke says:

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

  7. 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 .

  8. 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.)

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