text: why can light travel through space but not sound?   jayzzz ain't far off. sound travels by pushing air particles. best way to imagine it is by imagining a bunch of jerks standing in a line (kind of like this one jerk that answered one of my questions a while back). the first jerk pushes the next guy in line and he runs into and shoves the jerk in front of him and then pushes back on the jerk who pushed him. this continues through the line, so that jerks get compressed together and then push back and become separated. the distance from compacted jerks to separated jerks is one jerk wavelength.  now imagine a long line of people and there is only one jerk every millionth person. if that jerk shoves someone, they won't shove the person in front of them and they won't shove back on the jerk. this is how it is in space. the earth is full of jerks, however.  jerks actually refers to atomic matter and the "shoving" are particle "collisions" (actually they don't collide, the apparent collision is just pauli repulsion). in space there are lots, on earth there are none. on earth, the compacted jerks corresponds to overpressure of air, and separated jerks corresponds to underpressure in air (or any other dense molecular medium like water). in space, there is only a single molecule per millions of area of vacuum, the pressure is actually negative, and sound can't transmit.  it is proposed that light also requires an ether-like medium to travel through space, due to problems with hawking radiation that can only be solved if the quantum vacuum acts like a fluid. i'm going to cut it short at that however.