why can light travel in vacuum where sound cannot do so?
Answers
hey
Sound is the transfer of vibrational energy. As the name suggests, you need “something” to actually vibrate, for that to happen.
Vacuum has no such “thingies” (Virtual particles being virtual in presence). Space has a few particles but are scattered very far, and so the sound waves lose energy.
Light - this topic is a bit more complex. In fact, it has astounded scientists for years! What is light? Instincts might tell a “group of particles moving”. Yet, one's science book tells one that it has a “wavelength” too! So, maybe a wave?
Nope. It's both. Or to be more precise it has characteristics of both particle and wave. And something entirely out of the ordinary. This is the basic “particle-wave duality”.
But, even this explanation wasn't … complete.
So, QFT (Quantum Field Theory) proposed an interesting look. According to this theory, light and every other fundamental particle (like electrons, neutrinos, quarks) are actually just the “excitations” of their own fields.
For light, the field is called “electro-magnetic” field.
These fields are everywhere. I am aware that this may mislead. It shouldn't be taken as a “medium” like aether (that theory was put down many years ago).
Take it as … “fields”. Assigning numbers to each point in space. (But of course, that's a hand-wavey description.)
Somewhere the field values are zero, somewhere they are not. Those places where they are non-zero, that's what we would call light (or for other fields, their own respective particles).
Phonon (sound) is not a fundamental particle - hey, it's not even a particle. It pops up in the math like a particle. Is polite to our equations, and makes the Maths a heck of a lot easier. It's not something physical. That's why it doesn't have a field like light. In fact, these two are a completely different thing.
That's why light travels in vacuum yet sound cannot.
thanku :-)