# Particles and Waves

1. Sep 12, 2006

### Karthikeyan

Hi friends,
I have some question regarding particle and wave nature of EM energy.

1. What is a wave and a particle? How are they related?
2. Also, we know that sun light travels through the universe down to earth..so light can travel without any medium....But waves do require medium to travel..so how is it? Does the EM energy takes particle form to traverse medium less area and wave form in a medium?

2. Sep 12, 2006

### priya_india

A wave does not have matter but a particle does.
And who said wave needs a medium to travel ! well they are related by einstins relativity equation.E=mc square. and can be explained by the wave particle duality of quantum physics.
every particle is wave and wave is particle. it may seem strange but has meen proved.

3. Sep 12, 2006

### ZapperZ

Staff Emeritus
4. Sep 12, 2006

### Karthikeyan

Thanks for the replies...I asked this question becoz I had few basic doubts now that with these replies let me formulate them too
1. Fine that light can travel without a medium but how does it happen...In a medium I can say that the energy propagates itself through the medium but how is it where there is no medium
2. Fine again that E=mc^2 relates particle to wave, but I would appreciate a more practical explanation since that would help me understand few basics in quantum physics..I mean wave is energy packets right then what is particle...is it a single energy packet or something like that

5. Oct 1, 2006

confused!!

Does every particle is a wave or every particle acts as if guided by a wave between the position measurements? I am really confused about that.
Thanks

6. Oct 2, 2006

### mgelfan

It's not that anybody knows that light waves aren't disturbances in some medium. It's just that the medium is, so far, undetectable. So what would you say about this hypothetical medium? Anyway, Einstein developed a nice kinematics that doesn't require referencing the light medium -- and physicists can carry on with their work as if such a medium doesn't exist. But really, nobody knows.

A wave is a frequency distribution. A particle is what's being distributed.

For example, in quantum experiments involving very weak light going through, say, a double-slit apparatus and producing a predictable pattern (after thousands of 'dots' had been produced) of individually appearing 'dots' (that is, the patterns are generated dot-by-dot) on a detecting screen. You can think of the individual 'dots' as the particles (or photons) in this sort of situation and their distribution on the screen as the wave (or, in the case of a double-slit setup, what's produced via the interaction or interference of two waves).

What are the precise physical characteristics of the 'optical disturbance(s)' (the light) that travelled between the emitter and the detecting screen to produce the observed pattern? Nobody knows. But qm treats the situation between emission and detection as if it were a wave.