# Accelleration of the photon

1. Apr 18, 2007

### pixel01

Well, there has been another thread about the accelleration of photon, but it is when the photon move from one medium to another. Now i just imagine when i start to turn the light bulb on, the light also starts to propagate at c. So should photons have a certain accelleration value consequently?

2. Apr 18, 2007

### Hootenanny

Staff Emeritus
No, roughly speaking, when you turn on the light bulb the electrons in the filament atoms become excited, when they de-excite they emit photons corresponding to the change in energy levels. These photons are by definition travelling at c.

3. Apr 18, 2007

### rcgldr

Photons are emitted and captured at c.

What isn't clear to me is the time it takes for a photon to be emitted or captured. Assuming that a photon isn't infinitely small, then it could take a very short period of time to be emitted or captured. The other possibility is that photons are emitted and captured instantaneously (corresponding to an instantaneous change in the energy state of an electron).

4. Apr 20, 2007

### lpfr

Do not forget the Heisenberg uncertainty principle.
You can't know energy and time precisely. The product of the time incertitude and the energy incertitude will be greater or equal to h/4pi:
$$\Delta t\cdot \Delta E \ge {h\over 4\pi}$$
h is the Plank's constant.
Then, if you know exactly the energy of the photon you know nothing about the time of creation or of absorption.

Last edited: Apr 20, 2007