teetar said:
I've heard that basically photons can exhibit wave-like or particle-like based on what kind of experiment you perform to prove one or the other. However, are they hence both waves and particles at the same time?
This is a common question here at PF and one that requires a little delicacy when thinking about. First and foremost, you have to understand that the primary theory dealing with photons is called Quantum Electrodynamics (QED). From wiki:
http://en.wikipedia.org/wiki/Quantum_electrodynamics
(QED) is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved.QED mathematically describes all phenomena involving electrically charged particles interacting by means of exchange of photons and represents the quantum counterpart of classical electromagnetism giving a complete account of matter and light interaction.
QED has a very particular way of explaining things that you've probably never heard of before. It is a type of theory known as a Quantum Field Theory, meaning that it explains all matter and light as being excitations of an underlying field. Photons are excitations of the electromagnetic field, electrons are excitations of an electron field, etc. Within QED, there is no separation between the particle-like and wave-like properties. By this I mean that QED does not say that something acts like a particle sometimes and acts like a wave at other times. Nor does it does say that an object is both a particle and a wave at the same time. The particle-like properties (definite position upon measurement, quantized energy, etc) are fully described by saying that the particle is an excitation of the field. The wave-like properties (self-interference, wavelength, etc) are also fully described at the same time. You can say that in QED, objects are explained as being quantum objects with properties that don't correspond to normal, everyday language and intuition, such as being able to have both wave-like and particle-like properties. So, is a photon a wave, a particle, or both? The answer is that it is none of those things. It is a quantum object exhibiting both types of properties.
teetar said:
...and hence if you were to continue exciting the particle and it were to continue releasing the light from that spectrum, then shouldn't it eventually (after a long time) lose all it's mass to the photon?
No. By exciting the hydrogen atom you are giving it the energy it needs to release as electromagnetic radiation. Note that Einstein's equation, E=Mc
2, means that energy has mass. So when you excite the atom you give it energy and it becomes more massive as a result. When it releases this energy in the form of light, it becomes less massive since it has lost energy. In relativity, there are several different types of mass. A photon has zero rest mass, but has something else called relativistic mass. Relativistic mass takes into account the energy and momentum a system possesses, and since a photon has momentum (and energy), it has
relativistic mass even though it has zero
rest mass. Basically this means that if I have a box with perfects mirrors on the inside, full of light, it is more massive than the same box without the light. The relativistic mass of the photons all add up to give the system as a whole (box + light) more mass than just the box itself.
