So according to google:
a photon is a particle that transmits light.
Ok, but light is considered a wave, not a stream of particles(I'm pretty sure that this is what Young's double slit experiment proved?)
So what is it exactly? I assume something like wave-particle duality comes into play here, but i don't know much about it, other than the name, and what I can infer from the name.
Thanks for reading and hopefully answering. I'm really new to physics, but trying my best to learn it!!
You can see from other answers on this site that the word photon is used in many ways, and you see phrases like "the photon tranvels as a wave and interacts as a particle", and you get confused.
Now even before the photon comes to existence as a photon, its energy is stored in the electron field, the energy is part of the emitting atom/electron system, and as the electron relaxes, it transforms part of its energy to the EM field, and we say that the photon comes to existence. The photon, this QM phenomenon, the excitation of the EM field, as soon as it comes to existence, it propagates through space when measured locally, in vacuum, at speed c.
Now you mention the double slit experiment, and contrary to popular belief, the experiment is very well done emitting single photons at a time.
This is something beautiful about QM, this is what we call a photon, this QM phenomenon, that the laser is able to emit, one at a time, this quanta of light, is propagating through space, and we use mathematical models that model the photon as a wave when propagating.
Now it is very important to understand, though being counterintuitive, the photon does travel through both slits, and does take all possible paths. As long as it travels, it is best described by wave models, and it is delocalized.
The photons do not have a well defined trajectory. The diagram shows them as if they were little balls travelling along a well defined path, however the photons are delocalised and don't have a specific position or direction of motion. The photon is basically a fuzzy sphere expanding away from the source and overlapping both slits. That's why it goes through both slits. The photon position is only well defined when we interact with it and collapse its wave function. This interaction would normally be with the detector.
Shooting a single photon through a double slit
The only time we localize the photon itself, is when interacting with it, in this case whenever it hits the screen, and gets absorbed, that is when the photon ceases to exist, but its energy just gets transformed into the electron field again, becoming part of the atom/electron system's energy again.
A photon is a particle which obeys quantum mechanics rather than classical mechanics. As Dirac said
“In the general case we cannot speak of an observable having a value for a particular state, but we can … speak of the probability of its having a specified value for the state, meaning the probability of this specified value being obtained when one makes a measurement of the observable.”
In particular, particles do not have a classical property of position, but we can calculate the probability for where a particle will be found (or for a photon, where it will be annihilated).
It can be shown in the mathematical foundations of quantum mechanics (not usually covered in standard text books) that a consistent probability interpretation requires that the calculation follows the laws of wave mechanics, creating the illusion that particles have wave properties. The reason is that quantum mechanics describes truly indeterminate processes whereas in standard probability theory results are determined by unknowns.
I have shown the mathematical argument in The Mathematics of Gravity and Quanta
As Árpád explained, light - or rather electromagnetic radiation - begins with the emission of photons.
Even if the existence of these quanta of EM radiation is sometimes denied or sometimes does not seem necessary for the proponents of a pure QED worldview, they do exist. Furthermore, photons are indivisible units from their emission to their absorption. Only the interaction with subatomic particles leads to a re-emission of photons of different frequencies. Whatever happens during the transition through slits or near edges, it is and stays an interpretation of the fringes on the observer screen. Any try of an inside led to the disturbance of the pattern.
The interpretation as an amplification and extinction (bright fringes and dark fringes) is not holdable because on PSE it is said many times that photons are not interacting usually. A conclusion that the photons get deflected on edges, could be another view on what happens near edges.
If light is considered a wave, then what exactly is a photon?
Not every EM radiation is a wave with an oscillating behaviour. Light from an electric light bulb that is powered by direct current emits photons in a chaotic way, and no one will be able to measure any oscillation. The same is true for monochromatic light from a sodium vapor lamp.
But each photon emitted from these thermal sources moves forward oscillating with its electric and magnetic field. Imaging a photon as a bubble with shrinking and expanding electric and magnetic field components (perpendicular to each other and both in vacuum perpendicular to the direction of propagation).
How do we prove the existence of the photon field components? With the help of radio waves. They are generated by the synchronized acceleration of skin electrons and emit photons of the same polarization during each half-period. Their combined electric and combined magnetic fields can be measured. They are what was described above: they are oriented perpendicular to each other and both perpendicular to the direction of propagation.
So according to google: a photon is a particle that transmits light.
A photon is a particle that transmits energy and has a momentum. Human perception interprets some part of the EM radiation as light.
Ok, but light is considered a wave, not a stream of particles(I'm pretty sure that this is what Young's double slit experiment proved?)
I hope the above answers your question.
Classical light is a wave that can be interpreted quantum mechanically as defining the properties of photons. Assuming coherence, its energy distribution divided by $\hbar \omega$ describes the average expected photon density.
