What's the nature of light?
- Thread starter Asexperia
- Start date
Asexperia
Registered Senior Member
OK, I have 3 questions.
1- What's the vehavior of light when it travels through space?
2- What would it happen if a ray of light freezes or stops?
3- What's the frequency of the radiated heat?
DaveC426913
Valued Senior Member
Pretty broad question. What kind of behavior are you asking about? It follows a geodesic, which is curved in the presence of mass.
It can't. Unless the photons get absorbed.
What radiated heat?
I have a question that I think is relevant.
When an object, like a bell or something, makes a sound - the sound wave travels from the object in all directions. When I light a match in a dark room, light travels from the match in all directions. But suppose I had a light source that could emit a single photon. Which direction does the photon travel? Or does it disperse in all directions, like the sound wave from the bell?
When an object, like a bell or something, makes a sound - the sound wave travels from the object in all directions. When I light a match in a dark room, light travels from the match in all directions. But suppose I had a light source that could emit a single photon. Which direction does the photon travel? Or does it disperse in all directions, like the sound wave from the bell?
Asexperia
Registered Senior Member
For example, when We heat ourselves with a bonfire.
A photon is a quanta of an electromagnetic field
https://en.wikipedia.org/wiki/Photon
photon is a type of elementary particle. It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force (even when static via virtual particles).
Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a single photon may be refracted by a lens and exhibit wave interference with itself, and it can behave as a particle with definite and finite measurable position or momentum, though not both at the same time as per Heisenberg's uncertainty principle.
A light bulb that emits light in all directions emits individual photons in random directions. Since there are billions and trillions of them, the distribution ends up being very uniform in all directions.
If you could dim down the bulb to the point where it was only emitting a few photons per second, or something like that, then you'd notice that each photon is emitted in a random direction.
More advanced answer: Of course, the above assumes you're using some kind of detector (camera or screen or wall or your eye, or whatever) to actually detect the photons and deduce their directions of travel. Quantum mechanically speaking, each individual photon is actually emitted in all directions simultaneously. It doesn't have a particular direction until something detects it, at which point the wavefunction collapses.
DaveC426913
Valued Senior Member
What does that have to do with the other questions? This is not a coherent thought.
Well, you said something correct about what photons are, but you didn't actually answer the question that was asked.
Thanks - but I can read wikipedia too. Doesn't really help me visualize the answer to my "thought experiment".
This is better.
So am I basically asking a restatement of the double slit experiment?
If I set up a single detector, will it always detect the photon? Or will it only occasionally detect it?
EDIT: I know in my bell example above, that the sound is actually an energy wave travelling through a medium. There is no sound "particle", it's the air molecules bumping into each other than carries the wave. I'm having a harder time visualizing this with light as it doesn't require a medium. (Unless spacetime counts as a "medium".)
Last edited:
DaveC426913
Valued Senior Member
Photon[s].
It will detect a few photons. A bigger detector will intercept more photons over time.
Each photon that is emitted will essentially expand as a wave, but will only be detected at a single point, and there, the wave collapses.
Asexperia
Registered Senior Member
The radiated heat are infrared waves.
DaveC426913
Valued Senior Member
DaveC426913
Valued Senior Member
Your last line is most correct.
Light is neither exclusively particle nor wave. It has both particle-like properties and wave-like properties. Depending on how we choose to detect it will determine which properties we see.
The third choice in the OP, which I gave gives the answer...
Which is the same as ....
correct?
Really, we don't need that level of complexity to explain what's going on here. It's easier just to assume that for a light source emitting light in all directions, individual photons are like particles that are emitted in random directions. So, what you'll find at the microscopic level is that the intensity of the light isn't adjustable continuously, but rather it adjusts in "steps" equivalent to the energy of one photon. In other words, it is quantised. If light was just a wave, then we'd expect the intensity to vary in a continuous way.
Only occasionally, assuming your detector only covers one portion of the spherical surface surrounding the light source.
In the sound wave the intensity of sound is determined by the maximum distance that each air molecule is displaced from its equilibrium position as the wave goes past. With light, the intensity is determined by the maximum amount by which the value of the electric or magnetic field at a given point in space varies as the wave goes past. That's the wave picture. In the particle picture, the intensity is determined by how many photons go past that point in space every second.
Noice!