when something is producing light does it produce it in a steady stream or rapid pulses. The reason I ask this is because if light is created in a stream or unbroken beam of light then doesn’t it follow that the sorce of that light is creating the light at the speed of light (did I ever just say light a lot). If this is true is it also fair to assume that a flame breaks down lets say for example wood at the speed of light but at a microscopic level.
This isn’t exactly the way I want to word it but maybe through descussion I might be able to clarify my question.
IANA Physicist, but i believe light or other electromagnetic radiation is produced in a stream of discrete pulses, and these pulses are called photons. Photons are often generated because of electrons jumping orbits. An electron will move to a lower energy orbit, and emit a single photon to shed its excess energy.
The speed of light is measured in terms of distance and time. Light travels at 299,792 kilometers per second, or 186 282 miles per second, or 670,616,629 miles per hour, etc.
The rate at which light is produced is not measured in terms of distance and time. It’s measured in terms of energy and time. You’d say that the burning piece of wood was producing “x” many calories per second, or Joules per second, or Watts, or horsepower, etc.
You couldn’t say that the wood was burning at the speed of light.
Einstein also proved in 1905 that light is quantized, that is, it is produced as individual packets of energy that we call photons. In some situations you could say that you were producing “x” many photons per second. Whether you would call the light emitted by a fire a “steady stream” or “rapid pulses” depends very much on how you define the words “light”, “steady” and “rapid”.
I think it is misleading say that a source “creates light at the speed of light”, or “breaks down wood at the speed of light”.
A source could emit only one photon at a time. Is this a “stream” or a “pulse”? If it emits trillions in an picosecond, is this any different?
The light from the source travels at the speed of light (no!). How quickly the source is consumed is completely independent of this speed. Was this what you were thinking about?
How fast does the sorce emit the light in order to create a beam of light? Can the packet of light or Photon be diffrent sizes? Does the brightness directly corralate with the size of packets or how many packets there are?
How many photons per second does something produce light.
Is a light beam connected? Or are the packets seperate?
The rate (or speed) that photons are created does not matter. It’s the number of photons that matters.
Say you light a fire at night. By lighting a fire you are creating a chemical reaction that creates photons. As soon as enough photons are being created by the fire you will see them. Some people’s eyes are more sensitive to light than others so they will see the light created by the growing fire earlier.
Even if you treat light as a classical continuous wave, nothing has to move at the speed of light to create light. Try sticking your hand in a bathtub and moving it very slowly - the wave created will be much faster than your hand. When your vocal cord or speaker cone vibrates to create a wave (sound), it’s not moving at the speed of sound.
Ok your hand isn’t moving at the speed of the wave of course not but what about each atom that helps create the wave is it a short fast burst of speed even though the hand is moving very slowly the parts of your hand that make the wave may be moving very quickly
I think what shea is asking is “how fast is an electronic transition?”. (In which case, the difference between a transition and actual motion should be explained. If anyone fancies introducing him to Quantum Mechanics proper, be my guest.)
A photon interacting with a chemical bond must complete its interaction within the time it takes for the photon to cross the bond. For a typical bond length of 100 X10[sup]-12[/sup] meters, and c = 300 X10[sup]6[/sup] m/sec, that works out to a transition time of about 3.3 X10[sup]-19[/sup] seconds.
Maybe, but you can create light without a transition. All you need is to move an electron; this creates a disturbance of the electric field which propagates at the speed of light. In other words you can create light by shaking an electron. Admittedly you need relativistic electrons to create visible light this way, but relativisitc electrons are still slightly slower than light.
Sort of. When you get down to scales that small, the classical definition of an objects location breaks down, and you’re forced to use quantum mechanics to deal with the transition. When the location of an object, such as an electron or photon, can only described fuzzily, any “movement” of that object also becomes fuzzy. That makes calculating the classical speed at which an electron moves during a transition damned near impossible.
Light is emitted probabilistically. That is to say, if I have an electron in an excited state, it has a finite probability that it will decay into a more stable state and emit a photon. This is the most common way (but by no means the only way) photons are formed.
As soon as the photon is formed, the electron is in the lower energy state. There is really no “time” associated with the transition other than the one that you get from the Heisenberg Uncertainty Principle which states that the amount of energy times the amount of time has to be greater than a given constant.
Seeing as how atoms have finite sizes and electron levels are at finite distances, one could make a crude “estimate” as to how fast the electrons are moving between levels during the transition. This isn’t actual motion but is rather a nonsensical statement of “distance” between energy levels divided by the “uncertainty time” of the transition. The value works itself out to be (order of magnitude estimate only) 10^7 cm/s which is not even 1/1000 the speed of light.
So if what JS Princeton says is true doesn’t it make sense that light is emited in 1/1000th pulses. Or another way to say it the photons are 1/1000 apart from each other in a beam of light.
Look, there’s really no way to explain this without you having a basic understanding of quantum mechanics. What makes “sense” based on your everyday experience has little to do with it.
In a beam of light, photons are not “separated,” they can occupy the same space at the same time. This is because photons, having integral spin, are bosons and do not obey the Pauli Exclusion Principle. A laser beam is, in effect, a bunch of identical photons all occupying the same space.
JS that pretty much covers it, but another way to say it is that the transition time is the time during which the photon may be emitted, not the duration of the transition.
I’m gonna jump in, but please note I only have a BS Physics and got it 11 years ago but here is my understanding.
I thought the idea of electrons moving in and out of orbits different distances from nucleus was dead, and that you must simply speak of energy levels.
There was talk back in 1993 (talk was between me and my QM Professor, in the hallway, about glow in the dark material) that single excited atoms may emmit a photon the entire time it is transitioning, not a single event caused by the transistion. The idea was that there is a point at which the atom becomes unstable and the probablity that the atom is in an excited state starts to change. During this time where the state is unclear, the electron is actually transitioning in and out of the excited state, first only occasionally dropping to the lower state, then progressively more often in the lower state, until it spends most all it’s time in the lower state. This transistioning back and forth can either be thought to create the photon, or the photon can be thought to cause the electron to move.
To the OP. The question that should be asked is, after photons have joined, for example in a laser beam, is it possible to extract a photon, that carries the same energy it started with, or in other words, since the photons interact with each other, do they smear to together and lose thier individual energy, and simply grab the same amount back from the stream when they hit something, or do they hold on to the energy the whole time?