Photons Definition and 1000 Threads

Good afternoon all, A few days ago, I had been reading a book on general relativity and cosmology by Dr. Brian Greene, in which something was written that I found to be very profound. (At least, from the standpoint of my own ignorance on the subject.) I was wondering if any professionals could...

10 billion years ago, photons emitted at the surface of last scattering were being absorbed by whatever stuff was around. Those atoms would absorb those photons and release other photons, but these would not be primordial photons from the CMB anymore but photons emitted at a later time by the...

ok. this may sound stupid, first of all i asked this question because i have a doubt that "if a photon can see things around it will it be able to see its own reflection if it aproaches towards a mirror?" so i played a video of light being reflected in a mirror in slow motion and paused the...

Homework Statement Between which energy levels are the photons in this line transitioning? Wavelength= 660 * 10^-9 m Change in energy = 3.01 * 10^-9 A. 4 and 2 B. 3 and 2 C. 3 and 1 D. 2 and 1 Homework Equations...

1).Virtual Photons forms in pairs like particles and anti particles? or 2).by borrowing energy from future? or 3) in both ways?

Homework Statement how many photons (lambda=620*10^-9) must be absorbed to melt 2kg block of ice at 0deg into water at 0deg? and on average, how many H2O molecules does one photon convert from the ice phase to water phase? Homework Equations E=hc/lambda The Attempt at a Solution I have no idea...

Hello everyone, I would like to ask a couple of questions related with the interaction mechanisms of photons and electrons with matter. Through searching about this subject, I have concluded that they both have different penetration depth and different interaction mechanisms. But apart from...

First off, I'm not sure if this question should go here or in the homework section. It is an astronomy homework question BUT there are only physics subtopics and did not want to post it in the wrong section. Let me know if it should be moved to there! Homework Statement Consider a nebula...

A student asked me a question last night that stumped me. Suppose we have an atom in its first excited state A, and it's going to decay electromagnetically to the ground state B, losing energy E. We would expect this to occur through the emission of a photon with energy E. But what prevents it...

I've often heard the speed of light and time dilation related from the standpoint of a particle as being in constant motion at the speed of light with the vector rotated slightly off the temporal dimension and toward any combination of the three spatial dimensions. Does this mean photons...

New member here, would love to talk about superconductors, photons and electrons and energy conversion. Feel free drop drop me a question.

hi every one i am only 14 so can we please try and make answers in such a way that i will understand them. i am wondering as to why photons do not interact with the higes field many thanks Evenus1

do they deflect / accelerate electrons in an antenna? For an electron to accelerate it has to experience an electric field or changing magnetic field. What I can tell from the standard model a photon carries no charge = no electric field. Further a classic EM wave is defined by an E vector...

Is there a way to split gamma-ray photons into less energetic photons? And is the opposite possible, by combining low energy photons into a high energy one?

I have just started reading about a classical electromagnetic treatment of light-matter interaction (beginning with dispersion relations, and then moving on to the standard phenomena - reflection, refraction, etc.). The discussion begins with a forewarning that light is not 'continuous' as the...

The sun radiates its energy in all directions by emitting photons. As the photons travel as electromagnetic waves it reaches the earth. The photons collide with atoms and molecules in the atmosphere due the collision the energy of photons are emitted as heat. The atmosphere is thus heated and it...

hey! So oribital electrons can only absorb photons if they are the exact amount of energy between energy levels unless it is more than the ionisation energy. But why can't they? Couldn't they just emit the extra energy or 'keep' it? Thanks :smile:

See photo attachment! (question 1(b) and see answer on mark scheme underneath) How can three photons be emitted? Either the electron drops down from 3 to 1 and skips 2 emitting one big 12.1 eV photon OR it falls down in step emitting two photons 1.9eV and 10.2eV. How can it emit more energy...

Hello! I've read that electrons can only absorb photons of exactly the right amount of energy to move to a higher energy level, if its to little or too much then it doesn't absorb it at all, so my question: How can electrons be liberated from an atom with Kinetic energy when they can't absorb...

Hi, In QED it is stated that an EM field can be written as a sum of quantized oscillators (the photons). In "classical" Electrodynamics, it can also be shown that the EM field decomposes into normal modes. But both the quantized oscillators (in the Heisenberg picture) and the classical normal...

Homework Statement [/B] If 5 percent of the power of a 100 W bulb is radiated in the visible spectrum, how many visible photons are radiated per second? Homework Equations E=hf=hc/λ The Attempt at a Solution I know how to solve this, I just wanted to make sure. I will take 5 W or J/s as the...

In my book it is stated.When you keep the intensity constant and decrease the wavelength the photoelectric current decreases but I can't understand why? I thought it would stay the same since photoelectric current depends on the intensity of photons as more number oh photons means more e- released

Given sufficient energy a proton/antiproton pair can be created from photons in the laboratory. Does the (apparently) slight bias exhibited in the big bang apply to the laboratory? In other words, the universe is seemingly not made of antimatter, only "matter." Pushing this idea further, is...

Hi everyone, many (sigh), many years ago, when I was in high school, I recall a little discussion we had with some classmates, which I gave little thought to at the time, but thinking back to it now, could never really figure out. It was about relativity. The story was that nothing could reach...

I am not clear on the below, so any additional information would also be good. Let's say a pair of photons is entangled on 2 properties. When we measure on property A -- the values for property A (for both the entangled photons) becomes determinate/locked/fixed when we measure on property B...

I was trying to google it, but coudn't find any specific answer. Oxidation of Magnesium, for example, emits a lot of light. Is there a table of reactions by high much light they create ? What chemical reaction emits the highest number of photons per unit per time ? Thank you.

As we know light travels very very large distances from far far away galaxy reaches our eyes, why it is timeless, I mean particles like muon disintegrates in time but photon does not why?

Or, more specifically, what determinates the frequency of the photons emitted by a such a collision. I know that the number of photons produced depends on the spin and energy states of the initial particles.

Hi friends, this is my third post of my curiosity. :woot: First of all a photonic vacuum (as defined by me) is a region of space where there doesn't exist any type of photons or EM radiations ( those too which are beyond the detection of our present tech... i.e. including each and every...

Hello friends! I am a newbie here. I love quantum physics very much... especially the standard model of fundamental particles, QED, QCD, etc. I have an urge to create my own theory on space quanta (that's for another time...) but my main question is: Does anti-particle of a photon exist (i.e...

Hi I was posting on io9 on a thread that asked "what scientific fact transformed the way you view the world?" I posted I got that from Brian Greene in The Elegant Universe. Someone responded challenging me with. I'm really having a hard time making sense of his reasoning and why gravity...

1) Do photons eventually run out of energy and stop producing light? 2) If atoms are non-solid and more than 99% empty space, what is the photon illuminating when it hits a surface? 3) What is the actual light being produced, as opposed to the photon producing it? 4) is it possible for a Higgs...

Homework Statement Show that the number of photons in equlibrium at tempertaure t in a cavity of volume V is, N=[2.404 V (t/ħc^3]/Pi^2 The total number of photons is the sum of the average number of photons over all modes n->∑<s> Homework Equations n=Sqrt[nx^2+ny^2+nz^2] ωn=(n Pi c)/L...

Is there different types of light/particles of light? because all of these lights are different how it works, laser light, light from flash light, sun light. Why does flash light only illuminate only less area/more area depending on how much volts the battery is and a sun illuminates a whole...

Suppose you measure the spin of an electron with a sensor oriented in the +z direction and find that the spin is up (aligned with the sensor). Now if you immediately measure the spin of the electon with a sensor oriented in the -z direction, you are guaranteed that it will be down (oppositely...

Recently I've seen claims here on PF(from some highly trusted members), that photoelectric effect can be described without using the photon concept and so can't be a demonstration of the quantized nature of light. This demonstration is only provided by more advanced experiments. After that, I...

Hi! First sorry my little bad english :-) My question is... A photon leaves the surface of the sun. It needs approx 8 mins to reach the Earth. Or we can say - in the notion of relativity - that the Earth needs 8 mins to reach the photon. BUT! Photons moving at c. And if we solve the Lorentz...

Are photons the things which are constantly emitted from electric charges in all directions, which then interact with other electric charges, or are photons something else? If photons are constantly emitted from electric charges in all directions, and photons are particles, as the ring of...

Hi everyone. On these days, by watching solar panels and similar stuff, I just thought about it, and why they take such a wide surface to produce energy, and why their output is often low, as we all know. By navigating here on the internet, I've just seen a device called OPO (Optical...

BBC has a small article on how Prof Daniele Faccio of Heriot-Watt University and Prof Miles Padgett of Glasgow slowed a photon to less than c in "free space", which I pressume to mean a vacuum. Done by "changing the photon's shape" via some medium. When the photon returned to "free space" it...

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? I'm not sure if this is a proper question, or if I'm misunderstanding something, but...

I am knew only in year 9 but am doing some research on photons and was wondering how they have a mass of 0 as I thought every thing had to have a mass to be within the realms of reality or general relativity. but I might just be wrong and if so could you explain it to me simply why and the...

Since an electron generated a negative charge around itself and can push other electrons around itself, waves can travel through electrons. These are electromagnetic waves. But quantum theory proposes that the pushes between electrons happen in discrete packets. Electromagnetic packets called...

If photons have no mass, why would black holes attract light? I was told that photons have no mass. However I thought that black holes are called "black" because no light can go escape the gravity force in their vicinity. I somehow think that, if light is just photons, then it should not be...

I have a question concerning the paper "Quantum imaging with undetected photons". http://arxiv.org/abs/1401.4318 In the schematic (Fig. 1) a photon (idler) is created at NL1 and passing the object at O to be reflected further to NL2. It is then stated in the paper "By reflection at dichroic...

We can see galaxies/planets light years away determine their composition such such as if they have water et cetera. My question is if light takes billions of years to reach us from there how is that we can determine such things? Is the speed at which a telescope can zoom faster than the speed at...

It's my understanding (I might be talking senescence) that as an object approaches the speed of lights time starts to slow down, and if it achieves the speed of light time would stop. Do photons experience time?

I would like to create entangled photons at radiowave frequencies. To do this I thought it might help to understand as much details as possible how entangled photons are created by parametric down-conversion. Since the down-conversion doesn't happen often, what are the special conditions? Are...

I want to split a photon beam with no net angular momentum into two beams in both of which the sum of photon spins is not zero.

Do photons obey the conservation law of angular momentum?