Tagged Questions
28
votes
4answers
3k views
Why doesn't light kill me?
I was attending my philosophy class and in the middle of student presentations, I found myself mentally wondering off and thinking about light. After a few minutes of trying to piece together how the ...
0
votes
1answer
39 views
hurdles in creating (close to) infinite images
Let's put an object(hypothetical superman) inside a "well sealed" box containing only mirrors. Is it possible to create number of images that will be close to infinity, assuming that resolution of our ...
0
votes
4answers
150 views
Where do photons get their energy from?
If energy required to accelerate a particle to the speed of light is infinite then where do they get it from?
But first if photon's are massless, then why do they collide to some other thing and get ...
1
vote
1answer
104 views
Specific electron energy gap values $E_{i+1}-E_i$ vs. photons with arbitrary energy $\hbar \omega$
The energy levels of electrons in an atom are quantized $E_i$. A photon of a specific momentum $\vec p$ and energy $$\omega=(E_{i+1}-E_i)/\hbar$$ hits an atom and gets absorbed. Okay now say the ...
8
votes
2answers
615 views
Do photons lose energy while travelling through space? Or why are planets closer to the sun warmer?
My train of thought was the following:
The Earth orbiting the Sun is at times 5 million kilometers closer to it than others, but this is almost irrelevant to the seasons.
Instead, the temperature ...
0
votes
0answers
37 views
What gives photons their energy? [duplicate]
Possible Duplicate:
Does $E = mc^2$ apply to photons?
I've been to a presentation by a CERN scientist, and he briefly talked about photons. It was stated that photons have different energy ...
6
votes
2answers
310 views
Have red shifted photons lost energy and where did it go?
I think the title says it. Did expansion of the universe steal the energy somehow?
1
vote
1answer
112 views
Will a photon emitted from something moving quickly have a shorter wavelength?
If a photon is emitted from a light source moving at any speed, the photon will nonetheless always move at c (assuming it is emitted in a vacuum.)
If the speed of a photon's emitter cannot influence ...
1
vote
1answer
124 views
The energy carried from one winding of a transformer to another, in quantum terms
I have read in wikipedia this statement
"The energy carried from one winding of a transformer to another, in quantum terms is carried by virtual photons, not real photons" (wikipedia src: virtual ...
3
votes
1answer
186 views
If 100% of the energy from the sun is reflected back into space
100% of the energy from the sun is reflected back into space, it's just shifted from a low-entropy state to a high-entropy state, and from a high frequency (ultraviolet) to a low frequency (infrared). ...
5
votes
3answers
584 views
Kinetic Energy vs. Potential energy with regards to creating particles
So I know that when you collide particles with high enough kinetic energy, (kinetic energy = at least the rest mass of the particles you are making), you get particles.
How come potential energy ...
1
vote
0answers
242 views
Maxwell's Demon - laser cooling
There’s an interesting article on Scientific American
that tells how to cool individual atoms can bee cooled to within a very tiny fraction of Absolute Zero.
It uses two laser beams acting on a very ...
8
votes
2answers
705 views
Does $E = mc^2$ apply to photons?
Photons are massless, but if $m = 0$ and $E = mc^2$ then $E = 0c^2 = 0$. This would say that photons have no energy, which is not true.
However, given the formula $E = ℎf$, a photon does have energy ...
-2
votes
3answers
581 views
Anti-laser: How sure we are that energy is transported?
Reading this PE question
can-we-transport-energy-over-infinite-distances-through-vacuum-using-light, a related question arises naturally:
Is energy transported (by light)? -- (I did believed in this ...
23
votes
8answers
13k views
If photons have no mass, how can they have momentum?
As an explanation of why a large gravitational field (such as a black hole) can bend light, I have heard that light has momentum. This is given as a solution to the problem of only massive objects ...
19
votes
5answers
2k views
Do photons gain mass when they travel through glass?
Please correct me if I'm wrong, but I believe that photons slow down when travelling through glass. Does this mean they gain mass? Otherwise, what happens to extra kinetic energy?
I understand now ...
