# Tag Info

22

Yes, this is possible using nonlinear optics. This kind of frequency shift can be done using acousto-optic modulators and electro-optic modulators, and it is normally done in a transmission geometry. The basic idea is that you have a block of material whose refractive index depends on the acoustic pressure or on the local electric field, and then you make ...

16

It means that they don't meet, because as you correctly pointed out parallel lines never meet. Then what's the point in saying "they meet at infinity" if they never meet? Because you can obtain a parabola by an ellipse with focal distance $d$ in the limit where $d\rightarrow\infty$. In the ellipse rays from one focus get reflected to the other one, ...

10

When physicists say something "goes to infinity", what they mean is "as you take the limit, this value gets bigger and bigger without any bound, and will eventually exceed any number you choose". In the standard system of real numbers (which is used for most things in classical physics), infinity isn't actually a number; it's more like a ...

8

As Jon Custer said in a comment, the light returning from a receding mirror will be redshifted. This is easiest to see if you consider the problem in the rest frame of the mirror. A symmetry argument shows that light returning from a stationary mirror can't be Doppler shifted. If the experimenter emits two light wavefronts a time $δt$ apart, the worldlines ...

7

Prepare to have your mind blown: hold up a mirror to the night sky, and point it at a quasar. Flip it 45 degrees. You've now made the mirror image of that quasar travel several billion light years in less than a second. The motion of mirror images is virtual, just a mathematical construct, and relativity does not apply to it.

7

This statement is based on a mathematical construct known as projective space. The idea behind projective space is this. Start with the usual Euclidean space, $\mathbb{R}^3$. Now consider an infinite straight line passing through the origin. (We don't need an origin, but it makes the construct easier to visualize.) There are, of course, no endpoints of this ...

7

The books are just suggesting that as the object distance approaches the focus (from outside of the focus), the image distance will approach infinity.

6

Have you ever wondered why things show colour? Well when light is incident on a surface, light of certain wavelengths are absorbed and we see the complement colours.For example a green surface absorbs light of all colours other than green. But a white surface is a surface that reflects out light of all wavelengths unlike a black surface which absorbs all ...

3

Apart from the obvious relativitic mirror, mentioned in the other answers, in linear optics a frequency shift is not possible, because linearity implies that a wave of a specific frequency/wave number is only changed in amplitude, not in frequency by a transfer element. Therefore, what you might look for is nonlinear optics. Might be that there are some ...

3

These rainbows exist and our eyes do see them - they are just extremely thin, plus our brain filters out this information, but the edges of bright objects on dark background in the mirror do have a thin rainbow along them. Our eye is using this rainbow to infer the image comes from a mirror. I once saw an exhibit at a modern art museum - a seemingly black-...

2

Keep in mind that $R,T$ as defined in your text are the coefficients of the electric field, not of the intensity. The reason for the relation $R+1=T$ is simply that the electric field should be continuous across the boundary. Outside the material, you have an incident wave (coefficient of $1$) and the reflected wave (coefficient of $R$). Inside the material ...

2

when photons strike material objects, they are not bouncing off other photons- they are bouncing off clouds of electrons. Depending on how those electrons are being shared by adjacent atoms, the incident photons can either be reflected off or absorbed.

2

In addition to a receding mirror that @joncuster mentioned and @benrg elaborated on, you can coat any normal mirror with a wavelength shifter. There are many such materials that will absorb incoming short-wavelength photons and re-emit them at longer wavelengths. Often these wavelength shifting layers are transparent to their own light, so no matter which ...

1

It might help to slightly rephrase it. A Hey, these two lines are parallel! B Indeed. A I wonder where they meet? B Follow the lines, and you will see them meet when you have travelled an infinite distance. A But I will never complete a journey of an infinite distance! B Exactly. Or, maybe more tersely: A How far must I keep travelling to see these two ...

1

It works like this. You solve Maxwells equations. Then the potential tells you how many photons you can expect on average, that is, it gives you the average of a Poisson or Gauss distribution. This distribution is the experimental prediction. We only know how it works not why it works like this.

1

"Chair is a source of light" is an English phrase. Like many phrases, it has many meanings, and you have to ensure that the reader understands what you mean. Niels points out that, for virtually everyone, "chair is a source of light" is considered to be a false statement because we typically are only thinking of primary sources. However,...

1

Photons are not the only things in the universe. In fact, normal matter consisting of half-integer spin fermions do interact with light and can change their paths and reflect, absorb or emit them. Try reading Richard Feynman's quantum electrodynamics lectures. They are a good introduction to quantum electrodynamics and give you an accurate representation ...

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