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Questions tagged [optics]

Optics is the study of light, and its interaction with matter. It includes topics such as imaging systems, fiber optics, lasers, quantum optics, and more.

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511 votes
6 answers
81k views

How does light bend around my finger tip?

When I close one eye and put the tip of my finger near my open eye, it seems as if the light from the background image bends around my finger slightly, warping the image near the edges of my blurry ...
Daniel A.A. Pelsmaeker's user avatar
311 votes
2 answers
30k views

What is Chirped Pulse Amplification, and why is it important enough to warrant a Nobel Prize?

The 2018 Nobel Prize in Physics was awarded recently, with half going to Arthur Ashkin for his work on optical tweezers and half going to Gérard Mourou and Donna Strickland for developing a technique ...
Emilio Pisanty's user avatar
180 votes
7 answers
14k views

Why do we actually see the sun?

I haven't yet gotten a good answer to this: If you have two rays of light of the same wavelength and polarization (just to make it simple for now, but it easily generalizes to any range and all ...
user avatar
167 votes
9 answers
25k views

Could Legolas actually see that far?

The video “How Far Can Legolas See?” by MinutePhysics recently went viral. The video states that although Legolas would in principle be able to count $105$ horsemen $24\text{ km}$ away, he shouldn't ...
Ali's user avatar
  • 6,004
156 votes
1 answer
15k views

What is an "attosecond pulse", and what can you use it for?

The 2023 Nobel Prize in Physics was announced today, and it was awarded to Pierre Agostini, Ferenc Krausz and Anne L’Huillier, for “experimental methods that generate attosecond pulses of light for ...
Emilio Pisanty's user avatar
144 votes
3 answers
33k views

Why are the windows of bridges of ships always inclined?

What is the reason that the windows of ships' bridges are always inclined as shown in the above picture?
veronika's user avatar
  • 2,736
126 votes
5 answers
26k views

Why do wet objects become darker?

When something gets wet, it usually appears darker. This can be observed with soil, sand, cloth, paper, concrete, bricks... What is the reason for this? How does water soaking into the material ...
Suma's user avatar
  • 1,412
121 votes
7 answers
62k views

Why are most metals gray/silver?

Why do most metals (iron, tin, aluminum, lead, zinc, tungsten, nickel, etc.) appear silver or gray? What makes copper and gold have different colors? What atomic characteristics determine the color?
Ali Abbasinasab's user avatar
116 votes
6 answers
115k views

Why is glass transparent?

Once I asked this question from my teacher and he replied "Because it passes light.". "And why does it pass light?" I asked and he said, "Because it is transparent.". The same question again, Why ...
SMUsamaShah's user avatar
  • 5,387
110 votes
7 answers
20k views

How can we see an atom now? What was the scale of this equipment?

I've just seen this on the news - Single Trapped Atom Captures Science Photography Competition's top prize. Credit: David Nadlinger via EPSRC I am not a Physics major but I believe I do know the ...
Hanky Panky's user avatar
  • 1,109
98 votes
4 answers
18k views

Seeing something from only one angle means you have only seen (what?)% of its surface area at most?

Is there a logical/mathematical way to derive what the very maximum percentage of surface area you can see from one angle of any physical object? For instance, if I look at the broad side of a piece ...
BarrettNashville's user avatar
90 votes
7 answers
28k views

Why do metals only glow red, yellow and white and not through the full range of the spectrum?

Why don't metals glow from red to yellow to green to blue etc.? Why only red, then yellow and then white? Shouldn't all wavelengths be emitted one by one as the temperature of the metal increases? ...
Dieblitzen's user avatar
  • 1,637
89 votes
9 answers
15k views

What really causes light/photons to appear slower in media?

I know that if we solve the Maxwell equation, we will end up with the phase velocity of light being related to the permeability and the permittivity of the material. But this is not what I'm ...
Emitabsorb's user avatar
  • 2,452
84 votes
3 answers
10k views

Can photons be detected without being absorbed?

I am thinking about a detector that would beep if light passes through it. Is it possible?
Arik's user avatar
  • 841
84 votes
6 answers
9k views

Why does a rubber band become a lighter color when stretched?

I was stretching a pink colored rubber band, and I noticed that the longer I stretch it, the lighter the pink becomes. Why does this happen?
wavion's user avatar
  • 1,276
79 votes
1 answer
9k views

Why does soaking a fabric make it more transparent?

It's a well-known fact that when one soaks a thin piece of fabric, it will often become more transparent than it was before. What is the reason behind this? I can't put glass behind the fabric and ...
Isky Mathews's user avatar
  • 1,945
77 votes
3 answers
93k views

Why can we see the dust particles in a narrow beam of light (and not in an all lighted area)?

Let us say that I am sitting in a room with all the drapes open. Bright sunlight is coming through the window. The whole room is brilliantly lighted. I will not be able to see the dust particles ...
Masroor's user avatar
  • 759
75 votes
3 answers
15k views

Why do I see a saddle in this picture of a computer screen?

I am not entirely sure this is an appropriate question for PSE, however since many of you have such diverse backgrounds, I'll give it a shot. I have noticed that when one takes a picture of a computer,...
coreyman317's user avatar
75 votes
1 answer
57k views

Why does a window become a mirror at night?

In day, when you look in the room through the window out, you can clearly see what happens outside. At night when it's dark outside but there's light inside you can look in the window but it becomes a ...
Alon Gubkin's user avatar
74 votes
5 answers
34k views

Why is water clear?

Water appears transparent to visible light, yet most other objects are opaque. Why is that? Is there an explanation why water appears transparent? Is water transparent at all wavelengths, or are ...
D.W.'s user avatar
  • 983
72 votes
6 answers
15k views

Could a computer unblur the image from an out of focus microscope?

Basically I'm wondering what is the nature of an out of focus image. Is it randomized information? Could the blur be undone by some algorithm?
user273872's user avatar
  • 2,613
72 votes
9 answers
22k views

Why can't we see images reflected on a piece of paper?

Why can't you see a reflected image on a piece of paper? Say you put a pen in front of the paper, even when light rays are coming from other sources, hitting the pen, reflecting back, and hitting the ...
katana_0's user avatar
  • 1,195
72 votes
3 answers
16k views

Why do beams of light (from torches or other directed sources) not extend to infinity?

When I'm in a dark environment, and I turn on a torch, I can see the beam of light from the torch. To the best of my understanding, the main reason why I can see the beam of light is that the light ...
QCD_IS_GOOD's user avatar
  • 6,896
72 votes
2 answers
22k views

How to measure the wavelength of a laser pointer?

I'm working on something and I need to know the wavelength of the laser pointer that I'm using. Can you suggest me a way, using some optics formulae, or anything else to calculate the wavelength?
user avatar
71 votes
3 answers
14k views

How big would my telescope have to be if I wanted to see the Mars rover from my backyard?

I imagine that with a big enough telescope, I would be able to zoom in and see the Mars rover in enough detail to make out the details (like the wheels, cameras, etc.). How large would the telescope ...
Josh's user avatar
  • 1,315
70 votes
6 answers
12k views

Why isn't my calculation that we should be able to see the sun well beyond the observable universe valid?

I recently read an interesting article that states that a human being can perceive a flash of as few as 5 or so photons, and the human eye itself can perceive even a single photon. The brain will ...
Reggie Simmons's user avatar
68 votes
12 answers
34k views

Is it possible that there is a color our human eye can't see?

Is it possible that there's a color that our eye couldn't see? Like all of us are color blind to it. If there is, is it possible to detect/identify it?
MegaNairda's user avatar
68 votes
6 answers
15k views

How does light combine to make new colours?

In computer science, we reference colours using the RGB system and TVs have pixels which consist of groups of red, green and blue lines which turn on and off to create colours. But how does this work?...
Isky Mathews's user avatar
  • 1,945
68 votes
5 answers
8k views

What challenges needed to be overcome to create (blue) LEDs?

In light of today's announcement of the 2014 Nobel laureates, and because of a discussion among colleagues about the physical significance of these devices, let me ask: What is the physical ...
Martin's user avatar
  • 15.7k
66 votes
3 answers
4k views

What causes insects to cast large shadows from where their feet are?

I recently stumbled upon this interesting image of a wasp, floating on water: Assuming this isn't photoshopped, I have a couple of questions: Why do you see its image like that (what's the physical ...
OmnipresentAbsence's user avatar
65 votes
3 answers
9k views

Do sunrises and sunsets look the same in a still image?

A question that popped into my head: if I see a picture of the sun close to the horizon, in an unknown place, can I know if it was taken at sunset or sunrise? Do sunrises and sunsets look the same in ...
AlonMln's user avatar
  • 633
64 votes
4 answers
8k views

Why does the sun have to be nearly fully covered to notice any darkening in an eclipse?

I was looking at eclipse footage and I noticed that it doesn't get any noticeably darker until the very end when it suddenly all the light is gone. As the moon blocks out the Sun, I would expect that ...
Giulio Crisanti's user avatar
62 votes
7 answers
9k views

Why do some lights captured by the Webb telescope have rays and others don't?

On the images captured by Webb telescope one can see some lights with 6 rays, but most others don't have any. One would expect the optics to transform all light sources at infinity in the same manner. ...
Michael's user avatar
  • 1,951
59 votes
7 answers
10k views

Could a human beat light in a footrace?

Is there anything preventing the following experiment from being done right now? Imagine that a human ran from point 'a' to point 'b' while light particles that reflected off a clock moved ...
Josh's user avatar
  • 1,315
56 votes
5 answers
8k views

What is this wavy light coming through my blinds?

On many mornings I get this cool light pattern on my ceiling: It's light coming in through the blinds, but there is this rippling/wavy/moving effect. Its intensity varies (as can be seen a little in ...
Tom's user avatar
  • 647
55 votes
7 answers
12k views

How many atoms does it take for us to perceive colour?

Atoms individually have no colors, but when there is a large collection of atoms we see objects colorful, which leads to a question: at least how many atoms are required for us to see the color?
Syed Ilyas's user avatar
55 votes
4 answers
3k views

Do gravitational lenses have a focus point?

Do gravitational lenses have a focus point? Could I burn space ants?
Jitter's user avatar
  • 2,421
55 votes
1 answer
4k views

What causes the Sun to appear to be in front of a building in this picture?

I took this photograph a few days ago, during sunrise, using my smartphone camera and digital zoom: It seems that the sun is in front of the building. How is this explained?
Lior's user avatar
  • 3,369
53 votes
5 answers
2k views

Why doesn't a typical beam splitter cause a photon to decohere?

In many experiments in quantum mechanics, a single photon is sent to a mirror which it passes through or bounces off with 50% probability, then the same for some more similar mirrors, and at the end ...
Mark Eichenlaub's user avatar
52 votes
4 answers
7k views

What wavelengths of light does a banana reflect?

I do know that there are at least two types of yellow light: a light of a single wavelength of ~580 nm and a combination of green light and red light. (Technically, there could be more yellow light.) ...
dkssud's user avatar
  • 723
52 votes
2 answers
7k views

Why are gold mirrors yellow?

Why are golden mirrors yellow? Do they add a yellow component to the spectrum or absorb non-yellow components? If they absorb, then why are they used in telescopes being imperfect? If they add a ...
Dims's user avatar
  • 1,732
52 votes
3 answers
21k views

How does light speed up after coming out of a glass slab?

As I learned today in school, my teacher told me that when light enters a glass slab it slows down due to the change in density and it speeds up as it goes out of the glass slab. This causes a lateral ...
Amey Shukla's user avatar
52 votes
1 answer
25k views

Why does paper become translucent when smeared with oil but not (so much) with water?

When I smear oil onto a scrap of paper and rub it in, the paper becomes quite translucent; but when I attempt the same with water it doesn't as much. Why?
Mozibur Ullah's user avatar
51 votes
2 answers
32k views

Why do I see better under water using swimming goggles? [duplicate]

I am myopic (I don't really know if this is relevant or not) and I usually swim without contact lenses. My vision is clearly better underwater when I am using swimming goggles. I have tried to ...
S -'s user avatar
  • 1,563
50 votes
4 answers
5k views

How can an object absorb so many wavelengths, if their energies must match an energy level transition of an electron?

I believe I have a misunderstanding of some principles, but I have not, even through quite a bit of research, been able to understand this problem. My current understanding of transmission, ...
Ultralite's user avatar
  • 613
50 votes
5 answers
15k views

Why does the sky change color? Why is the sky blue during the day, red during sunrise/set and black during the night?

Why does the sky change color? Why is the sky blue during the day, red during sunrise/set and black during the night?
user avatar
50 votes
3 answers
12k views

How are classical optics phenomena explained in QED (Snell's law)?

How is the following classical optics phenomenon explained in quantum electrodynamics? Reflection and Refraction Are they simply due to photons being absorbed and re-emitted? How do we get to Snell'...
Sklivvz's user avatar
  • 13.5k
49 votes
8 answers
14k views

How is it possible there are UV photos while our eyes cannot detect UV waves?

I know this question sounds dumb, but please bear with me. This question came into my mind while I was looking at the photos in an astronomy book. How is it possible that IR and UV photos of stars and ...
Bored Comedy's user avatar
49 votes
5 answers
13k views

If a lens focuses all incoming light to a point, how do we get 2D images?

How do lenses produce 2-dimensional images, if a lens bends all incoming rays of light to intersect at the focal point? Shouldn't this produce a single dot of light on a screen placed at the focal ...
Kristin's user avatar
  • 601
48 votes
5 answers
4k views

What causes this pattern of sunlight reflected off a table leg?

My friend noticed an interference-like pattern around the table leg. However, we do know that interference patterns of sunlight produces rainbow colours. What seems to be happening here?
Luke's user avatar
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