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Why can we see objects in light, but not in the absense of light?

B

BigToque

Lifer
I'm just starting my intro chemistry class at university and just started learning about radiation, electrons, light, quantum numbers etc...

I've sort of had a hundred questions, but I haven't been able to think this one through yet.

I've come to the understanding (and correct me if I'm wrong), that all objects give off electromagnetic radiation due to electrons jumping orbitals. If the wavelength falls in the visible spectrum, we see the radiation as light.

Say an apple has some composition that gives off radiation that we perceive as red.

Why can we only see the red from the apple if the apple is in the presence of some other light? (eg, I can see the apple when I'm outside and the sun is shining, but if you put me into a completely dark room, I couldn't see the apple.)
 
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In terms of electron excitation, excluding the small probability that an electron jumps on its own to a higher level, you'll need some energy source to excite electrons - such as light.
 
Are you sure your actually going to a university...
Thoughts like that usually would cause one to fail horribly on the entrance examinations that were taken.

Unless they were done a few centuries ago anyways.
 
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BigToque said:
I'm just starting my intro chemistry class at university and just started learning about radiation, electrons, light, quantum numbers etc...

I've sort of had a hundred questions, but I haven't been able to think this one through yet.

I've come to the understanding (and correct me if I'm wrong), that all objects give off electromagnetic radiation due to electrons jumping orbitals. If the wavelength falls in the visible spectrum, we see the radiation as light.

Say an apple has some composition that gives off radiation that we perceive as red.

Why can we only see the red from the apple if the apple is in the presence of some other light? (eg, I can see the apple when I'm outside and the sun is shining, but if you put me into a completely dark room, I couldn't see the apple.)
Click to expand...

Are you sure you didn't confuse university with junior high?
 
The apple does emit electromagnetic radiation but none of the wavelength that our eyes pick up. When you see the apple in the daytime you're not seeing emitted lite but light from the "visible" spectrum reflecting off of it.
 
The apple actually isn't there when the lights are off. It goes into a state of quantum flux, and temporarily leaves this dimension. Turning the lights on realigns the quantum emitters and it reappears. It happens too fast to see it with your eyes; even high speed cameras are too slow to capture it, but the phenomena has been noted in research labs by observing surrounding objects. It's kind of like a black hole, where we haven't seen one directly, but their existence can be inferred by observing surrounding objects.
 
lxskllr said:
The apple actually isn't there when the lights are off. It goes into a state of quantum flux, and temporarily leaves this dimension. Turning the lights on realigns the quantum emitters and it reappears. It happens too fast to see it with your eyes; even high speed cameras are too slow to capture it, but the phenomena has been noted in research labs by observing surrounding objects. It's kind of like a black hole, where we haven't seen one directly, but their existence can be inferred by observing surrounding objects.
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Um, you know that apple emits and absorbs and reflects other forms of radiation when the lights are off right?
 
Hacp said:
Um, you know that apple emits and absorbs and reflects other forms of radiation when the lights are off right?
Click to expand...

For reals. Shut off the light photons and you're only turning off about .01% of the entire electromagnetic spectrum.
 
If you guys want to be like that you could also say it gives off that just for simply have some amount of momentum (if I remember correctly)... but you know thats not the level he was talking about. 🙁
 
Our eyes only see light, and as a general rule, only see light reflected off another surface. Usually when you see light directly from a light source, its too much and will burn your eyeballs out.
Also, if its simply too much light being reflected that can be pretty intense, such as a bright sunny day shining down on a field of snow.

As said before, the reasons apples are red is cuz they absorb every color EXCEPT red. Thats what gets back to you, so you see red.

TRIVIA:
Does anybody know what happens to your eyes at night, or in very low light?
 
You said, "I've come to the understanding (and correct me if I'm wrong), that all objects give off electromagnetic radiation due to electrons jumping orbitals. If the wavelength falls in the visible spectrum, we see the radiation as light."

Half right. All objects give off AND absorb electromagnetic radiation constantly, BUT not solely because electrons jump orbitals. The fall of an electron from one energy state to a lower one (which may or may not involve a change in orbitals) will release the energy difference between those two quantized states, and the radiation may be visible if it falls into the range of our eye's sensitivity. It might also fall into the ultraviolet range we don't see, or into the higher-energy X-ray region, or into the lower-energy near-infrared region. BUT there are other mechanisms of changing energy state that involve smaller energy differences, and those end up emitting electromagnetic waves usually in lower frequencies we can't see, like in the infrared region. It happens we DO detect some of those, however - we call that heat rays. Typically these mechanisms involve a part of a molecule which is vibrating at a certain frequency and energy level, and drops to a lower-energy state with less vibration going on. Even smaller energy changes that involve the changing weak forces of molecules close to each other in liquids and solids can absorb and emit microwaves. In fact, the absorption part is exactly how we heat food in a microwave oven. So, not all electromagnetic wave emission comes from electrons changing orbitals.

As many have said, the reason we see most objects is that they reflect - that is, fail to absorb - light already striking them from a high-energy source like the sun or an electric light bulb, or a flame. Most objects do this non-uniformly, so they absorb some light frequencies (energies, colors - it's all linked) more strongly than others, and we see what they do NOT absorb. The reason we don't see them in the dark (in the absence of a light source we can "see" there is no reflected light) is that they only emit lower-frequency electromagnetic waves that our eyes cannot detect. For example, an infrared camera ("night vision" devices are an example) that IS able to detect that radiation can see some objects if they are emitting more intense radiation than their surroundings. So they can see a person in an unlit room, but probably not a wooden table that is the same temperature as the rest of the room, because the table is not sufficiently different from the radiation output from everything else in the room.
 
Light (photons) is what your eye captures (image).

Light is an EM wave (spectrum)(many different frequencies/colors).

Light hits object (apple) which acts like a partial black body.

Apple absorbs all but redish frequencies of light. Bounces red back.

You see this bounced light.









This has been the coolest formatted post I have written.
 
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