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/sci/ - Science & Math

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4597368 No.4597368 [Reply] [Original]

How can a photon have a wavelength of something like 100 meters yet be absorbed by a single electron in a very small antenna?

>> No.4597379

It hits it.

>> No.4597378

because until the wavefunction collapses the photons probabiloty function has a wavelength of 100m

>> No.4597386
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4597386

I dunno OP, my shitty physics TA couldn't answer this question either.

Do single photons spread out across space as they travel? Wouldn't they be miles long by the time they get to Earth from the Sun?

>> No.4597389

Does it even mean anything to say you have a *single photon* with a well-defined wavelength? I'm honestly not sure. I feel like we'd have to go to QFT here, where photons are quantized excitations of the electromagnetic field.

>> No.4597394

>>4597378
So the frequency and wavelength of a photon correspond to its wave function?

What makes it collapse?

>>4597379
How does it hit it if it's a 100 meter wave?

>> No.4597405

>>4597389
That's sort of what I'm going with here. Apparently they do because they can self-interfere in cavity QED

>> No.4597408

>>4597394
>What makes it collapse?
there are various ideas about this

google copenhagen and many worlds for the two most accepted ideas

>> No.4597413

>>4597405
Actually, yeah. that's a very good point. Single photons DO have well-defined wavelength, as shown in the double-slit experiment for single photons.

But it also shows that photons are distributed, and can even interfere with themselves. That's probably your answer - photons are not little billiard balls.

Wave-particle duality up in this bitch.

>> No.4597415
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4597415

>>4597408
So we have no idea where a radio wave photon is if its emitted from a single atom?

I never knew the wave function was that big wow.

>> No.4597419

>>4597413
Caveat - there is an uncertainty relation here that means your wavelength is not *perfectly* defined, just like it is not perfectly spatially localized.

>> No.4597424

>>4597415
we know some probabilities of where it might be, and because of uncertainty principle we can locate the particle if we lose information about its momentum

>> No.4597442

because its a particle too

>> No.4597475
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4597475

What is hard to understand? The wavelength is in the direction of motion of the photon, it would only be a problem if the amplitude of the wave was something like 100 meters. But light doesn't have amplitudes, just number of photons.

>> No.4597489

>>4597475
>implying it's one dimensional

>> No.4597491

Sound waves may have wavelengths of decimeters, but you can still pick them up on a 3-cm long eardrum.

>> No.4597495

>>4597489

A "ray" og light is one dimensional

>> No.4597502

>>4597491
But you can't with individual phonons

>> No.4597510

>>4597475
Not OP, but how does this explain light of large wave length more readily passing through matter versus light with shorter wave length?

Seriously, the whole concept of it being a particle and a wave at the same time is retarded. There would have to be a better way to model what we are seeing.

>> No.4597516

>>4597495
The rays of geometric optics are an approximate model that breaks down when you can see wave behavior. A wave needs size in the directions perpendicular to its direction of motion. And the smaller you make that size, the more the wave spreads out due to diffraction.

>> No.4597518

the wave function isnt "real"
it spreads through the whole of the universe
stop thinking like its mechanics.

>> No.4597541

>>4597518
>the wave function isnt "real"
Then how can you explain the wave-like nature of matter?

The double slit experiment?

>> No.4597550

>>4597541
the experiment says that they act LIKE waves.
its an interpretation. as is the particle interpretation.
neither is right, neither is wrong.
i know this sounds hand-wavey but you better get used to it theres worse to come:

"it rotates INTERNALY, lets call this spin. but remember everyone, its not spinning. but it acts like it is. internally."

>> No.4597566

>>4597550
I'm not talking about spin. If it is a wave then how does it hit an individual particle? If it is a particle then how does it interfere with itself?

>> No.4597571

>>4597566
That's just it. It's NOT a wave. It just has some wavelike properties.

It's not a particle either. It just has some particlelike properties.

>> No.4597573

>>4597566
i know youre not talking about spin, i was giving you an example of how as a theoretical physicist you simply have to get used to things that we (currently) DO NOT UNDERSTAND.

wave particle duality is one of these things. If you could prove an answer to your question youd probably have answered every open question in physics.

we can only interpret what experiments show us and what is "allowed" to be seen by the uncertainty principle.

>> No.4597579
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4597579

>>4597571
Then WHAT THE FUCK IS IT DAMMIT?

>> No.4597584
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4597584

>>4597579
Photons are quantized excitations of the electromagnetic field.

That sounds short, but I recognize it's not really a full explanation. The full explanation is long and is all math. Pic related for what the problem is here.
http://en.wikipedia.org/wiki/Quantum_field_theory

>> No.4597587

>>4597579
Must be babby's first transition from religion to science

If you want to REAL answer then we DO NOT KNOW. For something to be SCIENCE, it needs to be confirmed by OBSERVATION. Else it is just philosophical circle jerking sociology-esque BULLSHIT.

>> No.4597589

>>4597584
But if they are quantized then its a particle

RIGHT?

>> No.4597593

>>4597589
Not in the way you're thinking, no. For instance, I'm pretty sure the mental model you're labeling "particle" includes the idea of having a single, definite location in space at all times.

>> No.4597596

k, this is now a troll thread.
no more posts.

>> No.4597603

>>4597593
If I pretend the springs on my mattress can only have certain values and I shake the mattress I can see where all the vibrations are. So why not?

>> No.4597604

>>4597584
Related, and more specific to the topic:
http://en.wikipedia.org/wiki/Quantization_of_the_electromagnetic_field

>> No.4597613

Basically, here's a way for you to think of this:
we're at the point with protons where they were back in the day with atoms when they couldn't actually observe them in detail: we've got a lot of ideas of why they do what they do, which can still turn out to be wrong, but we're describing what we can see of them and trying to make that make sense with all of the other stuff we know--trying to make it fit in is is really, really complicated to boot. Its inelegant and confusing as hell, but it's the best we can do with what we know now.

Maybe at some point in the future things will be different and we can offer up simple, elegant explanations because we have access to some new data, but until then this is what we've got.

>> No.4597624

>>4597603
I think because the "stuff that vibrates" is the field, and the field is not itself spatially discrete.
What I can say with more confidence is that photon states (the electromagnetic field modes being excited) are not spatially localized in that way.

tl;dr I'm pretty sure that's just a bad analogy for what the equations are like.
If you really want to understand this stuff, you have to go into the math.
>>4597604
http://en.wikipedia.org/wiki/Quantization_of_the_electromagnetic_field#Photon_states

>> No.4597628

>>4597624
(cont)
This might be relevant and more accessible. It's about the position operator for photons, and why it's problematic.
http://arstechnica.com/science/2009/03/why-photons-are-always-neither-here-nor-there.ars