Light

[Jonsy123]

Thanks 5614 (Jonathan).

[swansont]

That is precisely the point, e=hf shows that light must be a particle... then Young's double split shows it must be a wave.... hence wave-particle duality.

 

Quantizing the energy doesn't necessarily make it a particle, it's just that it's convenient in some ways to think of it that way.

[Severian]

Severian's model is constructed with the knowledge that light can be like both. In anycase, I like Severian's model for visualizing the concept of light. It's probably the best understanding we have of light.

 

It's not my model. I was explaining how it is from a Quantum Field Theory perspective. As you can tell from the name, QFT describes everything as fields, which can thus display wave-like properties, but the fields are quantised so their energy comes in lumps, so we can think of it as particles.

 

The fact that the fields are quantised is actually a big step. In plain old quantum mechanics, one only quantises the operators (the things which make the measurements) - this is known as first quantisation. So the position and momentum operators have weird commutation relations but the wavefunction (the field) is left as a classical object.

 

In QFT they go one step further and quantise the the field itself. The field is then composed of 'creation and annihilation operators' (they are basically the coefficients of a fourier series) which now have commutation relations and can create or destroy quanta of the field itself. This is know as second quantisation. (Some people don't like calling it that, because we really should have quantised everything in one go rather than going down the blind alley of one-particle quantum physics.)

 

I think the term particle is misleading because we tend to think of a little cannon-ball like object, which it definitely is not.

[mezarashi]

If he understands that he might be living in a 2D world, there's still hope for him...

 

Yes, and unfortunately for us, there is no ultimate-being to tell us what it is that we are lacking. All we know that there is something "incomplete" about our understanding of light. It's too difficult for us to see "the big picture", but we don't really know why (it might not be dimension related), but from our humanly observations, the so wave-particle duality is what we see.

[Jonsy123]

This might be off topic, but...

 

If it is possible to logically "conclude" our way out of this mess, base on available observations, but the main problem is brain power, then there might still be a chance, in 2-3 decades, when A.I rise.

 

It may sound futuristic, but if we really are at the boundary of our understanding with this issue, this might be the solution.

 

This might sound absurd, but think just how wider our world is in comparison to the world of the #2 smartest animal on the plant, the Chimpanzee. I saw a documentary where chimpanzees were practicing simple arithmetics (addition, subtraction, the meaning of zero etc.), even though they did it quite nicely, still, what do they know ?.

 

Now think of a computer IQ, which in relation to us, look at us like chimpanzees... shouldn't this be enough to figure out the wave/particle duality ? (and unite the 4 fundamental forces, while at it).

[mezarashi]

Now think of a computer IQ' date=' which in relation to us, look at us like chimpanzees... that's scary (but might be enough to figure out the wave/particle duality).[/quote']

 

I don't want to ruin your aspirations so soon, but as it stands, there is no Artificial Intelligence system that can "extensively" learn independently. A computer can only perform to the limit of human knowledge. If we want the computer to perform addition, we had better know what it is in the first place or else what would we put in the program? The only thing a computer help does is to speed up the calculations that would other wise take us billions of trillions of years with paper and calculator. So with this in mind, I don't think a "The Matrix" situation will become of us anytime soon.

[Jonsy123]

IBM is currently doing a project to digitally mimic the activity of the human cortex, using a supercomputer (they are not sure what they will get at the end, but everything is possible, eventhough this project's aim is not to produce a computer A.I). they said they are going to try and model every neuron and synaptic connection there is. If, at the end, in several decades, we will be able to build a computer brain, based on our own, using a far superior hardware, it might be it.

 

How many variables can a human scientist take into acount simultaneously ?, can we be simultaneously aware of every single word, idea and experimental result, expressed at the scientific literature regarding the area we are researching, and the areas relating to it ?. how much time do we need to check our calculations for accuracy ?, can we think 24 hours straight, without a single second of rest ?.

 

btw, here is a link to the IBM story:

http://www.newscientist.com/article.ns?id=dn7470

[danny8522003]

If the mass of a photon is 0 and p=mv, wouldnt it have 0 momentum? Or is the m used in this forumla its relativistic mass according to E=hf and E=mc^2?

[swansont]

If the mass of a photon is 0 and p=mv, wouldnt it have 0 momentum? Or is the m used in this forumla its relativistic mass according to E=hf and E=mc^2?

 

p=mv is a classical equation

 

E² = p²c² + m²c⁴

 

so, for a photon, p=E/c

[danny8522003]

Ok thanks.

 

If the sun just radiated only photons, would the mass liberated from the sun be calculated using hf=mc^2?

 

I.e. number of photons*relativistic mass of a photon*time

[5614]

e=mc^2 doesn't work for photons because they have 0 mass and so with that equation 0 energy, which is wrong, hence the extended version in Swanson's post #34 which includes momentum, which photons do have.

 

As well as using:

p=e/c

you can also use:

p=h/lambda

or:

momentum = plank's constant / wavelength

[danny8522003]

So how would you calculate the mass lost by the sun as it radiates photons?

[Klaynos]

So how would you calculate the mass lost by the sun as it radiates photons?

 

 

It's done quite simply really, you work out the intensity of light, and the energy lost due to that intensity then work out the mass required to generate that energy...

 

Or something very similar to that can't remember had to do it a year ago though remember it not being too hard...

[danny8522003]

I did it in my AS Physics class and we calculated the mass of the photons being liberated using m=hf/c^2.

[Severian]

Yes, that is fine. Something with mass provides energy E=mc² and then that energy is radiated away via E=hf. So the mass lost (by whatever gave the mass up to provide the energy) is hf/c².

 

(BTW, the lost mass is coming from several different fusion reactions.)

[danny8522003]

But photons dont have mass?

[ydoaPs]

no, they don't.