# If we had a microscope

1. Jul 30, 2008

that could be used with our naked eye and we could see photons, would they colllapse to a particle?

2. Jul 30, 2008

### humanino

you probably wish that I quit answering you. Yeah, I'm not going to do that now. Unfortunately, everybody else is busy

Anyway, I would be interested to see other people's answer. The way I understand it, to make sense of your proposal would be a very long and contrived construction.

Scattering of light by light does exist. In certain very specific situations (see details in Diphoton Generalized Distribution Amplitudes) you can somehow claim that you use a virtual photon to probe the "quantum fluctuation content" of a photon, thus constructing real 3D images of a photon.

But seriously, that's quite complicated, and even unclear how and when we'll be able to do that. Unless you go that far, the short answer to your question is "no"

3. Jul 30, 2008

### my_wan

First off this question presumes the wavefunction is the "real" state of the photon prior to being observed. The very question of collapsing wavefunctions is an open question. In fact it is rather trivial to demonstrate a situation where for a given observer a wavefunction has been observed to apparently collapse yet for another observer both the photon and the observer that witnessed the collapsed wave function remains a single un-collapsed wavefunction by the rules of QM.

Your question appears loaded with the presupposition that the collapse of the wave function is a real physical change of state. A presupposition that thus far has been impossible to pin down experimentally. If you want your answer according to QM then the answer is both yes and no, much like being both a particle and a wave. You would certainly observe something that appeared similar to a particle but then no individual photon has ever been observed to be anything other than a particle. We only deduce that it must have been a wave prior to detection due to the rules it followed to produce the detection pattern we see. QM works independently of the ontological weight we give concepts such as collapsing wavefunctions, etc. Frustrating yet that is the state we find ourselves in describing physical phenomena.

4. Jul 30, 2008

### humanino

I hope my_wan realizes that I provided a link to a paper explaining how to do what was proposed initially. Of course, some people prefer to discourse why things are impossible in principle rather than constructing a practical way to achieve goals.

5. Jul 30, 2008

### peter0302

Can you see your own eyeball?

Ok maybe not a perfect analogy. But leaving aside photon scattering as humanino suggested, nope, there's no way. Think about it logically for a moment. Your eyes work by sensing photons bounced off of other objects. Since the photons are all that your eye perceives, unless you could bounce one photon off another (which is extremely rare and difficult) there's nothing for your eye to see unless the photon hits it.

What are you getting at anyway?

6. Jul 31, 2008

### my_wan

I think you have missed the OPs point. Sabradin never asked if the microscope itself was possible. The microscope was a rhetorical devise to attempt to articulate a question about wavefunction collapse.

7. Jul 31, 2008

### wawenspop

My take is this: the photon before it is observed is a kind of fuzzy probability like a wave packet for example. And we could not 'see' that, but when we intercept it to 'see/observe' it than the wavepacket collapses instantly so that somewhere (statistically derived) the seeing device - say an atom absorbs the photon and glows or beebs or something - thus we think we see a photon, but we see the action it had on an atom/molecule.

Are you interested in what the photon is or 'looks like' whilst its travelling?

8. Jul 31, 2008

### humanino

Do you agree that, if there is no way to define such a microscope, there is no discussion ?

What's the difference ? How do you know what a photon is ?

9. Jul 31, 2008

### wawenspop

IMHO, a photon is a boson that is responsible for charged particles 'knowing' about the existence of other charged particles (and more..), but I don't think we can pin it down to being like things we know in everyday space-time. But we can discuss what it is at a variety of levels - I'm sure a Boson is not what you were thinking about, so I just guessed what you wanted to know.

10. Jul 31, 2008

### humanino

The paper I refered to earlier is pretty respectful of the standard model. I was talking about the photon as it is commonly defined. What I want to know is what you mean by
where you could replace "photon" by anything really, like in

11. Jul 31, 2008

### wawenspop

I was referring to Sabradins question and assuming he wanted to view a photon with a microscope as if it were travelling along and being viewed. I know its not possible to do that and I don't think we can even sensibly suggest what we think it might 'look like'. Its that point that makes them interesting to me, and I thought to Sabradin also - maybe I misinterpreted his question..

12. Jul 31, 2008

### humanino

I do think too Sabradin was talking about a regular microscope one could stick one's eyeball on and actually see a single photon. For a single photon, I too believe there is definitely no way to make sense of this idea.

However, all photons of the Universe are the same. By measuring such universal properties, one can actually construct an "image" of a photon as it appears to the other photons. Once you have this mathematical object, you can project it in various ways to actually see a picture with your eyes. That means, you can fix a scale and look at (for instance) the momentum distribution in the transverse plane of virtual u-quarks in a photon. This is due to the fact that u-quarks have charge and couple directly to the photon. Now you can even do the same for virtual gluons due to higher order coupling and non-singlet evolution when you run the QCD renormalisation scale, right ?

Of course, if you ask a purely theoretical question such as "what does a naked photon look like ?" then there is no way to make a 3D picture of a point. But that's pretty trivial.

13. Jul 31, 2008

### wawenspop

Hmmm ... virtual u-quarks? Now I am going to find out about those - sounds interesting.

14. Jul 31, 2008

### humanino

The article above points to a good reference :
Code (Text):
Theory of hard photoproduction
Michael Klasen
Rev. Mod. Phys. 74, 1221 - 1282 (2002)

15. Jul 31, 2008

### my_wan

Yes, to a point, which is one of the reasons I took exception to the presuppositions of the OP. The fact remains that the question concerned the nature of wavefunction collapse and not the nature of the hypothetical microscope. The principles of QM are independent of the specifics of how you define such a microscope. It depends only on the fact that the location of the photon is observed in some manner. In that respect there are a myriad of ways to rigorously define "microscope", none of which makes a bit of difference wrt collapsing wavefunctions. I therefore reiterate, the question was about the nature of collapsing wavefuntions and not about the microscope itself. QM is quiet clear that the technical specifications of "microscope" are inmaterial to the question of collapsing wavefunctions. The mere capacity to even in principle know the location of the photon is enough to answer this question.

16. Jul 31, 2008

### humanino

Please provide one that does not involve the process in the paper I cited. My bet is, you can't.

17. Jul 31, 2008

### my_wan

Aside from the fact this question continues to skirt the the fact that the OP question did not concern the microscopes specifications the answer is rather trivial: CCD, etc.

To continue dwelling on the microscope is to continue derailing the question the OP asked.

18. Jul 31, 2008

### humanino

[thread=247700]I already answered that[/thread] : the interaction of a single photon with any atom in the periodic table will clearly collapse its wavefunction, but I understand you were not aware of that. It's clear and trivial.

A CDD will certainly not allow you to see one single photon, in the sense that it will not provide you with 3D picture of a photon.

19. Jul 31, 2008

### my_wan

Answered what? I didn't asked a question... and what's with the ad homin concerning my state of knowledge? Are you referring to my knowledge of your responses in other threads or my knowledge concerning collapsing wavefunctions? Neither of which makes any sense to presume yet continues to derail the obvious point that the OP was not concerned with the nature of the microscope. I certainly never made any presumptions about you lacking any knowledge about collapsing wavefunctions, only that you continue to presuming the microscope rather than collapsing wavefunctions was central to the OP question.

So what? You don't need a 3D image, just a localized measurement (which a 3D microscope qualifies), to answer the OP concerning collapsing wavefunctions. Are you still missing the fact that the microscope was a rhetorical device?

This derail has probably gone on long enough...

20. Jul 31, 2008

### humanino

One can indeed interpret "see with our naked eye" as a localized measurement and this is not an image. However, if you want to discuss this aspect, you should do it in the other thread where it is appropriate. As you know since you have read the rules of the forum, one does not open 2 identical discussions within a few hours interval. So, in order to keep this thread alive, have another discussion, and because it is interesting by itself, this thread became 3D image of the photon. Please note that I'm not the one not following :tongue2:

21. Aug 3, 2008

### wawenspop

Its still an interesting thread in many aspects (no pun intended).
The collpase of the wave function is a hot issue and very interesting
to know what's going on in that wave packet when it collapses. I can't
wait to know on that one.

Also, photon - photon interaction is interesting because its a clash
of two bosons - which are field messenger particles for say two electrons
and must obey relativity to keep laws of physics consistent in
different frames of reference. But collisions between these particles themselves?
What is the mechanism (sorry about that word - its not a system of levers I realize)
for one photon 'knowing' about another photn with which its not entangled. Pls elaborate
(Humanino?). And what about the relative speeds allowed between two bosons?

22. Aug 3, 2008

### wawenspop

Democritus

worked out using logic that there must be atoms.
http://en.wikipedia.org/wiki/Democritus

One line of thought they used was that an object cannot 'go out
of existence' i.e. just dissappear into nothingness,
so that if we divide some object - a piece of paper, say -
again and again and again - ad infinitum it would go out of existence -
This is impossible (see above why) so there
must be a limit to how far we can divide something -
(we will call it an atom). Brilliant for 370 b.c. eh?

Another stroke of brilliance - there is a difference
between a void (absolute vacuum) and nothingness. What is it?
We can place an object into a void but we cannot place an object
into nothingness. Voila- Space-Time (well, hmmm... space anyway).

Now, the point is, that at QM sizes -very small - we are trying to deal
with 'stuff' outside of 'our' Universe. We are not in
'our' Universe but somewhere (sorry about the euclidean space
reference) else. That's where photons spend a lot of their
time and its all a little 'unkowable' for us space-time animals -
or can we solve that too?