Basic Double Slit Experiment Question

[Strange]

 

If the photons are passing down the slits as waves, then how do the photons make it through the slits without touching the walls of the slits and avoid being absorbed?

 

You still seem to think they are either particles or waves. You need to get over that.

 

But the answer is that a proportion of photons would be absorbed passing through the slit. The proportion that are absorbed is exactly the same as the proportion of energy that would be absorbed if you treat it as continuous waves.

 

But any individual photon will either get through or be totally absorbed. (Because they are quanta.)

 

QED tells you how to work out what proportion of the photons will be absorbed.

[Delbert]

 

1) As a test to see if the photons are ever able to pass through the central part of the barrier between the two slits, a complete barrier (without any slits) is set up to that thickness and the photons fired at the barrier to see if any photons pass through the barrier or are reflected. For arguments sake, we will take it that the results are that no photons passed through the barrier and very few photons were reflected, the vast majority being absorbed by the barrier.

In defining a barrier one has to say how wide it is. And unless it is of infinite width, there is a remote possibility that a photon or electron will be found the other side.

 

For example: you shine a torch at a target and see a roughly circular illumination that is brightest at the centre, with the illumination dimming the farther away from said centre.

 

The question is: is there a definable point from the centre where there is no light?

 

If not, then it's perfectly conceivable for some light to end far enough away from the centre to end up behind the torch! It may be only one photon over a suitable time period, but unless there is a definable point from the centre whereby there'll be no light, light there'll be at the back of the torch. Because if there isn't there has to be a definable point with no light which one can identify.

 

For the same reason that unless your barrier is infinitely wide, there will be photon or photons the other side.

Edited August 15, 2014 by Delbert

[swansont]

 

For the QED explanation of the pattern of the photons on the far detection screen, is that the photons, on exiting the slits interfere with each other's paths. This implies that the photons (whether as a wave or as multiple paths) while travelling down the slits would have encountered the walls of the slits at some point - and therefore be absorbed.

 

So the question is, if the interference is because the photons are waves, then the explanation is inconsistent with the photons being able to get through without being absorbed by the sides of the slits?

 

No, for the actual QED explanation (not your strawman version of it), light will have a probability of being absorbed and a probability of passing through the slit. There is nothing in QED that states that if any part of a wave encounters a boundary in any way that it gets absorbed. That's spectacularly wrong.

[Reaper79]

Remember the plasma ball? the globe with funky lights spewing everywhere, and when you touch the glass it would come to your finger and follow it until you let go.

 

That is sort of what's happening with the double slit experiment, the particle exists as a "blob" of energy which passes through both slits, just like a ghost and creates and interference pattern. But when you observe / interact with the "Blob" of energy it collapses to a single point ( or mostly a single point ) just like when you touch the glass on a plasma ball, and no interference patten can be seen.

 

All this talk of time travelling particles and the particles being "Aware" is just nonsense to me, the answer is obvious.... just don't ask me to do the math on that one

[Delbert]

Remember the plasma ball? the globe with funky lights spewing everywhere, and when you touch the glass it would come to your finger and follow it until you let go.

That's a interesting analogy. Although I don't think it quite fits. As we used to say: you big heap capacitor. The same way a neon screwdriver works.

 

But as for an analogy of the two slit experiment between looking and not looking at a slit, I think it needs a bit of imagination.

 

I certainly agree about the 'aware' business.

 

The universe is certainly a difficult place for us to quantify, specify or imagine.

 

Someone asked me how do fish in the depths of the ocean withstand the water pressure? I said: how do you withstand 15lbs per square inch air pressure? She said: there's nothing pressing on me because I can't feel anything. Indeed, and as I think we know, the ocean wouldn't exist if it wasn't for air pressure (water would boil off in a vacuum). In other words liquid water is a consequence of something, as my friend stated, that's not there because it can't be felt.

 

Perhaps similarly, it seems to me that what we call these particles (photons, electrons etc) are just events as a consequence of something else. Because the plain fact from experiments like the two slit, is that they do not act as an object we can identify. It is clear to me they are nothing more than events. And their apparent movement from place to place is the transfer of energy in the form of a multitude of actions and exchanges. Something which I think is supported by Feynman's Sum Over Histories.

Edited August 26, 2014 by Delbert

[swansont]

That's a interesting analogy. Although I don't think it quite fits. As we used to say: you big heap capacitor. The same way a neon screwdriver works.

 

But as for an analogy of the two slit experiment between looking and not looking at a slit, I think it needs a bit of imagination.

 

I certainly agree about the 'aware' business.

 

The universe is certainly a difficult place for us to quantify, specify or imagine.

 

Someone asked me how do fish in the depths of the ocean withstand the water pressure? I said: how do you withstand 15lbs per square inch air pressure? She said: there's nothing pressing on me because I can't feel anything. Indeed, and as I think we know, the ocean wouldn't exist if it wasn't for air pressure (water would boil off in a vacuum). In other words liquid water is a consequence of something, as my friend stated, that's not there because it can't be felt.

 

But is is, in fact, there. So I'm not sure what the point is.

 

 

Perhaps similarly, it seems to me that what we call these particles (photons, electrons etc) are just events as a consequence of something else. Because the plain fact from experiments like the two slit, is that they do not act as an object we can identify. It is clear to me they are nothing more than events. And their apparent movement from place to place is the transfer of energy in the form of a multitude of actions and exchanges. Something which I think is supported by Feynman's Sum Over Histories.

 

I think this is on the right track — physics doesn't claim that photons or electrons are real things, just that nature behaves in a certain way, some of which is described by QED. We have models in which we treat them as real things, but that's not quite the same claim. What we have are events (or interactions) that follow certain rules. Physics is all about finding out the rules. QED is a set of those rules. Light (or an electron) behaves as a wave, with certain properties that are quantized and is localized (to some extent) when undergoing an interaction. Those are some of the rules governing the behavior. Feynman's sum over histories is another.

[Delbert]

But is is, in fact, there. So I'm not sure what the point is.

I suppose my analogy is a bit skewed, but I was trying to relate something like the existence of vast amounts of liquid water being dependent on a consequence that at least one individual of my acquaintance thinks isn't there. Likewise this business about photons, electrons etc being a particle or a wave or even both depending which way we observe. Trying to describe it as such is just semantics and playing with words, I suggest. It seems to me there is no such thing that can be described as a thing with such properties. And my analogy was just something I thought whereby it could be related to the existence of liquid water, like liquid water can only exist with the constant action of countless other things (atoms) reacting and forcing into a liquid state. As I said, perhaps my analogy is a bit skewed, but I was trying to relate these particles to something we understand.

 

Doubtless, I failed.