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Old 18th Jan 2011, 13:57   #1
NeilFawcett
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Horizon - Reality - Twin slit experiment

On this weeks Horizon they showed the 'Twin Slit' experiment. In this experiment, they have two tiny slits, which they then fire photos of light at.

Imagine firing bullets through two neighbouring windows, with the pattern on the wall across the road, you'd expect to see two columns of marks.

Do the same with two slits and fire single photons from a laser though, and they suggest you get three groupings? Stranger still they continued to suggest if you then look at the individual photos as they approach the slits to see what's happening, the phenomenon stops happening?

Now my brain has trouble with this, so I'm wondering if someone can clarify it.

Is it really three groupings? Or more than that in a traditional interference pattern?

The suggestion is, there's some sort of interference (even though there's only ONE particle) so you don't get just the two expected groupings. If this is the case, when ONE particle is fired, is just one detected in the groupings, or even more strangely, are TWO detected in the groupings on the other sides of the slits?

And there suggestion, just looking at the experiment somehow changed it? How can that be? Surely the 'look' must be actually affecting the experiment itself?

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Old 18th Jan 2011, 14:01   #2
Xordium
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Watch this mate I think it will help you understand better.

http://www.youtube.com/watch?v=DfPeprQ7oGc

Any problems after that come back and I'll try and explain better.
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Old 18th Jan 2011, 14:29   #3
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Quote:
Originally Posted by NeilFawcett View Post
And there suggestion, just looking at the experiment somehow changed it? How can that be? Surely the 'look' must be actually affecting the experiment itself?
Holographic Universe theory:
http://www.youtube.com/watch?v=cJBoIz8yZDc
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Old 18th Jan 2011, 14:35   #4
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Originally Posted by mmj_uk View Post
Holographic Universe theory:
http://www.youtube.com/watch?v=cJBoIz8yZDc
Oh dear ... here we go again.
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Old 18th Jan 2011, 15:00   #5
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I watched Horizon last night on iplayer, blew my mind when the double particle thing stopped happening as soon as it was observed.
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Old 18th Jan 2011, 15:08   #6
Castiel
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Shall I really complicate things with the Quantum Eraser delayed choice experiment?

http://en.wikipedia.org/wiki/Delayed...quantum_eraser
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Old 18th Jan 2011, 15:14   #7
Wee Michelle
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Originally Posted by Castiel View Post
Shall I really complicate things with the Quantum Eraser delayed choice experiment?

http://en.wikipedia.org/wiki/Delayed...quantum_eraser
does it come with a highschool level video to watch?

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Old 18th Jan 2011, 15:18   #8
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Maybe the particle splits up then rejoins?


Everything in moderation. Including moderation itself.
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Old 18th Jan 2011, 15:21   #9
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I watched this last night but I'm too closed minded to understand...
Why did observing the experiment stop it from working?

Read some generic links on quantum computers this morning to try and get some sort of vague, primary school understanding. My brain was damaged in the process.

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Old 18th Jan 2011, 15:22   #10
Castiel
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Quote:
Originally Posted by MikeHunt79 View Post
Maybe the particle splits up then rejoins?
It has the properties of both particles and waves, known as wave-particle duality.

http://en.wikipedia.org/wiki/Wave%E2...rticle_duality
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Old 18th Jan 2011, 15:23   #11
Castiel
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Quote:
Originally Posted by Wee Michelle View Post
does it come with a highschool level video to watch?

dunno about highschool, but these are quite easy to understand.

http://www.youtube.com/watch?v=sfeoE1arF0I

http://www.youtube.com/watch?v=bnxHc6OqB7U


This may be of help as well. it is a shame my brother no longer posts here, he would know how to explain this stuff in layman's terms.

http://www.hotquanta.com/wpd.html
Last edited by Castiel; 18th Jan 2011 at 15:29.
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Old 18th Jan 2011, 15:33   #12
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I understand the split beam (as much as you can, its really exciting).

I get the jist of what they are doing here, they've offered 2 normal routes and 2 'blind' routes to see the overall difference with the 'watching/seeing' but I'm struggling with the conclusion and what it layers ontop of the original interfernce patern discovery.

Will watch them just now ta
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Old 18th Jan 2011, 15:56   #13
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Castiel, I am not sure layman's terms are possible here.

Quote:
Originally Posted by NeilFawcett View Post
How can that be? Surely the 'look' must be actually affecting the experiment itself?
To determine the outcome of any experiment in action you must interact with it. The experiment you are performing must interact with what you are measuring your observation with and likewise what you are measuring with must also interact with your experiment. With the measurements at this small scale the more exactly you measure one thing the less you can measure everything else.

I have been thinking how to describe the "how does the observation change things" and the only thing I can think of is as thus (this is not my scientific speciality hopefully we will get someone clever in later).

What you need to maybe think of is that an electron is something that can display the behaviour of either a particle or a wave. This is important because it adds a relativity component to it all which of course implies the circumstance of say an observation. In the same way people are not good or bad but display characteristics of the two depending on what conditions they are put under then electrons will also display the different behaviours of being particle-like or wave-like depending on a variety of factors. To go any further than that I think you really need to hit the books. I think it is maybe not too helpful to think of the observation as being some mystical component which both the horizon and the video I linked do in my opinion.
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Old 18th Jan 2011, 16:07   #14
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To determine the outcome of any experiment in action you must interact with it.
Sure, but it can be completely non-invasive and not affect the outcome in any way!

But the suggestion in Horizon was that something magical was happening just by 'looking'.

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Old 18th Jan 2011, 16:14   #15
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Quote:
Originally Posted by NeilFawcett View Post
Sure, but it can be completely non-invasive and not affect the outcome in any way!

But the suggestion in Horizon was that something magical was happening just by 'looking'.
It never does not interact what you make sure is that you are not changing the thing you are measuring. Nothing magical is happening just that the resulting behaviour has changed depending on what you are looking for.
Last edited by Xordium; 18th Jan 2011 at 16:38.
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Old 18th Jan 2011, 16:19   #16
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It is never non-invasive what you make sure is that you are not changing the thing you are measuring. Nothing magical is happening just that its behaviour has changed.
Of course you can analyse things in an non-invasive way?

I fire a bullet into a wall.

I then fire another bullet into a wall while filming it.

Has the second bullet been affected in any way compared to the first?


Back to Horizon - They implied the same with the individual photons. But I would agree, the outcome suggests the analysing did affect the outcome. But they did imply they have no idea why it affects it! So it would be akin to my second bullet veering every time I filmed it, and only when I filmed it.

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Old 18th Jan 2011, 16:33   #17
Xordium
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Quote:
Originally Posted by NeilFawcett View Post
Of course you can analyse things in an non-invasive way?

I fire a bullet into a wall.

I then fire another bullet into a wall while filming it.

Has the second bullet been affected in any way compared to the first?
No, what you have just done is to perform a good experiment. Your measuring tool did not in any way change what you were measuring. I should not have said it can't be non-invasive what I should have said there was that there will never be no interaction. This is to crux of the issue at point in the Horizon program. Would you expect the same result if the bullet had to pass through the camera on the way to the wall? Use that to then make a conjecture on why. Again I would re-iterate it is not the particle itself that is changing but its behaviour.
Last edited by Xordium; 18th Jan 2011 at 16:55.
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Old 18th Jan 2011, 16:55   #18
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To detect the presence of something, at the very least you need to bounce a photon off of it. This changes its momentum and so the experiment is affected.
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Old 18th Jan 2011, 17:10   #19
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To detect the presence of something, at the very least you need to bounce a photon off of it. This changes its momentum and so the experiment is affected.
In your example yes, we have affected the outcome. But Horizon implied we have no idea why our viewing of the experiment means the photo behaves only as a particle, but when we stop looking we then get the interference like a wave? And I'm sure a lot of more clever people than us have considered the 'viewing' and it's affect on the outcome?

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Old 18th Jan 2011, 17:14   #20
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Quote:
Originally Posted by NeilFawcett View Post
In your example yes, we have affected the outcome. But Horizon implied we have no idea why our viewing of the experiment means the photo behaves only as a particle, but when we stop looking we then get the interference like a wave? And I'm sure a lot of more clever people than us have considered the 'viewing' and it's affect on the outcome?
I said this way back:

Quote:
Originally Posted by maustin View Post
I think it is maybe not too helpful to think of the observation as being some mystical component which both the horizon and the video I linked do in my opinion.
What they should be saying as has been said thoughout this thread. When you perform that experiment and observe it you are observing with a measuring device that will change the outcome of the experiment. How exactly that measuring device then causes that outcome we see we do not know. But for the case of simplification they simply say we do not know how observing it changes it which is a completely different thing.
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Old 18th Jan 2011, 18:48   #21
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One thing I dont understand is what about us just being holograms.

I've heard that black holes shrink, so now they dont just dissapear? Or do they dissapear but still keep the information somehow.
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Old 18th Jan 2011, 19:08   #22
Castiel
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Haha, the more we 'know' about reality, the more 'unreal' is appears to be.
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Old 18th Jan 2011, 22:40   #23
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AIUI, when a quantum event is observed, its wave-form collapses.

But anyway, have a read of this: http://en.wikipedia.org/wiki/Quantum...93body_problem
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Old 18th Jan 2011, 23:05   #24
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I've tried and tried and I give up. My thoughts clearly far outpace my ability to articulate in this subject much to my shame.

I'll try later (now revisiting the subject of physics), but god my head hurts. Think I'll stick to history and politics, just have to remember things there
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Old 18th Jan 2011, 23:21   #25
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A brief summary would be that we have two appealing models to describe light, one analogous to waves in the sea and one involving very small balls flying all over the place. Neither model is all that great if you push them to the extremes, so you get results which aren't readily explained by either.

The next model up from the nice two is quantum field theory, however it marks the point where I accepted I was simply too thick to read physics. I don't believe it is possible to describe the results of the double slit experiment in layman's terms, as it's very difficult to explain it to undergraduate physicists. I suppose Feynman would argue this means we don't understand it well enough, and he's usually right about such things.

Best of luck guys. I'll stick to making things out of other things, and ignoring the finer details which make bugger all sense
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Old 19th Jan 2011, 19:31   #26
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Quote:
Back to Horizon - They implied the same with the individual photons. But I would agree, the outcome suggests the analysing did affect the outcome. But they did imply they have no idea why it affects it! So it would be akin to my second bullet veering every time I filmed it, and only when I filmed it.
Perhaps its because they predict one thing to happen, yet when they test it and analyse it it doesnt really happen as per their expectation/theory.

Therefore they must create a new theory that states that watching the experiment caused the expected outcome to not happen. Instead of accepting that the prior expectation/theory was infact incorrect?

The hologram theory makes no sense either. True the guy said that no one really understands it. Yes m friend because its not true and it makes no sense. It only begins to make sense when you have run out of other theories and start making things up and get a lot of people to jump onto the bandwagon to bring some small consensus and create a theory that doesnt fit into experiments that you can measure. Bringing me back to the first point i made...

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Old 19th Jan 2011, 20:23   #27
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Originally Posted by Nickg View Post
Perhaps its because they predict one thing to happen, yet when they test it and analyse it it doesnt really happen as per their expectation/theory.

Therefore they must create a new theory that states that watching the experiment caused the expected outcome to not happen. Instead of accepting that the prior expectation/theory was infact incorrect?

The hologram theory makes no sense either. True the guy said that no one really understands it. Yes m friend because its not true and it makes no sense. It only begins to make sense when you have run out of other theories and start making things up and get a lot of people to jump onto the bandwagon to bring some small consensus and create a theory that doesnt fit into experiments that you can measure. Bringing me back to the first point i made...
How do you know the hologram theory makes no sense, have you seen the equations, are you privy to the secrets of the universe?
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Old 19th Jan 2011, 21:17   #28
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The next model up from the nice two is quantum field theory, however it marks the point where I accepted I was simply too thick to read physics. I don't believe it is possible to describe the results of the double slit experiment in layman's terms, as it's very difficult to explain it to undergraduate physicists. I suppose Feynman would argue this means we don't understand it well enough, and he's usually right about such things.

Actually Feynman himself does a pretty good job of explaining the quantum mechanics interpretation of the Young's Slits Experiment in his Lectures on Physics. IIRC it's in Six Easy Pieces. He even explains why the observer changes the experiment, and why different forms of "observation" change it in different ways. It's intended for first-year undergrads, but it's still not that difficult to understand.


M

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Old 19th Jan 2011, 21:42   #29
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How do you know the hologram theory makes no sense, have you seen the equations, are you privy to the secrets of the universe?
Layered solid holograms that project a basement through so many walls and roofs and that'd solid enough to bounce a ball.off that actually and observably interacts and causes physical defortmation to the ball? But its a dense hologram? That makes no sense as a hologram is a projected image not a dense object.

Or are these imaginary new fangled hologram that haven't been invented yet but are used as a gap filler in a non event equation with made up properties that only fill their understanding of the problem but have little to.no basis in reality.

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Old 19th Jan 2011, 21:44   #30
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Quote:
Originally Posted by Nickg View Post
Layered solid holograms that project a basement through so many walls and roofs and that'd solid enough to bounce a ball.off that actually and observably interacts and causes physical defortmation to the ball? But its a dense hologram? That makes no sense as a hologram is a projected image not a dense object.

Or are these imaginary new fangled hologram that haven't been invented yet but are used as a gap filler in a non event equation with made up properties that only fill their understanding of the problem but have little to.no basis in reality.
The ball is also a hologram though, so surely that's completely irrelevant?

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