I'd always read that anyone that isn't shocked by quantum physics doesn't understand it. I wasn't shocked and therefore assumed I didn't understand.

Yesterday I was doing some reading and learned of a demonstration that shot light, one photon at a time, at a target and observed the pattern it made on the target.

When a card with two slots cut into it was placed between the light source and the target the pattern was identical to that of a normal beam of light. Therefore, when only one photon is shot at a time it doesn't pass through one slot or the other, but instead it passes through both slots.

This, I thought was strange, but it didn't shock me.

The next step was to add a sensor on each slot that could record the the photons passing through. But, when they did this, the photons DID go through one or the other of the two slots AND the pattern they made on the target changed!

So, looking at what was going on changed the outcome.

This I found shocking. Maybe I'm on the way to understand quantum physics.

I wonder how they managed to create a light source that released only one photon at a time.

Atoms when excited will have the electron shells raise energy states. When they drop back down to there initial level they release a photon that has the energy difference.

After the emission there is a delay until the atom will get into an excited state again. You can use this time to block any additional excitations.

Its all about windows of opportunity.

Here is an excellent idea to get single photons

http://www.sciencemag.org/content/290/5500/2282.abstract

They use a turnstile where only a single photon can go through at a time before the turnstile moves into the path of the next photon, it takes a moment before the turnstile completes the turn and then has an opening for the next photon. By breaking it up like this they get single photon pulses.

Yep that is "shocking."

Spooky to say the least.

That places a huge amount of importance on the conscious observer.

It means that without a conscious observer, the universe will cease to exist.

I was wondering that too.

I found it interesting that if you shine a flashlight into the darkness you cannot see the beam of light from the side unless there is something for it to reflect off of.

I wonder if you were in the middle of nothingness, and you had a flashlight and shined it into the nothingness, if you could see any of the light if there was nothing for the light to reflect off of.

It does no such thing. Any EM detector creates the same collapse. Unless you think EM detectors are conscious . . .

Interactions cause the collapse of the wave, the notion of observation is hugely oversold and used so often to confuse the subject.

Spooky action at a distance . . . YES, a need for awareness . . . NO.

What do you think an EM detector is for? Who reads it?

For that matter, how would you describe an observer?

Most people think "observer" means a conscious human being.

Others might say animals count as observers.

I think an observer is anything that can detect and react to anything else is an observer. It does not have to have 'human consciousness."

Its just a loaded word not really meaningful in modern physics. Interaction is the only word I use when describing the collapse of a wave function, ie what causes the dual light experiment to not create an interference pattern.

I read Stephen Hawking's latest book a little while ago - The Grand Design. He talked about the double slit experiment in quite some detail. I enjoyed reading about it, and the rest of the book too, and as i was reading it i felt like i was understanding it. But once i finished i realised i still knew next to nothing about Quantum Physics. I never quite grasped anything i was reading. Maybe im just not very bright, but then also i think most people struggle to really comprehend QM.

http://plato.stanford.edu/entries/qm-bohm/

Honestly I think most physicists make it harder than it needs to be.

The first thing everyone needs to understand is the representational nature of mathematics, the second thing they need to realize is that these are JUST descriptions. Imagine trying to describe an elephant, but you can only see about 4x4 inches worth of the elephant. If you could see 12 square inches of the elephants trunk you might think it a snake. If you could see its ear you might be very confused. Much of our physics is looking at a small piece coming up with maths that help us do equations, but do not give us a picture of the whole that is meaningful.

Bohmian mechanics really helps to visualize whats going on under the hood.

Thanks for the link, i have bookmarked it to read when i have more time.

Yes, interaction is a more accurate description than "observer."

Observer has too many assumptions concerning consciousness.

It is quite possible that the Universe is its own observer...

and we but an atom in its dream. If we did not exist the Universe would still observe itself.

Yes that is what I think.

Makes no sense in the context of the experiment in question.


ie does not match reality

That would depend upon which side of reality you are looking from.

Your side of my eyes or mine.

In context an observer is that which interacts with the particle and collapses the wave function. Which makes no sense to say the universe is its own observer: nonsense.

Physics deals with reality, not fantasy. You cant just make stuff up.

It would be like claiming that the universe has a special frame of reference where there exists an absolute time, or a special perspective where light does not travel at light speed: nonsense, it breaks the theories that work.

These concepts are wrong they do not work, we know becuase we can test it and becuase for them to be right too much that works would have to be wrong.

Physics is in an interesting place, not a good one in my opinion. Popular science sells, but think for a moment do you ever see a popular science chemistry book claiming that you can live forever . . . Deepak chopra style? What about a popular science biology book?

Do you see people in forums talking about how chemistry backs up there own spiritual notions of reality? I have not.

There is no industry for chemists to make up stuff and sell it for the woo woo crowd. Physics however, now becuase no one can visualize an entangled particle, or becuase they do not understand pilot wave Bohmian mechanics its easy to get a skin deep understanding and just make up stuff from there, then you just use word association to fit it to any idea you could possibly want.

Well science does not work like that.

We have an influx fiction writers trying to explain physics, its a mess.