I need a brainy person who knows quantum machanics

OK, so I've just seen a [rather low brow] doc on BBC2 about quantum mechanics, and the other day I saw this animation courtesy of the oh-so-ace Icasea blog:

So I pretty much understand what's being explained there (I never got it back in school a decade ago !). However, there's one thing that seems to contradict what's being said about the two slit (stop it !) experiment - So the particles can exist at two (or more !) places at once thus causing the interference pattern, however if observed/measured will go back to behaving as matter and so just go through one slit or another and thus no interference pattern is created. That's all good so far yeah ? (erm, I think !)

So the act of observation causes the particles to exist as just one state (hence in the schrodinger cat experiment the cat is definitely alive or dead once you open the box). What my little brain however doesn't quite understand is if this is the case, how come an interference pattern is detected in the first place if the act of observation would cause the particles to not behave in a quantum like manner (I'm not sure if I worded the question quite clearly !)

Head asplodes

Play nice, I was just curious !

I'm totally not your guy.

Then get the fuck out of the thread!

  On 11/17/2009 at 11:35 PM, Obel said:

Then get the fuck out of the thread!

Hahaha!

Acknowledgement of lack of contributions all round lol.

http://www.youtube.com/watch?v=EX1ABl1mv1M

Lol

you are not directly observing the particles you are observing a phenomenon that comes about because of the wave like properties of light. if you some how tried to stop the light in mid air, and observe each photon individually perhaps it would become clear that it was not a wave. I don't know maybe there are related experiments, I'll try to look some up.

also apparently when you only fire one photon at a time, you still get an interference pattern. The photon splits and interferes with itself. Thats the most interesting version of the experiment if you ask me. They have also constructed versions of that where they detect which slit a photon passes through yet it doesn't change the results.

I'll talk to my physics teacher about it tomorrow.

All I can say for now is that light is a wave.

  On 11/18/2009 at 12:47 AM, Xyrofen said:

I'll talk to my physics teacher about it tomorrow.

 

All I can say for now is that light is a wave.

light acts as a particle and a wave.

  On 11/18/2009 at 12:18 AM, Bubba69 said:

also apparently when you only fire one photon at a time, you still get an interference pattern. The photon splits and interferes with itself. Thats the most interesting version of the experiment if you ask me.

Yeah it goes into that on the video I posted at the top of the page

  On 11/18/2009 at 12:08 AM, Bubba69 said:

you are not directly observing the particles you are observing a phenomenon that comes about because of the wave like properties of light.

OK, I think this is definitely quite what I was missing. My house-mate came up with an explanation that was pretty similar to what you said. So the interference pattern is an observation of the effect of the particles, rather than an observation of the particles themselves. Is that it ?

well the experiment isn't being observed as the photons are shot towards the slits; they just expose and view the photo-sensitive surface that they hit after the photons have been shot. is this what you were asking? if not, i assure you i am not a moron, despite my misguided response. good day.

  On 11/18/2009 at 12:49 AM, Hoodie said:

  On 11/18/2009 at 12:47 AM, Xyrofen said:

I'll talk to my physics teacher about it tomorrow.

 

All I can say for now is that light is a wave.

light acts as a particle and a wave.

I like when it's a wave more.

  On 11/18/2009 at 12:50 AM, KY said:

well the experiment isn't being observed as the photons are shot towards the slits; they just expose and view the photo-sensitive surface that they hit after the photons have been shot. is this what you were asking? if not, i assure you i am not a moron, despite my misguided response. good day.

KY hit it. The act of watching it "in-vivo" causes the matter to act as a particle not as a wave. QM is the coolest study around.

  On 11/18/2009 at 12:18 AM, Bubba69 said:

also apparently when you only fire one photon at a time, you still get an interference pattern. The photon splits and interferes with itself. Thats the most interesting version of the experiment if you ask me. They have also constructed versions of that where they detect which slit a photon passes through yet it doesn't change the results.

I'm pretty sure this is due to quantum superposition which, from my understanding, states that a particle is in all possible states until it is observed. Basically it is a particle and wave until we observe and define it as such. Which relates to Schrodingers cat as well. While the cat is in the box it is both dead and alive since we don't actually know.

quanta can behave like waves and like particles depending on the experiment, it's foolish to say it "is" either of them, since it is what it is, and both waves and particles are just models used to describe them in different scenarios. reality is always way more fucked up than how you perceive it.

ps the doctor quantum video is slightly misleading because it just uses a giant fucking eye when talking about "observing" when at that scale, to observe something you actually have to get in there and interact with it which would inadvertantly alter its course anyway

  On 11/18/2009 at 4:36 AM, Funktion said:

ps the doctor quantum video is slightly misleading because it just uses a giant fucking eye when talking about "observing" when at that scale, to observe something you actually have to get in there and interact with it which would inadvertantly alter its course anyway

Yeah, I think this was the bit that confused me. Obviously I didn't think there was some huge uber eye using giant lasers an' that (though that'd be cool) but it was the way that they said just that the act of observing would change the result. What I didn't realise that in the quantum world that observing was more 'obtrusive' than just sticking some camera at something !

  On 11/18/2009 at 2:37 PM, xxx said:

Fuck physics. If this is the right experiment I'm thinking of, it disproves the theory that an "aether" was a medium through which light traveled. They used some mirrors, a coupla slits (could've used some of the stinky kind ooohh), a "LASER" and thus proved the wave-particle duality of light. I basically dropped out after this so don't listen to me.

Michelson and Morley expected to observe an interference pattern, so photons were considered as waves during the experiment.

Young's experiment didn't prove the duality because quantum mechanics has been created after his death. They (the sciencitsts of that time) just discarded Newton's theory in favour of Huygens'.

I quite enjoyed this as it patronised the fuck out of me, exactly how I need to be treated on the subject. Couldnt find the BBC version sorry, which if you find is much better, so you dont have to deal with the American voice over. I have a lot of annoying maths Oxbridge friends, they talk about the subject in a way that I can only be comfortable when im talking about putting condiments on toast.

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

Its worth bearing with.

quantum mechanics is fascinating but really fucked up at the same time.

(that's my contribution)

  On 11/18/2009 at 3:55 PM, ezkerraldean said:

quantum mechanics is fascinating but really fucked up at the same time.

(that's my contribution)

http://en.wikipedia.org/wiki/Ezkerraldean's_principle

  On 11/18/2009 at 3:55 PM, ezkerraldean said:

quantum mechanics is fascinating but really fucked up at the same time.

(that's my contribution)

yea, i agree. it will be quantum mechanics that will allow us to travel across the universe, if we survive long enough to figure it out. we just need to fold space and time,, which would require harnessing Planck energy (the power of a star).. shouldn't be that hard.

even Einstein thought there are alternate universes, simply because of the basic quantum theories of matter being able to exist in multiple places at once. since matter behaves totally different on a quantum scale it shows that something else is going on which we don't know much about.

there's always something going on that we don't know much about