Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5486
57,583 ₧

OK, well, the scary thing is that the effect disappears if the detectors are switched on. Even worse, we can fire an electron with the detector switched off, turn on the detector before it gets to the detector and it still disappears!

Maybe it would be best if you ask questions of me.

Mate de Vita
Kelli

2008 Oct 4 • 2453
159 ₧

OK, how about this for a start. Why does this happen?

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5486
57,583 ₧

It's to do with how the things are detected. The only way to detect a particle is to cause it to interact with something else. So, if an electron is going through a slit, you can fire a photon at it to see if it's there. This act of measurement causes the "collapse" of the wavefunction that describes the electron. It's no longer a wave, it's a localised particle.

melloyellow582
The Original Portmanteau


2005 Mar 22 • 12862
666 ₧

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5486
57,583 ₧

Essentially.

SRAW
Rocket Man

2007 Nov 6 • 2525
601 ₧

So does the electron, when fired one at time, exist in all possible states literally, and bumps into itself and creates a wave pattern?
And also when talking about waves and particles, does that mean that mean that the electron vibrates like a wave, or it somehow exists as both?
And is there any proof that they really do exist in all possible states, or do they exist only in one, but that we just do not know which?

SRAW
Rocket Man

2007 Nov 6 • 2525
601 ₧

and also when these scientists talk about models of electrons and atoms and whatever etc... does that mean that we may not know the true nature of them, but that these models simply describe how they behave?

phoenix_r

2009 May 13 • 905
17 ₧

There is no real definitive proof that they exist in all states, hence it being a theory; the slit experiment attempts to add some proof.

Basically the whole problem lies in what is known as the Observer Effect - the act of observation inherently changes that which is observed. One of the best ways to demonstrate this idea is Schrödinger's poor old cat. Schrödinger's cat is in a box, a room with solid walls and no windows - you cannot see or hear the cat from outside of the box. When you press a button outside the box, there is a 50% chance that the box will be flooded with poison which will kill the cat. You don't know the result of your button press until you open the box to check. What this means is that for all practical purposes, from when you press the button until you open the box the cat is simultaneously both alive and dead, and it is only your observation, the act of opening the box to check on the cat, that forces these probabilities to collapse into one of the potential outcomes.

SRAW
Rocket Man

2007 Nov 6 • 2525
601 ₧

But that still doesn't explain why there was the interference pattern, right? Because the particle interacted with itself which means that it REALLY existed simultaneously in multiple states, whereas the cat is either dead or alive. And also when the particle is fired, is it as a particle or as a wave? And yes I'm a newbie at this stuff, so don't hate for my dumb questions

and as for entanglement, from what I've read, it seems that there are 2 theories as for what happens - that either the entangled particles always have correlation properties, or that there's a higher dimension that somehow links them. So does measuring one automatically cause the other one to collapse? Or do we not know if it does, since measuring obviously would do that. And is there anyway to change properties of a particle without interfering when it is in simultaneous states? (edit: disregard the last one, cause it makes no sense, and also I imagine that measuring the particles would destroy the entanglement?) And what do you think really happens? And also if I seem to have no idea what I'm talking about, that would be the case

and also
http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser is a mindfuck

phoenix_r

2009 May 13 • 905
17 ₧

AFAIK it does not bump into itself per se, it is never more than one particle at any given moment of observation. While unobserved it is considered to behave like a wave, which is when the interference occurs.

SRAW
Rocket Man

2007 Nov 6 • 2525
601 ₧

Well ok, what gets me is how it acts both as a wave and then turns into a particle when interacted wit

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5486
57,583 ₧

That's all models are. Models. You can discuss what might "really" be happening, but when it comes down to it you have a model and an experiment. If the model predicts the outcome of the experiment, what else can you do?

That said, various folks have suggested ideas for what might be "actually happening" (a phrase I am not entirely comfortable with). You might be interested in the Many Worlds interpretation, the Copenhagen interpretation, Feynman's sum-over-histories interpretation... There are lots. Quantum mechanics is only concerned with the fact that things like subatomic particles electrons and protons etc. are not necessarily waves, nor are they necessarily particles. They can appear to have some of the properties of both, depending on how you observe them, but ultimately they are neither.

They key point in all this is that the double-slit experiment is weird if you think an electron (or indeed a photon) is a particle. If you assume it's a wave, whatever that might mean, there's no problem! Of course if you then go do a different experiment involving gold foil and a monochromatic source of light (the Photoelectric Effect) then you have to assume that photons are actually particles. As I said, it's weird if you assume they are one or the other. Thinking of it as some third thing with properties of both is better.


AAAAAAARRGHHH that is a horrid sentence, pls no

aaronjer
*****'n Admin


2005 Mar 21 • 5042
1,227 ₧

My favorite way to look at quantum mechanics is as thus:

"Quantum mechanics contains a set of scientific observations that so often defy logical or rational explanation that they are, at least for now, indistinguishable from magic."

Basically, trying to make sense of it is pointless until we make cooler science machines. It would be like cavemen trying to figure out atomic structure, no matter how hard they try they lack the tools.

One of my favorite unexplained universal properties? The base temperature of the universe is not zero. This is without background radiation or anything like that, with absolutely nothing we can detect present, it is still not zero. Which probably just means there's something there and we just can't detect it... whatever it is.

There's some debate about what the actual base temperature is... but the most enjoyable thing about it is that getting things below that temperature breaks physics completely, and the most demented shit starts happening. Like the apparent effect of gravity and solidity of objects just kinda turning off. Shit starts passing through shit and floating around. It's pretty fun. Electrical resistance also seems to not exist at those temperatures, so it's incredibly useful and somewhat explainable, and not just silly (but fun) like quantum stuff usually is.

aaronjer
*****'n Admin


2005 Mar 21 • 5042
1,227 ₧

No way, man. Setting out to prove theories is a great idea. Just observing and changing your theory accordingly is for nerds.

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5486
57,583 ₧

Perhaps I am misinterpreting, but what I meant is that experiment is the ultimate arbiter. You experiment, you make a theory that explains the experiment, maybe it makes a prediction you can test. Great. Anything else is masturbation. Saying that the experiment was an attempt at proof... well, it is what happens. Explaining it is the tricky bit.

At the moment, we are sort of in the "prediction" stage. Though it is expected, or rather hoped, that this will change soon. Say the next 20 years.

Also I have a bit of a problem with the universe, it has chosen some really shitty constraints. Like a speed limit that is not on the same scale as the distance scales of the universe, what the hell physics. Same with Planck's constant: 0 would be great, or a big number would be cool too. Turns out it's just really small. BO-RING.

phoenix_r

2009 May 13 • 905
17 ₧

Expound please!

aaronjer
*****'n Admin


2005 Mar 21 • 5042
1,227 ₧

Sarcasm

/Sarcasm

Also, I feel like there might be a connection between the irritatingly low maximum speed of light and the non-zero base temperature of the universe. I dream of the possibility that there is some undetected medium (the cause of slight temperature increase) through which light travels as a wave (when it feels like it) and that it could be manipulated to alter the speed of light.

SRAW
Rocket Man

2007 Nov 6 • 2525
601 ₧

errm isn't the background radiation(what I assume you're talking about) is just supposed to be what was radiation that was left of the big bang?

SRAW
Rocket Man

2007 Nov 6 • 2525
601 ₧

and I still don't get how something can travel as a wave and as a particle, unless it's like magic @_@

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5486
57,583 ₧

Not getting it is fine. The concept of a minimum temperature is a quantum effect, somewhat to do with the fact that a particle with zero temperature would have zero energy which would imply several things, all of which are infinite. We don't like infinite, as a general rule.

The CMBR has a temperature, it's about 3K. I think. That is not what Aaronjer is talking about. (Also, re: /sarcasm: I misinterpreted )

Fun fact! The hottest and coldest places in our solar system exist on none other than our planet! That's cool. Also, the average density of the universe is approximately one hydrogen atom per cubic meter, which is to say some 10^24 less dense than air at STP. You can safely conclude, therefore, that anybody you meet is a statistical anomaly.

Aaronjer, you might want to look at the Michelson-Morely experiment, it is very interesting. As regards a variable speed of light... there is a theory which suggests that actually mid sentence I have decided I am thinking of the wrong thing. Never mind!

zjamz: the experiment came first, kind of. A similar one did anyway. This necessitated new theory, not the other way around. The experimental result is all the proof you need that it happens, because, well, it does. This isn't the same as saying that the experiment proves the theory, because it only does not disprove it; however given the large body of experimental evidence so far acquired for QM it is held as accurate and correct by the vast majority of scientists. It is as accurate and precise as a measurement of the distance from New Yoik to London differing from the "true" value by the width of a human hair.


This final edit is somewhat my own opinion, but whatever.
It doesn't really matter, in the end, what is "really happening" in these experiments. All we can do is experiment -> measurement -> theory -> test -> refine, endlessly. There is a theory in which you can treat sound moving through solids as a particle, called a phonon. Now, we know that it ain't true. It's atoms vibrating. But it doesn't mean that this phonon cannot have a mass, a velocity, energy, and so on. And using this phonon theory you can predict very well the movement of sound through a solid. The model works - that is all we can ask of it. Anyways, as I said that's the way I see things. I've actually pretty much stopped doing science now, I graduated last summer and have moved onto a postgrad in high performance computing instead, so my thoughts are not necessarily the most coherent, accurate or indeed correct.

/walloftext

aaronjer
*****'n Admin


2005 Mar 21 • 5042
1,227 ₧

Oh, I totally agree with you. You experiment, and as a result disprove things unintentionally, and then believe simplest answer that remains until you end up unintentionally disproving it as well. Theories don't need to be proven, they need to be practical. It doesn't matter if it's 'actually wrong' if you can build a machine using it that does what you want it to do.

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5486
57,583 ₧

Exactly! I think. I wouldn't say it was wrong, so much as it is... a model, that, although not true, is accurate. Y'know what I am going to bed, because I think I have said the same thing several times now. I am, in fact, saying the same thing as 18 months ago. I've read through the thread. I'm an insufferable prick :(

SuperJer
Websiteman

2005 Mar 21 • 6663

aaronjer
*****'n Admin


2005 Mar 21 • 5042
1,227 ₧

Shut up, fag.

Down Rodeo
Cap'n Moth of the Firehouse


2007 Oct 19 • 5486
57,583 ₧

Confusing internet historians of the future.