Dual-slit experiment

There is indeed something fishy about there.

observation is an interaction, the smaller the thing you are observing the more your observing interaction affects it. Thats why when you look at a galaxy it doesn't give a fuck, but when you look at a single electron it's all like, don't taze me bro.

When a baseball is thrown through the air, does it "know" what path it's going to take ahead of time? It's not really a question worth asking in imprecise terms. When trying to discern how the baseball "knows" what path to take, we make recourse to physical laws, whose validity is determined only by their success in describing phenomena. Quantum mechanics is a framework for describing the results we get when we run certain experiments. There can be no counterargument to "this claim", as it's a testable one which reality has again and again borne out with virtually perfect accuracy and precision.

An observer can effect what happens in the end of an experiment not "just by looking at it", but by making a measurement. When we read the speed a baseball is going off a spedometer, we're making a measurement, but the energy it takes to do so is small enough that it only influences the movement of the ball itself in a negligible way. When we measure the speed or position of a small enough particle, the effect of measurement is no longer negligible, so we have made a framework to describe it as best we can. This becomes scientific fact when we test it again and again and find it to be accurate every time. There's nothing more to it than that.

Take the simpler case of a Mach interfermoter (pic related).

Without observation:
The particle moving from source to detector is described by a state vector. The state vector phase is altered 90 degrees at every reflection. All paths to the right deflector involve two reflections: the resulting state vectors are equal and in phase and constructive interference occurs. One path to the top deflector involves three reflections, the other only one. The state vectors are equal and out of phase and destructive interference occurs.

Without "observation" all particles reach the right detector.

With a sensor along the bottom path which interacts with the particle:
The particle/sensor is described by a state vector. Once again, the phase is altered at every reflection, but the vector also reflects the current status of the sensor. Paths to the top detector have the same phase, but are different wave forms (because one path involves the sensor at state 0 and the other the sensor at state 1) and do not interfere constructively. Paths to the right detector have different phase but also different wave forms (because again, the wave is a function of the sensor, which is binary variable) and do not interfere destructively.

With "observation" the particles reach each detector with 50% probability.

If this makes sense, you generalize to double slit by seeing that particle phase also evolves as a function of time and therefore of path length. All paths are of equal length in the interferometer but not in double slit. Phase differences lead to interference if there is no sensor but do not if there is a sensor.

pic, sorry

Ty both for lengthy answers.

>When we read the speed a baseball is going off a spedometer, we're making a measurement, but the energy it takes to do so is small enough that it only influences the movement of the ball itself in a negligible way.
This confuses me and I feel its the key to your explanations.

How can measuring the speed of a ball with, lets say, a radar device change its velocity?

I am no expert by any means and not the original answerer, but I assume he means that a radar device could influence the particle and even the ball, but it would not be noticeable on an object as large as a ball.

>How can measuring the speed of a ball with, lets say, a radar device change its velocity?
Radar uses electromagnetic waves which, even classically, carry momentum. So if you shoot radio waves at a baseball, it changes the ball's momentum ever so slightly. In this case the ball's momentum is just so much higher that for all practical intents and purposes, the change is negligible.

"Observation" in this context merely means the wall that the photons hit and has nothing to do with humans.

When flying through the air molecules empty space the light is a wavefunction and not a particle. Nothing more than a probability.
Once the light "interacts" ie crashes into the atoms of the wall, the wavefunction "decays" into a particle that has apparently hit the wall at a certain point.

What makes you think that? How do you define conciousness? If you define it as "what is necessary to collapse a wavefunction" you are right and a big part of the universe is concious.

However that is not the dictionary definition of the word concious.

Thank you for explaining

>Crazy hypothesis
why is it crazy?

Its probabilistic, not deterministic, so when you "observe" you're not determining the outcome. It kind of works like a dice. You know the dice can assume the numbers on its faces. When you throw the dice you will get only one of those numbers. If you look at the dice again after you threw it, you'll see that number again.

If you do this many times and take note of the results every time, you'll be able to find out the probability distribution of the outcomes of your dice. That would be our wave function. Your measurement is analogous to throwing the dice, and when you "look again" at the result would be the wave function "collapse"

I appreciate your reply user

>I am not retarded
Evidence needed

Let me try to explain in the standard Copenhagen interpretation. I'm going to be very, very loose an inaccurate, in order to impact some understanding.

Forget everything you know about physics, reality, etc. When a single electron is fired at the two slits, goes through the slits, and hits the detector screen beyond that, this is what happens. There is a description of the electron called a "wave", described by Schrodinger's wave equation. That wave is analogous to water wave. That wave travels outwards, encounters the slits, passes through the slits, and beyond the slits the wave interferes with itself, with peaks adding together, peaks and troughs canceling each other out. This creates a pattern in the wave at the detector screen of "high, low, high, low, high, low" etc. A "high" spot means that the electron is likely to "end up" there, and a "low" spot means the electron is not likely to end up there.

When we fire electrons one at a time, so that only one electron is in the area at a time, and then we measure the location of each hit, for thousands of trials, and overlay the results, we see the "high, low, high, low" pattern in the observed hit location data on the detector screen. This is not a phenomena of electrons interfering with other electrons. It's a phenomenon of single electrons interfering with themself.

to be continued.

In the real world, there is no such thing as "observation" in a strict sense. In order to observe something, there must be some interaction. For example, when you see a car, light is bouncing off the car and into your eyes. That light is an interaction.

So, you may still not be sold on the idea of the electron wave travelling through both holes, or the idea that electrons are actually quantum waves at all. So, let's put a detector at one of the two slits. What does this detector look like? Again, in very crude terms, it might be something like a constant stream of photons being aimed at one slit, and if some of the photons bounce off the electron passing through the slit, then we notice that some of the photons were disturbed, and from that we can deduce that the electron passed through that one slit.

When we do this, the interference pattern of "high, low, high, low" disappears. The pattern on the detector screen is simply flat.

In the language of quantum mechanics, very loosely, according to the Copenhagen interpretation, this is what happened. Without the detector, the electron wave travels through both slits, interferes with itself, gets an interference pattern in the wave, which causes the observed interference pattern on the detector screen over many, many trials.

When you add the detector, the interaction of the electron and the detector causes the wave function to collapse. After detection, the electron continues to travel along its merry way, but this new wave starts at one of the two slits, and therefore does not go through both slits, and therefore no interference pattern develops. The detector causes wave function collapse, and changes the scenario so that there is no electron wave that travels through both slits to interfere with itself on the other side.

Is this exactly right? No. I've taken some liberties, and I've chosen to use the language of the Copenhagen interpretation as opposed to other options.