Dabblings in Quantum Theory

Great Debates
1

According to a thought problem called Schrodinger’s Cat (pardon my spelling mistakes), a cat is in a box, and through some mechanism, has a 50% chance of either being killed or surviving upon the opening of the box (if someone would care to clarify, it would be very helpful). Therefore, according to quantum theory, the cat is both alive and dead before the box is open.

I’ve also read that for every decision that can be made there is an entirely new universe/dimension that is created for every possible outcome. This would obviously lead to an infinite number of universes that are completely unaware of one-another. The question is whether commuting between these universes would be possible.

So here’s what I can gather about all of this
(PREPARE FOR OVERSIMPLIFIED EXAMPLE)

If Bob has a choice of breaking a window, two possible universes exist: One with a broken window, the other without a broken window. In either situation, Bob remains constant.*

Now, if Schrodinger's Cat is applied to this situation, it can be inferred that the window is both broken and unbroken before the moment of impact.  Ergo, is  it not appropriate to assume that anything that can possibly happen is already happening?

If the above is true, then does this mean that there is fate? It would seem that way because any possible outcome is already being played out. SO how does our perception of ''time" play into all of this?

*or perhaps not. Since Bob can be said to exist in an infinite number of universes (some the result of Bob’s decisions, or decisions made from previously existing universes), it can be reasoned that Bob is also nonexistant in an infinite number of universes. Or does Bob simply implicitly exist in these latter universes?

2

I think you’re misunderstanding both the Schrodingers Cat thought experiment, and the many worlds interpretation of quantum mechanics.

Schrodingers Cat is meant to illustrate what happens at a quantum level - ie at the level of individual electrons and atoms. According to quantum theory, an electron can be in two places at once - but only when you don’t look at it. In fact it doesn’t really exist as a singular object at all - it is more like a cloud of probability, which only resolves into an electron when it is observed. However, this behavior only happens at the quantum level - macroscopic objects like a cat always behave classically, they are always in one particular place or state. If you did actually carry out the Schrodingers Cat experiment, the cat would always be alive or dead, it would never be both.

Suppose you have an electron which is in two places at once. You observe that electron, forcing it to be in one place or the other. The many worlds interpretation says that two universes are created at that point, in one you see the electron in one place, in the other universe you see the electron in the other place. However, these universes don’t exist until you make the observation. So it is not true that anything that can possibly happen is already happening. It just means that anything that can possibly happen will happen, but in different universes.

3

It’s the Shroedinger Cat Paradox, and you got it pretty much right.

The difference in the window experiment is that the window is in a state of being measured (seen) and so doesn’t exist in a quantum “flux”. The cat is inside a box and is not subject to measurement until the box is open. Once it is openned, the cat is definitley either dead or alive.

Fate has nothing to do with it, even as you have explained it. In the multiple universe version of quantum mechanics, each future state is possible, but there is no way of knowing which state you will actually find yourself in. As for time, some scientist would say that time does not exist. That our experincen of time is just the transition from one quantum state to the next.

BTW, this might be better discussed in the GQ forum, not in GD.

4

I’d like to add that even though there would be an infinite number of universes which includes Bob not breaking the glass or “Bobless” universes, it does not imply that your fate is sealed by any means. These universes would not be “stable unverses”

One thing the Schrodinger’s Cat Theory is making a point of is that the state of the cat can only be known by observing the cat. Which in this case is merely as simple as opening the box adn peering in.

On the matter of electrons, as Planet of the Shapes pointed out, they exist in a “cloud of probabiltiy” and it is said that electrons exist as both a particle AND a wave. How can this be? Well, it depends on the observer. In observing the location, the electron is a “particle.” But you say you’d also like to know the velocity? Well you can. BUT not at the same time as observing the location. When you measure the velocity,you are now measuring the electron as a “wave” Therefore, until you observe this electron, it exists as “both” a particle and a wave until the observer collapses the state vector and voila! It will be one or the other.
Schrodinger’s Cat is basically the analogy to describe this bizarre paradox.
See, it is impossible for us to observe things in the universe without affecting the outcome because we are participants as well as observers.

I have to warn you, I only study quantum theory as a “hobby” and am a laymen to the Nth degree. So for those higher up on the quantum food chain, corrections are not only welcome but encouraged.

5

I have always had a penchant for speculating on time travel and alternate universes, versus our perception of reality - that is until I “break my noodle”.

The argument against time travel is that physics alone wouldn’t not allow you to go back and undo something that physics allowed to happen: you cannot go back in time and kill your father before you were conceived. I happen to not agree with that. I believe that you would be able to do something that stupid. Physics doesn’t discriminate. Physics also theorizes that the combined amount of energy and matter in the universe is a constant, and must remain so.

This seems to relate directly to the multiple universe theory.

So what would happen in the above scenario? Here’s my take. You are born at moment X. When you are 18 years old (X + 18) you find a time machine and go back to X - 1 and kill your father. What would happen to you? I personally think that you already exist, so you cannot suddenly unexist - in at least one universe.

Since your father was killed before you were conceived, there is a universe where you will never exist. There is also a universe where you father was killed before you were conceived, but you still exist anyway. And there is another universe where you never got in the time machine to begin with, so nothing of note happened.

This lends a lot to fate. It pretty much says that fate exists, but in a more universal way. That is, several different fates exist, one for each possible outcome. So fate becomes inevitable, since every possible option will happen.

There are other quandries here. In the movie “The Time Machine”, the most recent version with Guy Pierce, the main character is a scientist/inventor. He is slightly late in meeting his fiance for an iceskating date. They then go off and get robbed, and she gets killed. Determined to reverse this, the main character builds the time machine, and three years later (in linear time) he goes back to five minutes before he met up with his fiance at the iceskating rink. He meets her before the original main character does, and he wisks her away. She then gets tramples to death by a horse and carriage. The main character is resigned to fate, saying, “I can come back a thousand times, and witness her die a thousand different ways.” That’s when he gives up on the present day and gets in his time machine and zooms off into the future past all that would be recognizable to him.

I want to dissect this situation. Here are the universes that would exist from this episode:

  1. The fiance dies after getting robbed. The main character lives out his life.
  2. The fiance is rescued by the time travelling main character only to die moments later by the horse and carriage. The main character lives out his life.
  3. The original main character cannot find his fiance at the iceskating rink, buries her body when he finds out she has been killed by a horse and carriage, and lives out his life.

Plus, any multitude of individual deviations from these events. So at the same time, the fiance is alive, dead, rescued, and dead again. The main character is simultaneously alive, has a double of himself running around, and then doesn’t even exist in this universe.

This begs the question: if he really did come back a thousand times to witness his fiance die a thousand different ways, wouldn’t there be a thousand clones of him, each one a few minutes older than the previous one, all over the place? The answer is obviously, “yes.” Maybe that is how humans will achieve immortality?

6

"The argument against time travel is that physics alone wouldn’t not allow you to go back and undo something that physics allowed to happen: " :smack:

I obiously meant, “The argument against time travel is that physics alone would not allow you…”

7

The problem is that somethng like Shordingers Cat is too large to count as a quatum measurment (as ill-defined as that is) and the wave function is collapsed before you can make the measuremnt6 anway.

8

Correct me if I’m wrong
I thought one either believed in
a) Collapse of the wavefunction
or
b) Many-worlds

Aren’t these supposed to be two different ways to interpret what’s going on?

In (a), you believe that Shroedingers Cat “collapses” to a live or dead state upon opening the box.
In (b), you believe that the Cat is alive in one universe and dead in another.

9

Chaos:

It’s really just two slightly different ways of looking at the same thing. While there might by an infinite number of universes (and one with a dead cat, another with a live cat) you can only observe one at any given time. You could just as easily say that “collapsing the wave function” was the same as “observing only one of the infinity of universes that exist”.

You have to understand that our brains are simply not designed to understand quantum phenomena. The whole wave/particle duality is just a construct that allows us to impose a system that we can understand (waves and particles) on a system that we can only understand thru mathematics. Truth is, we don’t know (and can’t know) if elementary particles like electrons are waves or particles-- they are most likely neither. They are something for which we do not have a physical model in the macroscopic world that in which our brains opperate. We can only say that in some instances they behave more like particles and in others they behave more like waves.

10

People have already explained Shroedingers Cat far better than I could anyway, but if you’re interested in Parallel universes, you might like this article…

11

Tir
I had read that article following a link posted in another thread (maybe by you?). IT BLEW MY MIND ! Loved it.

Mace
Ok. I understand quantum physics is COMPLETELY counter-intuitive. I still think one can come to understand it, at least as an artificial mathematical construct. (Not me of course, I don’t even understand diferential equations)
I understand that one could interpret quantum phenomena as implying a “wavewform collapse” OR “many-worlds”, and that one could never prove that either was the “correct” interpretation.
Or could you? Are there any precise predictions that could be tested by either theory?

12

The way I think of wave particle duality, is that a particle describes a wave with a very high frequency and what is classically though as a wave is a wave with a very low frequency. It’s very hard to show the wave-like nature of a particle with a short De Broglie wavelength and it’s very hard to demonstrate the particle-like nature of an em wave with a long wave length (rember wavelength = speed/frequency). Of course in the middle of the spectrum you have particles/waves that can clearly be demonstrated to have both particle and wave like nature even exhibting both at the same time.

13

As I understand it, there are physical effects which physicists know how to predict but think of in different ways. (As an analogy, if gravity was newtonion, you could imagine it as a central force or a distortion of space)

We hope that eventually one way will differ in how it predicts the universe, and then it will be theoretically possible to test them and see which works.

At the moment we have two ways which work, but neither of which is very satisfactory.

Is that fair?