# The crazy world of quantum mechanics.

#### I have no education!

Joined Sep 19, 2012
47
I'm not going to be silly enough to as ask why the double slit experiment is the way it is, i am however going to ask for some clarification on it.

My understanding

So, i understand the concept of the wave particle duality. Now if we try to measure which slit the photon goes through photon behaves likes a particle and if we do not measure it the double slit experiment shows that light behaves like a wave. This is quite mind boggling to me, and most others i would imagine hahaha!!

Now my question is this, if we are pointing the photon gun at a particular slit then should the photon not travel through this slit and so there is no need to measure which slit it went through?

Are things ultimately in all states at the one time before we measure them to find out which state they are in?

Also what is even more confusing to me is that this behavior is not present in the non subatomic world. I,e. schrodinger's cat must be alive or dead when it is in the box, as it simply cannot be alive and dead at the same time in the non atomic world

Any chat or insight would be very helpful as im completely out of my depth but generally very interested in such things!!

thanks

#### ErnieM

Joined Apr 24, 2011
8,196
Now my question is this, if we are pointing the photon gun at a particular slit then should the photon not travel through this slit and so there is no need to measure which slit it went through?
If you aim a photon at one slit then you have determined which slit it is going thru and thus it acts as a particle and no interference pattern emerges.

Are things ultimately in all states at the one time before we measure them to find out which state they are in?
Yes they are. Get used to it.

Also what is even more confusing to me is that this behavior is not present in the non subatomic world. I,e. schrodinger's cat must be alive or dead when it is in the box, as it simply cannot be alive and dead at the same time in the non atomic world
The cat is indeed both dead and alive at the same time. Note this is not to say it is sick.

#### I have no education!

Joined Sep 19, 2012
47
The way I understood it the cat analogy was that is was to describe the sub atomic world? Under your reasoning in a non sub atomic world is that people in coffins are both dead and alive?

#### I have no education!

Joined Sep 19, 2012
47
Also, by virtue of looking at the direction if the photon gun then you know where the photon is going through when you fire it? That's to say these things fire in straight lines? But the measurement part is when you put detectors at the slits to confirm it?

So it's really weird to say I know the photon should go through that slit and when I measure it it confirms it. But when I don't measure it the photon can go either slit, even though it's pointed at one of one them, or no slits at all?

Mind boggling!!

Joined Apr 16, 2011
540
The cat is indeed both dead and alive at the same time. Note this is not to say it is sick.
Check out the wikipedia entry for "Shrodinger's cat".

I think Shrodinger was using the thought experiment to illustrate a problem with quantum mechanics theory at the time. My reading of this and other articles is that Shrodinger thought the cat to be either alive OR dead at all times, not both.

Schrodinger's cat seems to have become a widely misunderstood thought experiment as far as I can tell. .... I wonder why that happened?

I seem to remember that Schrodinger deliberately chose an animal for his thought experiment, as it adds a new dimension to the conundrum. Presumably the Cat remains self aware all of the time that it is alive?

I found the Feynman lectures fascinating. I think he starts off by saying that we have no UNDERSTANDING of Quantum ElectroDynamics (I am guessing that QED is the later refinement of Quantum Mechanics) but we can observe what happens and make useful calculations and predictions using maths developed from observations of real life experiments.

If Feynman admits to not understanding the basics behind Physics, what hope do we have of understanding?

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#### Wendy

Joined Mar 24, 2008
22,647
The cat is also an observer, with interesting concequences.

#### socratus

Joined Mar 26, 2012
267
The cat is also an observer, with interesting concequences.

Of course cat is an observer.
But question is if this observer alive or dead.
And how can “ The law of conservation and transformation
energy/mass” be keeping in this situation?
=.

#### I have no education!

Joined Sep 19, 2012
47
So can I clarify something?

In the NON-SUB atomic world if i knew the status of the cat, that is it is alive or dead, before i put it in the box then it will always be in that state.

Is the cat analogy just an analogy for the SUB atomic world?

Thanks

Joined Apr 16, 2011
540
Is the cat analogy just an analogy for the SUB atomic world?
Schrodinger did not intend the thought experiment to be an analogy for anything. He was pointing out possible flaws in Quantum Mechanics theory.

I believe he was suggesting that it is ridiculous to suggest that the cat is both dead and alive at the same time, but that Quantum Mechanics theory might predict this ridiculous idea.

.... so while Quantum Mechanics is useful, I thing Schrodiner was suggesting that the theory may be incomplete or flawed. i.e. there is more to learn.

Please read the wikipedia entry. It explains what the "Cat" thought experiment was about much better than I can.

#### I have no education!

Joined Sep 19, 2012
47
There are no quantum effects in the non sub atomic world are there?

Joined Apr 16, 2011
540
There are no quantum effects in the non sub atomic world are there?
I think that this hits on the current dilemma in our understanding.

We have a theory for how the big stuff works, and we have a theory for how the really small stuff works. I think the problem is that the two theories do not tie up, and this is what drives physicists to keep searching for a better explanation that works at all scales.

When I say "we" I mean much cleverer people than me. I don't claim to understand any of this stuff, but I do find it all fascinating.

#### socratus

Joined Mar 26, 2012
267
There are no quantum effects in the non sub atomic world are there?
Can we see situation in this way ?

If cat is alive it has energy E=h*f.
If cat is dead it has energy E=Mc^2
What energy can the cat have during quantum diagnosis ?
=.

#### I have no education!

Joined Sep 19, 2012
47
Why would the cat have two equations governing the energy it has?

Why does it not have the same energy alive or dead?

thanks

#### socratus

Joined Mar 26, 2012
267
I think that this hits on the current dilemma in our understanding.

We have a theory for how the big stuff works, and we have a theory for how the really small stuff works. I think the problem is that the two theories do not tie up, and this is what drives physicists to keep searching for a better explanation that works at all scales.

When I say "we" I mean much cleverer people than me. I don't claim to understand any of this stuff, but I do find it all fascinating.
the big stuff works - . . . in the Classical physics.
small stuff works - . . . in the Quantum physics.
They are two different stuffs of one science - Physics.
The problem is that the two theories do not tie up.
How is it possible to connect them together clearly and logical ?
=.

#### socratus

Joined Mar 26, 2012
267
Why would the cat have two equations governing the energy it has?

Why does it not have the same energy alive or dead?

thanks
Can cat as an observer be alive or dead simultaneously ?

#### I have no education!

Joined Sep 19, 2012
47
No, what i meant was why does the energy i have in my mass change whether im alive or dead. Does ones mass change when they die? If so why not just use

E = MC^2 for both alive and dead people

#### socratus

Joined Mar 26, 2012
267
No, what i meant was why does the energy i have in my mass change whether im alive or dead. Does ones mass change when they die? If so why not just use

E = MC^2 for both alive and dead people
No, what i meant was
1.
why does the energy i have in my mass change whether im alive or dead.

2
Does ones mass change when they die?
=.

No,
if your mass changed - then your energy also must change too.

3
If so why not just use E = MC^2 for both alive and dead people
=.

Because in Quantum theory we use mass/energy and
not energy and mass as in Classic physics.
==.

why does the energy i have in my mass change whether im alive or dead. ?

#
There are more things in heaven
and earth, Horatio, than are
/ William Shakespeare,
Hamlet Prince of Denmark /
=.

#### ErnieM

Joined Apr 24, 2011
8,196
The cat is also an observer, with interesting concequences.
I fail to see how a dead cat may still classified as an observer.

#### Wendy

Joined Mar 24, 2008
22,647
A cat choking to death does tend to note it's own death, you are skipping the middle ground.

#### russ_hensel

Joined Jan 11, 2009
825
There are may interpretations of the Schroedinger equations, wikipedia covers some of them.

Quantum applies to both large and small systems and quantum effects may show up at large scale, a superconducting magnet.

Still solving a quantum equation for a macro scale system is very difficult unless something makes it simple like a crystal lattice. To really help in the interpretation we probably need a quantum description of the observer, never done as far as I know. This may also bring in considerations of statistical mechanics.

Even in classical mechanics there is no general solution for the n body problem, even with small n, point masses, and simple force laws.