Tell me about quantem physics

I'm having trouble grasping this concept. In my into philosophy book it explains (or at least I think it explains) that it is the theory that particles behave differently if observed than not observed. It says that if a particle is measured it will behave as a particle and if it is not measured it will behave as a wave. It then says that this affects free will and goes against classic physics by saying that the world is random and to paraphrase Einstein, "That God is playing dice with the universe." Am I missing something, as all of this doesn't seem to make sense to me.

Can anybody help me understand this?

Moved to Science/Math Forum for better responses.

Your "intro to philosophy" book is broken.

First off, it's conflating "observed" with measured. Second, quantum mechanics is only partially random: The wave function evolves in a strictly deterministic (even unitary!) manner. It is the wave form which describes the probabilities of particular measurements. So the probabilities all evolve deterministically. It is only the actual values of a particular measurement that are "random". This is the so called "measurement paradox". This is at the root of the so called measurement paradox.

Any attempt to rescue "free will" based on randomness at the quantum level is fundamentally flawed. We can't have free will based on deterministic processes but we can based on random one?

Finally, your "philosophy book" is neglecting the correspondence principle which says that in the classical limit, quantum mechanics describes classical physics so that all the quantum spookiness stays in the quantum realm, So the world that we actually live in is quite deterministic, at least according to physics.

EDIT:

Also, your book fails at philosophy. How do we know that the particle behaves as a wave when we're not observing it if we're not observing it?. The correct statement is that assuming that the particle behaves as a wave when not being measured leads to accurate predictions. On the other hand, Heisenberg's matrix mechanics make no assumption of wave like form whatsoever and directly addresses the observables themselves.

So, the world of the small has no affect on that of the large?

(Thanks for the move)

EDIT:

It may be my fault for paraphrasing my book poorly. It used an example of somebody using a plate to show that it is a wave when not observed. This is what it says:

"In a famous experiment, called by physicist Richard Feynman "the business of the holes," electrons behaved one way if they were observed another way if they were not. Imagine a barrier with two holes and a plate behind it to record "hits" Watched electrons, those measured by instruments, followed the expected path - they passed through one hole or other and were stopped by the plate. If experimenters simply examined the plate, however, it seemed as if each electron had passed through both holes. The conclusion: Unobserved electrons behave like waves, and part of the wave passes through each hole: observed electrons behave like particles."

That's the current understanding. At least to the best of my knowledge. I should say that I'm not a quantum physicist but do understand the mathematical formulation of the theory.

Alright, thank you for your help.

Ah, I saw this thread and started to feel sick because I HATE physics. But I thought "no, maybe it'll be interesting!"

I still feel sick (bleh...)

But I agree with the observation thing (the only part I understood as I skimmed over this thread). The first thing that popped into my head was "how do we know they behave diiferently when not observed when we're not observing them??" Meh.

Hopefully my sicky, sinking feeling will leave when I exit this thread. No offense to physics lovers! :cheeky:

Quote:

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Originally Posted by Raspberry

But I agree with the observation thing (the only part I understood as I skimmed over this thread). The first thing that popped into my head was "how do we know they behave diiferently when not observed when we're not observing them??" Meh.

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Because of the resulting interference pattern that indicate the particles not behaving like matter.